AC HiPot vs. DC HiPot testing of a 5kv vacuum bottle circuit breaker
- Thread starter LARON
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zog
Senior Member
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- Charlotte, NC
Although an ac high potential test is recommended, a dc test may be performed if only a dc test unit is available.
In this case the equipment must be capable of delivering 5 milliamperes for one minute. When a DC test voltage is used, a high field emission current from a microscopic sharp spot on one contact can be misinterpreted as a sign of a vacuum interrupter filled with air.
To avoid a misinterpreted test result, the open interrupter should always be subjected to both voltage polarities. That is, apply the DC Voltage:
- first, so that one contact of the interrupter is the cathode, and
- second, so that the other contact of the interrupter is the cathode.
A bad interrupter filled with air will have a similarly high leakage current in both polarities. A good interrupter with a good vacuum level may still have a high leakage current, but this will generally be in only one polarity. Such an interrupter usually has a tiny sharp spot on one contact that produces a high field emission current when the sharp spot is a cathode, but not on an anode. In addition, such an interrupter would also normally withstand the required AC voltage which is the definitive test of its vacuum integrity
In this case the equipment must be capable of delivering 5 milliamperes for one minute. When a DC test voltage is used, a high field emission current from a microscopic sharp spot on one contact can be misinterpreted as a sign of a vacuum interrupter filled with air.
To avoid a misinterpreted test result, the open interrupter should always be subjected to both voltage polarities. That is, apply the DC Voltage:
- first, so that one contact of the interrupter is the cathode, and
- second, so that the other contact of the interrupter is the cathode.
A bad interrupter filled with air will have a similarly high leakage current in both polarities. A good interrupter with a good vacuum level may still have a high leakage current, but this will generally be in only one polarity. Such an interrupter usually has a tiny sharp spot on one contact that produces a high field emission current when the sharp spot is a cathode, but not on an anode. In addition, such an interrupter would also normally withstand the required AC voltage which is the definitive test of its vacuum integrity
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
http://www.electricalmanuals.net/files/MV-HV-EQUIP/BREAKERS/CUTLER/VCP-W/IB-32-255-1F.pdf
See page 35.
As stated before AC is prefered. An AC Hi-Pot that can deliver the test voltage will cost about 50Gs, so not many companys will have them. They are also very large & heavy. Possibly larger & heaver than the breaker under test. A DC megger on the other hand is more portable & affordable.
See page 35.
As stated before AC is prefered. An AC Hi-Pot that can deliver the test voltage will cost about 50Gs, so not many companys will have them. They are also very large & heavy. Possibly larger & heaver than the breaker under test. A DC megger on the other hand is more portable & affordable.
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