Ee 444 electrical drives be(tx) 2012

PRACTICAL WORK BOOKFor Academic Session 2012

ELECTRICAL DRIVES (EE- 444)For

BE (TX)

Name:Roll Number:Class:Batch: Semester/Term :Department :

Department of Electrical Engineering NED University of Engineering & Technology

Electrical Drives Safety Rules NED University of Engineering and Technology Department of Electrical Engineering

SAFETY RULES

1. Please don t touch any live parts. 2. Please don t work bare footed. 3. Never use an electrical tool near water. 4. Never use an electrical tool that has fallen into water. 5. Don t carry unnecessary item with you during performance (like water bottle,

bags etc.) 6. Before connecting any leads/Connecting Wires make sure power is switch off. 7. In case of emergency, push the nearby red color emergency switch of any panel

or immediately call the laboratory staff. 8. In case of electricity fire, never put water on it as it will further worse the

condition; use the class C fire extinguisher.

Fire is a chemical reaction involving rapid oxidation (combustion) of fuel. Three basic conditions when met, fire takes place. These are fuel, oxygen & heat, absence of any one of the component will extinguish the fire.

If there is a small electrical fire, be sure to use only a Class C or multipurpose (ABC) fire extinguisher, otherwise you might make the problem worsen.

The letters and symbols are explained in left figure. Easy to remember words are also shown.

Don t play with electricity, Treat electricity with respect, it deserves

Figure: Fire Triangle

A (think ashes): paper, wood etc.

B(think barrels): flammable liquids

C(think circuits): electrical fires

Electrical Drives Contents NED University of Engineering and Technology Department of Electrical Engineering

CONTENTS

Lab.

No. Dated List of Experiments Page

No . Remarks

01 Introduction SACED TECNEL. 01

02

Introduction to the devices :

Diodes

SCR

IGBT s & MOSFET switches

03

03

(a) AC/DC Single-phase Not-Controlled Half-wave Rectifier with R load, RL Load.

(b)

AC/DC Single-phase Not-Controlled Full wave Rectifier with R load and R-L load

12

17

04

To study the effect of Free Wheeling diode on the output of single phase Not-controlled half-wave rectifier. 22

05

(a) AC/DC Three-Phase Not-Controlled Half-wave Rectifier with R load & R-L load.

(b) AC/DC Three-Phase Not-Controlled Full-wave Rectifier with R load & R-L load

26

32

06

(a) AC/DC Single-phase Controlled Half-wave Rectifier with R load, R-L load

(b)

AC/DC Single Controlled Full-wave Rectifier with R load & R-L load

37

43

Electrical Drives Contents NED University of Engineering and Technology Department of Electrical Engineering

07 To study the effect of Free Wheeling diode on the output of single phase controlled half-wave rectifier.

49

08

(a) AC/DC Three-phase Controlled Half-wave Rectifier with R load, R-L load

(b) AC/DC Three-Phase Controlled Full-wave Rectifier with R load & R-L load

53

59

09 DC/DC Chopper (BUCK). 64

10 To draw the Magnetization curve of self-excited Dc shunt Generator (Open circuit Characteristics O.C.C)

70

11 To draw the load characteristics curve of self-excited dc shunt generator 73

12 To draw the external and internal characteristics of separately excited DC generator

76

13 Speed control of a DC shunt motor by flux variation method 78

14 Speed control of a D.C. Shunt Motor by armature rheostat control method 81

15 To observe the starting of three phase Synchronous and Induction motor 83

Electrical Drives Lab session 01 NED University of Engineering and Technology Department of Electrical Engineering

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LAB SESSION 1 Object:-

Introduction to SACED TECNEL.

Apparatus:

SACED TECNEL (Software)

TECNEL

RCL3R Load module

Theory:

In electrical drives lab, we will use TECNEL/B hardware & RCL3R Load module. The front panel of Tecnel /B consists of:

Diodes module: 6 diodes.

Thyristors module: 6 Thyristors.

IGBTS Module: 6 IGBTS.

Capacitor module

Sensors module: 4 Voltage sensors & 2 Current sensors.

Power supply connections for Red Yellow Blue Phases (R, S, T), Neutral and Ground.

Practices schemes.

PROCESS DIAGRAM AND ELEMENTS ALLOCATION


Page | - 2 -

RCL3R. Resistive, Inductive and Capacitive Loads Module: Our Resistive, Capacitive and Inductive Loads Module (RCL3R) offers single and Three-phase resistances, inductances & capacitances.

The values are as follows: Variable resistive loads: 3 x [150 (500 W)] Fixed resistive loads: 3 x [150 (500 W) + 150 x (500 W)] Inductive loads: 3 x [0, 33, 78, 140, 193, 236mH]. (230V /2 A) Capacitive loads: 3 x [4 x 7 µF]. (400V)

Now load the TECNEL software in PC, the main screen will be look like this:

And the Plot screen will be look like this:

Electrical DrivesNED University of En

Object:-

Introduction to the devices

Diodes

SCR


Theory:-

1. DIODEelectric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's blocking current ithought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extracmodulation from radio signals in radio receivers.

Figure:

A diode is formed by joining two equivalently doped Pthey are joined an interestingholes and is of positive charge. The Ncontact of the Pmaterial. Hence the electron diffuses and occupies the holes in the Psmall region of the Nsemiconductor material, in the Pintrinsic semiconductorThis thin intrinsic region is called depletion layer, since itabove) and hence offers high resistance. diffusion of

Electrical Drives

NED University of Engineering and Technology

Introduction to the devices

Diodes

SCR


-

DIODE:-In electronics, a electric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's blocking current ithought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extracmodulation from radio signals in radio receivers.

Figure: (a) Construction of a semi

A diode is formed by joining two equivalently doped Pthey are joined an interestingholes and is of positive charge. The Ncontact of the P-Type and N

aterial. Hence the electron diffuses and occupies the holes in the Psmall region of the Nsemiconductor material, in the Pintrinsic semiconductorThis thin intrinsic region is called depletion layer, since itabove) and hence offers high resistance. diffusion of

majority carriers. In physical terms the size of

gineering and Technology

Introduction to the devices:


In electronics, a electric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's blocking current in the opposite direction (the thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extracmodulation from radio signals in radio receivers.

Construction of a semi

A diode is formed by joining two equivalently doped Pthey are joined an interesting

phenomenon takes place. The Pholes and is of positive charge. The N

Type and N-Type regions, the holes in the Paterial. Hence the electron diffuses and occupies the holes in the P

small region of the N-type near the junction to loose electrons and behaves like intrinsic semiconductor material, in the P-type a small region gets filled up by intrinsic semiconductor. This thin intrinsic region is called depletion layer, since itabove) and hence offers high resistance.



LAB SESSION


In electronics, a diode is a twoelectric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's

n the opposite direction (the thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extracmodulation from radio signals in radio receivers.

Construction of a semi-conductor diode

A diode is formed by joining two equivalently doped Pphenomenon takes place. The P

holes and is of positive charge. The N-Type semiconductor has excess electrons. At the point of Type regions, the holes in the P

aterial. Hence the electron diffuses and occupies the holes in the Ptype near the junction to loose electrons and behaves like intrinsic

type a small region gets filled up by

This thin intrinsic region is called depletion layer, since itabove) and hence offers high resistance. It s


LAB SESSION

is a two-terminal electronic component that conducts electric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's

n the opposite direction (the reversethought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extracmodulation from radio signals in radio receivers.

conductor diode

A diode is formed by joining two equivalently doped P-Type and Nphenomenon takes place. The P

Type semiconductor has excess electrons. At the point of Type regions, the holes in the P



This thin intrinsic region is called depletion layer, since itIt s

this depletion region that prevents the further majority carriers. In physical terms the size of

Department of Electrical Engineering

LAB SESSION 2

terminal electronic component that conducts electric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's

reverse

direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extrac

conductor diode (b) symbol of diode

Type and N-phenomenon takes place. The P-Type semiconductor has excess

Type semiconductor has excess electrons. At the point of Type regions, the holes in the P-Type attract electrons in the N



This thin intrinsic region is called depletion layer, since it

is depleted of charge (see diagram this depletion region that prevents the further

majority carriers. In physical terms the size of the depletion layer is very thin.

Lab session 02 Department of Electrical Engineering

terminal electronic component that conducts electric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while

direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extrac

(b) symbol of diode

-Type semiconductor. When Type semiconductor has excess

Type semiconductor has excess electrons. At the point of Type attract electrons in the N

aterial. Hence the electron diffuses and occupies the holes in the P-Type material. Causing a type near the junction to loose electrons and behaves like intrinsic

type a small region gets filled up by holes and behaves like

s depleted of charge (see diagram this depletion region that prevents the further

he depletion layer is very thin.


Page |

terminal electronic component that conducts electric current in only one direction. The most common function of a diode is to allow an

direction), while direction). Thus, the diode can be

thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extrac

Type semiconductor. When Type semiconductor has excess

Type semiconductor has excess electrons. At the point of Type attract electrons in the N-Type

Type material. Causing a type near the junction to loose electrons and behaves like intrinsic

holes and behaves like


he depletion layer is very thin.

