I purchased a Rotary Vertical Blanchard Grinder that has a 50 H.P motor that was originally wound for 3 phase and 50 hertz. I was told by the seller that I can run it at 60 hertz 3 phase without any problems. Over the last 6 years, I had the motor rewound two times and it costs thousands to rewind it, now it burned up again. The motor is an intregal part of the machine and can not be replaced with a new 60 hertz type. What can I do to prolong the life of the motor?
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Three phase motor burns out every three years ? WHY 1
- Thread starter bigj2
- Start date
I would question the sellers statement that a 50 Hz motor can run on 60 Hz. A motor is designed for a certain level of magnetic flux. This value remains relatively constant if the V/Hz ratio remains constant. How does the ratio of your supply voltage /60 compare to the motor rated volts /50? If the frequency has increased without an equivalent increase in voltage, then the motor is not developing its design torque which means it will draw more current to supply a particular load torque. This would explain the impact on motor life.
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1
- #4
Your original post neglects to state what the motor was originally namplated for:
______V.
______A.
______RPM
and what voltage you've been operating it on these past three years ... ?
Also, have you taken any current measurements when running it on 60 HZ supply ...
and, how much load (HP) are you running at ..?
Therein lie the answers .....
______V.
______A.
______RPM
and what voltage you've been operating it on these past three years ... ?
Also, have you taken any current measurements when running it on 60 HZ supply ...
and, how much load (HP) are you running at ..?
Therein lie the answers .....
bigj2
As the others suggest you should provide much more information:
What are the exact motor nameplate data ?
How is the motor driven ? Direct, y/d, softstarter, VFD ?
What is the load ?
Measure the current in all three phases and over a long time.
In addition to the above, consider to have temperature sensors installed in all three windings. It will give you two advantages:
- Will tell you how the motor really is loaded.
- Will protect the motor so that you dont have to rewind it.
As you allready have to open the motor up in order to rewind it, you have a great opportunity to do it now !
Another possible cause of insulation break down, can be voltage spikes. Measure the voltage over a longer time.
Possibly install "snubbers" to protect against overvoltage spikes.
As the others suggest you should provide much more information:
What are the exact motor nameplate data ?
How is the motor driven ? Direct, y/d, softstarter, VFD ?
What is the load ?
Measure the current in all three phases and over a long time.
In addition to the above, consider to have temperature sensors installed in all three windings. It will give you two advantages:
- Will tell you how the motor really is loaded.
- Will protect the motor so that you dont have to rewind it.
As you allready have to open the motor up in order to rewind it, you have a great opportunity to do it now !
Another possible cause of insulation break down, can be voltage spikes. Measure the voltage over a longer time.
Possibly install "snubbers" to protect against overvoltage spikes.
brucecranene
Mechanical
Installing a properly sized capacitor will make the motor run cooler and therefore longer. Also the power factor will be optimized to close to unity. And kw will be saved.
Previous post suggests motor will run cooler with capacitors. This is not really true. The motor power factor cannot be changed it is a function of design and interaction between coils etc.. The capacitors will change the power factor of the system but not of the motor. The system current will be lower but the vars supplied to the motor will be the same. They will be supplied from the capacitors instead of the system. My apologies for the rather cludgy explanation
brucecranene
Mechanical
True, the capacitor will supply the vars, just the point. When the "system" supplies the vars not all of the current is used for the maintenance of the magnetic field, the remainder goes to wasted watts, heat to the motor. By installining the cap, the wasted watts is no longer present, heating the windings, therefore the motor runs cooler, try it and see!
It is true that the capacitor will reduce wasted watts. However, these wasted watts will be in the power delivery system not in the motor. The reduction in losses in the supply line will improve the voltage levels and this will in turn reduce the current required by the motor and this will in effect make the motor run cooler. This impact will be most noticeable with long supply cables. Utilities have mobile capacitor banks that are used to improve voltage when required. With long cables motor will run cooler, with short cables I would think the effect would be minimal.
brucecranene
Mechanical
The wasted watts are all the way from the motor to the supply source. The effect of the cap is from the point of installation. The utility sponsored ones are usually connected on their side of the meter or just inside of the meter. In each case the cusomer does not realize the benefits of eliminating the the wasted watts. Puttting the caps on the motors load side of the contactor benefits both parties. The elimination of the wasted watts is not a small benefit. Up to 30% kw savings for the inductive loads can be realized. Not to mention a 10-30 F decrease can be realized in the motor. Also the vars are drastically reduced, allowing the utility to produce kw instead of vars or eliminating the cap banks. True the vars volts amps va kw are all the same from the cap to the motor, but what has changed is the system no longer "sees" the inductive load as an inductive load but rather a "resistive' load.
