LSIG protection

[Maurice Charlebois]

I am the process engineer of a remote plant. The site is large and serviced by a 25kv 3 phase private power line that we own. The service at the utility is a 600v 400A with step up transformer bank. Since the site is very large and the loads far appart, there are 200 A 600v service drops where needed. We were sold the idea that LSIG breakers on each main service could make the workplace very very safe by allowing any fault to be cleared by this device before causing any harm. Expect ally to the workers.

We don’t mind if whatever is on this service goes off in case of a fault. We don’t mind having to search what was the problem instead of having bangs and smoke. Most of the loads are pumps motors. With the largests being 75hp.

The first breaker was installed years ago and always performed as intended. Fuses would not burn but the breaker would trip. We recently had a line to line fault that created burns and smoke and burnt load fuses. Not used to this. I suspect that all the faults we encountered before were line-ground and the device handled this as planned, but the recent one was line-line and the settings are not as good for this type of faults.

I am not an electrical engineer but I understand most of the concepts, and when I talk to local specialists, they talk about the necessary coordination of the protections. It’s not that practical as a concept to apply with step up/step down and overhead power line protections that creates 40A on 600v for each 1A increment on 25kv, while the current on the primary is less than 10A…

My aim would be to set the LSIG as sensitive as possible to allow motor inrush current and nothing more. This would likely lead to the LSIG breakers clearing faults before the fuses pick up. I don’t care about this but apparently the code cares.

Any suggestions?

 

[ron]

The code does not require LSIG adjustability. Code does require protection with maximum values identified, but you can set it as low as you like if you have an adjustable breaker.

 

[Maurice Charlebois]

These breakers are adjustable. Any suggestions where to start?

 

[ron]

These breakers are adjustable. Any suggestions where to start?

Either do (or have done) a protective device coordination study or make all settings (except the long time pickup, which is the breaker handle rating) minimum and if they trip and you determine the system was operating normal, raise the setpoints starting with instantaneous until they don't trip anymore during normal operation.

 

[Maurice Charlebois]

Thanks Ron. I understand that there will never be a complete « fool proof » protection. We can not have this breaker detect a line-line fault below its long time pickup. There will always be some significant risks around electricity. Makes total sense.

I was kind of « oversold » on these breakers. I was told they would give instantaneous protection for all type of faults, phase loss and so on. That’s why I was looking at it as if there was a mysterious talisman in there. I Could not figure it out, because there was nothing to figure out. Reality check here I guess. Thanks again.

 

[mayanees]

These breakers are adjustable. Any suggestions where to start?

As Ron suggests, have a coordination study performed where the LSIG breaker is set precisely to trip before the fuses. That can also yield arc flash labels which are important for determination of the appropriate PPE to wear if doing energized work.

 

[jim dungar]

Thanks Ron. I understand that there will never be a complete « fool proof » protection. We can not have this breaker detect a line-line fault below its long time pickup. There will always be some significant risks around electricity. Makes total sense.

I was kind of « oversold » on these breakers. I was told they would give instantaneous protection for all type of faults, phase loss and so on. That’s why I was looking at it as if there was a mysterious talisman in there. I Could not figure it out, because there was nothing to figure out. Reality check here I guess. Thanks again.

Breakers can be supplied with additional functions such as Undervoltage and Phase Loss protection beyond the typical LSIG functions.
Your equipment drawings should show the breaker catalog number and options.

 

[Maurice Charlebois]

I am getting some homeworks here. Keep it coming, I am learning. Thanks.

 

[ron]

Thanks Ron. I understand that there will never be a complete « fool proof » protection. We can not have this breaker detect a line-line fault below its long time pickup. There will always be some significant risks around electricity. Makes total sense.

I was kind of « oversold » on these breakers. I was told they would give instantaneous protection for all type of faults, phase loss and so on. That’s why I was looking at it as if there was a mysterious talisman in there. I Could not figure it out, because there was nothing to figure out. Reality check here I guess. Thanks again.

By reducing the short time, instantaneous settings (for phase) and ground fault, you will be much faster response time from the breaker. With the addition of other accessories like undervoltage as mentioned by Jim, you can get even more protection modes.

 

[Jraef]

We were sold the idea that LSIG breakers on each main service could make the workplace very very safe by allowing any fault to be cleared by this device before causing any harm. Expect ally to the workers.

Someone sold you a bill of goods on that one. Slightly safer might be a valid statement, but if someone was thinking that the "G" in LSIG was the same as a GFCI type of personnel protection, that is dead wrong. That is GFEP (Ground Fault Equipment Protection), the trip levels for it are WAY more than what would be safe for a human to encounter. GFCI is 5mA protection. On a 600A Main breaker, the GFEP could be 200A and still be considered "acceptable". Hopefully I have misinterpreted your statement...

 

[Maurice Charlebois]

You did not. That’s what I wrote in my approximate language ability. There is double translation here: my language is French, and I am not fluent in electrical. I have no doubts about the statements made by the one who sold me on this idea. He had no interest in selling anything. He was a teacher, retired after a couple decades of being chief engineer at a major electrical equipment manufacturer. He knew his stuff. The course was in English, so a third translation. Lots of things get lost in translations, especially nuances. I clearly recall him saying that I would never get to the GFCI level of protection, but that for the size I need (250A), setting it to the minimum would add very significant safety compared to having nothing else than fuses. But it’s only part of the point.

You and others shed light on the fact that I ordered and had installed I piece of equipment that I do not master, which is the reason of me asking help here. Now that the equipment is in, as the user, it is more than time for me to understand clearly what I can expect of it and what not, and obviously how I can get the best out of it.
Thanks for helping me with your comments.

 

[petersonra]

For 200 amp breakers I don't see that the special features of an lsig breaker is going to substantially improve safety over a standard tm breaker.

It seems to me that the LS and I functions of such a breaker are mostly for coordination efforts. The ground fault part of it arguably might be worth something safety-wise. But I don't know how much it's worth, especially on such a small breaker. Allegedly it's supposed to be there to protect against some kind of arcing fault. I don't know how common those are.

 

[jim dungar]

Part of the problem is sing the words safe or safety as if they had very specific definitions. So the first thing to do is to reach an agreement on what we want the breaker to do.

An electronic trip breaker with LSIG can often be set to to trip at relatively low levels of current, such as 2X for short circuits versus the typical 6-10x for thermal magnetic breakers.
The G function can be set maybe as low as .1x the breaker rating so faults to ground, which are the most common fault, are removed extremely fast.
LSIG may provide 'selective coordination' which may reduce the amount of the facility power system which looses power due to a fault needing to be cleared.