Induction Generator 2

[hle42000]

My company's specialty is packaging Turbine with synchronous generator as a finished packaging for baseload or standby application. We have a new customer asking for an Induction generator instead. My understanding of Induction generator requires utility power to provide exciting to this generator? Why do they prefer Induction generator instead of synchronous generator? How are the control scheme devices different from Induction vs Synchronous generator?

 

[dpc]

They think it will be simpler/cheaper - but they are usually wrong.

For standby service, a synchronous machine should be used. An induction generator requires a source of excitation - normally the utility grid.

The induction machine can make sense (maybe) for applications where the generator only operates in parallel to the utility. It does not require synchronizing equipment, and for small generators, a standard induction motor can often be used. For any type of isolated operation, a synchronous generator is a necessity (for all practical applications).

David Castor

http://www.cvoes.com

 

[hle42000]

This project will be a baseload application. Are there any other electrical devices require for this kind of application? Do we have to do any kind of modification on our turbine side?

 

[dpc]

Baseload in parallel with utility or baseload as an island?

Just be aware that an induction generator is not constant speed. It has slip just like a motor, except that it will be running faster than synchronous speed. So an 1800 rpm motor must run above 1800 rpm to be an induction generator.

The induction generator would also have a horrendous power factor, so you may need to add some capacitors to correct the power factor to keep the utility from dinging you.

David Castor

http://www.cvoes.com

 

[purplepete]

Gents,
We had an interesting experience with an induction generator in the 1980s in Victoria Australia. A 12 MVA (approx) 22 kV 50 Hz unit was installed at the end of a 30 km overhead line. When put on line 1st time the 22 kV line volts fell to 50% at a country town half way along it. That's when we found out the inrush current for magnetisation was about 10 times full load current. This, apparently, is common for induction generators. I don't remember the fix, it may have been an autotransformer together with a re-conductoring of the overhead line for a large section.
They may be simpler but it is worth studying the fundamental differences between synchronous (i.e. excited) and induction machines.

 

[waross]

An induction generator for a base load application. Just mail my check for time spent to date. I won't call you and you won't call me.
purplepete
You can probably use a dual trace scope or a sensitive synchronizing circuit to synchronize the residual output with the line before energizing.

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

 

[jpts]

What kind of induction generator is this? If it is a normal squirrel-cage machine, you don't need any separate connection for providing excitation. You can also self-start squirrel-cage machine without grid supply by using capacitor bank between generator and grid. Rotor residual flux will cause a resonance in LC circuit and self-start the magnetization. After that, generator takes the excitation from the grid through the stator terminals. So yes, you need excitation power still from the grid (which means lower power factor), but not any additional connections for that. If you have a constant turbine speed, then squirrel-cage machine could be used.

If it is a so-called soubly-fed induction generator (DFIG), you will have a normal three-phase winding also in the rotor and you need to supply magnetization energy externally all the time. I don't think you can start such machine without grid power. If you have varying turbine speed, then you should use this, but you will probably need some power electronics to supply rotor magnetization (its frequency must vary)

About the inrush current.. Are you sure you are not confusing to locked-rotor current of an induction machine, which can be up to 10 times the rated current? This applies only in direct on-line start, when you connect the generator to grid from zero speed (you have slip = 1 at first). But if you drive the machine close to synchronous speed with turbine, and then close the breaker, I don't think you will have such high current.