Hello everyone, I am looking for some guidance on VB testing with a DC test set. Recently was out in the field and we were testing a 35kv vacuum breaker. NETA is slightly confusing with the information for myself at least. It recommended going into the IEEE book which I unfortunately don’t have. Can anyone break down what I should do when this application comes up again in the future and what documentations to look at.
Typically what I do, is look in the manufacturers manual.
Excerpt from HVI (https://hvinc.com/wp-content/uploads/2020/09/Vacuum-Bottle-Testing-2.pdf)
High voltage testing of vacuum bottles should be performed using AC voltage. DC voltage testing is not recommended by most bottle manufacturers and forbidden by some. Like on most high voltage electrical apparatus in a substation, AC testing should be performed to verify if the object can withstand the AC stress when in service. Depending on the item tested, usually the test voltage is 2 - 4 times over the utilization voltage and for perhaps a minute. The test object either holds the voltage or fails. There is nothing in-between. DC leakage currents are meaningless. In a bottle, there is no acceptable partial vacuum. It is either there or not. An AC stress test will determine that immediately. Another reason: The DC output voltage from various hipots is not predictable. Depending on the rectifier circuit, the peak DC voltage may be significantly higher than the average voltage read on the voltmeter and the ripple output is not known. This possibly excessive over voltage can result in the creation of x-rays and falsely failed bottles. Some manufacturers also worry about the DC voltage degrading the bellows and other parts within the bottle. Also, switchgear manufacturers worry that DC voltage degrades the insulators used between the bus and ground. Use AC.