In our 135 MW power plant we have got 220 kV switch yard with line 1 & 2 connected to a common bus and 2 nos of Generator transformers 4o MVA, 11/220 kV. We are exporting 7 MW power to Grid from our plant. Our line 1 & 2 are connected to substation at a distance of 5.2 KM. Our line 1 length is 5.2 mtrs and line 2 length is 7 kM as it was taken in a different route. During power export power flow is 6 MW in Line 1 and 1 MW in Line 2. We tried to balance this so many times but we could not. I think that the difference of power flow is due to length difference of the line. I e as the length increases line resistance also will increase. Line with lower length and lower resistance is carrying more power flow and the line which is of more length and resistance compared to other is carrying less power flow . Can any one clarify this point to me.

 

Sriram…

1) Are both lines similar regarding their electrical and construction parameters?

2) For MW values you stated, what are comparable kVAr values?

Regards, Phil Corso

 

T.Sriram,

Some additional clarification, please, and another question. You wrote:

> Our line 1 & 2 are connected to substation at a distance of 5.2 KM. Our line 1 length is 5.2 <b>mtrs</b>
> and line 2 length is 7 <b>kM</b> as it was taken in a different route.

You wrote Lines 1 & -2 are connected to a (the same?) substation, at a distance of 5.2 <b>KM</b>.

What is the length of Line 1: 5.2 mtrs or 5.2 KM?

In this substation, are both lines connected to the same transformer, or different transformers?

If the two lines are each connected to their own (separate) transformer, is the rating (KVA, voltage ratio) of each transformer the same?

If the two lines are each connected to their own (separate) transformer, do the transformers supply different "districts" or the same district?

Are there any power correction capacitors or other VAr control/reduction equipment in the substation?

And, last, as a matter of curiosity, why is it necessary or important to balance the exported power on the two lines?

Thanks!

 

Sriram... the line lengths you cited indicate that these are “short” transmission lines.

Thus, if their parameters are identical, then, total current and branch currents are inversely proportional to their respective impedances, hence their lengths! Thus,

It : Ia : Ib = (1/Lt) : (1/La) : (1/Lb)

Providing only total and line MW data is some help, but additional info is necessary! Please provide individual line-currents, sending-voltage, and receiving-voltage?

Phil

 

Sriram... additional info, Lt should have been identified as Le, representing the "equivalent" Line-Length, not the sum of both line lengths!

Phil

 

T.Sriram,

I believe what we are trying to say here is that the real power flow in the two lines is a function of the reactance of the two lines, the configuration of the substation, and the loads the substation is supplying. It's not simply about the difference in resistance of the two lines, but about the reactance of the lines and the load(s) at the substation.

It's not really clear exactly how the power generating side is configured, nor how the substation is configured.

That's why you've been asked to provide more information, including sending- and receiving voltages, etc.

It's very common that answers to seemingly simple questions like this are more complicated than anticipated. When dealing with alternating current circuits, the answer can be very complicated, indeed.