480v 60hp motor throwing breaker, now?

[paulengr]

Ages ago, the NEMA definition of "Service Factor" used to mention it being suitable for a "intermittent" use, without ever actually defining what "intermittent" meant. Somewhere a couple of decades ago, NEMA amended it to remove all reference to SF having a time frame associated with it, so OEMs have been using that to run motors into the SF continuously. What NEMA says now though is a bit more namby-pamby...'



So from the OEM's perspective, if that "reduced life expectancy" is still beyond their stated warranty period for their equipment, they are good with it. It's only the end user that suffers.

NEC at least covers this with a whole intermittent duty chart. You can calculate this out using %TCU. I would think that anyone selling this type of equipment should run those calculations because otherwise they would eat a lot of warranty claims. Especially submersibles are a VERY specialized motor. There are only a few (less than 4) motor shops in the US with the equipment to rebuild most of them. Most motor shops offer rebuild services but send the stators out to one of the specialty shops.

Not surprised about submersible life though for MOST users. This is not a normal application. The motor is water cooled. So cooling depends on temperature and clearly when it is sitting in a hole full of water at ground temperatures or better, it might last far longer.

 

[petersonra]

The HVAC manufacturers tend to be pretty cheap and my experience with them is they run well into the service factor much of the time. No reason not to. For the most part it won't hurt the motor. I've really never quite understood the point of having a service factor anyway. Why you would want to call a 115 horsepower motor a 100 horsepower motor escapes me. But I think it has something to do with the general proclivity of American engineering to over engineer stuff in the past. To me I don't see a whole lot of difference between applying a motor that is 100 horsepower with a 1.15 service factor and a 115 horsepower motor. Basically it's the same thing.

 

[retirede]

So you operate at 1.10. On a 1.15 SF motor what happens with a 1% voltage unbalance or a 10% overvoltage as per NEMA?

It can be a problem, for sure. The simple answer (as Jraef mentioned) is that motor life is shortened. It’s all about the ultimate temperature of the windings over time. By how much? Unknown without more complete details.

Other parameters may offset - motors are rated for 40C ambient, for example. Unless it 40C 100% of the time, you get some thermal headroom from operating below max ambient.

Real world experience in the industry is that virtually all motors operated this way will last more than 10 years and that is acceptable to our customers.

Note that most modern compressors utilize VFDs. So the constant load at 1.1 SF is becoming a thing of the past.

 

[paulengr]

It can be a problem, for sure. The simple answer (as Jraef mentioned) is that motor life is shortened. It’s all about the ultimate temperature of the windings over time. By how much? Unknown without more complete details.

Other parameters may offset - motors are rated for 40C ambient, for example. Unless it 40C 100% of the time, you get some thermal headroom from operating below max ambient.

Real world experience in the industry is that virtually all motors operated this way will last more than 10 years and that is acceptable to our customers.

Note that most modern compressors utilize VFDs. So the constant load at 1.1 SF is becoming a thing of the past.

I really, really doubt that last statement. Maybe this is true with centrifugal compressors but not screws at least. To begin with we have to consider all three technologies. The first is load/unload. It works but we usually treat it as a “baseline” technology...the one to beat. Next is turning vanes. What are those? It’s a slotted damper in the bottom of the screw that turns it into variable volume. Cheap upgrade. This provides variable flow efficiently with roughly a 2:1 turndown and no 5% performance hit running an electronic drive. Now below this point VFDs CAN be more efficient. But since motor integral fan cooling is no longer efficient the VFD requires a separate blower on the motor so the low end is more efficient with load/unload leaving a very narrow band around 1:2 to 1:3 turndown where VFD compressors are more efficient but better overall would be two smaller compressors with turning vanes. So when you calculate ROI the VFD compressor is a loser.

Different scenario with centrifugals but those aren’t nearly as common as screw compressors and recips.

 

[hillbilly1]

Just looked at a two year old screw compressor for a tire changing area.It was at a truck maintenance facility, and they thought it may have started a fire. The only thing, I could not find any evidence of it being the source. The motor was going bad though, four amps over FLC. They had major air line leaks, and compressor was starting ever couple of minutes with nobody using air. Did find the source of the fire though, they had holes in the block wall of the wash bay, that was common to the compressor wall, people were throwing trash and their cigarette butts into the hole!

 

[kwired]

NEC at least covers this with a whole intermittent duty chart. You can calculate this out using %TCU. I would think that anyone selling this type of equipment should run those calculations because otherwise they would eat a lot of warranty claims. Especially submersibles are a VERY specialized motor. There are only a few (less than 4) motor shops in the US with the equipment to rebuild most of them. Most motor shops offer rebuild services but send the stators out to one of the specialty shops.

