Connecting leads to substation transformer

[podobing]

When installing an oil filled 10 MVA transformer - 69 kV to 12.47 kV with lightning (surge) arrestors mounted near to the bushings, should the incoming (outgoing) leads be:
a) connected directly to the bushings with a tap going to the arrestor;
b) connected to the arrestor and continue through (no splice)to the bushing;
c) either a or b - does not matter.

I understand that electrically they should operate the same, but is there a mechanical reason to connect the leads (500 kcmil bare copper) directly to the bushing? To me, the bushing just looks a lot more mechanically substantial than the arrestor does. I am worried abot a short circuit or icing or ?? See attached photo - hopefully I was successful in attaching it. The 69 kV arrangement is the same.
Regards,
Dave

 

[collies99]

Both should hav

 

[collies99]

Both should have side loading specs and as long as they are installed within their mechanical limits they are ok.

Point to consider is your method "a" which would make the live parts as far away from the grounded parts, which can also come into play someday for limits of approach issues with vehicles ...

On a side note, the LA require their own ground conductor to carry the current when operating and not the tank, this can be one continuous for the three.

 

[davidbeach]

B is better. If you look at just the steady state, then either would be equivalent, but if you look at transient propagation the advantages of B become obvious.

 

[jghrist]

a) is better because if an arrester fails, it can be replaced easier without de-energizing the transformer. It also gives a little flexibility in height of the replacement arrester.

 

[Marmite]

I agree with jghrist. The protective zone of the arrester can indeed be different when mounted "behind" the protected plant, but it is not going to be significantly different if the arresters are right next to the bushings. Having the main current carrying connection going straight to the transformer bushing is advantageous because a failed arrester can be quickly cut away without disturbing the main current carrying connections, and hence the transformer can be quickly returned to service, albeit with depleted surge protection. This is the approach used by the utilities I have worked for.

Regards
Marmite

 

[podobing]

Guys,
Thanks to all for your input. I hope that I get the chance to return the favor someday.
Regards,
Dave