No idea from the limited information given.

Suggest you install recording amp meters on the feeds to the troublesome motors. May indicate if the overload is a 'spike' or a gradual build-up. ■

Dear Mr sganesh,

If there are no mechanical load reasons for the tripping of the thermal overload devices, there is one reason left.

A thermal overload relais trips when the thermal element in the relais becomes too hot.

The ambient temperature of the relais (possibly in a hot cabinet) + the heating due to the consumed current can activate the element.

Increasing the setting of the overloadprotection can compensate for the high temperature of the device itself.

A better solution is to install the overload protection in the same environmental condition as the motor , which has to be protected.

Also be sure that the temperature setting of the relais corresponds with the allowable temperature of the motor.

Hopefully, I am right, but I can be wrong.

Take care

Teus ■

Originally Posted by Teus Tuinenburg

If there are no mechanical load reasons for the tripping of the thermal overload devices, there is one reason left.

I know this sounds pedantic, but he didn't say there are no mechanical reasons for motor tripping, only none could be found. The reason for fitting a recording amp meter is to monitor what is happening with the motor. ■

Dear designer,

Installing a recording amp-meter is a good idea to prove mr sganesh’s statement that there are no mechanical causes, because he could not found them.

The temperature issue with thermal relays often is overlooked.

The events happen not just on one motor but on “motors”

Moreover, limited information generates limited answers.

Looking forward to hear the real cause of the problem, once it is solved.

Have fun

Teus ■

Teus,

From my first response

I did recognise there was more than one motor

But really, the original post was so lacking in hard information I nearly didn't bother to respond ■

Lacking information - true.

I have the experience twice, on different continents, where the electrical leads, in electrical conduit, intermittently grounded when thermal expansion caused two phases to touch. Heat-up, trip motor, stop, cool down, and repeat.

It took about 2 months to solve the first failure, in South Africa, and about a week, at a USA mine to get the client to do a proper electrical inspection, knowing the cause of the first failure.

Too many variables to study before finding the obscure. ■

Originally Posted by sganesh

I have raised this question " WHY EQUIPMENT SHOULD TRIP WITHOUT ANY REASON?" to my electrical engineers also, which is still baffling me.

Equipment doesn't trip without reason, you have yet to find out the reason why the equipment is tripping.

Enough talking, speculation and conjecture on this forum.

Get to the machines, take recording amp meters, full motor specifications, full overload specifications, but most importantly your investigative engineering brain. Once there be prepared to stay until the reason for the trips is found.

There is a reason for every action, you just need to find it and 'sitting' on the machines is where you will find it.

Oh, and when you have found it post the answer back here. ■

Dear Mr sganesh,

It is true that the insulation class of a motor is related to the operating temperature of the motor.

However, the Amps, indicated on the nameplate are ruling and therefore there is no connection between the insulation class of the motor and the thermal overload relay.

A rule of thumb is that the overload setting of the relay is at 105% to 110%.

If tripping occurs, then there is a real mechanical overload, which was ruled out in your thread.

Whether this is true, can be found with an Amp recorder (or Amp-meter) as mr designer rightfully advised.

In addition, the pattern of tripping can give an indication of the possible cause.

F.i. always at high ambient temperatures, full operation of the installation, many starts and stops in a short period.

Starting a problem investigation that re-occurs periodically is to check the design before initiating a search.

This can reveal a design error and at the same time, it tells you what to expect when you start measuring.

In my experience, it is also wise to talk and listen to the operators, responsible for fault finding and repairing the installations.

If you employ the right people, they are far smarter than you may think and your appreciation for their work will benefit the company in the future.

Back to the floor and find the problem. (As mr designer ordered)

Remote fault finding from Europe is not the most efficient way.

success

Teus ■

Originally Posted by Teus Tuinenburg

Dear Mr sganesh,

Remote fault finding from Europe is not the most efficient way.

Sure isn't ■

However, we are always willing to help,explain and assist in a polite manner and as good as we can.

That is the purpose of this forum. ■

Unfortunately it is sometimes necessary for responses to be forthright, but we’re all “big boys” here. ■

Dear designer

Why “big boys” between parenthesis?

have a nice day

Teus ■

Originally Posted by Teus Tuinenburg

Dear designer

Why “big boys” between parenthesis?

have a nice day

Teus

'cos I felt like it ??????? ■

Dear sganesh,

Thanks for the feedback.

The advise of designer, to check the Amps, was after all a valuable one.

The missing phase could also be checked with a simple multimeter, by measuring the voltages.

You stated earlier “After resetting, the motors starts again with normal amperes”.

However. with one phase missing, the starting current could certainly not have been normal, but significantly higher.

For the other cases of unknown tripping incidents, you must have gained some experience now, which will help you in finding the other problems. (I suggest together with the field electrician).

Do not give up

Teus ■

Umm,

There is still work to be done on site to get to the bottom of the problems. ■

Yup. The first thing I would do is taking a reading of the Amp load across all three phases followed by a voltage reading. The motor data tags are next, because they usually contain the full load amp data and nominal voltage and line frequency.

Let us hope the measured amps are not too close and that the measured voltage is above the nominal rating of the motor. A drop in voltage lets the amps shoot up really quick.

Hello sganesh,

please let us know if and what you may have found on site. I am dying to find out about the root cause of the problem.

All the best, ■

Mr. sganesh,

I have experienced such a problem that turned out to be self inflicted. At one of our high angle conveyors, in South Africa, we experienced such trips that didn't appear to make sense, since the tripped motors did not exhibit excessive heat.

The problem; the customer had chosen not to equip these motors with overload protection, rather they chose to simulate overload by PC programming. By monitoring the motor load they simplistically chose to shut down the motor when amperage load exceeded FLA (full load amps). Overload spikes are natural but not detrimental if they have no duration. Ultimately the problem was solved by dropping the simplistic programming. The motors performed fine without any overload problems.

Joe Dos Santos ■