The purpose of this procedure is to outline the key tasks and methodology that will be used in the event of a Steam Turbine Trip.
This document is intended to guide the control room operator during a Steam Turbine Trip. All efforts should be made to restart the Steam Turbine in a safe and timely manner and ensure that all the proper individuals are notified on any events pertaining the operations at Mesquite Power at all times. During steady state conditions, all efforts should be made to identify the cause of the trip and make a determination whether it is safe to restart the Steam Turbine without jeopardizing Mesquite Power personnel or equipment.
3.1 Steam Turbine Trip Tasks
Notify S.E.T and S.R.P of unit trip and inform them that the control room will light off Duct Burners if available on remaining Block in attempt to meet schedule. Notify Plant Manager and O&M Manager on the situation. Mobilize all available operations staff in the control room.
______Verify HRSG bypass valves are operating properly in automatic control. Bypass valves will shift to “Post Trip” on their own, place in calculated set point.
______Start 1 Demin transfer pump and ensure lag pump is in standby.
______Reduce Gas Turbine load to 100 MW (low end mode 6Q, Take out of AGC if applicable).
______Stabilize HRSG steam pressures and temperatures, monitor drum levels closely.
Note: If start up vents open during STG trip, slowly close them off in order to conserve hotwell level. Bypass valves should control pressure
______Light off Duct Burners on other block and ramp as necessary to meet load schedule. Let SET make decision to light DB's. It may not be economical to light DB's.
Note: Review STG MK V screen, Trip Checks and DCS Customer Trips to determine if the Steam Turbine Generator can be placed back in service. If for any reason the STG cannot be placed back in operation in a timely manner, notify Plant Manager and O&M Manager for instructions whether to shut down the Gas Turbines until the issues are resolved.
Note: If it is determined that the STG can be safely placed back in operation, notify S.E.T. and proceed in preparations for rolling the Steam Turbine.
______Lower all drum levels to -3 in anticipation of drum swells during HRSG blending process
______Lower Reheat pressure on both HRSGs by slowly lowering (in automatic) the set point on the Reheat bypass valves (SGJ-ACV-X008) to 100 psi using operator setpoint.
______Lower HP pressure on both HRSGs by slowly lowering (in automatic) the set point on the HP bypass valves (SGG-ACV-X008) to 875 psi.
______Lower LP pressure on both HRSGs by slowly lowering (in automatic) the set point on the LP bypass valves (SGG-ACV-X008) to 55 psi.
______Open the following steam line drains to satisfy STG start permissive.
- HP ABV-X011,X012
- P ABV-X001,X002,X005,X006
______Ensure all MK V and DCS start permissives are met.
______From DCS (Start Up master 2) screen 2 disable (STG status) IPC control and reset (Trip/Reset) STG.
______Roll the Steam Turbine in “Auto” as follows :
- Reset the Steam Turbine ( if Steam Turbine is still rolling press “Reset” twice so the speed setpoint comes up to actual speed )
- Verify “Reverse Flow”
- Initiate an auto/auto start sequence of the STG
- Select “Start”
- Select “Hold off”
______Roll the Steam Turbine in Manual as follows:
- Reset Steam Turbine
- Verify Reverse Flow
- Select Start
- Ensure “Holds Off”
- Select speed command of 83% (3000 rpm) and wait for oil temp to increase to >100F.
- Select speed command of 100%. If speed command isn't at 100%, the IV's will not open fully, thus preventing MS control valves from opening fully.
- Verify lube oil temperature to 85° F
______Record roll time in control room logbook
During the roll closely monitor the following:
______HP exhaust temperature limits
- Alarm 850 degf
- Trip 900degf
______LP Temperature Limits
- Alarm 400 degf
- Trip 450 degf
______Exhaust Temperature Limits
- Alarm 200 degf
- Trip 225 F
- Alarm 6 mils
- Trip 9 mils
______Differential expansion limits
- Alarm DEDX-1 long rotor + 386
- Trip DEDX-1 long rotor + 486
- Alarm REDX-1 long rotor + 616
- Trip REDX-1 long rotor + 720
- Alarm DEDX-1 short rotor -260
- Trip DEDX-1 short rotor -290
- Alarm REDX-1 short rotor -287
- Trip DEDX-1 short rotor -317
______Turbine speed will hold at 3000 RPM until lube oil temperature reaches approximately 100 degf.
______At 3600 rpm synchronize the STG (in auto synch mode), Record time in logbook.
______Ramp ST (15% LOAD COMMAND) to support forward flow.
______Place LP admission valve at 20% flow command ramp flow rate in 10 % increments once 100% flow is achieved raise LP bypass to condenser setting to 90 psi.
______In auto forward flow mode will transfer automatically (When ST IV's open >50%) at this time raise HP to CRH and HRH bypass set points to (1200 psi HP to CRH) (350 psi,RH bypass) place bypass valves in calculated set point. If mode is in Manual, select Forward Flow once IV's >50% and ALARM prompted to go to Forward Flow.
______With HP steam pressure is rising and IP and HP Drums are stable select the IPC “ON”. Check DCS screens insure that all HRSG and Steam Turbine drains are closed, check MK V screens insure that all group A, B, and C drains are closed.
______Record time in control room logbook
______Adjust plant load as necessary to support generation schedule.
______Check VARS maintain at unity.
______Return all Boiler Drum levels to normal level