
Previously, these scenarios were usually ignored and filed under 'Mysteries of the universe'
because they only occured once or twice a year and because disturbance recordings were not
commonly used in normal medium-voltage substations for fault verification. However, when disturbance
recorders were introduced as a common feature of protection relays this phenomenon received a name
and defined characteristics. One such characteristic is the occurence of high magnitude current
spikes, which –compared to residual voltage– are in the opposite direction of the current spike in
faulty feeders and concurrent in healthy feeders. Handling these unique characteristics requires a
completely different set of tools than what traditional directional earth fault protection can offer. The
following figures present three intermittent earth fault situations experienced by relays in a substation..
Figure. 5.3.6 - 98. An intermittent earth fault in a medium size network tuned close to resonance, as seen by a faulty feeder relay.
A
AQ
Q-F215
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Instruction manual
Version: 2.04
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