07-04-2013 01:21 PM
I have worked around a couple of facilites that required water fire suppresion systems in the engine room. I think an arc flash resulting from water entry into a properly maintained and operating generator is pretty unlikely. However, if there is a catastrophic failure of the tail end and resulting arc flash event from that, dumping water on it may or may not cause more of a problem.
Ideally, if I have had to deal with water fire suppression systems in engine/generators rooms with MV generators I had developed a few of my own guidelines you may or may not suitable.
The Fire suppression system has to integrate with the genset E-Stop circuit.
The E-Stop circuit has to immediately trip the breaker and stop excitation (preferrably by opening the power circuit to the AVR NEVER by opening the field output).
The generator must be suitably electrically protected, preferably properly applied ground, stator ground and differential protections, with these types protecttions hitting the LOR and the LOR interfaced with teh E-Stop circuit.
Spray/fog nozzles not installed directly over air intakes for both the engine and the generator.
Design of water based fire suppression system needs to assure resistance to false actuation, this means being careful where heat activated sensors, fire eyes and smoke detectors are mounted and what they are aimed at. In just about every system I worked on we had to go back and do some form of redesign because the fire system contractor/designer and the generator set provider hadn't "talked" before hand.
You also need to consider the impact of things like package mounted radiators, if the engines is still running when system is activated will the radiator fans pull all the suppression away from the fire? In some engine rooms with supression systems we would pipe air intakes from outside the space.
A lot of things to consider, and never found any good overall "rules of thumb", always had to look at each project and see if and how any kind of fire suppression system could be applied that meet the customer's needs and didn't compund issues coming from a fire in a generator space.
Hope that helps,
07-07-2013 06:29 AM
Thanks Mike. I was interested to see if anyone else could provide evidence that water mist suppression systems have been approved for use in HV areas by Lloyds or Underwriters Laboratories. As far as I can see UL has only approved this product in Ordinary Hazard Group 1. These sets are 11000V at a remote onshore LNG processing facility and will provide utility power for the local community. The other problem is the excitation control and MOCB are located in a seperate building to the gensets, making the point you mentioned about the E-stop controlling these devices VERY difficult.
07-07-2013 01:12 PM
Funny how often I hear that integrating engine controls into remote switchgear as being "difficult". You have interface already being run, start and stop commands and engine speed bias at a minimum, and usually alarm and fault indications as well. So why in ANY case would you not interface engine controls with at least tripping the breaker on a fault or E-Stop? Trust that the reverse power or other protections will get the unit off line? On any generator in a network, especially an MV generator I think the ability to kill excitation should be a standard consideration ( as long as properly done). I personally like the AVR power run thru normally closed contacts on the lock out relay, so when it trips for any reason it will stop excitation. If it's important enought to hit the LOR, it's important enough to turn off the AVR, at least in my opinion.
My current favorite way to do this is to add in input into the multifunction generator protective relay for the E-Stop circuit, this way it can hit the LOR as needed, and you have a record in the cause of the trip. But that's just my opinion.
07-07-2013 02:44 PM
Mike, I should clarify that statement about being difficult..... Australian fire safety regulations prohibit shutdowns to be initiated over communications networks. In this instance, the SCADA system detects the E-stop status and opens the MOCB and excitation circuit via Ethernet & modbus. As the PLC model is not approved as a fire safety device in Australia, even hardwiring the shutdown would not make it compliant.