Review: Protective Relaying Midterm Exam
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Questions and Answers

What are the three electrodes usually found in a thyristor?

  • Emitter, collector, and base
  • Cathode, diode, and resistor
  • Positive, negative, and neutral
  • Anode, cathode, and gate (correct)
  • Which relay can differentiate internal and external faults effectively?

  • Thermal relay
  • Low impedance relay
  • Static differential relay
  • High impedance relay (correct)
  • What is the main role of the bus bar in a supply system?

  • Ensure voltage balance
  • Prevent current transformer saturation
  • Carry fault currents safely (correct)
  • Interrupt the power supply
  • What is the purpose of using a linear coupler instead of conventional current transformers in protective relaying?

    <p>To overcome saturation in large fault currents</p> Signup and view all the answers

    Which type of relay is commonly used for protecting generators and transformers from internal faults?

    <p>Static differential relay</p> Signup and view all the answers

    How is the connection between contacts and a bimetallic strip made in a simplest thermal relay?

    <p>By a spring</p> Signup and view all the answers

    What is the operating value of a phase comparator of a mho distance relay scheme?

    <p>ILZR−ZL</p> Signup and view all the answers

    Which type of supply does the Induction type relay work on?

    <p>Alternating current (AC)</p> Signup and view all the answers

    What component is considered the 'heart' of a static relay?

    <p>Measuring element</p> Signup and view all the answers

    In a directional power relay, when does the relay operate?

    <p>When power flows in a specific direction</p> Signup and view all the answers

    What does the Definite or Fixed time function element provide in relays?

    <p>Defined time delay</p> Signup and view all the answers

    How does a differential relay operate?

    <p>When phasor difference exceeds a predetermined value</p> Signup and view all the answers

    What is the main factor that determines the operation of distance relays?

    <p>Ratio of voltage and current</p> Signup and view all the answers

    In an impedance relay, which type of torque is produced by the voltage element?

    <p>Reset torque</p> Signup and view all the answers

    Why are static relays considered to place a reduced burden on protective transformers compared to electromagnetic relays?

    <p>Lower VA requirements</p> Signup and view all the answers

    What is a key requirement for static relays in terms of auxiliary supply?

    <p>Surge suppression</p> Signup and view all the answers

    Which type of relay is known as the simplest type of relay?

    <p>Electromagnetic attraction relay</p> Signup and view all the answers

    What is the term used for overcurrent level detectors in relays?

    <p>Fault current level detectors</p> Signup and view all the answers

    What type of relay employs active semiconductor devices like diodes and transistors?

    <p>Static relay</p> Signup and view all the answers

    In distance time relays, what is the time of operation proportional to?

    <p>Fault distance</p> Signup and view all the answers

    Which component pivots when attracted towards the coil in a directional relay?

    <p>Plate made of iron</p> Signup and view all the answers

    What type of relay can withstand overload for minutes or hours depending on the magnitude of the overload?

    <p>Thermal relay</p> Signup and view all the answers

    Which relay operates based on the comparison of phase angles and magnitudes of currents entering and leaving the system?

    <p>Current differential relay</p> Signup and view all the answers

    In a reactance relay, how is the operating torque obtained?

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

    What is the function of the filter circuit in static relays after rectifiers?

    <p>Smoothing of d.c. voltage</p> Signup and view all the answers

    What is the restraining value of a phase comparator in a reactance distance relay scheme?

    <p>ZRIL</p> Signup and view all the answers

    What is a limitation of static relays?

    <p>Variation of characteristic with temperature and age</p> Signup and view all the answers

    In Relay with Break type contact, how are the relay coil and trip coil of each phase connected?

    <p>In series</p> Signup and view all the answers

    Where does the energy for relay coils in static relays come from?

    <p>Supply using C.T.s</p> Signup and view all the answers

    What is the primary advantage of induction type cup relays?

    <p>Produce steady non-vibrating torques</p> Signup and view all the answers

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