Non PLC question

Hi guys;

I know im not suppose to ask non PLC questions here but im not sure where else to go. We are experiencing some trouble with blowing a main substation fuse (always the same phase). When we replace the fuse everything is ok. The fuse is blowing every month to 2 months. Is it possible surges outside the mill could be causing it? We are planning to get a power analysis done but this will take some time. I just thought that maybe somone else has seen this problem at their work place and could give us somplace to start looking. Again I apologize for asking in this forum but I knew that there are lots of electricians like myself that use this site regularly.

Thanks
Ernie

... i do not believe that anybody is able to help you with this, and you already know there is only ONE reason why fuse can blow, you better ask electrician who had seen the thing

....just to expand

this is a 44kv 40amp fuse feeding a 44kv/600v tranformer. When the fuse blows the plant is down. No branch breakers are tripped.
It seems odd....

Has there been a discrimination study carried out? May be worth while.

Have the cables to and from the sub been checked? Has the transformer been checked? Does it only happen on very hot days?

There are a multitude of questions that can be asked like this.

Hope this helps in some small way.

And here is a shot in the dark too.. ( because it happened recently)

Do you have power factor correction in this sub station?

If so has the capacitors or PFC fuse for this phase failed.

Yes we have an oil sample done for the transformer done annually. We do have power factor capacitors and we did have a problem a couple of months back with that breaker in the PDC but that was fixed. It was hot the first couple of times but the last few times it was fairly cool (18-20C). I guess we could meggar the cables and the PDC. Maybe the insulators are cracked? The last time was a day ago so it just now is becoming a concern. The last few times we thought that it could be a surge (because we have a history of bad power being at the end of the line and hydro generator is about 400km away). There is no evidence that somthing is wrong in the plant.

I appreciate the feedback...

Megger test won't be suffcient for 44kV cables. Is this a structure mounted fuse or internal to an enclosure? Has the quality of the fuse holder and insulators been evaluated?

Just another shot in the dark. Is there any patter to these fuse blowings? Monday morning, first of the month, just after midnight, etc?

If by chance, the sub is running near the capacity of those fuses, perhaps someone down the road is firing something big up and there is a dip in the voltage over the high power lines that come to your place. Voltage drops, amps go up, maybe? We have had some similar mysterious overloads or tripping of circuit breakers, that I realized this pattern forming. We got the utilites co involved and found out that our neighbors to the south fired up some huge compressors or ?? mid mornings ever other Monday. They did this, one of our compressors tripped out its motor overload. Another time, we had a pattern of our computerize conveyor having 1-3 motor overloads trip out. That too had a pattern of happening in the wee hours of the night, like just after midnight. That deal came and went in after it had happened like a half dozen times but never found the cause. 6 months or so after that, the one compressor had it's monday morning episode. The utility co helped us locate the cause and those issues soon came to an end with out an inhouse changes or repairs.

Have you asked neighbors sharing the same power source to see if they are having similar problems?

If you can, look for evidence of tracking or corona damage on your switchgear and insulators downstream of the fuse. I had a similar problem a couple of years back. Plant would be dark (no load) usually had just rained or high humidity and the main breaker would trip at the substation. I would check everything I could see and did not find anything. Finally, I found a 13.8KV switch that was tracking down the insulator to ground only when the conditions were right. The problem boiled down to the switchgear being mounted on a concrete pad and was hanging over the pad about 2" creating an air gap. This gear had been in place for about 25 years and had been cleaned once per year. We replaced the insulators, covered the gap and installed heaters in the gear. Have not had this problem since.

Not sure about Canada, but here in the US, the HV side of power distribution points is the province of the power company. If there is a problem on that side, it is on them to diagnose and fix the problem. I doubt seriously that you have a plant problem that is showing up as a blown fuse on the primary of the DP xfmr. My $.02US

bwheat said:

If you can, look for evidence of tracking or corona damage on your switchgear and insulators downstream of the fuse.

Click to expand...

When I read the 1st post this is the 1st thing that came to mind. The track might not be enough to cause a breach until you get a change in humitiy or a slight power surge.

This was my first thought too, bad connections can cause many issues.

I have seen some strange situations where certain conditions caused arcing, in some cases the evidence of arcing was not visible until you did a very close inspection that sometimes required removing the holder(s).

One freaky situation was during a storm. I was in a control room on one side of the plant and a colleague was on the other side of the floor working in a main panel. We had a power outage for a second and the lights went out, these were halide lights so it takes about 15 minutes for them to come back on. The system was still working. I happened to look over where my colleague was (with the open panel) and saw flashing but when I went to the panel I did not see anything...I walked back towards the control room but looked back and saw it again....for whatever reason you could not see the arcing if standing directly in front of the panel. With closer inspection we found evidence of it arcing across the fuse. Humidity was a factor in that situation too.

One option is to use a thermal imaging device. Thermal cameras
can get you information on temp rise from one phase to another.
I've seen many fuses and switches fail over the years without
any "visible to eye" reason, but once shot with a thermal
imaging device it became apparent that it was much hotter than
the other phases and led to premature failure.
There are companies around that have these cameras or if you
have a friend at a local fire company (some fire companies have
these)maybe you could borrow theirs.
Good luck,
Bob

Ernie,

Are there also power reactors (inductor coils. in addition ot the capacitors on the substation? If so, the reactor (for the phase with the blown fuse) may be going bad (insulation breakdown), or may have a "track" built up across the insulators.

This is not to be taken lightly. Something is WRONG in any case. If it is a symptom of an impending substsation melt-down, you will be well advised to spend time and money to determine the cause. A data logger to record (and document for possible future legal suits)) the voltages and currents might be called for here. At least it will show that you were trying to find the problem.

The most worrisome part is that none of your downstream fuses are blowing. Either your downstream fuses are not properly coordinated, or the problem is in the primary side of the substation. I pray that your system is properly coordinated. If so, that narrows the possible problems dowm to the substation.