Motor Tripping Due to Low Current

Short the relay out and see what happens.

A 1000HP motor is going to make a big hole in your wallet if when it goes wrong.

Why is there a low current trip? For conveyors mechanical faults are normally checked by overload and speed sensors. For tandem drives load sharing could be a reason for low current sensors.

BTW, having to look what a Fibrizor is hasn't improved my temperate. Why not say a pulp mill?

Some sort of funny problem in site, i guess.

Thank you Mr. TonyS for your response.

Over load does not take place, but when the current is nearing the over-load current limit, the sensor gives a command to slow-down the conveyor.

DHAYANANDHAN.S

How does it slow the conveyor down? Is the motor variable speed?

By overload current limit I assume you mean high limit. I thought tripping the motor on low current was your problem.

Dear Mr. Codemaster,

Thank you for your response.

The slowing down of the raw material feeding conveyor is of VFD and the sensors are installed - which picks up the current increase level, and reduces the speed.

You are right, the problem is tripping of motor due to low current.

DHAYANANDHAN.S

One thing that low current could detect is a broken belt (or other drive components), which might keep a load of product from being dumped on the floor, or other problems.

Also, quit shouting in the thread title.

Agreed. That's the only reason I can think of to trip on low current.

Resting the trip point to something above no-load (bare shaft) current, but below current drawn when the conveyor is unloaded, would avoid spurious trips but still stop on broken belt etc.

Should have said "resetting" not "resting". iPad predictive text at it again, god I hate it!! Anybody know a way of switching it off?

Dear Mr.Tornado,

There is no damage to the conveyor and the raw material feeding is quite ok,

The stoppage of the conveyor is related to external factor not linked to the feeding of raw material. or the fibrizor.

DHAYANANDHAN.S

Thank you Mr.Tornado,

The Conveyor is Rake type and not belt conveyor. The feed does not fall on the floor. The moment fibrizor motor trips, the electrical inter-lock between the fibrizor motor and rake conveyor motor stops the conveyor motor.

I will stop shouting. ( I hope you will appreciate that I will follow your advise)

DHAYANANDHAN.S

Undercurrent disconnection is normally provided on longish conveyors to stop the motor in the event of a carry belt or shear pin breakage.

This is generally a more reliable method to detect breakage than product flow or belt travel monitors.

Picture a long conveyor where the belt breaks near the boot roller (the product input end), there may be sufficient friction to allow the rest of the belt to continue to travel, and product flow or travel sensors may not detect the breakage for some considerable time, during which much belt will have piled up between the drive rollers and the tension tower/loop take up system. Severe damage can occur, and re-threading can take a lot of time.

Low motor current sensing will detect the break much more rapidly and save damage and time in getting back into production.

The relay should only shut the system down under very low load conditions such as a breakage, so if it is doing so for any other reasons, there is a problem.

The system will work fine without the relay - unless the belt breaks.

Dear Mr.spades,

Thank you for your response. Pl. refer my reply (No.10) to Mr.Tornado (post no.2), the same reply by me holds good for this point also. There is no breakage of the conveyor since it is a rake type.

I have not attempted so far to by-pass the under current relay. I think I can take a chance, now.

DHAYANANDHAN.S

How is it that the conveyor can be stopped yet the motor should continue to run? That sounds like a clutch must be involved. The description so far sounds like it is either poorly designed or being operated in a hazardous way. Perhaps a clutch is being used to regulate the flow of material and that is causing the low current sensor to kick it out?

Perhaps you are trying to operate a Continuous Duty Motor in an Intermittent mode? If so, then when it breaks down as it surely will, replace it with the right kind of motor and speed controller.

Dear Mr. NotUrOrdinaryJoe,

Thank you for your response. The motor is working continuously and intermittent operation is not there. The motor is directly coupled with a flexible coupling and speed is constant.

There is a facility to regulate the feed to the fibrizor through a variable speed conveyor. When the motor gets near to over-load, the control system will reduce thr rate of raw material feed.

