Neutral Point AC Withstand Voltage Test of 500kV Main Transformer at Tingzikou Power Station

Introduction: The AC withstand voltage test is the most effective and direct method for identifying insulation strength of power transformer and also an important component of preventive test. Because the voltage of AC test is higher than running voltage and power transformer has great safety margin after the test, AC withstand voltage test is vital to ensuring safe operation of power transformer. The paper briefly introduces the method of neutral point AC withstand voltage test of 500kV transformer at Tingzikou hydro-power station.  

Key words: power transformer, AC withstand voltage test, insulation strength; Tingzikou hydro-power station  

Introduction  

Four sets of 500kV outdoors three-phase double-coil OFWF power transformers, produced by TBEA, are installed at Tingzikou Water Control Hub. Its rated capacity is 310MVA and rated voltage is 525 ± 2 × 2.5%kV/15.75kV. The connection method is YNd11. The oil or SF6 bushing is utilized to connect the high voltage side of transformer with GIS. The low voltage side adopts oil or gas bushing to connect IPB. The running transformer will degrade and form the fault when its insulation are exposed under the electric field, temperature and mechanical vibration for a long time. However, the neutral point AC withstand voltage test can detect whether the transformer neutral point has insulation faults and whether the insulation level conforms to relevant standards and technical requirements.