Transformers

Transformers

Transformer Ratings • VA rating • Cooling – 1000 kVA 55°C ONAN

• Frequency • Voltage • Phase

Separate Windings N1 N2 V1

I1

V2 V1

V2

I2

=

N2 N1

=

I1 I2

Autotransformer N1

V1

I1

V2 V1

N2

=

N2 N1

V2 I2

=

I1 I2

Connections INPUT Vb1

Va1

Vc2

b2 a2

Va3

Vb3 Vc3

Vc1

Off Load Tap Changers

On Load Tap-Changers Line

HV Voltage Varying

Reactors Neutral End 8 Bypass Switch

Vacuum Switch

7 6 5 4 3

Selector Switch

2 1

LV Cont Voltage

B

B 2

2

1 A

1 A

(1)

(2)

B

B 2

2

1

1

A

A (3)

(4)

B

B 2

2

1

1

A

A (5)

(6)

B

B 2

2

1

1

A

A (7)

(8)

B

B

A

2

2

1

1 A

(9)

(10)

Tap-Changer Sequence 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 Thermocouple R winding "hot Spot" oil bath

Transformer Oil

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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