Crucial tests on air-core neutral grounding reactors

In February 2022, experts from our KEMA Labs facility in Prague, Czech Republic , have successfully performed a test on an air-core neutral grounding reactor with an inductance greater than 100 mH for the customer, Coil Innovation GmbH, from Austria.

Neutral Grounding Reactors are single phase reactors generally connected between ground and neutral of transformers or generators in order to control single line-to-ground faults at a desired level. Indeed, the neutral ground circuit in the transformer provides the return path for the fault currents. To limit this current, impedance – either in the form of a reactor or a resistor – is installed in the neutral circuit. Therefore, the testing in such components is crucial to verify that they function to the most of their ability in order for the power transformer to keep working properly after fault currents that may occur .

Due to the large inductance of the specific reactor, the test carried out by KEMA Labs was very interesting from a technical point of view because the drop voltage on the reactor reached a value well over 100 kV, so the test circuit had to be properly designed not only in terms of current when in case of failure the current from generators could reach up to 140 kA, but also in terms of voltage.

In this respect, 10 dynamic short circuits were applied to the reactor , which is far more than requested by the IEC standard, and then the reactor was subjected to a thermal short circuit current 3,15 kA for 2 s. After each test, a detailed inspection was successfully performed on the reactor.