Load Shedding Cbus Lighting for Emergency Generator

Hi all,

I have been given the task of installing a 175kva Emergency Generator for a major Department Store. My main issue is the lighting chassis which is Cbus controlls 4 channels in use - 50% lighting, 50% lighting, Spot Lighting and Back of House lighting. I have 155 amps on all three phases. I can reduce this to 94 amps by turning off 50% lighting.

My train of thought was to have a phase fail relay installed into the Automatic Transfer Switch which will be monitoring Generator supply. The normally open contact on the pfr relay i was thinking of hooking up to a bus coupler and have it installed in the ATS. In affect whenever power from the generator is supplied the pfr relay will close contact and close contact on bus coupler - i was going to try have the bus coupler programmed to switch off 50% lighting load whenever the generator is running. this will reduce load level on the generator to satisfactory level. My issue is because the Cbus will be without power during changeover will it be possible to have the bus coupler as an input? I cannot have full load current being slammed onto generator without causing issues. Then i though if i uncheck the restore box for 1 x 50% lighting it would prevent it from automatically restoring power to selected channel output? I have seen where a normally closed relay is used that is fed from a current sensing relay located in the ATS. When generator power is present it energises the relay in the lighting board which open circuits the output channel power to lighting contactors. This is an option but i am convinced there is an easier method. I have tried contacting Clipsal rep who gave me a number of a guru but did not get a response. Hoping the gurus on here can give some input. I am no guru but have completed cbus basic program course and have some knowledge in the field. Thanks in advance for any ideas with this.

 

I don't have a specific solution for you, but I would warn you against using a load shedding method that is effectively just turning off loads via C-Bus.
The danger here is someone or something can just turn them back on again and overload the generator.

I think the design should be foolproof in that when full mains is available it holds in several contractors to supply the whole system, and when only generator power is available it only holds in some. That way no user or logic can just turn stuff on.

As for how you do this with C-Bus it depends on how it has been wired. you need to make sure you have sufficient power supplies to keep the active segments running while other segments are off. Ideally they would be built as several small networks connected by bridges, so you can isolate them easily.
Failing that you might be able to keep all the C-Bus network alive and just switch out the feed to the load side of your relays/dimmers etc.

Anyway I'm sure others will have ideas as well, but the crucial thing is to not just load shed by issuing off commands.

Cheers

Rohan

 

My first thought was to remove some complete units from the system.

Basically, selected units are powered by the ATS/Generator, others are not. So if there is a blackout all will go off and when the genset returns power only the selected unit will boot up. The system will not complain about units not being present - yeah there may be some switches that don't do anything because the group they are turning on is no longer on the system, but that's not an issue either.

Your pfr as an input to an Aux relay - I'm not sure if they are edge triggered or not, so it the relay is on/off (which ever state indicates a power fail state) then I am not sure if the aux input will see that at power up to turn on the group used to control the loads you want turned off. Some bench testing would be required here.

Back of house lighting may be an area that you can look at changing to LED to help reduce load - that typically does not go over well suggesting that fitting be changed out.

I think for safety reasons you should look at hardwired control as the primary method of load shedding and then software as a secondary. I wont go over well if the software glitches in some funny way and takes out the gen tight when its needed. My first option is works this way. You could also put follower contacts on the power supplies to each of the units that you don't want powered so if the pfr is off then they are off as well. Couple of ways to skin this cat.

If you go down the path of removing units, check the power consumption/supply for the network based on the reduced units. All the consumers will still be present (key inputs, PIR's etc) and if the units are supplying power and some are not present then power available will be reduced and may not be enough. Easy enough to get around though - add separate C-bus power supplies that only come on when the gen is running.

Just some quick thoughts that may get you going.

 

Hi There,

I had this exact situation a few years back. Being that you are happy to shed a general portion and not specific loads it is easier. I just installed a NC contactor in between the Cbus relay and the loads I wanted to inhibit. Most generators of that size will have a Deep Sea controller (or similar) either on the gen-set or remotely mounted in a control panel. These will have an 12v output that goes high when the gen-set startup signal is active. Use this to power your intermediate contactor. This solution means that the user has no ability to override the inhibit and also when mains power is restored the lights will return to the state they were in before the power fail event.
Hope this helps.

Regards,
Brent

 

I shed some loads using the output unit Logic tab. Once the power fail my generator 12V output relay drives an input to Comfort II Ultra alarm panel which in turn sets a Cbus Group address. I use the Logic tabs to AND the outputs so no matter what the user does he cannot enable the output for those units.

If however the user has access to the Cbus or Comfort programming side he might be able to figure out which group controls the shedding and override it hence Brent's idea is safer using contactors to disable the loads.

Ingo

 

Thanks for the feedback fella's.

I have decided to install a single pole modular contactor off generator auxilliary contacts on changeover switch. This is going to energise whenever generator is supplying power. I am also installing a single pole modular contactor with normally closed contacts on load side of relay outputs to interlock with contactor on generator auxilliaries. This will prevent 50% lighting from being energised whenever the generator is supplying power and stop overloading generator. As above, didnt want to rely on any programming to prevent from happening as chance that full lighting being power in event of issues. Thanks again.