WELCOME TO THE PRESENTATION ON STEAM TURBINE PROTECTIONS

WELCOME TO THE PRESENTATION ON STEAM TURBINE PROTECTIONS AND GOVERNING SYSTEMS AT ESCI, HYDERABAD BY BHEL – PS SR, CHENNAI 8 -9 Dec, 2004

CONTROLS OF LARGE UTILITY TURBINES Presentation By Srinivasan Selvaraj

Main Control Systems n n n n Electro-Hydraulic Governing System (EHTC) Turbine Stress Evaluator (TSE) LP Bypass Control System (LPBP) Gland Steam Control System (GSC) Protection System Turbovisory System (TSI) Automatic Turbine Tester (ATT)

Electro-Hydraulic Governing System (EHTC)

EHTC: Advantages n n n Safe Operation of Turbine in conjunction with Turbine Stress Evaluator (TSC) Excellent Operation Reliability and Dependability Low transient and steady state speed deviations

EHTC: Advantages n n Dependable control during load rejection Reliable Operation in case of Isolated Grid

Critical Measuring Devices n n Speed Probes (3 Nos. ) and associated circuit elements Load Transducers (3 Nos. ) Electro-hydraulic Converter housed in Governing Rack (1 No. ) Position Feedback Transmitter of EHC

Control Loops Speed Control n Load Control n Pressure Control n

Speed Control: Main Functions n n n PD Controller Start Up & Shut Down of Turbine Synchronizing with grid Providing Min. Load Operation of Turbine over entire range of Load in case of Load Controller Failure

Load Control: Main Functions PI Controller n Provision of load reference limiter n Frequency influence option n

Pressure Control: Main Functions PI Controller n Initial pressure control n Limit pressure control n

Nr Nrtd _ + Nact Pr Prtd + + Pmax + Prsum SPEED CONT. PD M I N _ + LOAD CONT. PI M A X M I N HYD EL Pact Fact _ + Fref p. REF _ _ + + PRESSURE CONT. PI p. ACT 0 P LIMIT PRES. R INIT. PRES. S Governing Scheme for KWU Turbines

FROM ELEC CONTROLLER HYD EL STARTING DEVICE MIN M I N TO CONTROL VALVES HYD SPEEDER GEAR Governing Scheme for KWU Turbines

Additional Functions Tracking device option n Load shedding relay n Auto Synchronizer n Isolated grid operation n

Tracking Device Functions The starting device keeps varying automatically with variation in the position of EHC. In case the EHC fails the starting device will restrict the raise in the load.

Load Shedding Relay Functions During sudden load throw–off conditions, there will tendency for the speed to raise rapidly. To avoid such conditions the LSR gives a close command for closure of the control valves for a brief moment. The magnitude of load throw, time duration of closure of control valves are settable in the LSR.

Auto synchronizer Functions The auto synchronizer accepts Gen and Grid Potential transformer signals. To match the frequency and voltage of the Generator, the auto. Sync. Unit gives Speed raise/lower command to EHTC and voltage raise/lower command to AVR. After parameter matching the auto sync. Unit generates a command for Synchronizing the unit

Auto synchronizer Functions After parameter matching the auto sync. Unit generates a command for Synchronizing the unit

Turbine Stress Evaluator (TSE)

Turbine Stress Evaluator n n Compares thermal stress in the monitored components with the permissible limits and generates margins. The temperature margin is fed to the set point controller – speed and load. Derives start up criteria for ATRS

TSE: Components Monitored n n n Emergency stop valve. HP control valve. HP casing. HP shaft. IP shaft.

TSE: Measuring Points n n Surface and mid wall temperatures of (Ti & Tm) Surface and mid wall temperatures of casing. Derived value for HP and IP shaft temperatures from specified locations respective casings. ESV HPCV HP in

TSE: Operating Modes n n Three modes viz. , fast, normal, slow available. The increased fatigue rate associated with fast mode can be compensated by more slow mode operation.

TSE: Margins n n n For any component, the difference Ti –Tm represents the actual thermal stresses. Depending on the value of Tm and operating mode the permissible value of thermal stress is determined. From the difference between the permissible stress and prevailing actual stress the margin is derived.

TSE: Margins n n The margins of different components are provided in the Bar graph form in the TSE monitor. The reference variable derived from the minimum margin acts directly on the turbine control system.

LP Bypass Control System (LPBP)

LPBP system: Main Features Enables alternative path for dumping steam from RH outlet to condenser bypassing IP and LP turbine. n. Maintains RH pressure from a criteria representing the HP turbine flow. n. Works in conjunction with HP bypass systems and when necessitated by the system. n

LPBP system: Main Features Provides fixed and variable set point. n. Protects the condenser by water injection. n. Hydraulically protects the system when the water injection press. is v low or condenser press. is v high n

LPBP system: Pressure control Process variable for control loop is acquired from Press. Transmitter in RH line. n. Two set values viz. Fixed set point and variable set points are formed and maximum value is used as reference. n

LPBP system: Pressure control Fixed set point is varied with push button in the control desk. n. Variable set point is derived from I stage pressure of HP turbine which is an indicative parameter of steam flow. n. Manual operation of valves is possible with push buttons in the control desk. n

I stg. press PT f(x) Fixed setpoint M A X + PI Cont. From EHC LVDT - PT + Valve Lift PID To EHC RH press LPBP Scheme for KWU turbines

Gland Steam Control System (GSC)

Gland Steam Pressure Control n n n Maintains the Gland steam header pressure at required value. Provided with two control valves viz. seal steam control valve and gland steam control valve. Process variable is the header pressure from a transmitter.

