Converting a 5.5kW, 1455 RPM 3-Phase Motor to Generator: Capacitors, Voltage Regulator, 220V Output

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At one time, for tests, I made 3.5kW generators from a squirrel-cage motor, it was enough to disconnect the connections (star connection in my case) so that I had each winding lead separately, then I connected a capacitor, or rather capacitors (large capacity required), later it was enough to give a direct voltage ( e.g. 12V - a few seconds) for any output in order to magnetize the rotor, then with the capacitor connected to turn the engine and what revolutions, I can not say higher than the rated speed. The motor was automatically excited due to the residual magnetization and further operation is possible because the energy accumulated in the capacitors magnetized the rotor all the time. On this 3.5kW motor I connected a 1.6kW farel (it heated without any problems) to about 2kW it was possible to receive current, and exceeding 2kW the motor lost synchronization and the rotor had to be magnetized again with DC voltage. The motor generated a voltage of over 300V on the other two windings, you can make the regulator or let it go through the transformer to adjust to 230V but the question is what frequency is the generated voltage ??

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How to convert an 3phase electric motor to a 3phase generators?

A 3-phase permanent magnet synchronous motor can be used as a generator simply by attaching something that will turn the shaft and connecting a load to the motor terminals. The terminal voltage and frequency will be proportional to the speed at which the shaft is turned. The voltage will vary somewhat as the load changes. This type of motor is not very common.

A synchronous motor that has a DC power supply connected to the rotor through slip rings can be used as a generator in the same way. A battery or some other independent DC power source is required at least to get the generator started. An automotive alternator works that way. This type of motor is usually only manufactured in very large sizes.

By far, the most common type of motor is the 3-phase induction motor. In a 3-phase induction motor, the energy in the magnetic field is constantly circulating back and forth between the power source and the motor. In order to operate as a generator, a source is required for the circulating energy. If the motor is connected to a 3-phase source and initially operated as a motor, it can be operated as a generator by increasing its speed slightly above the speed at which it operates as a motor. A battery and an inverter / converter circuit that is designed for the purpose, can allow an induction motor to act as a generator. Some less complicated circuits with capacitors, can probably be used, but they may not always start reliably and may be sensitive to the characteristics of the load.

What's new is that each squirrel-cage induction motor, for example, which has 1480 rpm and its synchronous speed is 1500 rpm, it is enough to just exceed the barrier of 1500 rpm, i.e. increase the speed to over synchronous only the condition is one motor first must be powered from the network and then with another drive increasing its speed as above.

yngel1987 wrote:

What's new is that each squirrel-cage induction motor, for example, which has 1480 rpm and its synchronous speed is 1500 rpm, it is enough to just exceed the barrier of 1500 rpm, i.e. increase the speed to over synchronous only the condition is one motor first must be powered from the network and then with another drive increasing its speed as above.

This method is most often used in small hydroelectric power plants, as it allows to return energy to the grid without complicated frequency and phase control systems.

http://youtu.be/COmX3JdlMBo
added:
laskolasko2000
Generator from a 3-phase squirrel-cage motor

During motor operation, the asynchronous motor receives from the network the inductive reactive power used to generate the magnetic field and the active power converted into work, the useful rotational speed of the rotor in relation to the speed of the rotating stator field is lower, which is described by the slip.

The asynchronous squirrel-cage motor works as a generator when:

Apply the drive to the motor connected to the network. In this case, the rotor must be driven to over-synchronous speed.
The reactive power will be taken from the grid, the active power will be pumped into the grid
Since the power of the network is many times higher than the power of the generator, the generator will be naturally synchronized with it.
The rotational speed of the generator will be slightly higher than the synchronous speed, the difference will depend on the power supplied to the shaft.
However, this solution is not suitable for use in a portable generator.


Second solution
Most electrical machines are reversible, i.e. a generator, under certain conditions, may be an engine, and the engine may be a generator, it is also the case of a squirrel-cage asynchronous motor
by the way, the synchronous generator can go into motor operation and work with zero excitation, although it is a very undesirable operation.

