Motor Tripping on Locked Rotor?

have you mesured the draw with a meter?it might just be a bad control, or its settings

I have a clue.

1. Motor current normal.

2. "no sign of over current before tripping takes place on load jam protection; also during motor running condition"

3. "pump shaft rotates freely, numbers of time."

4. "protection provided in abb relay"

You seem to be saying that everything looks normal but that one of several motors is tripping out. On the assumption that there is not a "invisible/quick physical overload" situation that is properly being protected against, then the load protection relay is faulty OR the motor has to have an internal short that is giving too high a "normal" current (which you seem to say is not the case) OR the relay is an earth leakage type and there is a very small amount of leakage in the motor. An alternative to "leakage in the motor" is that the earth and neutral supplies are crossed or "cross leaking". The later case would more likely be quick and immediate, rather than just occasionally.

The one thing I can guarantee is that there will be a reason !!!!

basic troubleshooting and elimination is escaping him

You have a relay that is tripping on a load jam condition. Your motor is mechanically seizing then. It might be seizing because a bearing is failing and intermittently locking up. Your mechanical load might seize the motor then shatter under the impact leaving a freely moving motor after the trip. Measure a trip with a time based instrument. Believe your instrumentation or go home.

There has never been any indication of an over-amp of the motor.

Tigerdon is chasing his tail.

Until proper testing is performed, I believe the controller is working properly to protect motor and wiring. It seems far more likely we have an ESO condition than a false tripping controller.

could be a faulty controller! if you have another swap it out. If you have some means of trending the motor operation while running that might shine some light on the problem.

Or you do have a overload problem and your controller is not giving you the right message.. again swap the controller out!

One other thing what are you pumping? Does the density change?

Check the wiring through the circuit.

Ive had this issue before and found burnt or loose connections in the connection box on the motor or along terminal strips (which melt and sometimes cross phase or ground)...

I think all the possibilities have been covered by previous posters here.

Assuming that wiring, fuses and phase direction have been properly set:-

I think personally that the current sensing has either been set too low and/or the timing has been set too fast.

I will wait and see what the final result is.....

The OP has NOT supplied full details to assist us up to now either......

1.84xIn for 100ms. Hmm, seems odd to me. A locked rotor situation is more like >6In for >6 secs (6000 ms!). Is this a recommended setting ?

Recommended by whom: the motor manufacturer, Gary in the mail room, the system engineer, that cute receptionist?

since he already stated the shaft turns freely its clear the roto is NOT locked

The motor, even if unloaded, will draw 6-8 times I_n won't it ? And this high current will last for several seconds. So, my (perhaps ignorant) doubt.... what does 1.84 In for 0.1 sec do ? Has ABB recommended this setting?

Its as you say, wrong.

The cute receptionist does not have a clue!!!

Locked rotor would indicate a physical obstruction.

You'd find that in a bearin or gearbox.

Even without power applied.

Its an issue with one of the phases missing...they arent looking into it completely. Only other item is a contactor with something loose in it but even that can be found without current. They should follow the path of the current until they find it.checking and tightening each part of the circiut. It shouldnt be THAT long...lol and if it is, well there ya go! :)

You are assuming the "tripping on locked rotor" is actually meaning there IS a locked rotor condition. At a setting of only 184% FLC, that is NOT defining this as a real locked rotor condition.

You are so right!!!

settings provided by engineering by coordinating motor performance curve with relay curve........ at a time of motor starting"in abb relay " startup supervision" function starts and block other function like earth fault and over current during starting phase..... however these last up to motor starting time which is very less ..compared to load jam prorection which is povided with 100ms .....

GA

And funny too, thanks.

Since it appears that all possible areas have been exhausted try doing a single phase test on the rotor. Here is how:

1. Disconnect motor from mechanical load. Provide appropriate safety protection for shaft

2. Apply 1/2 rated voltage to two leads of the motor with a clip on ammeter to watch the current.

3. Apply voltage and have someone slowly turn the rotor. If the ammeter jumps at certain points in the rotation then you have a short or break in the rotor bars. If it rotates around with no ammeter deviations then I do not know.

4. Warning the amps could be higher than expected so gage your power supply wires the same as your feeders and feed from an appropriate sized breaker

Welcome to the asylum Gord.

As you may notice in this very thread, the idea of measuring what is actually happening instead of purely theoretical speculation will, at times, be considered too mundane, and almost pedantic here.

I'm with you on this one. Measure what is actually needed and then set trip relays to allow it to happen.

Once again, welcome to the asylum.

Please open the pump casing & check for any foreign object in it. I guess there must be small object in side. When you rotate pump with hand it is free because the rpm is not sufficient to lift that object but when pump is started the object is lifted & it gets trapped between the gap of impeller & casing tripping the pump on locked rotor.

For fire pumps they select high tripping current rated protective device

funny being here, too many random engineers. the engineers in blankets their degrees is google.

do some secondary and primary injection test on your CTs and Relays, something is wrong with your wiring and physically check the bearings, some bearings dont show the restriction. it comes on and clears.

There is startup supervision during motor starting time which blocked overcurrent, earth fault& locd jam ........protection functions Sometime motor trippes during starting and some time after starting and running of say half an hour...however there is no sign of overload overcureent at a time of tripping on load jam ........

The humble thermal overload relay which costs less than $10 perhaps, does not require blocking any protection function... single-phasing, locked rotor, general overload etc. It is incomprehensible to me as to why an expensive electronic relay needs to override certain protection functions while starting....effectively leaving the motor unprotected during starting ... strange.

GA

Well RANTED put!!

There is startup supervision during motor starting time which blocked overcurrent, earth fault& locd jam ........protection functions Sometime motor trippes during starting and some time after starting and running of say half an hour...however there is no sign of overload overcureent at a time of tripping on load jam ........

Excuse me but there is a sign of over current conditions, the relay tripped. Unless you test the current drawn with a separate instrument that is sufficiently fast enough to capture and store the current during a tripped condition you cannot say that an overload did not happen.

Where does all of this lead us? If an independent current measurement shows the relay is making a false trip then you should replace the failing component (relay or CT). If the relay is tripping on a real fault then you must find the source of the momentary mechanical bind.

Repeating the same information is over and over will not help.

according to given situation your relay is seem to be faulty...so connect and other load{less than Motor) with relay and check if relay trip then replace the relay...