Gland Steam Pressure Control n n The electro-hydraulic actuator have inbuilt pump and it is powered by separate power supply. In the event of pump failure, the valve remains stay put.

Seal steam valve Set point. + - PI Cont. f(x) EHC PT Leak steam valve GS header press 100 EHC Leak steam valve Seal steam valve Command To Valve 0 f(x) Cont. output 100 GSPC Scheme for KWU turbines

Protection Systems

Protection Systems n Electrical Protection Systems n Hydraulic Protection Systems

Electrical Protection Systems n n n n Emergency PB (UCB) Lub Oil Pressure Very Low (2 out of 3) Fire Protection Trip Turbine Trip from ATRS Axial Shift Very High (2 out of 3) Over-speed Trip MFT Relay Acted from Boiler (2 out of 3)

Electrical Protection Systems n n n Generator Protection Trip Vacuum Low Trip HP Exhaust Temperature Very High(2 out of 3) Generator Cold Gas Temperature Very High Exciter Hot Air Temperature Very High Liquid Level in Generator Bushing Very High (2 out of 3)

Hydraulic Protection Systems n n Over-speed Trip 1 & 2 Vacuum Low Trip Axial Shift Hand Trip Lever 1 & 2

Features of Protection Systems n n n Cyclic Test done periodically for each Trip input Fault at input level will be annunciated Testing can be done online 2 out of 3 logic ensures reliability and avoid spurious trippings 2 separate Processor Units realize the Protection Logic with dedicated IOs.

Features of Protection Systems n n Data of both processors matched through Serial Communication and discrepancy annunciated 2 separate Solenoids provided in Hydraulic System for redundancy First cause of trip will be annunciated Online Testing of Final Tripping elements through ATT

Resetting of Protection Turbine Trip Solenoid stays in energised condition until the following conditions are fulfilled. n Command from individual Trip ceases n Both ESVs Closed n Trip Oil Pressure less than 2 kg/sq. cm

Turbovisory System (TSI)

Turbovisory Instruments n n n n Absolute bearing vibration Absolute shaft vibration Axial shift Relative expansion – HP Relative expansion – IP Relative expansion – LP Overall expansion

Automatic Turbine Tester (ATT)

ATT : Features Individual testing of each turbine protective devices. n Pretest ensures substitute devices. n Monitoring of program steps for execution within a certain time. n Interruption if trip is initiated. n Automatic reset of program after a fault. n

Automatic Turbine Tester Sub group – Safety Devices. n Sub group – HP/IP valves. n

ATT: Safety devices Remote trip device 1 & 2. n Over speed trip device 1 & 2. n Low vacuum trip device. n Thrust bearing trip. n

ATT: HP/IP Valves HP stop & control valve 1 n HP stop & control valve 2 n IP stop & control valve 1 n IP stop & control valve 2 n

ATT: LOGICS for safety devices Release condition for start n All protective device in operating condition. 1 st step command n Checking of Provision of control fluid for enabling test

ATT: LOGICS for safety devices Release condition for 2 nd step n Pressure before changeover valve > 5 kg/sq cm. 2 nd step command n Takes care of over speed trip-1 during test.

ATT: LOGICS for safety devices Release condition for 3 rd step n Pressure before changeover valve < 2 kg/sq cm. n Pressure between sol. valve >5 kg/sq cm. 3 rd step command n Takes care of over speed trip-2 during test.

ATT: LOGICS for safety devices Release condition for 4 th step n Pressure between sol. valve <2 kg/sq cm. 4 th step command n Provision of control fluid.

ATT: LOGICS for safety devices Release condition for 5 th step n Pressure before changeover valve >5 kg/sq cm. 5 th step command n Changeover valve to test position.

ATT: LOGICS for safety devices Release condition for 6 th step n Trip oil Pressure >5 kg/sq cm. n Changeover valve test position. n Aux startup fluid < 2 kg/sq cm. 6 th step command n Testing of remote trip device 1 & 2.

ATT: LOGICS for safety devices 7 th step command n Testing of over speed trip device 1 & 2. 8 th step command n Testing of low vacuum trip device 9 th step command n Testing of thrust bearing trip device

ATT: LOGICS for valves Start conditions n All stop valves 100 % position n Load controller in action n Load < 66. 6 % n Trip oil pressure > 2 kg

ATT: LOGICS for valves Step I command n Control valves - HP & IP Step II command n Stop valves – HP & IP

Automatic Turbine Run-up System (ATRS)

Automatic Turbine Run-up System (ATRS) n n Acquisition, analysis and collation of various parameters during Startup Sequential Control of Drives Unit Synchronization and Minimum Load Operation Organised and hierarchically arranged as Sub Group Control (SGC), Sub-loop Control (SLC), and Control Interface

ATRS: Functional Group

THANK YOU !