In order for the 3f engine to work as a generator, active power must be supplied to the shaft in the form of a drive - the matter is taken care of by the internal combustion engine, and inductive reactive power
Inductive reactive power can be supplied from the network or generated on site - appropriately selected capacitors are enough because the production of capacitive reactive power is synonymous with the consumption of inductive reactive power
this solution is suitable for applications in a portable generator

Buddy, you have everything in my film.
Even in the jungle, this solution is the easiest and the cheapest way.

Hello
this and I will also write for the doubters
I have a factory generator that works like that
if someone wants, he can come and feel himself
motor + capacitors, my version is a little better because
it also has a driver that connects capacitors depending on the load
but the basic version doesn't have it, so it will go without it too
once I had an adventure that after a long time he would not wake up
so I had to treat it with a battery as colleagues wrote
and the fact that it turns up at lower speed is also true
greetings

Kszumek here laskolasko2000 (this is my video on YouTube) if you can enter the name and parameters of this aggregate.
Regards.
Mariusz.

kszumek wrote:

which, depending on the load, connects the capacitors

Another fabulist? And how many of these capacitors are disconnected and connected? How many times have I written about this.

You have the rest here

opto17 wrote:

In order for the 3f engine to work as a generator, active power must be supplied to the shaft in the form of a drive - the matter is handled by the internal combustion engine, and inductive reactive power
Inductive reactive power can be supplied from the network or generated on site - appropriately selected capacitors are sufficient because the production of capacitive reactive power is synonymous with the consumption of inductive reactive power
this solution is suitable for applications in a portable generator

kszumek wrote:

I have a factory generator that works like that
if someone wants, they can come and feel for themselves

Except there's no cage on the rotor, just winding and poles, haven't you seen that mate?

Secondly, the excitation of an asynchronous motor is a very inconvenient matter, how to compensate for reactive power and when overcompensating for too large capacity, after turning off the power, the motor switches to generator operation due to the load inertia, generating a voltage much higher than normal, which I probably don't need to write.

kszumek wrote:

and the fact that it turns up at a lower speed is also true

You wanted to flash, and here ..... ass. We are constantly talking about an over-synchronous generator because that is what the squirrel cage motor is.

Friend @ opto17 he presented the matter beautifully and reliably. :idea:

Strumien swiadomosci swia wrote:

generating a voltage much higher than normal, what is the risk of it, I do not need to write.

In self-excited generators this phenomenon does not occur.

Stream of consciousness
So my video is a scam ????
It is because of people like you that don't try to do anything themselves.
And because he wrote that it is impossible, maybe we don't ... ????
We say no to unbelievers ????
It works for me and don't mislead people.
This is the cheapest emergency generator.
For propulsion, the best mower engine maintains its revolutions under load by itself.
So much for the topic ?.

@lasko @Spring of holy awareness he didn't mean you. I saw the video, I know it works. I built not one generator - I repaired it.

Christopher
This is sorry.
I just can't explain why many electricians say it is impossible to do.
A moment ago my wife gave me a great answer ????
.... BECAUSE THESE THEORETICS ....
there is something about it

@lasko Maybe because with the entry into force of MOSFETs and thyristors (AVR pulse regulators), this circuit has lost its popularity, because it actually behaves a bit unpredictably depending on the load.

Hello
Does an unbelieving friend want to make a bet with me ???
I am even able to undress and prove that there are no magnets there
and the regulator connects 3 additional capacitors through a special contactor containing additional contacts with resistance in series
limiting current surge at the moment of switching on
in a system where such an engine works as a generator without the mains
it will wake up at much lower revolutions
tested not theorized !!!

my old post on this chiller
https://www.elektroda.pl/rtvforum/topic979980.html
greetings

kszumek wrote:

a system where such an engine works as a generator without the mains
it will wake up at much lower revolutions

What's strange about that?

But please don't mix over-synchronous braking work with under-synchronous generator work.
M It is not the voltage that is interesting, but the frequency in such a system.
Because this is how it is systematized about electrical engineering.

Hello
I do not know, I am running away from here, because it is difficult to discuss here
I read that it is impossible without the network that it is impossible
maybe I will find pics, I would put it somewhere
control system with current measurement on transformers,
the contactor because it was quite unusual,
rotor
I measured the frequency but not
I tested what will happen under the load
I suspect it might fall a bit but I don't think that's much
greetings