SIPROTEC 7SK81

The SIPROTEC 7SK81 is a multi-functional motor protection relay designed to protect asynchronous motors of all sizes. The relays have all the necessary functions to be utilized as a backup relay to a transformer differential relay. 

It provides numerous functions to flexibly respond to system requirements and to deploy the invested capital economically. 

It also provides 4 low-power current transformer inputs and 3 optional low-power voltage transformer inputs. With the same low-power current transformer (LPCT), a wide range of primary rated line currents can be covered. Objects with rated currents in the range of 20 A to 2500 A can be protected when using low-power current transformers.

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DESCRIPTION

Basic Features

  • Exchangeable interfaces
  • Freely assignable LEDs 
  • Six-line display
  • Instantaneous and definite time-overcurrent protection (phase/neutral) (50, 50N, 51, 51N)
  • Directional time-overcurrent protection, ground (67N)
  • Directional overcurrent protection, ground (definite/inverse) (67Ns, 50Ns))
  • Displacement voltage, zero-sequence voltage (59N)
  • Trip-circuit supervision (38)
  • Undercurrent monitoring (37)
  • Temperature monitoring (38)
  • Thermal overload protection (49)
  • Load jam protection (51M)
  • Locked rotor protection (14)
  • Undervoltage/overvoltage protection (27/59)
  • Forward-power, reverse-power protection (32)
  • Overfrequency/underfrequency protection(81O/U)
  • Breaker failure protection (50B/F)
  • Phase-balance current protection (negative-sequence protection) (46)
  • Unbalance-voltage protection and/or phase-sequence monitor-ing (47)
  • Lockout (86)