Lab session 02

Page | - 3 -

terminal electronic component that conducts electric current in only one direction. The most common function of a diode is to allow an

direction), while direction). Thus, the diode can be

thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extract

Type semiconductor. When Type semiconductor has excess

Type semiconductor has excess electrons. At the point of Type

Type material. Causing a type near the junction to loose electrons and behaves like intrinsic

holes and behaves like an


Lab session 02


Figure: (a)

Due to formation this depletion layer the diode will not conduct until the depletion overcome, that is 0.above that narrow depletion layer (0.in the flow ojunction, for both silicon and germanium are called forward characteristics and shown below.Diode is mainlwave rectificathalf is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Halfin a one-phase supply, or with three diodes in a

Figure:- Half wave rectification process in which negative half cycle is annulled by diode

Review

A diode

When voltage is applied across adiode is said to be

When voltage is applied across a diode is said to be

The voltage dropped across a conducting, forwardvoltagetemperature, an

Silicon diodes have a forward voltage of approximately 0.7 volts.

Germanium diodes have a forward voltage of approximately 0.3 volts.

The maximum reversecalled the

Electrical Drives


(a) Formation of depletion Layer.

Due to formation this depletion layer the diode will not conduct until the depletion , that is 0.3 V for Germanium and 0.

above that narrow depletion layer (0.in the flow of current. Graphs depicting thjunction, for both silicon and germanium are called forward characteristics and shown below.Diode is mainly used to perform rectificationwave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half

phase supply, or with three diodes in a

Half wave rectification process in which negative half cycle is annulled by diode

diode is an electrical component acting as a oneWhen voltage is applied across a

is said to be When voltage is applied across a

is said to be The voltage dropped across a conducting, forwardvoltage. Forward voltage for a temperature, and is fixed by the chemical composition of the PSilicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts. The maximum reversecalled the Peak Inverse Voltage


Formation of depletion Layer.

Due to formation this depletion layer the diode will not conduct until the depletion V for Germanium and 0.

above that narrow depletion layer (0.f current. Graphs depicting th

junction, for both silicon and germanium are called forward characteristics and shown below.y used to perform rectificationion, either the positive or negative half of the AC wave is passed, while the other

half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half



is an electrical component acting as a oneWhen voltage is applied across a

is said to be forward-biasedWhen voltage is applied across a

is said to be reverse-biasedThe voltage dropped across a conducting, forward

. Forward voltage for a d is fixed by the chemical composition of the P

Silicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts. The maximum reverse-bias voltage that a

Peak Inverse Voltage


Formation of depletion Layer.

Due to formation this depletion layer the diode will not conduct until the depletion V for Germanium and 0.

above that narrow depletion layer (0.3 V for Germanium and 0.f current. Graphs depicting the current voltage relationship

junction, for both silicon and germanium are called forward characteristics and shown below.y used to perform rectificationion, either the positive or negative half of the AC wave is passed, while the other

half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be achieved



is an electrical component acting as a oneWhen voltage is applied across a

diode in such a way that the biased.

When voltage is applied across a diode in such a way that thebiased.

The voltage dropped across a conducting, forward. Forward voltage for a diode varies only slightly for changes in forward current and

d is fixed by the chemical composition of the PSilicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts.

bias voltage that aPeak Inverse Voltage, or PIV rating.

(b) Forward

Due to formation this depletion layer the diode will not conduct until the depletion V for Germanium and 0.7 V for silicon. An increase in the applied voltage

V for Germanium and 0.e current voltage relationship

junction, for both silicon and germanium are called forward characteristics and shown below.y used to perform rectification, converting ion, either the positive or negative half of the AC wave is passed, while the other

half is blocked. Because only one half of the input waveform reaches the output, it is very wave rectification can be achieved

phase supply, or with three diodes in a three-phase


is an electrical component acting as a one-way valve for current. in such a way that the

in such a way that the

The voltage dropped across a conducting, forwardvaries only slightly for changes in forward current and

d is fixed by the chemical composition of the PSilicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts.

bias voltage that a

diode can withstandrating.


Forward

characteristics of diode

Due to formation this depletion layer the diode will not conduct until the depletion V for silicon. An increase in the applied voltage

V for Germanium and 0.7 V for silicon) results in rapid rise e current voltage relationship

junction, for both silicon and germanium are called forward characteristics and shown below., converting A.C into unidirectional

ion, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very

wave rectification can be achieved phase

supply.


way valve for current. in such a way that the

in such a way that the

di

The voltage dropped across a conducting, forward-biased diodevaries only slightly for changes in forward current and

d is fixed by the chemical composition of the P-N junction. Silicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts.

can withstand

without breaking down is



Due to formation this depletion layer the diode will not conduct until the depletion V for silicon. An increase in the applied voltage

V for silicon) results in rapid rise e current voltage relationship

for forward biased PN junction, for both silicon and germanium are called forward characteristics and shown below.

into unidirectional ion, either the positive or negative half of the AC wave is passed, while the other

half is blocked. Because only one half of the input waveform reaches the output, it is very wave rectification can be achieved with a single diode


way valve for current.

in such a way that the diode allows current, the

diode prohibits current, the

diode

is called the varies only slightly for changes in forward current and

N junction.

Silicon diodes have a forward voltage of approximately 0.7 volts.

Germanium diodes have a forward voltage of approximately 0.3 volts.



Page |


Due to formation this depletion layer the diode will not conduct until the depletion layer voltageV for silicon. An increase in the applied voltage

V for silicon) results in rapid rise for forward biased PN

junction, for both silicon and germanium are called forward characteristics and shown below.

into unidirectional D.C. In half ion, either the positive or negative half of the AC wave is passed, while the other

half is blocked. Because only one half of the input waveform reaches the output, it is very with a single diode


allows current, the

prohibits current, the

is called the forward varies only slightly for changes in forward current and


Lab session 02

Page | - 4 -

voltage

is V for silicon. An increase in the applied voltage

V for silicon) results in rapid rise for forward biased PN

. In half ion, either the positive or negative half of the AC wave is passed, while the other

half is blocked. Because only one half of the input waveform reaches the output, it is very with a single diode

allows current, the

prohibits current, the

forward varies only slightly for changes in forward current and


Lab session 02


Page | - 5 -

Figure: V-I characteristics of Diode

THRYRISTOR (SCR):-A silicon-controlled rectifier is a four-layer semiconductor device that controls current. SCR consists of four layers of alternating P and N type semiconductor materials and it has three terminals called anode, cathode and gate. The SCR is uni-directional device, meaning it passes electron current only in one direction, from cathode to anode when positive gate signal is applied. It is named as controlled rectifier because it can control the amount of power flowing from source to load. It can be made to conduct for whole part of positive half cycle or for small part of positive half cycle. The SCR will turn on and conduct current when following two conditions are satisfied.

1. It has forward biased voltage across its anode and cathode of at least 0.7 Volts. Forward biased condition exists when anode is more positive than cathode.

2. It has a positive voltage applied across the gate.

Figure: Thyristor Construction, schematic symbol, forward biasing for normal operation

Volt-Ampere Characteristics Figure below illustrates the volt-ampere characteristics curve of an SCR. The vertical axis + I represent the device current, and the horizontal axis +V is the voltage applied across the device


Page | - 6 -

anode to cathode. The parameter IF defines the RMS forward current that the SCR can carry in the ON state, while VR defines the amount of voltage the unit can block in the OFF state.

Figure:- V-I Characteristics of SCR

Biasing The application of an external voltage to a semiconductor is referred to as a bias. Forward Bias Operation

A forward bias, shown above in figure as +V, will result when a positive potential is applied to the anode and negative to the cathode.

Even after the application of a forward bias, the device remains non-conducting until the positive gate trigger voltage is applied.

After the device is triggered ON it reverts to a low impedance state and current flows through the unit. The unit will remain conducting after the gate voltage has been removed. In the ON state (represented by +I), the current must be limited by the load, or damage to the SCR will result.

Reverse Bias Operation

The reverse bias condition is represented by -V. A reverse bias exists when the potential applied across the SCR results in the cathode being more positive than the anode.

In this condition the SCR is non-conducting and the application of a trigger voltage will have no effect on the device. In the reverse bias mode, the knee of the curve is known as the Peak Inverse Voltage PIV (or Peak Reverse Voltage - PRV) and this value cannot be exceeded or the device will break-down and be destroyed. A good Rule-of -Thumb is to select a device with a PIV of at least three times the RMS value of the applied voltage


Page | - 7 -

SCR Phase Control In SCR Phase Control, the firing angle, or point during the half-cycle at which the SCR is triggered, determines the amount of current which flows through the device. It acts as a high-speed switch which is open for the first part of the cycle, and then closes to allow power flow after the trigger pulse is applied. Figure two below shows an AC waveform being applied with a gating pulse at 45 degrees. There are 360 electrical degrees in a cycle; 180 degrees in a half-cycle. The number of degrees from the beginning of the cycle until the SCR is gated ON is referred to as the firing angle, and the number of degrees that the SCR remains conducting is known as the conduction angle. The earlier in the cycle the SCR is gated ON, the greater will be the voltage applied to the load. Figure Three shows a comparison between the average output voltages for an SCR being gated on at 30 degrees as compared with one which has a firing angle of 90 degrees. Note that the earlier the SCR is fired, the higher the output voltage applied to the load.

