Capacitor Bank for Low Load on Generator

Unless the generator operator is charging for a low power factor as part of the tariff, and there would seem to be no need if the load is low, forget it. There will never be a payback.

<...what are the implications of running my generator on such a low load?...>

Here's some:

• Excessive capital commitment or hire costs to support the load.
• Over-sized supply cables to support the load.
• Excessive fuel consumption to support the load.
• Higher cranage costs to install and remove the generator.
• Higher haulage costs to convey the generator to and away from site.
• Excess capacity on the generator could prejudice installations elsewhere on the site.
• Noise.
• Fumes.
• Higher maintenance costs.
• Etc.

I don't understand the capacitor "Load Bank." A load bank is, usually, resistive (could be resistive with an inductive component)

Capacitors are, usually, used to start a motor; they can also be used to modify the "Power Factor" so that voltage and current are in phase and an induction motor appears to be only resistive.

The selection of the proper value capacitor bank lies in the inductance of the circuit, the LRA, running current, etc.

196KVA is merely volts times amps. Is the 670KVA rating operating or surge? What is the measured load a. at ambient; b. at running temperature (may be as high as 85C)? What is the poer factor, now? Is tis calculated or measured?

What do you expect to gain by reducing the power factor (?)?

- Generators don't generally like running with a capacitor bank. In my experience, where we have a mains supply backed by standby generator with power factor correction capacitor banks on the system, the systems is designed so that when the mains fails and a switchover to the standby generator occurs, the power factor correction capacitors are deliberately dis-engaged. They are only returned once mains comes back. I'd have to research the theory behind this, but this is standard practice; this is applicable at your size of generator.

- secondly, I don't understand your objective. The capacitor bank in theory would reduce your load, but it's not a good idea for the reasons descirbed above. If you are talking about a load bank (which is a differnent thing altogether, and is normally resistive or inductive), this would utilize your generator cacacity alright, but to to what advantage? I was asked about the issue of underutilization on a larger generation system, and this is what I found out from a generator supplier. Generators should run at 30% of full load of the generator to reach full operating temperature. If it was below this, you could periodically install a load bank in parallel with the site load.The necessity for the above procedure arises because of the occurrence of 'wet stacking' (burning oil) if the generator is run continuously at below 30% of rated load. I understand that If the avoidance measures described above are carried out for 1 hour in every 24 hours the problem can be avoided.

You are at 30% load, so I don't really see why you have an issue. Disucss with a good generator supplier. Hope I've helped somebody.

Following points should be considered as far as generator is concerned:

1. What is the power factor of generator load? If it is too low ( excitation current increases with lower power factor) and you have limitation from rotor heating due to over excitation (which I doubt should be at about 30% of rated MVA) then only you should attempt to add capacitor load to bring the excitation current within permissible limit, otherwise not.
2. Low load should not be a concern for the generator (it may be of concern for prime mover) except that generator(as well as overall plant efficiency will be lower at such a low load.
   

Running a Generator set on low load (< 40% of full load) for long period will make it consume (burn) lubrication oil, which in turn will produce carbon deposits on the pistons and valves. This will need de-carburising on the long term. Also, the overall fuel consumption will be higher for per kw generated than if you were running at arround 50% or higher. This is because there is a minimum power consumption to operate all the accessories like the cooling fans, oil pumps, water pumps etc...

Capacitor Bank: This is only usefull if you are correcting the power factor of the load being served. It does not increase the load on the genset by itself.

What you need is a passive dummy load of a sort to increase the load on the genset (if you insist on running this size generator on such a low load on a continuous basis!?). These loads can be a bank of resistors, rated as required ... You should consult the manufacturer or an experienced Engineer in this domain. Otherwise install a smaller genset.