Electrical Buss Duct

[2799]

I am trying to benchmark best practices in the area of electrical buss duct testing for predictive / preventive maintenance. Here in our facility, we have 400 & 600 amp 480 volt three phase buss ducts supplying power to all of
our equipment and due to age and contamination, are beginning to experience ground fault and phase to phase failures in some areas. The only thing I know to do is to shut down the equipment, power down the buss and perform a
high-pot test. However, shutting down a whole section of buss is not an attractive solution. Infrared analysis has not been of much use due to ambient and reflected energy. I'm thinking about ultrasonic but don't know if that is a viable option.

Any help with this matter will be greatly appreciated.

 

[electricpete]

One important area to keep track of will be the availability and proper operation of space heaters, at least if the system is outdoors. We have had failure of 13.2kv outdoor nonsegregated phase bus duct which occured during startup after extended layup.

Likewise for outdoor bus duct the weather tight integrity is important. Rust penetration or poor seals can get you.

I assume that if contamination is a problem then cleaning would also be part of your shut-down maintenance.

 

[busbar]

Production loss from electrical failures may spur replacement funding. It is very stressful trying to keep electrical distribution working any degree of reliability in aged equipment, particularly if maintenance has been a low priority. Unfortunately, sometimes it takes the cost of human injury to force the issue. Old bus duct is spooky stuff.

 

[peebee]

There some newer motor testing packages out there that can monitor motor insulation resistance while the motor is energized. Maybe they'd work for busducts, too, I have no idea.

 

[jbartos]

Suggestion: There are several industry standards that deal with the topic. E.g.
ANSI/IEEE C37.23
IEC 439-2
BS 5486: Part 2
NEMA BU1
etc.

 

[tucan]

First get a good thermographer, have all lights turned off and use an elevated platform to perform the IR scan. It will work if you have athermographer who understands condition under which you get optimal readings and can read the instrament accurately.

 

[Jerry123]

Being a 480 volt bus duct a hipotential test and ultra sonic is not the way to go. If you did have an hipotential test performed I would like to know at what voltage and what was the current reading. 480volt switchgear should be tested at 1000Vdc for insulation resistance. A ultra sonic I believe is for medium to high voltage switchgear testing for corna discharge. I am glad to see that your protective functions on you circuit breaker are working and for that sake you are lucky. The down time for repairs of fail bus duct is substantial.

If the bus duct is short in length you might consider replacing it. The time and money spent to find and repair the defective areas can add up fast and might lead to replacing all of the bus duct anyways.

If your getting ground faults and phase-to-phase faults, you’re in bad shape. I would get a testing specialist there to find out the integrity of the bus duct and will have a better understanding of your situation.

 

[ScottyUK]

Some of the bigger phase-isolated bus ducts use a slight (1-2psi) positive pressure to ensure that any leakage is outward, thus keeping the inside dry and clean.

Depends if you have plant air, and can stand a continuous drain on it.

 

[peebee]

I'm not familiar with ultrasonic -- what is that?

 

[advidana]

I known that this is not what you want to hear but if you are having all these failures it is time to replace all the bus duct. The life of your equipments has ended. If you don't act, then you may have a fire in your facility or someone may get injured. Eleven percent of of all industrial fires result from malfunctioning electrical equipment.

Check NFPA 70b, it may establishes requirements for this kind of maintenance. Again, I don't think any type of testing will effectively prevent failures from old bus equipment that is already failing. It will only give you a false sense of security.

 

[jbartos]

Suggestion: Visit

http://www.ecmweb.com/ar/electric_ensuring_good_bus/

etc. for more info on bus duct intallation

 

[alehman]

Before replacing, carefully evaluate if you can what has led to the failures besides old age. You mention contamination. It would be wise to consult with manufacturers about your specific environment before selecting a replacement.

 

[rbulsara]

As advidana said bite the bullet and replace the Bus duct, It's time man!

You are fighting a loosing battle and only waiting for a disaster!

 

[lengould]

You haven't mentioned the style of the busduct, but by the sound of it I would guess one of the "plug in" open style busducts rather than the totally enclosed "metalclad"s.

Assuming open plug style, chances are your environment has deposited significant contamination onto the support insulaters etc. I've has success in similar situations by doing a total shutdown, then physically cleaning ALL supporting insulation after removal (and cleaning) of all plug units. If your plant can stand it, high pressure washing with good water (call one of the pole line mtce wash crews in). Use a clean air hose to blow out and standing water, leave to dry 12+ hrs with low humidity, megger completely, downfuse to minimum then turn it on (fingers crossed, protective gear). I've used procedure on 800A and 1200A 600V ducts, no further problems.

Consider de-comissioning a small section of it before the shutdown. Tear it out, strip it down, keep for emergency replacement parts during main shutdown.

Use megger testing, not HyPot, which will likely create failures itself. An infrared camera might spot tracking from conductive contaminants on the insulation blocks, but thats pretty late to detect a problem. By the time a thermograph sees it, it will be too late to make the next scheduled shutdown. Visual inspection and regular recorded megger tests (keep records, record temp and humidity at test time, do it OFTEN) then monitor for trends, analyse records prior to any failure event.

If you have metalclad stuff failing, scrap it out unless you can see obvious points to upgrade.

 

[jbartos]

Suggestion: Visit

http://www.parkdetroit.com/Busway Manual.pdf

for:
NON-SEGREGATED & SEGREGATED BUS DUCT INSTALLATION MANUAL

 

[lengould]

Hi jbartos. Good website, but an unusual discussion of connecting .600 kv duct (taping / puttying joints?). I've managed and worked construction and maintenance on many installations / several mfgrs 600V busduct from 600 to 3000 amps, and never seen anything but simple bolted bus joints called for by mfgrs. My guess is Park Electric must specialize in higher voltages. The 3000A installation was done under direct mfgr eng. inspection (FPE) since it was quite new for them at time, but only required torqued bolts and dry mating surfaces.

Good table of test voltages though. Agree with limiting test voltage to 1.65 kv for .635 kv equipment. Suppose a HyPot tester could be used if set properly, but when meggers are so much simpler, cheaper, (and rugged) that's what I'd use.