Vertical Pump Tripping on Overload

Please check the rated RPM on name plate,(1750 Is no load RPM not rated) and measure actual RPM of motor with tachometer on fully loaded conditions.

Measured value of RPM should be = or > of rated RPM.Also check if there is a provision of cooling, and is it working ok.

After doing this you can also check if one or more coils of motors are shorted or burnt?

my frind, 1750 is indeed the rated speed of the motor.

for the motor windings, the resistance was checked by electrician and they confirmed that the motor is ok.

the pump was also uncoupled and the motor was tested along for 24 hours and didn't trip.

The overloads (heaters) are designed to trip on an overcurrent condition. The proper way to check is to take amp readings on all 3 phases. The readings will be consistant within + 1-2%, and below the FLA on the nameplate of the motor if everythingis ok. If the readings are higher than the FLA then there is a problem. The heaters should be sized to 150% of the FLA to prevent nuisance trips and are not designed for short circuit protection.

1. If all phases are high then that is indicative of a mechanical load.
2. If there is an appreciable difference in the readings then that is indicative of an electrical failure.
1. Check the line voltage on all 3 phases to determine if single phasing.
2. If voltage checks good, measure the resistance of the motor with a megohmeter, if this shows continuity between phases and open to ground chek the branch circuit wires in the same manner.

Once you have followed noshorts advice then from a mechanical perspective you can check wear ring and neck bush clearances and roughness of impeller shrouds and casing volutes.

Internal recirculation due to excessive clearances and or roughness of surfaces can have a dramatic effect on pump efficiency.

Have you tried or can you try restricting the outlet? If you restrict the outlet on a centrifugal pump you reduce the load on it. If there is usually any restriction on the outlet and this as been removed, it can overload the motor.

the pump discharge line have a gate valve to open or close the the discharge. the pump also have a common circulation valve with sister pump. both pumps discharge lines are conected to a common header that have a an MOV.

How about the bearings?

Is the pump PERFECTLY vertical/level?

syes the pump is perfectly vertical

Low temperatures in the molten sulphur may be one. If the material is approaching its melting temperature, then its viscosity will be rising, adding to the burden on the pump, and it may be clogging, in which case instead of being a pump, the device is acting as a macerator instead.

my frind,

the sulfur temperature is maintined btween 280 & 300 F. If temperature went down then the sulfur will solidify and this vibrate the pump, will rise the load on the motor suddenly and an abnormal sounf will be heard.

Is the <...abnormal sounf...> that of the circuit protective device operating?

It is assumed (but please check)

- The motors (both) are same ratings.

- The Overload trip settings are same for both.

Please check the setting of the overload trip relay, since some times it has been found to get disturbed especially if it trips a few times too many.

can you check and compare the amperes of the motors (even untripped condition will give you some idea).

In case of this type of failures check

What are the differences between them - eg one new, one old. One clocked too many hours more with respect to another, which one (tripping one or the other)

When this phenomenon started, what has happened a fwe days before this?

The motor may be overloaded electrically-

Winding fault (already checked)

By the winding deterioration (you have already checked, did you check the tan delta and other features like PI value etc?)

Voltages/wiring to inputs - check whether some loose contact, cable size or some other features (eg loose contact) are making the voltage available to this motor go low forcing the current up. Check the input cable too, for some minor fault.

Unbalanced voltage reaching the motor (only this one, not the other- again due to some cable fault or contact fault or some other high load tapping point taken from this JB)

Mechanical

- Friction (bearings) you have already checked, OK (also the fault at this RPM will give you clear audible signal).

- Setting of pump - Checked, OK.

- Fouling of impellers under hot condition - due to less clearance - new pump/ some distortion in pump due to accident/ effect of heat/... You have checked freeness under cold condition. try to check the running clearance in hot/ check the cold clearance and compute the hot clearance/ compare the two pumps.

- The lase is the increase in flow- can be due to impellers themselves or due to lower clearance or some other factor, this can be over come by reducing the flow to the pump.

-

Found a link (it is for water irrigation pump) but it is equally applicable.

http://www.irrigationcraft.com/overload.htm

You can go through other parts of the web pages too from the home and the connected links

http://www.irrigationcraft.com/learning_page.htm

I would have given you an excellent, but the spell check was not used. Therefore, I can only give a "Good Answer"!

Look at post 3 again.