Figure:- SCR output waveform (a) When forward biased (b) Triggering at different angles

The voltage actually applied to the load is no longer sinusoidal, rather it is pulsating DC having a steep wave front which is high in harmonics. This waveform does not usually cause any problems on the driven equipment itself; in the case of motor loads, the waveform is smoothed by the circuit inductance.

MOSFET (Metal oxide Semiconductor Field Effect Transistor):- The metal oxide semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a transistor used for amplifying or switching electronic signals. It has three terminals gate, source and drain as shown below. Unlike the bipolar junction transistor (BJT), the metal-oxide-semiconductor field effect transistor (MOSFET) is composed of a bulk substrate of metal oxide ions, which form n- and p-charged regions in order to amplify analog voltages across a circuit. Figure shows the basic of a MOSFET. Note the charged n-regions in the substrate and the four


Page | - 8 -

terminals (3 active, 1 grounded). Furthermore, unlike the BJT, the operation of the MOSFET is determined by a voltage rather than a current.

n+ n+p

Bulk (or substrate)

Source

Gate

Drain

Diagram of the composition of a MOSFET

Like the bipolar junction transistors, the MOSFETs are composed of two different semiconductor regions, n and p. Instead of creating a current through the device by filling of holes in the p region, the MOSFET forms a channel of the positively charged n layer between the two n sections, as shown in Figure 1. This channel forms when a voltage is applied across the gate, attracting the electrons in the n region nearer to the gate charge. The strength of the gate voltage determines the geometry of the channel and the current that passes through it. Figure below shows the drain characteristic of the MOSFET, the relationship between the drain-source voltage and the drain current. Like the collector characteristic of the BJT, the MOSFET drain characteristic uses two voltages and the gate voltage to construct a series of characteristic curves for the device.

Figure 1 Drain characteristic for a MOSFET

Two voltages are keys to the operation of the MOSFET, the threshold voltage and the gate voltage. The threshold voltage TV is the voltage at which the MOSFET begins to conduct the

electrons from the drain to the source. The difference between it and the gate voltage, GV ,

determines the flow of the electrons through the channel. If the difference between the threshold and the gate is negative, no current flows. If this difference is greater than zero, current flows between the two terminals.


At a certain point within the the channel thinsdifference between the gate voltage and the threshold voltage is greater than or equal to the threshold voltage, this pinch

IGBT (INSULATED GATE BIPOLAR TRANSISTORA power transistor that has characteristics of both MOSFET and bipolar junction transistors (BJTs).is called IGBT.switching with greater ease of control. IGBTs are found in home appliances, eledigital stereo power amplifierspower semiconductor device, noted for high efficiency and fast switching. It switches electric power in many modern appliances: electric cars, conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width modulation and lowMOSFETs with the highcombining an isolated gate FET for the control input, and a bipolar power transistor as a a single device. The IGBT is used in mediumpower supply, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high curhundreds of amperes with blocking voltages of 6000

Figure:- Electronic symbol of IGBT

IGBT switching characteristics:that of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing collector current due to the stored charge in the Noff loss and requires an increase in the dead ti

Electrical Drives


At a certain point within the the channel thins

, not allowing electron flow between the two

difference between the gate voltage and the threshold voltage is greater than or equal to the threshold voltage, this pinch

INSULATED GATE BIPOLAR TRANSISTORtransistor that has characteristics of both MOSFET and bipolar junction transistors

is called IGBT.switching with greater ease of control. IGBTs are found in home appliances, eledigital stereo power amplifierspower semiconductor device, noted for high efficiency and fast switching. It switches electric power in many modern appliances: electric cars, conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width modulation and low-pass fiMOSFETs with the highcombining an isolated gate FET for the control input, and a bipolar power transistor as a a single device. The IGBT is used in mediumpower supply, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high curhundreds of amperes with blocking voltages of 6000

Electronic symbol of IGBT

GBT switching characteristics:that of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing collector current due to the stored charge in the Noff loss and requires an increase in the dead ti


At a certain point within the saturation region, not allowing electron flow between the two

difference between the gate voltage and the threshold voltage is greater than or equal to the threshold voltage, this pinch-off occurs

Figure:


is called IGBT.

IGBT handles high current, a characteristic of BJTs, but enables fast switching with greater ease of control. IGBTs are found in home appliances, eledigital stereo power amplifiers

Thepower semiconductor device, noted for high efficiency and fast switching. It switches electric power in many modern appliances: electric cars, conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width

pass filters. The IGBT combines the simple gateMOSFETs with the high-current and lowcombining an isolated gate FET for the control input, and a bipolar power transistor as a a single device. The IGBT is used in mediumpower supply, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high curhundreds of amperes with blocking voltages of 6000


GBT switching characteristics:-The switching characteristics of an IGBT are verythat of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing collector current due to the stored charge in the Noff loss and requires an increase in the dead ti


saturation region

, not allowing electron flow between the two difference between the gate voltage and the threshold voltage is greater than or equal to the

off occurs

Figure:- MOSFET schematic symbols


IGBT handles high current, a characteristic of BJTs, but enables fast switching with greater ease of control. IGBTs are found in home appliances, ele

The

insulated gate bipolar transistorpower semiconductor device, noted for high efficiency and fast switching. It switches electric power in many modern appliances: electric cars, conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width

The IGBT combines the simple gatecurrent and low saturation

combining an isolated gate FET for the control input, and a bipolar power transistor as a a single device. The IGBT is used in medium-power supply, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high curhundreds of amperes with blocking voltages of 6000


The switching characteristics of an IGBT are verythat of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing collector current due to the stored charge in the Noff loss and requires an increase in the dead time between the conduction of two devices in a half

saturation region, a pinch-

, not allowing electron flow between the two difference between the gate voltage and the threshold voltage is greater than or equal to the

MOSFET schematic symbols



insulated gate bipolar transistorpower semiconductor device, noted for high efficiency and fast switching. It switches electric power in many modern appliances: electric cars, trains, variable speed refrigerators, airconditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width

The IGBT combines the simple gatesaturation-voltage capability of bipolar transistors by

combining an isolated gate FET for the control input, and a bipolar power transistor as a -

to high-power applications such as switchedpower supply, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high current handling capabilities in the order of hundreds of amperes with blocking voltages of 6000

V, equating to hundreds of kilowatts.

The switching characteristics of an IGBT are verythat of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing collector current due to the stored charge in the N--drift region. The tail current increases the turn

me between the conduction of two devices in a half


-off occurs. The , not allowing electron flow between the two termi

difference between the gate voltage and the threshold voltage is greater than or equal to the

MOSFET schematic symbols

INSULATED GATE BIPOLAR TRANSISTOR):- transistor that has characteristics of both MOSFET and bipolar junction transistors


insulated gate bipolar transistor

power semiconductor device, noted for high efficiency and fast switching. It switches electric trains, variable speed refrigerators, air

conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width

The IGBT combines the simple gatevoltage capability of bipolar transistors by

combining an isolated gate FET for the control input, and a bipolar power transistor as a power applications such as switched

power supply, traction motor control and induction heating. Large IGBT modules typically consist rent handling capabilities in the order of

, equating to hundreds of kilowatts.

The switching characteristics of an IGBT are verythat of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing

drift region. The tail current increases the turnme between the conduction of two devices in a half


off occurs. The pinchterminals. Generally, if the


transistor that has characteristics of both MOSFET and bipolar junction transistors IGBT handles high current, a characteristic of BJTs, but enables fast

switching with greater ease of control. IGBTs are found in home appliances, ele

or IGBT is a threepower semiconductor device, noted for high efficiency and fast switching. It switches electric

trains, variable speed refrigerators, airconditioners and even stereo systems with switching amplifiers. Since it is designed to turn on and off rapidly, amplifiers that use it often synthesize complex waveforms with pulse width

The IGBT combines the simple gate-drive characteristics of the voltage capability of bipolar transistors by

combining an isolated gate FET for the control input, and a bipolar power transistor as a power applications such as switched



The switching characteristics of an IGBT are verythat of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing



Page |

pinch-off

means that

Generally, if the difference between the gate voltage and the threshold voltage is greater than or equal to the


switching with greater ease of control. IGBTs are found in home appliances, electric cars and is a three-terminal

power semiconductor device, noted for high efficiency and fast switching. It switches electric trains, variable speed refrigerators, air


drive characteristics of the voltage capability of bipolar transistors by

combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in power applications such as switched-mode



The switching characteristics of an IGBT are very

much similar to that of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing


Lab session 02

Page | - 9 -

means that Generally, if the



ctric cars and terminal

power semiconductor device, noted for high efficiency and fast switching. It switches electric trains, variable speed refrigerators, air-


drive characteristics of the voltage capability of bipolar transistors by

switch, in mode


much similar to that of a Power MOSFET. The major difference from Power MOSFET is that it has a tailing

drift region. The tail current increases the turn-me between the conduction of two devices in a half-

Lab session 02


Page | - 10 -

bridge circuit. The Figure shows a test circuit for switching characteristics and the Figure 9 shows the corresponding current and voltage turn-on and turn-off waveforms. IXYS IGBTs are tested with a gate voltage switched from +15V to 0V. To reduce switching losses, it is recommended to switch off the gate with a negative voltage (-15V).

