RCS-985G Generator Protection

The RCS-985G is a generator protection intended for the application to sophisticated generators, including turbogenerators,hydro-generators, gas turbine generators and pumped-storage generators. It supports wall surface mounted and flush mounted......

  • Overview
  • Functions
  • Features

The RCS-985G is a generator protection intended for the application to sophisticated generators, including turbogenerators, hydro-generators, gas turbine generators and pumped-storage generators. It supports wall surface mounted and flush mounted in a control panel. The RCS-985G is fully compatible with IEC 61850 communication with an additional communication unit.

Protection for Generator
  • Current differential protection. (87G)
  • Unrestrained instantaneous differential protection. (87UG)
  • DPFC current differential protection. (87G)
  • High sensitive transverse differential protection. (87G)
  • Longitudinal zero sequence overvoltage protection for turnto- turn fault. (59N/60)
  • DPFC directional protection for turn-to-turn fault. (67)
  • Two stages phase-to-phase distance protection. (21G)
  • Voltage controlled overcurrent protection. (51V)
  • Current blocking element at generator’s terminal.
  • Fundamental zero sequence overvoltage protection for stator earth fault. (64G1)
  • Third harmonic protection for stator earth fault. (27/59TN, 64G2)
  • Two stages of one-point-earth fault protection of rotor. (64R)
  • Two-point earth fault protection of rotor. (64R)
  • Definite and inverse time stator thermal overload protection. (49S)
  • Definite and inverse time negative sequence overload protection of rotor. (46/50, 46/51, 49R)
  • Loss-of-excitation protection. (40)
  • Out-of-step protection. (68/78)
  • Two stages phase-to-phase overvoltage protection. (59G)
  • Phase-to-phase undervoltage protection. (27G)
  • Two stages definite time over-excitation protection. (24)
  • Inverse time over-excitation protection. (24)
  • Reverse power protection. (32G)
  • Reverse power protection during generator shutting down. (32G)
  • Three stage underfrequency protection. (81G)
  • Two-stage overfrequency protection. (81O)
  • Startup/shutdown protection of generator.
  • Accidental energization protection. (50/27)
  • Voltage balance function. (60)
  • Under-frequency overcurrent protection.
  • Voltage transformer supervision. (47/60G)
  • Current transformer supervision. (50/74)
  • Mechanical protection.

Excitation System
  • Current differential protection for exciting-transformer. (87T)
  • Current differential protection of AC exciter. (87G)
  • Overcurrent protection. (50P/51P)
  • Definite and inverse time thermal overload protection for exciting windings. (87G)
  • Current transformer supervision of excitation set. (50/74)

Monitoring and Metering
  • Automatic self-supervision
  • Fault recording
  • Event recording
  • Present recording
  • Front communication port (RS232)
  • Rear communication ports to host
  • Rear communication port to printer
  • Time synchronization
  • Voltage and current drift auto-adjustment.

  • The CPU hardware comprises of one microprocessor and two digital signal processors(DSP). The two CPU systems can operate in parallel with a fast A/D converter. The logic calculations are processed by microprocessor and the protection calculations are carried out by DSP, ensuring that the real time calculation of all protection relays can be completed in a sampling interval.
  • The fault detectors in CPU processor are used to supervise tripping outputs. The relay drives the tripping output only when the fault detectors in CPU module and MON module operate simultaneously so as to avoid maloperation caused by hardware component failures.
  • The RCS-985G can be used as main and backup protection of generators. Protection information such as sampled data and binary inputs are shared between all protective elements.
  • The RCS-985G can be applied to various circuit breakers with its elaborately designed tripping matrix.
  • The percentage differential protection adopts variable slope restraint characteristics, and the actual unbalanced differential current effect can be simulated. The phase current waveform is identified to prevent maloperation due to CT saturation.
  • The DPFC percentage differential protection is used to reflect deviation components of differential current. It can detect small fault in transformers and generators, and is immune to CT saturation due to the high restraint coefficient.
  • The CT current output will be corrected before calculation to eliminate the influence of different CT ratio
  • Two discrimination principles for inrush current are provided: harmonics restraint and waveform distortion restraint.
  • CT saturation detecting logic can prevent mal-operation in case of external fault and improve operational performance under condition of internal fault. For external faults, maloperation can be avoided if the transfer time from primary to secondary side of CT is no less than 5ms.
  • The transverse differential protection adopts the percentage phase current restraint and the floating threshold to enhance ensitivity and reliability. The filtration ratio of third component can be increased to over 100 with the application of frequency tracking technique, digital filter technique and Fourier transformation technique.
  • More than 500 sampled data including differential current and phase angle can be displayed on LCD. More than 1500 internal data of equipment can be supervised by the dedicated auxiliary software which enables users to be aware of the operational status of RCS-985G.
  • The stator ground fault protection adopts the proportion of third harmonic voltages of generator output and neutral point. This criterion ensures that no unwanted alarm can be sent during startup/shutdown process of the generator.
  • The rotor earth fault protection adopts ping-pong principle. Its DC input uses high performance isolated amplifier. Realtime display of voltage and insulation resistance of the rotor as well as the location of its ground point can be realized.
  • Loss of excitation protection adopts open criterion. Many criterions such as stator impedance, reactive power, rotor voltage, busbar voltage and active power reduction of stator can be combined flexibly. Requirements of operation of different type generator-transformer unit can be met then.
  • Triple impedance elements are adopted by out-of-step protection, power swing and out-of-step can be discriminated correctly. It can also locate the swing center and can make real-time record of number of pole slipping of internal swing and external swing respectively.
  • VT circuit failure supervision is integrated. Two groups of VT inputs are equipped for generator end. If one group fails the equipment will send alarm and switch to the healthy group automatically. It doesn’t need to block protective function relevant to voltage of generator.
  • CT circuit failure alarm and blocking is integrated. This function adopts percentage differential principle. Detection ability of CT circuit failure can be enhanced significantly and unwanted operation can be avoided then.
  • The connector type can be selected as plug in/out terminal connector or screw terminal connector. The unique plug in/out terminal connectors from the relay rear panel to the terminal blocks on the rack or cabinet makes the onsite commissioning and replacement much easier than the traditional screw terminals when you do the commissioning.
  • Various GPS clock synchronizations are provided: second/ minute pulse via binary input or RS-485, message via communication ports and IRIG-B synchronization.
  • The relay is equipped with Ethernet ports with IEC 61850 (one additional communication unit is required) and RS-485 ports with IEC 60870-5-103.