Properly Sizing an Overload

[moldingppmm]

Hello all.

I'm having a issue with a motor in my shop.

I have an injection molding shop that has a pump that circulates water to the machinery. A few years ago, the motor that was on the pump went, so I ended up going out and buying a new one.
Everything was fine until the last few months. I've been having a lot of issues with my electrical service over the years, mostly when we get any weather that starts with gusts of wind and up, we single phase really bad. As winter has started, I've had this motor blow the windings twice already...in 4 weeks. I've lowered the fuse amps, which didn't help when I phased last night. So here I am, with another blown up motor.

I don't know much about motor circuits but, I'm assuming that my overload needs readjusted or I need a smaller one. Am I correct with this? I really can't afford $600 every 2 weeks.

Info from the motor:
Weg Model: 007360T3E184JM
7.5 HP

That's all I can read on the motor, I'll post a grainger link below that has the info...

Link to Grainger: http://www.grainger.com/product/WEG-Pump-Motor-4EUU2
If it doesn't come up, it's #4EUU2


Thanks for the help in advance...I appreciate it.

 

[augie47]

You definitely should check the overload setting compared to the motor nameplate amperage.
There are some situations where there would be some difference such as either the motor or controller being in a very different temperature environment but for the most part the OL rating should match the nameplate.
Considering the $600 you quoted, it might well be a good investment to install a phase monitor relay which would disconnect the motor on phase loss.

 

[meternerd]

Have you asked to POCO about the single phase problem? Sounds like they have issues. Ditto on the phase monitor relay. It may protect your motor, but you shouldn't have to deal with single phasing due to wind. If you're having problems, others likely are too. Talk to others on your circuit and if it's not just you, have everybody else gang up on the POCO. Sometimes it's hard to identify where the problem is, because 'till it's broke, you can't fix it. But they can install recorders, fault locators, etc. to find out what's up....just a question of motivation....

 

[moldingppmm]

You definitely should check the overload setting compared to the motor nameplate amperage.
There are some situations where there would be some difference such as either the motor or controller being in a very different temperature environment but for the most part the OL rating should match the nameplate.
Considering the $600 you quoted, it might well be a good investment to install a phase monitor relay which would disconnect the motor on phase loss.

I actually have a phase relay on my main, which doesn't always work... I need to check my OL settings. Should I set it at the amp on the nameplate? or go a little over? I'll look into the PMR for that circuit.

Have you asked to POCO about the single phase problem? Sounds like they have issues. Ditto on the phase monitor relay. It may protect your motor, but you shouldn't have to deal with single phasing due to wind. If you're having problems, others likely are too. Talk to others on your circuit and if it's not just you, have everybody else gang up on the POCO. Sometimes it's hard to identify where the problem is, because 'till it's broke, you can't fix it. But they can install recorders, fault locators, etc. to find out what's up....just a question of motivation....

They actually came out last night because my building was phasing when I went in, no idea how long it lasted. They actually stayed all night and replaced my transformer. Not sure why, but they did. The guy said it could be on the building side, but I'm sure that was to pass the blame. I'm not sure about anyone else having issues, I'll check with neighbors, although I'm surrounded by houses, and there's no other industrial phase buildings.

They're closed today, but I'll call and give an earfull and at least see if I can get some sort of monitoring on my service...



I'll have to check into the monitor, I don't know much about them, time to do some investigating...

Thanks everyone

 

[augie47]

Here's an article:\

http://ecmweb.com/content/basics-selecting-overload-relays

 

[Jraef]

A standard NEMA OL relay will not protect your motor from single phasing unless the motor is almost full loaded to it's capacity. When a phase is lost while it is already running, the other two phases will increase in current, but if your load on the motor is lower than the motor's capacity, the amount it increases to may still be less than the FLA rating, so the OL relay will not notice. But at the same time, the single phase power feed creates what is called "negative sequence current" in the rotor, which opposes the rotation direction and "fights" the stator current, increasing the amount of heat inside of the motor without necessarily increasing the current draw. So because the OL relay selection is ASSUMING a healthy motor, the motor is over heating with a current too low to cause it to trip. Changing fuses will not have any effect for the same reason.

As to Phase Monitor Relays, the biggest problem is that many of the cheaper ones only monitor voltage. If you get a phase failure while motors are spinning already, the voltage monitors will often be fooled by the regenerated voltage from the un-powered legs of those spinning motors, the exact same phenomenon that we call a "rotary phase converter" for getting 3 phase out of a single phase source. So those things are really only good for preventing a re-start after a phase loss, but they rarely trip on a phase loss while things are running.

