voltage generator for megger

[mpj111]

Older megger (insulation tester) generates 500V , by rotating the winder somthing like a stepup T/F. What is the technology behind new small electronic meggers. Its a battery operated and small size. In theoritically how it generate 500V or even 1000V to test insulations.
Does it realy generats high voltage, or does it use different technology (such as high frequency) to test insulation.
Many thanks in advance.

 

[Paul Obrien]

I had a 500V soild state megger in the 70's so they're not new, Yes they do generate 500 & 1000V . They have to generate the voltage in order to test insulation breakdown faults, HF wouldn't do this. Diode cap voltage multipliers or transformer based inverters will do this the trick is to make sure the output voltage is correct

 

[RODALCO]

I use a Kyoritsu 3132 and a Avo BM 25 daily for powerboard work.

The Kyoritsu has 250, 500 and 1000 DC Volts ranges for insulation testing and has test modes for 3 Ohm and 500 Ohms for low resistance testing for the like of elements or low circuit shorts in LV cables.

The megger runs on 6 * 1.5 Volts AA batteries for many 100's of insulation tests. In it is a DC to DC converted to step up the voltage to the required voltage level for testing.
Bear in mind that the test voltage will be lower on a low ohm fault. For example:
Test a cable which has an insulation value of 100 k Ohms at 500 Volts, the actual voltage across the test terminals and clips from the megger may be 200 Volts DC although the meterscale is callibrated for this.
The above cable would be faulty anyway.
In case of a healthy cable the reading may be 50 Mega Ohms or higher, The output voltage of the megger will be 500 Volts or 1 kV whatever scale was selected.

The BM 25 i use is for High voltage cables 11 and 33 kV.
This megger (insulation tester) has ranges of 500, 1000, 2500 and 5000 Volts.
Max reading is 5.5 Tera ohms, as well as a timer, leakage readings, breakdown and capacitance for polarity analyses of HV cables.
This BM 25 has 2 * 12 Volts sealed accu's which are rechargeable and good for many tens of tests.

The old crankhandle megger has a AC step up transformer, rectifier to get DC.
The beauty of that one is that it requires NO batteries.