Frequent Tripping of 30kW Motor

Is any protection relay provided for the motor. In such case pl. provide the setting details.

this is a old starter, the BMR is set at 44 amps-trip.

If the motor full-load current of the motor is 50A, why is the trip set to only 44A?

What is the supply voltage?

What is the rise in pressure across the pump?

What is the volumetric flowrate through the pump?

_{<subscribes to discussion>}

Setting of trip at 95% is a general practice here, it shall go up to 105%. Motor can withstand up to how much percentage of the FLC for LT < 160kW and HT upto 3MW ?

Supply Voltage:415+/-5.

<...it shall go up to 105%...>

Not recommended.

Set the motor overload device to the same full load current as is stated on the motor rating plate, otherwise there is a risk of the motor becoming damaged and unusable due to overheating. Manufacturers do put these things on their ratings plates for a reason!

In the original poster's case, the trip current needs to be 50A. The question as to why it is set to only 44A remains unanswered at this point, as do several other questions that, when answered, would enable the forum to advise quickly.

Hi,

The 9/7 ratio is not applicable here because the pump curve is not linear. If he has the the pump curves for Q/H and power it might help him to see if the amps are within order.

I think the OP is talking about kg/cm² .

Sorry, We know now that the units used are m³/Hour.

In this case, the increase in amps is proportional to the square of the Volume increase, therefore, (9/7)² x 23 =38.02 A which is correct and consistant with the measured value.

Is this correct? - I thought that power varies as the cube of the flow, but do the affinity laws apply as the pumps are presumed identical?

Hydraulic power = pgHQ

Given, the head will also vary, but it will be lower so using the ratio 9/7 is a reasonable case (efficiency at the two flow is also an unkown but would commonly be higher at the higher flow). Or do I not understand this correctly?

Affinity laws do not apply here directly (I think).

The best way is to use the pump curves which we do not have.

The Power curve is not exactly linear at the points he is writing about.

Looking at the values, he should probably be having a high pressure (~ 350 m H2O)?? with the 7m3/h and 23A loading...? We can only guess when no curve or values for pressures.

He should check why the flow is 9m3/h and bring it down to the same 7 as the other and check the current before assuming that something is wrong with the motor or the assembly...

<...power varies as the cube of the flow...>

Not in a pump. Power is the volumetric flowrate multiplied by the rise in pressure divided by the efficiency. Which is why, without these data, the forum cannot determine whether the motor is correctly sized and, from that, advise the original poster on the electrical arrangements that drive it. Which is what the original poster asked for help with.

You understand it correctly except that power varies directly as the flow. Hence the use of the ratio of 9/7. The formula for hydraulic power is correct.

The affinity laws do not necessarily apply here unless the impellers are of different diameters.

Power varies as the cube of the diameter.

If the discharge line is blocked then the flowrate will be low-to-zero, in which case the pump isn't doing any work (apart from heating the fluid in its case) and the current should fall back.

eloborate the details of motor protection device.

Because the poster himself marked it OT, though I don't know why.

Yes indeed. 44 amps for run can easily escalate to a greater load. You're running caustics through the puppy. Look for caustic-type failures. When you hear hoofbeats, think horses, not zebras. Look for crud (technical term, that) on your contacts.

What truth is there in the rumour that crud is an acronym for Chemical Reaction, Unidentified Deposit?

Assuming BMR = Bi-Metal Relay???

Is that what is tripping? You keep saying the motor is tripping, but motors do not trip. It is either the overload relay (BMR?) or a circuit breaker or a fuse clearing, or there is some other protective device that is tripping, such as a vibration relsy, torque relay etc.. Please let us know which. Also, when you recorded the current as being 30% FLC, was that recorded when the "motor tripped"? Or was that recorded as part of a normal operation?

To effectively troubleshoot this, you need to know exactly what is happening at exactly when. Anything else is an exercise in futility.

You are running 30 kW on DOL? What is the inrush current drawn by the motor?

Cheers,

RRV

www.econserve.in

<...discharge rate of 9 kG /m2& stand by pump is 23 Amp at 7 kG/m2...>

The units are not a flowrate. Please explain these units.

M3 / hr...any more doubts please??

That's better. m³/h is a volumetric flowrate.

No doubts, just a need for more information:

• What is the rise in pressure at these flowrates?
• What is the supply voltage?
• if the motor full-load current is 50A, then why is the trip set to 44A?

When the forum gets answers to these questions, it can advise as to whether the motor is correctly sized......

