05-21-2017 12:41 PM
The engine does not dictate the ability to drive VFD or other high harmonic loads, the generator end and the voltage regulator do.
Alhough I would not expect underfrequency trips. An underfrequency trip indicates the engine is overloaded and cannot maintain RPM, and is wholly a function of the engine/governor. An undervoltage trip may or may not be associated with the engine, if the unit is setup for UFRO (UnderFrequency RollOff) or Volts/Hz, this is where the voltage will drop per a linear rate (adjustable in most newer regulators), then the undervoltage condition may be a symptom of the loss of speed control due to overload. If only undervoltage trips occur at the load levels you describe, then it is likely a generator or AVR (or both) issue.
I have seen cases where the engines are driven by electronic governors using voltage and frequency sensing (loadshare type governors) where load harmonics did cause speed control problems, but these were on older units, most newer digital speed control systems have good filtering to prevent those kinds of problems.
You will need to provide much more detailed information to get a better understanding of what the actual root cause of your problem is.
05-21-2017 12:30 PM
In general I would say not, testing at unity with a resistive load bank only fully checks the engine output.
Is the generator properly sized to the 0.6 power factor? Or does the unit not see the low power factor at higher loads?
My personal opinion is that all generators servicing critical or severe applications (and I would say oil and gas falls into that) should at least be initially tested with a resisitive/reactive load bank to full kW and kVA rating of the package.
05-20-2017 10:04 PM
05-20-2017 09:46 PM - edited 05-20-2017 09:47 PM
A resistive load bank pretty much just tests the unit at unity power factor, so you can take the engine to full load but not the generator end.
A reactive load bank (properly sized) will allow you to apply full kVA load on the generator without overloading the prime mover.
As for harmonics, to see if your generator and voltage regulator will play nice with the high harmonic site loads, then the best solution is to try and simulate those type loads. Of course hardly anyone goes to that expense. Baylor used to do some pretty extensive testing that included harmonic loads, but not sure if that continued when they were bought by NOV.
Harmonics usually cause the AVR to improperly interprete the sensing voltage and cause the generator voltage to go high or low.
Your best solution may be good design practises, like quality AVR's, PMG or AREP exctiation systems, and proper sizing for high harmonic loads.
05-20-2017 10:02 AM