Power Transformer

The 141kv tap, will give you 7303 volts secondary.

The 144kv tap will give you 7150 volts secondary.

It is up to you whether you want the downstream system voltage to be a little lower, or a little higher.

I would vote for a little higher..

I know you are correct with the higher tap setting, lower voltage ratio, but how did you calculate the voltages? Each tap would have a different ratio.

Assuming you are correct, I agree go with the slight overvoltage for the no-load situation, since the load will drag it down.

High side system voltage = 143000volts

143000/7200= 19.86:1 ratio

Tap X= 141000/7200= 19.58:1 ratio

Tap Y= 144000/7200= 20:1 ratio

143000/20= 7150volts

143000/19.58=7303 volts

This is assuming the high side voltage is 143kv

Agree: "143000/7200= 19.86:1 ratio" is the desired ratio with the grid supply at 143000V and a desired output of 7200

How can you assume an output of 7200 on Tap X an Y with the selections of 141, and 144

With the information provided, All I can calculate is the ratio of the current selection.

Unless we have the ratios of the other taps, I think we are assuming the Transformer was ment to deliver exactly 7200V, Most transformers are sold with a range of outputs, and inputs, not a single output voltage

This transformer has taps for voltage 144 kv,141 kv, 138 kv, 134 kv, and 131 kv

This is a typical high side power transformer tap changer, of which the secondary taps are not adjustable. The 7200Volts is what has been specified as desired output voltage over a range of input voltages as shown above..

I don`t believe I`ve ever seen a low side tap changer on a large distribution transformer (say 4MVA) and up, but I would be interested in learning..

OK, Assuming it was ordered to meet exactly 7200 V output

I found one spec that said:

" The high voltage will be provided with a no-load tap changer with full capacity taps, two 2½% below and two 2 ½% above rated voltage."

To calculate this the next tap Up (141) would reduce the voltage by .025:

• present reading 7450 - 186.5 = 7264V

and the last tap of (144) would be

• 7263.75 - 181.6 = 7082 V

Without the exact specs of the new transformer, we are just guessing, however, both our calculations agree the 141 tap is the best selection.

I agree to Vote a little Higher. Question: does loading change either IP or OP. & Is the Actual IP Volts, Slightly Higher or Slightly Lower Than Posted on Label. Suggest if the Actual IP Volts is 145, than using the 144 tap would give you the desired 7200 Volts on Secondary. Chears.

At the 143kv tap it will give you 7300 volts and some change, as your facility loads up you will likely see this come down to 7275 / 7250, of which will be close to the voltage you are looking for..

If the utility is feeding you 145kv, and your tap is at 145kv your secondary voltage will be exactly 7200V.

Basically what you are doing when you increase voltage taps is adding turns to transformer, and when you decrease you are removing turns.

Dear

To get the correct voltage at secondary side we need to see the transformation ratio

= V1/V2 i.e 143000/7200 = 19.86 it comes

Now your requirement is 7200V and

At present you are getting 7450V .. on 138KV here your transfomermation ratio showing 18.52 ( There is something wrong )

So the difference of voltage is 250V high.

As you mention the tap setting is

1. 144KV
2. 141KV
3. 138KV
4. 131KV

So kindly check the manufacture catlogue and with

1 Transformeration ratio

2. Transformer efficency

3. Connected load & load power factor

then only you can get correct tap setting

Hope the explanation will help you

Now lets start from the beginning.. If the tap is set at 138KV, and the secondary is 7450V, and the incoming line voltage is 143kv then you have:

Incoming line actual voltage 143000/7450 (actual secondary voltage)= 19.19:1 ratio.. If you look at the numbers below 19.19 almost exactly matches the 138kv tap setting ratio. I do not see what the problem is??

144000/7200= 20:1 ratio

141000/7200=19.58:1

138000/7200=19.16:1

134000/7200=18.61:1

131000/7200=18.19:1

Hi,

From your details there are 5 taps. But Please clarify whther your system Voltage on HV side is 143 kV & 7.2 kV in the LV Side.

If so, check with OLTC name plate. There shall be a normal tap at which the HV Volatge will be 143 kV & LV side Shall be 7.2 kV.

Based on the details you furinshed I feel 141 KV shall be normal tap.

N.Suresh