Transformer-Feeder Protection Methods
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Questions and Answers

What is the minimum earth fault current that can be detected by the sensitive earth fault method?

  • 15 A
  • 10 A
  • 20 A
  • 4 A (correct)

    • What type of networks is the Delta-I-method typically used for?

  • Resonant grounded networks
  • Inductive grounded networks
  • Low-impedance grounded networks (correct)
  • High-impedance grounded networks

    • What is the function of the event recorder in the IKI-35 relay?

  • To save event logs with a relative timestamp (correct)
  • To trip the circuit breaker
  • To measure phase currents
  • To provide a backup power source

    • What is the purpose of the two alarm relays in the IKI-35 relay?

    <p>To be configured as NC or NO contacts and for different messages</p> Signup and view all the answers

    Why does the IKI-35 allow earth fault location without direction?

    <p>Because there is an overcompensation current during an earth fault</p> Signup and view all the answers

    What type of CT is optional for inductive grounded networks using the sensitive earth fault method?

    <p>Balanced core CT</p> Signup and view all the answers

    What are the two methods of testing the IKI-35 relay?

    <p>Primary current injection and secondary voltage injection</p> Signup and view all the answers

    What should be deactivated during the testing of the IKI-35 relay?

    <p>Inrush-suppression</p> Signup and view all the answers

    What type of relay is the IKI-35?

    <p>Self-powered relay</p> Signup and view all the answers

    What is the purpose of the CTs in the IKI-35 relay testing?

    <p>To inject primary current</p> Signup and view all the answers

    What is the recommended approach for testing the IKI-35 relay?

    <p>Conduct both primary and secondary testing</p> Signup and view all the answers

    What is the significance of the CT-clamps in the IKI-35 relay testing?

    <p>They are used to apply simulation voltage</p> Signup and view all the answers

    What type of current is measured in earth fault protection?

    <p>Residual current</p> Signup and view all the answers

    What is the purpose of a balance earth CT?

    <p>To measure the residual current in a three-phase system</p> Signup and view all the answers

    What is the characteristic of definite time overcurrent protection?

    <p>Trips the circuit breaker after a fixed time delay</p> Signup and view all the answers

    What is the purpose of the IDMT curve in relay protection?

    <p>To determine the operating time of the relay</p> Signup and view all the answers

    What is the function of a self-powered RMU relay?

    <p>To record the integrated disturbance of electrical quantities</p> Signup and view all the answers

    What happens when the fault current is more than 1.2 A and less than 6 A in a relay protection scheme?

    <p>The relay trips the circuit breaker by inverse time</p> Signup and view all the answers

    What is the purpose of the time delay overcurrent protection?

    <p>To delay the tripping of the circuit breaker</p> Signup and view all the answers

    What is the characteristic of instantaneous overcurrent protection?

    <p>Trips the circuit breaker instantly</p> Signup and view all the answers

    What is the purpose of the CT ratio in a relay protection scheme?

    <p>To step down the current to a measurable level</p> Signup and view all the answers

    What is the purpose of the disturbance record functionality in a self-powered RMU relay?

    <p>To record the integrated disturbance of electrical quantities</p> Signup and view all the answers

    Study Notes

    IKI-35 Relay Protection

    • The IKI-35 relay can be used for either low-impedance grounded networks with earth faults of more than 15 A (using the Delta-I-method) or inductive grounded networks with an optional separate balanced core CT (using the sensitive earth fault method).
    • The IKI-35 acts as a transformer-feeder protection and allows earth fault location without direction due to overcompensation current during an earth fault in the transformer-feeder.

    Alarm Relays and Event Recorder

    • The IKI-35 has two alarm relays that can be configured as NC or NO contacts and for different messages (overcurrent pick-up, short-circuit, earth fault, tripping).
    • The event recorder can save 20 events with a relative timestamp, allowing for checking of overcurrents, tripping, and the corresponding phase currents.

    Earth Fault Detection

    • Earth fault detection is measured using the residual current, which is the sum of the secondary currents of the current transformer or balance earth CT around the three-phase cables.
    • See Figure 1-3a and Figure 1-3b for earth fault detection diagrams.

    Relay Testing and Commissioning

    • The IKI-35 relay can be tested by either primary current injection into the CTs or secondary sided by means of a simulation-voltage to be applied at the CT-clamps.
    • Attention: Deactivate the inrush-suppression for primary or secondary test of IKI-35.

    Earth Protection

    • The earth protection function operates with measurement of the residual current carried out using the sum of the secondary currents of the current transformer or balance earth CT around the three-phase cables.
    • See Figure 2-2-1 for earth fault protection by using three balance CT's.

    Protection Characteristic Reading

    • The operating time characteristics for the IKI-35 relay follow the IEC 60255-3 standard.
    • See Table 2.2.1 and Figures 2-2-2, 2-2-3, 2-2-4, 2-2-5, and 2-2-6 for the operating time characteristics.

    IDMT Curves

    • The IDMT curves are used to determine the operating time characteristics of the IKI-35 relay.
    • The curves have four zones: Zone 1 (no trip), Zone 2 (inverse time), Zone 3 (definite time), and Zone 4 (instantaneous overcurrent).

    Disturbance Record Functionality

    • Some self-powered RMU relays have the feature of recording the integrated disturbance of the electrical quantities (monitored values).
    • This feature is useful for trouble-shooting and analysis.

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    Description

    This quiz covers the Delta-I-method and sensitive earth fault method for detecting earth faults in electrical networks. It highlights the applications and limitations of each method.

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