PCS-978 Transformer Protection

The PCS-978 numerical protection system can provide full-scheme protection and control in one rack for various transformer applications, including two-winding transformers,three-winding transformers and auto-transformers. It also can be used to......

  • Overview
  • Functions
  • Features

The PCS-978 numerical protection system can provide full-scheme protection and control in one rack for various transformer applications, including two-winding transformers,three-winding transformers and auto-transformers. It also can be used to protect shunt reactors. Up to 36 analog input channels including current and voltage inputs are provided. The extensive functional library, programmable logic and configurable I/O are integrated to meet flexible applications. The unique current differential protection includes the unrestraint current differential element, percentage restraint current differential element and DPFC differential element.

The PCS-978 reserves two sets of CT input for dual breaker protection in one-and-a-half breaker and ring breaker arrangements. To enhance the accuracy of data sampling, the frequency-tracking function is used to trace the real-time current/voltage value.

Protection and Control
  • Transformer restrained current differential protection. (87PT)
    Three slopes are provided for the restraint characteristic of percentage current differential protection. It also integrates the inrush current blocking, CT saturation discrimination, over excitation blocking, CT ratio compensation and unique vector group compensations.
  • Unrestrained current differential protection. (87UT) The unrestraint current differential protection instantaneously responds and clears a serious fault immediately.
  • DPFC baised current differential protection. (87DT)
    Deviation of Power Frequency Component (DPFC) differential current protection is sensitive to turn-to-turn fault and high resistance fault and is immune to load current.
  • Reactor restraint current differential protection. (87R)
    Inrush current can be distinguished to avoid maloperation of current differential protection by detecting harmonic.
  • Reactor unrestrained current differential protection. (50/87UR) Biased current differential protection consists of CT saturation and harmonic blocking elements
  • Reactor DPFC biased current differenital protection. (7/87DR)
    DPFC biased current differential protection is regardless of the load current and is sensitive to small internal fault current within the reactor.
  • Restricted Earth Fault Protection. (REF)
    Zero sequence differential protection is used as REF for each Wye-connection winding to detect sensitive ground fault. Up to 3 REF protections are provided.
  • Winding differential protection. (87W/87N)
    Winding differential protection has high sensitivity to internal earth faults. Up to 3 winding differential protections are provided.
  • Inter-turn fault protection. (32G/21G)
    Inter-turn protection consists of zero-sequence power directional element and zero-sequence impedance element.
  • Overexciation protection. (24)
    Overexcitation protection based on the ratio of voltage and frequency is provided.
  • Underfrequency and overfrequency protection. (81U/81O)
    Under frequency protection with df/dt blocking and over frequency protection are both provided. The frequency is derived from positive-sequence voltage.
  • Mechanical protection. (MR)
    Under frequency protection with df/dt blocking and over frequency protection are both provided. The frequency is derived from positive-sequence voltage. Up to eight channels of mechanical protection are provided for tank.
  • Four stage phase overcurrent protection (50P/51P/67P)
    Overcurrent protection can be supervised by voltage element, harmonic element and directional element. IDMT curves complied with IEC and ANSI are provided for selection. Up to four overcurrent protections are provided.
  • Four stage zero sequence overcurrent protection for each side. (50N/51N/67N)
    Overcurrent protection can be supervised by voltage element, harmonic element and directional element. IDMT curves complied with IEC and ANSI are provided for selection. Up to four zero-sequence overcurrent protections are provided.
  • Two-stage residual overvoltage protection. (59G)
    IDMT curves complied with IEC and ANSI are provided for selection.
  • Two-stage definite-time and inverse-time phase overvoltage protection. (59P)
    IDMT curves complied with IEC and ANSI are provided for selection.
  • Four-stage undervoltage protection. (27)
    Rate-of-change of voltage is provided for the blocking.
  • Thermal overload protection. (49)
    Thermal overload protection based on fundamental current or harmonic current is provided for tripping and alarm.
  • Breaker failure protection. (50BF)
    Breaker failure protection for each breaker is supplied to initiate re-tripping and adjacent breaker tripping.
  • Pole disagreement protection. (62PD)
    External binary input and zero-sequence/negative-sequence current are used to detect the pole disagreement state of the circuit breaker.
  • Phase overcurrent alarm element. (50PAlm)
    The output could be used for the initiation of cooling system and this element is not supervised by General Fault Detector element.
  • Phase-to-phase impedance protection for HV and MV side. (21P)
    Users have options to select the forward direction or backward direction by logic setting, and power swing blocking logic is integrated to improve the safe operation.
  • Phase-to-ground impedance protection for HV and MV side. (21G)
    Users have options to select the forward direction or backward direction by logic setting, and power swing blocking logic is integrated to improve safe operation.
  • Power swing blocking. (68)
    The unique power swing blocking logic is integrated to improve the safe operation of impedance protection.
  • Voltage and current drift auto adjustment.
    The relay continually and automatically traces the voltage and current drifts and adjusts the zero point to the normal value.
  • Frequency tracking.
    Frequency tracking is provided to accommodate the frequency shift in power system.

