Generator and VFD 1

[SilverArc]

Hi,

If any body has experience of running VFD with an emergency diesel generator. Do they cause any issues. It will be a vector controlled PWM four quadrant regeneratiev AC drive.

I am just for any possibilities in general.

Thanks

 

[CJCPE]

You need to be concerned about the harmonic content of the VFD input current. If the VFD is large compared with the size of the generator, it may interfere with the generator’s voltage regulator. Check with the generator manufacturer. The resulting harmonic voltage distortion may interfere with other loads connected to the generator. The generator will probably not be able to absorb much regenerated energy returned to the source by the drive. The four quadrant input section design is very important. It may or may not have an active front end designed to reduce harmonic current compared to an ordinary PWM VFD.

Look at:
thread237-177159
thread238-179433

 

[waross]

It depends;
What are the relative sizes of the generator and the VFD?
What are the other loads on the generator?
You don't want any regenerated power getting back to the generator.
Good practice would to be to connect a load bank in parallel with the drive that is large enough to absorb the regenerated energy.
If you are certain that under all circumstances any regenerative power will be absorbed by other loads and none will make its way back to the generator you may decide to dispense with the load bank.
You may find numbers ranging from 10% to 20% allowable regenerated power back to a diesel, but I have seen fuel injection systems on diesel engines that made the engine so "loose" that I would not trust them with more than 5% regenerated power, if that much.
Bottom line, avoid sending regenerated power back to the genset. If it is unavoidable, get recommendations from the engine manufacturer, in writing if possible.
respectfully

 

[pooslinger]

I know it been a long time since you posted this but I was searching for past VFD forums and found it. I do this all the time at 7 differnt locations that are critical. These things run fine on a diesel generator. If you go with an automatic transfer switch, don't buy low bid. Get a good one. Past problems were excess concact bounce that would fault the drives and a manual reset was needed. I am assuming that the generator is sized to the facility it is running.

 

[powerjunx]

It does really interferes your gen system. Evidently, most offshore rigs has battled harmonics for some case to case basis where genset system is the sole power provider.
CJCPE has good points.







"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[catserveng]

We have some fairly general recommendations when I customers ask us about this,

Use properly sized line reactors for the VFD.

If it has PF correction capacitors, they should be disabled when on emergency power, or you have to add resistive load to offset the leading power factor effects.

Low cost voltage regulator options usually don't work well with VFD's, make sure you have three phase sensing. We find systems with PMG excitors seem to have way fewer problems with VFD's.

Try to limit kVA size of VFD to less than 60% kVA rating of generator. I don't have a good mathamatical reason for it, but based on experience with a lot of systems over the last few years, this has been a good number for us.

Make sure the VFD has the ability to function in an "island" or "off-grid" mode, meaning has a wider voltage and frequency tolerence so when you get load transients and resulting voltage and frequency changes, the VFD doesn't shut off.

As stated by others, make sure the THD, K factor and crest factor of the VFD are all within the capabilities of the generator. Be surprised how many times someone buys a generator and no one checks.

Standby units usually don't have much in the way of electrical protection, although newer genertor control packages usually have lots of capability. We usually enable the over-voltage and over current protections, or add them if the unit has a large VFD or high harmonic content load.

I believe EGSA is working on a set of generic guidelines to address this issue, just not sure when they will have it published.