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Transformer Riddle No. 30 - Power Transformer Arrester Connection
On a substation 3 phases tranformer 34500 V / 480-277 V, I would to know what is better or recomended.

On MV side, to connect the lines first to surge arrestors and then a jumper to bushings or connect directly to the bushings and then with a jumper to the surge arrestor.

Author : Ronald Vincenti - From: Costa Rica, Latin America
Wed, September 16th, 2009 - 18:07
In connection way of surge-arrester, the term of distance to protected subject is important. Generally mention has already been made of the desirability of connecting the surge arrester as close as possible to the equipment it is intended to protect. It is also important that the neutral end should have a low resistance connection to earth of adequate cross-sectional area. At currents of 10 kA or more, any resistance in these connections will mean a significant additional voltage is seen at the transformer terminals over and above the nominal protection level of the arrester. Below figure shows a typical installation adjacent the HV terminal of a substation transformer. The lengths L, a1 and a2 must be kept as short as possible.
In your concerned subjects, each chosen connection which aid you to obtaining of shortest and straightest connection ( for decreasing of surge impedance) is more desirable.

Author : Hamid - From: Iran
Wed, October 7th, 2009 - 15:24
If you want to protect the equipment then the surge arrestor should be connected to the line and then by a jumper to bushing . The arrestor should be placed as close as to the transformer . In few cases the arrestor is mounted on a metallic support fixed onto the arrestor .
The only care to be taken in is to see that when the arrestor fails ( blasts ) , the  fragmented pieces of the arrestor should not hit the bushing ( if you are not using blast proof type arrestor ) which may otherwise cause more damage . 
Author : R K Mohapatra - From: India
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