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DIELECTRIC WITHSTAND TESTER

Various types of defaults, breakdowns, are mentioned into the international electrical safety testing standards such as the burning, the perforation, the flash over, … and several types of detection are applicable. This article is dedicated to clarify and show in a video the various types of default that can occur in case of a default on an equipment.

The electrical safety standards mention most of the time "Neither perforation nor flash over", this means that the high voltage should not perforate, should not destroy your sample when tested in high voltage : this test is called a hipot test or a flash test, a clare test, a dielectric strength test, an electric strength test, a hi-pot test, a hy-pot test, a dielectric withstand test.

See below what is a perforation or a flash over.


A flash-over is when the high voltage can not destroys a too
strong insulating part, and then go over it in order to flash with
a ground part.

 

 

But when you do such a hipot test, you can set (Imax, Delta I) or not (burning, detection Off) a current limit in order that if the current over pass this set limit, then the high voltage tester will stop  and keep displayed at which voltage and current the default appeared.
With our MG series or XS series of dielectric strength testers, you can choose of having an Imax current limit or Delta I current limit.

Imax detection
If you set a limit for instance to 5 mA for your high voltage test, then our equipment will trip if the current breakdown is higher than 5 mA. But this can already damage your unit or you can have some not detected little breakdowns that could be future Imax ; we call them delta I.


A perforation is when the high voltage test really destroys
the insulating part, go through it by making a hole.

Delta I detection
The delta I is a typical breakdown of 1 mA amplitude or more but during a fixed time of 10 µs (see our document on Electrical safety testing & most popular electrical safety standards to know more) that could occur while hipot testing and that has been analyzed by Sefelec since years like being a future Imax.
So detecting Delta I will let you do prehensive investigation and foreseeing future problems on your products. Also it avoids damaging to much a product in case of a price sensitive equipment under test.

The ideal choice we offer in our unit is the combined mode : "Imax + Delta I" detection which will detect the first one that appears : so you test according to the standards + anticipate any future problems on your products ; this is the ideal method.
Sefelec has been at the origin of this method more than 40 years ago and still now this is used by many companies, or has been copied by many competitors.







A perforation is when the high voltage test really destroys
the insulating part, go through it by making a hole.

No detection (Off), Burning
Finally, the Off mode, also called No detection of burning, will just provide as much as available current in our units in order to burn the default you can have in your sample.
This is mostly used for investigations in order to find a weak part in a product, or identify where a default is ; typically sometimes you identify a default but do not see it. If you burn it you can easily see it, thanks to noise, smoke, arcing, flashing or smell.
An other solution could be to do a test in a dark room and look for an arc.



A burning is when the high voltage test really destroys
the insulating part, go through it by making a hole, but we generate
until burning the default or the insulating part.

Results
Below you can see on our tested insulation coupon, what are the test results, with the different types of detection.

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