HV Pressure Test (Power Frequency 1-Minute Withstand) on In-Service Equipment

[JezNZ]

Hi,

Is there any applicable guidance notes on pressure testing in-service MV (11kV operating, 12kV rated) equipment (de-energised) that has been extended.

Manufacturers' guidance notes require a 28kV pressure test for commissioning the new tier. The technicians wanted not to perform it, due to the age of the existing bus (16yo), however our inspector declined this, requesting us to perform it, but perhaps at a reduced voltage. I've contacted the manufacturer, however in the meantime I wondered if there are any guidance notes anyone is aware of, I couldn't find anything searching IEEE / IEC.

Thanks

 

[thermionic1]

NETA has specifications for an acceptance (new) and maintenance (existing) tests.

 

[Gr8blu]

JeNZ: The general rule-of-thumb is to perform "maintenance level" testing at 65% of "new" test level. For an AC test, the typical "new" value for a rotating machine is (2*E + 1000) volts. In your case, that would be (2 * 12000 + 1000) = 25 kV. Breakers and contactors may be slightly higher, but not by much.

DC Test value would be 1.7 * (AC value). Thus a "new" DC test would use 1.7 * 25 = 42.5 kV.

Converting energy to motion for more than half a century

 

[JezNZ]

Hi,

FYI the manufacturer responded with an 80% of 26kV value = 20.8kV.

 

[VLFit]

The 28 kVac number is for a factory test on a new coil. If you have rewound a coil and are testing it in your shop, this would be at 80% of the 28 kVac, or 22.4 kV. If you are testing an old coil not rewound, then the 65% number is good, or 18.2 kVac. Often used is the 2Uo + 1000 for the test voltage, and then use the same multipliers. This yields test voltages slightly lower than the above mentioned.

When doing this test, you will have to know the capacitance of the coil to calculate the AC current draw at the test voltage. A=2pifVC.

Many do not want to perform an AC Withstand test like you are describing, since the coil may fail, then what? A blown coil in need of rewind. A diagnostic test of Partial Discharge and/or Tan Delta can be performed, at lower voltages and for short duration.

Hope this helps