Arrestor Connection
Arrestor Connection
(OP)
I am looking for some input on these pictures. http://ww w.electric al-contrac tor.net/Fo rum/Images /SurgeArre stor-1.jpg
http://ww w.electric al-contrac tor.net/Fo rum/Images /SurgeArre stor-2.jpg
This is the 12KV secondary of one of two step up transformers on a rush project. I did the terminations last week prior to the transformers being delivered so that when they arrived the men on the job could just bolt them up. (I am on a job 100 miles away) They sent me these pictures today because the surge arrestors you see in the photos were not expected to be there. The concern is two fold.
1. The #6 connecting the arrestor to the HV bushing was factory installed. As you may be able to see it is a 600V THHN insulated conductor. What I have seen in the past is unshielded 15KV cable making this connection inside equipment.
2. The arrestors are mounted directly under the HV bushings and had to be loosened and pushed aside to get the power conductors landed. This moves the top terminal closer to the tank.
My suggestion, since they are owner supplied transformers, was to notify the owner/engineers of or concerns and we are awaiting there direction.
Does everyone else here see this problem??
- Nick
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This is the 12KV secondary of one of two step up transformers on a rush project. I did the terminations last week prior to the transformers being delivered so that when they arrived the men on the job could just bolt them up. (I am on a job 100 miles away) They sent me these pictures today because the surge arrestors you see in the photos were not expected to be there. The concern is two fold.
1. The #6 connecting the arrestor to the HV bushing was factory installed. As you may be able to see it is a 600V THHN insulated conductor. What I have seen in the past is unshielded 15KV cable making this connection inside equipment.
2. The arrestors are mounted directly under the HV bushings and had to be loosened and pushed aside to get the power conductors landed. This moves the top terminal closer to the tank.
My suggestion, since they are owner supplied transformers, was to notify the owner/engineers of or concerns and we are awaiting there direction.
Does everyone else here see this problem??
- Nick






RE: Arrestor Connection
I don't know what affect the changed spacing will have on the situation, but I wouldn't want to be anywhere near that transformer if there is ever enough overvoltage to cause the arresters to operate.
RE: Arrestor Connection
RE: Arrestor Connection
The #6 wire is a little small but the 600V insulation would not concern me unless the clearance between any portion of it and ground or another phase is inadequate. It does not seem to be the case here. We actually see this type installation fail fairly often when the arresters are mounted lower than in this situation and the grounded outer jacket of the phase conductor(s) is postioned too close to the bare terminal on top of the arrester. By the way, based on the number of skirts on the arresters, there is a good possibility they are rated too high to be of much value on what appears to be a 12kV solidly grounded system.
RE: Arrestor Connection
You need to make sure that the air gap has the equivalent BIL of the installation (probably 110 kV). The impulse insulation level of an air gap depends on the configuration, but one source I have squirreled away (unknown origin) gives the level of a 5 inch gap as 106-114 kV. Unless you can get better information, I would treat this as a minimum for the spacing between the top skirts of the arrester and either the tank or the bottom skirts of the cable termination.
RE: Arrestor Connection
For pad mounted transformer surge protection, elbow arrester is the proper application.
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For MV insulated underground cable protection, consider installing surge arrester at the riser pole
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RE: Arrestor Connection
You didn't need to use skirted terminations in this case. Indoor unskirted would have worked and given more clearance.
Insulating red board could be used between the phases, but it is not required unless the phase seperation is not adequate.
JTK
RE: Arrestor Connection
RE: Arrestor Connection
All in all, my concerns would be the size of the wire to the arrestor (not really the insulation - although this will come into play some since you moved the arrestors)and the issue with moving the hot side of the arrestors closer to a grounded metal surface.
Stevenals comments about combining the grounds at the bottom of each arrestor are valid ones. Keep the current out of the inside/shell of the transformer.
RE: Arrestor Connection
RE: Arrestor Connection
I have seen installations just like that before. In every case we yanked them out and installed them on the pole as they should be. I don't see the clearance as a problem at 12kv. The problem is with those mov type arrestors, when they blow..they blow. One blown arrestor in that confined space can take out multiple cables.
Your terminations look fine. It's just the factory set up that is junk.
HP
RE: Arrestor Connection
I see quite a bit of it in Central America. No Codes and no learning curve. Some contractors use THHN for transformer primary connections on 13,800 Volt systems and 34.500 volt systems.
After a few years of tropical sunshine, the outer covering splits off and starts to fall away. It hangs off the cable in streamers 3,4, or 5 feet long. Scares the ---- out of me.