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sberbece (Electrical) (OP)
15 Oct 08 12:21
Hi all !

I have to review a tender bid submission for a 34.5 kV, 14 MVAr power factor correction capacitor bank, equipped with a shunt reactor tuned to 5th harmonic.
The 3 Ph symmetrical SC in the PCC is aprox. 20 kA/1sec.
The unit is comprised from a capacitor bank (spited unearthed star) in series with the shunt reactor.

The tender specification calls for 3 x single phase shunt reactor, but the Contractor tries to sell a 3 phase shunt reactor (made in Korea).

In my short experience, all HV shunt reactors I've seen in the HV substations are single phase.
I guess, the single phase reactors are easier to manufacture. They could present the advantage of a lower impact against the other reactors, in case of a single phase fault. Probably there are many other pro & cons regarding these two constructive solutions.

I would like to know if indeed 3 phase shunt reactors are used in similar applications like the one I've describe above.

Thank you!
 
Helpful Member!  scottf (Electrical)
15 Oct 08 17:51
sberbece-

Are these air-core reactors?

A 3-phase air-core reactor is simply 3 single phase units stacked...normally with the center-phase wound in the opposite direction for countering short-circuit forces.

3-phase stacked air-core reactors are typically slightly more expansive than single-phase arrangements due to the insulators normally needing to be strong on the bottom and middle phase.

There is typically little to no difference in the actual coils.

 
prc (Electrical)
16 Oct 08 0:21
I think what sberbece is referring  to is a series reactor and not shunt reactor ie reactor terminals connected in series.Shunt reactor is connected between line and earth for compensating the line cpacitance in EHV lines.Series reactor is used for limiting short circuit currents or filtering harmonics as in capacitor banks or converter/inverter stations.
scottf (Electrical)
16 Oct 08 15:51
prc-

You might be correct, but the comments on 3-phase versus single phase for air-core still hold for series reactors too.

 
prc (Electrical)
17 Oct 08 0:50
Scottf- Iwas not commenting or judging your input.I thought shunt reactors and series  reactors are entirely different species and I just want to be get assured.

One more point is whether these are oil filled  air cored units.In such a case, three phase unit is always better than single phase units.I agree that  nowadays trend is for air insulated, air cored,   series reactors.
scottf (Electrical)
17 Oct 08 15:31
prc-

My point on air-core reactors is basically, there really isn't a three-phase reactor, but rather different arrangements of single-phase reactors.

Oil-filled, being iron-core, are of course different.

 
prc (Electrical)
17 Oct 08 23:50
scottf, I beg to differ.I myself delivered three phase,oil filled, air cored series reactors.In such units there can be a core around the coil as a shield.Sometimes it will be aluminium.But inside winding will be without CRGO.
I agree with you -in air insulated,air cored series reactors there is not much difference between three phase or single phase.If the quality is good user need not worry.
sberbece (Electrical) (OP)
18 Oct 08 7:09
Thank you scottf and prc.

Prc, you right, I have mixed the terms, shunt reactor is not same thing as a serie reactor.

 
scottf (Electrical)
18 Oct 08 18:16
prc-

I've never heard of or seen an oil-filled air-core reactor. Why would it need to be oil-filled?

Up until a year ago, I worked for one of the main air-core reactor manufacturers...never ran into something like you describe. Who makes air-core oil-filled units?

Thanks
 
prc (Electrical)
20 Oct 08 1:56
scottf,Please see Chapter 7 section 7.15 of J&P Transformer Book titled Series Reactors.Oil filled series reactors is quite common and probably only solution for higher ratings.
scottf (Electrical)
20 Oct 08 14:34
prc-

Don't have the book. Is it online?

What kind of higher ratings do you mean?

Air core (non oil-filled) series reactors are commonly applied up to 765 kV.

The only time I see oil-filled reactors being used is in shunt applications over 115/138kV or where the inductances are of a level that iron-core designs are needed.

 
prc (Electrical)
21 Oct 08 6:35
scottf- J&P transformer Book is the Bible of transformer engineers,published from UK since 1925.I quoted from 12 th edition published in 1998.Latest edition 13th (2007)also contains similar information ie details of oil immersed coreless reactors and cast in concrete air cored reactors.There is the photographs of active part of a 30 MVA oil filled series reactor.

I used to supply even smaller oil filed series reactors.

765 KV series reactor winding in air?What about corona?Why series reactor is required at 765 kV?Can you post details.

When I say higher rated,higher voltage and MVa.In UK ,I understand they have very large series reactors-1000MVAR like.
scottf (Electrical)
21 Oct 08 8:26
prc-

Technology for air-core (open) reactors has come a long way since the old concrete designs. A 30 MVA air-core (open) reactor is quite common now. Single coil designs up to 300 MVA have been made.

The applications I was involved in at 765 kV were mainly cap bank installs and we supplied the in-rush reactors. Also supplied a few current limiting reactors at that level, as well as one set of very large load balance reactors for balancing/controlling loads on transmission lines.

As for corona, corona rings and special terminal connectors were used of course, but it wasn't an especially difficult issue.
 
KJLRSA (Electrical)
27 Oct 08 4:02
Hi sberbece

Sorry for replying to an old post, I was only able to login today.

We manufacture Harmonic filtering for the South African Market and almost all of our outdoor PFC applications are with 3 x single phase air core reactors that are stacked vertically. We generally keep the iron core reactors for indoor use as they are IP00 rated.

We offer air core 3phase reactors but in actual fact they are 3 x 1ph reactors with centre coil wound in opposite direction.

The one thing to watch out for with air core over iron core is that there must be no closed loop magnetic steel within the magnetic radius of the reactor - this includes rebar reinforcing in the plinth. This isnt a problem for iron core reactors.

 
model70man (Electrical)
12 Nov 08 11:46
Hello.  My company builds and sells metal enclosed power factor correction capacitor banks and metal enclosed harmonic filter banks, both up to 34.5 kV.

We design and build all of our harmonic filtering reactors.  We probably build 95% of them as 3-phase, dry type, iron core.  We build single phase iron core also if our customer so specifies.

We also build air core reactors, including those used for harmonic filtering, but prefer to go with dry type, iron core due to the concerns with the magnetic fields of air core reactors.  We build shunt reactors in oil-filled pad mount designs only.

This is a very interesting thread.  Thank you.

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