Assuming that this particular motor is sq.cage induction motor& starting current is as a standard is 6*FLC. You have not mentioned the L-L voltages. As a thumb rule in general 2% voltage difference( L-L ) is allowed to restrict negative sequence current produced due to unbalance voltages. For example if there is 2% difference, and stg. current is 6*FLC, negative sequence current will be apprrox. 12% of main line current.Also heating effect of this current will be nine times higher than main line current, which may generate additional heat to BMR and effected tripping.Also after frequent tripping calibration of BMR may be lost and it suggested that BMR should be replaced appropriately.Also check condition of the bearings( bearing temp. may be indicative. ). Sometimes due to high frictional effect in bearings, motor current may increase.In general in BMR, current setting is done 105% of FLC.

Things I would do from experience: 1. I would put ac drives on both pumps and set these drives by the nameplate specs on the motor and the rpm of the pump. 2. Replace the pump and motor that is tripping. 3. Pumps need to be primed before pumping starts. 4. Make sure that when you do your motor rework/repair, that your motor is dynamically balanced. 5. Make sure that when you do your pump rework/repair that the pump housing is magnafluxed and that the pump is dynamically balanced. 6. If you can not afford an ac drive, update your starter to a solid state starter(an older bimetallic starter can cause problems). 7. Do lazer alignment on both pumps and motors setups.

After you indicated that the volumes pumped are different: 9 compared to 7 m³/h then:

1- It is normal that the current goes up from 23 to 38 Amps because the power consumption is proportional to the current and proportional to the Square of the volume change:

Amps at 9m³/h compared to the 23A for 7m³/h= (9/7)² x 23 = 38.02A (consistant with your measurement).

2- If you check properly, you will find that this pump discharge valve has been opened to allow more flow hence the increase in Amperage. This seems normal unless you want to reduce the flow rate and reduce the motor current back to 23A (going from 7 to 9 cubic metre per hour is 28.5% increase ).

3- Therefore, if you do not need the increase in flow rate, then go back and reduce the flow rate: then you might not have a tripping pronblem with the same setting (44A on breaker O/load).

Otherwise, increase the setting to 50A (motor nameplate rating) and this should clear your problem. The reason for tripping even at 44A setting might be due to ambiant temperature being high and a derating necessity(?).

Basis of reasoning: The breaker contacts and connections look to be OK (you should and maybe have already done a check...?) because the current drawn by the motor at the flowrate mentioned is consistent with expectation.

4- If at 50A, the tripping continues, then the O/Load device could be defective and needs changing.

Cheers and good luck.

clear the Caustic line which is accumulated in dwn side

dear friend,

Sometimes the relays and contractors starts abnormal functioning due to prolong use. So you may change them temporarily and have a test. Also check the CT's.

Everything it appears is alright with motor and pump. Still it trips on overcurrent. I suggest the following line of action:

1) Please interchange the motor with the standby and run both and check their parametrs particularly the current drawn. This would pinpoint problem area - pump or motor.

2) On the pump side since you have cheked on vibration and free movement only, I would suggest to have the pump impeller examined for its blade erosion at tips.

BB Raina

The forum is still waiting for pump pressure rise and volumetric flowrate information several days later, with a view to advising on whether the motor is correctly sized................

THE PROBLEMATIC MOTOR WAS ELECTRICALLY RELEASED FOR OPERATION AFTER INCREASING THE SETTING OF THE BMR TILL 95% AND IS FOUND TO RUN HEALTHY. REFERENCE TO VARIOUS DISCUSSIONS AND SUGGESTIONS FROM THE FIRM , IF (IN FUTURE) THE MOTOR TRIPS OR FUSES ARE BLOWN, I WILL REPLACE THE BMR. WHICH I UNDERSTOOD TO BE THE FAULT CAUSING ELEMENT. THE CONNECTIONS OF THE CT ETC ARE ALSO CHECKED FOR TIGHTNESS.

STILL FURTHER IF THE PROBLEM OF TRIPPING ARISES,AS SUGGESTED, THE PROBLEMS IN PUMP SHALL BE CHECKED.

THANK YOU.

I would still request you to interchange the motors and check the amperage of the problematic motor by running it on the standby pump.

BB Raina

....and do also quote the pressure increase and volumetric flowrate in this forum, so that others may advise on whether the motor is undersized for the load. The problem may still be a hydraulic one, and not an electrical one.

Do turn off Caps Lock before posting again. It costs nothing to be polite. Take the risk!

_{<unsubscribes from discussion>}

He may not be knowing what it means by posting in capitals.

BB Raina

Dear Bar Man Sir,

I do accept yr suggestion, what is the prob if the letters are in caps lock. The motor is not undersized and is correctly sized. Hence motor sizing is not a problem.

Dear Pratapji

In email communications writing in capitals is equivalent to shouting at a person. You may not be knowing. Nothing wrong as such.

BB Raina