Earth leakage relay

[louis1979]

I have a submersible 8kw pump protected by an earth leakage relay set at 30ma instantaneous. The pump starter 1000v supply has an earth leakage set at 200mA instantaneous.the 1000v volts comes from a 11kv/1000v skid muonted substation with an earth leakage set at 2A at the hv switch.water got into the pump contact block and the 11kv earth leakage set at 2A tripped first before the 200mA and 30mA.was it because of 3phase to ground fault.scratching my head coz as a sparkie I hve to give a repor.Help please.

 

[VEBill]

Is the "pump contact block" before the two more-sensitive relays? If so, then it seems simple.

 

[louis1979]

Yes the pummp contact block is before the two more sensitive relays

 

[VEBill]

As this (high power systems) isn't exactly my subject area, so please wait for confirmation from others before acting on this probable explanation.

Each Earth Leakage Relay, on my assumption that they operate the same as a Ground Fault Interrupter (GFI), uses a simple transformer core basically in common mode to detect a net difference in current between the Hot and Neutral; both sides of the circuit passing through the same core, cancelling except for the difference (ground leakage). Any ELRs further down the circuit from the fault cant't detect any difference because they're not installed in the part of the circuit where any difference exists.

 

[dpc]

If the leakage current exceeds the pickup setting of all three devices, it is a race to determine which devices operates first. Unless there are time delay settings that coordinate, the fact that the three devices have different pickup settings really doesn't tell you which will operate first if the current exceeds the pickup of all three devices.

 

[louis1979]

Oh okay it makes great sense thank you.