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bashir01219
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OLTC_11KV & OLTC_440V

08/03/2020 1:29 AM

We have a central substation where we step down voltage from 33KV to 11KV and distribute at different plant. We have OLTC with the 33 to 11 substation.

At plant location we further step down voltage from 11KV to 440V, for end user. Should we go with another OLTC for this?? If anyone have similar situation pls. help.

Which one is better OLTC at both end or main end ? and why ??

Thanking in advance.

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SolarEagle
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#1

Re: OLTC_11KV & OLTC_440V

08/03/2020 2:00 AM

Why do you need to change taps?

https://en.wikipedia.org/wiki/Tap_changer

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bashir01219
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#2
In reply to #1

Re: OLTC_11KV & OLTC_440V

08/03/2020 2:19 AM

for stabilize the line voltage, generally we install OLTC.

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Stef
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#6
In reply to #2

Re: OLTC_11KV & OLTC_440V

08/04/2020 5:34 AM

From my experience the OLTC is always on the transformers so in your case 33/11KV with the highest voltage because the currents being switched are smaller and the reactors used for split taps as the changer operates are smaller.

When more than one tap changer is used on the supply system the one closest to the generation does the work and any subsequent tap changers are under the control of supervisory systems and their need to change is governed external to their AVR.

Any boost for the droop of the lower voltage 11KV to 440v can be handled by stepping the off load changing of the tapping switch. As said elsewhere it is possible with two tap changers in series they can end up chasing their tails and doing more tap changes than are needed. Remember that with two tap changers the maintenance required is at least doubled

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PWSlack
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#3

Re: OLTC_11KV & OLTC_440V

08/03/2020 5:10 AM

It depends upon the tolerance in voltage at various places along the network.

The forum is not in any position to assess this, as it doesn't have access to real-time data on the existing network nor the design information for the additional equipment.

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bashir01219
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#4
In reply to #3

Re: OLTC_11KV & OLTC_440V

08/03/2020 6:57 AM

it's a new project and in design phase (6 MW substation)

Loads are mainly Pharmaceuticals machinery, and chiller/compressor/HVAC etc.

We are taking power from national grid and secondary source is DG.

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PeterT
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#5

Re: OLTC_11KV & OLTC_440V

08/03/2020 9:55 AM

You pretty much never see two OLTCs in series like you describe. There is too much trouble with trying to coordinate their settings so that the second one won't be trying to compensate for the changes the first one is making, or else the second one won't actually have to operate much because the first is doing its job well.

Your first job is to determine where the cause of the voltage variation comes from. If it is from the Utility (source) side, then the 33kV transformer is the place to put it. Then the whole 11kV system and below will see the benefit of the compensation.

If the 440V load is the main source of voltage variation, then you may be best to have the OLTC at that location. However, this won't help any other loads that would be on the 11kV system. So you have to decide what fits your need best.

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bashir01219
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#7
In reply to #5

Re: OLTC_11KV & OLTC_440V

08/04/2020 7:04 AM

Thanks.

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SolarEagle
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#8
In reply to #7

Re: OLTC_11KV & OLTC_440V

08/09/2020 5:47 PM

I think we would need a wiring diagram of the distribution network, and approximate loads, to make a recommendation...then a typical scenario of what would trigger the need for a tap change, in all anticipated circumstances, shedding and increasing electric supply to either the system or specific feeds...If the typical demand increase is triggered by a system wide demand, or by certain branches, then the answer could be either or both, depends on the branch demand percentage of the total load, if a branch demand exceeds a large percentage of total demand then the tap would be best placed on the main distribution, if the load increase is triggered by a small branch that is a small percentage of the total demand, then the tap is best placed at the branch feed...If both scenarios are anticipated, and the branch feed is a small portion of the total load(ie: will not trigger a main tap change) then both taps would be required...

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bashir01219
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#9
In reply to #8

Re: OLTC_11KV & OLTC_440V

08/11/2020 3:08 AM

Thanks.

It's helped a lot.

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nesubra
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#10

Re: OLTC_11KV & OLTC_440V

12/03/2020 4:58 AM

Since OLTC is already there it will take care of any variation in incoming voltage which is 33 KV.So 11KV side will have a stable voltage and hence you dont need a OLTC on 11/440 Transformer .

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bashir01219 (4); nesubra (1); PeterT (1); PWSlack (1); SolarEagle (2); Stef (1)

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