HPBYPASS FLOWS

              HPBYPASS flow, the flow in the hpbypass line in the system is called as HPBYPASS flow. In general during the running condition of a thermal power plant there will not be any flow in this region and hpbypass flows are zero. During the unit shutdown or trip condition the hpbypass valves are present and flow is established. Then why do we need to know about the hpbypass flows?

             Monitoring the HPBypass flows during the unit running condition is very much important and the flows are maintained in the feedwater loop. If in running condition HPbypass flows are established then there is some amount of steam lost from the system and is bypassed from the HP bypass. So this additonal amount of steam is to be supplied to compensate for the flow in the HP bypass line and it should be fed through the feedwater loop and hence the flows are added to the HP bypass loop.

case study:
Suddenly there is rise in the feed water flow and the level of drum started to increase very fast and there is no manual intervention and the Hpbypass valve is fully closed.

Solution:
As the hpbypass valve is fully closed, first isolated the hpbypass flow condition from the feedwater loop by making its value zero. Then went to the location, the flows are generally calculated using the Differential pressure transmitter (DP) , found out that there is a leak in impulse line of the DP transmitter beause of which there is high pressure maintained on one side and low pressure on the other which transmitter assumed to be flow and raised the feedwater flow. Closed both the impulse line and rectified the leak and working fine.