TRANSFORMER PROTECTION

7.4. Differential Relays

Figure 10: Differential protection for a generator phase winding.

Transformer Protection

• Problem 1: For a 45 MVA, 11 kV/66 kV, Y-∆ transformer design a percentage differential scheme. Use 125% overloading to find CT ratios.

• What is the minmum recommended percentage bias?

Transformer Protection Example

Magnetizing Inrush

Harmonic Restraint • Flow Chart

Percentage Bias Differential Relay with Harmonic Restraint

Inter-turn Faults in Transformers

Volts/Hertz Relay Characteristics

Protection During an Earth Fault

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Condition for a fault in middle of phase C on 13.2 kV Side

Problem 2: Connection Diagram

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Differential Protection for a Generator Connected in Star with four terminals

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