PF and Harmonics Correction for generator systems 2

[mkees]

I am doing some investigating, I have 4 gensets connected in parallel, and generating 13200vac. I have been told there are serious pf problems as well as harmonics coming from the load. The voltage from the gens. is transformed to 480vac before going to the load. I am uncertian what the load is, and can't really get any answers about the load. Anyway the pf swings wildly at times, and there are a lot of harmonics. What can be done to correct the PF and harmonics problem? and how do these problems effect the generators?

 

[Skogsgurra]

Swinging wildly and lots of harmonics? Sounds like some big thyristor controlled drives. They have a very bad PF at low speeds and decent PF near rated speed. They also produce lots of harmonics.

In my world, the customer should do something about that problem - not you.

Gunnar Englund

http://www.gke.org

 

[mkees]

Thank you for your response, This has been an ongoing problem with this customer (almost 1 year) and no solution. I am the new guy in the office, so guess who became responsible.

 

[rbulsara]

mkees:

We design and deal with such systems a lot. Firstly, it is not a harmoic problem as you generators are on 13.2kV side or is very unlikely. Has anybody even measured any pf or other power quality. It is very typical of people to make loose statements without proper investigation and monitoring. By your admission you are not certain what the load is?? How do you expect even to tackle the problems. You said voltage problems. What voltage problems. What actually happens?

The vahgue problems you desribe are generally related to impproper setting of load share modules and voltage regulators, droop settings etc. The AVRs can also be set for VAR contorl or PF control makes sure all of these are properly set and you need a thorough system testing.
I would think only one of the generaor has problem.

There must be manucacturers of the generators, switchegar and controls, what do they say? What has beeen done and checked so far? Hire qualified consultants to help you out, if manufacturers or the service company fail to do so.

 

[dpc]

If these generators are fairly old, you might want to investigate the voltage regulators. There were problems with certain Basler regulators being susceptible to powerline harmonics and RFI. Newer versions have better shielding and isolation.

We used to run into this on standby generators serving large VFDs at pump stations. But this was probably 15 years ago, or longer.

I agree that some actual measurements might be in order.

 

[stevenal]

mkees,

Try not to be so judgmental. Low pf, pf swings, and harmonics are not problems in themselves (the customer might be another story). Funny how a fancy new meter can convince folks that a problem exists they were previously ignorant of. What's the real problem? Where's the smoke coming from?

 

[Skogsgurra]

Guys! I am surprised at you. You seem to have joined forces telling the OP that his problems are non-existant, that he doesn't have harmonics, that no-one measured anything, that he dreamed it all up, that harmonics do not propagate from LV to HV. Was ist los?

Gunnar Englund

http://www.gke.org

 

[rbulsara]

gunnar:

In fact he has not even described the problem, he thinks it is harmonic related. He thinks there is harmonic problem, but where is the data or how did they reach that conclusion?

Only problem is 'serious' power factor problem,which could be resolved by as simple a task as as adjusting excitation. Why not define the problem first? Harmonic is the least of the issues when generators are on the primary side of a transformer and harmonic loads are on the secondary side.

 

[rbulsara]

again I 'assumed' that OP is male,..big mistake...I should have said he/she)

 

[stevenal]

I don't think his problems are non-existant. An unhappy customer is certainly a problem. The electrical "problems" described, however, are just some measurements categorized as problems by some one else (same customer?). As you already pointed out, these characteristics can be expected of some types of loads.

 

[waross]

I would hope that you have a KVARHr meter alongside the KWHr meter and are penalizing the customer for his "Bad power factor". That is the usual method of a utility dealing with power factor issues. The customer has a choice as to fix or pay. That makes it his problem. This is done by utilities world wide.
respectfully

 

[stevenal]

Waross,

I'm not sure that mkees is a utility guy, sounds more like a contractor. That certainly qualifies as a problem if too high utility charges can be lowered economically.

Is this the problem? thread238-161553

 

[mkees]

Folks, thanks for all the comments, let me respond to the easy stuff first. I am a male, and I work for a dealer of a major gen manufacturer, I am new at power generation, I have spent my time up till now in industrial automation. Anyway about a year ago 3 of these gens burned up. I am getting many stories from many people, and the bottom line is no one really knows what caused it, and all evidence has been destroyed.
I have learned that the load is motors and some on vfd's and some just regular starters. Demand drives the number of running generators, typically only one or two gens are running, and of course they are cycled so as to keep the operating hours about the same.
There are data collection devices connected at the switchgear, and I did manage to download some information from one gen.. The power factor averaged averaged about .7 there were 2 spikes in a 24hr period one went to .98 and the other went to .6.
I have been advised by my management to check for transient voltages on the 13.2kv side, honestly I don't even know what that is, and if it is real, does a meter exist to measure such a thing? and this system can't be turned off, so is there someone to connect such a meter? I could play the stupid new guy and accidently shut it down, make the connections and then get fired. Can any one provide advise? where do I start?

 

[Skogsgurra]

Good to get some more input.

Yes, you can usually connect your power quality analyzer (which should have transient capture) to the 110 V secondaries of the voltage transformers that exist in your system. A direct connection to the 13 kV side is usually not possible, recommended or needed.

Get a consultant with a good track record (references!) and let him do the analysis. You do not have the qualifications to do it yourself - even if your employee thinks that you have it.

Gunnar Englund

http://www.gke.org

 

[mkees]

Thanks for the advice Gunnar

 

[Skogsgurra]

employee -> employer

Gunnar Englund

http://www.gke.org

 

[Snoball]

Maybe a wiring error on cross current CT's is causing the CT to be grounded on both sides when paralleling breaker closes,rather than placing the CT in circuit.

 

[waross]

Three generators burned up.
No records.
Lots of different stories.
Generators started and connected as needed.

Sounds like someone was sleeping and 3 generators were running when there should have been 4.
The normal result of such a situation is burned generators, lost records, CYA (Cover Your Assets), different stories.

This may have been related to the load from the customer, but is probably not related to harmonics or power factor.
Possibly a new employee was mis-informed and was watching the KW meter instead of the KVA meter. (With a fluctuating PF).

A possible exception would be a one time transient which simultaneously damaged all three gensets. Probably lightning, a load induced or switching induced transient may be repeated from time to time.
respectfully

 

[Rodmcm]

Perhaps we should go back to basics mkees, you may not know the load at the customer site but if you have access to the generators and they are the only thing supplying the load then you know most everything about the load.
I would start with a comprehensive multifuction power monitor ( PQM or something like that) or even the readings from the protection relay and find out the nature of the load over time. Measure MW/pF/VArs and Volts for a start, measure harmonics as a second set of readings. Every generator has a generation capability, is the load within the envelope for one or many of these?
Measure the basics,look at the generator sizing, then pose the questions.

 

[Snoball]

I thought it over more maybe all your protective relays except one gen were jumped out. Maybe at shorting service blocks or shipping splits.