hi-pot testing versus megger insulation testing 5

[mriechert]

I am looking into the advantages of doing an AC-Hipot test versus doing a megger (I think it is otherwise known as DC-Hipot test) on electronic equipment.

I am trying to get information together so that I can write a report but I am having trouble trying to compare the two tests.

I have been doing megger checks on electronic equipment to ensure that the connectors pins are suitably insulated from the case etc etc. However some vendors of electrical equipment also recomend in their testing procedure to do a Hi-pot test, I have been avoiding this test because I believe it degrades the insulation and therefore the life of the unit. I am also wondering what the dielectric test would tell me that the megger test doesn't.

any help i.e. links etc would be appreciated thankyou.

 

[dbaird]

Go to

http://www.sotcher.com/techdocs/tech12.html

A "megger" is not the same as a "Hipot" tester.
DIELECTRIC STRENGTH
Dielectric Strength (often called Hi-Pot or high potential) is commonly specified for production testing of electrical products. It is conducted by applying a high voltage between mutually insulated portions and ground. Normally the high voltage is applied to the current carrying wires holding the product's case (or exposed metal parts) at ground potential.

It is not intended to cause insulation breakdown or that it be used to detect corona. Rather it serves to determine whether insulating materials and spacings are adequate. When a product is faulty the application of test voltage will result in either a disruptive discharge or high fault currents. The results are a qualitative PASS or FAIL in lieu of measured values.
INSULATION RESISTANCE
Insulation resistance (often called megger) is a measurement of the insulation itself. This test is widely used to test the condition of wiring in a building or large motor. It is also often specified by BSI. It is very similar to the line voltage leakage test in that it is measurement of the insulation. It is not as useful for product safety testing as it is harder to relate to the amount of shock someone might receive. It is an ideal test for studying, measuring and recording the long-term stability of an insulating material. Tests are normally conducted at 100 or 500 volts DC. The results are measured in terms of megohms of resistance.



David Baird
dbaird@gemcity.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[elecmec]

mriechert:

The hipot test is a subjective test, which as a rule of thumb, applies 1000 volts plus two time the maximum circuit voltage, to all the elements of the circuit with respect to the chassis. When solid state devices are used, they are usually wired together for protection. This voltage is applied for some time, usually one minute. After applying this voltage successfully, that is the hipot tester does not trip, or no corona or arcing are present, the megger test is performed. The megger test will reveal possible damge from the hipot test. The megger usually applies 500 volts, which was needed for the passive resistance meters used years ago. Todays resistance instruments can measure billion or trillion ohms resistance with only a few volts. Check contractual materials. Applicable specifications will prevail.
Elecmec

 

[mriechert]

Thankyou very much for your help and information.

However I am still concerned that performing a Hipot test after repair, especially minor repairs, is more detrimental than beneficial. Even though the highpot test does not intend to cause any insulation degradation.

 

[jbartos]

Suggestions:
1. Visit other postings on this subject in this Forum
Thread237-8885
Thread238-10015
Thread248-9323
2. The high pot test is needed to reveal any deficiency in insulation and creepages. If it is not performed, any larger spike or voltage surge could cause a serious damage and outage/downtime. There is however a legitimate concern since some materials do not accept DC high pot test well, e.g. cross-linked polyethylene. Therefore, very low frequency high pot tests are being used. See the middle reference in 1. above.