# Harmonics on load side of transformer



## Flex277 (Jun 2, 2014)

Got a service call I am going to tomorrow for a truck stop, that is having problems burning up drivers and various other pieces of equipment supposedly due to Harmonics. The POCO has confirmed it is not on there line side but on the load side and isolated to one phase. POCO is bringing a harmonics meter to help distinguish where it’s coming from. Am I to believe that computers,motors,fluorescent ballast can cause harmonics, but what is the fix. Im a little new to this kind of issue. Has anyone ever dealt with this? Any pointers before heading into it. Thanks


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## telsa (May 22, 2015)

Start by being suspicious of the neutrals.

Jacked up neutral connections can easily read as harmonics issues.

Ditto for under-sized neutrals, especially neutrals that are undersized because their run is too long.

( You'll see a lot of that. )

Also watch out for connections that have gone sour. The original install did not fully protect the connections from the elements.

These go from being okay -- to going weird -- and the owner hasn't a clue as to why they're acting up.

These faults are so common that you have to check them out first off.

A rotten Hot connection can also come off as if it has harmonics issues. The gear is being starved for voltage... especially as the circuit becomes fully loaded. These can be real foolers as they test fine with a DMM. Marginal connections can drive you crazy.

You have to test them under load, usually.


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## telsa (May 22, 2015)

Also, the transformer, itself, could be crapping out on one phase.

Corona discharge can do crazy things. You'd have to kill power and meg that puppy out.


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## brian john (Mar 11, 2007)

First, the effects of harmonics are almost always overblown. In 32 years of performing harmonic investigations, I only found a few instances where harmonics were the issue.

Harmonics like "grounds" are a catch-all phrase for I do not know the problem.


But if it is a harmonic issue 


Utilize a true RMS amp-clamp and measure A, B, C and neutral currents. Calculate what neutral currents should be and compare that to the measured neutral current.


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## brian john (Mar 11, 2007)

What voltage transformer Primary and Secondary




> Am I to believe that computers, motors *WITH VFD's*, fluorescent ballast can cause harmonics, but what is the fix.


I hear the ballast issue all the time and while they can contribute to harmonics I have never seen ballast cause major issues.

DO NOT freak out when you hear about high levels of current harmonics unless the current level exceeds the neutral rating. Voltage harmonics (which are a by-product of current harmonics) is what you should look at anything above 5% may be a concern.

Google harmonics and do some reading.


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## Flex277 (Jun 2, 2014)

brian john said:


> First, the effects of harmonics are almost always overblown. In 32 years of performing harmonic investigations, I only found a few instances where harmonics were the issue.
> 
> Harmonics like "grounds" are a catch-all phrase for I do not know the problem.
> 
> ...




How should you calculate your neutral current to what it’s supposed to be?


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## paulengr (Oct 8, 2017)

Flex277 said:


> How should you calculate your neutral current to what it’s supposed to be?


If you have NO single phase ,(line-neutral) loads, you still have charging current in big systems. This tells how to estimate http://apps.geindustrial.com/publib...FjAHegQIBhAB&usg=AOvVaw3PwWTCyokZUQn0sdmS87rv

If you have single phase (line-neutral) loads then measure and add those together.


Sent from my SM-T350 using Tapatalk


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## brian john (Mar 11, 2007)

paulengr said:


> If you have NO single phase ,(line-neutral) loads, you still have charging current in big systems. This tells how to estimate http://apps.geindustrial.com/publib...FjAHegQIBhAB&usg=AOvVaw3PwWTCyokZUQn0sdmS87rv
> 
> *If you have single phase (line-neutral) loads then measure and add those together.
> *
> ...


For 3-phase?

I use to have the formula on my laptop but this site shows you how.

If A, B, and C are the three phase currents, the formula to find the neutral current is the square root of the following: (A^2 + B^2 + C^2 - AB - AC - BC).

https://www.hunker.com/12470226/how-to-calculate-neutral-currents


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## telsa (May 22, 2015)

Wye would you ask that ?


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## brian john (Mar 11, 2007)

Flex277 said:


> How should you calculate your neutral current to what it’s supposed to be?


Transformer voltage I am assuming Delta Wye 480-208/120?

There are harmonic mitigation devices but most are very expensive the other option is a larger transformer. K rated transformers are sold based on harmonics but most are nothing more than a beefed transformer, more steel or copper.

A standard dry-type transformer is K-rated K1, K4, K 13 are common transformers sold for non-linear loads.


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## paulengr (Oct 8, 2017)

brian john said:


> For 3-phase?
> 
> I use to have the formula on my laptop but this site shows you how.
> 
> ...




