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  • PCS-985B/AW Generator-Transformer Unit Relay

  • PCS-985 generator-transformer unit relay can be applied for turbo-dynamo, gas-turbine, hydro, pumped storage and nuclear power generator with different connection modes. It supports conventional CT/VT and ECT/EVT, and provides interfaces for power plant automation.

    For medium to large generator, two sets of PCS-985 protections can be used to achieve duplicated protection configuration. Two PCS-985 protections use different CT groups, and main and backup protection in one PCS-985 share one group of CTs.

    • PCS-985B provides complete electric quantity protection of a turbo-dynamo or nuclear power generator-transformer unit which usually comprises generator, main transformer, step- down transformer and exciter or excitation transformer.
    • PCS-985AW can be applied for a large-scale hydro or pumped storage generator-transformer unit with different connection modes. 
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Generator protection
  • Unrestraint current differential protection. (87UG)
  • Percentage restraint current differential protection. (87PG)
  • DPFC differential protection. (87DG)
  • Split phase transverse differential protection. (87SG)
  • Incomplete differential protection 1. (87IG)
  • Incomplete differential protection 2. (87IG)
  • High sensitive transverse differential protection. (87S)
  • Longitudinal zero-sequence overvoltage protection for inter- turn fault. (59N)
  • DPFC directional protection for inter-turn fault. (7/67)
  • Calculated longitudinal residual overvoltage protection for inter-turn fault. (59N)
  • Phase-to-phase impedance protection. (21P)
  • Voltage controlled overcurrent protection. (50P/51P)
  • Fundamental zero-sequence voltage protection for stator earth fault. (59G)
  • Zero-sequence overcurrent protection for stator earth fault. (51G)
  • Third harmonic overvoltage ratio protection for stator earth fault. (27/59TN)
  • Third harmonic overvoltage differential protection for stator earth fault. (87TN)
  • 100% stator earth-fault protection with voltage injection. (64S, with RCS-985U)
  • Rotor one-point earth-fault protection with ping-pong principle. (64R1)
  • Rotor two-point earth-fault protection with ping-pong principle. (64R2)
  • Rotor earth-fault protection with voltage injection.(64R)
  • Definite-time stator overload protection. (49S)
  • Inverse-time stator overload prot ection. (49S)
  • Definite-time negative-sequence overload protection. (46)
  • Inverse-time negative-sequence overload protection. (46)
  • Loss-of-excitation protection. (40)
  • Out-of-step protection. (78)
  • Overvoltage protection. (59)
  • Undervoltage protection. (27)
  • Definite-time over-excitation protection. (24)
  • Inverse-time over-excitation protection. (24)
  • Reverse-power protection. (32R)
  • Low forward power protection. (32F)
  • Sequential tripping reverse-power protection. (32R)
  • Underfrequency protection. (81U)
  • Overfrequency protection. (81O)
  • Inadvertent energization protection. (50/27)
  • Startup/shutdown protection of differential current. (SS)
  • Startup/shutdown protection of zero-sequence voltage. (SS)
  • Breaker failure protection. (50BF)
  • Low-frequency overcurrent protection. (50LF)
  • Excitation Transformer/Excitor Protection
    • Differential protection. (87E)
    • Overcurrent protection. (50P/51P)
    • Overload protection. (49)
    Main Transformer Protection
    • Unrestraint current differential protection for generator- transformer unit. (87U)
    • Percentage restraint current differential protection for generator-transformer unit. (87P)
    • Unrestraint current differential protection. (87UT)
    • Percentage restraint current differential protection. (87PT)
    • DPFC differential protection. (87DT)
    • Restricted earth-fault protection. (REF)
    • Voltage controlled overcurrent protection at HV side. (50P/51P)
    • Phase-to-phase impedance protection at HV side. (21P)
    • Ground overcurrent protection at HV side. (50G/51G)
    • Directional zero-sequence overcurrent protection at HV side. (67G)
    • Inverse-time zero-sequence overcurrent protection at HV side. (51G)
    • Gap zero-sequence overvoltage/overcurrent protection at HV side.
    • Definite-time over-excitation protection. (24)
    • Inverse-time over-excitation protection. (24)
    • Pole discrepancy protection at HV side. (62PD)
    • Breaker flashover protection.
    • Zero-sequence voltage alarm at LV side. (59G)
    • Overload alarm. (49)
    • Initiating cooling. (49)

