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SKC

Microprocessor-based current differential relay with overcurrent, earth fault and thermal elements

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The differential current relays type SKC is intended for the protection of generators, large motors, two winding power transformers and short lines.
The relay SKC feature the following characteristics:

  • seven current inputs, where six are provided for current phase measurements and the last one dedicated for residual current measurement;
  • internal compensation of phase shift and ratio matching for transformers differential function (87T); conventional external compensation can also be selected with external CT's;
  • stabilizing circuit with dual slope with variable bias makes the differential functions of SKC relay insensitive to external fault (87T, 87G);
  • second and fifth harmonic restraint stabilization with strong magnetizing inrush currents and overexitation condition (87T) based on numerical processing of differential current (DFT algorithm);
  • alernative set thresholds for 49-50-51-50N-51N/87N protection functions which are automatically enabled upon detection of high second harmonic above a programmable set-point to prevent tripping for transformer energization (inrush);
  • earth fault protection insensitive to thirth and higher harmonic components;
  • selectable operation curves with independent or dependent time (first thresholds) for overcurrent and earth fault functions;
  • trip counting performed for each function;
  • shorting values of input quantities corresponding to the four last operations (START or TRIP) and trace memory with pre and post trigger;
  • four final relays, independently programmable as energized/de-energized and latched/no-latched;
  • three signalling LEDs (ON,TRIP,ALARM);
  • two digital inputs circuits;
  • double set-point groups (bank A and bank B)
  • blocking circuits to perform accelerated protection schemes either with programmable logic from internal funtions with block circuits of external protection relays;
  • trip circuit supervision (TCS)
  • breaker failure protection (BF)
  • serial communication circuit RS485 with MODBUS RTU protocol;
  • real time clock with memory backup;
  • continuous monitoring of internal circuits ;(SELF TEST).
SKC - Serie S ()

Specifications


Key:   standard standard optional optional alternative alternative


Applications

  • Transformer

Protection functions

  • Thermal image (49)
  • Phase overcurrent (50/51)
  • Residual overcurrent (50N/51N)
  • Differential protection for generators and motors (87G/87M)
  • High impedance restricted earth fault (87NHIZ)
  • Biased differential for transformer (87T)
  • Breaker failure (BF)