Either get a current based phase loss monitor, or better yet, replace your overload relays with solid state OLs from the same mfr, 99% of which now come with current based phase loss protection.

IEC overloads are often sold as having "phase loss protection", which is partially true. Their bi-metal OL sensors are connected to a balancing spring that requires equal force from all 3 phase sensors. If one goes away, the balancing spring serves to shift the mechanical trip mechanism to be physically closer to the sensors, meaning it takes less of an overload to make it trip. It helps, however it is not fool proof and plenty of people still lose motors on single phasing with them too.

 

[petersonra]

I actually have a phase relay on my main, which doesn't always work.

That seems odd. What does this phase relay do? Shunt trip the main?

 

[Research1]

Single phase motor protection

Single phase motor protection

First, get the service fixed. Call the utility, it is their job to provide sustained 3 phase power.
If your are single phasing the whole building during high winds look for a loose connection in the incoming service wires.

Next, look into motor overload relays with single-phase protection. Eaton ? Cutler Hammer makes one.
What it does is measures the current in all three phases. When the phase currents are different by some percentage, it trips and takes the motor off line. It also indicates that it was a single phase trip.
A motor can continue run while being single phased for several minutes. It cannot start on single phase. The single phase trip time on start is 10 to 30 seconds.

Best regards Jerome

 

[Aleman]

A standard NEMA OL relay will not protect your motor from single phasing unless the motor is almost full loaded to it's capacity. When a phase is lost while it is already running, the other two phases will increase in current, but if your load on the motor is lower than the motor's capacity, the amount it increases to may still be less than the FLA rating, so the OL relay will not notice. But at the same time, the single phase power feed creates what is called "negative sequence current" in the rotor, which opposes the rotation direction and "fights" the stator current, increasing the amount of heat inside of the motor without necessarily increasing the current draw. So because the OL relay selection is ASSUMING a healthy motor, the motor is over heating with a current too low to cause it to trip. Changing fuses will not have any effect for the same reason.

Great explanation on why standard OL doesn't protect against phase loss. Thanks!

We have a bunch of pump carts that run off cord drops. The drops get abused and sometimes a wire will pull loose on either the drop or power cord. And we lose motors even though
they have OL's on them. This explains it and it makes sense. Usually motors don't run at FLA, actual current will be less and the OL is at 125% of FLA. Seems like a recipe for smoked motors.

Now I need to find a manual starter with electronic overload that will catch phase loss. We like to use those because then no control box is required, a simple pump cart control.

 

[klRc80]

My first post in the forum

My first post in the forum

Hi all, this is my first post in the forum, so go easy on me if I make a faux pas.

Regarding solid state phase imbalance/loss protection:

I happen to come across the 2 products below on a website yesterday that may be applicable to moldingppmm
's situation. Is it correct to say that (if the first device in the link below actually measures current in the 3-phases) the first product will trip if I can magically disconnect one phase of the motor winding in the motor while for the 2nd linked product below (assuming it only measures the incoming voltage), it will happily think that there's nothing wrong?

On the first link below, it claims that it "Detects phase failure even at 95% voltage feedback from the motor". However it is only connected to L1, L2, L3 at one point and is not in series with the load. I wonder how is it able to sense that.

Either get a current based phase loss monitor, or better yet, replace your overload relays with solid state OLs from the same mfr, 99% of which now come with current based phase loss protection.

BTW Jraef, what are your thoughts in using traditional thermal OLs on contactors plus one of the devices in the link below versus using solid state OLs plugged under contactors?

Kris

http://klocknermoeller.com/emr4/emr4-a400-1.htm

http://klocknermoeller.com/emr4/emr4-w500-2-d.htm

 

[Jraef]

Hi all, this is my first post in the forum, so go easy on me if I make a faux pas.

Regarding solid state phase imbalance/loss protection:

I happen to come across the 2 products below on a website yesterday that may be applicable to moldingppmm
's situation. Is it correct to say that (if the first device in the link below actually measures current in the 3-phases) the first product will trip if I can magically disconnect one phase of the motor winding in the motor while for the 2nd linked product below (assuming it only measures the incoming voltage), it will happily think that there's nothing wrong?

On the first link below, it claims that it "Detects phase failure even at 95% voltage feedback from the motor". However it is only connected to L1, L2, L3 at one point and is not in series with the load. I wonder how is it able to sense that.



BTW Jraef, what are your thoughts in using traditional thermal OLs on contactors plus one of the devices in the link below versus using solid state OLs plugged under contactors?

