Ways to reduce the generated power in one wind generator 4

[petronila]

Dear All

Some customer is speaking about reduce the power in one wind generator,the history is the wind generator is equiped with squirrel cage induction motor that works like generator. the think is this people only need generate 100 KW and the wind generator can generate 300 KW. Is not possible to do mechanical modifications.

I know could be possible install some resistance in order to "burn" power but really this issue is new for me the other idea is replace the motor by one of 100 kw but with exacly sizes (frame ) and same shaft diameter.

How to do it??

All inputs are wellcomme


Thanks and regards


Carlos

 

[MiketheEngineer]

Feather the props somewhat??

 

[Compositepro]

It should also be pointed out that it is not the generator that determines the power output it is the wind speed and size of propeller. If you don't load the prop, brake it, or feather it, it will speed-up until it is destroyed.

 

[msquared48]

Can you backfeed the extra energy into the power grid?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Skogsgurra]

Structural and chemical seem to be the motor/generator experts nowadays. Can't you read? Petronila says: "Is not possible to do mechanical modifications"

We are used to Mike's answers. And we do not like them. Has Mike lured otherwise competent members to dabble outside their expertise?

What if I started giving "advice" in chemistry or bridge-building?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[petronila]

Hello msquared48

Is not possible to backfeed extra energy, thats the real problem, we need to waste that extra energy. For it I was speaking about the resistance connection in order to do some current divisor or something like that.

Quote: "It should also be pointed out that it is not the generator that determines the power output it is the wind speed and size of propeller", Thanks Compositepro but in this case the wind generator is designed to take the wind speed like a primotor, blades speed up and moves a gearbox, gearbox moves the generator and then you have electric energy, all overspeed could be detected by PLC protection and generator will be disconected, of course if you have a terrible wind you could have an overspeed, but usually the wind farms are calculated by previus study that take account the wind conditions.


Regards


Carlos

 

[LionelHutz]

I'm with Compositepro, the turbine needs to be loaded at all time. Your response about disconnecting the generator during an overload makes no sense. The turbine blades should never be able to overload the generator and you should never drop the load off the generator during high wind and high output conditions. You have to put brakes on or rotate the blades out of the wind if you want to stop generating.

Could you explain how the whole power system is being build so that you ended up with a cutoff level of exactly 100kW? I'm assuming this is some sort of islanded system?

I'd want to look at the turbine feeding storage and the storage powering inverters if the power required is 100kW. I don't know how you could successfully match wind turbine to power usage on a 1:1 ratio with a direct connected turbine.

 

[petronila]

Hi LionelHutz

This wind generator don´t belogs to one interconected system, not inverters, not step up transformers, is only a wind generator that will feed some load and is not synchronized with others wind generators. Think in small village very away from big power station, but located in a windy place, that people needs only 80 KW so 100 KW is OK, the problem is the available wind genearator is 300 KW, so what to do with 200 KW? they can´t share energy with no body and they are looking for a economic but technical solution. The blades are fixed and can´t be redirectioned to regulate power (no mechanical modifications are possible).


A possible solution could be Rewind the generator to 100 KW but controling the speed, this is essencial, output is related to the slip an a good control of load via speed could be the key that will avoid generator overloading.

Thanks for the inputs

Regards

Carlos

 

[Strong]

How about electric resistance heating of a large water tank? The hot water can be used for cleaning and heating.

Walt

 

[DRWeig]

Man, this one has kept me awake. I've designed a few induction generator systems for waste energy recovery (gas pressure, steam, natural water flow). However, I have always had a heavy power grid available to back-feed.

First, a few curiosity questions: How is the induction generator excited? Is there an existing generator powering your small islanded "grid," or do you have another method? What sets the frequency other than the speed of your wind turbine? How is the voltage regulated?

I hate to think about wasting 200 kW on a regular basis. Figure out something useful. Strong's suggestion is good if you have a use for that much hot water. Irrigation pumps? A brightly-lit park? Lionel's suggestion about storage batteries? Pump uphill to make a new lake?

You can always get a resistive load bank, as you have suggested. No matter what you choose, the controls would be quite a challenge for me. The load bank will need to be 300 kW, so that it can dissipate the full power of the generator in the event that all the end users turn their switches off.

I wish I had more time to spend on this one. I'll be watching this thread.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[iop995]

300kW is maxim load accepted by generator and don't mean that if your load is 100kW, difference of 200kW must be diverted / sended to another loads. Power consumption is imposed by load value not by generator power capability. You need to regulate excitation of induction generator to keep frequency and voltage as stable posible.

 

[LionelHutz]

You are talking about a windmill with no mechanical speed controls. I don't see how you'll successfully run a wind turbine with an induction generator as the only power source and maintain anything close to a fixed voltage and frequency. I would not expect a wind turbine with an induction generator to work as more than say 15% of the "grid" capacity. In other words, I'd want to see >1.5MW of load on your "grid" all powered from stable generation sources before adding this wind turbine.

An induction generator wind turbine requires a stable grid to fix the voltage and frequency as well as maintain speed regulation on the turbine.

You do understand that with wind the power varies by the wind speed cubed. A small change in wind speed causes a large change in the available output power. How would you ensure the load is able to track the available power?

