Clean time grading is only possible if the dropout time is approximately the same. If the devices are used in parallel with electromechanical relays in networks with intermittent faults, the long dropout times of the electromechanical devices (several hundred milliseconds) can lead to problems in terms of time grading. This provides backup protection for high-resistance faults beyond the transformer. In line protection, the two-element phasebalance current/negative-sequence protection permits detection on the high side of high-resistance phase-to-phase faults and phase-to-earth faults that are on the low side of a transformer (e.g. Phase-balance current protection (ANSI 46) (Negative-sequence protection) As an option it is possible to make use of the circuit-breaker position indication. Breaker failure is detected if after a trip command, current is still flowing in the faulted circuit. of an upstream (higher-level) protection relay. If a faulted portion of the electrical circuit is not disconnected upon issuance of a trip command, another command can be initiated using the breaker failure protection which operates the circuit-breaker, e.g. The response threshold I IE> evaluates the r.m.s. The selectivity required with intermittent earth faults is achieved by summating the duration of the individual pulses and by triggering when a (settable) summed time is reached.

The normal earth-fault protection cannot reliably detect and interrupt the current pulses, some of which can be very brief. During intermittent activity, however, star-point resistors in networks that are impedance-earthed may undergo thermal overloading. Such faults either simply cease at some stage or develop into lasting short-circuits. Intermittent (re-striking) faults occur due to insulation weaknesses in cables or as a result of water penetrating cable joints. The function can also be operated in the insensitive mode as an additional shortcircuit protection. (Sensitive) earth-fault detection (ANSI 50Ns, 51Ns/50N, 51N)įor high-resistance earthed networks, a sensitive input transformer is connected to a phase-balance neutral current transformer (also called core-balance CT). Control via keyboard, binary inputs, DIGSI 4 or SCADA system.

Commands for control of a circuit-breaker and of isolators.Time-overcurrent protection (definite-time/inverse-time/user-def.).

Ge transformer serial numbers