That assumes ALL your loads are line-neutral. Any line-line loads have no neutral current at all except through the star of the wye. They don’t flow through a 4 wire system. If they are all wye connected that would be right.

Most motors up to most NEMA sizes for instance are delta connected internally because it gives almost twice as much torque in the same volume. Most lighting is wye. Transformers are frequently delta and even single phase is often 480:120 not 277:120.

So your formula gives maybe an upper limit and might work in commercial but it’s not even close in most industrial plants.


Sent from my iPhone using Tapatalk


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## brian john (Mar 11, 2007)

paulengr said:


> That assumes ALL your loads are line-neutral. Any line-line loads have no neutral current at all except through the star of the wye. They don’t flow through a 4 wire system. If they are all wye connected that would be right.
> 
> Most motors up to most NEMA sizes for instance are delta connected internally because it gives almost twice as much torque in the same volume. Most lighting is wye. Transformers are frequently delta and even single phase is often 480:120 not 277:120.
> 
> ...


So you consider a truck stop an industrial application?


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## telsa (May 22, 2015)

Per my earlier posts: figure on bad connections.

1) Only a very old and abused transformer would experience corona discharges.

2) Truck stop circuits just don't lend themselves to the generation of harmonics, as the vast bulk of the loads will prove to be L-N... and modern electronic ballasts just don't kick out crazy amounts of harmonics... not to the scale that would have the Poco hopping about.

3) The truck stop environment leads one to suspect failing connections -- perhaps more than one. Did some trucker bump into some gear?


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## brian john (Mar 11, 2007)

telsa said:


> Per my earlier posts: figure on bad connections.
> 
> 1) Only a very old and abused transformer would experience corona discharges.
> 
> ...


I wish the OP would tell about the transformer, is it a 13.2KV to 480/277 or 208/120 utility owned or customer owned 480-208/120. Which since the utility is involved then I suspect it is the former. If it is a utility transformer no matter the problem (loose connection) and they fix it they will blame harmonics and grounding. BECAUSE IT IS NEVER THEIR PROBLEM


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## joebanana (Dec 21, 2010)

All you need is a fiddle player, a banjo, and a bongo banging chimpanzee, and you can start a band. 
Wait......what?...........Oh.........harmonICS.......that's different.
Never mind.


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## Flex277 (Jun 2, 2014)

brian john said:


> I wish the OP would tell about the transformer, is it a 13.2KV to 480/277 or 208/120 utility owned or customer owned 480-208/120. Which since the utility is involved then I suspect it is the former. If it is a utility transformer no matter the problem (loose connection) and they fix it they will blame harmonics and grounding. BECAUSE IT IS NEVER THEIR PROBLEM




Sorry for the delay, primary voltage coming in is 7200/12470 and secondary is 120/208. The transformer was put into commission in 2015. The problems the truck stop has been having have been building up and increasing more as of lately. Burned up drivers and changing contactors for there coolers left and right.
So a week prior the POCO attached there harmonics tester in there transformer for 3 days. The data showed a peak of 200% and a base line of 8% for THD. All consistent during a four hour period from 730 to 1130.
The truck stop is shared with a Hardee’s and this is where all the problems are happening. Someone told me to check the wiring to the compressors on the coolers. POCO is also gonna bring a thermal camera so we can check connections.


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## brian john (Mar 11, 2007)

Flex277 said:


> Sorry for the delay, primary voltage coming in is 7200/12470 and secondary is 120/208. The transformer was put into commission in 2015. The problems the truck stop has been having have been building up and increasing more as of lately. Burned up drivers and changing contactors for there coolers left and right.
> S*o a week prior the POCO attached there harmonics tester in there transformer for 3 days. The data showed a peak of 200% and a base line of 8% for THD. All consistent during a four hour period from 730 to 1130.*
> The truck stop is shared with a Hardee’s and this is where all the problems are happening. Someone told me to check the wiring to the compressors on the coolers. POCO is also gonna bring a thermal camera so we can check connections.


That is meaningless unless they told you the Voltage THD % and the Current THD%, was the 200% on the neutral voltage or current % of the load at the time.


8% current THD can be nothing if the voltage THD is 1-3%. 

8% current THD can be nothing if the transformer is 1/3 loaded.


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## Flex277 (Jun 2, 2014)

brian john said:


> That is meaningless unless they told you the Voltage THD % and the Current THD%, was the 200% on the neutral voltage or current % of the load at the time.
> 
> 
> 
> ...






























This is what they gave me


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