3 Phase Neutral Reduction

[ActionDave]

You seem to be stuck with this ballast idea. My point was not in reference to ballasts.

Where else would the harmonics come from?

 

[Besoeker]

Where else would the harmonics come from?

Various sources. Phase controlled dimmers for example. Single phase VSDs, Switch mode power supplies. Battery chargers. UPS systems.

 

[ActionDave]

Various sources. Phase controlled dimmers for example. Single phase VSDs, Switch mode power supplies. Battery chargers. UPS systems.

First, you said it was the lighting department of your company that had the problem leading to the notion that the problem was with the lights.

Second, there are millions of buildings in cities here and on your continent I'm sure that have all those loads on old three phase star systems that don't have neutral problems. I understand things like data centers and similar needing special attention, but I don't see neutrals burning up in regular office buildings and hotels and casinos.

 

[JFletcher]

I could see one of those Mega hotels in Dubai having hundreds of kilowatts of load from Led drivers with poor design. And such hotels probably have things that we can't even really conceive of here like vending machines that dispense gold coins.

 

[George Stolz]

First, you said it was the lighting department of your company that had the problem leading to the notion that the problem was with the lights.

Second, there are millions of buildings in cities here and on your continent I'm sure that have all those loads on old three phase star systems that don't have neutral problems. I understand things like data centers and similar needing special attention, but I don't see neutrals burning up in regular office buildings and hotels and casinos.

Why head them off, they're on a roll. I routinely run 8AWG neutrals for 12 AWG ungrounded conductors because I saw Backdraft in high school... :roll:

Code allows reduced neutrals. Depending on what the loads are it might be a smart move. It would be good if the OP would fill in some gaps.

 

[electrofelon]

S
It is not a potential. Triple-n add in the neutral. That is not in question.

But what is in question is how much harmonics it has. You seem to be treating it black and white, like if its electronic, there is some textbook worse case scenario of harmonics.

You seem to be stuck with this ballast idea. My point was not in reference to ballasts.

Note I said this : "electronic ballast/driver/power supply"

I am not saying this is never an issue, just very rare. Perhaps that case you were involved in was a perfect combination of "dirty" electronics and a high percentage of line to neutral loads, etc...? Maybe they do things differently there. Here in the states you would have lots of line to line loads, and you would have tons of neutral overhead because we essentially size the neutral as if the line to line loads were line to neutral loads (because generally we just provide a full neutral for three phase services).

 

[Besoeker]

But what is in question is how much harmonics it has. You seem to be treating it black and white, like if its electronic, there is some textbook worse case scenario of harmonics.

I'm treating it as it was. Not a text book example. A real life case. And not bad ballasts. I can elaborate but that won't change what actually happened.
Not my jurisdiction. I just happened to be there to unpick the screw up. And it wasn't the only one. Unique only in terms of scale.

 

[Besoeker]

First, you said it was the lighting department of your company that had the problem leading to the notion that the problem was with the lights.

I thought I had laid that erroneous assumption to rest.

 

[kwired]

But what is in question is how much harmonics it has. You seem to be treating it black and white, like if its electronic, there is some textbook worse case scenario of harmonics.




Note I said this : "electronic ballast/driver/power supply"

I am not saying this is never an issue, just very rare. Perhaps that case you were involved in was a perfect combination of "dirty" electronics and a high percentage of line to neutral loads, etc...? Maybe they do things differently there. Here in the states you would have lots of line to line loads, and you would have tons of neutral overhead because we essentially size the neutral as if the line to line loads were line to neutral loads (because generally we just provide a full neutral for three phase services).

A difference between there and here - such hotel here would likely have 480/277 service and separately derived systems for 120 volt loads. Other then any 277 volt lighting probably not much producing harmonics on the service neutral.

There service is likely 400/230, no separately derived systems. All those 120 volt loads that we have here are 230 volt and line to neutral there. Service neutral sees harmonics from all the 230 volt loads in the facility.

 

[Besoeker]

All those 120 volt loads that we have here .............

usually have a 3-phase origin?

 

[electrofelon]

usually have a 3-phase origin?

But if supplied through a delta -> wye transformer, they would not accumulate on the service neutral.

 

[Besoeker]

But if supplied through a delta -> wye transformer, they would not accumulate on the service neutral.

But the neutral of the WYE/Star?

 

[kwired]

usually have a 3-phase origin?

But if supplied through a delta -> wye transformer, they would not accumulate on the service neutral.

Yes.

But the neutral of the WYE/Star?

Possible there can be harmonic issues on the separately derived system(s). My point was the service neutral isn't seeing a majority of the harmonic current. Any 277 volt lighting may be about the only thing creating harmonics on the service neutral. If you had multiple 208/120 transformers for separate areas of the facility - you have thinned the effects down compared to if all those non linear loads were connected directly to the main supply.

 

[Besoeker]

Yes.

Possible there can be harmonic issues on the separately derived system(s). My point was the service neutral isn't seeing a majority of the harmonic current. Any 277 volt lighting may be about the only thing creating harmonics on the service neutral. If you had multiple 208/120 transformers for separate areas of the facility - you have thinned the effects down compared to if all those non linear loads were connected directly to the main supply.

In the particular case I mentioned the supply was 15MVA with about 3MW of line to neutral 230V leading edge phase-controlled dimmers. That's why the lighting division was involved. They have since developed a range of controllers that can be configured for either leading or trailing edge control which alleviates some of the problems thy have had in the past. I still had to do the calcs for their proposals. Once bitten, twice......etc.