Kris

http://klocknermoeller.com/emr4/emr4-a400-1.htm

http://klocknermoeller.com/emr4/emr4-w500-2-d.htm

My thoughts:
A) I used to work for KM, the device in the second link can definitely be fooled by motor regen. They tend to be good for putting into a larger system, for example behind a main fused switch, to detect a blown fuse, over/under voltage or phase reversal (good if you use portable plug-in generators) and tie into an overall control circuit to turn everything off. But on a single motor starter, I have seen them be fooled.

When I was there though, the version in the first link was not yet made. I have seen this claim made by other voltage sensing devices in the past, and have seen those fail to protect an individual motor. Not that exact unit, but others like it that claim the "95% voltage feedback from the motor" like this one does. They are likely all using the same algorithm, and it appears to have limited ability when connected to one motor circuit. That one by the way is also only sensing voltage, not current. It is looking for a voltage imbalance, which will LEAD to a current imbalance, but I found that the problem is that if you set it tight enough to not be fooled by regen, you end up getting nuisance tripping from relatively common voltage imbalances that happen on utility supplies thought a work day in the real world, so after 5 or 6 nuisance calls, it ends up adjusted to where it no longer picks up a single phase if the motor is running when it happens.

B) Adding a device like that to a single motor starter will cost far more than just replacing the standard OL relay with a solid state version, which offers added benefits as well. So it's basically pointless.

 

[Jraef]

...
Now I need to find a manual starter with electronic overload that will catch phase loss. We like to use those because then no control box is required, a simple pump cart control.

So far, Siemens are the only ones with a manual starter that has a solid state overload in it, but I can't remember if it needs control power or not. I think it does, but you can look for info on the 3RA6 series. Allen Bradley will be releasing one some time later this year, but I don't know any details on it yet. It's difficult to self-power a solid state OL with enough energy to trip a manual starter mechanism.

("Self-powered" in SSOLs means that the power to run the electronics in the OL is derived from the current sensors used in the relay itself, rather than an external power source. Because it is very low voltage DC tapped off of hall effect sensors, it is very limited, usually only enough to run an ASIC chip and charge a capacitor to store some energy to pull in the trip relay. A Manual Motor Starter usually needs more mechanical force than that can deliver, so using that self powered concept on a MMS would mean redesigning the entire MMS Operating mechanism from the ground up.)

 

[kwired]

One also has to weigh cost of a replacement motor, cost of being down if the motor needs replaced, cost of a simple vs, more complex protective device, and the frequency of phase loss events. If you have fairly reliable power and not so critical loads, maybe it is financially acceptable to go with the lesser cost install even though you may occasionally need to change a motor. Higher torque loads will trip simpler thermal overloads much easier on single phase condition as well compared to lower torque loads.

 

[kwired]

Whether OP changes his overload protection or not, I still think he needs to resolve the issue/ have POCO resolve the issue causing this frequent single phasing condition. If POCO will not do anything maybe have Power monitoring done and show them there is a problem. Could be as simple as a weak connection on a primary line that fails when the weather is just right for it, may be in the right place on the system that you are the only customer that is effected by it.

Not too long ago I had power issues at home (I live in rural area) where we would have an occasional "blink" in the voltage. I asked POCO supervisor to check into it. He called me back and said they found a weak connection on a pole a couple miles down the road and that probably was the cause - problems did go away after that. A few years back we did get similar "blink" and seemed to always be about the same time of day, and only during irrigation season when load on system was higher. That following winter we had a major ice storm that took down a lot of lines - that problem went away after the rebuild - but my guess was a similar intermittent weak connection was the issue and it happened to be in a location that had to be rebuilt, or at least something that was re - terminated during the rebuild.

 

[Jraef]

I was doing a small project out at a very remove gravel pit, and in the middle of it, the plant went down. I wasn't their official electrician, but I was the only one there at the time, so I checked into it. They had lost a phase, but I didn't have any tools to be able to check the primary feed. Call the utility (So Cal Edison) and they called back in 15 minutes telling me they checked their system and everything was fine. I knew that was not enought time. Since I couldn't do anything else, I left the site and about 10 miles down the lonely little road leading to this plant, I came across one of the primary wires laying on the ground, having started a grass fire. Yep, everything was fine...

My project out there was adding soft starters for all of the big motors, because they had expanded the plant and had trouble with voltage drop. I told them even before I took the job that it likely wasn't going to work, because the one-line indicated the primary service was too small. But SCE kept saying no, it was fine. Yep, everything was fine...

 

[kwired]

I was doing a small project out at a very remove gravel pit, and in the middle of it, the plant went down. I wasn't their official electrician, but I was the only one there at the time, so I checked into it. They had lost a phase, but I didn't have any tools to be able to check the primary feed. Call the utility (So Cal Edison) and they called back in 15 minutes telling me they checked their system and everything was fine. I knew that was not enought time. Since I couldn't do anything else, I left the site and about 10 miles down the lonely little road leading to this plant, I came across one of the primary wires laying on the ground, having started a grass fire. Yep, everything was fine...

