Low Pressure Condensate Drain Pump

Is it trying to pump steam instead of steam condensate?

The pump is pumping condensate water from drain cooler to deaerator steam power plant

CHECK WHETHER IT IS OPERATING NEAR ITS BEP OR NOT.

I would first check for obstructions in the flow path: possibly a discharge valve not fully open or a stuck check valve. Unless the pump was rebuilt just before this problem began, impeller clearance is not likely to be the source.

When you inspect the unit, look carefully at the thrust bearing. The pump will spin freely by hand, but when operating, the pump exerts an axial thrust as reaction to pushing the water. The thrust bearing prevents the shaft from actually moving upward. If it is worn, it will allow axial movement of the shaft during operation, reducing clearances and possibly causing rubbing in either the pump or the motor.

The lower pump bearing (or bushing) could also be worn.

Interesting thing about pumps and the impellers.

If your pump is over amping, by cutting down the impeller it actually has the opposite effects of what one would expect.

Is the pump flow much higher than designed? Do you have a minimum flow line that is flowing more than designed, missing an orifice or something like that, what about a PRV on the discharge side that is leaking by allowing more flow than designed.

Zero load on the pump motor is when pump is running at shutoff head.

Max load on motor is when pump is running with max flow.

Therefore check:

Does drain tank have automatic level control system? Is the level control system part of motor control circuit or does the level control operator a flow valve? Typical application would be a three way valve that directs flow either to booster pump suction or returns to drain tank, thus is possible that three way valve is returning all flow to drain tank and thus maximum flow through drain pump occurs when three way valve is in return to drain tank mode. This mode would be when drain flow to tank is at lowest value, no drain flow to tank, so valve recircs all flow back to tank to maintain level.

If above not the case, then check:

Have electrician take resistance readings on motor windings . . . take cold readings when motor has not been in operation for long enough to be at ambient temperature. Place motor in operation, allow to come up to operating temperature and take resistance again. Compare readings. Sometimes insulation breakdown in motor occurs only when at operating temperatures.

Question:

Is this a single motor or is there another motor/pump in the system, a backup to the one experiencing the problem? Does the #2 motor have the same problem?

Check line voltages:

If voltage to motor is dropping, due load increase on the power source, or if motor is operated below design, the amperage will be higher.

Another possiblity is contactor that controls motor:

Check the contactor!!! Contactor contacts sometimes burn. Burned contacts in the contactor heat up and arch. The arch represents a voltage drop. As arch increases, the current flow rises. Eventually causing the breaker to open.

Check amperage upstream of contactor and amperage at motor.

I have 4 x 400 MW steam power plant that contain 1 LP Drain Pump each unit, under 200 MW load LP drain condensate tank be sucked by main condensor, above 200MW Main condensor sucking sistem not enough to maintain LP Drain tank level. so pump has to operate pumping fluid to deaerator tank by level control valve to maintain LP drain tank level. 3 unit LP drain pump else no problem... 55 ampere, only unit 3 reach 75 ampere

I had a similar situation with a fan motor.

Fan operated fine for months then started tripping circuit breakers upon startup.

Fan and motor were fine, no problems (I.E. "perfect")

Looked at other things and noted fan was exhausting wet mildly corrosive environment air.

Fan and motor were rooftop out of air-stream but Electrical components were not.

Found corrosion/oxide build-up in junction box inside space (gradually adding resistance to circuit as time progressed)

Have you checked over electrical contactors, disconnect boxes, motor control center etc. to see if you have similar condition?

Good luck.