Details of 300 Hz Leakage current presence in the Variable speed drives (VSD).
Leakage current is caused by:
- "not-ideal" characteristics of every insulation laying between living parts and ground
- components connected between living part (any phase) and ground by purpose, for example overvoltage protection, EMC filter, etc.
When speaking about VSD, the leakage current has 2 parts:
1. Due to built-in EMC filter that is connected to the ground via capacitance, there is permanent constant part of leakage current at the same frequency as supply network. (50 or 60Hz). Note that built - in EMC filter can be disconnected from ground, which is especially required in IT networks
2. Due to VSD operation principle when potential on living parts (DC+, DC-, motor phases U.V,W) is permanently changed with high rise and fall (high dv/dt), there is current flown to the ground via stray capacitance. ic=C*dv/dt. Almost all VSDs have 3-phase input rectifier (also called 6-pulse bridge) which means that DC bus is regularly charged 6 times during 20ms (20ms is period of 50Hz supply), this result in dv/dt rise at the rectifier output with frequency 6-times AC supply frequency.
6pulses * 50Hz = 300Hz pulses in leakage current.
發佈於: 施耐德電機Taiwan
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