My project out there was adding soft starters for all of the big motors, because they had expanded the plant and had trouble with voltage drop. I told them even before I took the job that it likely wasn't going to work, because the one-line indicated the primary service was too small. But SCE kept saying no, it was fine. Yep, everything was fine...

We don't have those kind of problems very often with POCO's here - but they are still publicly owned not for profit organizations. They do put extra revenue back into building a better system instead of lining the pockets of owners with it, and we have a fairly reliable system except when mother nature comes and shows just how much power she still has.

When I am driving country roads and see a problem on a pole I call the supervisor at the local POCO - they thank me and depending on how serious the problem is they plan accordingly to have it repaired. A neutral conductor that came loose from its mount maybe hangs there a few days, but at least they know about it, but when sparks are falling from a weak connection at a cutout (seen those a few times) they are coming out ASAP, I just happened to see a future failure before it fails in most of those instances.

 

[Aleman]

So far, Siemens are the only ones with a manual starter that has a solid state overload in it, but I can't remember if it needs control power or not. I think it does, but you can look for info on the 3RA6 series. Allen Bradley will be releasing one some time later this year, but I don't know any details on it yet. It's difficult to self-power a solid state OL with enough energy to trip a manual starter mechanism.

I like the 3RA6 series and we have using them in our panels for motors that don't need drives. They do need control voltage so they aren't a stand alone controller. They are easy to change out because everything
snaps into place.

I did some looking and see that Allen Bradley makes a manual motor starter that protects against phase loss, MS132 series. These types are nice because you can mount them in a little plastic box and
no other control is needed. http://new.abb.com/low-voltage/products/motor-protection/manual-motor-starter

We have been using a similar product made by Siemens but without any phase loss protection. I have been telling the guys to just set our OL's at FLA and not at the 125% for the time being and unless we get a
lot of nuisance trips we will stay with that.

 

[Jraef]

...

I did some looking and see that Allen Bradley makes a manual motor starter that protects against phase loss, MS132 series. These types are nice because you can mount them in a little plastic box andno other control is needed.
...

That's not Allen Bradley, too many "B"s...

That device protects against phase loss exactly the same as all IEC bimetal overload devices do, it's just that ABB stretches the truth more than others in their description. As I said above, it will only trip on a phase loss if the motor is close to fully loaded, because all it does is skew the trip point of the overload a little lower than normal. If the motor is lightly loaded it may never trip, or at least not until the insulation fries and there is a phase to phase internal short, at which point it is too late. All IEC overload relays and manual motor starters with bimetal trips do this, including the one you said you use from Siemens, and the ones from Allen Bradley. There is nothing different about that ABB unit other than their marketing department. Everyone else calls it "phase loss sensitivity" which is a little more apt, although people still over interpret that too.

The official term for that feature, when Klockner Moeller invented the technology in the 50s, was/is "differential phase current imbalance under-curve adaptation", which you can imagine was a 3 mile long sentence in German. But that was apparently not sexy enough for the marketing people. KM lost their patent rights to it in the late 70s, which is when just about everyone else in the world (except NEMA mfrs in North America) adopted it.

 

[Aleman]

That's not Allen Bradley, too many "B"s...

That device protects against phase loss exactly the same as all IEC bimetal overload devices do, it's just that ABB stretches the truth more than others in their description.

Well that sucks. I was wondering if it was a stretch since there is no control voltage for it work with. I want to get away from needing to build a control box with a power supply and
switches. But it seems that in order to truly protect a motor you need to do just that.

 

[Jraef]

Well that sucks. I was wondering if it was a stretch since there is no control voltage for it work with. I want to get away from needing to build a control box with a power supply and
switches. But it seems that in order to truly protect a motor you need to do just that.

Viable option, not too involved:

Allen Bradley enclosed mag starter with E1 Plus SS OL relay, line voltage control (so no control transformer is necessary), Start-Stop PB on the cover.

It's not just because they happen to sign my paycheck twice a month (I'm in a different division anyway), it's because I know that the aux contacts on the E1 Plus SSOL are rated for up to 600VAC, making them suitable for using line voltage control, regardless of your line voltage. The E1+ is also one of the few SSOLs that does not need a separate source of control power, it is powered by the current flowing through it, and it has true current based phase loss protection built-in.


IEC version, you can get it with a NEMA starter too.


There may be other options out there, but nobody pays me to care any more...