Asychnronous Motor-Generator
Asychnronous Motor-Generator
(OP)
We have an asynchronous motor (slipring rotor) to run our short-circuit Generator which produces electricity for our testing procedures. Power factor = 0.9
During a capacitive current test we need only a capacitive current. During operation the output from our generator consists of both active and reactive power (am i right?), and the capacitive current will come from the reactive power side.
So is it possible to save the active power part of the generators output if it is not needed ? How could we do that ?
During a capacitive current test we need only a capacitive current. During operation the output from our generator consists of both active and reactive power (am i right?), and the capacitive current will come from the reactive power side.
So is it possible to save the active power part of the generators output if it is not needed ? How could we do that ?





RE: Asychnronous Motor-Generator
If your load consumes only reactive power then that's it. Where do you think the active power goes?
Is it the 0.9 power factor you are tninking about? That is only part of the specification - not anything that always applies. If load power factor is close to zero (as capacitive load is) then the generator will see (and deliver) just that load. No active power - except some losses.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Asychnronous Motor-Generator
Your last two paragraphs do not make much sense, but I gather you are asking if this machine can be used as a condenser (like capacitors), then the answer is no. Synchronous machine can do that as its excitation can be controlled.
Rafiq Bulsara
http://www.srengineersct.com
RE: Asychnronous Motor-Generator
Does the load always dictate what kind of power mix is being output ?
RE: Asychnronous Motor-Generator
Rafiq Bulsara
http://www.srengineersct.com
RE: Asychnronous Motor-Generator
RE: Asychnronous Motor-Generator
The asycn motor (the prime mover) does not supply reactive power, ever. Only active power.
The power factor of a synchronous generator in stand alone mode is solely dependent on nature of the load.
Rafiq Bulsara
http://www.srengineersct.com
RE: Asychnronous Motor-Generator
Rafiq Bulsara
http://www.srengineersct.com
RE: Asychnronous Motor-Generator
The question about deliver or consume reactive power is dependent on what one has defined as source and sink. The convention is that inductances consume reactive power and that capacitors produce reactive power. But the definition is a lot more arbitrary than it is for active power.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Asychnronous Motor-Generator
Active power and reactive power is a way to quantify the effects of a phase shift between the voltage and current.
Your active power will be I2R. If R is taken as the R of the load and connections to the generator terminals, If the R of the generator is added, this will be the total active power including internal generator losses.
The Reactive power is I2X. Normally, X is taken as the load reactance, but under short circuit conditions the generator X becomes significant.
If you use series capacitors to get a reactive current, your generator will supply active power based on the test current and the total resistance, internal generator resistance and external test connection resistance.
Bill
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"Why not the best?"
Jimmy Carter
RE: Asychnronous Motor-Generator
Your test generator is a synchronous machine driven by an induction motor (aka asynchronous motor) a slipring machine. There is no electrical connection between the test generator and the supply to your induction motor.
The generator is absorbing reactive VARs from the capacative test load, and supplying some few KW of active power to the test setup (losses). It is irrelevant that the generator nameplate reads 0.9 PF. The PF in this case is nearly zero and is dictated by the test setup only.
No you cannot "save the unused active power" because there is not any to speak of.
Get back to the basics of electrical machines, especially if your work in the test room requires this knowledge.
Such test setups were common in electrical manufacturers factories in the old days. The knowledge seems to have departed unfortunately.
rasevskii
RE: Asychnronous Motor-Generator
Seriously, did you never take any circuits courses? Your load always dicates what power is provided by the source. A source won't just have it' rated power "go away to nowhere". Any power produced by the source has to go to a load.
No, the generator will not just "output" a nameplate power. The generator will supply whatever current and power factor the load requires from it. Yes, you can get both an active and reactive power output if the load requires both.
The generator power factor rating is used to know how much reactive power you can also get from that genset. For example, a 1MW machine rated 0.9 power factor means it can also provide around 484kVAR while providing 1MW. The machine may also have a curve showing the kVAR for different MW loads.
RE: Asychnronous Motor-Generator