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

2. CONTROLS OF LARGE UTILITY TURBINES
Presentation By
Srinivasan Selvaraj

3. Main Control Systems 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)

4. Electro-Hydraulic Governing System (EHTC)

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

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

7. Critical Measuring Devices
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

8. Control Loops
Speed Control
Load Control
Pressure Control

9. Speed Control: Main Functions
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

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

11. Pressure Control:Main Functions
PI Controller
Initial pressure control
Limit pressure control

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

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

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

15. 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.

16. 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.

17. 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

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

19. Turbine Stress Evaluator (TSE)

20. Turbine Stress Evaluator
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

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

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

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

24. TSE: Margins 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.

25. TSE: Margins
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.

30. LP Bypass Control System (LPBP)

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

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

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

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

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

36. Gland Steam Control System (GSC)

37. Gland Steam Pressure Control
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.

38. Gland Steam Pressure Control
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.

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

40. Protection Systems

41. Protection Systems Electrical Protection Systems
Hydraulic Protection Systems

42. Electrical Protection Systems
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)

43. Electrical Protection Systems
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)

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

45. Features of Protection Systems
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.

46. Features of Protection Systems
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

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

48. Turbovisory System (TSI)

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

50. Automatic Turbine Tester (ATT)

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

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

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

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

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

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

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

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

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

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

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

62. ATT: LOGICS for valves Start conditions All stop valves 100 % position
Load controller in action
Load < 66.6 %
Trip oil pressure > 2 kg

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

64. Automatic Turbine Run-up System (ATRS)

65. Automatic Turbine Run-up System (ATRS)
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

66. ATRS: Functional Group

67. THANK YOU !