| Large amount of domestic and international operating experience and information demonstrate that the damage of inter-turn insulation in winding constitutes the majority in high-voltage electrical machine operating accidents. Especially, the commonly use of vacuum switch greatly increases the amplitude and steepness of switching over-voltage acting on windings of the electrical machine. The inter-turn insulation of high-voltage electrical machine's winding is seriously jeopardized by the switching over-voltage. And, the accidents rate concerning high-voltage electrical machine has a tendency of increase.It is known to all that many factors affect the turn-to-turn insulation reliability of high-voltage electrical machine's winding. It is also a comprehensive and complicated problem to seek the reason for winding's turn-to-turn insulation damage. But there remained a common agreement that the over-voltage is major reason which result in winding's turn-to-turn insulation damage. Under the normal operating status, the operating voltage is very small. The maximum is in the hundred volts or so. The winding's turn-to-turn insulation strength is enough to bear the volts too. But the maximum of over-voltage amplitude is as high as six to seven times value of the rated phase voltage, and the steepest wave head is about 0.2μs. The steeper wave head over-voltage can form non-uniform voltage distribution. Having no proper protection measures together with various of winding's turn-to-turn insulation defection, it is likely to go beyond its deserved winding's turn-to-turn insulation strength and bring about the accidents.To guarantee the winding's turn-to-turn insulation reliability, power systems have to take effective protective measures, and it is important that electrical machine manufacture company should improve winding's turn-to-turn insulation quality as well as adopt effective test means, test criterion and test device to distinguish and eliminate the defective coils, so that the new electrical machine will have enough insulation level. With the development of large capacity and high voltage electrical machine, there is a higher demand on the winding's turn-to-turn insulation. New detection criterion for high-voltage electrical machine winding's turn-to-turn insulation is accordingly formulated in China. A higher demand on test application is put forward in new criterion JB/10098-2000. It is imperative to develop a new type of test device for high-voltage electrical machine winding's turn-to-turn insulation because the existing test device can not meet the demand.By analyzing high-voltage electrical machine winding's turn-to-turn insulation and using domestic and international experience for reference, a new generation of test device ZJ-45 for high-voltage electrical machine winding's turn-to-turn insulation is successfully developed .The test device ZJ-45 utilizes impulse voltage method to exert impulse voltage on coil and determines if the quality of the coil is excellent or inferior through observing impulse current frequency variation. For all the electric machine produced in China, it can meet the test demands according to JB/T10098-2000 criterion.ZJ-45 test device can steadily apply impulse voltage of 45kV on high voltage coil, and the rise time of the output voltage wave can meet with all the demands of new criterion JB/T10098-2000. The problem of discharging to the grounding system at the instant that DC supply is switched on is solved, hence the burning of the main discharging gap is greatly reduced. The heat dissipation property of main discharging gap made from entire copper material is better than the older. The design of surface of discharging gap is more reasonable. The gap and the bracket is the same body, and the two halves of the copper ball is always kept in the same axis when they are pulled close or apart each other, so that the problem of non-uniform electric field is solved. Multi-electromagnetic separating system is adopted for control of ZJ45 test device, to enable s... |
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