The turn-off speed of an IGBT is limited by the lifetime of the stored charge or minority carriers in the N--drift region which is the base of the parasitic PNP transistor. The base is not accessible physically thus the external means cannot be applied to sweep out the stored charge from the N--drift region to improve the switching time. The only way the stored charge can be removed is by recombination within the IGBT. Traditional lifetime killing techniques or an N+ buffer layer to collect the minority charges at turn-off are commonly used to speed-up recombination time.


Page | - 11 -

The main advantages of IGBT over a Power MOSFET and a BJT are: 1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced. 2. Low driving power and a simple drive circuit due to the input MOS gate structure. It can be easily controlled as compared to current controlled devices (Thyristor, BJT) in high voltage and high current applications. 3. Wide SOA. It has superior current conduction capability compared with the bipolar transistor. It also has excellent forward and reverse blocking capabilities.

The main drawbacks are: 1. Switching speed is inferior to that of a Power MOSFET and superior to that of a BJT. The collector current tailing due to the minority carrier causes the turn off speed to be slow. 2. There is a possibility of latch up due to the internal PNPN Thyristor structure.

Electrical Drives NED University of Engineering and Technology

Object:

AC/DC SingleApparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Single-phase halfNot-controlled rectifiers are constituted by diodes that, aas not-controlledvoltage of fixed magnitude.conducts only in half cycle of the input, otherwise open.

From a theoretical point of view, they may be considered as switches that arepositive voltage between anode (A) and cathode (K) the switch isvoltage is negative.

The behavior of the rectifier will depend considerably on the used

Pure resistive load (R)Inductive load (Rcoil is annulled, although the

Circuit Diagram

Procedure:1. Carry out the assembly E1UK shown in the above figure2. Connect the respective load to its terminals one by one.

For R Load

Electrical Drives University of Engineering and Technology

AC/DC Single-phase NotApparatus:

SACED TECNELTECNEL or TECNEL/BRCL3R Load moduleConnecting Wires

phase half-wave notcontrolled rectifiers are constituted by diodes that, a

controlled

elements, provide a dependent voltage of fixed magnitude.conducts only in half cycle of the input, otherwise open.

From a theoretical point of view, they may be considered as switches that are

opened or closed depending on the direction positive voltage between anode (A) and cathode (K) the switch isvoltage is negative.


resistive load (R)Inductive load (R-L),coil is annulled, although the

Circuit Diagram:

Procedure:

Carry out the assembly E1UK shown in the above figureConnect the respective load to its terminals one by one. For R Load

Use Fixed R= 300ohms plus variable resistance in series.


phase Not-Controlled

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

wave not-controlled rectifiers:controlled rectifiers are constituted by diodes that, a

elements, provide a dependent voltage of fixed magnitude.

In half wave rectifiers, diode conducts only in half cycle of the input, otherwise open.

From a theoretical point of view, they may be considered as opened or closed depending on the direction

positive voltage between anode (A) and cathode (K) the switch is


resistive load (R): where the voltage is annulled when itsL),

where the conduction continues until thecoil is annulled, although the

output voltage inverts its polarity.

Carry out the assembly E1UK shown in the above figureConnect the respective load to its terminals one by one.



LAB SESSION

Controlled Half-wave Rectifier with R load

controlled rectifiers:controlled rectifiers are constituted by diodes that, a

elements, provide a dependent In half wave rectifiers, diode

conducts only in half cycle of the input, otherwise open.




where the voltage is annulled when itswhere the conduction continues until the


E1UK Model



Electrical Drives

LAB SESSION 3

wave Rectifier with R load

controlled rectifiers:

controlled rectifiers are constituted by diodes that, aelements, provide a dependent output

In half wave rectifiers, diode conducts only in half cycle of the input, otherwise open.




where the voltage is annulled when itswhere the conduction continues until the


E1UK Model




3

(a)

wave Rectifier with R load,

controlled rectifiers are constituted by diodes that, acts output

In half wave rectifiers, diode

From a theoretical point of view, they may be considered as opened or closed depending on the direction of the vo


closed, and it is opened if the


load type, so we may have:

where the voltage is annulled when its

direction changes.where the conduction continues until the

moment when the current in the output voltage inverts its polarity.

Carry out the assembly E1UK shown in the above figure

Connect the respective load to its terminals one by one.


Lab Session 03 (a)Department of Electrical Engineering

,

RL Load.

of the voltage applied. That is closed, and it is opened if the


direction changes.moment when the current in the


Lab Session 03 (a)


Page | -

ltage applied. That is with a closed, and it is opened if the


direction changes.

moment when the current in the

-

12 -

with a closed, and it is opened if the

moment when the current in the

Electrical Drives Lab Session 03 (a)

NED University of Engineering and Technology Department of Electrical Engineering

Page | - 13 -

And sample the following parameters: Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure)

Figure: Uncontrolled Half Wave Rectifier R Load

For different values of R the RMS voltage will vary across the load, which can be calculated using multi meter.

S. No Load Resistance V rms Voltage Across Diode

1. 300 + 75

2. 300 + 120

For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage.

S. No Load Impedance V rms Voltage Across Diode

1. 300

+ 75 + 140mH 2. 300

+ 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure)



Page | - 14 -

Figure: Uncontrolled Half Wave Rectifier RL Load

3. Load the SACED TECNEL program in PC and the window corresponding to this practice

Select Practice Option

AC/DC Single-phase Not-Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.

Question:

Define the following terms: 1. Ripple Factors: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Harmonics: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Fundamental Frequency: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________



Page | - 15 -

4. Power Factor: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. Rectifiers: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Waveforms:

R LOAD

Fig: Input Voltage Fig: Output Voltage across R Load

Fig: Load Current IL

Fig: Output Voltage across Diode



Page | - 16 -

R-L LOAD

Fig: Input Voltage Fig: Output Voltage across RL Load


Fig: Output Voltage across Diode D1

Electrical Drives Lab Session 03 (b)


Page | - 17 -

LAB SESSION 3 (b)

Object:

AC/DC Single-phase Not-Controlled Full wave Rectifier with R load and R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Single-phase full-wave not-controlled rectifiers: By the use of four diodes, rectifier circuit performance can be greatly improved. The entire supply voltage wave is utilized to impress current through the load.

Figure: Single-phase, full-wave diode rectifier: (a) Circuit diagram and (b) load voltage and current waveforms for R load.

The behavior of the rectifier will depend considerably on the used load type, i.e. R Load or RL Load.

Circuit Diagram:

B2U Model



Page | - 18 -

Table 1: Single-Phase Diode Rectifier Circuits with Resistive Load

Procedure:

1. Carry out the assembly B2U shown in the above figure 2. Connect the respective load to its terminals one by one.

For R Load Use Fixed R= 300ohms plus variable resistance in series.

And sample the following parameters: Input voltage V4, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure)

Figure: Uncontrolled Full Wave Rectifier with R load



Page | - 19 -

And measure the following quantities S. No Load Resistance V rms Voltage Across D1

1. 300 + 75

2. 300 + 120



1. 300

+ 75 + 140mH 2. 300

+ 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure)

Figure: Uncontrolled Full Wave Rectifier with RL load



AC/DC Single-phase Not-Controlled full wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.



Page | - 20 -

Waveforms:

R LOAD



Fig: Supply Current IS

Fig: Output Voltage across Diode D1 Fig: Output Voltage across Diode D3



Page | - 21 -

R-L LOAD

Fig: Input Voltage Fig: Output Voltage across RL Load



Fig: Output Voltage across Diode D1 Fig: Output Voltage across Diode D3

Electrical Drives Lab Session 04


Page | - 22 -

LAB SESSION 4

Object:

To study the effect of Free Wheeling diode on the output of single phase Not-controlled half-wave rectifier.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Freewheeling diode:- The behavior of the rectifier will depend considerably on the used load type, so we may have: when using a load with inductive character, the following effects appear:

when the input voltage is inverted, a peak of negative voltage appears in the output, and it is not annulled until the current becomes zero.

In a part of the cycle, the current is interrupted, that is, the conduction is discontinuous.

These two effects may be eliminated, as well as the reduction of the harmonic content, with the introduction in parallel with the load of a diode called Freewheeling Diode (FWD) or Flying Diode. When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil is inverted. It begins to act as a generator, forcing the conduction of the FWD and the load current going through it, annulling the peak of negative voltage, as we can see in the following.


We may see here that from 10ms the waveform of the current load (graph in previous page) is an exponential one, that proves the discharge of the coil for the resistance through the FWD. This is corroborated by the input current, ceasing at 10ms.Circuit Di

Procedure:1. Carry out the assembly E1UK shown in the above figure2. Now connect a diode in 3. Connect the respective

For RL Load with FWDObserve how the conduction angle increases as we increase L (0to measuring with the voltmeter the

S. No

Observe how the output current varies

And sInput voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure)


We may see here that from 10ms the waveform of the current load (graph in previous page) is an exponential one, that proves the discharge of the coil for the resistance through the FWD. This is corroborated by the input current, ceasing at 10ms.Circuit Diagram:-

Procedure:

Carry out the assembly E1UK shown in the above figureNow connect a diode in Connect the respective For RL Load with FWDObserve how the conduction angle increases as we increase L (0to measuring with the voltmeter the

S. No

Load

1. 300 2. 300


And sample the following parameters:Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure)

Electrical Drives

University of Engineering and Technology

We may see here that from 10ms the waveform of the current load (graph in previous page) is an exponential one, that proves the discharge of the coil for the resistance through the FWD. This is corroborated by the input current, ceasing at 10ms.

