Will Earth Leakage Protection Work on Delta?

vector sum of three phase current must be zero. If exceeds 300ma for 300ms(don't know ur setting) it will generate trip signal

Hi Sostoall, I was under the impression that RCD's were supposed to trip at 30ma not 300ma.

The only problem that I can see is that sometimes the RF Filter network in the VSD can cause false tripping of the RCD.

Cheers

Joe

If there is absolutely no connection anywhere between the neutral point and earth then it is a pure floating neutral.

In this case if one of the phases has a ground fault the corresponding phase will take zero potential and all other phases will be shifted relative to it. This features also exists in case of isolations.

An easy example may be a single phase transformer with primary and secondary isolated (no common neutral or earthing, at least on secondary side including at load), with a center tap (say the tap gives 0-110-220V).

Now if one of the lines corresponding to 0 (or 220) are earthed (deliberately or due to an earth fault) then the voltages will be 0,110 and 220 at the three taps (the phases corresponding to primary will be depending upon winding and which tap is earthed). However if the earth point is on middle tap one gets 110,0,110 V. And in neither cases a ground fault current exist since the current does not get the chance to loop back.

The question here is not the star or delta but what is done with the neutral (or the virtual neutral) at any point not electrically isolated.

hi,

greetings from India,

Normal Practice to use DG which is stationary at one place is,

1. make Neutral to earthed separately.

2. make Chassis (body) earthing in another pit.

3. measure N to Earth point voltage which must be below 5 v for healthy operation

(in case of DG - load balancing i.e. equal phase distribution is important)

earth fault relay will operate only when there is fault in line to earth which occurs due to failure in insulation over the conductor

in your case you are not using Neutral point assuming all the three phases are consumed equally for VFD operation.

any over current in any phase due to earth fault will be treated w.r.t earth only inside the relay system.

in conclusion irrespective to type of connection of motor / drive earth leakage protection will work.

Refer: http://cr4.globalspec.com/thread/69915/Earth-Leakage-relay

Vinu_answers Sure_answers

Please check the following link. This explains protection in detail for similar situations where the transformer can not or is not grounded.

http://siemens.siprotec.de/download_neu/applications/SIPROTEC/english/Appl_09_E_F-Protection_for%20Systems_with_isolated_Starpoint_en.pdf

Stupid question, but even more stupid to not ask... sounds like can not use an ELCB (4 pole, as no neutral exists). Have to use an earth leakage relay, yes?