After a voltage surge in the grid, we noticed that the fire fighting pump:200kw started up for a few seconds before shutting down. The fire fighting pump was on auto and was set to automatically come on after water pressure falls below 6.8 bar.

What could be the cause for this? The setup is a standby power plant and when this occurred the plant was not running and was receiving backfeed from the grid.

 

Just a guess, but it may be that you have a small "Jockey Pump" on your fire system that maintains the pipe pressure, and it may have a Voltage Monitor Relay associated with it. So when the "surge" is detected by that VMR, the jockey pump shuts down, the pressure drops below 6.8 bar, and the fire pump comes on.

 

Is the Fire Water pump logic PLC, electronic or relay?

What is the pressure measurement? Pressure switch or transmitter?

Possibly the FW pump controller saw a low pressure because the power surge or drop (?) affected the pressure measurement.

What type of fail safe logic does the FW pump have? Does it start on a power failure?

 

The jockey pump is part of the system but when the motorized pump came on, the system pressure was well above 6.8 bar.....actually it was around 9 and the pump coming on was instantaneous:immediately a power surge is experienced.

 

The fire water pump logic is a relay.

Pressure measurement that triggers the pump is through a pressure switch.

There is no fail safe logic for the FW motorised pump.

The pressure switch is from Danfoss It is quite rudimentary in nature much more like an electromechanical relay. Could it be possibly affected by a voltage surge??