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Anonymous Poster

Student

09/18/2008 1:05 PM

what are advantages of meggering?

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Guru

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#1

Re: Student

09/18/2008 6:25 PM

It is a good predictor of the ability of the insulation to withstand voltage breakdown over a long period of time and under extreme conditions. It's sort of like the idea that, if you had a rope that you wanted to use to lift 100 N for a long period of time, you would test it quickly at 500 N to see if it started to break.

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#2

Re: Student

09/23/2008 4:03 AM

Hello "Guest",

Megger is a Registered Trade Name, originally to Evershed and Vignoles Ltd of the UK.

Early units were beautifully crafted varnished wooden boxes with dovetailed joints, and were wound by hand, which turned an internal DC Generator.

Various test Voltage Meggers were made: 500VDC, 1,000VDC, 5,000VDC.

Used for testing the DC Resistance of Insulators and Insulation, in Megohms scaled on an analogue meter.

When testing a large alternator winding, the person winding the 5,000 Volt Megger had to continuously wind the handle for more than 15 minutes per phase connection, as the large capacitance to the alternmator earthed frame was considerable.

Meggers and other Insulation testers these days are often electronic, and may be either battery or Mains powered, which saves the "winding arm" of the Test Engineer or Technician's assistant.

Read more about the Megger (includes picture of an older 500 volt one) here: http://en.wikipedia.org/wiki/Megger

Later Insulation Testers are often called "HiPot" Testers refer: http://en.wikipedia.org/wiki/Hipot

Further useful information is here: http://www.globalspec.com/reference/7455/Best-Methods-for-Safe-Hipot-Testing

Kind Regards....

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#3

Re: Student

10/08/2008 10:30 AM

Not to 'megger' runs the risk of the insulation failing under load and taking out the supply fuses. Depending on the size of the installation, the results could be quite spectacular....

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