RCS-978 Transformer Protection

The RCS-978 relay is a full scheme protection used for the main and backup protection for various transformer applications, including two-winding transformers, threewinding transformers, and auto-transformers. Up to 6 CT inputs can be integrated in......

  • Overview
  • Functions
  • Features

The RCS-978 relay is a full scheme protection used for the main and backup protection for various transformer applications, including two-winding transformers, three winding transformers, and auto-transformers. Up to 6 CT inputs can be integrated in the current differential protection.The RCS-978 is recommended to be applied to transformers of high voltage level. The device is fully compatible with IEC 61850 communication with an additional communication unit.

  • Percentage restraint differential protection. (87T)
  • Unrestrained instantaneous differential protection. (50/87UT)
  • DPFC current differential protection. (7/87DT)
  • Common-and-serial-windings differential protection only for autotransformer (87ST)
  • Restricted Earth Fault Protection. (REF)
  • Definite-time and inverse-time overexciation protection. (24)
  • Voltage controlled directional overcurrent protection of HV side. (50P/51P/67P)
  • Inverse-time overcurrent protection of HV side. (51P)
  • Zero sequence overcurrent protection for HVside. (50N/51N/67N)
  • Ground overcurrent protection for HV. (50G/51G/67G)
  • Zero-sequence overvoltage protection of HV side. (59N)
  • Voltage controlled directional overcurrent protection of MV side. (50P/51P/67P)
  • Inverse-time overcurrent protection of MV side. (51P)
  • Zero sequence overcurrent protection for MVside. (50N/51N/67N)
  • Ground overcurrent protection for MV. (50G/51G/67G)
  • Voltage controlled directional overcurrent protection of LV side 1. (50P/51P/67P)
  • Inverse-time overcurrent protection of LV side 1. (51P)
  • Voltage controlled directional overcurrent protection of LV side 2. (50P/51P/67P)
  • Inverse-time overcurrent protection of LV side 2. (51P)
  • Zero sequence overcurrent protection for LVside. (50N/51N/67N)
  • Thermal overload protection. (49)
  • Overload alarm functions of each side. (49)
  • Overload initiating cooling function of HV side. (49)
  • Block on-load tap changing during overload of HV side. (49)
  • Definite-time and inverse-time overexciation alarm function. (24)
  • Zero-sequence overvoltage alarm functions of two branches of LV side. (59N)
  • Breaker failure initiation for HV side and MV side. (50BF)
  • VT circuit failure supervision VTS
  • CT circuit failure supervision CTS
  • CT saturation detection
  • Inrush current detection
  • Overexcitation detection
  • Voltage and current drift auto adjustment.
  • 64 latest fault reports, 8 latest fault waveforms, 256 latest abnormality reports and 1024 latest binary status input change reports.
  • GPS clock synchronization.

  • Main and backup protections are integrated in one set of protection equipment. Protection information such as sampled data and binary inputs is shared by all elements.
  • Δ→Y transfer method is used to adjust phase angle of secondary current on each side of the transformer. Therefore, the restraint current and differential current can be phase-segregated to distinguish the faulty phase only with inrush current characteristic when transformer is energized.
  • Two discrimination principles for inrush current are provided: harmonics restraint and waveform distortion restraint.
  • The DPFC percentage differential protection is immune to load current and is sensitive to small internal fault current in the transformer.
  • The calculated zero sequence current is used in zero sequence differential protection (or called restricted earth fault protection) and common-and-serial-windings differential protection to avoid mal-operation resulting from mistaken polarity of zero sequence CT of each side of transformer. Moreover CT ratio compensation of secondary zero sequence current is realized by software.
  • The positive sequence current restraint element is adopted to eliminate the influence of difference of transient characteristic and saturation of various CT on zero sequence percentage differential protection.
  • Distinguishing open and short circuit of CT against fault is more reliable due to the combination of voltage and current value method.
  • The maximum requirements of backup protection of all sides of transformer are provided. The tripping output circuit can be configured by tripping matrix and suitable to any mode of tripping.
  • The built-in reliable power swing blocking logic can properly supervise the impedance protection during a power swing. The power swing blocking logic can make the relay stand aside for an external fault during a power swing and pickup for an internal fault.
  • The RCS-978 relay is designed based on NR’s well established and proven hardware platform of multiprocessor. Two CPU modules are adopted in the relay. Each CPU module has one microprocessor and two digital signal processors (DSP). All CPUs can operate in parallel.
  • 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.