EXP.NO. 1 DATE:

REGULATION OF 3–PHASE ALTERNATOR BY EMF AND MMF METHODS

AIM:To predetermine the regulation of 3-phase alternator by EMF and MMF methods

and also draw the vector diagrams.

APPARATURS REQUIRED:

SL.NO Name of the Apparatus Type Range Quantity1 Ammeter MC 0 – 1/2 A 12 Ammeter MI 0 – 5/10 A 13 Voltmeter MC 0 – 10 V 14 Voltmeter MI 0 – 600 V 15 Rheostat Wire

wound250 Ω, 1.5 A 1

6 Rheostat Wire wound

1200Ω, 0.8 A 1

7 Tachometer Digital --- 18 TPST knife switch -- -- 1

THEORY:The regulation of a 3-phase alternator may be predetermined by conducting the

Open Circuit (OC) and the Sort Circuit (SC) tests. The methods employed for determination of regulation are EMF or synchronous impedance method, MMF or Ampere Turns method and the ZPF or Potier triangle method. In this experiment, the EMF and MMF methods are used. The OC and SC graphs are plotted from the two tests. The synchronous impedance is found from the OC test. The regulation is then determined at different power factors by calculations using vector diagrams. The EMF method is also called pessimistic method as the value of regulation obtained is much more than the actual value. The MMF method is also called optimistic method as the value of regulation obtained is much less than the actual value. In the MMF method the armature leakage reactance is treated as an additional armature reaction. In both methods the OC and SC test data are utilized.

PRECAUTIONS:

(i) The motor field rheostat should be kept in the minimum resistance position.

(ii) The alternator field potential divider should be kept in the minimum voltage position.

(iii) Initially all switches are in open position.

REGULATION OF 3-PHASE ALTERNATOR BY EMF AND MMF METHODS

TABULAR COLUMNS

OPEN CIRCUIT TEST:

S.No.Field Current (If) Open Circuit Line

Voltage (VoL)Open circuit Phase

Voltage (Voph)Amps Volts Volts

SHORT CIRCUIT TEST:

S.No. Field Current (If)Short Circuit Current (120%

to 150% of rated current) (ISC)

Amps Amps

REGULATION OF 3-PHASE ALTERNATOR BY EMF AND MMF METHODS

TABULAR COLUMNS

EMF METHOD:

SL.NO. Power factor

Eph (V) % Regulation

Lag Lead Lag Lead

MMF METHOD:

SL.NO. P.F Vph(V)

If1(A)

If2(A)

Ifr(A)

Eph (V) % Regulation

Lag Lead Lag Lead Lag Lead

PROCEDURE: (FOR BOTH EMF AND MMF METHODS)

1. Note down the name plate details of the motor and alternator.2. Connections are made as per the circuit diagram.3. Switch ON the supply by closing the DPST switch.4. Using the Three point starter, start the motor to run at the synchronous speed by

adjusting the motor field rheostat.5. Conduct Open Circuit test by varying the potential divider for various values of

field current and tabulate the corresponding Open Circuit Voltage readings.

6. Conduct Short Circuit test by closing the TPST switch and adjust the potential divider to set the rated armature current and tabulate the corresponding field current.

7. The Stator resistance per phase is determined by connecting any one phase stator winding of the alternator as per the circuit diagram using MC voltmeter and ammeter of suitable ranges.

PROCEDURE TO DRAW GRAPH FOR EMF METHOD:1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS

Field current).2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field

current)3. From the graph find the open circuit voltage per phase (E1 (ph) for the rated

short circuit current (Isc).4. By using respective formulae find the Zs, Xs, Eo and percentage regulation.

