Motor Situation Overspeed?

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eanton22

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I have a situation where a power feed is supplied to the motor.

If the breaker of the power feed trips, I know we have an overcurrent in the power feed.

In general, what does the motor see? Overcurrent? Would the motor be overspeeding??
 
I would think the motor would see an overspeed since current and speed are proportional. Any thoughts on this??
 
If the circuit breaker feeding the motor trips due to an overcurrent, then the overcurrent would normally be caused by a fault, phase-to-ground or phase-to-phase, in the cable feeding the motor or in the motor itself. In either case it would not cause an overspeed on the part of the motor. Speed is a function of frequency and number of poles.
 
Power is proportional to speed by P = rotational speed x T.

Where power is V*I. If the current increases wouldn't that include the speed? Clarification??
 
Isn't it also possible that the motor was just seeing an increase in load, raising the torque required of the motor and thus the current, without a change in speed?

Kent
 
What about DC motors? It's been a while since I have had to deal with one, but if I remember correctly, I believe it was a shunt, or a series winding motor could over speed if the field was lost, I think. It's been a long time since I had any DC motor theory. Someone that does a lot of industrial could probally answer this.
 
Is this a new install?

Is this a new install?

Is this a new install?

Was anything changed rewired or replaced prior to overspeed issue?

How/where are you measuring the overspeed and how much over the motor base speed is being measured?

What are the following:

Motor HP / FLA

Overload size or setting in amps

CB size
 
eanton22 said:
So what your saying is the increase in current has no affect on the motor???
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If the motor current increases that would most likely be because of either a fault or an increase in mechanical load on the shaft. Increaing the load generally slows the motor down (unless it is part of a servo system).
 
hillbilly1 said:
What about DC motors? It's been a while since I have had to deal with one, but if I remember correctly, I believe it was a shunt, or a series winding motor could over speed if the field was lost, I think. It's been a long time since I had any DC motor theory. Someone that does a lot of industrial could probally answer this.
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In a series wound DC motor the field and armature are connected in series so if you lost the field you would get not current and the motor would stop. On the other hand, if you lost the load, the motor could overspeed. The only applications where I have come across series motors are traction and starter motors for vehicles.

In my experience, shunt wound DC motors are more common in industry than series. Lose the field on those and yes, it can seriously overspeed to the point of throwing off the armature windings. Very messy that is.
 
In my experience, shunt wound DC motors are more common in industry than series. Lose the field on those and yes, it can seriously overspeed to the point of throwing off the armature windings. Very messy that is.[/QUOTE]

I believe you are referring to a compound wound motor, if you loose the shunt field you are left with a series wound motor and if it was not connected to a load it would tear itself apart.
 
Besoeker said:
In my experience, shunt wound DC motors are more common in industry than series. Lose the field on those and yes, it can seriously overspeed to the point of throwing off the armature windings. Very messy that is.
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We used to call that "slinging the solder" out of a DC motor.:smile:

steve
 
hillbilly said:
We used to call that "slinging the solder" out of a DC motor.:smile:

steve
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It'll do that too if you stall it for any length of time. The current continuously goes through the same com segments and they are generally not made for that.
 
hillbilly1 said:
What about DC motors? It's been a while since I have had to deal with one, but if I remember correctly, I believe it was a shunt, or a series winding motor could over speed if the field was lost, I think. It's been a long time since I had any DC motor theory. Someone that does a lot of industrial could probally answer this.
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Series motors would run to destruction if a load wasn't connected. direct loading via a mechanical coupling was preferable, not a belt drive due to the danger of throwing the belt/s. They are superior for high torque applications as opposed to DC shunt motors.

Regards
 
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