Direct Connected Generator Protection:

Direct connected generators are normally of smaller ratings and a typical scheme of Direct Connected Generator Protection for a 30 MW generator is shown in Fig. (6.21).

It consists of the following protections:

  • Unbiased differential protection.

  • Backup overcurrent protection.

  • Negative phase sequence protection.

  • Standby earth fault.

In addition to these protections the following may also be provided:

  • Field failure protection.

  • Rotor earth-fault protection.

  • Reverse power protection (to be provided on back pressure turbine sets and engine driven sets).

Direct Connected Generator Protection

Relay Tripping Functions:

The various systems have been described simply as means of operating the protective relays whose function is to energize a multi contact tripping relay, which in turn operates the following:

  • The main circuit breaker to isolate the generator from the system.
  • The neutral earthing switch, if any, to interrupt earth-fault current.
  • The field switch to begin the decay of the generated voltage feeding the fault, in some cases by switching in a suppression resistor.
  • An alarm relay.

Relays on the unit transformer LV side trip only the unit transformer, leaving the generator in service. The auxiliary protections energize the alarm relay.

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  2. Generator Transformer Protection
  3. Unbalanced Loading Protection of Generator
  4. Percentage Differential Relay Protection of Generator
  5. Self Balance Protection System of Generator
  6. Generator Inter Turn Fault Protection
  7. Rotor Earth Fault Protection of Generator
  8. Loss of Excitation Protection in Generator
  9. Earth Fault Protection or Leakage Protection
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  12. Measurement of High Direct Current
  13. Direct Current Resistivity Method
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