distribution lightning arrestors: Source or Load side of disconnects?

[tinfoil]

We are having a bit of a debate in my local group of utilities regarding where lightning arrestors should be placed wrt disconnect switches on radial disitrbution systems.

We all agree that the lead lengths (both 'hot' and 'ground') need to be kept to a minimum wrt the equipment being protected, but we are not in agreement when it comes to the disconnects.

One group favours putting the arrestor on the 'line' side of the switches that isolate cable dips, transformers, reclosers, etc so that they are still 'in-service' when the device is isolated.

The other group feels that although the chance of lightning damaging a transformer/cable/etc is remote if its cutout switch is open, you would still be removing the only lightning protection available to the xmfr if the arrestor were to be placed on the line side. In addition, it is easier to keep the lead lengths shorter when the arrrestor is on the load side of the switch.

Is there a definitive standard or study done to resolve this? Assume that we are not willing to pay for arrestors on BOTH sides.

 

[jghrist]

The arresters main function is to protect the equipment, although their presence does reduce line outages. Because the number of isolated pieces of equipment on a line would normally be small, I don't think that having the arresters on the equipment side of disconnects would make a statistically significant difference in the line outage rate.

I would go with putting the arresters on the equipment side in order to keep lead lengths short. An exception might be where the disconnect is a fused cutout with a small non-surge resistant fuse link. On the other hand, if the arrester failed on the equipment side of a fused disconnect, the fuse may prevent a line outage. Then again, if the lightning arrester failed and the ground lead isolator operated properly, reclosing would restore service to the line if the arrester were on the line side, but if it were on the equipment side, the fuse would probably blow and the customer would be interrupted. Back to the other hand, at least if the fuse blew, you would know you had an arrester failure and the equipment would not remain unprotected.

The only thing you can say for sure is that not everyone will agree on the proper place for the arrester.

 

[cuky2000]

QUESTION: Is there a definitive standard or study done to resolve this?

Check EPRI Report EL-1140, "Study of Lightning Current Magnitude Through Distribution Arresters."

COMMENT
<sub>As closer the arrester is from the transformer better dielectric protection. However, if standard fuse is installed, increase of fuse blow up will be expected. On the other hand, increasing the fuse size will reduce the overcurrent protection of the transformer.

Personally. I’m in favor of install the arrester in the transformer tank from the simplicity of installation point of view and improve dielectric protection in the transformer as shown in the enclose sketch. .</sub>

RECOMMENDATION FOR UTILITY APPLICATION:
_{Since is not intuitive obvious for everyone the benefic of changing present practice in an existing utility, it is suggested to do a detail study addressing cost benefit, life cycle cost and O&M issues. A test case in a few units could help to evaluate if the pros and cont of this proposal.}

The enclose site has a good discussion in this matter

http://www.sandc.com/webzine/050602_1.asp

 

[stevenal]

Connect arrestor on the load side of disconnect to keep leads short. Use a hot line tap on the arrestor lead, so that transformer can be heated up without the arrestor if the arrestor is suspect.

 

[cuky2000]

Tinfoil,

The enclose site have information regarding the topic that you are searching.

Good luck

http://www.cooperpower.com/Library/pdf/92003B.pdf