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Join Date: Feb 2010
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EHT Transmission Line Transposition

02/17/2010 4:29 AM

In the EHt transmission line why transposition is done? Is the transposition depends on distance ?or depends on voltage. Is there any clear relation between transposition distance & voltage level?? Plz provide the reference book too.

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Guru
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#1

Re: Transposition

02/17/2010 5:56 AM

Transposition is used to ensure that the phase-to-phase and phase-to-ground capacitance of each of the phases is equal. It is not generally needed or used over short distances.

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#2
In reply to #1

Re: Transposition

02/17/2010 6:03 AM

Short distance means what like 80 Km or less ??

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Guru
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#3
In reply to #2

Re: Transposition

02/17/2010 6:08 AM

Guess so - don't know if there are any hard-and-fast rules. Transposition was used in the early days in the UK, but it was later evaluated and found to be unnecessary and is no longer used.

It is used in countries where the transmission lines may be 100's of km long.

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#4

Re: EHT Transmission Line Transposition

02/18/2010 12:37 AM

Transposition done to eliminate the Ferranti effect. Due to line to ground capacitances, some times receiving end voltage is more than sending end voltage and this is called Ferranti effect. For short line, < 60Km we can neglect this effect. 60 to 150 KM is medium and >150KM is long transmission line.

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#5

Re: EHT Transmission Line Transposition

02/28/2010 7:59 PM

Due to different spacing of the conductor with respect to ground and other conductors, the reactance of each phases are different. This causes unbalance voltage at the end of the line. Therefore the line must be transposed at two intervals dividing the line into 3 equal sections, where each conductor occupys a position for 1/3...

It depends on the tower geometry. For example an equal spaced delta configuration does not require transposition while a horizontal one does.

You would have to work out the need for tranpostion by calculating unbalance without transposition. If it is less than you limits, then no need for transposition. Got nothing to do with Ferranti effect.

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