PROBLEM : CC PUMP CAVITY TEMPERATURE HIGH

OCCURRENCE :

In one of the 500 MW units, the cavity temperature of one of the running CC pumps, was going high upto 55 deg.C., when the unit was operating around 400 MW.

ANALYSIS :

It was initially thought that the cooler attached to the CC pump is not performing properly either due to choking of the filter provided inside the CC pump motor cavity or due to ineffective performance of the cooler. But while making thorough inspection, during unit shut down, it was identified that the drain valve in the cavity pressure transmitter’s impulse line was passing and water was dripping through the common drain outlet pipe.

This established that the motor cavity water was getting leaked out through this passing valve and hence the hot water, from boiler was percolating to the cavity of the motor. The cavity temperature measurement thermocouple, which is placed just above this pressure sensor’s tapping point, identified higher temperature.

RESOLUTION :

The passing drain valve in the instrument impulse line was replaced. The cavity water filling was established. The pump was taken into service, when the unit was re-started. The cavity temperature of the pump became normal and the performance of pump is satisfactory.

CC PUMP

Thermocouple

Pressure Transmitter

Drain Valve