Chapter 2 422 Transformer 1

transcript

CHAPTER TWO Page 65 (4th Edition) Transformer

2.1 (P-57) WHY TRANSFORMER ARE IMPORTANT TO MODERN LIFE

2.2 (P-57-58) TYPES AND CONSTRUCTION OF TRANSFORMER (cont…..

Unit Transformer

Grid Transformer

Distribution Transformer

Sub-Station Transformer

More Distance HV Low I2R Losses

3 –Phase Transmission Line

Primary and Secondary Windings A two-winding transformer consists of two windings interlinked by a mutual magnetic field

– Primary winding – energized by connecting it to an input source

– Secondary winding – to which an electrical load is connected and from which output energy is drawn.

Mutual Flux

NP NSVP VS

AC Generator

Transformer

Source

Another Transformer

Resistive or inductive or combined

RatiotionTransformaaI

Circuit - Ideal Transformer Why?

No Leakage Flux

No Losses -{No Winding Resistance Losses}

- [No Core Losses due to eddy current and hysterisis]

Core of a transformer

Primary Side (P)

Secondary Side (S)

2.2 (P-57-58) TYPES AND CONSTRUCTION OF TRANSFORMER

Core Type Transformer

Mutual Flux M

Shell Type Transformer

Mutual Flux M

Question: (Must Know)

Why transformer, motors and generators cores are made of laminated iron core (steel sheets)?

The primary and secondary windings in a physical transformer are wrapped one on top of other with the low-voltage winding innermost. Such an arrangement serves two purposes:

1. Insulating the high-voltage winding from the core.

2. If the two windings were separated by a distance on the core, would results in much leakage flux

Iron core

Terminals

Secondarywinding

Insulation

PrimaryWinding

SecondaryWinding

Multi-layerLaminatedIron Core

2H1 H2

WindingTerminals

Shell Type Shell Type –both windings on same leg

2. Why the transformers, motors and generators cores are made of iron why not from copper, Aluminum, glass, plastic or wood?

3. Why the transformer, motors and generators cores are made of laminated steel sheets (i.e. not solid steel) . Why ?

4. Laminated steel sheets are insulated from each other to (a) increase the eddy current (b) decrease the eddy current (c) increase the Hysterysis losses (d) decrease the hystyresis losses (f) decrease the mutual flux

Find the correct answer with justification/explanation.

Question:

1. Can we use the primary as a secondary or secondary as a primary?

Mutual Flux

NP NSVP VS

What is Hysterisis loss?

What is Leakage flux (inductance)?

Primary & secondary winding’s resistance are not shown in the circuit

Question: Do we have secondary winding leakage flux (inductance), if the load on the secondary side is not connected? Why?

2.3 (P-58-61) THE IDEAL TRANSFORMER

The ideal transformer has the following properties:

No iron or copper losses

No leakage flux

A core of infinite magnetic permeability and of infinite electrical resistivity

Flux is confined to the core and winding resistances are negligible

In instantaneous quantities

2.3 (P-58-61) THE IDEAL TRANSFORMER (cont…..

Input voltage (Vp) and the output voltage (Vs), between the input current (Ip) and the output current ((Is) betweenthe primary turns (NP) andthe secondary turns (NS)

p In rms quantities

a: turns ratio (transformation ratio)

tiNtiN

tvdttd

From Ampere’s law

Dividing (1) by (2)

Equating (3) and (4)

…………….. (1)

…………….. (2)

………………......……….. (3)

…………………..……….. (4)

………………….. (5)

Voltage polarity: Dot convention: Phase dots are used to indicate polarities

Sketch of an ideal transformer Schematic symbol of a transformer

• The direction of the windings determines the polarity of the voltage across the secondary winding with respect to the voltage across the primary

• The center tap (CT) transformer is equivalent to two secondary windings with half the voltage across each

• Center tap windings are used for rectifier supplies and impedance-matching transformers

Dot : Center Tapped Transformers

TRANSFORMERS

Question• A step-up transformer has a ratio of 1 to

10. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is

• (a) 1 W• (b) 10 W• (c) 100 W • (d) 1000 W• (e) none of these

Question• A step-up transformer has a ratio N of 1

(P) to 10 (S). Neglecting slight losses, if 1 Amp of current go into the primary coil, the current coming from the secondary coil is

• (a) 0.1 Amp• (b) 1 Amp• (c) 10 Amp • (d) 100 Amp• (e) none of these

Problem for Transformer• In the circuit shown, how many volts are

impressed across, and how many amperes flow through, the light bulb?

Answer: 0.1 amp; 100:10 = 120:V, V = 10V; 10 x 1 = 100 x ?, so ? = 0.1

Transformer problem• An ideal transformer has 50 turns in its

primary and 250 turns in its secondary. 12-V AC is connected to the primary.

• Find: (a) the volts AC available at the

secondary, (b) the current in a 10-ohm device

connected to the secondary, and (c) the power supplied to the primary.

Solutionprimary voltage secondary voltage

primary turns secondary turns

50 25012 x 250

V= = 60 volts50

V 60I x = x 6 amps

R 10Power to primary = Power to secondary

P x VI =60 x 6 =360 watts

jQ = /90o

-jQ = /-90o

Power in an Ideal Transformer

outssppin

outsss

inpppp

sssout

SIVIVS

IaVIVQ

PIVaIa

sincossin

coscoscos

Real power P supplied to the transformer by the primary circuit

Real power coming out of the secondary circuit

Thus, the output power of an ideal transformer is equal to its input power.

The same relationship applies to reactive Q and apparent power S:

Question from class student.

What is actuator?

Ans: Next Slide

Electro-Mechanical

What is a Actuator?

• Actuator is a device which produce mechanical energy (output motion) in response to some type of energy input.

Energy

Electrical

Thermal

Fluid• Hydraulic• Pneumatic

Mechanical

Chemical

Actuator Motion

Rotary

Linear

Complex

Many actuators rely on electromagnetic forces to create their action.

Chapter 2 422 Transformer 1

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