Motor Unbalance Situation
Motor Unbalance Situation
(OP)
Hello All,
I am currently assigned to a Paper Mill and ran into a situation were a Wood Hogger No. 3 motor is going out on Phase Unbalance via a Multilin 269 Motor Protection relay. The Alarm is set at 10% 12A over FLA and the trip is set for 20% 24A over FLA. The motor installed is a 500HP 2300V FLA 112 1184RPM Westinghouse Industrial Severe Duty Motor. I was told that the motor is driving a drum that has giant hammers that are coming into contact with the bark thus breaking the bark into finer pieces. PT's are connected on the load side of contactor to motor and the PT's are all measuring a balanced output of 2.47kV. The CT's are 150/5 and connected through a shorting TB then into the relay. One observation was that in recent days the bark was water logged and caused the tripping occurence to be more frequent. Another note is that a previous 800HP motor was connected and sent out to be tested while the 500HP motor is presently handling the current load. The 500HP motor is also showing unbalance symptons. Any bones thrown at me is greatly appreciated. Thanks in advance.
I am currently assigned to a Paper Mill and ran into a situation were a Wood Hogger No. 3 motor is going out on Phase Unbalance via a Multilin 269 Motor Protection relay. The Alarm is set at 10% 12A over FLA and the trip is set for 20% 24A over FLA. The motor installed is a 500HP 2300V FLA 112 1184RPM Westinghouse Industrial Severe Duty Motor. I was told that the motor is driving a drum that has giant hammers that are coming into contact with the bark thus breaking the bark into finer pieces. PT's are connected on the load side of contactor to motor and the PT's are all measuring a balanced output of 2.47kV. The CT's are 150/5 and connected through a shorting TB then into the relay. One observation was that in recent days the bark was water logged and caused the tripping occurence to be more frequent. Another note is that a previous 800HP motor was connected and sent out to be tested while the 500HP motor is presently handling the current load. The 500HP motor is also showing unbalance symptons. Any bones thrown at me is greatly appreciated. Thanks in advance.





RE: Motor Unbalance Situation
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Motor Unbalance Situation
RE: Motor Unbalance Situation
A current imbalance can be caused by a high resistance connection somewhere. Often connections loosen due to thermal cycling. Has anyone re-tightened ALL the connections lately?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Motor Unbalance Situation
RE: Motor Unbalance Situation
RE: Motor Unbalance Situation
RE: Motor Unbalance Situation
RE: Motor Unbalance Situation
If that's close to the exact wording of his response, I would consider that a brush-off answer. In other words, somebody is assuming that, maybe even by just reading the nameplates, not by actually measuring. I would want to know the exact voltages read phase-to-phase and phase to ground on both sides of each PT.
I have noticed lately that since the advent of stricter implementation of the space suit thing, field people are uncomfortable in them and tend to rush through tests or make generalizations so they can get out of them, then overstate their findings to avoid suiting up again. Insist on a detailed voltage report.
In the mean time can you even just go look at a switchboard meter somewhere upstream of this starter? That would not find any problems within the starter but it would confirm or eliminate any upstream issues. or does the 269 have the MTM metering module on it? If so, you could read the voltages right at the meter.
RE: Motor Unbalance Situation
1) Motors are wound on a laminated steel stator core. The stator laminations have a grain which results in the magnetic permeability being spacialy non linear. If you compare the inductance on two quadrature axis, you will find that the inductance in one axis does not equal the inductance in the other (unless you orient the two axis at 45 degree to the grain)
If the steel is rotated as the laminations are punched, you can get a balanced field in the gap. In many cases, the flux in the gap is not balanced due to grain orientation in the lamination steel. This results in an imbalance in the line currents into the motor when connected to a perfectly balanced supply.
2) In any supply, there are inherent imbalances. These imbalances can be due to slight variances in impedance in transformers and line impedances, or even just an imbalance in other connected load.
The important factor is not the magnitude of the voltages on each of the three phases, it is the balance of the three phase vectors. It is possible to have a situation where the three phase magnitudes are equal, but the angles are not and this will cause an imbalance in the current. If there is a vector imbalance, it will show up if you do a phase to phase voltage check, and a phase to neutral check. One of the measurements will show an imbalance. Most (all?) supplies have an inherent imbalance which may not be obvious as it may be an imbalance in supply impedances and/or voltage vectors.
In many cases where there is an imbalance in motor current, it can be difficult to see the reason why, but if you rotate the connections to the motor, you will find that one combination will maximize the imbalance, and one combination will minimize the the imbalance, essentially using the imbalance in the motor to cancel the imbalance in the supply.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Motor Unbalance Situation
I wrote down the driven equipment info to get an understanding of the driven equipment and found the following website. h
Thanks for everyones help. I will let you know what transpires.
Jason
RE: Motor Unbalance Situation
respectfully
RE: Motor Unbalance Situation
Thanks for the link JBUDA54.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Motor Unbalance Situation
Voltage unbalance is a likely cause, but not the only possible cause. Some other causes mentioned above.
"...motor is going out on Phase Unbalance via a Multilin 269 Motor Protection relay. The Alarm is set at 10% 12A over FLA and the trip is set for 20% 24A over FLA"
What does that mean? Vector sum of three curretns exceeds FLA+20? That would be a very high unbalance setpoint. Does the relay record the actual currents at the time of trip?
Is it running or starting when it trips?
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RE: Motor Unbalance Situation
Jason
RE: Motor Unbalance Situation
We found out yesterday that the unbalanced trips were nuisance trips. The data logger showed at the time of the trip, the phase currents were only 2% different. The Multilin 269 has an entire page in the book on this type of trip, especially with this type of application. We changed the Multilin out with a 369 which looks at unbalance in a different way. In addition to this, we activated the thermal circuitry for measuring unbalanced trip. This is used to make an additional check using the RTD's in the motor. Only time will tell, however the Hog ran at 20 Ton/Hr last night. The system is down today for a Field Day. We will continue to monitor. By the way, the voltages were around 2% different from phase to phase.
Since I am not as familiar with the 269 vs the 369 can anyone elaborate on this?
RE: Motor Unbalance Situation