Leading Power Factor Without Capacitive Load

1. Induction motors draw lagging current, no way around that. My guess is that full load would be 0.9 power factor, 25 degrees lagging: no load almost 90 degrees lag, a swing of 65 degrees, centred on about 60 degrees.
2. How do you know the meters are true??
3. I think the one of the coils of the power factor meter are in the wrong phase/polarity, giving, for example, a 60 degree error which moves "zero phase" indication to 60 degrees lag. Thus the power factor swings to both lead and lag as the motor current phase changes with load. Because you see "lead" at full load, first guess is current input is from wrong phase (120 degrees giving a polarity change, the vector is over 90 degrees away from what it should be).
4. You need to check CT and VT positions and polarities very thoroughly and check meter/transducer connections against the instrument maker's diagram. There may be a wiring error compared with drawings, or a drawing error compared to correct connection. There might be more than one error! This test should have been done at commissioning. Since all units behave same, it looks like a drawing error.
   
5. I suggest a battery "flash" polarity/connection check from HV bars to meter transducer terminals to verify what is really connected to what and its polarity. Of course, you must do that Test with proper isolation and grounding for safety.
   

A good suggestion, JRaef. However, Synchronous motor on fixed excitation moves from lag towards lead as shaft load is increased. But that is with constant supply voltage, the transfo regulation drops supply voltage as as load increases - which moves phase the other way.

Maybe there is a computerised AVR box set to give this characteristic.

And do not forget that the transfo reactance would cause a lagging HV input power factor on full load resistive. To put unity power factor on HV system at full load the secondary (motor) current would have to have a leading power factor.

So over to the original post Satendrakumart for more information, like the actual values of machine voltage and power factor at no load and full load.

In reply to his query on the benefits of having a motor drawing leading current, it does make it possible to run the system near unity power factor giving lower current and losses and better voltage regulation.

7. Is it possible that the induction motor is running faster than it's synchronous speed ? so instead of drawing current from system it supplied the system.

I think u have to double check your meter and try manually calculate the power factor Pf=E/(V*I*1.732)

Thanks to all for your valuable comments, I would like to clarify:

1. All motors are induction motors, and these are connected at Auxiliary trafo of Power Plant.

2. I have checked all possibility of CT / PT phase reversal by trial & error method.

3. Two generators are kept at different loading. One Generator is kept in load mode at full loading. Other is kept at about 50 to 75 % loading as per requirement and it is kept in speed mode.

4. I checked Energy meters with portable meter (power quality analyzer). When it is connected to any of one phase, graph clearly shows leading current 10 to 15 degree with respect to voltage.

Dear Satendra............several questions are popping up my mind.......what is the measured power factor at the 6.6kV bus? are all the motors showing leading power factor? motors have DOL starters or soft starters??

1 thing is obvious........if without any investment you are getting leading power factor..........you are a lucky man.......actually it is better not only for your motors but also for your system.....if finally you find out the actual reason..........please intimate teh same...........i have never came across this kind of situation

Dear 67model

Thanks a lot. I have to recheck the connections thoroughly for line-to-line vs line-to-neutral voltage, before replying.

Is capacitor bank is permanently connected across the induction motor and it is giving over compensation? You may please check it.

Thanks,

Manindra