Generator parallel operates with Invertor Output 1

[alexcflee]

I have a project, need to parallel a generator set with an invertor output.

Generator; 20KW, 600V 3 Ph. 60Hz at 1800 rpm.
- Governor,Electronic always runs at constant speed 1800 rpm, no load to full load.
- Voltage regulator, Digital, self excited, constant output 600V, no load to full load.

Looking for advises from whoever have experience for this application.

 

[davidbeach]

Constant ... no load to full load.

I hope you don't really believe that, because it certainly isn't true. There will be deviations, and there are time constants that limit how fast it can get back to the "constant" value. And it's probably all too slow for a grid interactive inverter to stay paralleled.

 

[ScusaMe]

Let me know when the SMOKE clears !

 

[ScottyUK]

Of course the inverter can be designed to track the gird, or in this case the generator. Much more complex though.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Drivesrock]

Is this just a change-over from one to the other or constant parallel operation required?

If a change-over, I think you stand a chance but you need synchronising relay, filters, contactors and more hardware plus something to control the drive or generator to synch to the other party.
I quickly searched the forum and found this thread where this has been discussed before but there may be more.

http://www.eng-tips.com/viewthread.cfm?qid=278446

I have successfully paralleled an inverter and the mains for this purpose of a change-over of the connected motor from the drive to the mains so that the drive could start another motor.

What is your application?

 

[LionelHutz]

What kind of inverter? A grid-tied renewable energy inverter or a inverter (VFD) that is used to control a motor?

It's possible that block-loads could be an issue paralleling a grid-tied inverter to a genset. However a grid-tied inverter must be designed to work with weaker grid connections so it might not be an issue. Other than that, I wouldn't expect any extra issue compared to using utility power. The grid-tied inverters protect themselves fairly well against variations in the power source and shut-down when necessary.

 

[alexcflee]

Thanks all for the information.
In this project, there are three sources; Utility, Inverter( grid-tied type ) and generator. We are the generator supplier.
There is an intend to parallel all sources together.
I am planning to add; a synchronizer, a Load Shar Module ( LSM ) to provide droop and control the output active power (KW) of the generator, a new AVR with doop and addition KVAR/PF controller to control the reactive output.
Will it work?
Please advise!

 

[waross]

If your generator is paralleled with the grid, then we start over.
The grid will hold the generator frequency stable. All you need is a droop governor and set it over speed to pick up a base load.
eg: If the governor has 3% droop, and you set the speed 3% fast, the generator will be fully loaded and stable.
You still have to control the excitation. The grid will set the voltage but PF control may be used to control the excitation.
The grid will pick accommodate load swings.
The invertor will be connected to the grid and will not see frequency variations.
BUT, what else have you forgotten to tell us??

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

 

[davidbeach]

So, you're the generator supplier and you believe that BS about "Constant ... no load to full load"? Or you just want your customers to believe that?

 

[alexcflee]

There are numbers of operation requirement;
- Utility only
- Utility with Inverter
- Utility with Generator
- Utility with Inverter and Generator
- Inverter only
- Inverter with Generator
The most difficult for me is the Inverter with Generator. What should I be carefull and take precustion?
Looking for advise and suggestion!

 

[waross]

That should be the inverter supplier's problem.
Two solutions;
1> The inverter must be frequency agile and able to track generator frequency variation.
2> Accept that the inverter may not play well with the generator.

With a very steady load at 60 Hz (or 50 Hz) the inverter may work with the generator. Any load swings may cause the inverter to drop out.
If the inverter drops out on a reduction in load the system may become unstable.
You may have to change the excitation control from PF control to voltage control when going from parallel operation to island operation.

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

 

[alexcflee]

Waross,
Thank you for your advise. I will run the generator governor in isochrous mode and short-cct the droop CTs on the AVR when I run the generator in islanding.

 

[waross]

You may want to reassess running in isochronous when you are on the grid. The integral unction of the isochronous controller will see an error and try to correct. This will result in the generator going all the way to full fuel or all the way to 0% load. A full fuel condition may cause the alternator to be overloaded. It is not uncommon for a prime mover to have enough power at full fuel to overload the alternator.

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

 

[LionelHutz]

One other thing, this inverter could over-power the genset and load. Someone will have to ensure the inverter isn't putting out more power than the islanded grid requires. Well, actually less than required since you'll likely always want some minimum base load on the genset.

 

[jfpe]

What is the kW rating of the inverter? What are the minimum and maximum load?

I have the same concerns as LionelHutz.

-JFPE

 

[waross]

In consideration of the previous two posts, you may want to consider reverse power protection.

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