Design part is OK and a similar arrangement is working elsewhere and not tripping due to low-line current.

DHAYANANDHAN.S

Check may be you have this relay or similar.

Or this.

Makes me wonder.

Or you may have ground fault/leak somewhere.

Thank you Mr. small, for your response.

I will post the picture of the relay fitted, with details tomorrow.. There is no ground fault/leakage any where.

DHAYANANDHAN.S

I suspect (if i am not mistaken), it tripped over voltage relay, since you add up caps on the motor, sudden stop means disconnecting line current->decreases abruptly, so voltage raises up enough to trip over voltage relay at line side.

The remedy for this is transfer the caps connection downstream the motor relay, so that, when disconnect happens it wont affect line side power supply protection or do it in a separate switch having the same separate disconnect.

Dear Mr.small,

Thank you for your suggestion.

You have mentioned as "transfer the caps connection downstream the motor relay, so that, when disconnect happens it wont affect line side power supply protection or do it in a separate switch having the same separate disconnect"

I will try this and inform you and this forum - about the outcome of this attempt.

DHAYANANDHAN.S

Dear Mr.small,

The relay Details are as follows

Make: Microelecttrica, Milano, Italy.

Model: MM30.

The picture could not be posted and pl.inform your mail Id., through PERSONAL MESSAGING facility in CR4. I will send the picture of the relay. Alternatively you can down-lad and refer. The Instruction Manual for this relay contains 17 pages in English Language.

Surprisingly there are 3 Identical Relay of this type, fitted to the Panel Board in the Boiler Feed Water Pump, 3 numbers, and the low-current tripping sensor is disabled. The H.P. of the Motor is 300 and Speed 2880 RPM.

My point is when it is disabled in feed water pump, why not remove or by pass this sensor/relay for the Low Current tripping.

DHAYANANDHAN.S

Mr. D.

This is simple google search for specs sheet of MM30. This is complete motor protection relay with 13 protective functions. It is not advised to by pass safeties, otherwise you just throw that expensive relay without good use.

In the elevator industry, by passing or jumper habits leads to horrific fatality of passengers, but this is quite exaggerated but could also happen in your case to some extent if you by pass protection.

It runs with modbus RTU, via rs485 to your pc. There is mScom program interface, plus trip and real time recording to show what went wrong.

I believe, you could see/diagnose what went wrong in the log, eliminating 12 possible malfunctions check.

If you could access this, record what were the logs and come back here for some info.

May be the only problem is you only need to adjust some settings to some safe extent.

Dear Mr.small,

Thank you for your immediate response and noted your points carefully.

I will go by your advise and check and come back here. As you said, Safety of Personnel and Safety of Equipment cannot be compramised.

Thanks,

DHAYANANDHAN.S

You seem to be missing the point. They said the PURPISE of the under-current trip function would BE for detecting a broken mechanical component. Whether or not you choose to disable that function of not is up to you, there is no need for under-current protection from the standpoint of the motor itself. Just keep in mind that usually, someone does not needlessly add expensive sensing devices to a control system without reason. So what they are warning you about are POTENTIAL consequences for the machine.

PUPOSE... Not purpise! Freaking iOS spell check missed it...

Porpoise? Prepuce? Propose? Papoose? Purpose? Precipice?

(Sorry, couldn't resist.)

Geez, I give up...

put me in the slippage/broken belt camp

Not actually being there to see what you have I can only hazard a guess but have you checked to make certain your gear box and conveyors, bearings etc are in proper working order? Nothing hung up in rollers etc. ?

Dear Mr.LukeS,

Thank you for your response.

The rake conveyor gear box and related chain drive, rollers etc. are in tact, no problem in this segment.

DHAYANANDHAN.S

First,I would consult with the manufacturer of the system and determine if it is

acceptable to change the set limit,if the limit is adjustable.

If so,make very small incremental adjustments,and note original settings in case you must return to the initial settings.

What indicators are active to indicate the cause was a low current condition:

PanAlarm panel,man/machine interface,etc.?

