MV Switchgear corrosion

[koperry]

I was recently involved with an issue of a 25kv switchgear that had flashed over and tripped on the utility side. I was not involved in the original installation which was only 3 years ago. The gear is rated for outdoor use and it is. I had met with the mfg. rep and according to him the gear looked to be 20 years old. All of the breaker stabs were covered with a thick green corrosion. In the PT drawer there was tracking all over the PT's. The interior of the gear was covered in a moist greasy coating that proved very difficult to clean. CT's connections were the same, hardware was rusted, etc.

Everything seems to be sealed well and installed properly. Not sure if it wasn't cleaned properly in the beginning or something from the inside out has failed and got on to everything. It does seem to be heavier near where the flash over occurred.

There is a large cooling tower in the vicinity and several of the people involved think this could be the culprit. Personally it looks to be from the inside out. If it were from the outside one would think the film would be all over the outside as well. The filters seemed to have this film on the inside not the outside.

Anyone ever heard of or seen this problem?

 

[big john]

...There is a large cooling tower in the vicinity and several of the people involved think this could be the culprit....

I'd put a lot of money on that being true. Cooling towers can cause wicked severe corrosion because of a high concentration of minerals and contaminates in the evaporation loop.

...Personally it looks to be from the inside out. If it were from the outside one would think the film would be all over the outside as well...

That could be due to a lot of things: Interior doesn't get cleaned by rain, the interior surfaces may have a different finish, it could be due to condensation.

What I can say is I've seen a ton of switchgear corrosion and it has always been due to exterior environment.

 

[Jraef]

Might be a known issue often called "greening" of conductors caused by the plasticiser used in some older PVC wire insulation, which is what is used in THHN / THWN cable. The plasticiser (pthalate) was added to make the conductor more pliable, but under the right conditions of heat and humidity it could separate from the PVC and migrate by wicking action to basically anything that has conductors attached to it somewhere and gets all over everything. Pthalate plasticiser was officially banned from PVC and other plastic consumer goods, but I don't think it was ever banned from wire insulation, yet for the most part people stopped using it in the 70s because of this issue. When the copper prices soared a few years ago, people started selling old stock of cable that had been warehoused for decades and some wire suppliers turned to "alternate" resources from places like China, well known for using materials that are otherwise not considered appropriate elsewhere. You might want to get someone looking into this with the cable supplier because if that's what it is, the gear might be toast. The pthalate itself is clear, greasy and hard to clean, but when it gets hot, it reacts with sulfur (present in the air in many areas) and copper from the conductors to form copper sulfide, which is corrosive, conductive, and... green!

There is an IEEE write-up about this somewhere if you look hard enough.

 

[zog]

Might be a known issue often called "greening" of conductors caused by the plasticiser used in some older PVC wire insulation, which is what is used in THHN / THWN cable. The plasticiser (pthalate) was added to make the conductor more pliable, but under the right conditions of heat and humidity it could separate from the PVC and migrate by wicking action to basically anything that has conductors attached to it somewhere and gets all over everything. Pthalate plasticiser was officially banned from PVC and other plastic consumer goods, but I don't think it was ever banned from wire insulation, yet for the most part people stopped using it in the 70s because of this issue. When the copper prices soared a few years ago, people started selling old stock of cable that had been warehoused for decades and some wire suppliers turned to "alternate" resources from places like China, well known for using materials that are otherwise not considered appropriate elsewhere. You might want to get someone looking into this with the cable supplier because if that's what it is, the gear might be toast. The pthalate itself is clear, greasy and hard to clean, but when it gets hot, it reacts with sulfur (present in the air in many areas) and copper from the conductors to form copper sulfide, which is corrosive, conductive, and... green!

There is an IEEE write-up about this somewhere if you look hard enough.

This?

http://www.google.com/url?sa=t&rct=...9WNtulNa43bvRnEHw&sig2=TQF0aZuuqppTNWD2TBPS5w

 

[zog]

I was recently involved with an issue of a 25kv switchgear that had flashed over and tripped on the utility side. I was not involved in the original installation which was only 3 years ago. The gear is rated for outdoor use and it is. I had met with the mfg. rep and according to him the gear looked to be 20 years old. All of the breaker stabs were covered with a thick green corrosion. In the PT drawer there was tracking all over the PT's. The interior of the gear was covered in a moist greasy coating that proved very difficult to clean. CT's connections were the same, hardware was rusted, etc.

Everything seems to be sealed well and installed properly. Not sure if it wasn't cleaned properly in the beginning or something from the inside out has failed and got on to everything. It does seem to be heavier near where the flash over occurred.

There is a large cooling tower in the vicinity and several of the people involved think this could be the culprit. Personally it looks to be from the inside out. If it were from the outside one would think the film would be all over the outside as well. The filters seemed to have this film on the inside not the outside.

Anyone ever heard of or seen this problem?

Space heaters working?

 

[koperry]

Might be a known issue often called "greening" of conductors caused by the plasticiser used in some older PVC wire insulation, which is what is used in THHN / THWN cable. The plasticiser (pthalate) was added to make the conductor more pliable, but under the right conditions of heat and humidity it could separate from the PVC and migrate by wicking action to basically anything that has conductors attached to it somewhere and gets all over everything. Pthalate plasticiser was officially banned from PVC and other plastic consumer goods, but I don't think it was ever banned from wire insulation, yet for the most part people stopped using it in the 70s because of this issue. When the copper prices soared a few years ago, people started selling old stock of cable that had been warehoused for decades and some wire suppliers turned to "alternate" resources from places like China, well known for using materials that are otherwise not considered appropriate elsewhere. You might want to get someone looking into this with the cable supplier because if that's what it is, the gear might be toast. The pthalate itself is clear, greasy and hard to clean, but when it gets hot, it reacts with sulfur (present in the air in many areas) and copper from the conductors to form copper sulfide, which is corrosive, conductive, and... green!

There is an IEEE write-up about this somewhere if you look hard enough.

Looks to be right here.

http://static.schneider-electric.us/docs/Electrical Distribution/0110DB0301.pdf