Monitoring and Metering
  • CT saturation detection.
  • Inrush current detection.
  • Overexcitation detection.
  • Harmonic blocking function.
  • CT failure detection supervision.
  • VT failure detection supervision.
  • Tripping circuit supervision.
  • Self diagnostic.
  • Fault Recorder.

Communications
  • Two 10Base-T/100Base-TX (RJ45) ports and two optional 100Base-FX ports with IEC 61850-8-1 MMS and GOOSE for non-time-critical message, IEC 60870-5-103 over TCP/IP or DNP 3.0
  • Two RS-485 rear ports with IEC 60870-5-103
  • Six or Eight 100Base-FX ports with IEC 61850-9-2 Sampling Value and GOOSE for time-critical message
  • One RS-485 rear port for clock synchronization
  • One RS-232 rear port for printer
  • One faceplate RJ45 port for testing and setting
  • Clock synchronization via Pulse-Per-Second, IRIG-B and SNTP

  • Two-stage residual overvoltage protection. (59G) IDMT curves complied with IEC and ANSI are provided for selection.
  • Two-stage definite-time and inverse-time phase overvoltage protection. (59P) IDMT curves complied with IEC and ANSI are provided for selection.

  • CT transient detection element based on the ratio of zero-sequence current to positive-sequence current is provided for REF to eliminate the influence of CT transient characteristic difference.
  • The PCS-978 provides RTD input module and DC mA input module to detect the oil-temperature.
  • Maximum six groups of CT inputs for differential protection are provided.
  • 24 vector groups are available for the application to twowinding transformer.
  • 288 vector groups are available for the application to 3-winding transformer.
  • Optional inrush current distinguished principle is provided: harmonic criterion (second harmonic and third harmonic) or waveform distortion.
  • There are two optional modes for harmonic criterion: self-adaptive blocking mode and phase-to-phase cross blocking mode. Self-adaptive blocking mode can prevent maloperation during transformer energization effectively and ensure high speed for internal faults under normal operation.
  • Fifth harmonic or third harmonic criterion applied to detect overexciation condition.
  • The Δ→Y vector group compensation is used to adjust the phase angle of secondary current and the inrush current feature is reserved in each phase to realize phasesegregated inrush current restraint for percentage differential protection.
  • The DPFC restraint current differential protection is immune to load current but sensitive to small internal fault current within the transformer.
  • The restraint current differential protection with initial restraint slope consists of sensitive and conventional differential elements as well as independent CT saturation criterion.
  • Maximum 4 group CT and 1 neutral CT inputs for REF protection are provided.
  • The CT saturation detection function based on 2nd and 3rd harmonics is adopted to avoid maloperation.
  • The amplitude of residual voltage is compensated to ensure that the zero-sequence power directional element can distinguish the direction correctly when system impedance is too small.
  • Voltage for overexcitation protection calculation is the RMS value of three phase voltages which is not affected by frequency fluctuation.
  • Directional element can be selected to control each stage phase overcurrent protection with three options: none direction, forward direction and reverse direction.
  • Disturbance records are composed of 64 fault reports and 64 disturbance waveforms. The file format of waveform is compatible with international COMTRADE91 and COMTRADE99 file. Up to 80 analog inputs and 200 binary inputs can be recorded, and three oscillograph triggering mode are supported.
  • The relay is compatible with IEC 61850-8-1 MMS, GOOSE and IEC 61850-9-2 Sampling Value and provides the independent interfaces for station bus and process bus respectively.