PROCEDURE TO DRAW GRAPH FOR MMF METHOD:1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS

Field current).2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field

current)3. Draw the line OL to represent

FORMULAE:1. Armature Resistance Ra = Ω

2. Synchronous Impedance Zs = O.C. voltage S.C. current

3. Synchronous Reactance Xs = √ Zs2 – Ra2

4. Open circuit voltage for lagging p.f = √(VcosΦ + IaRa)2 + (VsinΦ + IaXs)2

5. Open circuit voltage for leading p.f. = √(VcosΦ + IaRa)2 + (VsinΦ – IaXs)2

6. Open circuit voltage for unity p.f = √(V + IaRa)2 + ( IaXs)2

7. Percentage regulation = Eo – V x 100 V

RESULT:Thus the regulation of 3-phase alternator has been predetermined by the EMF and

MMF methods.

EXP.NO. 6 A DATE:

LOAD TEST ON 3-PHASE SQUIRREL CAGE INDUCTION MOTOR

AIM:To draw the performance characteristics of 3-phase squirrel cage induction motor

by conducting load test.

APPARATUS REQUIRED:

S.No Name of apparatus

Range Type Qty.

1. Ammeter (0-5)A MI 12. Voltmeter (0-600)V MI 13. Wattmeter (600V,5A) UPF 24. Tachometer Digital 15. 3-Ф

autotransformer1

FUSE RATING;

125% of 4.8A=6A=10A

THEORY:

A 3-phase induction motor consists of stator and rotor with the other associated parts. In the stator, a 3-phase winding is provided. The windings of the three phase are displaced in space by 120º.A 3-phase current is fed to the 3-phase winding. These windings produce a resultant magnetic flux and it rotates in space like a solid magnetic poles being rotated magnetically.

PRECAUTIONS-

1.TPST switch is kept open initially.

2.Autotransformer is kept at min. voltage position.3.There must be no load when starting the load.

PROCEDURE-

1.Connections are given as per circuit diagram.2.3-Ф induction motor is started with DOL starter.3. If the pointer of one of the wattmeter readings reverses, interchange the current coil terminals and take the reading as negative.3.The no load readings are taken.4. The motor is loaded step by step till we get the rated current and the readings of the voltmeter, ammeter, wattmeters, spring balance are noted.

FORMULAE USED-

1) % slip= (Ns-N/Ns)*1002) Input Power = (W1+W2)watts3) Output Power = 2∏NT/60 watts4) Torque = 9.81*(S1-S2)*R N-m5) % efficiency = (o/p power/i/p power)* 100

GRAPHS-

1) Output Power vs Efficiency2) Output Power vs Torque3) Output Power vs Speed4) Output Power vs %s

RESULTThus the performance characteristics of a 3-Ф squirrel cage induction motor by conducting load test has been drawn.

EXP.NO. 7 DATE:

NO LOAD AND BLOCKED ROTOR TEST ON 3- PHASE INDUCTION MOTOR

AIM: To conduct the no load & blocked rotor test on 3- phase induction motor& to draw the equivalent circuit of 3- phase squirrel cage induction motor.

APPARATUS REQUIRED :-zS.NO NAME OF

APPARATUSRANGE TYPE QTY

1. Voltmeter (0-600)V(0-150)V

MIMI

0101

2. Ammeter (0-10)A MI 01

3. Wattmeter (600V,5A)(150V,10A)

UPFLPF

0101

4. Connecting wire As required

FUSE RATING :-

125/100 * 7.5 A ≈ 10A

THEORY :-

A 3-phase induction motor consists of stator, rotor & other associated parts. In the stator,a 3- phase winding (provided) are displaced in space by 120. A3- phase current is fed to the winding so that a resultant rotating magnetic flux is generated. The rotor starts rotating due to the induction effect produced due the relative velocity between the rotor Winding & the rotating flux.

PRECAUTIONS :-

NO LOAD TEST –

(1). Initially TPST switch is kept open.(2). Autotransformer must be kept at minimum potential position.(3). The machine must be started at no load.

BLOCKED ROTOR TEST -

(1). Initially the TPST switch is kept open.(2). Autotransformer must be kept at minimum potential position.(3). The machine should be started on full load.

