power quality problems

[bgdiablo]

A electrical testing company came in and did a power analysis and did not provide a engineers report of recommendations. We were asked to look into the problems they were having.

The customer is a hospital and of course can not shut off power to check or do testing, which creates its own set of problems.

There is excessive noise on all phases as well as harmonics. The facility is 20+ yrs old. Dealing with a 480V primary 120/208V 50KVA Westinghouse transformer with a name plate temp. rise of 5 degrees C. feeding 7 panels on 3 floors with the neutral bars being used as feed thru end to end. Load is operating at 1/3 of nameplate and balanced fairly close.

Transformer is running hot and suspect the harmonics is playing a major factor in the problem.

Grounding of X0 was installed on a water pipe not building steel which I personally don't agree with.

I seem to have more questions than answers. While increasing the KVA rating will help the heat issue, not 100% sure that would be the right way to go since more equipment is becoming electronic in the medical field.

Thinking of maybe a K rated xfmr but not sure cause of the small motor loads be served as well.

 

[dereckbc]

Best practice is to feed sensitive equipment with a delta fed isolation transformer(s). Otherwise there is no way to isolate motor/mechanical and lighting loads from sensitive loads.

 

[beanland]

Harmonics

Harmonics

If transformer heating is from harmonics, harmonic filters can be installed on the 120V side to reduce harmonics in the transformer which should cool it down.

Newer electronics use IGBT front ends, switching at high frequencies, which have lower harmonics and better power factor.

 

[brian john]

A electrical testing company came in and did a power analysis and did not provide a engineers report of recommendations. We were asked to look into the problems they were having.

Besides the heating of the transformer what issues are you having with equipment operational issues?

The customer is a hospital and of course can not shut off power to check or do testing, which creates its own set of problems.

EVERYBODY CAN GO DOWN! The question is orderly or uncontrolled.

Grounding of X0 was installed on a water pipe not building steel which I personally don't agree with.

Accidentally or intentionally steel, piping and metallical components are all bonded.

 

[bgdiablo]

other issue is with their IT dept. who says they have lost equipment cause of power issues. They just replaced the UPS...since it was 8 yrs old.

As far as grounding, true piping structural steel etc should have been ground and bonded at time of original install, doesn't mean that it still exist today after 20+ yrs with changes and renovations. I personally see that problem too many times. That is why I prefer the building steel.

Yes there can be a outage... well after many attempts to schedule it to happen. The last one took 1 yr + to change a couple of bad breakers... the pass the buck sin drum !

Poly phasing is out as well.

Thanks for your help

 

[76nemo]

Your water supply grounding may be as good as it gets. Have you looked at the rating of your neutrals? Your harmonic issue is right in your hands, look at the issue with a PQA. Harmonics can be a huge issue in the medical field, the electronics keep getting more elite. Bottom line is you are maybe looking at some more pulls. Sounds like your system was properly under rated.

 

[brian john]

As far as grounding, true piping structural steel etc should have been ground and bonded at time of original install, doesn't mean that it still exist today after 20+ yrs with changes and renovations. I personally see that problem too many times. That is why I prefer the building steel.

I do loads of grounding investigations and I can't not think of any cases where there was an issue of steel over water pipe. Proper bonding of neutrals and grounds is the number one cause I see.

My point was in most building today's all metallic components are common in a building whether intentionally or accidentally.