Testing medium-voltage (MV) cables with the high-potential (“hi-pot”) test is typically part of an MV cable testing program. In Parts 4 and 5, we looked at the DC and AC versions of this test. The very low frequency (VLF) version is, in many ways, similar to the high-pot (more so the AC version). It’s simple, and the test equipment is both inexpensive (relatively speaking) and very portable. Unlike the DC hi-pot (and like the AC hi-pot), it does not have the space charge drawback.
Like the AC hi-pot, it’s generally a “go/no go” test and is good for identifying high-impedance and conductive defects in cables. Unlike the AC hi-pot, it doesn’t simulate service conditions or factory tests. And unlike either hi-pot, it’s considered a destructive test. Even though it generally does not create additional aging effects, it may cause existing defects to grow rapidly (even during the test) especially in older cables. It could, because of elevated voltage levels, cause existing defects to bridge together.
Consult IEEE 400.2 for more information about VLF testing.
