3INSTRUMENTATION PRESSURE MEASUREMENT: TWO Nos. PRESSURE TRANSMITTERS PROVIDED IN THE UPSTREAM OF HP BYPASS PRESSURE CONTROL VALVES, IN THE MAIN STEAM LINE.RANGE : 0 TO 200 kg/sq.cmTEMPERATURE MEASUREMENT:TWO Nos. K-TYPE DUPLEX THERMOCOUPLES ARE PROVIDED IN EACH LINE, LOCATED AT THE DOWNSTREAM OF EACH HP BYPASS PRESSURE CONTROL VALVES.RANGE : 100 TO 450°C.
4PROCESS MONITORING PRESSURE / TEMPERATURE MEASUREMENT: The 4 to 20 mA analog signals received from the Pressure transmitters and the mV signals received from Thermocouples are digitally processed in the DCS. These signals are monitored to generate internal and external digital signals for interlocks and alarm generation.
5ALARMS, INTERLOCKS and PROTECTION The following are the main Alarms generated in the system:Pressure/Temperature transmitters failure.Main steam pressure too high.Downstream temperature high/very high.Tracking Pressure set point failure.Pressure control valves opened more than 2%.Pressure control valves closed less than 2%.Hydraulic Oil pressure too low.Any fast opening criteria operated.Any closing criteria operated.
6ALARMS, INTERLOCKS and PROTECTION The following are the important interlocks provided in the system:When the Pressure control valves are closed less than 2% andin Manual mode, a forced close signal is provided to preventthe valve from drift open.When the Main steam pressure is too high, then the Fastopening device is activated.Whenever the pressure control valve is opened more than2%, then the associated Spray control valve will switchoverto Auto mode, if it was in Manual mode before.When the system is in auto mode and if the process signal isfailed, then the associated control loop will be switched tomanual mode.
7ALARMS, INTERLOCKS and PROTECTION The following are the important interlocks provided in the system:When the down stream temperature of Pressure control valvesis too high or when the condenser vacuum is low, then thePressure control valves are closed on priority.When the Turbine trips or when the Generator CB is open,the opening device is activated to prevent Boiler trip.
8LEGEND HP / LP BYPASS SYSTEM HRH MSL BP BOILER HPT MPT LPT CRH NRV CRH LPCCONBPELBPEBDBFPLEGENDBP : HP BYPASS VALVE BD : HP SPRAY ISOLATION VALVE CON : CONDENSORLBP: LP BYPASS VALVE BPE : HP SPRAY VALVE LBPE : LP SPRAY VALVEBFP: BOILER FEED PUMP CRH : COLD REHEAT LINE LPC : LP COOLERHPT: HIGH PRESSURE TURBINE HRH : HOT REHEAT LINE LPT : LOW PR. TURBINEMSL: MAIN STEAM LINE MPT : MEDIUM PR. TURBINE