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LV Motor Stall Protection Requirement(Stalling Time).

LV Motor Stall Protection Requirement(Stalling Time).

LV Motor Stall Protection Requirement(Stalling Time).

(OP)
Hello,

I have an issue with setting MPR(Motor Protection Relay).
Researching any code & Standard for Motor Stall Time requirement,
I found that NEMA MG-1 requires motors to be manufactured so that it withstands at lease 12s of Stalling time.

Since our motors are built based on IEC Standard, I need to find any statements in IEC that defines this protection.
Is there any IEC Standard that deals with same requirement?

Thank you for your help!

RE: LV Motor Stall Protection Requirement(Stalling Time).

Do you have the motor thermal curves? Setting the overload to protect the motor thermally takes care of the stall time but you can find the stall time looking at the curves.

RE: LV Motor Stall Protection Requirement(Stalling Time).

(OP)
Yes, we do have motor thermal curves.

But we have distinct features called Stall Protection.
Basically, it seems to be pretty similar to Thermal OL(49) curve setting as Definite Time.

We have hundreds motor in LV level, which will be very difficult to set its own specific Stall Protection in accordance with each and every motor data sheet(Thermal curves).
That's why if all motors are built in IEC Standard, we can set all LV motors with same stall protection setting.

If you can provide any insight on this matter, it would be much appreciated.

Thank you,

RE: LV Motor Stall Protection Requirement(Stalling Time).

An old school solution to stall protection was the use of a zero speed switch.
This was occasionally used for expensive motors in applications where stalls could occur.
If the motor stopped turning or if the motor did not start to turn within a set time, the motor was disconnected immediately.
This was a good solution during the transition from "U" frame motors to "T" frame motors. The common motor protection devices in use at that time were not quite up to protecting the newer "T" frame motors with much shorter allowable stall times than the "U" frame motors.
We now have much more sophisticated protection relays available, but for the occasional application, the old school zero speed switch may be worth consideration.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: LV Motor Stall Protection Requirement(Stalling Time).

I agree with waross and nevertheless my experience in this domain it is from 50 years ago a rule of 3.5 times rated current and 1 second delay was always safety.

RE: LV Motor Stall Protection Requirement(Stalling Time).

Why the time goes faster as we get older? I am sorry, I exaggerated a bit: only 30 years ago from.[blush]

RE: LV Motor Stall Protection Requirement(Stalling Time).

So, is this protection for being stalled during starting or for the motor stalling while running?

Something like 300% for a couple of seconds would work fine for stalling once running. The motor will quickly come to a stop once the load reaches the breakdown torque and that typically occurs somewhere between 200% and 300% current.

RE: LV Motor Stall Protection Requirement(Stalling Time).

We have different thermal curves to protect the motor. In North America, Class 20 is the most common. Class 20 means: 750% of the motor current flowing would result in tripping time of 20 sec or less. In Europe, Class 10 is more common meaning tripping time reduced to 10 sec for the same overcurrent.

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