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Topic Title: 11KV/400V transformer
Topic Summary: why is the on-load tap changer not applied to the MV/LV transformer for voltage regulation?
Created On: 14 October 2012 10:42 PM
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 14 October 2012 10:42 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Hello everyone,

As we all know, tap changer is the most common way for voltage regulation on the power system and it is usually applied to the HV/MV transformer. My question is that why the on-load tap changer not applied to the MV/LV transformer for voltage regulation?
 14 October 2012 10:55 PM
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dlane

Posts: 690
Joined: 28 September 2007

Cost and neccessity.

An onload tapchanger is a very expensive device and also in need of regular maintenance. To install then in MV/LV transformers would make them much more expensive.

In a well laid out network the tapchanging required due to load variation can be done at a higher voltage level and the voltage levels at LV set via a manual off-load tapchanger.

Kind regards

Donald Lane
 14 October 2012 11:04 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Thanks for your reply.

I agree with you. Now the tap changer is not necessary for the LV network, as the traditional LV loads are generally small and operating in a regular way. In the future, as some volatile loads such as EVs are connected, maybe adopting tap changer on the MV/LV transformer is one way to control the voltage.
 15 October 2012 08:58 PM
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cookers

Posts: 205
Joined: 10 February 2012

Such distribution power transformers that give a regulated output are available, they are usually sold as "Voltage Regulators" or "Voltage Stabilisers".

Most of the world has to cope with an unstable and varying voltage supply!
 17 October 2012 02:31 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

I think you are right. Devices such as "Voltage Regulators" or "Voltage Stabilizers" are usually used for voltage regulation.

I think in the UK, most these devices are located in 11KV or higher voltage networks. In 400V LV networks, generally there is no voltage control devices. Is this right?
 17 October 2012 04:50 PM
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cookers

Posts: 205
Joined: 10 February 2012

you are correct.

However rather dubious commercial claims are being made about how such "regulated output" power transformers might improve energy efficiency. The Carbon Trust have tried to dispel the myths surrounding such things.

http://www.carbontrust.com/media/77191/ctg045.pdf
 17 October 2012 10:22 PM
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alancapon

Posts: 5810
Joined: 27 December 2005

Originally posted by: SWORDLOVER
. . . Now the tap changer is not necessary for the LV network, as the traditional LV loads are generally small and operating in a regular way. . .

That is not quite correct. An off-load tap changer is required for the LV network to compensate for the voltage applied to the transformer's primary terminals, depending on its position in the network. Additional load on the LV side may also require a different tap, to set the LV within statutory limits. As Donald said, as on-load tap changers are generally expensive, the "day to day" regulation is carried out at a higher voltage level where fewer devices are required.

In long LV rural overhead networks, regulators are employed at LV, generally to accout for the voltage drop between the supplying substation and that point, such that additional properties may still receive statutory voltage. These will generally be 1:1 transformers with a few taps and a voltage control relay of some sort.

Where single-phase loads are particularly unbalanced, a "balancer" may be employed. Unlike the regulator, the balancer is a purely wound device with no moving parts. It is a cross-connected star - zig zag transformer and "relocates" the system neutral, such that all phase to neutral voltages are the same.

Regards,

Alan.
 17 October 2012 11:39 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Thanks for your explaination!

The regulator, used on the rural LV network and the "balancer" are both new to me. So I want to know whether the employment of these devices is very common in the UK. I think both the voltage drop and voltage unbalance can be resolved by using thicker conductors, which may be cheaper than the adoption of transformer based "regulators" and "balancers". I am very interested in the "balancer" mentioned by you, and could you please recommended some public literatures to me about the "balancer"?

Best Wishes!
 18 October 2012 12:32 AM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Originally posted by: cookers

you are correct.



However rather dubious commercial claims are being made about how such "regulated output" power transformers might improve energy efficiency. The Carbon Trust have tried to dispel the myths surrounding such things.



http://www.carbontrust.com/media/77191/ctg045.pdf


I just read the document introduced by you. I think in the future, most loads would be power electronic interfaced, which makes the load become supplying voltage independent. As a result, the voltage management equipments would be less effective in energy saving and power quality improvement.

Edited: 18 October 2012 at 11:00 AM by SWORDLOVER
 21 October 2012 09:25 PM
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ArthurHall

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Joined: 25 July 2008

As Alan said above regulators and balancers were mainly used on long LV overhead lines. In my experiance they were used mainly in the fiftys and sixtys when electrical demand was growing quickly. Their main advantage was that they were a quick fix until the network could be reinforced. I havent heard of them being fitted in the last thirty odd years. Although some remain in service>
In any case the number of long LV OHL's tend to be on the decrease.
 04 March 2013 09:38 PM
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SWORDLOVER

Posts: 23
Joined: 30 September 2010

Originally posted by: ArthurHall

As Alan said above regulators and balancers were mainly used on long LV overhead lines. In my experiance they were used mainly in the fiftys and sixtys when electrical demand was growing quickly. Their main advantage was that they were a quick fix until the network could be reinforced. I havent heard of them being fitted in the last thirty odd years. Although some remain in service>

In any case the number of long LV OHL's tend to be on the decrease.


In the future smart grid, there would be many large loads such as electric vehicles and heat pumps. They would significantly change the load profile; Even if the low voltage radial feeder is short, large voltage drops may happen. Do you think the "balancer" might be reused for voltage regulation in the future to avoid the network reinforcement.
 05 March 2013 04:27 PM
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ArthurHall

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Joined: 25 July 2008

The static balancer and a voltage regulator are different beasts. The balancer is connected at the remote end of a line, it consists of a zig-zag winding connected so that higher voltage phases pull up the voltage of lower voltage phases. It as its name sugests balances the voltages.
A voltage regulator is normaly fitted about half way along a line and is a buck or boost device, it has a moving coil that increases or decreases the voltage in a linear manner, no steps.
I have not heard of either of these units being fitted in recent years.
I would expect that if voltage regulation is required due to embeded generation it would be done using electronics such as an SVC or a SATCOM unit. In practice the G59 regulations are strict enough that embeded generation does not give too many problems.
IET » Energy » 11KV/400V transformer

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