Alternator asynchronous motor

[Christophe]

Here is what you need to know to transform an asynchronous motor into a generator.

The handling is quite easy because it is enough to add a (single-phase) or 3 (three-phase) capacitors on the supply of the coils.

A) To start

A document to read on the conversion of engine to alternator, generator or dynamo (depending on engine technology)

B) For the values ​​of the capacitor to put:

- Coarse approach: The capacitance in µF of this capacitor is calculated as follows: 2% of the motor power in W

- Finer approach (value in µF I presume?):

here is an exel calculation table which gives you the exact value
https://www.econologie.info/share/partag ... A7FBhN.xls

C) Here is a specific example made by our dear André:

On my test bench small panton engine it is a 1/2 hp single phase 110volt engine which acts as generator it is enough to place in parallel a capacitor of 8 to 16 microfarad type paper (coming from ballast mercury lamp) a load of 3 lamps lamps of 100watt and it is quite stable there is just the frequency and voltage which adapts at RPM , but if the drive around the speed indicates the engine it is good
I used this assembly for a long time to do my load tests

Andre

the engine is used to start then it becomes generator for the load

[boubka]

Hello
a little reminder if gene auto exit by capacitors it is necessary if there is no voltage regulator to connect only a resistive load cos p = 1 (resisitances, incandescent lamps) otherwise the reactive power increases and we risk cramming everything
this was rightly said by papyrus in a previous post on the paddle wheel
here is a doc leroy sommer (it says at the end of the text)

Operation of asynchronous motors in asynchronous generator

[boubka]

wikipedia sources:
In electrical engineering, for an asynchronous machine, we speak of hypersynchronism when the speed of the rotor becomes greater than the speed of the rotating field (nominal speed). We then speak of an asynchronous generator or a hypersynchronous generator. This principle is for example applied in wind turbines to produce electricity.

Power balance of the machine operating as a generator

Compared to the previous case, the useful power becomes the electric power supplied to the network and the mechanical power is the power absorbed.

* P_a \,: absorbed power = mechanical power supplied to the machine,
* P_u \,: useful power = electric power transmitted to the network.

The losses are the same as for engine operation.

[Christophe]

Interesting doc Leroy Somer: this means that with the trick of the capacitor to transform an asynchronous motor into a generator and not connected to the network, one can only supply mainly resistive loads?

[boubka]

basically yes ... there are other tips with condos in series but you need a fairly constant speed

I quote (I do not know the source)

In the case of autonomous operation, the problem is quite different. In fact, the stator quantities are no longer imposed and it is necessary to supply the machine with the reactive power necessary for magnetization. The voltage and frequency produced by asynchronous generators are not always constant, but it is possible (using a frequency converter) to supply a fixed voltage and frequency.
The simplest case then consists in connecting, in parallel to the stator winding, a bench of capacities.



This makes it possible to obtain the adequate amplitude of the voltage. In this operating case, the speed of rotation of the machine must be fixed within a limited range in order to maintain a frequency of the stator variables close to 50 Hz.

Another approach consists in connecting, in addition to the capacities in parallel, other capacities in series with the load.


This approach ("short-shunt connection") makes it possible to reduce the load voltage drop. The role of parallel capacities remains the same. But series capacitors serve as regulators: the higher the load current, the higher the reactive power they generate and vice versa. This makes it possible to maintain a practically constant level of magnetization in the machine, and therefore a constant voltage. In addition, in autonomous operation, the system is intended to supply an isolated consumer. This assumes that the load is not necessarily balanced and that it is variable over time.



The addition of capacitors in series makes it possible to maintain, even in case of unbalanced load, a constant voltage across the generatrix.

but for use 220 v 50 hz without a complicated regul I think that the solution is this:
rectifier; cc transport; inverter
namely q a three-phase rectifier with six diodes is easily achievable

in auto production the asynchronous generator and valid for pure resistances (water heater, simple convector, light etc) but for storage or use network it is preferable to use the generator continues much less complicated (just just a voltage regulator and of an inverter)

[chatelot16]

it is very nice this idea of ​​capacitor but there is no reason that it is stable: a few µf too much and the voltage goes up too high, a few µf less it goes down and defuses

on the other hand in single phase it works provided that the capacitor is not on the useful output winding but on a quadrature winding, like a two-phase motor

the at least one fixed capacitor can be used without needing to change it according to the inductive or capacitive load

there are quite a few 2000w generator sets that have this kind of asynchronous alternator with a 60µf capacitor: it is difficult to distinguish them from 2000w alternator with rotating diodes which also have a 60µf capacitor

in three-phase the asynchronous alternator also works but it is necessary to replace the 3 capacitors by a three-phase inverter which will regulate the voltage by simulating a variable capacitor

[boubka]

Hello
schema found on several wind power sites!
they also speak of "short-shunt connection" ... according to them the serial capacities are fixed ??

[Other]

Hello

Even on a single phase a capacitor in series stabilizes according to the load its capacity must be large enough to support all the amperage of the generator.
the parallel condenser must be balanced according to the generator (although there is a good tolerance)

Andre

[toucantoto]

on the other hand in single phase it works provided that the capacitor is not on the useful output winding but on a quadrature winding, like a two-phase motor

Hello,
Can you schematize me what you say?
I have a single-phase asynchronous washing machine motor, in motor I feed the main winding directly on 220V and the secondary winding through the permanent capacitor of 16 microF. As a generator, should I simply add a parallel condo on the main winding? Should we also disconnect the connection from the secondary winding?
Thank you

[fajelo]

Hello
schema found on several wind power sites!
they also speak of "short-shunt connection" ... according to them the serial capacities are fixed ??

I want to transform a tri motor from 9 to 10 kwatts into a 380 volt generator
this equipment will be connected to my second home to have my autonomy
Thank you for your cordial response