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Topic Title: Loop impedance measurement through an inverter
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Created On: 30 March 2012 02:15 PM
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 30 March 2012 02:15 PM
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I am looking at doing earth loop impedance measurements on a machine to determine if the fusing on inverter supplies is suitable for EN60204 compliance. E.g. using an installation tester such as Metrel MI 3000.

No problem with conventional motors, but what about servo motors and motors powered by inverters?

Any risk of damage to the inverter? I guess not because all the tester does is create a 2 cycle earth fault and measure the current during the fault. Most modern inverters can take that sort of thing in their stride.

Will it get meaningful results anyway?
 06 May 2012 01:53 AM
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You won't get results, as the drive will see it as a fault. Also the cables from the VSD are protected by that. If you need an impedance value to satisfy the paperwork, then use Zs= Ze +(R1+ R2).
The drive instructions often have max cable lengths and cable sizes in the manuals anyway.
 12 June 2012 12:30 PM
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If completing a live test, which I presume you are, could you not complete the test across the inverter?
 18 June 2012 04:01 PM
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The input of the variable speed drive will have capacitors connected line to chassis which will confuse the 4 cycle pulse from the tester.
A more reliable test would be achieved with the inverter drive disconnected.

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