Development and application of low frequency short-circuit current on-site heating device for the UHV converter transformer

The short-circuit method produces heat from inside of transformer insulation, which have better drying efficiency than traditional hot oil circulation method using vacuum oil filter, and is suitable for heating large-scale power transformers, such as UHV converter transformers at site. However, power frequency short-circuit heating device has many disadvantages such as high voltage, complex composition, large area and great weight, and it was not applicable for site. In order to overcome those shortcomings, the low frequency short-circuit heating device was developed based on ultra-low frequency sinusoidal pulse width modulation (SPWM) technique. It reduced the voltage and power capacity by decreasing inductance of the transformer windings at low frequency, and therefore it was simpler, smaller and lighter. The device had been applied on the ±800 kV UHV converter transformer, and had achieved remarkable effects. All applications indicate that the low frequency short-circuit heating device could heat the large scale transformer fast and evenly, and it is safe, convenient, and suitable for site.