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Protective Relay Applications Flashcards

7 cards from real NETA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Protective Relay Applications flashcards as text

  1. For a phase-to-phase fault on a three-phase system, which sequence components are present?

    Answer: Positive and negative sequence only

    A phase-to-phase fault produces positive and negative sequence currents but no zero-sequence current because no path to ground exists.

  2. What is the significance of the time-current characteristic curve (TCC) for an overcurrent relay?

    Answer: It shows the relay's operating time as a function of fault current magnitude

    The TCC graphically shows how quickly an overcurrent relay operates at various multiples of pickup current, enabling coordination with other devices.

  3. In protective relay coordination, the time margin between upstream and downstream device curves is known as the:

    Answer: Coordination time interval (CTI)

    The coordination time interval (CTI), typically 0.2–0.4 seconds, ensures the downstream device clears the fault before the upstream device operates.

  4. Which relay function protects a generator against motoring (the generator acting as a motor)?

    Answer: Reverse power relay (32)

    The reverse power relay (32) detects when real power flows into the generator, indicating it is motoring, which can damage the prime mover.

  5. What is the purpose of a reclosing relay (79) in distribution system protection?

    Answer: To automatically reclose a circuit breaker after a transient fault clears

    The reclosing relay (79) automatically recloses the breaker after a trip, restoring service if the fault was temporary (e.g., lightning-caused arc).

  6. During NETA acceptance testing of a protective relay, what is the minimum insulation resistance test voltage typically applied to relay coils per NETA ATS standards?

    Answer: 500 V DC

    NETA ATS Table 100.1 specifies 500 V DC for insulation resistance testing of relay coil and contact circuits rated up to 250 V.

  7. A digital (numerical) relay differs from an electromechanical relay primarily because it:

    Answer: Processes sampled digital values using a microprocessor to implement protection algorithms

    Digital relays sample input quantities, convert them to digital values, and apply software algorithms to perform multiple protection functions simultaneously.