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Anonymous Poster

Surge Arrestor Lead Length

11/17/2010 1:02 AM

We have a surge arrestor installed for 11/0.433kV dry type transformer at primary side. BIL of transformer is 75kV. Arrestor rated voltage is 12Kv, distribution class. We have used a 1.1Kv Voltage grade 1CX70 Sq.mm Aluminium cable from surge arrestor to earth and the length is roughly around 50mtrs. My question is this high lead length will pose problems as I heard that lead length should be kept short. How long lead lengths will have an affect on transformer?
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Bluestone
Guru

Join Date: Nov 2006
Location: OH USA
Posts: 549
Good Answers: 27
#1

Re: Surge Arrestor Lead Length

11/17/2010 9:58 AM

Your ground lead length may be a problem that can significantly reduce or eliminate the surge protective margin between the arrester discharge voltage and the transformer BIL. Surge current flowing through the line and ground leads causes an inductive voltage drop (V = L di/dt) that is added to the arrester discharge voltage (if the lead wires carry surge current and are electrically in parallel with the transformer). For straight lead wires the inductive reactance is approximately 0.4 microhenries/foot. If the lead wires are coiled, the reactance is much higher. The resulting protective margins can be determined by comparing the arrester / transformer insulation coordination curves from steep wave through power frequency.
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ashoktoshniwal
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Join Date: Aug 2006
Posts: 183
Good Answers: 2
#2
In reply to #1

Re: Surge Arrestor Lead Length

11/18/2010 1:47 AM

Are you sure that the inductive reactance of straight lead wires is 0.4 microhenry/foot?

Thanks and regards

Ashok Toshniwal
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bubbapebi
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Join Date: Apr 2007
Posts: 414
Good Answers: 19
#3
In reply to #2

Re: Surge Arrestor Lead Length

11/18/2010 3:29 AM

Here's a calculator.

http://www.consultrsr.com/resources/eis/induct5.htm

Both the length and the diameter of the conductor must be taken into account.
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ashoktoshniwal
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Join Date: Aug 2006
Posts: 183
Good Answers: 2
#4
In reply to #3

Re: Surge Arrestor Lead Length

11/20/2010 2:44 AM

Many thanksfor this useful info. Is there any similar calculator for calculating inductance when a coil is impressed with non-sinusoidal voltage wave? e.g. Choke for filtering after rectification using SCRs/Thyristors.

Thanks and regards

Ashok Toshniwal
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keirastone
Participant

Join Date: Dec 2010
Location: USA
Posts: 4
#5

Lead answer

12/15/2010 8:59 AM

Hi, i just read your forum about the Reactance conductor and i almost remember something that there is a good reactive power which gives it full throtole without having the affair with the non conductor.

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anneparker
Participant

Join Date: Apr 2011
Posts: 2
#6

Re: Surge Arrestor Lead Length

04/28/2011 4:53 AM

Hi, I think that calculation regarding inductance are just fine because it is meeting the requirement in the experiment.Seeing all the reading of voltage , lead choke, wave and frequency are leading in a good way.

lead answer @ leading way
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anneparker (1); ashoktoshniwal (2); Bluestone (1); bubbapebi (1); keirastone (1)

Previous in Forum: RVT - Residual Voltage Transformer   Next in Forum: Why to use class PS CT's for Differential Protection?

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