200 % Neutral

[Alwayslearningelec]

I read an article/blog at lunch and it mentioned 800A feed.... 2 sets of 4" with 5-600mcm & 1- 1/0 ground and a 200% neutral. It did not state the size of the neutral. How is this calculatedor is one of the (5)600mcm conductors the neutral? Thanks

 

[maghazadeh]

I read an article/blog at lunch and it mentioned 800A feed.... 2 sets of 4" with 5-600mcm & 1- 1/0 ground and a 200% neutral. It did not state the size of the neutral. How is this calculatedor is one of the (5)600mcm conductors the neutral? Thanks

2 of the (5) 600 MCM are neutral, very common for harmonic effect reduction on the neutral conductor. it probably did not say (and a 200% neutral), it say (with or for 200% neutral).

 

[Alwayslearningelec]

2 of the (5) 600 MCM are neutral, very common for harmonic effect reduction on the neutral conductor. it probably did not say (and a 200% neutral), it say (with or for 200% neutral).

Thanks!!!

 

[bob]

When noted, 100% neutral means it is the same as the phase conductor.
Obviously 200% is twice the size of the phase conductor.

 

[Besoeker]

That third harmonic can be a pain in the proverbial for the neutral.
Been there.

 

[bob]

Besoeker
What is the higest % reading you have seen on the neutral?

 

[Besoeker]

Besoeker
What is the higest % reading you have seen on the neutral?

Compared to line current, about 160%
Stuff overloaded.

It was a serious practical issue in one of the world's few or only seven star hotel.
A very prestigious project for one of our other divisions.
It irks me a bit that I was called to come up with solutions at the eleventh hour when, had the system design had crossed my desk at the outset, we could have come up with a more elegant solution.
Fire fighting.

Anyway, flight booked and the limo, complete with uniformed driver came to pick me up in the early morning.
Not really my style but I indulged that bit of VIP treatment.

On site and presented a few options.

In the event, third harmonic filters in the neutral were fitted. It wasn't my preferred solution. And still isn't. But it suited the bean counters.
I'm still not comfortable with it.

 

[ron]

Compared to line current, about 160%
Stuff overloaded.

It was a serious practical issue in one of the world's few or only seven star hotel.
A very prestigious project for one of our other divisions.
It irks me a bit that I was called to come up with solutions at the eleventh hour when, had the system design had crossed my desk at the outset, we could have come up with a more elegant solution.
Fire fighting.

Anyway, flight booked and the limo, complete with uniformed driver came to pick me up in the early morning.
Not really my style but I indulged that bit of VIP treatment.

On site and presented a few options.

In the event, third harmonic filters in the neutral were fitted. It wasn't my preferred solution. And still isn't. But it suited the bean counters.
I'm still not comfortable with it.

When did this occur, recently?

What do you suspect were the large non-linear loads causing the condition?

I generally don't size neutrals larger than the phase conductor anymore, because many offenders have become more sinusoidal to be sold in Europe and they use the same design here.

 

[Besoeker]

When did this occur, recently?

Maybe depends on what you call recently. It was about seven or eight years ago.

What do you suspect were the large non-linear loads causing the condition?

Primarily controlled lighting. Dimmers. About 3MW worth of the little blighters. None a problem itself but in aggregate......

Here's one of the harmonic spectrum analyses I did for a single channel. It was based on actual measurements with a digital scope and the data dropped into a spreadsheet. The harmonic spectrum was calculated from that.

It illustrates the problem quite well. The fundamental component is about 4.2A and the third harmonic (Hn₃) about 2.2A or maybe a shade more.
The system is three phase. With same load on each of the three phases, the fundamental components cancel. But the Hn₃components add arithmetically.
So the neutral current from this component alone is 6.6A. Or over one and a half times the current in each phase.

I generally don't size neutrals larger than the phase conductor anymore, because many offenders have become more sinusoidal to be sold in Europe and they use the same design here.

The installation I mentioned above was in the Middle East.
As you are probably aware, my main area of activity is in the variable speed drives field.
The usual customer specification requires compliance with the Electricity Association's G5/4 which is, to a significant extent, concerned with supply voltage distortion at the point of common coupling. (Sounds a bit rude but I'm sure you know what I mean.)

There is a "harmonised" IEC standard (IEC61000) for harmonics but, from memory, it is applicable to equipment that draws between 16A and 75A which would exclude your average dimmer, CFL. wall warts etc. In fact anything that draws less than about 3.7kW at nominal voltage.
It may have been updated since, but I'm aware that it was current (no pun intended) in 2005.

 

[ron]

The usual customer specification requires compliance with the Electricity Association's G5/4 which is, to a significant extent, concerned with supply voltage distortion at the point of common coupling. (Sounds a bit rude but I'm sure you know what I mean.)

There is a "harmonised" IEC standard (IEC61000) for harmonics but, from memory, it is applicable to equipment that draws between 16A and 75A which would exclude your average dimmer, CFL. wall warts etc. In fact anything that draws less than about 3.7kW at nominal voltage.
It may have been updated since, but I'm aware that it was current (no pun intended) in 2005.

IEEE 519 has limits at the PCC (utility meter) for both voltage and current. This leaves lots of possibility for interaction between equipment before it raises a flag at the PCC. My understanding was that European standards had limits per piece of equipment, which is why we were seeing improvement overall here at the PCC per IEEE 519. I'm not sure about the power limits for that regulation, but I guess it makes sense.

 

[Besoeker]

IMy understanding was that European standards had limits per piece of equipment, which is why we were seeing improvement overall here at the PCC per IEEE 519. I'm not sure about the power limits for that regulation, but I guess it makes sense.

Yes, I was aware if IEEE 519 but I don't have a copy.
The European IEC 61000 does give limits for individual pieces of kit but for a limited range of ratings.

 

[Besoeker]

Yes, I was aware if IEEE 519 but I don't have a copy.
The European IEC 61000 does give limits for individual pieces of kit but for a limited range of ratings.

I suppose the bottom line, regardless of directives, standards, and regulations, is whether a particular installation has or had problems.
The one I cited did.
It could have resulted in serious consequences.
I don't know whether any applicable codes were breached.
Stuff that could have been foreseen at the design stage was not taken into account. The supply of equipment was just that and that's what our division provided. Product. Not system design. That ought to have been undertaken by the design consultants.
It was evident, in retrospect, that the consultant(s) on the electrical design had not come across this potential issue previously and didn't take it into account.
Should they have?
I think yes. But you don't know what you don't know. It clearly wasn't perceived as an issue by those who should have been doing the perceiving.
But, not surprisingly, it resulted in the blame game.

I'd have much preferred to walk away at that point. I'd provided possible solutions. Done huge amounts of number crunching. Provided cost estimates.
Job done. Support for another division. And no revenue for my time.

Didn't quite work out that way.