Figure:

Carry out the assembly E1UK shown in the above figureNow connect a diode in antiConnect the respective RL For RL Load with FWD

Observe how the conduction angle increases as we increase L (0to measuring with the voltmeter the

Load Impedance

+ 75 + 140

+ 75 + 23


ample the following parameters:Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in



Figure:- E1UK Model

Carry out the assembly E1UK shown in the above figureanti-Parallel manner with the First diode as shown below

RL load to its terminal.

Observe how the conduction angle increases as we increase L (0to measuring with the voltmeter the

average output voltage.

Impedance

+ 140mH + 236mH


ample the following parameters:

Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in

Electrical Drives


E1UK Model

Carry out the assembly E1UK shown in the above figuremanner with the First diode as shown below

load to its terminal.

Observe how the conduction angle increases as we increase L (0to average output voltage.

V rms

Observe how the output current varies for different


Department

We may see here that from 10ms the waveform of the current load (graph in previous page) is an exponential one, that proves the discharge of the coil for the resistance through the FWD. This is

Carry out the assembly E1UK shown in the above figure

manner with the First diode as shown below

Observe how the conduction angle increases as we increase L (0to average output voltage.

Voltage Across Diode

for different

L values with R=3


Lab Session Department

of Electrical Engineering



Observe how the conduction angle increases as we increase L (0to 236mH) with R=3

Voltage Across DiodeD1

L values with R=375


Lab Session 04


Page | -



mH) with R=37

Voltage Across Diode

D2

.



-

23 -


75 ,




Page | - 24 -

Figure: Uncontrolled single phase Half Wave Rectifier RL Load & FWD.

4. Load the SACED TECNEL program in PC and the window corresponding to this practice 5. Select Practice Option 6. AC/DC Single-phase Not-Controlled Half wave Rectifier option 7. Select the respective sample sensors 8. Check the connections and switch on the equipment. 9. Press the Data Capture button. 10. Visualize the parameters measured and save them in the corresponding file.

Switch off the equipment

Question:

Define the following terms:

1. Free Wheeling Diode ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Effect of FWD on RL Load Output ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________



Page | - 25 -

3. Fundamental Frequency: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 5. Rectifiers: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Waveforms:-

R-L LOAD WITH FWD

Fig: Input Voltage Fig: Output Voltage across R-L Load


Fig: Diode Voltage

Electrical Drives Lab Session 05(a)


Page | - 26 -

LAB SESSION 5 (a)

Object:

AC/DC Three-Phase Not-Controlled Half-wave Rectifier with R load& R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Three-phase half-wave not-controlled rectifiers: Three-phase electricity supplies with balanced, sinusoidal voltages are widely available. It is found that the use of a three-phase rectifier system, in comparison with a single-phase system, provides smoother output voltage and higher rectifier efficiency. Also, the utilization of any supply transformers and associated equipment is better with poly-phase circuits. If it is necessary to use an output filter this can be realized in a simpler and cheaper way with a poly-phase rectifier.

Figure: Three-phase, half-wave diode rectifier with resistive load: (a) circuit connection, (b) phase voltages at the supply, (c) load current.



Page | - 27 -

Table: Three Phase Uncontrolled Rectifier with Ideal Supply

Circuit Diagram:

M3UK Model Procedure:

1. Carry out the assembly M3UK shown in the above figure 2. Connect the respective load to its terminals one by one.


And sample the following parameters: Input voltages (V2, V3, V4), Output voltage V1, Output current I1, Diode voltage V5 (as shown in figure)



Page | - 28 -

Figure: Uncontrolled Three Phase Full Wave Rectifier with R load

Also measure the following quantities using multi-meter.

S. No Load Resistance V rms Voltage Across D1 1. 300 + 75

2. 300 + 120



1. 300

+ 75 + 140mH 2. 300

+ 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltages (V2, V3, V4), Output voltage V1, Output current I1, Diode voltage V5 (as shown in figure)



Page | - 29 -

Figure: Uncontrolled Three Phase Full Wave Rectifier with RL load



AC/DC Three-phase Not-Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.

Here you can also study and visualize what will be the effect of inverting the polarization of the three diodes.

Secondly suppose that, due to an over-voltage, one of the diodes is in open circuit. Study and visualize what effect provokes the output voltage.



Page | - 30 -

Waveforms:

R LOAD

Fig: Input Voltages R,S,T Fig: Output Voltage across R Load



R-L LOAD




Page | - 31 -





Page | - 32 -

LAB SESSION 5 (b)

Object:

AC/DC Three-Phase Not-Controlled Full-wave Rectifier with R load& R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Three-phase full-wave not-controlled rectifiers: The basic full wave uncontrolled (diode) rectifier circuit is shown in the following figure. The diodes D1, D3, D5 are sometimes referred to as the upper half of the bridge, while diodes D2, D4 and D6 constitute the lower half of the bridge. As with the half wave operation the voltages at the anode of the diode valves vary periodically as the supply voltages undergo cyclic excursions. Commutation or switch off of a conducting diode is therefore accomplished by natural cycling of the supply voltages and is known as natural commutation. The load current IL is now unidirectional but the supply currents are bi-directional. In order to permit load current to flow, at least one diode must conduct in each half of the bridge. When this happens the appropriate line to line supply point voltage is applied across the load. In comparison with the half wave bridge, in which supply phase voltage is applied across the load, the full wave bridge has immediate advantage that peak load voltage is 3 times as great. Circuit Diagram:

B6U Model

Procedure:

1. Carry out the assembly B6U shown in the above figure 2. Connect the respective load to its terminals one by one.


And sample the following parameters:



Page | - 33 -

Input voltage V4, Output voltage V1, Output current I1, Diode voltage V3 (as shown in figure)

Figure:- Three phase not controlled full wave rectifier with R load

Also measure following quantities using multi-meter

S. No Load Resistance V rms Voltage across D1 1 300 + 75

2 300 + 120

For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. V av =

S. No Load Impedance V rms Voltage across D1 1 300 + 75 + 140 m

H 2 300 + 120 + 236mH

Observe how the output current varies for different L values with R=375. Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1, Diode voltage V3, Output current (load) I1 (as shown in figure)



Page | - 34 -

Figure:- three phase not controlled full wave rectifier with RL load



AC/DC Three-phase Not-Controlled full wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.



Page | - 35 -

Waveforms:

R LOAD




R-L LOAD




Page | - 36 -


with L=140mH Fig: Load Current IL

with L=236mH

Fig: Output Voltage across diode



Page | - 37 -

LAB SESSION 6 (a)

Object:

AC/DC Single-phase Controlled Half-wave Rectifier with R load, R-L load and R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Single-phase half-wave controlled rectifiers: The controlled rectifiers are constituted by Thyristors. The Thyristor is basically a diode controlled by positive voltage among gate (G) and anode (A). The main difference between controlled rectifiers and not controlled Rectifiers is based on the fact that the Thyristor conduction and non-conduction states can be controlled externally.

Figure:- single phase half wave controlled rectifier a) circuit connections b) output voltage waveform

The Thyristors can be made to conduct during the whole part of positive cycle or for some part of positive cycle, in this way we can control the amount of power flowing from source to load in controlled rectifiers. In this lab session we will deal with rectifiers which are capable to decide the moment when we may trigger the Thyristor by using PC.

The behaviour of controlled rectifier will depend, to a great extent, on the load type used. Pure resistive load (R): where the voltage is annulled when its direction changes. The average output voltage for resistive load will be :

V average = [1 + cos ] V/2

Inductive load (R-L), where the conduction continues until the moment when the current in the coil is annulled, although the output voltage inverts its polarity. The average output voltage for RL load will be :



Page | - 38 -

V average = [ cos

{cos( + )}] V/2

In order to separate the output voltage and the load type, we may use the freewheeling diode (FWD), which avoids the inversion of polarization in the output voltage.

Circuit Diagram:

E1CK Model

Procedure:

1. Carry out the assembly E1CK shown in the above figure 2. Connect the respective load to its terminals one by one.

For R Load Use Fixed R= 300 ohms plus variable resistance in series.

And sample the following parameters: Input voltage V2, Output voltage V1, Output current I2, Thyristor voltage V3 (as shown in figure)

Figure: Controlled Half Wave Rectifier with R Load



Page | - 39 -

For different values of R the RMS voltage will vary across the load, which can be calculated using multi meter.

S. No Load Resistance V rms Voltage Across Thyristor

1. 300 + 75

2. 300 + 120


S. No Load Impedance V rms Voltage Across Thyristor

1. 300

+ 75 + 140mH 2. 300

+ 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V2, Output voltage V1, Thyristor voltage V3, Output current (load) I2 (as shown in figure)

Figure: Controlled Half Wave Rectifier RL Load



Page | - 40 -



AC/DC Single-phase Controlled Half wave Rectifier option

4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.