    Auxiliary Transformer
    • Unrestraint current differential protection. (87UT)
    • Percentage restraint current differential protection. (87PT)
    • Voltage controlled overcurrent protection at HV side. (50P/51P)
    • Voltage controlled overcurrent protection of branch 1 at LV side. (50P/51P)
    • Voltage controlled overcurrent protection of branch 2 at LV side. (50P/51P)
    • Zero-sequence overcurrent protection of branch 1 at LV side. (50N/51N)
    • Zero-sequence overcurrent protection of branch 2 at LV side. (50N/51N)
    • Overload alarm. (49)
    • Initiating cooling. (49)

    Miscellaneous
    • Mechanical protection. (MR)
    • Fault detector. (FR)
    • Voltage and current drift auto adjustment.
    • VT circuit supervision. (VTS)
    • CT circuit supervision. (CTS)
    • CT saturation detection. (CTS)
    • Inrush current detection. (VTS)
    • Self diagnostic.
    • GPS clock synchronization.
    • Fault Recorder.
    • IEC61850 MMS & GOOSE for station bus
    • IEC60870-5-103 protocol
    • MODBUS protocol
    • DNP 3.0 LAN0



  • High-performance unified hardware and realtime calculations This relay adopts high performance CPUs and DSPs, internal high-speed bus, and intelligent I/O. Both hardware and software adopt modular design, which can be flexibly configured.
  • Independent fault detector elements The unique hardware design with two independent data acquisition paths can prevent the maloperation due to the hardware component failure. The tripping output is continuously supervised by the independent fault detector element executed in the separated CPU. It will significantly enhance the reliability.
  • Variable slope percentage differential protection Variable slope percentage characteristic is adopted for current differential protection. If the pickup slope and maximum slope are reasonably set, high sensitivity can be gained during internal fault, while transient unbalance current can be avoided during external fault.
  • DPFC percentage differential protection DPFC percentage differential protection reflects only deviation components of differential current and restraint current, it is not effected by load current. It can detect slight fault within transformer and generator. Besides, it is insensitive to CT saturation since its restraint coefficient is set comparatively high.
  • Detect CT Saturation by asynchronous method For external fault, waveform discrimination of phase current and differential current is adopted. Maloperation will not occur if the CT correct transfer time from primary to secondary side is not less than 5ms. For internal fault, the device will operate quickly.
  • High-sensitive transverse differential protection By adopting frequency tracking, digital filter and Fourier transformation, the filtration ratio of third harmonic component can reach more than 100. All these countermeasure guarantees the reliability of protection in all occasions.
  • Percentage restraint interturn protection The device adopts new criteria of generator current percentage restraint technique to ensure the accurate operation during inter-turn fault occurs in stator winding and prevent maloperation during external asymmetric fault occurs.
  • Stator earth-fault protection Through the realtime adjustment of coefficient of amplitude value and phase, the PCS-985 makes differential voltage between generator terminal and neutral point 0 in a normal operation condition. When stator earth fault occurs, the criteria tend to operate reliably and sensitively.
  • Stator earth-fault protection with external voltage injection principle The protection adopts digital technology to calculate the earth fault resistance accurately. The protection is adaptive for various operation conditions, such as stillness, no-load, shutdown, startup and connected to power grid.
  • Rotor earth-fault protection with ping-pong principle DC current is input by high-performance isolated amplifier. Via switching two different electronic switches, the PCS- 985 solves four different ground-loop equations to compute rotor winding voltage, rotor ground resistance and earthing position on real time and display these information on LCD.
  • Rotor earth-fault with external voltage injection principle The protection method is adaptive to various lead-out mode of rotor windings, and both single-end injection and doubleends injection can be selected. The fault location can be measured if double-ends injection is selected.
  • Loss-of-excitation protection Loss-of-excitation protection optionally combines stator impedance criteria, reactive power criteria, rotor voltage criteria and busbar voltage criteriato meet various demands of different generator units.
  • Out-of-step protection Out-of-step protection adopts three-impedance element (gains from positive-sequence current and positive sequence voltage of generator) to distinguish out-of-step from steady oscillation. In addition, the protection can accurately locates the position of oscillation center and record the oscillation slid numbers of external and internal oscillation respectively in real-time.
  • VT circuit failure supervision
    Two groups of VT inputs are equipped at the generator terminal. If one group fails, the device will issue an alarm and switch over to the healthy one automatically. It does not need to block protection element relevant to voltage.
  • CT circuit failure supervision
    Reliable blocking function can prevent the device from undesired operation due to CT circuit failure or AC sampledcircuit failure.
  • Powerful communication function 2 independent Ethernet interfaces and 2 independent RS- 485 communication interfaces are provided. Power industry communication standard IEC60870-5-103, Modbus protocol and new generation substation communication standard IEC61850 are supported.
  • Complete event recording function 64 faults and operation sequence, 64 fault waveforms, results of 256 self-supervision reports, and 1024 binary signal change reports can be recorded.