B3 4.2

  1. Faults must be minimized or cleared to:
    • protect equipment from damage
    • prevent the escalation of system trouble
    • minimize interruption of service to customers
    • protect human life
  2. A∅                       A∅
    Open Circuit A∅
  3. When B∅ circuit comes into contact with the A∅ or C∅ circuit
    Phase-to-Phase ground
  4. When one of the phases comes into contact with ground
  5. In order to maintain Power System stability and continuity of customer service, some form of                  is needed
    System Protection
  6. What are the most common devices designed to detect fault current and isolate fault
    • Fuses
    • Direct-acting trips on CBs
    • Relays
  7. Combine the function of fault detection and circuit clearing in one device
  8. Characteristics of fuses
    • They are single phase devices.
    • They maintain a fast-operating speed.
    • The tripping time is non-adjustable.
    • They must be replaced after an operation
  9. Fuses are best suited for                where they do not operate in conjunction with other protective devices
    branch circuit protection
  10. In the                 fuse the complete fuse assembly must be
    replaced each time it blows
  11. The                  fuse is constructed so the casing can be easily dismantled and the blown link can be replaced with a new fuse link of proper amperage and voltage ratings
  12. Non-current limiting fuse, with the link contained in an explosion chamber - used in Station Service
    Expulsion Fuse
  13. The                is a non current-limiting fuse which consists of a glass tube, a fuse element and an arc extinguishing liquid
    liquid fuse
  14. The fuse element is surrounded by a tube liner of compressed boric acid
    Boric Acid Fuse
  15. Fuses used extensively for service with potential transformers and control power transformers.
    Silver Sand fuse.
  16.                 are normally used in underground distribution circuits where voltages do not exceed
    Oil fuse cutouts
  17.                   is one in which the breaker is tripped by direct mechanical action when the current reaches a pre-determined value
    A direct-acting trip device
  18. Direct acting trips and fuses can only be employed for              protection
  19. True/ False

    Relays can be used to protect against undervoltage,
    overvoltage, unbalanced phases, low frequency, current differential, and phase angle comparison
  20. Measuring instruments equipped with auxiliary contacts
    that operate when the quantities flowing through them either exceeds or drops below a predetermined value
  21. True/False

    Relays may not be used to locate a fault by measuring the
    line impedance (distance) from the relay to the fault
  22. Used where an instantaneous operation is required in a relay with an adjustable pick-up.
    Plunger type relay
  23. A relay that consist of a disc positioned between two magnetic poles that is not instantaneous
    Induction-Disc type relay
  24. A relay does three things in order to accomplish its purpose. It must:
    • sense
    • decide
    • act
  25. A relay does three things in order to accomplish its purpose. It must
    • sense
    • decide
    • act
  26. True/False

    The sense function in a relay input circuit. If the input circuit is connected to a source of voltage or current, the relay is monitoring an electrical quantity.
  27. The                 function of a relay, is accomplished by mechanisms within the relay (relay movement). This mechanism is adjusted to respond to a specific level or degree of input
  28. The                function is done by closing relay output contacts that most often are used to open or trip circuit breakers
  29. What the four basic characteristics of relay
    • Sensitivity - able to distinguish between normal/abnormal conditions
    • Selectivity - recognize a fault and trip the appropriate number of CBs
    • Adjustable - trip CBs within the proper time
    • Reliability - must operate correctly and with certainty
  30. A device located under the bushing, with the primary side  connected to the source to be monitored and the secondary side is connected to the relay circuit
    Current transformer
  31. Reduce bus or line voltage to 120 volts.
    Potential Transformer
  32. A short in the                circuit may prevent the relay from seeing the fault
  33. A DC short in the relay circuit may cause a to               blow
  34.                 are installed in the positive side of the DC to allow relays to be manually blocked
    Blocking switches
  35. True/False

    The Circuit Breaker status signals, and the Relay Trip Circuit, are made up through pallet switches, known as the A & B
    pallets for the circuit breaker
  36.                  is used in system protection schemes to monitor relay tripping frequency signals
    Carrier equipment
  37. Carrier Equipment includes such items as:
    • Pilot Circuit
    • Microwave Transmission
    • Wave Traps
  38. Provides the path for the terminals of a monitored
    line section to communicate, The two most common methods used by the Department are to transmit an audio-frequency tone over a leased telephone line or use the line itself
    Pilot Circuit
  39. True/False

