PCS-931 Line Differential Relay

The RCS-931 relay is an advanced current differential protection with stepped distance elements and over current elements intended for main and backup protection for transmission lines with single-pole trip, three-pole trip and auto-reclosing......

  • Overview
  • Functions
  • Features

The RCS-931 relay is an advanced current differential protection with stepped distance elements and overcurrent elements intended for main and backup protection for transmission lines with single-pole trip, three-pole trip and auto-reclosing schemes. Phase segregated current differential, zero sequence current differential and DPFC differential are combined into the unique current differential element. It also integrates voltage protection, frequency protection, breaker failure protection and stub protection.

The relay can be used to protect the overhead lines and underground cables of all voltage levels, including series compensated lines, double-circuit lines, weak infeed (WI), short lines and extremely long lines. It is fully compatible with IEC 61850 communication. RCS-931 line differential relay is also suitable for two-terminal and three-terminal applications.


Protection and Control
  • Phase-segregated current differential protection. (87)
    Dynamic charging current compensation technology and CT saturation detection are integrated to realize a combination of both sensitivity and security of current differential protection.
  • Zero sequence current differential protection. (87)
    Zero sequence current differential protection integrates the dynamic charging current compensation technology and CT saturation detection, aiming at quickly detecting and clearing the ground fault.
  • DPFC differential protection. (87)
    Deviation of Power Frequency Component (DPFC) differential current protection is sensitive to high resistance fault and is immune to load current variation.
  • DPFC distance protection. (21D)
    Innovative Deviation of Power Frequency Component(DPFC) distance protection can quickly clear faults.
  • Four zones of phase-to-phase distance protection. (21P)
    Four zones of phase-to-phase distance protection integrates the memorized positive sequence voltage polarization, direction characteristic, load blinder and unique low-voltage distance element. The fourth zone is the reversal directional protection. Mho and quadrilateral characteristics are provided for selection.
  • Four zones of phase-to-ground distance protection. (21G)
    Four zones of phase-to-ground distance protection integrates the memorized positive sequence voltage polarization, reactance characteristic, direction characteristic, load blinder and unique low-voltage distance element. The fourth zone is the reversal directional protection. Mho and quadrilateral characteristics are provided for selection.
  • Four stages of directional phase overcurrent protection. (67P, 50/51P)
    Overcurrent protection can be supervised by voltage element and directional element. IDMT curves complied with IEC and ANSI standard are present for selection.
  • Four stages of directional zero sequence overcurrent protection. (67N, 50/51N)
    Overcurrent protection can be supervised by voltage element and directional element. IDMT curves complied with IEC and ANSI standard are present for selection.
  • Breaker failure protection for one or two breakers (50BF)
    Breaker failure protection can be applied to one breaker and two breakers.
  • Two stages of under voltage protection and two stages of over voltage protection (27/59)
    Under/over phase voltage protection and under/over (positive sequence, negative sequence or zero sequence) voltage protection are provided.
  • Four stages of underfrequency protection and four stages of over frequency protection (81)
    Frequency is calculated reference to the positive sequence voltage. The protection can be supervised by the df/dt element and the undervoltage element.
  • Stub protection for T-Zone in 3/2 breaker arrangement. (50S)
    Stub protection is introduced to protect T-zone in a one-anda- half breaker scheme or a ring breaker scheme.
  • Time phase overcurrent protection during VT failure. (51P VT)
    Time phase overcurrent protection will be enabled if phaseto- phase distance protection is blocked by VT failure.
  • Time zero sequence overcurrent protection during VT failure. (51N VT)
    Time zero sequence overcurrent protection will be enabled if phase-to-ground distance protection is blocked by VT failure.
  • Broken conductor protection (46BC)
    The ratio of negative to positive phase sequence current (Ι2/ Ι1) is adopted to detect the broken conduct.
  • Switch-onto-fault (SOTF) logic.
    Switch-onto-fault logic is used to clear fault during manuallyclosing and auto-reclosing.
  • Out-of-step tripping. (78)
    The out-of-step status is detected in the relay and it can be used to trip the transmission line.
  • Unique power swing blocking logic. (68)
    The power swing blocking logic can prevent mal-operation during external fault a power swing and clear the internal fault in power swing.
  • Thermal overload protection. (49)
    The output of thermal overload protection can be set to tripping or alarm.
  • Dead zone protection (50DZ)
    It is provided to clear the dead zone fault between CT and breaker.
  • Synchronism check. (25)
    Synchronism check and dead bus or dead line check are both provided for auto-reclosing.
  • Auto-reclosing (single and/or three-pole for one or two breakers). (79)
    Single/three pole auto-reclosing is applicable to one or two breakers. Priority logic is integrated for use on one-and-ahalf breaker application and ring breaker application.
  • 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 failure supervision.
  • VT failure supervision.
  • Tripping circuit supervision.
  • Self diagnostic.
  • Auxiliary power supervision.
  • Event recorder including 1024 disturbance records, 1024 binary events, 1024 supervision events and 1024 operating logs.
  • Counter of circuit breaker operation (single-pole tripping, three-pole tripping and reclosing).
  • Disturbance recorder including 64 disturbance records with waveforms (The file format of disturbance recorder is compatible with international COMTRADE file.)

