Hi-pot testing vs. meggering 6

[birddogger]

Could someone briefly explain to me the difference between meggering and hi-pot testing of cables? I know that meggering involves placing a DC current, usually no more than 2 times the rated AC voltage, between the cable and ground to test the insulation resistance.

Hi-pot testing involves a much larger voltage I know, but I'm confused as to what you're looking for. Is it leakage current? Either way, aren't you basically looking for the same result (insulation resistance)?

Thanks in advance.

 

[sjvanhecke]

You are correct in assuming that a megger and a Hipot test are basically looking for the same thing, but a Hipot test is typically done at a much higher value and for a lonegr duration if the cable is above 600V.

 

[electricpete]

"Either way, aren't you basically looking for the same result (insulation resistance)?"

Only if the resistance is perfectly linear.

As voltage is increased there may be partial discharge or breakdown.

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[edison123]

Megger, a non-destructive DC instrument, checks the insulation resistance of the cables (between cables or cbales to ground).

Hi-pot (AC or DC), a potentially destructive test, tests the dielectric strength of the cables i.e the ability withstand rated and higher than rated voltages that are experienced during the operation.

While a high megger value doesn't necessarily indicate the dielectric strength (the ability to withstand high voltages), a low megger value (which is normal in cables)doesn't necessarily mean that the cables will fail the hi-pot test. I have seen cables with excellent megger values fail the hi-pot while their poorer cousins taking it on the chin comfortably.

So, meggering and hi-pot are not one and the same.

 

[DanDel]

birddogger, a Megger is used to apply a voltage(usually below or at the equipment rated voltage) and the results are in megohms, gigohms, tera-ohms, etc(resistance). The voltage is usually adjustable in steps, 500V, 1kV, 2.5kV, & 5kV.
A Hipot has continually adjustable voltages up to 80kV and above, and the results are in microamps(leakage).
Both instruments are used to check the quality of insulation.
The Megger test is usually non-destructive because the voltage levels used are at or below the equipment ratings, while the Hipot tests are usually destructive, for the opposite reason.