Flashover in incomer busbar

[tengineer]

We have Siemens 3AH3 type VCB installed in our 33kv Substation for powering furnace transformer via another breaker - 3AH4 type.

From past two due to Maximum Demand there has been frequent "on load" "switching off" of this breaker-3AH3 type (around 40 times a day).
Before that this breaker rarely operated on load.

Yesterday there was a flashover in incoming busbar of this breaker.
I wanted to ask if this flashover could be a result of frequent on-load operation of this breaker.

Thanks and regards

 

[big john]

Was this equipment off for any longer durations than it had been in the past? The only thing I could think of is if it was suddenly allowed to get much cooler, this may have allowed the insulation and contaminates to absorb humidity.

What type of transformer is on the line side and are there any grounded points or surge protection equipment?

 

[mgookin]

We have Siemens 3AH3 type VCB installed in our 33kv Substation for powering furnace transformer via another breaker - 3AH4 type.

From past two due to Maximum Demand there has been frequent "on load" "switching off" of this breaker-3AH3 type (around 40 times a day).
Before that this breaker rarely operated on load.

Yesterday there was a flashover in incoming busbar of this breaker.
I wanted to ask if this flashover could be a result of frequent on-load operation of this breaker.

Thanks and regards

Can you clarify the underlined part?
Two days? Weeks? Months? Years?

 

[tengineer]

Was this equipment off for any longer durations than it had been in the past? The only thing I could think of is if it was suddenly allowed to get much cooler, this may have allowed the insulation and contaminates to absorb humidity.

What type of transformer is on the line side and are there any grounded points or surge protection equipment?

Hi,
Nothing like that, it had been on for weeks.

Further details :
The Load is a 100MVA furnace transformer of Electric arc furnace and another 24MVA furnace transformer.

Supply side has two transformers 120MVA(I/C1) and 80MVA(I/C2) which are run in parallel. From these two incomers a bus is charged from which both load transformers(100MVA and 24MVA) are supplied via there own VCBs.

Yesterday flashover occurred in incoming busbar of I/C1. We repaired it overnight.
Today afternoon same thing happened with I/C2.

 

[tengineer]

Can you clarify the underlined part?
Two days? Weeks? Months? Years?

Sorry, my bad. two days.

 

[mgookin]

Sorry, my bad. two days.

No problem. And welcome to the forums.

So what changed 2 days prior?

 

[big john]

Was the first flashover in any sort of proximity to the second? I can an easily see carbon contamination from the fault precipitating a second flashover.

You still haven't mentioned any intentional grounding. I'm wondering if you are getting serious switching transients from the large floating inductive loads.

 

[tengineer]

No problem. And welcome to the forums.

So what changed 2 days prior?

Our captive powerplant is giving less power to our section, so we have to import power from grid. Due to this our load gets disconnected when Maximum demand controller alarm goes off. This Maximum demand thing came into picture two days back.

 

[tengineer]

Was the first flashover in any sort of proximity to the second? I can an easily see carbon contamination from the fault precipitating a second flashover.

You still haven't mentioned any intentional grounding. I'm wondering if you are getting serious switching transients from the large floating inductive loads.

First and second flashover locations are not near. No chance of contamination.

I am not sure about the grounding, the incoming transformers are not under my authorized area. I can certainly enquire about it.