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Topic Title: Distribution Network
Topic Summary: 22KV or 11KV
Created On: 06 August 2009 05:20 AM
Status: Read Only
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 06 August 2009 05:20 AM
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Badshah

Posts: 38
Joined: 22 July 2009

Which one is best..22KV or 11KV....presently our network is 11KV network..we are opting for 22KV. what are the advantages and disadvantages going for 22KV
 06 August 2009 08:19 AM
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Al

Posts: 60
Joined: 02 February 2009

You say you are already going for 22kV so someone has made a decision? what did they say?

Al
 06 August 2009 08:28 AM
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ArthurHall

Posts: 736
Joined: 25 July 2008

I seem to remember that there is a 'law' which states that the most efficient voltage for transmission of power is 1Kv per mile.
 06 August 2009 08:43 AM
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Al

Posts: 60
Joined: 02 February 2009

Originally posted by: ArthurHall

I seem to remember that there is a 'law' which states that the most efficient voltage for transmission of power is 1Kv per mile.


So load does not come into it?
I assume the lenghth of Badshah site has not changed?
come on.
 06 August 2009 10:40 AM
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Badshah

Posts: 38
Joined: 22 July 2009

Higher officials in our company had already made decision and they are working on 22 KV Distribution Network. We are going to have both 11KV and 22KV Distribution network. I dont know the reason..Just want to know what diffrence it will make?
 06 August 2009 11:34 AM
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broadgage

Posts: 1306
Joined: 07 August 2007

A 22 KV overhead line will be more expensive to erect since larger insularors, and possibly longer and stronger poles will be required.
Greater clearences will be required, though not by that much.
If buried cables are to be used, they will be more expensive, though the cost of labour and trenching should be similar.

Small transformers, as might be used for individual customers, will probably be more expensive for 22KV input than for 11KV input.

Very large electric motors are available to work directly on 11KV, thereby saving the cost of a transformer and the losses therein.
22KV motors are much less available.

On the other hand, a 22KV line can carry twice the power of an 11KV line, presuming the same wire size, and it wont cost twice as much.
If capacity is limited by voltage drop, rather than wire temperature, then the 22KV line can carry four times the power.

In many parts of the world, power demand is increasing rapidly.
In such cases, whenever doubt exists as to what voltage to use, I would almost always suggest the higher voltage, even if more costly in the first place, it should be more future proof.
 06 August 2009 01:51 PM
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McN41R

Posts: 40
Joined: 09 August 2006

Generally as broadgage said. The only thing I would add is to consider what voltages will be used and where.

I you look at the voltages that you will use and how to best use the voltages that you need without having unecessary steps. For example if you were using 400V (general power), 11kV (distribution, motor control centres or district cooling etc) and connecting to the authority at 132kV then you would be adding voltage steps, equipment and protection where it would not really be required.

Some authorities dont like customers transforming down from 22kV to 400V in a single step and hence 11KV was very popular. I see much more acceptance of this now.
 06 August 2009 03:45 PM
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pbarnfather

Posts: 33
Joined: 10 July 2008

At a previous utility we had both 22kV and 11kV networks.

In urban areas, 22kV did not seem to offer any advantage. Equipment (notably switchgear and cable joints) was larger and more expensive. Industrial loads of >5MVA were unusual, so the greater load carrying capacity did not come into it. Even though it was possible in theory to connect many more customers to a 22kV feeder, we did not do this in practice because long, complicated feeders do not help you meet security of supply targets! As a result, much of the extra capacity of 22kV systems went under utilised.

I belive that much of the urban 22kV system in this utility was installed when larger (i.e 10MVA+) industrial loads were more commonplace and 6kV was preferred in low-load urban areas. When I was there, no new 22kV systems were being commissioned and many were being converted to 11kV operation. Also, industrial customers did not generally want 22kV connections; they preferred something they were familiar with (3,6 or 11kV).

In rural areas, the slightly higher cost of 22kV overhead lines and equipment was offset by the reduced number of primary substations required. Therefore in a purely rural setting, 22kV seemed preferable. Transforming 22kV to 400V in one step was normal practice.

Given the comparatively low price of modern 11kV equipment, and the fact that 33/11kV primary substations are rather smaller and cheaper than they used to be, it seems that 11/12/15kV is currently regarded as optimum for many utilities.

It would be interesting to hear why 22kV has been chosen in this case. Presumably you have either large industrial loads or long rural networks (or a combination of both).
 07 August 2009 09:07 AM
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Badshah

Posts: 38
Joined: 22 July 2009

Our Distribution network is in urban areas but with very high density residential complexes, towers.
In 11KV system, RMU is being operated manually. Is it possible to have a ring system in 22KV and to do operation manually in 22KV system?
 07 August 2009 10:50 AM
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pbarnfather

Posts: 33
Joined: 10 July 2008

A 22kV system can be configured and operated in exactly the same way as an 11kV system. Some utilities class 22kV as a "transmission" voltage (and design the system accordingly), but it's also quite possible to do conventional distribution at 22kV.

So yes, open rings with manual RMUs can be used at 22kV. Functionally they're exactly the same as 11kV units, only bigger (and more expensive).

Possibly the advantage in your case is the ability to supply twice the load off a single distribution feeder (typically ~10MVA for 22kV vs. ~5MVA at 11kV, depending on your equipment specification and planning policy). If there is very limited space for primary substations and distribution cable routes, then it's possible that 22kV is more cost-effective than 11kV.

Bear in mind that, if you do put twice the number of customers on an open ring, you will have twice the number of customers off supply for a typical medium-voltage fault...

I'm sure someone will have looked at the costs and benefits very carefully; such decisions are not made lightly because conversion of a network from 11kV to 22kV can be expensive!
 09 August 2009 06:18 AM
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Badshah

Posts: 38
Joined: 22 July 2009

We are not converting 11KV to 22KV. New nerworks planned are to be configured in 22KV.
 09 August 2009 02:45 PM
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sfchew

Posts: 589
Joined: 10 December 2002

The choice of the voltage for distribution has to be made on very practical approach. The capacity for transfer is obviously of major concern. 22KV system will be more costly than 11KV but the investment is necessary if the future anticipated loads can justify the choice of voltage. 22KV can deliver twice as much power as 11KV using the same amount of conductor sizes.

So the decision is easy to make.

Regards
Chris Chew
 10 August 2009 01:09 PM
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musashah

Posts: 15
Joined: 30 March 2009

Hi,
I've worked with two different utilities in two different parts of the world, and both were using 11kV as well as 22kV systems.
The reason of choosing a 22kV system instead of 11kV is the higher load density at single intake points like for industries, Residential / Comercial high rise buildings, Residential complex, Big retailers, etc. 22kV systems is operated, maintained re-furbished similar to 11kV systems but it offers benefits of low line losses, and much higher loads can be distributed with fewer cable in trenches, which means that applicable cable de-rating factors are also reduced. Moreover, RMUs, Transformers, cables, and all other equipment rated 24kV is readily available in bulk quantities.
At both utilities the idea was introduced to distribute at 33kV instead of 22kV, it is approved at one of them for all loads higher than 5MVA. But with 33kV systems usually the switchgear is GIS (due to size constraints in city areas) which is quite costly. I believe it is cost involved & load density which compelled utilities to use 22kV instead of 33kV systems.
Hope this clears the reaosn of choosing 22kV systems.

regards,
Musa

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Musa Shah
IET » Energy » Distribution Network

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