05-31-2010 10:16 AM
Hallo every body:
We have five Caterpillar Mak Gen-Set type 16CM32C same rated power at same speed 750 rpm run in parallel in isochronous mode, the problem is during starting big load abut 50-60% of the rated power of one Gen-Set the system frequency drop below 48 Hz and we have load shedding system set at 48 Hz for delay 5s, so some loads disconnected by load shedding to over come the reduction of system frequency:The Gen-Set run at approx. 50% of the rated power during receiving of big load.
How we can over come this problem
06-02-2010 11:27 PM
In general terms, a 50% block load resulting in less than 2 Hz frequency drop is not a realistic expectation for a turbocharged engine, especially a medium speed engine. Typical frequency response for a block load of this size is closer to 4-5Hz, depending on voltage rolloff (volts/hertz setting). The type of load being applied also has influence. Other considerations, ambient conditions, fuel type, state of engine tune,
Some things, like governor settings may help, but you likely need to reevaluate your loading and protection requirements if you want the ability to block load these units.
ISO8528 part 5 is the generally referenced guide for generating set response and stability. Also there should be some info available from CAT on expected voltage and frequency deviation for differing transient load response.
06-06-2010 09:52 AM
Thanks Mr. Mike L.
Did you agree with me to say that the Gen-Sets running at parallel operation at more than 50% of load will more stability during starting of big load than when it is run at less than 50% of load?
06-06-2010 11:15 PM
Depends on your rating and turbo match, generally if I had to pick up a large load in a paralleled system, as in your case, a load that would apply about 50% rated load to each unit, I would not try to do it at 50% of rated load. All units in a parallel system will not likely react the same, so the fastest reacting unit will hog some of the load initially, and may hit the fuel stop, limiting it's ability to pick up the load and cause a system instability. Likely you need to be above 25-30% load to get the turbo's spooled up a bit, but I would not apply a load that takes me right to the max rating and expect best possible transient response.
Your overall installed system dynamics will drive the actual response, your best option is to put a recorder on the system recording voltage and frequency and apply the load at 5% increments from 25 to 50% load before block loading and record the actual transients, than based on the response of the voltage and frequency you can best decide you next course of action.
Hope that helps,
06-16-2010 04:50 AM
Yes my electronic governor is 723+ (Woodward), but I need the recommendation of CATERPILLAR (Mak) about the permissible minimum limitation and it"s maximum time delay of under frequency protection for Mak engine.
Thanks for all
06-19-2010 12:05 AM
The start ramp feature of the 723 (and many other Woodward controls) is for the initial transition from zero to idle or rated speed, to limit overshoot when starting an engine.
The settings that are adjusted to improve transient response is the gain, reset, compensation, gain window, etc. The multiple gain breakpoint feature allows the engine dynamics to be better tuned at different actuator output ranges to compensate for non-linear response of the engine, helps provide better transient response and stability, especially on medium speed and natural gas engines.