Agitator RPM is getting more than the design RPM when we checked with tachometer?
What is the measured RPM and what is the design RPM?
Is the motor running at its rated speed?
Is there a gearbox/pully?
Can you confirm your tachometer is correct?
Is this speed measured with material in the tank or empty
Is the rpm specified under load? Was the measurement made under load or in free air?
Actually it is a Reactor which is connected with HMI control system and the rpm trail taken without load
The measured rpm is 120 but actual design RPM as per gearbox ratio is 114 and is having vertical motor coupling no belt coupling and rpm taken empty condition
Is the motor speed as it should be? Or it is also running ≈5% fast?
Actually we are not decoupled the motor we measured the output RPM from the agitator. And motor RPM is 1440 and gearbox ratio is 12.6
My guess, based on all that would be electrical supply to the motor from the controller. I’d check all fuses, breakers, etc, to make sure everything is in good shape. I’d be surprised if any of that would fail in a way to allow excess power, but that would be the first area I checked. If that all looks right, the controller programming itself would be the next place I looked. Make sure the electrical supply coming from the controller matches the rating. It may simply be that whatever feedback or input it is relying on the set the speed is not right or may not be calibrated.
This honestly isn’t really my area though, so I’d bet there are others here who could diagnose it for you.
I recommend you talk to the motor vendor about this no-load trial to see if there is an issue.
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Your readings indicate possibly some inconsistencies.
Rated RPM x gearbox ratio equals a highly unlikely number.
120 RPM x 12.6 = 1512 RPM.
That is a highly unlikely speed for a grid connected and unloaded induction motor.
The no load speed of the closest standard motor is slightly less than 1500 RPM.
Working through a 12.6:1 ratio that would be slightly less than 119 RPM.
Close to 119 RPM unloaded is to be expected from a machine rated at 114 RPM under load.
You are probably worried about a slight measurement error.
It could be meter calibration or possibly parallax error reading the instrument.
Do not discount some rounding error in the stated gearbox ratio.
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A motor primer.
The speed of an induction motor approaches (but never reaches) synchronous speed.
The(unreachable) synchronous speed of a motor depends on the number of pole pairs (1 North and 1 South make up a pair) and the frequency. In a three phase motor there will actually be a pole set for each phase but that factor is not taken into account when determining synchronous speed.
The speeds for a motor fed 60 Hz current are determined by dividing the number of pole pairs into 3600.
So: 3600 RPM, 1800 RPM, 1200 RPM, 900 RPM, 720 RPM, 600 RPM.
The speeds for a motor fed 50 Hz current are determined by dividing the number of pole pairs into 3000.
So: 3000 RPM, 1500 RPM, 1000 RPM, 750 RPM, 600 RPM.
The motor always runs slightly below synchronous speed.
The difference is the slip speed or the slip frequency.
This induces an EMF in the rotor which drives the rotor current that,in turn, develops the rotors magnetic field.
No slip, no induced EMF.
How much slip?
At 60 Hz the most common slip speeds are from 40 RPM to 60 RPM depending on the motor design.
The speed over the slip range is mostly linear with loading (including windage and bearing friction).
At full load, the motor will be at full slip, which is another way of saying at rated speed.
So a motor rated at 1760 RPM will run very close to 1800 RPM with no external load and will run at 1760 RPM at full load.
So what do your readings tell me?
A no-load speed of 120 RPM is so unlikely as to be a mistaken reading.
Your speed range from no-load to full load is reasonable.
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Is this perhaps a “universal” motor, i.e. a brushed DC motor driven by an SCR device, or a diode bridge across the AC mains?
Otherwise, agree with Waross that the rpm reading is unlikely and could be measurement error.