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Partial discharge measurement method

time:2020/11/20   source:华天电力  reading:270 time

For electrical equipment operating in the power grid, such as high-voltage electrical equipment such as cables, capacitors, transformers, transformers and motors, the insulation withstand voltage level is designed according to its operating voltage level. Under normal conditions, its insulation performance can withstand operating voltage. Due to poor manufacturing processes, the insulation of electrical equipment may have bubbles, impurities, cracks, etc. inside. This insulation will appear inside the insulation under the action of high-voltage alternating electric fields. Periodic partial discharge. Because its discharge energy is very small, it will not break down the entire path at once, but it can reduce the insulation performance, or even lose the withstand voltage performance. Over time, this partial discharge will cause the entire insulation breakdown and explode, giving the power grid safe operation It has a great impact on the reliability of power supply and causes great economic losses to users and society. Therefore, attention should be paid to the partial discharge of electrical equipment.


The partial discharge phenomenon inside the insulation of electrical equipment is periodic. It goes on repeatedly with the change of AC voltage, and discharges when the amplitude of AC voltage is maximum. When a partial discharge occurs inside the insulator, energy in the form of light and sound waves will also be generated.


Partial Discharge Detector.png


The measurement methods of partial discharge are generally divided into non-electric measurement method and electrical measurement method.


The non-electric measurement method is mainly the ultrasonic method. Its purpose is to detect the location of partial discharge. The electrical measurement method is a measurement method using high-frequency pulse current. It is widely used due to its high sensitivity and ease of use. The partial discharge tester is made according to the principle of high-frequency pulse current method.


Through the detection of partial discharge, the insulation defects of electrical equipment can be reflected. This kind of test is non-destructive and replaces the destructive withstand voltage test to a certain extent. The test voltage should ensure that it will not cause penetrating discharge. When testing the partial discharge amount of a certain device, the pulse current generated by the partial discharge of the test object is amplified and sent to the measuring instrument. After the discharge capacity is corrected, the discharge capacity value is measured. For different types of equipment and insulation, the discharge value is also different. Manufacturers of high-voltage electrical products have factory test standards, which can be assessed with reference to the standards.


To make the power grid operate safely. For newly put into operation equipment, technical testing of partial discharge must be carried out. Unqualified products shall not be put into operation. The equipment that has been installed on the power grid and operated must also be tested according to regulations. Those who are unqualified should exit operation, so as to avoid major accidents such as explosion caused by partial discharge of the equipment and power outage of the power grid.


Attention should be paid during the test: the wiring of the test loop must be correct, the contact part of the wiring must be firm, and the entire test system must be properly grounded. Before the test, set the sensitivity of the instrument to the minimum value required and gradually increase the pressure. Pay attention to the indicator value of the meter at any time, and power off if any abnormality is found.


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