Power Breaker used to control motors

[philly]

I was at a major manufacturers industrial facility recently and found that in their 480V LV Switchgear they use the power breakers to feed the motors without any contactors or overload protection.

These power breakers are electrically operated breakers that simply open and close to start/stop the motor without any contactors or overlaod protection. They simply use the LSI protection the breakers trip units to provide feeder/motor protection and try to adjust these settings as close as possible to the motor characteristics and damage points.

Has anyone ever come across this before? Seems like it would be in violation of the requirements in Article 430. I should mention that this is in the Oil & Gas industry so perhaps this may be some sort of standard in that industry.

 

[Sahib]

Those power breakers might definitely have thermal over load element for motor protection; not of instantaneous trip element only type.

 

[Jraef]

It's not that uncommon for motors that basically almost never shut down, except for emergencies and scheduled maintenance, a situation not uncommon in refineries. Breakers, motorized or not, are not built to be turned on and off a lot like a contactor. But in these circumstances, even 1,000 operations is more operating years than the rest of the refinery would last. As to the protection, there are several circumstances in which the motor thermal protection can be very widely interpreted and they will often take full advantage of that because, like I said, they are NOT going to shut them down unless it is a major issue already. So it's not quite like a fire pump, but from their standpoint, it is almost "run to destruction" because if they ever tripped on OL, the cost to the refinery could be millions of dollars.

If they are just being cheap and cycling these motors on and off a lot using the breakers, that is "penny wise, pound foolish", because they will be replacing those breakers a lot more often than they would a contactor.

 

[petersonra]

I used to do some stuff that controlled MV motors. I am pretty sure all of the MV motors were controlled directly by motorized circuit breakers.

 

[zog]

I was at a major manufacturers industrial facility recently and found that in their 480V LV Switchgear they use the power breakers to feed the motors without any contactors or overload protection.

These power breakers are electrically operated breakers that simply open and close to start/stop the motor without any contactors or overlaod protection. They simply use the LSI protection the breakers trip units to provide feeder/motor protection and try to adjust these settings as close as possible to the motor characteristics and damage points.

Has anyone ever come across this before? Seems like it would be in violation of the requirements in Article 430. I should mention that this is in the Oil & Gas industry so perhaps this may be some sort of standard in that industry.

Well if they have LSI trip unit they do have overload protection...that's the "L". I do see this set up used, it is rough on the breakers and will require more frequent overhauls since typical LV air breakers recommended overhaul cycle is around 2,000 operations, and I would not skimp on that, the coils, contacts, operating mech, and arc chutes are taking a lot of abuse.

 

[philly]

It's not that uncommon for motors that basically almost never shut down, except for emergencies and scheduled maintenance, a situation not uncommon in refineries.

This is exactly the case here were these motors are never shut down so it sounds like this is not all that uncommon.

Well if they have LSI trip unit they do have overload protection...that's the "L".

You are correct. What I meant to refer to was "thermal" protection that is usually provided by motor overloads or relays. Overloads usually have some degree of thermal memory/retention to protect motor from frequent starts, etc... but with these motors hardly ever starting/stopping as mentioned I guess overload protection doesn't become all that critical. I guess you can get an LSI trip curve to get as close as possible to mimicking a class 10/20/30 overload.

 

[kwired]

It's not that uncommon for motors that basically almost never shut down, except for emergencies and scheduled maintenance, a situation not uncommon in refineries. Breakers, motorized or not, are not built to be turned on and off a lot like a contactor. But in these circumstances, even 1,000 operations is more operating years than the rest of the refinery would last. As to the protection, there are several circumstances in which the motor thermal protection can be very widely interpreted and they will often take full advantage of that because, like I said, they are NOT going to shut them down unless it is a major issue already. So it's not quite like a fire pump, but from their standpoint, it is almost "run to destruction" because if they ever tripped on OL, the cost to the refinery could be millions of dollars.

If they are just being cheap and cycling these motors on and off a lot using the breakers, that is "penny wise, pound foolish", because they will be replacing those breakers a lot more often than they would a contactor.

Even if they never shut them down they about need to monitor motor current so they can plan a shutdown if something is outside certain limitations, or it will shut down anyway when it fails altogether. That is still overload protection in my book, just not direct overload protection.

 

[zog]

Even if they never shut them down they about need to monitor motor current so they can plan a shutdown if something is outside certain limitations, or it will shut down anyway when it fails altogether. That is still overload protection in my book, just not direct overload protection.

Depending on the trip unit used they can monitor anything they want to

 

[Jraef]

Even if they never shut them down they about need to monitor motor current so they can plan a shutdown if something is outside certain limitations, or it will shut down anyway when it fails altogether. That is still overload protection in my book, just not direct overload protection.

Right, no argument from me. It's just that when using an LSI ETU, the L function is essentially the same I²t curve you will find in a motor thermal OL relay, so since it will be adjustable to the motor amps, it does provide the same protection. The caveat is, the only thing it can do is trip the breaker and that can be hard on the breakers if it happens a lot, so ultimately more costly to replace than a contactor (or the contacts on a contactor).

 

[zog]

Right, no argument from me. It's just that when using an LSI ETU, the L function is essentially the same I²t curve you will find in a motor thermal OL relay, so since it will be adjustable to the motor amps, it does provide the same protection. The caveat is, the only thing it can do is trip the breaker and that can be hard on the breakers if it happens a lot, so ultimately more costly to replace than a contactor (or the contacts on a contactor).

You can replace the contacts on a breaker as easy as on a contactor

 

[Jraef]

You can replace the contacts on a breaker as easy as on a contactor

Power breakers, you're right. Insulated case or molded case, no so much. But this question was about power breakers, so yes. I'm still never going to be comfortable with doing lots of operations with breakers.

I did a project years ago in Eastern Washington for an irrigation pump pulling water out of the Columbia River, 900HP 460V, across-the-line starting. It started in May (at night) and stopped in October. We used a 2000AF power breaker with an ETU where the L function was programmed at 140% of the motor FLA to protect the motor. 1 start + 1 stop per year, that breaker was going to last longer than me...