Question on harmonics

[ArchieMedes]

Hi to all,

I would like to ask if abnormally high harmonics (triplens, 5th) on the secondary side of the transformer can be transferred back to the primary side of the transformer?
I know physically both the sides of the transformer are not connected but is there an exception like amount if current passing through primary or secondary, flux, etc that would allow the harmonics to be transferred?

Thanks

 

[T.M.Haja Sahib]

Yes. It can.

 

[ArchieMedes]

Thanks for the reply.

So does this means that harmonics can also be transferred the other way, from primary of the transformer to the secondary?

My purpose is I want to isolate where the harmonics is coming from. I want to know if it is coming from downstream loads or from other loads which traverse to the upstream.

Hope you can shed light to this matter. Thanks again.

 

[T.M.Haja Sahib]

The power utility has started to impose penalty to their high voltage customers for injecting harmonics into their grid. To mitigate such penalty, the consumers should install harmonic filtering equipment in their premises.
You may determine whether the harmonics come from the utility side by checking at the point of common coupling after switching off your harmonic creating loads.

 

[T.M.Haja Sahib]

A copy of letter received from the power utility for one of our telephone exchanges in connexion with harmonics mitigation is attached herewith for more clarification on the subject under discussion.

 

[Besoeker]

Thanks for the reply.

So does this means that harmonics can also be transferred the other way, from primary of the transformer to the secondary?

They can and often are in my experience.
We provide variable speed drive systems and often have to provide guarantees of the level of harmonic distortion they will produce.
Before and after tests give existing background distortion and the additional distortion when the new equipment is put into service.
In UK, the usual limit is the Electricity Association G5/4 technical document but I've seen sites where the limits were exceeded before our equipment was connected.
We have lots of electronic gizmos these days that take non-linear current, each not a lot but when added up from homes, offices and factories, the aggregate effect can be very significant.

 

[Besoeker]

Thanks for the reply.

So does this means that harmonics can also be transferred the other way, from primary of the transformer to the secondary?

My purpose is I want to isolate where the harmonics is coming from. I want to know if it is coming from downstream loads or from other loads which traverse to the upstream.

Hope you can shed light to this matter. Thanks again.

Some further thoughts.
Triple n harmonics generally arise from single phase equipments such as televisions, computers, dimmers.
The other common series is 6n?1 (5th, 7th, 11th, 13th etc) generally comes from three phase equipment and variable speed drives are one of the chief culprits.

 

[hardworkingstiff]

I thought I read once that a Delta/Wye transformer would keep the harmonics on the load side of the transformer. Is that accurate?

 

[Besoeker]

I thought I read once that a Delta/Wye transformer would keep the harmonics on the load side of the transformer. Is that accurate?

We sometimes use Ddyn0 transformers for 12-pulse drives. That keeps the harmonics down on the supply side, the lowest order being 11th harmonic but it is still there. The transformer doesn't change that.

 

[ArchieMedes]

So if transformers can transfer harmonics, it means that it would be difficult to isolate if the harmonics is generated by the transformer secondary/load side or from upstream of the transformer which is caused by other loads on the circuit connected on the same bus/circuit?

 

[T.M.Haja Sahib]

So if transformers can transfer harmonics, it means that it would be difficult to isolate if the harmonics is generated by the transformer secondary/load side or from upstream of the transformer which is caused by other loads on the circuit connected on the same bus/circuit?

Nothing is difficult to do if you have enough. money. So what is your problem?

 

[ActionDave]

Nothing is difficult to do if you have enough. money. So what is your problem?

Waiting for you to open your wallet, perhaps.

 

[Besoeker]

So if transformers can transfer harmonics, it means that it would be difficult to isolate if the harmonics is generated by the transformer secondary/load side or from upstream of the transformer which is caused by other loads on the circuit connected on the same bus/circuit?

You can filter them out or attenuate them with passive or active harmonic filters.
I've done both for large drive and UPS systems.
Active filters are expensive.
And the design of passive filters is not for the faint hearted.

 

[T.M.Haja Sahib]

Waiting for you to open your wallet, perhaps.

Iam ready to become his busIness partner.

 

[Besoeker]

Nothing is difficult to do if you have enough. money.

Except, according to you, operating a 90degC rated conductor at its 90degC rating.
In fact, not just difficult. Impossible.

 

[T.M.Haja Sahib]

I thought I read once that a Delta/Wye transformer would keep the harmonics on the load side of the transformer. Is that accurate?

Yes. It is accurate as far as triplen harmonics are concerned. These harmonics are absent on the primary side of the Delta/Wye transformer.

 

[T.M.Haja Sahib]

.. according to you, operating a 90degC rated conductor at its 90degC rating.

Sorry, I never stated it.

 

[T.M.Haja Sahib]

So if transformers can transfer harmonics.....

Power transformers do not just transfer harmonics; they themselves can be sources of harmonics. For example, in a star/delta or star/star transformer, if the neutral of the primary is not connected to the source neutral, the secondary voltage is distorted with triplen harmonics, even though there is no distortion of voltage on the primary side of the transformer.

 

[Besoeker]

Sorry, I never stated it.

No?

Nowhere XLPE cable or any 90C cable for that matter is designed to be operated at its 90C rating.

On triple n harmonics, I have evidence of those, third in particular, on the secondary side of an 11kV to 400V transformer at a pumping station. Since, at the time, the secondary wasn't loaded, they must have come from the primary.
It surprised me at the time but I've since seen it elsewhere.
The proliferation of single phase non-linear loads is the culprit.

 

[T.M.Haja Sahib]

No?

I never stated that 90 degree C rated power cable could be operated at 90 degree C.