Communications
  • Single- or double- pilot channel based on dedicated optical fiber or multiplex channel(C37.94 or G.703 with external converter).
  • 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 PCS-931 can quickly clear the internal fault for the whole line and the typical operation time is 10ms for a closein fault and 25ms for a remote fault.
  • The relay is based on NR’s well established and proven UAPC hardware platform with multi-processor architecture. The multi CPU technology supports parallel operation simultaneously.
  • The PCS-931 adopts high restraint factor and self-adaptive floating restraint threshold to realize both high reliability and sensitivity even in the CT saturation.
  • Data exchange between PCS-931 in different substations can be achieved by dedicated optical fiber or G.703/C37.94 communication interface. Error bit statistic and loss of communications detection are supplied to determine the health of communication channel, measure and continuously compensate channel delay.
  • The dynamic charging current compensation technology is integrated to acquire accurate differential current for application on long overhead lines or cables.
  • The CT ratio of different terminals can be regulated by setting the relevant configurable coefficients in software.
  • The PCS-931 can receive/send the tripping commands from/to the protection at the opposite terminal via fiber optic channel.
  • Each zone of phase-ground distance protection is provided with independent zero-sequence compensation.
  • The sensitive DPFC distance protection is less affected by power swing and thus is integrated to target quick clearance of internal fault.
  • The patented adaptive floating threshold method is insensitive to system unbalance and disturbance. The measuring element can achieve high security and high speed simultaneously.
  • The unique built-in power swing blocking logic can properly supervise the distance protection during a power swing. The power swing blocking logic can prevent mal-operation for an external fault and quickly clear the internal fault during a power swing.
  • Up to four shots single and/or three pole auto-reclosing with synchro-check and dead line/bus check are provided for multi-breaker configuration. The priority logic of multi-breaker auto-reclosing is integrated.
  • Instantaneous, definite time and inverse time (IDMT) characteristics are available in phase overcurrent protection and the zero sequence overcurrent protection which can be controlled by directional protection and/or under voltage protection through logic setting.
  • Three zones of forward distance element and one zone of reverse distance element are provided.
  • Users can select either Mho or quadrangle with Mho characteristics for distance protection. The load blinder function is also integrated.
  • The independent phase selection element can select the faulty phase and make a phase trip correctly, even for a high resistance fault.
  • 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 any mal-operation.
  • Optional connector type: one is the plug in/out terminal connector and the other is the screw terminal connector. The unique plug in/out terminal connectors are used to connect the rear panel to the terminal blocks on the rack or cabinet, making on-site commissioning and replacement much easier than using traditional screw terminals.
  • 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.