Question:

Define the following terms: 1. Ripple Factors: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 2. Harmonics: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Fundamental Frequency: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. Power Factor: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. Rectifiers: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________



Page | - 41 -

Waveforms:

R LOAD

Fig: Input Voltage Fig: Output Voltage across R load


Fig: Output Voltage across Thyristor

R-L LOAD

Fig: Input Voltage Fig: Output Voltage across R-L load



Page | - 42 -


Fig: Output Voltage across Thyristor Th 1



Page | - 43 -

LAB SESSION 06 (b)

Object:

AC/DC Single-phase Controlled Full wave Rectifier with R load and R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Wires

Theory:

Single-phase full wave controlled rectifiers: By the use of four Thyristor, rectifier circuit performance can be greatly improved. In full control single phase rectifier the Thyristor are divided into the two group, one with common anodes and other with common cathodes as shown below in the figure.

Figure: Single-phase, full-wave controlled rectifier: (a) circuit diagram and (b) load voltage and current waveforms for R load.

Thyristor Th 1 and Th 4 will conduct when input voltage is positive.

Thyristor Th 2 and Th 3 will conduct when input voltage is negative.

The average output voltage for R load will be: V average = (1 + cos ) V/

The average output voltage for RL load will be: V average = ( cos ) 2V/

The behavior of the rectifier will depend considerably on the used load type, i.e. R Load or RL Load.



Page | - 44 -

Circuit Diagram:

B2C Model

Table 1: Single-Phase Controlled Rectifier Circuits with Resistive Load

Procedure:

1. Carry out the assembly B2C shown in the above figure 2. Connect the respective load to its terminals one by one.


And sample the following parameters: Input voltage V4, Output voltage V1, Output current I2, Thyristor voltage (V2 , V3) as shown in figure



Page | - 45 -

Figure: Controlled Full Wave Rectifier with R load

And measure the following quantities

S. No Load Resistance V rms Voltage Across Thyristor

1. 300 + 75

2. 300 + 120

For RL Load Observe how the conduction angle increases as we increase L (0 to 236mH) with R=375 , measuring with the voltmeter the average output voltage.

S. No Load Impedance V rms Voltage Across Thyristor

1. 300

+ 75 + 140mH 2. 300

+ 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the different samples.

And sample the following parameters: Input voltage V4, Output voltage V1,Thyristor voltage (V2, V3), Output current (load) I2, Supply current I1 , as shown in figure



Page | - 46 -

Figure: Controlled Full Wave Rectifier with RL load



AC/DC

Single-phase Controlled full wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.

Waveforms:

R LOAD

Fig: Input Voltage Fig: Output Voltage across R load



Page | - 47 -



Fig: Output Voltage across Thyristor Th 1 Fig: Output Voltage across Thyristor Th 3 R-L LOAD




Page | - 48 -



Fig: Output Voltage across Thyristor Th 1 Fig: Output Voltage across Thyristor Th 3



Page | - 49 -

LAB SESSION 07

Object:

To study the effect of Free Wheeling diode on the output of single phase controlled half-wave rectifier.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Freewheeling diode:-

The behavior of the rectifier will depend considerably on the used load type, so we may have: when using a load with inductive character, the following effects appear:

when the input voltage is inverted, a peak of negative voltage appears in the output, and it is not annulled until the current becomes zero.

In a part of the cycle, the current is interrupted, that is, the conduction is discontinuous.

These two effects may be eliminated, as well as the reduction of the harmonic content, with the introduction in parallel with the load of a diode called Freewheeling Diode (FWD) or Flying Diode. When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil is inverted. It begins to act as a generator, forcing the conduction of the FWD and the load current going through it, annulling the peak of negative voltage, as we can see in the following.

Consider the above figure which shows the assembly of Thyristor and Free Wheeling diode.

Figure:- Controlled Half wave rectifier with FWD



Page | - 50 -

The circuit works as follows: In the positive semi cycle, during the interval in which the Thyristor is switched on, the input voltage appears in the output with no changes. When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil is inverted, thus, the coil works as a generator. As a consequence, the freewheeling diode is directly polarized, and the load current circulates through. The negative peak of the output voltage that took place in the previous paragraph is annulled. This may be better appreciated in the following graphs

Circuit Diagram:-

Procedure:

1. Carry out the assembly E1CK shown in the above figure 2. Now connect a diode in anti-Parallel manner with the Thyristor as shown below 3. Connect the respective RL load to its terminal .

For RL Load with FWD Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage.

S. No Load Impedance V rms Voltage Across

Thyristor Th 1

1. 300

+ 75 + 140mH

2. 300

+ 75 + 236mH



Page | - 51 -

Observe how the output current varies for different L values with R=375 . And sample the following parameters: Input voltage V2, Output voltage V1, Output current I1, Thyristor Voltage V3

Figure: Controlled Half Wave Rectifier RL Load with FWD



AC/DC Single-phase Controlled Half wave Rectifier option 5. Select the respective sample sensors 6. Check the connections and switch on the equipment. 7. Press the Data Capture button. 8. Visualize the parameters measured and save them in the corresponding file. 9. Switch off the equipment.

Question:

Define the following terms:

1. Free Wheeling Diode ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Effect of FWD on RL Load Output ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________



Page | - 52 -

3. Fundamental Frequency: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 5. Rectifiers: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Waveforms:-

R-L LOAD WITH FWD



Fig: Thyristor voltage



Page | - 53 -

LAB SESSION 08 (a)

Object:

AC/DC Three phase Controlled Half-wave Rectifier with R load & R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Wires

Theory:

Three-phase half-wave controlled rectifiers: Three-phase electricity supplies with balanced, sinusoidal voltages are widely available. It is found that the use of a three-phase rectifier system, in comparison with a single-phase system, provides smoother output voltage and higher rectifier efficiency. Also, the utilization of any supply transformers and associated equipment is better with poly-phase circuits. If it is necessary to use an output filter this can be realized in a simpler and cheaper way with a poly-phase rectifier.

Figure: Three-phase, half-wave controlled rectifier with resistive load: (a) circuit connection, (b) phase voltages at the supply, output voltage, output current.



Page | - 54 -

Table: Three Phase Controlled Rectifier with Ideal Supply

Circuit Diagram:

B6C Model Procedure:



And sample the following parameters: Input voltage (V2,V3, V4), Output voltage V1, Output current I1, Thyristor voltage V5 as shown in the above figure.



Page | - 55 -

Figure: Controlled Three Phase Full Wave Rectifier with R load

Also measure the following quantities using multi-meter.

S. No Load Resistance V rms Voltage across Th 1 1. 300 + 75

2. 300 + 120

For RL Load Observe how the conduction angle increases as we increase L (0 to 236mH) with R=375 , measuring with the voltmeter the average output voltage.

S. No Load Impedance V rms Voltage across Th 1 1. 300

+ 75 + 140mH 2. 300

+ 75 + 236mH

Observe how the output current varies for different L values with R=375 . Save the different samples.

And sample the following parameters: Input voltage (V2,V3, V4), Output voltage V1, Output current I1, Thyristor voltage V5 as shown in the above figure.



Page | - 56 -

Figure: Controlled Three Phase Full Wave Rectifier with RL load



AC/DC

Three Phase Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.

Here you can also study and visualize what will be the effect of inverting the polarization of the three Thyristor.

Secondly suppose that, due to an over-voltage, one of the Thyristor is in open circuit. Study and visualize what effect provokes the output voltage.



Page | - 57 -

Waveforms:

R LOAD




R-L LOAD




Page | - 58 -





Page | - 59 -

LAB SESSION 08 (b)

Object:

AC/DC Three-Phase Controlled Full-wave Rectifier with R load& R-L load.

Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires

Theory:

Three phase controlled full wave rectifier:- Three phase controlled full wave rectifier is just like assembly of two controlled, three phase half wave rectifiers. One with common anodes and other with common cathodes as shown below.

Figure:- Three Phase controlled full wave rectifier with resistive load a) Circuit connections with load b) load voltage and load current

waveforms.

Th 1, Th 2, Th 3, conduct when the voltages Vr, Vs, Vt respectively are most positive provided that the Thyristor have been triggered.

Th 4, Th 5, Th 6, conduct when the voltages Vr, Vs, Vt respectively are most negative provided that the Thyristor have been triggered.

The average output voltage for R load will be: 60 (direct conduction ) V average = (cos wt) 3 3V/

60 (discontinuous conduction) V average = (1 - 3/2 sin + 1/2 cos )3 3V/

The average output voltage for RL load will be:



Page | - 60 -

60 (direct conduction ) V average = (cos ) 3 3V/

60 (discontinuous conduction) V average = (sin wt - 3/2 sin + 1/2 cos )3 3V/

Circuit Diagram:-

B6C Model

Procedure:



And sample the following parameters: Input voltage V4, Output voltage V1, Output current I1, Thyristor voltage V3 (as shown in figure)

Figure:- Three Phase controlled full wave rectifier with R load.



Page | - 61 -

Also measure the following quantities using multi meter. S. No Load Resistance V rms Voltage across D1 1 300 + 75

2 300 + 120

For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. V av =

S. No Load Impedance V rms Voltage across D1 1 300 + 75 + 140 m

H 2 300 + 120 + 236mH

Observe how the output current varies for different L values with R=375. Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I1, Thyristor voltage V3 (as shown in figure)

Figure:- Three Phase controlled full wave rectifier with RL load.



