Generator loadbank calculations
Generator loadbank calculations
(OP)
When using a purely resistive loadbank how do you calculate the load current. This is to load check lets say a 100KVA generator at 0.8 powerfactor. this is how i thought it was done
kva = kw/pf therefore if the powerfactor was at unity then 100kva = 100kw therfore the generator would be loaded at 100kw
however i have recently started a new job and the techies say to calculated the load use this formula
100kva * 0.8 = KW then times the answer by 1.39
100kva * 0.8 = 80kw
80kw *1.39 = 111.2 kw
the generator should be loaded at 111.2kw resistive load.
I don't see the relationship of this calculation on any generator i have come across or am i missing something.
I think the answer they gave me was due to the diesel engine fitted to the alternator.
Any help would be appriciated
kva = kw/pf therefore if the powerfactor was at unity then 100kva = 100kw therfore the generator would be loaded at 100kw
however i have recently started a new job and the techies say to calculated the load use this formula
100kva * 0.8 = KW then times the answer by 1.39
100kva * 0.8 = 80kw
80kw *1.39 = 111.2 kw
the generator should be loaded at 111.2kw resistive load.
I don't see the relationship of this calculation on any generator i have come across or am i missing something.
I think the answer they gave me was due to the diesel engine fitted to the alternator.
Any help would be appriciated





RE: Generator loadbank calculations
RE: Generator loadbank calculations
If the load is in excess of 80 KW the motor will be overloaded, and may slow down.
If the load is in excess of rated current the windings will be overheated.
Use nameplate voltage and nameplate KVA to find the max current if it is not given on the nameplate.
I prefer to use current rather than KVA because of the number of times that I have seen generators operated at other than nameplate rated voltage.
A good instance was a customer who needed a 50 KVA set at 120/208 volts.
The supplier sold him a set rated at 50 KVA, 120/240 volts 4 wire delta. At 208 volts the kva rating de-rated to 43.3 KVA.
I have encountered other instances.
That said, There may be a good reason why your techies are using a 39% overload on their test. Why don't you ask them the reason?
David; Did you mean maximum RATED current?
(max current would happen at 100kW/1.0pf)
Respectfully
RE: Generator loadbank calculations
RE: Generator loadbank calculations
----------------------------------
Sometimes I only open my mouth to swap feet...
RE: Generator loadbank calculations
RE: Generator loadbank calculations
I beleive the 1.39 factor was used to calculate the current (load) and it relates to a 415V system. And there is some confusion on part of the OP between amps and kW.
Amperes=kVA*1000/(sqrt 3*V), for a 3 phase system
For V=415V, 1000/1.732*415 yeilds 1.39
So ampere load for a 100kVA,415V 3 phase gen will be 1.39*100kVA= 139A.
or for 80kW, it will be 80*1.39= 111.2A (not kW)
The basic formulas are:
kW=kVA*pf
0.8 is a typcical power factor for genetator sets.
For resistive loads: kW=kVA and pf is 1.0
Since the engine (primemover) is rated only for real power kW, the load should not exceed 80kW (100*.8). As a engine-generator set, one should not exceed either of its kW or kVA limits. With a resistive load, you reach kW limit, much sooner than the kVA limit.
RE: Generator loadbank calculations
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Generator loadbank calculations
RE: Generator loadbank calculations
I would use a different philosophy for testing, however.
I would deliberatly exceed the KW loading.
How else can you determine whether the dead-rack, or maximum fuel adjustment in the engine governor has been properly set?
Many (most) of these sets have an engine that is capable of overpowering the generator. The governor is set to limit the prime mover power at the rated voltage.
For example, if a set is rated at 240 volts and then is used at 208 volts, it will be overpowered unless the governor is adjusted.
A load bank is seldom available in the field and a compromise solution to voltage changes in the field is to pay close attention to the connected load and the over current protection.
You can often load a 100KVA set up to 100% current by reducing the voltage setting 20%. Of course you have to recalculate the resistance value at the new voltage level.
respectfully
RE: Generator loadbank calculations
I'd love to hear back from howitz to see if he was right....
RE: Generator loadbank calculations
Only if howitz got back to us.
RE: Generator loadbank calculations
Howitz