The more information you provide the better feedback you will receive.

imagine you have never seen the machine,and do not even know what a Fibrizor

machine is.

Could you determine the problem from the information you have given?

<...no response from Motor Manufacturer...>

Stop wasting time waiting. Use the telephone to contact the equipment manufacturer, not email! The telephone is instant, interactive, and cannot be ignored. The email account may not even be serviced any more, and senders are not in a position to know.

Dear Mr.PWSlack,

Thank you for your response. I will contact the Motor manufacturer as well as the Panel Board supplier and I will come back to you.and post the details here.

DHAYANANDHAN.S

Please note PWSlack is a CR4 username, and does not convey a gender.

There is no need to reply directly. A posting here in this thread will enable others to assist with this conundrum.

<unsubscribes>

Dear Mr.HiTekRedNek,

Thank you for your response and you have referred "This can cause many problems,including over voltage,and reverse current flow through the motor stator,resulting in an actual over current condition due to excessive rotor slip."

My opinion is also revolving around the points referred by you. But excessive slip does not occur. Generally the induction motor is designed for 4% slip and in our case the slip is very less and in the name plate the Speed is indicated as 742 RPM, which corresponds to (750 - 742)/750 = 8/750 = 0.016 or 1.066 % Slip.

One point I want to refer here is the Fibrizor Motor is to be designed for 15% slip, which is the Norm for this Industry and has Auto-Slip Resistor. But this motor slip is too less and for the first time I am coming across such low slip.

You have referred about the switching off the capacitor in steps and presently we are doing this only. partly switch off the capacitors so as to keep the P.F. 0.8 lag. A similar relay is connected to the Boiler Feed pump ( Refer Post No.28 in reply to Mr.small) and the relay is DISABLED or BY-PASSED.

As Mr.Tony has suggested I have determined to by-pass the relay and work and observe what is happening. I will post the observations to this forum.

DHAYANANDHAN.S

probably one of your better answers. he's consumed with PF and getting fooled

It sounds as though the low current trip setting is too high, and it may be a fine margin between too high and just right. The purpose of the trip is to indicate a broken belt and the motor spinning with no load because the belt has broken/come off, etc. What it has detected is the motor spinning and the belt spinning and no load being carried on the belt.

Procedure:

1. Refer to the original commissioning documentation, where the correct setting for the trip will have been recorded.
2. Simply adjust the present setting to agree with the as-commissioned record.
3. Create an additional record to confirm that this has been done.

"Robert is your mother's brother." - Anon.

I suspect that the VFD is suffering from re-generation voltage spikes that are being introduced to the system by the added PF correction capacitors.

I suggest you attach a good quality three (3) channel voltage recorder or use an oscilloscope to monitor and record the voltage and current waveforms for several start, run, and stop cycles.

Because you have modified the circuit electrical operating conditions by adding capacitors the volts-per-hertz ratio for all motor speeds is most likely not correct either.

You may have to add a high impedance resistor bank across the motor leads to filter out the voltage spikes and stabilize the VPH numbers.

I would not do anything without consulting the FVD and motor manufacturers for their input, advice, and approval.

If you are not an electrical engineer, . . or even an electrician . . . then hire one and have him solve the problem for you.

You DO NOT IMPROVE the power factor of a motor by adding capacitors . . . . you are improving the power factor you draw from the system.

What kind of motor do you have ? An INDUCTION motor? . . Or a synchronous motor? . . .

The only way of improving the power factor of an induction motor is to adjust its operating voltage. You are not likely to have the means to adjust voltage for a 1MVA load. Are you certain that this motor is running at rated voltage?

The way to adjust the power factor of a synchronous motor is to adjust the current in teh field windings. Is the speed on the nameplate really marked as "750" RPM? and not "740" RPM ? ? "750" RPM would indicate a synchronous motor . . so go and look where the field current can be adjusted and adjust it closer to unity power factor.

AND stop adding capacitors to improve the power factor . . . this is SILLY when operating a synchronous motor.

Oleh