Not surprised about submersible life though for MOST users. This is not a normal application. The motor is water cooled. So cooling depends on temperature and clearly when it is sitting in a hole full of water at ground temperatures or better, it might last far longer.

One other issue with submersibles is flow. Sitting in a hole full of water at ground temp only keeps it cooled if there is flow. If no flow it eventually heats up water surrounding it, is a slower warm up than for most air cooled motors and can ride through temporary no or low flow cycles.

 

[retirede]

I really, really doubt that last statement.

It’s a free country...

 

[hillbilly1]

It’s a free country...

For now.......LOL!

 

[ptonsparky]

Several years ago we put a VFD on a well that supplied a housing development that had suffered several submersible pump motor failures. At 20 HP they weren't happy. FWIW the electrician servicing them at the time had bypassed the overloads to make sure it ran, even though it was detecting a current imbalance. Along with the pump installer we gave very careful consideration as to the water flow around that motor. Too low and we would have had to put a shroud around the motor to make sure it moved that water and replenished it with cooler.

One other issue with submersibles is flow. Sitting in a hole full of water at ground temp only keeps it cooled if there is flow. If no flow it eventually heats up water surrounding it, is a slower warm up than for most air cooled motors and can ride through temporary no or low flow cycles.

 

[kwired]

Several years ago we put a VFD on a well that supplied a housing development that had suffered several submersible pump motor failures. At 20 HP they weren't happy. FWIW the electrician servicing them at the time had bypassed the overloads to make sure it ran, even though it was detecting a current imbalance. Along with the pump installer we gave very careful consideration as to the water flow around that motor. Too low and we would have had to put a shroud around the motor to make sure it moved that water and replenished it with cooler.

Small single phase domestic wells you generally have thermal protector embedded in the motor, still doesn't do it any good to keep cycling every time it cools only to trip after somewhat short run time again. Not only is it hard on motor windings, but probably heats up the pump parts as well, including bearings and seals which leads to other mechanical failures.

 

[garbo]

Hey all,
I've recently provided power for my client's latest purchase a used grain mill. The mill has a WEG 3ph 60hp motor and came with a pre-wired starter.
I ran the circuit to the machine and installed a 90amp Siemens BQD series breaker in the load center. We initially tested the machine & starter with just the starter and it seem to run fine. A few days later I installed a 100a non-fused safety switch beside the starter, now when we turn the machine On via the starter it trips the breaker within a second or two. The only other thing that has changed aside from installation of the safety switch is the belts were adjusted. I've checked all the voltages and verified the correct connections, I'm obviously missing something here. Hope someone can point me in the right direction. I've attached a few photos below.
Thank you

Note: The phase to phase voltage on-site is actually 495v

For last 50 years usually only went 125% over motor full load amps for the circuit breaker except for guess some would call high start up amps like in air compressors & air conditioners. Had several air compresdors that shut off at 120# and were okay with a 125% breaker but on a few for large truck garage compressors that shut off at 150# we would have to go with a circuit breaker 135 to 150% over motor FLA. Once worked in a dangerous old centrifuge that you had to hold in start button for over 30 seconds until it came up to speed then push in run button. Breaker had to be around 200% of motor FLA to not trip. When tech was done working on unit only 1 electrician was allowed to stay in room in the event it blow up.

 

[kwired]

For last 50 years usually only went 125% over motor full load amps for the circuit breaker except for guess some would call high start up amps like in air compressors & air conditioners. Had several air compresdors that shut off at 120# and were okay with a 125% breaker but on a few for large truck garage compressors that shut off at 150# we would have to go with a circuit breaker 135 to 150% over motor FLA. Once worked in a dangerous old centrifuge that you had to hold in start button for over 30 seconds until it came up to speed then push in run button. Breaker had to be around 200% of motor FLA to not trip. When tech was done working on unit only 1 electrician was allowed to stay in room in the event it blow up.

source and/or line impedance sometimes has an impact.

Seen motors that worked for years with no problem on marginally sized breaker, then change the source, increase the service/feeder capacity or other similar activity that lessens impedance and all of a sudden that breaker that never tripped before randomly trips when starting - all because starting current is allowed to be higher than it used to be because of lower circuit impedance.

 

[Jraef]

Who does that? Trying to think of I’ve ever seen this.

You must not have looked at the photo in the first post of the label from the WEG OL relay. It specifically says "Use fuses only".