Re: OT? woodgas, engine, induction motor as generator

Jim Wilkins wrote:
On Jul 18, 12:52 am, jk <kles...@xxxxxxxxxxxxxx> wrote:

Power is transmitted across the air gap, by the rotor
attempting to be turned faster than synchronous speed. The difference
between the generator speed, and the synchronous speed is the slip
speed. This slip, (just like when used as a motor) is what determines
how much power is transmitted. The frequency however is unaffected.

jk


I thought a motor sent power into the line when it ran at the
synchronous speed with its phase ahead of the line, and drew power
when the phase was behind the line.
It will send power to the mains when the speed is ABOVE synchronous. At exactly synchronous speed, the mains will excite the stator iron, but there will be (approximately) no flux in the rotor, as there is no slip. Line current will be minimal at sync speed.

To correct what someone said previously, when running above sync. speed, the induction alternator will appear as a CAPACITOR, not an inductor. The phase angle shifta as you cross sync. speed, and induction motors appear as inductors, so induction alternators must appear as capacitors. The phase angle varies with load, just like on an induction motor. So, at light load, the apparent capacitance is dominant, and the line current will be nearly 90 degrees leading. At rated load, the line current will be nearly in phase with the voltage. This could be one reason to not use an insanely huge motor as an induction alternator (compared to the size of the engine/waterwheel, etc.), as the power factor will always be low, and you will be feeding huge capacitive VARs to the mains, possibly cooking the pole transformer.

Jon

Jon
.

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    ... We are preparing to build 2 woodgas cogeneration units that will feed power back into the grid through a net metering contract. ... We will use that knowledge to send one phase's output of a 125 HP 3 phase induction motor back into the power line. ...
    (rec.crafts.metalworking)
  • Re: OT? woodgas, engine, induction motor as generator
    ... We are preparing to build 2 woodgas cogeneration units that will feed power back into the grid through a net metering contract. ... We will use that knowledge to send one phase's output of a 125 HP 3 phase induction motor back into the power line. ... I remember mentioning the "any induction machine is a generator". ...
    (rec.crafts.metalworking)