emergeny transfer harmonics

[ohmhead]

Well question upon tranfer to emergency we have harmonic distortion in the power .

At normal load good clean power .

generator no load good clean power .



upon transfer with load dirty power now is a issue .

This has been tested by a certif testing company for us not our company as requierd per spec .

This is a paralled generator system what are your opinions on this issue generally elevators are drives and on emergency this is a new project nothing wrong with connections wiring or size of equipment ?


Any input has anyone seen this before ?


Could grounding effect this or elevators drives ?

 

[ron]

What percentage of the overall generator capacity is made up of drives, UPS's and other nonlinear loads?

 

[Besoeker]

Well question upon tranfer to emergency we have harmonic distortion in the power .

At normal load good clean power .

generator no load good clean power .



upon transfer with load dirty power now is a issue .

The generator impedance is likely to be higher ot much higher than the impedance of your normal supply. Non-linear currents will thus have a greater affect on the waveform from the generator.

 

[winnie]

I think that Besoeker hit the nail on the head.

I bet that if you measure harmonic _current_ flows to your loads, that you will see relatively high harmonics when operating on normal power. But because your normal power supply is very 'stiff' (low impedance, low voltage drop, however you want to describe it), the harmonic current is being provided with very little voltage distortion.

When you switch to your generator(s), then this same harmonic current causes much greater distortion of the higher impedance source.

-Jon

 

[brian john]

The utility source has more power to supply than your generator, think of it as throwing a rock in a lake the ripples are small compared to throwing the sam rock into a 5 gallon bucket of water.

What issues are you experiencing?

 

[ohmhead]

The utility source has more power to supply than your generator, think of it as throwing a rock in a lake the ripples are small compared to throwing the sam rock into a 5 gallon bucket of water.

What issues are you experiencing?

Well Brian we just finished a hospital after final turn over the owner had a engineering firm come out and test the emergency system .

The hospital is operating now this is the owner testing his system .

They are saying our power is dirty on emergency only .


When they test normal power its fine .

When they test the generator with no load its fine .


When they test with load on generator its dirty .

First i like to thank everyone for the input i did a little reading on harmonics and generators at Eatons site they had a good page on just this subject and yes you guys are right on the key point of the issue impedance .

The load impedance and the generator are off a little seems the generator is not the correct size and the engineer who designed the system is now wondering what he was thinking .

This is a new project and every wire and all equipment is in fine shape its the elevator loads that are mostly used on this generator .

One engineer said that the generator normally is 3 or 4 times the kva of the kw of the load to get harmonics down to be acceptable .

Guess were going to try the new harmonic filters they have today the ones that inject current into the harmonic currents or change out the two generators on that load which is not going to happen .

Ill let you know what the results of this is when they make up there minds i think the generator is the problem from what ive read.

Take care

 

[brian john]

Well Brian we just finished a hospital after final turn over the owner had a engineering firm come out and test the emergency system .

The hospital is operating now this is the owner testing his system .

They are saying our power is dirty on emergency only .


When they test normal power its fine .

When they test the generator with no load its fine .


When they test with load on generator its dirty .

First off it is not your electricity that is "dirty" it is the owners and the designers. Unless you made some installation mistakes.

First i like to thank everyone for the input i did a little reading on harmonics and generators at Eatons site they had a good page on just this subject and yes you guys are right on the key point of the issue impedance .

The load impedance and the generator are off a little seems the generator is not the correct size and the engineer who designed the system is now wondering what he was thinking .

This is a new project and every wire and all equipment is in fine shape its the elevator loads that are mostly used on this generator .

One engineer said that the generator normally is 3 or 4 times the kva of the kw of the load to get harmonics down to be acceptable .

Guess were going to try the new harmonic filters they have today the ones that inject current into the harmonic currents or change out the two generators on that load which is not going to happen .

Ill let you know what the results of this is when they make up there minds i think the generator is the problem from what ive read.

Take care

There are several ways around this and I bet you will get some work out of this. Unfortunately for the end user.

 

[Besoeker]

Guess were going to try the new harmonic filters they have today the ones that inject current into the harmonic currents

Active harmonic filters are effective - and expensive.
Sometimes they are the right solution.
But often passive filters can provide mitigation at a fraction of the cost.
Maybe you or the project manager need to get an independent view on the best solution if it can stand the cost.

I have experience in this field and I get offered some consultancy work from it.
Usually I give a daily rate for measurments, analysis, and recomendations.
If the customer uses us as a supplier, I waive the consultancy fee.

I'm not touting for business here. Just suggesting an approach you might take.

 

[ohmhead]

Active harmonic filters are effective - and expensive.
Sometimes they are the right solution.
But often passive filters can provide mitigation at a fraction of the cost.
Maybe you or the project manager need to get an independent view on the best solution if it can stand the cost.

I have experience in this field and I get offered some consultancy work from it.
Usually I give a daily rate for measurments, analysis, and recomendations.
If the customer uses us as a supplier, I waive the consultancy fee.

I'm not touting for business here. Just suggesting an approach you might take.

Well iam just a electrician in the field layout and install work and get paid by the hour .

Our company will not make the call on what is to be done its now a engineer issue . But you have been most helpfull and i thank you .

I come to mikes site to learn and look at problems with the code or just everyday electrical issues most of the time .


I just happen to do mostly power distribution only for my company so i see lots of different projects thur the years and lots of things that come up and look into solutions on my own as i need to know why . Its funny but years ago no one knew or looked at harmonics but today its a big issue and its getting more interesting .

Take care best to you