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Application of DC generator DC test

time:2021/1/13   source:华天电力  reading:239 time

A certain section of the cable’s insulation is damaged, a certain part is severely damp, the joint process is not strictly grasped, the sealing is not tight, etc., are all possible sources of failure. However, due to the long distance of the cable, the method of mechanical inspection is time-consuming and laborious. Moreover, it is difficult to find internal defects. Using the DC high voltage test, you can find the specific fault location by slowly boosting the voltage on the premise of first determining the actual failure degree of the cable, for example, the long-distance high-voltage transmission connected to the high-power transformer outlet of the upper-level substation If the electrical waste has the above-mentioned fault points, it is very likely that the power supply equipment of the upper-level substation will frequently trip due to excessive leakage current during the power transmission process or the switch quick-break trip.


At this time, the use of DC high voltage generators for DC withstand voltage detection can quickly help us locate the fault location of the connector. We can apply a DC voltage to the end of the cable and closely monitor the leakage current value in the area where each cable connector is located. , It is possible to accurately determine the location of damage by using intuitive methods such as observation and sound measurement. After processing and repairing these parts, with the help of DC high voltage detection, recording the value and change trend of the leakage current, the joint repair can be judged Whether it meets the specified requirements, so as to determine that the faulty cable is a defect, it is not easy to be found.


DC Hipot Tester.png


The purpose of the DC withstand voltage test is to check the insulation strength of the cable itself, so the measurement of leakage current needs to take into account both safety and accuracy. In terms of safety, it is better to connect the micro-amp meter to the low-voltage side. The position or angle of view of the ammeter is to avoid work hazards in a high-voltage environment as much as possible, but the stray current in this connection current channel flows through the microammeter together with the main circuit current, which has a certain impact on the measurement accuracy.


Therefore, to weigh the measurement needs, the micro-ammeter can be installed on the high-voltage end of the test system, and the meter body can be insulated and shielded from the ground at the same time. Insulating rods, different DC high-voltage generators, and silicon rectifiers can be equipped during contact operation The reverse working voltage that can withstand is different. The rectifier circuit in the figure considers the peak value of the AC voltage, the surge voltage of the power supply, the self-inductance voltage of the load, the voltage superposition of the power supply and the filter capacitor, etc., from the equipment used From a perspective, the reverse working voltage is limited to less than half of the reverse peak voltage of the silicon rectifier stack to ensure the continuous and safe operation of the rectifier components.


If the rectifier stack is operated in series, voltage equalization measures should be taken for the components to prevent the partial voltage of a component from being too large, which exceeds the rated load-bearing capacity of the unit component. If there is no feasible voltage equalization method, the rectifier should be The operating voltage of the stack is appropriately reduced. When the AC voltage is used for the voltage test, the voltage will reach the peak value twice in one cycle of the voltage alternating. At these two peak points, regardless of the polarity of the voltage, the measured object Will withstand voltage.


When a DC high voltage generator is used for DC voltage testing, the DC test voltage needs to be twice the effective value of the AC test voltage before it can be equivalent to the peak value of the AC voltage. For example, 1500V AC voltage corresponds to the DC voltage that can generate the same electrical stress. It should be 2121V. At the same time, because the DC withstand voltage test voltage is relatively high, it has a special effect on the discovery of some local defects in the insulation. Moreover, compared with the AC withstand voltage test, the DC withstand voltage test equipment is lighter and more convenient for the The insulation damage of the test object is relatively smaller, and it is easier to find the local defects of the test object.


At the same time, it should be noted that the test data will have errors due to the influence of the environment, instrument accuracy and other factors. Of course, the DC high voltage test will not be an exception. The actual leakage current value of the power cable may have a certain gap with the final value of the microampere meter. This is because the DC high-voltage generating device will also generate a small leakage current when the no-load boost reaches the specified test voltage. The actual recording should fully consider the size of the no-load leakage current, and make small adjustments to the measured data. To reduce the error, get closer to the true value.

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