Generator Testing

[KAA]

Hi

The following generator is available at a particular site
Generator rating 300KW (375 KVA) , L-L Voltage 380V, L-N Voltage 220 V, Power factor 0.8, Current at 0.8 pf is 570A, Frequency 60Hz, 3phase 4 Wire System

The generator is provided with the following calibrated instruments with Recorder to check the performance
a) Generator Output Voltage
b) Generator Output Current
c) Generator Output Frequency

Only Resistive load bank is available

The following additional Test is to be undertaken to check its performance. " Transient Voltage Regulation at rated speed at 0.4power factor"

To achieve the requirement the following step was to be done
1) Step down load to 71% of KVA

The recorder shall state the recovery time which is actually required.

Kindly provide details on the calculation of the Load or load current to be considered and how to achieve the result required by the client. Your help would be highly appreciated

 

[RajT]

You state that you have a resistive bank which means that any tests with it will be at unity pf and thus will not comply to the requirement of tests at 0.4pf. If however you do want to carry out tests at 0.4 pf then you will also require a reactive load bank so the pf can be varied to suit.
The gen is usually tested at 60% pick up load at its kW rating ie say 180kW and load shed at 100% of its rating ie 300kW both at unity pf. This tests however only checks the integrity of the engine and not so much the alternator.

Assuming that you do have a reactive load bank (say 500kVAr)
which can be variable in styeps pf say 100kVAr) then you should first impose 60% of kW load and then start adding kVAR until 0.4 pf is reached.
You should then disconnect this mixed lump load and switch it on the gen so that the tests criteria is met.
Record dips/recovery in volts and speed. Current is not too important

 

[KAA]

Hi RajT
Yes you are correct what we have here at present is unity power factor load but we need to test as stated above. I could have done the test if I had reactive power load. But due to some constrains I can only use unity power factor. Do you have any other method of achieving the same.

Thank You

 

[RajT]

There is no other simple method other then having a reactive bank as I explained earlier.
A crude way is to start a 100kW induction motor which will give you a low pf (at starting) of say 015 - 0.2.
and since that is what the gen is likely to do in service, one can argue that the requirements have been met. Note that you do not increase the size of the motor much from 100kW as then with the high starting kVA demand from the motor may stall the gen set.

Looking from another point of view, the requirements to tests at .4 pf can be seen as being too onerous as the usual value is 0.8 based on IEC and probably ANSI aswell, unless the gen is for a specific special duty.

Also testing at very low pf only checks that the AVR is capable of forcing the alternator field to deliver the vars.

The weakest link on a gen set is not so much the alternator or the AVR (a low cost item relatively) but rather the engine itself and it is the engine which needs to be really proven well and for that ofcourse you only need the unity pf bank you have on you.


Finally, (I am not sure which part of the globe you are at)if you must comply with the requirements then you could or should be able to hire a reactive load bank of the size required from your local gen hire companies or atleast they would be able to put you in touch with someone who does.