Study on features of ferromagnetic resonance 110 kV substation and it´s eliminating method

Based on the oscillograms recorded during tests of ferromagnetic resonance in many 110 kV substations, this paper reveals some important features which are not yet known and different from that in a 10-66 kV neutral isolated system. It also suggests a method, by the aid of zero sequence channel of the open delta winding of potential transformer, as well as the assistance of introducing a positive sequence auxiliary line into the resonance circuit as a damper, to eliminate the resonance both of zero sequence and positive sequence nature. Based on this method a computer-aided resonance eliminating device, using thyristors as damping elements, has been developed and operated successfully in some substations in China for five years. This paper also introduces the structural principle of this device