平顶山干式变压器：平顶山干式变压器雷电冲击电压试验

平顶山干式变压器雷电冲击电压试验 　　
为了考核平顶山干式变压器主、纵绝缘的冲击强度是否符合国家标准的规定和研究改进平顶山干式变压器的绝缘结构，要进行冲击电压试验。
所谓雷电冲击试验，就是在平顶山干式变压器绕组的端子上施加一种模拟真实的雷电波形的冲击波。对平顶山干式变压器或其他电气设备，在此种冲击波的作用下进行考验，看其能否通过(或破坏)。截波是相当于雷电波进入变电所时发生了保护间隙或空气绝缘的闪络而产生的波形，是雷电全波被突然截断的波形，电压急剧降落至零。其截断时刻可发生在波前或波尾。截波试验也同样是对平顶山干式变压器设备的考验。
本试验必须有产生冲击波的装置。该装置称为冲击电压发生器，相应的一些测量仪器，主要有测量球极、分压器和观察冲击波形现象用的高压示波器等。标准规定试验波形全波为1.2±30%/50±20%μs(波前/半峰值时间)和截波时间为2—6μs的截波.截波过零系数(即截断后第一个振荡峰值和截波幅值之比)在0.25—0.35的范围内。冲击试验装置仅较大平顶山干式变压器厂和试研单位具备，一般单位可将平顶山干式变压器委托试研单位试验。

在冲击电压试验前.平顶山干式变压器应进行下列准备工作：
1)大型平顶山干式变压器要进行真空注油，中小型平顶山干式变压器注油后也要抽真空。而后还要静放数天，使油中气泡尽可能逸尽。冲击电压试验对这一点要求特别严格，因油中有气泡存在时，由于气泡放电往往会造成对试验结果的误判断。
2)应进行全部项目的例行试验，包括绝缘特性测定、外施耐压试验和感应耐压试验.以检查绝缘是否存在缺陷。
3)尽可能进行一次低电压冲击波下的电压分布测量，以掌握绕组各部的电位和梯度分布，估什各部绝缘裕度。
4)将平顶山干式变压器调到电压小分接位置，这是对纵绝缘考验严厉的情况。
平顶山干式变压器内绝缘应用负极性冲击波试验，而外绝缘则用正极性冲击波试验，先试全波后试截波。采用逐级升压法，即在试验电压的50%、75%、100%下，每级冲击3次，每次间隔1min。
冲击试验的顺序为(GB1094. 3-1985标准规定)；
1）一次或几次降低电压的全波冲击试验。
2)一次100%的全波冲击试验；
3)一次或几次降低电压的截波冲击试验；
4)两次100%的截波冲击试验；
5)两次100%的全波冲击试验；
冲击试验应逐相进行，非被试相应短接接地，油箱接地。
在冲击试验中，绝缘如果有扭伤，可从示波图崎变中进行判断。
即可用对比试验电压波形变化和绕组中性点电流波形及低压侧电容电流波形的方法来判断绝缘是否已拐伤。

Lightning impulse voltage test

In order to check the transformer primary, the impact strength of the vertical insulation compliance with the provisions of national standards and research to improve the transformer insulation structure to conduct the impulse voltage test.
The so-called lightning impulse test, a simulation of real lightning waveform shock wave is imposed on the terminals of the transformer winding. Transformers or other electrical equipment, the role of such a shock wave test to see whether it can pass (or destruction). Chopper is the equivalent of a lightning wave to enter the substation protection gap or air insulation flashover occurs when the waveform is the waveform of the lightning full-wave was suddenly truncated voltage sharply landing to zero. Its truncated moment can occur in the wave front or wave tail. Chopped wave test is also a test of the transformer equipment.
This test must be generated shock wave device. The device is called the impulse voltage generator, the corresponding number of measuring instruments, the main measurement of spherical polar divider and observation of high-pressure shock wave phenomena such as an oscilloscope. The standard specifies the full-wave test waveform was 1.2 ± 30% / 50 ± 20 μs (wave front / peak time) and chopper 2-6μs chopper chopper zero coefficient (ie, truncated after the first oscillation peak and the ratio of the cross-sectional volatility of the value) in the range of 0.25-0.35. The impact test device only transformer factory and test research units with the general unit transformer commissioned to test the research unit test.

Before the impulse voltage test transformer should be the following preparations:
1) a large transformer to vacuum oiling, small and medium-sized transformers have to vacuum oiling. Following that, a quiet place a few days, so that the oil bubble as far as possible Yat do. When the impulse voltage test on this point particularly demanding, due to the presence of air bubbles in the oil bubble discharge often leads to mistaken judgment on the test results.
2) should be routine testing of all projects, including the insulating properties of the determination of the applied voltage withstand test and induction voltage withstand test to check the insulation for defects.
3) under a low voltage shock wave voltage distribution measurement as much as possible in order to grasp the potential and gradient of the winding ministries estimate insulation margin, even ministries.
4) switch to the voltage minimum tap position, which is the most severe case of vertical insulation test.
Insulation applications inside the transformer negative shock wave experiments, the outer insulation with a positive polarity of the shock wave test trial after the first try full-wave chopper. Step step-up method, in the test voltage of 50%, 75%, 100% for each level the impact of three times at intervals of 1min.
The order of the impact test (GB1094. 3-1985 Standard Provisions);
1) one or several lower voltage full wave impulse test.
2) a 100% full wave impulse test;
3) one or several lower voltage cut-off wave impulse test;
4) Two 100% cut-off wave impulse test;
5) Two 100% of the full wave impulse test;
The impact test should gradually phase, non-test corresponding short circuit grounding, tank ground.
In the impact test, the insulation, if there are sprains, can be judged from the oscillogram of distortion.
You can use the comparison test voltage waveform changes and winding neutral point current waveform and the low pressure side of the capacitor current waveform to determine the insulation whether Abduction injury.

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