Study of Super-low Frequency AC Withstand Voltage Test of Large-scale Generator

Liu Chenlin, Yin Hong
HIMALAYAL - SHANGHAI - CHINA

Abstract: The paper puts forward a super-low frequency withstand voltage test equipment, which combines high-voltage generator of super-low frequency sine wave and super-low frequency voltage measuring system. Advantages of applying this equipment to AC withstand voltage test are analyzed. Then take 3# generator of some nuclear power plant as an example and describe test methods and procedures. The feasibility and reliability of this super-low frequency AC voltage test of high-power generator are verified and worthy of attention.          

Key Words: generator, super-low frequency, AC withstand voltage test

Under the background of increasing capacity of motor in nuclear power plant, we face a trend of fast development of generator winding against frame and ground capacitance. The capacity of transformer used in the power frequency AC voltage test for motor stater winding has also improved greatly. Test equipment is large in scale, causing many inconveniences in actual operation. Against this problem, relevant researchers put forward that we can try to reduce the work frequency of AC withstand voltage test. That is, routine 50Hz can be reduced to super-low 0.1Hz. The aim is to reduce the capacity unit of test generator. In other words, test equipment with low capacity can be used to complete high-frequency test. Therefore, it is of important value to verify the withstand voltage performance ofhigh-power generator in the nuclear power plant. 

1.Basic Components of Super-low Frequency Withstand Voltage Test Equipment
Equipment of super-low frequency withstand voltage test is composed of two parts. One part is high-voltage generator of super-low frequency sine wave while the other is voltage-measuring system of super-low frequency. Working principle of high-voltage generator of super-low frequency sine wave is as follows: first, power-frequency source forms relatively stable DC voltage through rectification mode; then convert into 1000Hz high-frequency voltage through inverting current. The high-frequency voltage can form negative and positive polarity high voltage through voltage step-up and a series of operation; through dealing with peak and phase of voltage-sensitive elements, sine wave is formed and adjusted; finally the 0.1Hz sine wave voltage is output.  Working principle of the other is in the following. First of all, with the support of voltage divider, the voltage of high-voltage signal is divided; then conduct the signal sample and sampling data is transmitted to terminal display; finally, SCM (Single Chip Microcomputer) is used to calculate the test voltage value and show test results at the terminal.