Transformers

Transformer Ratings

� VA rating� Cooling

� 1000 kVA 55°C ONAN� Frequency� Voltage� Phase

Separate Windings

N1

N2

I1 I2V1 V2

V1

V2 N2 I1

I2N1

= =

Autotransformer

N1

N2I1

I2

V1 V2

V1

V2 N2 I1

I2N1

= =

Connections

Vc1

INPUTVa1 Vb1

Vc2 a2b2

Va3 Vb3

Vc3

Off Load Tap Changers

On Load Tap-Changers

LVCont

Voltage

1

2

3

4

5

6

7

8

HVVoltageVarying

Line

NeutralEnd

Reactors

VacuumSwitch

BypassSwitch

SelectorSwitch

(3) (4)

A

B

1

2

A

B

1

2

(1)

A

B

1

2

(2)

A

B

1

2

(6)

A

B

1

2

(5)

A

B

1

2

(8)

A

B

1

2

(7)

A

B

1

2

(10)

A

B

1

2

(9)

A

B

1

2

Tap-ChangerSequence of Operation

Transformer Losses

� No-Load� Hysteresis� Eddy Currents� A tiny winding loss due to exciting current

� Winding Losses� Vary with the square of the load

Copper Losses

Core Losses

Laminated Core

Transformer Hot Spot

R

Thermocouple

Transformer Oil

winding "hot Spot"oil bath

Core Heating

Instrument Transformers

� Step down values to safe levels for measurement� Potential Transformers

� Also called voltage transformers� Standard output 120V

� Current Transformers� Standard output of 1 or 5 amps� Metering and relaying standards� Can produce high voltages if open circuited

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