Synchronous Machine Load Angle

Dear Guest,

If you had logged in I would give you a "Good Answer" for your succinct explanation. But, as I know not who you are, I'll simply give you a verbal pat on the back.

The higher the torque angle, the more reactive power you're generating (and consequently the less 'active' (real) power)). Synchro-generators have a maximum power-generation capability given in KVA at a given load angle (often (always?) cos x = 0.8) and the maximum active power generated is (maximum KVA rating * cos x). Maximum reactive power is (maximum KVA rating * sin x).

To generate the desired total power, the synchro-generator's excitation is adjusted. To generate active and reactive power in the desired proportion, the load angle is adjusted. One can set the proportion between active and reactive power (within limits) through the generator's controls.

The cause for this angle: like Guest says above, it's the rotating magnetic field generated by the rotor that 'pulls' the stator's rotating field , and it's the angle between the two in the generator that generates current in the stator. If there were to be no angle, no current (and thus no power) would be induced in the stator, and the stator wouldn't be 'magnetically locked' to the rotor. And if there's no current in the stator, there's no power being generated, by definition.

As load increases, the generator's controls will make the adjustments needed to preserve the desired angle. However, as the power generated approaches the generator's maximum capacity, the generator SLOWS (i.e., its frequency drops). This happens when a loads on a grid approach the generation capacity of the generators connected to it; when that happens, the frequency (the rotation speed) of all the generators drops a bit. That sends a signal to grid operators to call for more (add more)power generation.

In the past few years, grid operators in some areas of North America (and I think in Europe, too) have begun to pay generation firms for 'frequency support' services. Here 'frequency support' means having generation capacity ready to support the frequency, that is to raise it (to near 60 Hz) when loads on the grid approach the maximum capacity of the generators connected to it.

Cheers! DZ

Thanks !! got it