Harmonics Impact Over Protection System of Power Generator

A theatre encountered a situation where incorrect operation of the earth fault protection system of a back-up generator tripped the circuit breaker unexpectedly when dimmer loads were fully used.

The generator was used to supply critical loads via an automatic transfer switch (ATS) and the problem was caused by high levels of third harmonic current produced by dimmers and an inappropriate installation of neutral and ground system.

Consequently, current would flow in both neutral and ground system even in normal load conditions causing errors to current detection of earth fault protection system. To resolve the situation, the existing 3- pole ATS was replaced by a 4-pole type to separate neutral and earth currents and allow the earth fault protection system to operate reliably.