Research On Technique And Device Of Turn-to-turn Insulation Test For Large Electrical Machine's Pole Coils

Large electrical machines are the fundamental equipments for electric energy production. It has important effect on the safe and stabilizing operation of entire electric power system. Large amount of domestic and international operating experiences and data indicate that the damage of inter-turn insulation of pole coils constitutes the majority in large electrical machine operating accidents. So, it is obligatory to take appropriate measures to ensure the reliability of pole coils'turn-to-turn insulation of large electrical machines.There are many measures to improving pole coils'turn-to-turn insulation level, for example, adopting the new insulation material, improving turn-to-turn insulation structure and manufacturing technique of pole coils. But it is more important that the electrical machines manufacturing companies adopt reasonable effective test methods, test standard and test devices to remove those defective pole coils which are hazardous for safe operation of electrical machines to ensure that pole coils have sufficient turn-to-turn insulation intensity in new electrical machines.Because of some shortcomings of present methods used to test turn-to-turn insulation of pole coil of large electrical machines, for example, the impulse voltage method used generally at present has no way to apply even voltage across the tested coil; the test method of mid-range frequency generator set has such shortcomings as high costs, large room needed, difficult to move and low output voltage. It is necessary to study a new test method and device used to test turn-to-turn insulation of pole coils to ensure the turn-to-turn insulation reliability of pole coils and decrease operating accidents of large electrical machines.Referencing to the information at home and abroad, a new turn-to-turn insulation test method for pole coils is presented and the test device is designed foundationally. The following work has been carried out:Firstly, combined with the measured parameters of typical pole coils, their equivalent circuit with distributional parameters is set up at high frequency; the frequency response is analyzed by Pspice software; and, appropriate upper limit of frequency of testing voltage source is determined.Secondly, combining of high power electronic switching technique and parallel resonance skill of the test circuit, a technique scheme of test device used for large electrical machine's pole coil turn-to-turn insulation test is presented, and the key segment of this scheme is simulated by means of a typical pole coil.At last, the key circuit of this device is built in the laboratory to test a model coil. The testing result shows that highly sine waved voltage at the frequency of several thousands Hz is able to be formed in the tested coil by this device, and the current of tested coil is much lower than one at the frequency of 50Hz. All above prove that this pole coil turn-to-turn insulation testing method and design scheme of device are feasible.