PROCEDURE :-

NO LOAD TEST -

(1). Connections are given as per the circuit diagram.(2). Precautions are observed and motor is started on the no load.(3). Autotransformer is varied to have rated voltage applied.(4). The meter readings are then tabulated.

BLOCKED ROTOR TEST :-

(1). Connections are given as per circuit diagram.(2). Precautions are observed and motor is started on full load or blocked rotor position.(3). Autotransformer is varied to have rated current flowing in motor.(4). The meter readings are then tabulated.

FORMULA USED-

FOR NO LOAD TEST-

Wsc = √3 Vo IoCOSФ watts Iw = Io cosФ amps Ro= V0/ Iw ΩXo= Vo/Iu Ω

FOR BLOCKED ROTOR TEST-

Wsc =3I2*Ro wattsRo1 = Wsc/3(Isc)2 ΩZo1 = Vsc/Isc ΩXo1 = √Zo1^2-Ro1^2 ΩRESULT:-

Thus the no load and blocked rotor test on 3-Фsquirrel cage induction motor is performed and the equivalent circuit of 3-phase squirrel cage induction motor has been drawn.

TABULAR COLUMNS

NO LOAD TEST: S.No Voltage

Voc

Volts

Current Ioc

Amps

Wattmeter readings (W1)

W1 x mf1

Wattmeter readings (W2)

W2 x mf2

Observed ActualWatts

Observed ActualWatts

1

Voc= open circuit voltageIoc = open circuit current

BLOCKED ROTOR TEST:

S.No. Voltage Vsc

Volts

Current Isc

Amps

Wattmeter readings(W1)

W1 x mf1

Wattmeter readings(W2)

W2 x mf2

Observed ActualWatts

observed ActualWatts

1.

Vsc = short circuit voltageIsc = short circuit current

EXP.NO. 9 DATE:

STUDY OF INDUCTION MOTOR STARTERS

AIM: To study and connect

(1) Direct Online Starter(2) Auto transformer Starter(3) Star Delta Starter(4) Rotor Resistance Starter

APPARATUS REQUIRED:SL.NO NAME OF APPARATUS QUANTITY

1. DOL Starter 1 No.2. Auto transformer Starter 1 No.3. Star Delta Starter 1 No.4. Rotor Resistance Starter 1 No.

THEORY:NECESSITY OF STARTERS:

An induction motor is similar to a secondary short circuit three phase transformer so if normal voltage is applied to the motor it takes 5 to 6 times of normal current from the mains and starting torque is also increased to around 1.5 to 2.5 times of their full load torque. This initial excessive starting current is objectionable, because it will produce large line voltage drop, which in turn will affect the operation of the other electrical equipments connected to the same mains. So the starters are used to reduce the starting current of induction motor and also to protect the motor and also used to protect the motor from overloading and low voltages.

TYPES OF STARTERS:(1) Direct Online Starter(2) Auto transformer Starter(3) Star Delta Starter(4) Rotor Resistance Starter

DIRECT ON LINE STARTER [DOL STARTER]:-

Generally when the starter winding of on induction motor are connected to the Supply directly .a very large current of about 5-8 times full load current flow initially. such a starting .of the induction motor is called direct on line starting. The initial stage current decreases of the motor starts accelerating and running at normal speed. Unlike d.c motors where such a starting can damage the windings due to a lsent 0/- back Emf at start induction motor can le started .This way through out not expandly in a short space of time called cycling .The only effect of the shorting is the sudden line voltage drop that occurs which may affect other electrically equipments on the same time line .hence direct an line

starting is not advisable for motor with rating greater than 5 HP. The points to be kept in mind for DOL starting are

Whether other electrical equipment connected to the same lines can with

stand The sudden voltage fluctuation caused by the starting.

Whether the generator and distribution system can with stand the high voltage Dip and large current drawn .

