BIL vs "partial discharge"

[jraef]

On a side note to this excellent discussion thread238-124184, can anyone shed some light for me on how BIL relates to "partial discharge" ratings used outside of the US? Here is a sample text from a specification that I must address. I don't have access to these standards, but someone told me that partial discharge was a different test but similar to BIL testing. So I want to use data from our BIL testing to respond to this.

"...starter shall be tested for Partial Discharge (Corona Free) according to EN50178 and HD 625.1 S1:1996 (Electronic
equipment for use in power installations)"

"Venditori de oleum-vipera non vigere excordis populi"

 

[alehman]

I'm not familiar with the standards you mention, however I don't know how they would be directly. BIL relates to ability of the insulation to withstand high voltage transients without a "full" discharge. These tests are conducted with very high voltage impulse generators.

Partial discharge typically results from incipient insulation breakdown (tracking or corona) at normal operating voltage. Partial discharge testing is sometimes used to locate weak spots in insulation. PD testing is normally conducted at operating voltage up to a few times nominal. I suspect that's what they want.

 

[jraef]

Thanks, that's what I was looking for. It appears then that these PD testing standards are more formalized versions of Hi-Pot and dielectric testing.

"Venditori de oleum-vipera non vigere excordis populi"

 

[cuky2000]

BACKGROUND:
This is primarily focus in power cable insulation. Here is some background to perhaps help better understand the rational of cable rating compiled from experience and different sources around the world.

There are two major philosophies for routine ac voltage test levels on HV cable:
(i) The volts per mil (thickness), popular in USA is more suitable for oil-paper insulated cable
(ii) Rated cable voltage, used in Europe and introduced recently to USA by the insulated Cable Engineers Association (ICEA). Applicable to solid dielectric insulation.

When the ICEA changed to the rated voltage concept for ac testing, it had at the same time decided to make the dc test level a function of the BIL of the polymeric insulated cables.

..can anyone shed some light for me on how BIL relates to "partial discharge" ratings used outside of the US?

There is not obvious relation between the BIL and PD.
BIL is a go-no go test with an impulse wave intended to simulate the effect of a lightning discharge. Impulse testing is a design parameter for fluid-filled cable but the rational for testing solid-dielectric insulation is not so clear since this test provide a wide variation of results.

Partial discharge, on the other hand, is intended to diagnostic the cable insulation quality based on the partial discharge activity produce by voids or contaminated particles in the insulation. Sample of the PD Cylindrical Test Method used by ASTM and IEC are described in the sketch below.

<sub>Partial Discharge Definition:
IEC Std 60270: [blue] “Localized electrical discharge that only partially bridges the insulation between conductors and which can or cannot occur adjacent to a conductor.”[/blue]

IEEE Std 400: [blue] “A partial discharge is an electrical discharge (formation of a streamer or arc) that does not bridge the entire space between two electrodes.”[/blue]</sub>

….. It appears then that these PD testing standards are more formalized versions of Hi-Pot and dielectric testing
There are significant differences between the hipot test and PD testing.

Unlike traditional High Potential Testing, partial discharge testing is not destructive to an insulation system. (Hi-pot testing is typically a “go-no-go” test --the cable either fails or it doesn’t). In addition, “even massive insulation defects in extruded dielectric insulation cannot be detected with DC...”

See the enclose figure for comparison between different tests

http://www.ecmweb.com/images/archive/310ecm08table.jpg