    Wave Trap filters the audio-frequency tone, thus preventing the
    carrier signal from going beyond the circuit is it monitoring
  40. Used in Receiving Stations (RS) for transmission and sub-transmission line protection and as back-up protection on banks in Substations
    Overcurrent relays
  41. True/False

    When overcurrent relays are used to protect lines, only the Receiving Station end of the line will be tripped by the relay
  42. When overcurrent relays are used to protect banks, normally
    only the bank                  will trip
    high side circuit breakers
  43.                   overcurrent relays have no intentional time delay, they are used for tripping when extremely high current values are present
  44.                 overcurrent relays have a time delay element, the time delay is needed so that tripping can be coordinated with other relays or fuses.
  45. Protects lines in Distributing Stations, Trips only the local end of the faulted line
    Directional Overcurrent
  46. True/False

    Directional overcurrent uses an overcurrent relay with a directional element that requires both current and voltage
  47. Protects, a particular piece of equipment such as, a
    transformer, condenser, generator, or bus Trips all sources and loads to the faulted circuit.
    Differential Relays
  48. True/False

    Sudden pressure relays are commonly used to protect transformers
  49. One of the most common sudden pressure relays used on the Power System is the               relay
  50.                    compare the voltage or current on both sides of the equipment being protected
    Differential Relays
  51.                    is a back-up protection used to clear a fault if a circuit breaker fails to trip
    Breaker failure
  52. What of relay trips the bank low side circuit breakers when the frequency drops below a predetermined value
    Under-frequency Relays
  53. True/False

    Under-frequency relays are used at most receiving and switching stations.
  54. True/False

    Bank low side circuit breakers trip on under-frequency. The load is dropped, but the Transmission System and Station Service are maintained.
  55.                         protects capacitors and trips the capacitor source CB
    Phase-Balance Relays
  56. Protects Transmissions lines and trips both ends of the faulted line
    Distance Relays
  57. True/False

    Distance relays are directional, which means they look in only one direction for a fault
  58. When a fault occurs a long distance away, the bus current increase is                than when the fault is close in. Conversely, when the fault is a long distance away the bus voltage                 will be less than when the fault is close in.
    less, decrease
  59. True/False

    Distance relays are not designed to operate on line to ground faults because the impedance changes constantly
  60. True/Fasle

    The impedance of a transmission line depends on
    the length of the line
    the size of the conductor
    the material used to make the conductor
    the spacing between conductors
    the height above ground
  61. True/False

    Phase comparison relays are similar to differential or pilot wire relays, phase comparison relays compare the phase angle and current magnitude of the line at each terminal
  62. True/False

    If a receiver stops getting the Guard Frequency without immediately receiving a trip frequency, a "loss of guard" or "transfer trip signal" alarm is initiated
  63. What are the transfer trip relays used by DWP
    • Direct Under-reaching Transfer Trip
    • Permissive Under-reaching Transfer Trip
    • Permissive Overreaching Transfer Trip
  64. In this method, the relays are set to protect 80 to 90% of the line. If a fault is detected, a trip signal is sent to the local circuit breaker and the transmitter sends a trip signal to the remote end.
    Direct Under-reaching Transfer Trip
  65. The transfer trip signal and               must be received simultaneously to initiate a remote trip
    permissive relay signal
  66. This method of transfer trip protection uses directionally controlled relays set to overreach the remote terminal.
    Permissive Overreaching Transfer Trip
  67. Relays that operate in order to assist another relays or devices
  68. Once the auxiliary relay is energized by the protective relay, it is                 .
    Sealed In
  69. The general philosophy of relay application is to divide the power system into                  .
    protective zones
  70. True/False

    The Screw-Base Plug fuse and the Cartridge fuse. The Cartridge fuse is the type most often used by the Department.
  71. Why must the CTs must never be energized with the secondary open
    This will result in very high impedance across the open.
Card Set
B3 4.2
System Protection