LT 3 Phase Motor

You are absolutely right.

If he measured the amps after the motor has reached full speed, there will be no softstarter influence!

he should check the cables and connections.

dear sir...

thank u for suggestions,

yes sir, u r correct, y phase cable lug was bit loose at motor terminal plate.

we done re termination work. but still slight differnce in amps.

we checked the motor, and cable also. also megger values are good.

why it is happening sir. ?

Simple test:

"Rotate" the phase conductors at the motor, meaning move R to Y, Y to B, B to R, then retest the currents. If the problem follows the shift, then it is in the conductors. If the problem stays in the same place, it is in the motor windings.

If the problem completely goes away, you had more than one bad connection and you just fixed it!

...or winding damage within the motor. The first thing to do it to turn off Caps Lock, then change-out the motor for the stock spare prior to a detailed assessment of both the cable and the motor.

Information as to why the test was carried out would give a clue as to what is going on and why. Please explain.

Softstarters with their high frequency sometimes lies amper klamps. You should check reading current from Softstarters display .

Although the sum of the currents of all phases are almost same and mr.Tornado gave you good recommendations .

Good luck

?

"Softstarters with their high frequency..."

Soft starters do not change the frequency.

Depending on the soft starter design, many do change the stator current frequency from a lower frequency to a higher frequency. The common method of controlling this inductive load is through PWM. This will create all sorts of very high harmonic frequency voltage components. Remember the Fourier series fundamentals.

I admit that I'm making a semantics argument here. Hence my OT marking.

Semantic rebuttal to a semantic argument:

Only drives change the frequency, we were discussing soft starters, specifically LT (Low Tension or Low Voltage) soft starters. But I'll give to you that very large Medium Voltage synchronous motors are often started using LCI (Line Commutated Inverter) drives and they are functionally used as 'soft starters' because once accelerated, they are run at full speed. That was not what was being discussed here though and I thought it best to dispell the incorrect statement before it got out of hand.

A basic low voltage soft starter is not changing the frequency, it is reducing the voltage via phase angle firing of the thyristors. They only turn on for part of each cycle within the sine wave, but the fundamental frequency being sent to the motor is still 60 or 50Hz as the case may be.

It could be an imbalance of currents due to wrong order of parallel laying phases.

For instance order A1-B1-C1 C2-B2-A2 it is a symmetrical arrangement and no imbalance occurs. Other order of phases could produce current imbalance. However, for such difference as in Y1-Y2 [445-23] case, it is hard to say that. It could be something else: contact resistance, different length, temperature differences and other.

I'd start with the largest draw....Mr Tornado gave you good advice

Disconnect from starter and test motor Insulation resistance(Mohms) and winding resistance (ohms) of each phase.

There's definitely a fault in the circuit so disconnect power supply cables to the motor and measure winding balance across phases, it should b the same. If it ok then measure insulation resistance of the windings. When connecting bek power cables make sure there are no loose connections. Make sure supply cables to the motor are not damaged