AC/DC Three-Phase Controlled Full-wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.



Page | - 62 -

Waveforms:

R LOAD

Fig: Input Voltage R, S, T Fig: Output Voltage across R Load



R-L LOAD

Fig: Input Voltage R , S , T Fig: Output Voltage across RL load



Page | - 63 -


with L=140mH Fig: Load Current IL

with L=236mH

Fig: output voltage across Thyristor



Page | - 64 -

LAB SESSION 09

Object:-

DC/DC Chopper. Apparatus:

SACED TECNEL

TECNEL or TECNEL/B

RCL3R Load module

Connecting Wires Theory:-

Chopper is used to convert the unregulated DC input to a controlled DC output with a desired voltage level. It is a static device which gives variable dc voltage from a constant dc voltage source. Chopper is also known as dc-to-dc converter. There are basically two types of the chopper:

1. Step down chopper (BUCK) :- In step down chopper output voltage is less than input voltage.

2. Step up chopper (BOOST) :- In step up chopper output voltage is more than input voltage.

Basically, we may obtain a variable voltage from a fixed direct voltage by way of connecting and disconnecting the source from the load by using a switch, so the average value of the output voltage may depend on the opening and closing rhythm of the controllable switch. In this case it will be an IGBT. They are, thus, called Commuted Direct Current Converters.

The input voltage chopping to obtain a lower average value is the Chopper operation principle. The average value of this voltage will depend on the ratio of the T on time (conduction time) and the period T, called work cycle.

The average value of voltage is given by above formula;

Therefore, the variation of the average output voltage can be made in three ways:



Page | - 65 -

By closing the switch at a fixed frequency (1/T) and delaying its opening (varying the work cycle using Ton).

By acting on the switch with a variable frequency, but always leaving the switch closed at the same time (fixed Ton).

By acting on the switch in a mixed way, that is, acting the same as in the latter case only with a variable conduction time.

The most general sketch for this type of converters is the following one:

Figure:- BUCK chopper

The function of the output filter is to cut down the output intensity. The freewheeling diode prevents any dangerous over voltages that may damage the switch, since the current in the load circulates through it as soon as it is annulled, and there is no abrupt variation of the current in Lout. The source possesses internal impedance Rg, and Lin and Cin constitute the input filter, which has a double function:

Limiting the over voltages that will take place in Lg when the switch is opened.

To cut down the intensity supplied by the source, and consequently the curling of its output voltage.

There are two ways of operation of a chopper which are given as under : Direct conduction mode The intensity that circulates through the load fluctuates between maximum and minimum values, never to the point of being annulled. As it will be seen later on, it is caused by the ratio of the period of time that the switch is closed and the time that the coil needs to discharge all its energy previously stored. This is also called direct current regime. Discontinuous conduction mode The intensity for the load is annulled at a certain moment during the Toff period (time during which the switch is opened). The time during which the switch is opened is bigger than the one



Page | - 66 -

required by the coil to give away all its energy, therefore when the following period starts the intensity will be zero. Also called regime of discontinuous current.

To study the circuit operation, we will analyze the two states that the switch may present (opened or closed).

when switch is closed as , as shown in figure the diode is reversed biased . switch conducts the inductor current , this results in positive voltage across inductor.

when switch is opened , as shown in figure the current iL continues to flow. The diode is forward biased and current now flows (free-wheeling) through the diode



Page | - 67 -

CIRCUIT DIAGRAM:-

Figure:- BUCK model

PROCEDURE:-

1. Carry out the assembly BUCK as shown in the above figure. 2. Connect the respective load to its terminal . 3. Select the following sensors.

Input Voltage (V1), Output Voltage (V2), Input Current (I1) and Output current (I2) 4. Introduce 500 Hz as frequency and 50% as duty cycle. 5. Obtain and analyze the output voltage, determine its average value and check it with

voltmeter, analyze how R variations effect the voltage 6. Obtain and analyze output current and determine its average value. Analyze how variations

of R effect the maximum and average value.

For RL Load S. No Load Impedance Input Voltage (V1) Output Voltage (V2) V av

1. 600 +236mH 2. 600 + 472mH



Page | - 68 -

Figure:- Circuit Diagram of DC/DC Chopper with RL Load.



AC/DC CHOPPER option 8. Select the respective sample sensors 9. Check the connections and switch on the equipment. 10. Press the Data Capture button. 11. Visualize the parameters measured and save them in the corresponding file.

Switch off the equipment.

S. No Load Impedance Input Current (I1) Output Current(I2) 1. 600 +236mH

2. 600 +472mH



Page | - 69 -

Waveforms:-

Fig: Input Voltage Fig: Output Voltage across load

Fig: Load Current Fig: Input Current



Page | - 70 -

LAB SESSION 10

OBJECT

To draw the magnetization curve of self-exited DC shunt generator (open circuit

characteristics curve O.C.C).

APPARATUS

1. Bench 10-ES/EV or Bench 14-ES/EV 2. DC multi-range ammeter 3. DC multi-range voltmeter

CIRCUIT DIAGRAM

THEORY

The magnetization characteristics, also known as No load or Open circuit characteristics, is the relation between emf generated and field current at a given speed.

Due to residual magnetism in the poles, some emf is generated even when filed current is zero. Hence the curve starts a little way up. It is seen that the first part of the curve is practically straight. This is due the fact that at low flux densities reluctance of iron path is being negligible, total reluctance is given by air gap reluctance which is constant. Hence the flux and consequently the generated emf is directly proportional to exciting current. However at high flux densities iron



Page | - 71 -

path reluctance is being appreciable and straight relation between emf and field current no longer holds good. In other words saturation of poles starts.

PROCEDURE

1. Connect the shunt field to armature terminal through the ammeter, switch and rheostat. 2. Connect the multi-range voltmeter across the terminals of armature. 3. Press yellow switch on and increase AC voltage of induction motor (prime mover) by

the help of 3-phase autotransformer until it reaches at normal speed. 4. Note the reading of voltmeter which indicates the voltage due to residual magnetism. 5. Close field switch and excite the field at low current. 6. Increase the field current in steps and note the voltage each time. 7. Take at least 11-12 readings. 8. Tabulate the reading and draw the curve between armature induced emf and exciting

current

OBSERVATIONS

S. No. FIELD CURRENT IF (A)

TERMINAL VOLTAGE

VT (volts)

1

2

3

4

5

6

7

8

9

10

11

12



Page | - 72 -

RESULT

1. The curve starts somewhat above the origin. The voltage at zero excitation is due to

residual magnetism of the field, which is necessary for building up the voltage of self-excitation generator.

2. The voltage increases rapidly at first and then changes a little in value at higher excitations indicating the effect of the poles saturation.

EXERCISE:

Answer the following questions:

What do you understand by Self Excited ? If this is a self-excited machine then why there is a need of supplying voltage to the auto transformer?

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________



Page | - 73 -

LAB SESSION 11

OBJECT

To draw the load characteristic curve of self-excited D.C shunt generator.

APPARATUS


CIRCUIT DIAGRAM

THEORY

Load characteristic curve is the graphical representation which shows change in terminal voltage with respect to change in load. After building up of voltage, if a shunt generator is loaded then terminal voltage drops with increase in load current. There are three main reasons for the drop of terminal voltage for a shunt generator under load.



Page | - 74 -

i) Armature Reaction

Armature reaction is the effect of magnetic field set up by the armature current on the

distribution of flux under main poles of a generator. Due to demagnetizing effect of armature reaction, pole flux is weakened and so induced emf in the armature is decreased.

ii) Armature Resistance

As the load current increases, more voltage is consumed in ohmic resistance of armature circuit. Hence the terminal voltage (Vt = E

IaRa) is decreased where E is the emf induced in armature under load condition.

iii) Drop In Terminal Voltage

The drop in terminal voltage (Vt) due to armature resistance and armature reaction results in decreased field current, which further reduces emf induced.

For a shunt generator Ia = IL+ If

E = Vt + IaRa

PROCEDURE

1. Make the connections as shown in circuit diagram. 2. Press yellow switch on and increase AC voltage of induction motor (prime mover) by

the help of 3-phase autotransformer until it reaches at normal speed. 3. When motor reaches rated speed, close the shunt field switch. 4. Increase field current by changing the field resistance until the terminal voltage reaches to

220 volt. 5. Close the switch of load and vary the load current by means of load rheostat. 6. Note down the meter readings from all meters carefully.



Page | - 75 -

OBSERVATIONS

S. No If(A) IL(A) VT(V) Ia=If+IL

Vd=IaRa

Ra=0. 5 ohm

1

2

3

4

5

6

7

8

RESULT

The terminal voltage of a D.C. generator is maximum at no load, which decreases with increasing load.



Page | - 76 -

LAB SESSION 12

OBJECT

To draw the external and internal characteristics of separately excited DC generator.

APPARATUS


CIRCUIT DIAGRAM

Figure: Separately Excited DC generator

THEORY

The load or external characteristic of a generator is the relation between the terminal voltage and load current. The characteristic expressed the manner in which the voltage across the load varies with I, the value of load current. The internal or total characteristic of a generator is the relation between the emf actually induced in the generator Ea and the armature current Ia The internal characteristic of the generator, which is separately excited, can be obtained as below:

Let: Vt= Terminal voltage, Ia = Armature current, Ra = Armature resistance

Then, Ea = Vt + IaRa

Ia = IL

Therefore if we add drop of armature (IaRa) to terminal voltage Vt we get actually induced emf (Ea).



