dielectric breakdown current

[enjuhnear]

I am looking for a minimum current leakage I should use for a pass/fail value in a hi-pot test. I am testing with respect to creep over a flat surface on which there is potential for settling of hygroscopic chemical residue. I've checked in UL standards and a few different google searches, but I'm struggling to find a pass/fail threshold, and the justification for that value.

System is 480V with ground and neutral. Test instrument has a max of 5mA trip. I plan to use a 1 second ramp to 3000VAC with a 1 minute dwell. 60Hz.

I am creating a test plan to investigate the most effective means of insulating a 3 phase w/gnd plug using butt contacts to combat creep leakage over the surface of a plug in a mild to harsh chemical wash down environment. The device is already IP69 rated. no presence of explosive atmosphere. I can provide more application information if you wish, but for now, that may just be "noise".

I'm new to the forum (first post), so apologies if this answer is floating out there elsewhere. I've looked but the keywords I'm searching are not hitting.

 

[Ingenieur]

are you looking for leakage at rated voltage or dielectric withstand?
can't the connector mfg give you both?

 

[SG-1]

I can give you some general guidelines for dielectric testing.

On our low voltage equipment we use what are called bang sticks. The test set is adjusted for 3000VAC & the sticks are used to touch the enclosure & the bus bars. Their is no magic number for leakage. The specimen either holds the voltage or there is a dielectric failure that turns off the test set. Dwell time is one or two seconds.

On our medium voltage gear the wiring is tested at 1500V for 1 minute. The magic number for pass or fail is the maximum output of the test set (750mA). The test set will turn itself off if the specimen fails, because the failure will draw the full 750mA & then some. In this case the voltage is ramped up at 1000V per second max.

If you are looking for a value I would suggest using a Megger. We used to megger the backboard of a CM-22 network protector during refurbishing. I seem to remember it had to read 10Meg-ohms.

 

[Ingenieur]

for mv equip with 1500 vac you pass at <750 mA leakage?
that is only 2 kOhm

so at 12.47 kv you can leak >6 A

 

[Sahib]

for mv equip with 1500 vac you pass at <750 mA leakage?
that is only 2 kOhm

so at 12.47 kv you can leak >6 A

That 750 mA setting is for failure mode and not for pass leakage current which would be very much less.

 

[SG-1]

for mv equip with 1500 vac you pass at <750 mA leakage?
that is only 2 kOhm

so at 12.47 kv you can leak >6 A

This test is for the wiring (600V SIS VW-1) Now imagine there are 15 structures with several hundred wires in each one. A single structure may only be 1-10 ma. All the wiring is shorted together & tested. All the electronic devices have been disconnected. When the mA reading is high it is usually a space heater leaking to the frame. The fun is trying to figure out which one. We are really looking for damaged insulation on the conductors, caused by scrapes or being pinched.


I did not mention the dielectric testing for the bus, which is conducted at 19 to 80 KV AC depending on the BIL of the gear.

Feel better now ?

 

[Ingenieur]

This test is for the wiring (600V SIS VW-1) Now imagine there are 15 structures with several hundred wires in each one. A single structure may only be 1-10 ma. All the wiring is shorted together & tested. All the electronic devices have been disconnected. When the mA reading is high it is usually a space heater leaking to the frame. The fun is trying to figure out which one. We are really looking for damaged insulation on the conductors, caused by scrapes or being pinched.


I did not mention the dielectric testing for the bus, which is conducted at 19 to 80 KV AC depending on the BIL of the gear.

Feel better now ?

still not clear
so the 750 mA applies to testing a network of mv cables at 1500 vac
or 600 vac building wire?
the first post said mv?

 

[SG-1]

still not clear
so the 750 mA applies to testing a network of mv cables at 1500 vac
or 600 vac building wire?
the first post said mv?

To quote myself "On our medium voltage gear the wiring is tested at 1500V for 1 minute."
I was trying to say the control wiring in the medium voltage product is tested at 1500V. The 750mA is for the most part an arbitrary figure.

If damaged insulation is detected the current will spike to the available fault current the test set can provide until the internal circuit opens.

 

[Sahib]

SG-1, As you say, your test kit is for go or no go ie to reveal any potential fault in the equipment. As for safe usage of equipment, a meggar test is also necessary. Isn't it?

 

[Sahib]

still not clear
so the 750 mA applies to testing a network of mv cables at 1500 vac
or 600 vac building wire?
the first post said mv?

Evidently it is 600V. For MV testing, the proof or test voltage would. be at least 1500/600 times rated MV.

 

[Sahib]

Duplicate.

 

[Ingenieur]

To quote myself "On our medium voltage gear the wiring is tested at 1500V for 1 minute."
I was trying to say the control wiring in the medium voltage product is tested at 1500V. The 750mA is for the most part an arbitrary figure.

If damaged insulation is detected the current will spike to the available fault current the test set can provide until the internal circuit opens.

thnx
go/no go
basically 0 or current limited short

 

[publicgood]

Did you look at NETA acceptance?

 

[SG-1]

thnx
go/no go
basically 0 or current limited short

Yes, we are on the same page now.
The current limit stops just short of flames.

 

[SG-1]

SG-1, As you say, your test kit is for go or no go ie to reveal any potential fault in the equipment. As for safe usage of equipment, a meggar test is also necessary. Isn't it?

Megger is not a standard production test.

For 5kv & up Partial Discharge sensors & protection can be installed.

 

[Sahib]

Megger is not a standard production test.

For 5kv & up Partial Discharge sensors & protection can be installed.

Perhaps you are talking about product security and Iam talking about life safety. No?

 

[Sahib]

I am looking for a minimum current leakage I should use for a pass/fail value in a hi-pot test. I am testing with respect to creep over a flat surface on which there is potential for settling of hygroscopic chemical residue. I've checked in UL standards and a few different google searches, but I'm struggling to find a pass/fail threshold, and the justification for that value.

System is 480V with ground and neutral. Test instrument has a max of 5mA trip. I plan to use a 1 second ramp to 3000VAC with a 1 minute dwell. 60Hz.

I am creating a test plan to investigate the most effective means of insulating a 3 phase w/gnd plug using butt contacts to combat creep leakage over the surface of a plug in a mild to harsh chemical wash down environment. The device is already IP69 rated. no presence of explosive atmosphere. I can provide more application information if you wish, but for now, that may just be "noise".

I'm new to the forum (first post), so apologies if this answer is floating out there elsewhere. I've looked but the keywords I'm searching are not hitting.

As discussed above, hipot test is a destructive test. You may not find a pass threshold leakage current through
it. But you may use a meggar to record the insulation values and also leakage current values by calculating from the readings. By periodic insulation measurement, you could trend it and thereby find out pass leakage currents and threshold fail leakage current also.

 

[enjuhnear]

As discussed above, hipot test is a destructive test. You may not find a pass threshold leakage current through
it. But you may use a meggar to record the insulation values and also leakage current values by calculating from the readings. By periodic insulation measurement, you could trend it and thereby find out pass leakage currents and threshold fail leakage current also.

Thanks. I didn't thing i had a meggar in my lab, only a hi-pot. That was the direction I was hoping to be able to take anyhow. I think that will give me more relevant data to the purpose of this test anyhow. And as I was typing, I took a break to do some digging through the lab, and lo and behold, I was able to uncover a meggar kit.

Thanks for the pointer to convince me to look deeper.