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Negative sequence overcurrent relay and protection assemblies

Negative sequence current relays are primarily applied to protect generators and motors from dangerous overheating due to unbalanced currents. They are also used in transmission systems to detect unbalanced conditions and faults. RXIIK 4 is a modern microprocessor based negative sequence overcurrent relay. The relay has the possibility of setting a fixed time or an inverse time overcurrent characteristic.

Two setting levels are available for alarm and tripping. Two setting groups are available and can be selected via binary input or the front HMI. RXIIK 4 comprises a transformer isolated input unit for the three-phase current, a microprocessor based measuring unit and the front accessible HMI unit. The RXIIK 4 requires auxiliary DC power fed from a universal 24-250 V DC/DC converter type RXTUG 22H. RXIIK 4 has five programmable output relays, which can be independently selected to operate from any of the included functions in the relay. It is possible to have several outputs operated from one function. There are six available functions that can be selected for these outputs;

In Service
I - Start
I - Alarm
I - Trip
Thermal block
Group 2 settings active

Main Features:

  • Generator and motor applications and for general power system use such as:
    • Unsymmetrical loading which increase the negative sequence current.
    • Phase interruptions e.g. a broken conductor.
    • Failure on one or two poles of a breaker or disconnect-switch at opening and closing
  • Earth-fault detection in solidly earthed system
  • Inverse characteristic or fixed time
  • Individual alarm and trip ranges
  • Thermal memory
  • Settable reset time
  • Five independent output relays selectable
  • Individual alarm and trip ranges
  • Trip information & service values available via the HMI
  • Test switch, DC/DC converter and heavy-duty trip relays are available as specified options

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