electricpete
Electrical
One other small effect. Installing cap may raise the motor terminal voltage, providing slight improvement in efficiency (under most circumstances).
brucecranene
Mechanical
Jbartos
What type of process has this type of dynamics that would cause dangerous oscillations. What type of damage are you talking about. chronic or acute. I've put these on plastic extrusion, elevators etc without any apparent damage. Do you have a sourse reference?
What type of process has this type of dynamics that would cause dangerous oscillations. What type of damage are you talking about. chronic or acute. I've put these on plastic extrusion, elevators etc without any apparent damage. Do you have a sourse reference?
So, JB, perhaps you'd like to suggest a methodology to use to perform such analysis ... rather than to just throw our such a statement without foundation or without sufficient explication that would make it useful.
Not saying you are incorrect, Joseph, but you really do need to provide more information so that those who are not familiar with such consideration will be able to relate to your statement, understand what you mean, and have some guidance as to how to perform such an analysis.
Otherwise, Joseph, the statement in and of itself, provides no useful information and is hardly worthy of any consideration.
Kind of like telling a starving man to eat something ... without providing him any food.
You leave him with an empty stomach.
j
Not saying you are incorrect, Joseph, but you really do need to provide more information so that those who are not familiar with such consideration will be able to relate to your statement, understand what you mean, and have some guidance as to how to perform such an analysis.
Otherwise, Joseph, the statement in and of itself, provides no useful information and is hardly worthy of any consideration.
Kind of like telling a starving man to eat something ... without providing him any food.
You leave him with an empty stomach.
j
Code:
Ωjbartos
Electrical
- Jan 15, 2000
- 6,440
- 0
- 0
Suggestion to brucecranene (Mechanical) Dec 6, 2003 marked ///\\Jbartos
What type of process has this type of dynamics that would cause dangerous oscillations.
///E.g. eccentric punch presses, and generally, any periodic engagement of load via mechanical clutches or electromagnetic couplings. This should not be difficult to identify for mechanical engineer or technician or handyman.\\ What type of damage are you talking about. chronic or acute.
///I did not mention any damage. The electrical equipment or loads are often very well protected. Therefore, the word "dangerous may be interpreted in terms of tripping the circuit and load.\\ I've put these on plastic extrusion, elevators etc without any apparent damage
///These types of loads tend to be better behaving loads for electrical motor, unless ten (? mechanical challenge) people start simultaneously jumping up and down in the elevator.\\ Do you have a sourse reference?
///Visit
for:
Cyclic load insensitivity: HTS motor field windings operate at nearly constant temperature unlike conventional motors and, therefore, are not subject to thermal fatigue.
for:
Note: Current oscillations can also be caused by a cyclically varying load.
for:
Studies in Dynamic Simulation and Analysis of Var compensators Feeding Cyclic Loads - A Feasibility Study of an AR model.(With G Govinda Rao, J Gopalachar and K Parthasarathy).
\\
What type of process has this type of dynamics that would cause dangerous oscillations.
///E.g. eccentric punch presses, and generally, any periodic engagement of load via mechanical clutches or electromagnetic couplings. This should not be difficult to identify for mechanical engineer or technician or handyman.\\ What type of damage are you talking about. chronic or acute.
///I did not mention any damage. The electrical equipment or loads are often very well protected. Therefore, the word "dangerous may be interpreted in terms of tripping the circuit and load.\\ I've put these on plastic extrusion, elevators etc without any apparent damage
///These types of loads tend to be better behaving loads for electrical motor, unless ten (? mechanical challenge) people start simultaneously jumping up and down in the elevator.\\ Do you have a sourse reference?
///Visit
for:
Cyclic load insensitivity: HTS motor field windings operate at nearly constant temperature unlike conventional motors and, therefore, are not subject to thermal fatigue.
for:
Note: Current oscillations can also be caused by a cyclically varying load.
for:
Studies in Dynamic Simulation and Analysis of Var compensators Feeding Cyclic Loads - A Feasibility Study of an AR model.(With G Govinda Rao, J Gopalachar and K Parthasarathy).
\\
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