VSDs and RCD/ELCB problems 1

[kafelnik]

Greetings,

I am currently experiencing some problems regarding Earth Leakage Circuit Breakers (ELCB's) / Risidual Current Devices (RCD's) and their tripping.

The VSD being used has an internal EMC filter, and I have been advised that using a differing VSD with an external EMC filter may reduce the leakage current.

I would very much like to know what exactly causes the earth leakage, can it be quantified, and how using an external rather than internal filter may be beneficial.

Thanks in advance for your assitance.
Kaf

 

[jbartos]

Suggestion: The earth leaking currents are common-mode currents that are returning to the source. The external EMI / EMC filter may actually increase the earth leaking current. Ultimately, it may be necessary to increase the trip setting somewhat in the Earth Leakage Circuit Breakers (ELCB's) / Residual Current Devices (RCD's).
Also, the internal EMC filter may be deficient or incorrectly designed.

 

[jbartos]

Suggestion: Also visit web, e.g.

http://www.mtecorp.com/tutemi/

etc., for more info

 

[ozmosis]

You should be very careful using ELCB's in conjunction with a VSD.
The first issue is the problem you have experienced so far: tripping due to the high leakage currents from the EMC filter. A standard EMC filter will 'leak' approx 30 to 50mA and so this is the reason for the trips. You can purchase low-leakage filters but do not go down this route without first checking the type of ELCB. The other aspect is the motor cabling you have. If using screened motor cables, this too will increase the leakage currents, espacially if they are long (>25M/75ft)
Do you know what type of ELCB you have? Chances are it is a Type A.
A number of drive companies will advise not to use an ELCB in conjunction with a VSD. The following standards: DIN VDE 0160, section 5.5.2 and EN50178 section 5.2.11.1 will provide further information on this subject.
The other aspect, besides nuiscance tripping, is the fact that Type A ELCB's will potentially not pick up the distorted waveform created by the VSD. This is the reason why certain VSD companies advise the use of Type B ELCB's. These are very expensive but are designed to pick up the pulsed waveform from a VSD (known as Alstromsensitiv).
I would advise first to check with the VSD supplier and get their specific advise and either remove the ELCB or fit a type B and focus on the drive unit (remove the filter, fit low-leakage filter and assess motor cables etc)