PCS-921 Circuit Breaker Protection

The PCS-921 numerical relay provides the protection of circuit breakers with breaker failure protection, pole discrepancy protection, dead zone protection, phase/neutral overcurrent protection, single and/or three-pole auto-reclosing and synchronism......

  • Overview
  • Functions
  • Features

The PCS-921 numerical relay provides the protection of circuit breakers with breaker failure protection, pole discrepancy protection, dead zone protection, phase/neutral overcurrent protection, single and/or three-pole auto-reclosing and synchronism check functions. The PCS-921 relay employs the programmable logic, configurable I/O and definable 3-color LEDs to provide flexibility for the specific applications. Frequency tracking is used to minimize the sampling error caused by system frequency fluctuation.

The PCS-921 relay adopts the advanced multi-processor platform, providing the interfaces to station bus and process bus respectively and supporting IEC 61850-8-1 MMS, GOOSE, IEC 61850-9-2 Sampling Value. In addition, RJ-45 faceplate port for testing and setting to make commissioning and maintenance easier.

Protection and Control
  • Breaker failure protection (50BF)
    Re-tripping the own breaker and tripping the adjacent breakers will be issued if the external tripping command is received but the overcurrent element does not drop off. To improve the sensitivity of generator/transformer protection, the neutral and negative-sequence overcurrent elements are provided besides phase overcurrent element.
  • Pole discrepancy protection (62PD)
    The pole discrepancy is detected using the breaker auxiliary contacts, and the asymmetrical current element could be selected as an additional criteria.
  • Dead zone protection (50DZ)
    The adjacent breakers will be tripped if the fault between CT and breaker (dead zone) is detected via the initiating binary input from external protection, breaker auxiliary contacts and overcurrent element.
  • Two stages of phase overcurrent protection (50/51P)
    Second harmonic element could be selected to block the overcurrent element to avoid the maloperation due to transformer inrush current.
  • Two stages of neutral overcurrent protection (50/51N)
    Second harmonic element could be selected to block the neutral overcurrent element.
  • Synchronism check (25)
    The criteria could be set as frequency difference, voltage difference, and phase angle difference. And the checking condition could be selected as live-bus to dead-line, deadbus to live-line or dead-bus to dead-line.
  • Single and/or three-pole auto-reclosing (79)
    Up to 4 shots could be selected for the single-/three- pole auto-reclosing.
  • Voltage and current drift auto adjustment
    The relay continually and automatically traces the voltage and current drifts and adjusts the zero point.
  • Frequency tracking
    Frequency tracking is provided to accommodate the frequency shift in power system. Monitoring and Measurement
  • VT circuit supervision (VTS)
  • CT circuit supervision (CTS)
  • Self diagnostic
  • Auxiliary power supervision
  • Event recorder including 1024 disturbance records, 1024 binary events, 1024 supervision events and 1024 operating logs
  • Disturbance recorder including 64 disturbance records with waveforms (The file format of disturbance recorder is compatible with international COMTRADE file.)
  • Counter of circuit breaker operation (single-pole tripping, three-pole tripping and reclosing)

Communication
  • 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

  • The relay is based on NR’s well established and proven UAPC hardware platform with multi-processor architecture. The multi CPU technology supports parallel operating simultaneously.
  • The two independent data acquisition paths can prevent any undesired trip caused by component failure. One works as a fault detector and the other is designed for protection and its logic. Tripping outputs are supervised by the fault detector to prevent a mal-operation.
  • The sensitive DPFC fault detector element is integrated to target on the quick response to short-circuit fault.
  • 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.