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Sunday, August 1, 2010

troubleshooting defective jet water pump motor for drainage system

This morning, our jet water pump cannot draw water out in the Cable Trench Drainage at the substation. In just one year of operation, it baffles us that the water pump is already unusable. Anyways, here are the step by step procedures that we did in trying to repair our beloved pump:

1) First, we checked the water level of the drainage. The water level is higher compared to the foot valve level. This is the normal condition of water level.
1) Next, we checked the foot valve of the water pipe and the spring and stopper are still in good condition. There is no obstruction found at the foot valve opening.
2) We noticed that when the jet pump is energized for a few seconds, the motor pump body overheats easily.
3) Then we removed the top cover and checked the wires, capacitors and relays. Make sure that the breaker or switch of the water pump is properly tag to caution other personnel from operating the motor.
4) After thorough visual inspection,we did not see any signs of burning from the wires. The jet pump circuit is also in good condition with no cut wires and loosed connections observed.
5) We checked if the capacitors are defective. We measured the capacitance of the starting and running capacitors and the values obtained are still within the nameplate rating. The capacitors do not have any signs of cracks or leaks which are symptoms of capacitor failure.
6) We noticed that the thermal overload relay does not operate even if the motor pump body is already hot.
7) We tested if the windings are either open, shorted or grounded. If the winding is open, the value of resistance will be very high. This is caused by cut windings inside the motor. Another possibility is shorted winding. The resistance between two windings will be very low or zero and it is usually caused by winding breakbown that may have caused two windings touching each other internally. Grounded winding is characterized by failure of either legs of the winding that caused them to touch the body of the motor. So when measuring the resistance of the winding with respect to the body of the motor, the value is very close to zero or zero. We found out that phase A winding is shorted to the motor body.

Here are our conclusions:
The thermal overload relay may have failed which caused the motor winding breakdown. This relay should serve as protection of the motor winding so that the power going to the pump motor will be cut off in case high temperature of the motor windings is experienced.
The jet pump motor is recommended for rewinding.
The jet pump is not for continuous operation unlike the real submersible dewatering pump. Since we used it for draining out the water from drainage, we may have operate it beyond its recommended operating duty.

We have requested for a replacement already and hopefully we could install it this week.


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