Effect of test/ applied voltage on Insulation Resistance? [Megger]

[Rejeckted]

Hi all,

I was wondering does the insulation resistance value change with applied voltage?

For ex. lets say if I have an equipment and I test it with 2.5kV and get X value of IR. Does this value change if I conduct the same test with 5kV?

Best!
Chris

 

[IRstuff]

It might, because it might not necessarily be a resistance in the classical sense, i.e., it could be a leakage or breakdown phenomenon

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[itsmoked]

Indeed. The fact that the number isn't infinite shows that some current is flowing and so more voltage can affect whatever the mechanism is that's allowing the leakage.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

dc step voltage test (IEEE 95) or ramp test steadily increases voltage and looks for non-linear increase in current as an indicator of approach to insulation breakdown. There are capacitive / absorptive components which decay away after each step increase in test voltage, so timing aspects of the test are important.

See beginning at paragraph 24 here
FACILITIES INSTRUCTIONS, STANDARDS, AND TECHNIQUES Volume 3-1 TESTING SOLID INSULATION OF ELECTRICAL EQUIPMENT


=====================================
(2B)+(2B)' ?

 

[che12345]

Dear Mr. Rejeckted (Electrical)(OP)31 May 22 15:58
"....#1. does the insulation resistance value change with applied voltage? #2. For ex. ..... test it with 2.5kV and get X value of IR. Does this value change if I conduct the same test with 5kV? "[/color]
#1. Yes. " the insulation resistance value change with applied voltage "
#2. Yes. The value change.
FYI: 1. An equipment rated say >3.3-12kVac is usually (IR) tested at 2.5-5kVdc.
Attention, do not apply (2.5kVdc) (IR) test on equipment rated [<1000Vac] !
Che Kuan Yau (Singapore)

 

[Gr8blu]

Rejeckted I suggest you read the standard documenting the concept of testing insulation resistance. That standard is IEEE 43:2013. It contains what the test is, what it does (and does not) tell you, and the impact different environmental scenarios have on the results - including differing test voltages. Note that this standard is recognized and used internationally, even though the "parent" document is North-America-centric.

Converting energy to motion for more than half a century

 

[JezNZ]

Assuming no breakdown, as this is covered well by others' posts:
The greater the voltage, the greater leakage current, so the greater the degree of accuracy to which the measuring instrument can be used to determine the insulation resistance.