If the generator is always too powerful then you should be looking at modifying it. Either cut down the blades or change their pitch or simply replace them to lower the power produced.

 

[petronila]

Thanks to all for the inputs
I am not an expert in wind genertion matters, and I am not discussing about your inputs the informtion that you are receiving is the feedback from the customer and I see maybe the customer are not providing clear information. I am going to ask him more about the grid.

Maybe could be good if you cn share some information about this induction generators( Some papers)

Thanks again

Carlos

 

[waross]

There is too much mis-information and too little basic knowledge of generator theory here to try to sort out. There are a few things that may help such as adding a disk to block some of the blade area or better, turning the unit out of the wind based on the loading, but we have been stymied by the prohibition on mechanical changes.

You need to regulate excitation of induction generator

Great idea. Do you have a diagram??
bye


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iop995]

To control excitation of IM need to use indirect methods as there are not direct acces to do that. IM may be self-excited by a capacitors bank or may use an external source. Some details may be found at

http://www.nrel.gov/docs/fy00osti/26713.pdf

or even more in google "self excited induction generator".
Using IM as generator and in not grid connected mode, need also a so called "load controller"; a practical example may be found here

http://ludens.cl/Electron/picelc/picelc.html

 

[waross]

Yesterday was a long day.
I apologize for my short answer, petronila.

Basic generator types:
1. Load dependent;
This may be a standby generator, an islanded prime power generator or a swing generator. The controls monitor the frequency and control the power into the prime mover so that the power in equals the power out plus losses.

2. Fixed load;
Many large grid generators are run in fixed load mode. The load dispatch center will contact the generator operators and dictate the amount of power they desire from each site. Some plants will be designated swing generators and will adjust the power into the grid to compensate for small load changes. When large load changes are trending the fixed load generator operators will be instructed to change output accordingly.
Conventional generators are capable of operation in either load dependent or fixed load mode. However some prime movers and power sources are better suited to fixed load operation. The efficiency at low power levels is also a factor in the load control commands issued to a fixed load grid generator.

3; Fuel availability mode.
This mode is generally used to reclaim energy from waste or unused sources and the generator output depends on the availability of fuel for the prime mover.
This may be a "Run of the River" hydro plant, a turbo generator using the steam from a recovery boiler, land-fill gas recovery, or other uses of otherwise wasted energy.
These generators are typically connected to a larger system which is capable of absorbing all the power generated. Somewhere in the larger system there will be a swing generator which, in addition to compensating for load changes, will compensate for the changes in the input to the grid from the fuel available generator.

Controls:
Typically alternators are tightly frequency controlled by the governor or by connection to the grid and voltage controlled by an Automatic Voltage Regulator (AVR).

An induction generator has no controls. The frequency is controlled by the grid. The voltage is speed dependent. The excitation current is drawn from the grid. Capacitors may be used to supply the excitation current but they do not control the excitation, they divert the excitation current so that it is supplied by the capacitors rather than from the grid.

A wind turbine typically is connected to a system that will accept the total output. This may be a grid, large or small, or a battery bank or other means of storing energy. If you have a geographical feature that may be dammed to create a reservoir, pumped storage may be an option.

Wind energy is generally a fuel availability source. Running an induction generator islanded in fuel availability mode presents two non trivial issues.
A> Controlling power output.
B> Controlling voltage and frequency.

A, Power; you must either limit the power in by feathering the blades, spoiling, changing the angle of attack, braking or diverting the wind. Alternately you may generate full power and waste the excess.
Boiling water may be the best option. Boiling not heating! Based on a 200 kW load test years ago, I would suggest something in the order of 1000 gallons a day up in smoke or steam. Someone else do the math please.
You may not be able to generate in a light wind, and you will probably have to somehow stop the turbine in very strong winds.
Wind turbines are not suitable for prime power except for very small systems where a battery bank to store energy is feasible.

B, Controls; Well perusal of a couple of links shows that the ELC is intended for micro-hydro and not recommended for wind applications. It may be adaptable.
Does your Induction generator include a rectifier and inverter package? That is probably the only feasible way to control frequency and voltage from an induction generator driven by a wind turbine.
Rewinding the induction generator. Then it would take much less wind to overload and destroy the generator. If the wind energy captured by the blades exceeds the capability of the generator by very much the generator may be overloaded and destroyed, the turbine may overspeed and self destroy or both.
This project may not be possible with the available funds.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Hi Bill,

Many wind generators are dual-feed induction machines. There some good explanations turned up by Google. I think it is an interesting design of machine.

I think Carlos' problem may be difficult to resolve without either mechanical alterations to the machine to modify its capability to extract power from the wind, or provision to export into a larger system or dump the excess power generated into a load bank. If there is another method of dealing with this I'm interested to learn.

 

[LionelHutz]

with squirrel cage induction motor

Yes, it's an interesting design but it's not present here.

 

[ScottyUK]

Yes, I'm aware of that. That's why the comment was addressed to Bill, not to Lionel...

 

[LionelHutz]

I'm not sure what your point was mentioning it at all in this thread. That design is no more suitable for the application in question than an induction generator is.