In case of loads having high inertia like centrifugal oil separate time may also be a factor

REASON FOR AVOIDING FAST CYCLING

At start the starting current Ist is about 5-8 times normal full load current .therefore The starting heat generated itself is related to 1st as

Hst α Ist2

And Hst is 26-64 times normal heating also at start there is no winding and other losses . Hence repeated starting in short space of time or fast cycling may cause successive heat and damage of coil .

HOW THE STARTER WORKS:

Control circuit: Thus circuit consists of conductor coil in series with start button stop Button and over load trip contacts is called control circuit. When the start button is pressed the control circuit energized to via lines of the 3 phase supply is connected the control coil the contactor classes and starts The motor after releasing the start .It spring back but the contactor is kept enargised by another auxillary winding . When the stop button is released proceed, it break the circuits & the contactors trips & the motor stops. Under excess current leaving drawn the over current trip coil are energized magnetic coil or the normally open (NO) the overload trip contact and stop the motor.

AUTO TRANSFORMER STARTER

This stator is useful and suitable for motor in which each and of the 3-phase are not all throughout and hence are not suitable for star delta starting gapped or variable autotransformer can be used for starting. The autotransformer are generally used for large motor drives like electric cargo pumps because of cost factors .

STAR-DELTA-STARTER This starter is used in case of motor which are built normally with a delta connected stator winding. Basically it consist a two way switch that connected the motor star type of the time of start and delta type under normal running connection . The advantages of having a star connected winding the voltage applied over each motor phase is reduced to 1/√ 3 times the normal value and the current to 1/√3 time normal value . But the starting torque is also reduced by a factor of 1/√3.

ROTOR RHEOSTAR STATOR

This stator is used for starting slip motors in this the stator terminal are Connected to supply via a variable resistance in series to the stator circuit . The controlling resistance is after connected rheostat type with resistance being gradually cot out as Motor gain speed. The two advantages of this starting is:- 1) starting current is reduced 2) starting torque is increased due to power factor improvement. The controlling rheostat may be of speed or contactor type and may also be manual or auto noted. The starter also consist of low voltage and over current protective devices. There is inter locking mechanism for ensuring proper operation of line contactor and starter. This method is similar to the starter used for starting dc motor in which too, the resistance is cut out gradually ones the motor was started running normally. PRECAUTIONS:

(1) All connections should be tight.(2) Metallic body of every equipment used must be properly earthed.

PROCEDURE:1. Connect the DOL starter with the motor terminal in one side and motor switch on

another side as shown in figure.2. Put ON the switch and press the start button (green) of the starter to start the

motor.3. Press the stop button (red) to stop the motor.4. Connect the auto transformer terminals with the motor terminals and motor switch

as shown in figure.5. Now adjust the required settings on autotransformer starter that is above 60%.6. Out ON the switch, now the motor will start running. When the motor speed

reaches to about 80% of the normal speed, then move the handle of the starter and to other side for giving full voltage to the motor.

7. Connect the Star Delta starter with the motor on one side and motor switch in another side as shown in figure.

8. Put on the switch and move the handle of the starter first in downward position thus connecting the winding first in Star and after a few seconds move it in upward position thus connecting the winding in Delta connection.

9. Connect the rotor resistance starter with the motor on one side and motor switch on another side as shown in figure.

10. Put ON the switch and start the motor with the rotor resistance.

RESULT:

Hence various types of the three phase induction motor starters have been studied

LOAD TEST ON DC SHUNT MOTOR

Ex. No. Date

AIM:

To perform load test on the given D.C shunt motor and to obtain the

performance characteristics.

APPARATUS REQUIRED:

Sl.No. Name Range Type Quantity

1 Voltmeter MC

2 Ammeter MC

3 Rheostat Wire wound

4 Connecting

wires

5 Tachometer Digital

FORMULAE:

PRECAUTIONS:

1. The motor field rheostat should be kept at minimum resistance

position.

