Darlington TCV20 Project

The Temperature controlled valve 6721 0-TCV20 together with its controller 64230-TT20 control the cooling water (LPSW) flow through the Generator Hydrogen Coolers to maintain generator hydrogen temperature constant. Better TCV and TT were installed to minimize degradation/aging of generator insulation and to reduce the risk of a unit trip on high gas temperature. The new controller improves the response time of the control loop so that no manual intervention is required during TG run-up and address the issue of obsolescence. The new control valve has a linear characteristic covering the full operating range of the valve, in particular at the bottom end of the valve.
The temperature control must be responsive and capable of handling seasonal lake temperature fluctuations. The Temperature Control System is required to provide cooling control over a wide range of operating conditions. The TCV must be able to handle the high LPSW flow during summer when reactive power is high and lake temperature is high as well as the low LPSW flow during winter when the reactive power is low and lake temperature is low. The generator is designed to operate at full MW with one H2 cooler isolated. The TCV and TT may operate in split ranges in order to meet the seasonal variations of cooling demand.