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DC high voltage generator device test voltage

time:2020/10/13   source:华天电力  reading:245 time

Generally speaking, the DC high voltage generator meets the DC withstand voltage test of cables below 220KV voltage level under the power frequency condition, but in some special occasions, some cables and electrical rated voltage levels have special requirements. For example, the voltage of underground cables and electricity in my country's coal industry is different from the ground rated voltage, which is only 6KV. In this case, how to set the test voltage for the DC high-voltage generator device?


According to regulations, different cables require different test voltages and pressurizing times. Take XLPE cables as an example. The 6KV cable mentioned above requires a DC test voltage of 25KV and a duration of 5 minutes.


In general test, it is necessary to slowly increase the voltage from 40% of the full test voltage to the full voltage for 5 minutes. If it is a new cable line that is less than one year old, the power outage will only last for one month. It can be done at 50% of the specified test voltage and lasts for 1 min. If the power is cut for one year, it should be done in accordance with the general test requirements.


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Specific test voltage and pressurization time requirements for different cables, and specific test requirements. It is explained in detail in the power cable preventive test procedure.


The breakdown forms of solid dielectrics include electrical breakdown, thermal breakdown and electrochemical breakdown. The same dielectric can have different breakdown forms under different external conditions.


(1) Electric breakdown


Due to the existence of the external electric field, ionized electrons accumulate enough energy in the strong electric field. Make them collide with each other and cause electric breakdown. It is characterized by fast process and high breakdown voltage.


(2) Thermal breakdown


The breakdown voltage decreases rapidly with the extension of temperature and voltage application time. At this time, the breakdown process is related to the thermal process in the dielectric, which is called thermal breakdown; when the ambient temperature and voltage application time increase, the thermal breakdown voltage decreases; As the thickness increases, the average breakdown field strength will decrease.


(3) Electrochemical breakdown


Under the action of an electric field, a chemical change may occur in the dielectric as a result, which irreversibly increases the conductance of the dielectric, and finally leads to breakdown, which is called electrochemical breakdown; chemical changes usually lead to increased dielectric loss, so electrochemical breakdown The final form is often thermal breakdown.


(4) Breakdown along the surface


In the actual insulation structure, there are often gas or liquid media around the solid medium, and the breakdown often occurs along the interface of the two dielectrics and on the side with lower electrical strength, which is called creeping breakdown; the creeping breakdown voltage ratio is single The dielectric breakdown voltage should be low. The edge of the capacitor electrode and the insulator at the end of the motor wire (rod) are prone to creeping discharge, which will cause great damage to the insulation.


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