Page | - 77 -

PROCEDURE

1. Make the circuit as shown in circuit diagram. 2. Press yellow switch on and increase AC voltage of induction motor (prime mover)

by the help of 3-phase autotransformer until it reaches at normal speed. 3. When motor reaches rated speed, close the shunt field switch. 4. Increase field current by changing the field resistance until the terminal voltage reaches

to 220 volt. 5. Close the switch of load and vary the load current by means of load rheostat. 6. Note down the meter readings from all meters carefully.

OBSERVATIONS

S. No IL(A) If(A) VT(V) Ea = Vt + IaRa

(V)

1

2

3

4

5

6

7

8

RESULT

From the graph it is observed that the terminal voltage across generator decreases as the load increases.



Page | - 78 -

LAB SESSION 13

OBJECT

Speed control of a DC shunt motor by flux variation method.

APPARATUS

1. Bench 13-ES/EV or Bench 15-ES/EV 2. DC multi-range ammeter 3. DC multi range voltmeters

4. Digital tachometer

CIRCUIT DIAGRAM

Fig: DC Shunt Motor

THEORY

This method is used to increase speed of DC motor above base speed. To understand what happens when the field resistance of dc motor is changed, assume that the field resistance is increased then the following sequence of cause and effect will take place

1. Increasing Rf causes If to decrease

2. Decreasing If Decreases

3. Decreasing

lowers Ea 4. Decreasing Ea Increases Ia 5. Increasing Ia increases Tind

6. Increasing Tind makes Tind>Tload, hence speed increases. 7. Increasing speed increases Ea



Page | - 79 -

8. Increasing Ea decreases Ia 9. Decreasing Ia decrease Tind until Tind= Tload at higher speed. Naturally decreasing Rf would reverse the whole process and speed of motor will decrease.

It is important to bear in mind, changing field resistance does not affect torque induced, at the end its magnitude remains same but at higher or lower speed depending upon change in resistance.

PROCEDURE

1. Make connections as shown in the circuit. 2. Keep the motor starting rheostat at its maximum position and field rheostat at its minimum

position while starting motor. 3. Start the motor by pressing yellow switch "ON" without load. 4. Adjust the motor start rheostat to its minimum value. 5. Decrease field current by the help of field rheostat step by step and take readings of field

current and speed from digital tachometer at every step. Adjust the field rheostat to give maximum speed at which it is safe to operate the motor.

OBSERVATIONS

S. No Field Current Speed

If(A)

N (RPM)

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

RESULT

Speed increases as the field excitation decreases.



Page | - 80 -

EXERCISE:


Why do we set the armature rheostat at maximum and field rheostat at minimum? _______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

After starting motor, why do we set the Ra to its minimum?

______________________________________________________________________________________________

______________________________________________________________________________________________

______________________________________________________________________________

__________________________________________________________________________



Page | - 81 -

LAB SESSION 14

OBJECT

Speed control of a D.C. Shunt Motor by armature rheostat control method.

APPARATUS

1. Bench 13-ES/EV or Bench 15-ES/EV 2. DC multi-range ammeter 3. Voltmeters

4. Digital tachometer

CIRCUIT DIAGRAM

Fig: DC Shunt Motor

THEORY

This method is used to decrease speed of DC motor below base speed. To understand what happens when the armature resistance of DC motor is changed, assume that the armature resistance is increased then the following sequence of cause and effect will take place

1. Increasing Ra causes Ia to decrease 2. Decreasing Ia decreases Tind

3. Decreasing Tind makes Tind<Tload, hence speed decreases.



Page | - 82 -

4. Decreasing speed decreases Ea 5. Decreasing Ea increases Ia again. 6. Increasing Ia increases Tind until Tind = Tload at lower speed.

Naturally decreasing Ra would reverse the whole process and speed of motor will increase. It is important to bear in mind, changing armature resistance does not effect torque induced ,at the end its magnitude remains same but at higher or lower speed depending upon change in resistance.

PROCEDURE

1. Make connections as shown in the circuit. 2. Keep the motor starting rheostat at its maximum position and field rheostat at its minimum

position while starting motor. 3. Start the motor by pressing yellow switch "ON" without load. 4. Adjust the motor start rheostat to its minimum value. 5. Increase the value of starting resistance by the help of motor start rheostat step by step and

take readings of voltage across armature and speed from digital tachometer at every step.

OBSERVATIONS

S. No Armature Voltage Speed

Va (V)

N (RPM)

1.

2.

3.

4.

5.

6.

7.

8.

RESULT

Speed is very nearly proportional to the applied voltage in the case of armature control method.


OBJECTTo observe the starting of three phase Synchronous and Induction motor

APPARATUS

1. 3- Synchronous motor2. 3- Induction motor3. Variable 34. DC Supply5. Tachometer

THEORY

To understand how the IM. The application of threethe rotor. The own field. synchronous speed. The reversal of any two applied phases causes the rotatrotate in opposite direction (w.r.t. to previous one). In this fashion an Induction motor works

Electrical Drives

University of Engineering and Technology

OBJECT

To observe the starting of three phase Synchronous and Induction motor

APPARATUS

Synchronous motor

Induction motorVariable 3- AC supplyDC Supply

Tachometer

RY

To understand how the he application of three

the rotor. The voltages are induced on the rotor bars(short circuited at both ends), developing its . Both fields interact with each other causing the rotor to move at speed less than the

synchronous speed. The reversal of any two applied phases causes the rotatrotate in opposite direction (w.r.t. to previous one). In this fashion an Induction motor works

Figure: Induction Motor



Synchronous motor

Induction motor

AC supply

To understand how the induction motorhe application of three-phase ac

voltages are induced on the rotor bars(short circuited at both ends), developing its Both fields interact with each other causing the rotor to move at speed less than the




LAB SESSION 15


induction motorphase ac

power causes a rotating magnetic field to be set up around voltages are induced on the rotor bars(short circuited at both ends), developing its

Both fields interact with each other causing the rotor to move at speed less than the synchronous speed. The reversal of any two applied phases causes the rotatrotate in opposite direction (w.r.t. to previous one). In this fashion an Induction motor works


Electrical Drives

LAB SESSION 15


induction motor

works, apply the three phase ac supply on stator of power causes a rotating magnetic field to be set up around




LAB SESSION 15


apply the three phase ac supply on stator of power causes a rotating magnetic field to be set up around



Lab SessionDepartment of Electrical Engineering




synchronous speed. The reversal of any two applied phases causes the rotating magnetic field to rotate in opposite direction (w.r.t. to previous one). In this fashion an Induction motor works

Lab SessionDepartment of Electrical Engineering

Page | -



ing magnetic field to rotate in opposite direction (w.r.t. to previous one). In this fashion an Induction motor works

Lab Session

15


-

83 -



ing magnetic field to



Page | - 84 -

To understand how the synchronous motor works, assume that the application of three-phase ac power to the stator causes a rotating magnetic field to be set up around the rotor. The rotor is energized with dc (it acts like a bar magnet). The strong rotating magnetic field attracts the strong rotor field activated by the dc. This results in a strong turning force on the rotor shaft. The rotor is therefore able to turn a load as it rotates in step with the rotating magnetic field. It works this way once it s started.

However, one of the disadvantages of a synchronous motor is that it cannot be started from a standstill by applying three-phase ac power to the stator and dc to its rotor. When ac is applied to the stator, a high-speed rotating magnetic field appears immediately. This rotating field rushes past the rotor poles so quickly that the rotor does not have a chance to get started. In effect, the rotor is repelled first in one direction and then the other. A synchronous motor in its purest form has no starting torque. It has torque only when it is running at synchronous speed. A squirrel-cage type of winding is added to the rotor of a synchronous motor to cause it to start. The squirrel cage is shown as the outer part of the rotor in figure. It is so named because it is shaped and looks something like a turn able squirrel cage. Simply, the windings are heavy copper bars shorted.

Hence, three phase synchronous motor is not self-started. At the starting time, it behaves as induction motor and gets accelerated. Once it approaches speed near to synchronous speed, its rotor winding is excited then synchronous motor start rotating at synchronous speed. If we have given rotor supply at start, motor will just produce humming sound.

PROCEDURE

For Induction Motor: 1. Make the circuit and switch on three phase ac supply and observe the performance. 2. Now reverse any of the two phases and verify double field revolving theory.

Figure: Synchronous Motor



Page | - 85 -

For Synchronous Motor: 1. Make the circuit and switch on both ac and dc supply and observe the performance. 2. Disconnect dc supply, switch on ac supply and observe the performance. 3. When motor run near to synchronous speed, which already calculated, switch on dc supply

also and observe the behavior.

OBSERVATIONS:

Speed of Induction Motor: rpm

Calculate: Slip speed =

Slip =

Speed of Synchronous Motor =rpm

EXERCISE:


Why Induction motors have high starting current? ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Write three differences between Induction & Synchronous motor. _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Date post:	18-Oct-2014
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