Dreaded Harmonics

[danilo]

Hello Guys,

Good Day!

appreciate your views about dreaded harmonics in the system..in our building,the 225kva,460/230v emits unusual heat from its core winding that im afraid may damage the insulation of the equipment.The unit is only 60% loaded of mostly non-linear loads (computers,ups etc.) and yet emits heat as if its 125% loaded because i cannot even touch its enclosure.

thanks for your prompt comments.

Danilo

 

[dereckbc]

Re: Dreaded Harmonics

danilo, are you using a "K" rated transformer? with oversized neutral to accomidate the heat? There are two options, K-rated transformers or oversized transormers.

 

[danilo]

Re: Dreaded Harmonics

Dear Dereck,

im so glad with your prompt reply..yes,its k-4 rated xformer with delta/wye connection.tried also checking the phase current difference but found minimal discrepancies also.thats why im worried of its imminent breakdown anytime.

sorry not so sure of its neutral sizing.

appreciate your valued time again.

thanks

 

[charlie]

Re: Dreaded Harmonics

Use a true RMS meter to check the load. It may be overloaded and you not know it. A K8 or K13 may be needed for your application.

Is this a 1? or a 3? transformer? The voltage configuration leads me to think it is a 1?.

 

[danilo]

Re: Dreaded Harmonics

Dear Charlie,

its a 3ph xformer tapped to 4000A busduct via tap -off breaker.It serves the main distribution panel board with five(5) branches of 3ph load also.The load side feeds the call center and other admin offices,mostly loads are packaged type aircons and computers.

i think the cost of changing it from k4 to k8 or k19 is prohibitive at the moment.im really looking at the best cost effective solution with less cash out.

thanks again for your time.

Danilo

 

[charlie tuna]

Re: Dreaded Harmonics

danilo,
i have come across transformers that just run "hot" - very hot! now, the loads that this transformer feeds seem to be important to your operation and a 60 per cent loaded 225 kva tranformer is feeding alot of equipment. invest in the installation of a data recorder to see whats happening inside this transformer. if you don't have one rent one or hire someone to monitor it for a week. you are trying to make a decision on "assumptions" and the replacement cost or upgrade costs of this size unit warrents proper engineering practices. i do infrared scanning and power monitoring and i see less harmonic problems today than i did ten years ago. actually, harmonic problems have not been as much of a problem as they were first expected to be. i have come across large transformers that you could fry an egg on---and if you come across them on a weekend when they are operating on a light load---they seem just as "hot"! and when we monitor them the load is well within specs.... this report may show unbalanced loading which could be the real problem???????

 

[petersonra]

Re: Dreaded Harmonics

It may be that your perception of how hot the thing is may be in error.

I would get a surface mounted thermometer and measure the temperature and then check the manual or with the manufacturer and see what tmeperature it is rated for.

Some of these things just tend to run hot.

You might want to check and see if it is getting adequate ventilation as well. Its sort of amazing how warm one of these things can get if it is placed too close to the wall and the air flow is disturbed.

 

[danilo]

Re: Dreaded Harmonics

Thanks Folks,

might as well heed your advise to undergo thorough checking of the transformer to find out whats going on inside it.

by the way, should real dreaded harmonics is present in the equipment?is k rated or oversized transformer the only solution?how about putting up a filter? which do you think is better,cost wise and efficiency wise?

gracias!

Danilo

 

[dereckbc]

Re: Dreaded Harmonics

Filters do not stop harmonics downstream, they just divert the heat off the transformer to the filter. So yes they can help.

A filter is a add-on item and if you have the space OK, but IMO it is a bandaid. A "K" rated transformer is really the most cost effective prevention in terms of space, material, and labor.

[ January 25, 2005, 10:38 PM: Message edited by: dereckbc ]

 

[danilo]

Re: Dreaded Harmonics

Well, it seems i need to capitalize this expense for this year coz of high cash out involvement because we have eighteen( 18 ) dry type transformers with k4 rating that need to be replaced..ill check first the data recorder if harmonics presence is killing the equipment.If yes, i might consider installing filter if it can do wonder to some units before i decide to replace the rest with the new ones.

guys,any more caution about filter installation?

thanks

 

[charlie tuna]

Re: Dreaded Harmonics

danilo,
one of the buildings i built and have maintained along with the management company for the past twenty five years is a 55 story office building. most of the floors are total office type loads --- computer -- copier -- fax --etc.--those loads that can create harmonic problems. the floors were originally wired with the standard practice of "common neutrals" on branch service circuits. the floors are typical--with a 480v-3p-4w bus duct and bus taps to feed 75 kva transformers - delta-wye connected to supply branch circuit panels 120-208v-3p-4w.. none of the original transformers were "k rated". twenty years ago this new term "harmonics" entered our trade and we began the practice of using separate neutrals to new loads and using "k rated" transformers on tenant expansion work. i would guess that half of the tenant transformers are now "k rated" since many of the original base building transformers are still in use. in twenty five years, i have seen one transformer fail due to harmonics and another fail due to overload! i also have done the infrared scanning of this building since 1989 and have done all of the system troubleshooting in the buildings electrical system since it's inseption. i see harmonics as a problem that is weakening within our industry due to wiring practices. i have found that if i take a simple test using an amp probe on a three phase secondary feeding a panel and find the current on the panels neutral close to normal considering the unbalanced readings between the a-b-c phases there will be low harmonic effects within this panel's circuits. when we see a large difference in neutral current flow that does not make sense considering "unbalanced loading" between a-b-c phases we suspect it is due to harmonic distortion and is proven with our data recorders. again, this has been my own observation. the original none "k rated" transformers function fine. as i wrote above, some transformers run hot--same manufacturers--same size--and similar loads! some run noisey! while others are quiet with larger loads. i think its got to due with the make up of the cores within the transformers--maybe the amount of iron in the core or the thickness of the insulating materials or how tight the cores are wrapped??? there is another office building we have serviced that has one "monster" transformer feeding a bus duct that serves the low voltage (120/208v)to the entire building. "hot" is not the word that discribes this "monster's" surface temperature!! it is not 50 per cent loaded-- forget cooking eggs---i could fry you some bacon on this thing!!! but its been there since the building was built over twenty five years ago --- used to serve the hurricane center's office until it was relocated ten years ago!!!