Power Quality Questions

H

Hermie17

Member
Location
Kansas
Occupation
Industrial Electrician Journeyman
Hey guys, first post here. I am a journeyman in Kansas. I have about 4.5 years of experience in the trade, all industrial, heavy commercial. I am a learner/researcher by nature and I have gotten a long way on that, but I am starting to run into the limits of what I am comfortable suggesting without some schooling or expert advice. I have started getting involved with my companies PQ studies and PF mitigation. We have always sent our PQ readings out to an ex Evergy (our power provider) engineer for advice on how to fix the problems.. I would like to learn how to read those reports and just generally understand what the safe tolerances for harmonics and PF is.

Right now, I have the reports from a Metal Anodizing plant. They use some good sized rectifiers for that, and they are dealing with pretty bad harmonics. I have done a fair amount of research on it and I think a 50kvar detuned capacitor bank would be their best option. Next best would be just small isolation transformers before each rectifier. That would, at minimum, limit the harmonics that the rest of the plant would see.
(Either of these options is gonna run $40k plus by the time material and labor are all included.)

I guess my question is, Is this a good thing for me to try to figure out? Or should i leave this to Electrical Engineers and stick to pulling wire? I don't plan on going to college for an engineering degree. Is this just something out of my pay grade that's gonna get me burned if i try to figure it out and suggest/install systems without EE support?
 
Power factor corrections and Power factor calculations is a matter of practice and having the right information. Most of the time, people don't care about power factor unless the utility is billing for KVAR / KVARH rather than just kW / KWH. Providing corrections should be too hard to do mathematically speaking. But I would suggest having a P.E. double check your work.

For distortions, you could dive into some of the IEEE papers on Total Harmonic Distortion and identifying the types of distortions in waveforms.

Doing the math to make corrections might be a little different. It depends on how deep you want to get.

Some of the people that sell power quality software and tools have easier to read white papers that also help. Identifying the causes by reading the PQ data is probably 80% of it.

I know a couple of guys that got to be better than me at these things. They specialized in relay protection equipment testing, set up, etc. It got to the point where we suggested he just take a PE test and he passed lol. So don't be afraid to learn more about it.
 
Hermie17 said:
I would like to learn how to read those reports and just generally understand what the safe tolerances for harmonics and PF is.

Right now, I have the reports from a Metal Anodizing plant. They use some good sized rectifiers for that, and they are dealing with pretty bad harmonics. I have done a fair amount of research on it and I think a 50kvar detuned capacitor bank would be their best option. Next best would be just small isolation transformers before each rectifier. That would, at minimum, limit the harmonics that the rest of the plant would see.
(Either of these options is gonna run $40k plus by the time material and labor are all included.)

I guess my question is, Is this a good thing for me to try to figure out? Or should i leave this to Electrical Engineers and stick to pulling wire? I don't plan on going to college for an engineering degree. Is this just something out of my pay grade that's gonna get me burned if i try to figure it out and suggest/install systems without EE support?
Click to expand...
I would start by not spending any money before defining what the problem is you are trying to fix? Is the power factor an issue at the plant? How much money is low PF costing the company per month in the electric bill? Are harmonics causing an issue? Is heating effects reaching concerning level? Is there equipment malfunctioning and harmonics the suspect? Need to understand if there is a problem first.
 
solarken said:
I would start by not spending any money before defining what the problem is you are trying to fix? Is the power factor an issue at the plant? How much money is low PF costing the company per month in the electric bill? Are harmonics causing an issue? Is heating effects reaching concerning level? Is there equipment malfunctioning and harmonics the suspect? Need to understand if there is a problem first.
Click to expand...
They have rectifiers burning out too fast and 6-8v back feeding on the ground. They are rated at .83 pf on the electric bill so their adjusted demand kW and kwh total are high as well as a $500 pf charge. My reports show 8-10%THD on the 5th and 7th harmonic. A little higher in the 3rd but not terrible. Cap bank would help with PQ/PF but may amplify harmonics, but a detuned cap bank with a passive filter might be just the trick..... They need a ground farm with isolated grounding for their DC distribution as well. That is probably the worst problem they have. Safety wise
 
Question: are they being billed for a poor displacement power factor or a poor distortion power factor.

I'd expect lots of rectifiers to produce distortion PF. Capacitors help with displacement PF.

Phase shift transformers are the classic way to reduce distortion PF from rectifiers.
 
winnie said:
Question: are they being billed for a poor displacement power factor or a poor distortion power factor.

I'd expect lots of rectifiers to produce distortion PF. Capacitors help with displacement PF.

Phase shift transformers are the classic way to reduce distortion PF from rectifiers.
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I don't know, the scope looks relatively smooth, amps leading. There are some transients. How would I tell if it was distortion vs displacement pf?
Also wouldn't isolation transformers ahead of each rectifier be the standard way to install rectifiers?

Also my PQ report shows their PQ dropping as low as .63
 
Hermie17 said:
I don't know, the scope looks relatively smooth, amps leading. There are some transients. How would I tell if it was distortion vs displacement pf?
Also wouldn't isolation transformers ahead of each rectifier be the standard way to install rectifiers?

Also my PQ report shows their PQ dropping as low as .63
Click to expand...

The scope won't tell you what they are being billed for, that is a question for the power company. I don't even know if power companies bill for distortion.

If amps are leading volts then you have a capacitive power factor. Adding capacitors will make that worse. Note that a leading power factor is rare, so I'd suspect an instrument error.

Transformers can be specified to provide different phase shifts. This shifts around the peaks of the rectifier conduction. By having different rectifiers with different phase shifts you smooth out the conduction peaks and reduce overall harmonics.

Where you say 'the scope looks relatively smooth', where is this being measured, and where are the harmonic distortions being measured?
 
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