Utility Powerhouse Generators
Utility Powerhouse Generators
(OP)
I was wondering, are the large generators that utilities use to generate power, synchronous type? I was wondering how they produce a pure sine wave and don't translate a power factor reflective of a wound motor turned into a generator, say a power factor of 30 degrees leading .8660 PF. When I do load checks on large motors and they are no longer using power but are still rotating they generate power and it seems to be the angle of the load (30 degrees) plus 180 degrees due to Current transformers. This equals 210 degrees of delivered power with a power factor of .8660 so how does a generator at a utility produce a power factor of 1.0? Peetey






RE: Utility Powerhouse Generators
Your measurements are most likely on induction motors. Induction motors by definition have self-induced fields which always require an external source of reactive power. That means they operate with lagging power factor.
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You may wish to find a text book on electric machines to get a better explanation.
RE: Utility Powerhouse Generators
On one machine that I maintained for the better part of 5 years the no load current of a 60 Horsepower motor was 30% of full load current. This would imply that no load reactive power is 50% of full load reactive power.
One explanation is that half the reative power contributes to production of countervoltage and the other half helps push power across the air gap in order to produce torque. There are more complicated models and explanations but that is the simplest.
Mike Cole
RE: Utility Powerhouse Generators
On a related note, there are four-quadrant definitions and “polarities” assigned to power flow in AC systems, based on combinations of real and reactive power. {Harmonic quantities add another ‘dimension’ to the diagram.}
RE: Utility Powerhouse Generators
RE: Utility Powerhouse Generators
RE: Utility Powerhouse Generators
Peetey, SWAGwise, 60Hz stator voltage may be 13-25kV in synchronous generators. Note that this voltage, although in a similar range, usually does not correspond with local distribution voltage.