Looking for opinions of this situation old buswork

[wbd]

Hello,

I have a situation at a power plant that is 100 years old and the last update of equipment appears to be in the late 1940's or 1950's. The situation I'm concerned about is the 2 buses in the plant. They are constructed with steel pipe for framework with rubber insulation holding up the copper bus bars. There are 3 bars per phase, approx. 1/4" x 4 - 6 inches and are about 8 feet in the air, horizontal. There are vertical bus bars to the breakers, bolt in DB-75 and DB-100's. This bus work is fed by a three winding transformer via a DA-75 breaker on each secondary winding. This is 480V delta system with ~52kA bolted fault current. There is a marble panel board about 2 feet in front of each structure with the breaker control handles and associated meters and relays.

The breakers had the old trip devices replaced with AC Pro units to reduce the AFH from Extreme Danger to Category #2 a year or so ago.

My concern is that, regardless of reducing the AFH to Cat. #2, there is still a danger with the open bus work and an arc flash. There is no metal enclosure to contain any blast.

I'd be interested to hear other's opinions of this situation.

Thank you in advance for your comments.

 

[davidbeach]

Actually open bus has a lower AFH than enclosed bus for the same prospective fault as the energy can dissipate in all directions instead of just one.

I'd actually be much more concerned with 50-60 year old rubber insulation than I would with open bus.

 

[alehman]

Are you concerned about accidental contact with the exposed bus? Is it in a location with controlled access?

I'd probably be more concerned with the breakers. Have they been maintained and tested recently (other than replacing the trip units)?

 

[apowerengr]

I agree w/ Davidbeach - open air = less arc-blast hazards. If the equipment is adequate from an interrupting rating and the buswork is adequate from an ampacity rating reinsulate it and let it be. I assume you have a ground fault detection scheme in place for this 480 delta system? Copper busbars age gracefully.