Temperature rise and DC current capability tests of star-point reactor used in HVDC transmission

Abstract

Star-point reactors are grounding devices installed in HVDC stations between the converter transformer secondary side and AC side of converter arms to provide a reference to ground. Such reactors are used as high-impedance grounding on the converter side of power transformers, providing high impedance path for the fundamental harmonic (i.e. 50 or 60 Hz) and a low impedance path for DC current, eliminating DC current flowing through the transformer windings. Temperature rise and DC current capability tests of 420 kV star-point reactor are presented in this paper. The purpose of temperature rise test is to verify that temperatures that can damage the insulation of star-point reactor will not be reached with the specified service conditions. The temperature rise test was carried out according to the requirements of the IEC 61869-3 standard and client’s request which included simultaneous application of fundamental, 3rd harmonic voltage and DC excitation. The inclusion of 3rd harmonic excitation of an amplitude up to 15% simulates voltage harmonic distortion which may appear in the power system at the location of star-point reactor installation. Prior to temperature rise test, DC current capability test was performed. The goal of this test is to determine the value of DC current at which the saturation point is reached. DC current is injected through star-point reactor while AC voltage is applied. Two different cases are considered regarding AC voltage: test with fundamental voltage harmonic and test with fundamental voltage harmonic with superimposed third voltage harmonic. Test circuit is proposed which is suitable for generation of complex voltages composed of fundamental harmonic and superimposed third harmonic with amplitudes up to 15% of the applied fundamental harmonic. The proposed test circuit was also used during the temperature rise test and it is applicable for testing of HV equipment with rated voltage up to 420 kV.