RCS-985

RCS-985 Generator-Transformer Unit Protection

Application The RCS-985 relay provides a complete set of multi-functional for a wide range of application, covering generator-transformer  unit, generator, main transformer, auxiliary transformer, excitation transformer and exciter. It is suitable for various applications from small generators to sophisticated large

generator-transformer unit systems. Either complete functions or partial functions are available in the following functional block diagram. It is fully compatible with IEC 61850 communication with an additional communication unit.

Functional Block

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Functions

Auxiliary Transformer  ●

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Generator-Transformer Unit ●

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Unrestraint current differential protection. (87U) Percentage restraint current differential protection. (87P)

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Generator  ●

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Unrestraint current differential protection. (87UG) Percentage restraint current differential protection. (87PG) DPFC current differential protection. (87DG) Phase-splitting transverse differential protection. (87SG) Sensitive transverse differential protection for the stator interturn fault. (87) Longitudinal zero sequence voltage protection for the stator  inter-turn fault. (59G) DPFC power directional protection for stator inter-turn fault. (32DS) Phase-to-phase impedance protection. (21P) Voltage supervised overcurrent protection. (50P/59, 51P/59) Zero sequence overvoltage protection for stator ground fault. (59G) Third harmonic undervoltage protection for stator ground fault. (27TN) Rotor one-point ground fault protection. (64R1) Rotor eld two-point ground fault protection (64R2) Denite/inverse time overload protection for stator. (49S) Denite/inverse time overload protection for rotor. (49R) Loss-of-excitation protection. (40) Out-of-step protection. (68) Overvoltage protection. (59) Undervoltage protection for synchronous condenser. Denite/inverse time over excitation protection. (24) Reverse power protection. (32G) Low forward power protection. (32F) Under frequency protection. (81) Over frequency protection. (81) Startup/shutdown generator protection. (SS) Voltage balance function. (60) Accident energizing protection. (50/27) Axis fundamental frequency current protection. (51FF) Axis third harmonic current protection. (51TH) Low frequency overcurrent protection. (51LF)

Main Transformer  ●

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Unrestraint current differential protection. (87UT) Percentage current differential protection. (87PT) DPFC current differential function. (87DT) Restricted earth fault protection. (REF) Phase-to-phase impedance protection at HV side and MV side. (21P) Voltage supervised overcurrent protection at HV side and MV side. (50P, 51P) Voltage supervised directional overcurrent protection at HV side and MV side. (67P) Zero sequence overcurrent protection at HV side and MV side. (50G, 51G) Zero sequence directional overcurrent protection at HV side and MV side. (67G) Zero sequence overvoltage protection for HV side and MV side (59N) Zero sequence current protection for HV side and MV side (50N, 51N) Zero sequence overvoltage alarm at LV side. (59G) Thermal overload protection. (49) Air blast initiation function. (49)

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Unrestraint current differential protection. (87UT) Percentage current differential protection. (87PT) Voltage supervised overcurrent protection. (50P, 51P) Voltage supervised overcurrent protection for branch A and branch B of LV side. (50P, 51P) Zero sequence overcurrent protection for branch A and branch B of LV side. (50G, 51G) Zero sequence voltage protection for branch A and branch B of LV side. (59G) Current differential protection for branch A cable and branch B cable of LV side. (87C) Thermal overload protection. (49) Cooling initiation function. (49)

Excitation Transformer or Exciter  Current differential protection. (87E) Overcurrent protection. (50P, 51P) Denite/inverse time thermal overload protection. (49) Miscellaneous Mechanical protection. (MP) CT failure detection logic. VT failure detection logic. Controlling circuit supervision. Voltage and current drift auto adjustment. Self diagnostic test. GPS clock synchronization. Fault Recorder. 32 fault event reports, 32 alarm event reports and 32 binary input changing reports. High resolution oscillography of last 8 oscillograms (compatible with international COMTRADE format) Rear communication ports: Ethernet (Optional) and 4 RS-485 with IEC 60870-5-103 protocol, 1 RS-485 with clock synchronization, 1 RS-232 or RS-485 with printer. 2 RS-485 ports could be set as optical interfaces. Front communication port: 1 RS-232 for testing and setting. ●

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Features ●

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An independent general fault detector is equipped in management module. Power source of output relay can be connected only when the fault detector operates. Besides, various other fault detectors are provided for various protection functions. Tripping outputs of protective elements on CPU module is valid only when the corresponding fault detector on management module pickup. Any component failures during normal condition will not cause unwanted operation. Variable slope percentage characteristic is adopted for  differential protection. The slopes can be so set that high sensitivity can be got during internal fault and transient unbalance current can be avoided during external fault. In order to prevent unwanted operation of differential protection due to CT saturation, measures to discriminate CT saturation are provided for phase current on each side. DPFC percentage differential protection reflects only deviation components of differential current and restraint current and is not affected 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. Inrush current discrimination technique is used for the

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equipment. Second harmonic and waveform of current can be used for discrimination of inrush current by option. CT saturation detecting logic can be put into operation automatically by the protection according to occurring sequence of DPFC of restraint current and DPFC of  differential current, to ensure the security in case of external fault but reliability in internal fault cases. For external fault, criterion of waveform of current is adopted. Unwanted operation will not occur if the correct transfer time from primary to secondary side of CT is not less than 5 ms. As to internal fault, the equipment will operate quickly. High sensitive transverse differential protection adopts percentage phase current restraint and floating threshold. The equipment can operate for internal fault with high sensitivity and not operate for external fault with high security. New criterions for percentage current differential protection of generator are integrated in the relay. DPFC current is used as restraint for external three phase fault. DPFC and negative sequence current are used as restraint for external unbalance fault. Longitudinal zero sequence voltage is used as restraint for small turn-to-turn fault of stator. Stator ground fault protection adopts third harmonic voltage as the criterion. It can adopt proportion relation of third harmonic voltages between generator output and neutral point around parallel operation of the generator with the system. This criterion ensures that no unwanted alarm can be sent during startup/shutdown process of the generator. Rotor ground fault protection adopts ping-pong principle. Its DC input uses high performance isolated amplier. Real-time 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 criterion such as stator impedance, reactive power, rotor 

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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 and system swing and out-of-step can be discrimi nated 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 enhanced significantly and unwanted operation can be avoided then. The connector type can be selected as connectorized wiring connector and crimp terminal connector. The unique connectorized wiring connectors from the relay rear panel to the terminal blocks on the rack or cabinet makes the on-site commissioning and replacement much easier than when you do the commissioning using the traditional screw terminals on the rear panel. Various GPS clock synchronizations are provided: second/ minute pulse via binary input or RS-485, message via communication ports and IRIG-B synchronization. The format of event report is compatible with international COMTRADE le. 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.

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