Overheated lugs and blown fuses

[sferrari]

A couple of days ago I was on a service call on a 250hp 3p 480vac ag well that blew a 400A fuse. The fused disconnect feeds an autotransformer soft starter. The equipment is pretty old and worn out. The fuse holders/lugs/wires for the blown fuse had clearly overheated. I cleaned the corrosion as well as I could, installed the fuse and powered up the system. They needed water badly. Voltage and current balance were good. I'm told that it only ran for 2 hours before the fuse blew again. When it blew, it also overheated/shorted one of the terminations in the peckerhead.

We got a new bucket and fuses. We're replacing it and the conductors between it and the starter tomorrow. I won't be there because I need to be somewhere else. I REALLY don't want this problem to persist after our electrician finishes tomorrow.

Could the generally crappy condition of the conductors/fuse holder be the cause of blowing fuses? If so, could someone explain what's happening there?

Any help would be greatly appreciated.

 

[RCC1]

Any and all those loose, or corroded connections can cause heat. Lots of time it will cause you to loose one phase. You will most likely blow a fuse then. If this MCC bucket has problems, I would suggest you have them do some thermographic work on the MCC. I would be willing to bet that there are other MCC buckets getting ready to do the same thing. The short in the motor junction box will also blow the fuse.

 

[xptpcrewx]

A couple of days ago I was on a service call on a 250hp 3p 480vac ag well that blew a 400A fuse. The fused disconnect feeds an autotransformer soft starter. The equipment is pretty old and worn out. The fuse holders/lugs/wires for the blown fuse had clearly overheated. I cleaned the corrosion as well as I could, installed the fuse and powered up the system. They needed water badly. Voltage and current balance were good. I'm told that it only ran for 2 hours before the fuse blew again. When it blew, it also overheated/shorted one of the terminations in the peckerhead.

We got a new bucket and fuses. We're replacing it and the conductors between it and the starter tomorrow. I won't be there because I need to be somewhere else. I REALLY don't want this problem to persist after our electrician finishes tomorrow.

Could the generally crappy condition of the conductors/fuse holder be the cause of blowing fuses? If so, could someone explain what's happening there?

Any help would be greatly appreciated.

Sounds like a motor overload situation. Fuses holders/lugs/wires don't all simultaneously overheat by themselves...

 

[sferrari]

Any and all those loose, or corroded connections can cause heat. Lots of time it will cause you to loose one phase. You will most likely blow a fuse then. If this MCC bucket has problems, I would suggest you have them do some thermographic work on the MCC. I would be willing to bet that there are other MCC buckets getting ready to do the same thing. The short in the motor junction box will also blow the fuse.

This entire system just needs to be overhauled. The inside of the starter panel looks like a war zone.

When I had a cover off of the panel board, I'm pretty sure I saw One-Eyed Willys skeleton in there behind the bussing.

 

[sferrari]

Sounds like a motor overload situation. Fuses holders/lugs/wires don't all simultaneously overheat by themselves...

It has a Motorsaver 777 on it. The current/voltage that it's seeing is pretty accurate.

That being said, I didn't check the parameters on the Motorsaver.

 

[xptpcrewx]

It has a Motorsaver 777 on it. The current/voltage that it's seeing is pretty accurate.

That being said, I didn't check the parameters on the Motorsaver.

Worth a look. You could have a SEL-710-5 on it, but even that wouldn't make a difference if it was set incorrectly.

 

[Hv&Lv]

This a submersible pump I’m assuming?
sounds like the pump is going bad. The impeller wears out and starts binding against the sides as the pump is running.
Put a PQM on it and zoom in on the sine wave at the trip event and you will probably see the amps spike just before the voltage sags.

does the motor saver record any events? I’m not familiar with that particular relay.

 

[Jraef]

When a fuse holder over heats, the spring clip that helps put tension on the fuse will soften and lose its strength, making it more likely to over heat again. Once it has turned color, you should replace it. For some of the more common and long lasting fused disconnects, replacement clips are available. But of really old or oddball stuff, sometimes you have to replace the entire works.

Also on Autotransformer starters, sometimes people mess with the transition timer, thinking they are "saving energy" by stretching out the start time (not true). When they do that, the starter stays in higher starting current mode longer than it was supposed to, which stresses everything. That timer should be around 5 seconds, 15 at the absolute outside. If it takes longer than that, they need a different way of starting it.

 

[xptpcrewx]

This a submersible pump I’m assuming?
sounds like the pump is going bad. The impeller wears out and starts binding against the sides as the pump is running.
Put a PQM on it and zoom in on the sine wave at the trip event and you will probably see the amps spike just before the voltage sags.

Also on Autotransformer starters, sometimes people mess with the transition timer, thinking they are "saving energy" by stretching out the start time (not true). When they do that, the starter stays in higher starting current mode longer than it was supposed to, which stresses everything. That timer should be around 5 seconds, 15 at the absolute outside. If it takes longer than that, they need a different way of starting it.

I am having flashbacks of operators deliberately increasing the O/L pick-up and/or time-delay settings after experiencing a few "nuisance trips", then calling someone out when the motor finally burns up the rest of the circuit - when you get there they act like they have no idea what happened.

 

[ptonsparky]

I’m thinking you had two separate problems, fuse clips and the peckerhead issue. Not surprising for the age.

 

[DrSparks]

Sounds like a motor overload situation. Fuses holders/lugs/wires don't all simultaneously overheat by themselves...

All it takes is one weak point in a system to cause catastrophic failure. Metal parts conduct (sink) heat from the other metal parts they are connected to. So if you have corroded lugs or fuse clips, they heat up the metal around it, which can cascade into complete failure. In particularly harsh or damp locations, this problem is severely exacerbated. A schedule of regular maintenance is prudent: pulling out fuses and cleaning the clips and fuse ferrules. I also recommend ditching mechanical lugs for compression crimp terminations. Unbolt the lugs from the busbars and bolt the crimped conductors in its place.