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Observing the precaution the DPST switch is closed and the motor is

started with the help of 3-point DC starter slowly.

3. The motor field rheostat is adjusted and the motor is brought to rated

speed.

4. Load on the motor is varied with the help of pony brake arrangement.

5. Spring balance, ammeter, voltmeter and speed readings are noted down for

various line currents as the load is applied. Care must be taken to avoid the speed

reaching dangerously high values while reducing the load.

S.NoV(Volts)

I(Amps)

N(rpm)

S1(Kg)

S2(Kg)

S1~S2(Kg)

T(Nm)

Input(Watts)

Output(Watts)

Efficiency

6. At a minimum safe load the DPST switch is opened.

7. Disconnect and return the apparatus.

TABULAR COLUMN:

MODEL GRAPH:

RESULT:

The load test on the given D.C shunt motor was conducted and its performance

characteristics were drawn and the following conclusion can be given based on the

performance curves

OPEN CIRCUIT CHARACTERISTICS OF SEPARATELY EXCITIED DC GENERATOR

Aim: Date:

To draw open circuit characteristics of the given separately excited DC

generator.

Apparatus required:

Sl.No. Name Range Type Quantity

1

2

3

4

5

Voltmeter

Ammeter

Rheostat

Tachometer

Connecting wires

MC

MC

Wire wound

Analog

Precaution:

The field rheostat on the motor side must be kept at minimum

resistance position at the time of starting.

The field potentiometer on the generator side must be kept at

maximum potential position at the time of starting.

DPST switches must be kept open at the time of power on.

Procedure:

Connections are given as per the circuit diagram.

Observing the precautions the motor side DPST switch is closed.

The motor is started with the help of three- point DC starter slowly.

The speed is measured with the help of a hand tachometer.

If the speed is below the rated value, then it is brought to the rated

value by adjusting the field rheostat.

With DPST switch on the generator field side open the voltmeter

reading is noted down. (This is the residual voltage at the rated speed

at which the motor-generator set is running now.)

The DPST switch on the generator field side is closed.

By adjusting the potentiometer on the generator field side suitably for

various increasing field currents, note down the terminal voltages till

around 125% of the rated voltage. The speed is maintained constant

throughout this process.

The generator terminal voltage is minimized to zero.

The speed is brought down to minimum value and the motor is

switched off with the help of DPST switch. (Note the starter holding

coil releasing the handle else bring it back to start position)

Tabular column :

Speed = _________rpm

S. No. If (amps) Eo (volts)

MODEL GRAPH:

Eo

If

Result

SPEED CONTROL OF DC SHUNT MOTORAim: Date:

To vary the speed of the given dc shunt motor by the following methods.

(i).Armature control method (below rated speed)

(ii).Field control method (above rated speed)

Apparatus Required:

Sl.no Name of the apparatus Range

Type

Quantity

1.

2.

3.

4.

5.

Ammeter

Volt meter

Tacho meter

Rheostat

Connecting wires

M.C

M.C

Analog

Wire wound

Precautions:

1. The field rheostat must be kept at minimum resistance position at

the time of starting

2. The armature rheostat must be kept at maximum resistance position at

the time of starting

Procedure:

(i).Armature control method:

Make the connections as per the circuit diagram

Switch on the supply

Keep the field current constant and for different armature voltage (by

varying armature rheostat) note down the corresponding speed.

Bring back the rheostat to initial position and switch off the supply

(ii) Field control method

Switch on the supply

Start the motor by closing the DPST switch

Keep the armature voltage constant and for various field current note

down the corresponding speed.

Bring back the rheostat to initial position and switch off the supply

MODEL GRAPH

Armature Control method Field control method

Speed rpm Speed

rpm

Armature voltage (volts) Field current (amps)

(i).Armature control method:

Field current (If ) =

SL.No Armature voltage(volts)

Speed(rpm)

(ii) Field control method

Armature voltage (Va ) =

SL.No Field current(amps)

Speed(rpm)

Result:

LOAD TEST ON SINGLE PHASE TRANSFORMER

Aim: Date:

To perform load test on a single phase transformer and determine its

performance characteristics

Apparatus Required:

Sl.no Name of the apparatus Range

Type

Quantity

1.

2.

3.

4.

Ammeter

Volt meter

Watt meter

Connecting wires

M.I

MI.

Dynamo meter

Formulae:

Input power = W1 x M.F1 watts

Output power = W2 x M.F2 watts

Output power

Efficiency = X 100 %

Input power E 02 - V 2

Regulation = X 100 %

E 02

E 02 - No load secondary voltage

V 2 - Secondary voltage at various loads

M.F – Multiplication factor

W1, W2 - Wattmeter readingsMultiplication factor (M.F) = V I cos

No of divisions in the watt meter

Precautions:

Auto transformer must be kept at minimum potential point

There should be no load at the time of starting the experiment

Procedure:

Make the connections as per the circuit diagram

Switch on the supply and vary the autotransformer to get rated

primary voltage

Note down the no load readings

Add the load in steps and note down all the meter readings till the

rated secondary current is reached

Remove the load and bring back the autotransformer to original

position.

Switch off the supply

MODEL GRAPH

Efficiency Regulation

%

Output power in watts

Result:

OC AND SC TEST OF SINGLE PHASE TRANSFORMER

Aim: Date:

To perform open circuit and short circuit test on a single phase transformer and

predetermine the efficiency at various loads and also draw the equivalent circuit.

Apparatus Required:

Sl.no Name of the apparatus Range

Type

Quantity

1.

2.

3.

4.

Ammeter

Volt meter

Watt meter

Connecting wires

M.I

MI.

Dynamo meter

Formulae:

From open circuit test:

W0 = V0 I0 Cos 0 (watts)

Cos 0 = W0

V0 I0

I w = I0 Cos 0 ( Iron loss component)

I = I0 Sin 0 ( magnetizing component)

R0 = V0 / I w (resistance to represent core loss)

X0 = V0 / I (reactance to represent magnetizing component)

W0 = No load input = core loss = Wi = Iron loss I0 - No load input current

V0 – No load rated input voltage

From short circuit test:

R01 = Wsc

Isc 2

Z01 = Vsc

IscX01 = Z01

2 - R012

R01 - equivalent resistance of transformer referred to primary side

X01 - equivalent reactance of transformer referred to primary side

Z01 - equivalent impedance of transformer referred to primary side

Wsc – Full load copper loss

R02 = R01 x K 2

X02 = X01 x K 2

Z02 = Z01 x K 2

% Regulation = I2 R02 Cos + I2 X02 Sin X 100 %

V2

+ lagging Power factor

- leading powerfactor

Cos - Power factor

Efficiency at various loads = X * KVA * P.f * 100 %

X * KVA * P.f + Wi + X 2 Wsc

X – Load ratio

Precautions:

Auto transformer must be kept at minimum potential point

Procedure:

Open circuit test:

Make the connections as per the circuit diagram

Switch on the supply and vary the autotransformer to get rated voltage

Note down ammeter ,voltmeter and wattmeter readings.

Bring back the autotransformer to original position.

Switch off the supply

Short circuit test:

Make the connections as per the circuit diagram

Switch on the supply and vary the autotransformer to get rated short

circuit current.

Note down ammeter ,voltmeter and wattmeter readings.

Bring back the autotransformer to original position.

Switch off the supply

Equivalent circuit referred to primary side:

Equivalent circuit referred to secondary side:

Model Graph

Open circuit test

Short circuit test:

Load ratio X

Output power

upf 0.8

RESULT

Sl.]no

Vovolts

Ioamps

Wodiv

Wo x M.Fwatts

Sl.]no

Vscvolts

Iscamps

Wscdiv

Wsc x M.Fwatts