Control of Heat Processes

Transcription

1 PG 30 kwietnia 2011 Slide 1 of 66

2 Turbine power PG test P = m ṁ 0 H η i η m η g m coefficient which takes into account extraction flows Slide 2 of 66

3 Turbine regulation PG 1. Quantative adjustment varied ṁ 0 2. Quality adjastment varied H Changes in other parameters are the consequence of these changes Slide 3 of 66

4 Steam distribution PG 1. Throttle distribution 2. Group distribution 3. Bypass distribution 4. Combination of above Slide 4 of 66

5 Turbine regulation PG Slide 5 of 66

6 PG Slide 6 of 66

7 Losses PG Slide 7 of 66

8 Sample characteristics of the turbine PG Slide 8 of 66

9 throttling ratio = efficiency regulations η ro = H 0 H PG Slide 9 of 66

10 Full and partial load on the turbine PG Slide 10 of 66

11 PG The efficiency of the internal control throttling η i0 = η ro η i0 Slide 11 of 66

12 PG Slide 12 of 66

13 lifts PG Slide 13 of 66

14 PG Slide 14 of 66

15 Characteristics of group distribution PG Slide 15 of 66

16 Characteristics of group distribution PG Slide 16 of 66

17 Power and efficiency of the group distribution PG Slide 17 of 66

18 The characteristics of steam with a different number of valves in the group distribution PG Slide 18 of 66

19 PG Slide 19 of 66

20 PG Slide 20 of 66

21 Bypass distribution characteristics PG m y inlet massflow m x bypass massflow m total massflow Slide 21 of 66

22 The efficiency of the turbine with bypass regulation PG Slide 22 of 66

23 PG Speed regulation a percentage of rated speed the change in speed when the power output of the turbine is gradually changed from rated output to zero output under the following conditions: 1. Steam conditions constant 2. Speed changer set at rated conditions 3. Turbine under no external control device % Speed regulation = zero output) rated power output) (0.01)(r/min at rated output) Slide 23 of 66

24 Speed regulation PG Slide 24 of 66

25 Speed variation PG a percentage, the total magnitude of speed change, or fluctuations from the set speed This characteristic includes dead band and sustained oscillation. % Speed variation = (change in r/min above set speed)+(change in r/min below set speed) (0.01)(rated speed) Slide 25 of 66

26 Dead band PG a characteristic of the speed-governing system that is commonly known as wander the insensitivity of the speed governing system that is defned as the total speed change during which there is no resultant change in the position of the governing valves to compensate for the speed change. Slide 26 of 66

27 Stability the measure of the ability of the speed-governing system to position the governor-controlled valves so that sustained oscillations of speed are not produced during a sustained load demand, or following a change to a new load demand. PG Slide 27 of 66

28 Speed rise PG the maximum momentary increase in speed obtained when the turbine is developing rated power output at rated speed, and the load is suddenly dropped to zero. % Speed rise = zero power output) rated speed (0.01)(rated speed) Slide 28 of 66

29 PG Slide 29 of 66

30 Set point PG the value of the controlled variable that the governor or the regulator is set to maintain under fixed conditions. Slide 30 of 66

31 PG Speed compensation a device that responds to movement in the governing system and loads the governor a predetermined amount This loading compensates for the inherent regulation of the governor and results in a settled regulation of lower value than the inherent It is often referred to as reset device, droop correction, proportional speed, or floating action. Slide 31 of 66

32 Isochronous governor PG a governor that controls for constant speed or, theoretically, has no regulation. Slide 32 of 66

33 Direct-acting allow only the speed sensitive portion of the governor to supply the force to position the governor valve. PG Slide 33 of 66

34 A relay governor system PG provides for a servo or a power supply element to amplify the force positioning the governor valve Slide 34 of 66

35 Hunting Extreme oscillation about the set point PG Slide 35 of 66

36 PG NEMA Classifications In the United States, governors in general are rated by NEMA (National Electrical Manufacturer s Association). NEMA class Adjustable speed range [%] Maximum steady-state speed regulation [%], no load to full load Maximum speed variation plus or minus [%], at rated cond. Maximum speed rise [%] A B C D Slide 36 of 66

37 NEMA Classifications PG Overspecd Trip System Settings NEMA class Trip speed [%] above rated speed A 15 B 10 C 10 D 10 Slide 37 of 66

38 Mechanical-hydraulic governor system PG Slide 38 of 66 Type T sealed, mechanical-hydraulic oil relay governor

39 Mechanical-hydraulic governor system PG Slide 39 of 66

40 Mechanical-hydraulic governor system PG Mechanical-hydraulic governor systems are suitable for: most turbine-driven pumps, fans, compressors, small generators, etc. Slide 40 of 66

41 Mechanical-hydraulic governor system PG Friction Lost motion Misunderstanding Deterrents: Slide 41 of 66

42 PG all the steam flows through a single governing or throttling valve to the turbine nozzles At part loads wherein much throttling may be required, the turbine will be inefficient because of the energy dissipated by throttling. : single seated (most 3 4- and 1-in valves) double seated (2, 3, 4, 5 1 2, and 7-in valves) Slide 42 of 66

43 Double-seated steam admission valve PG Slide 43 of 66

44 PG usually use a type of valve which is commonly called a venturi value used for higher pressures and flows because of its superior flow lift characteristics A series of such valves are then used (that is, 4, 5,6, or 7) for finer control and better part load economy In a multivalve turbine, the steam flow is divided and directed to several nozzle groups Each nozzle group is controlled by an individual valve. Slide 44 of 66

45 Venturi valves and bar lift mechanism PG Slide 45 of 66

46 PG PG All PG governors have similar basic elements regardless of how simple or complex the control may be. These basic elements include: 1. Oil pump with complete built-in governor oil system including the relief valve to limit maximum oil pressure. 2. Centrifugal flyweight head pilot valve assembly to control flow of oil to and from the governor power cylinder assembly. 3. Power cylinder assembly to operate turbine control valve. 4. Compensating system to give stability to the governor. 5. Means of adjusting the governor speed setting. Slide 46 of 66

47 PG The Woodward PG governor PG turbine with Woodward PG-PL governor. Slide 47 of 66

48 PG PG The Woodward PG governor a mechanical oil relay governor The mechanical force developed by the governor weights is transmitted by oil pressure to a power piston moving the governor valve. The advantage of this system is: only a small amount of force is required to move the pilot valve, as opposed to the large amount of mechanical force necessary in a direct-acting system smaller, more accurate elements may be used friction losses are thus reduced to a minimum better governor control Slide 48 of 66

49 PG PG PG Governores Modifications: PG-PL governor (includes an integral air speed changer; otherwise, it is similar in operation to the standard PG governor) PG-PH governor (Used for turbine-generator units where the regulation is required to permit the generator to parallel a utility system or another generator.the output of the power piston is fed back into the speeder spring. The governor valve movement is, therefore, proportional to spring force. This provides the governor with regulation.) Slide 49 of 66

50 PG The Woodward electric type governor is intended for: speed control of steam driving generators, pumps, fans, compressors, paper mill machinery. Slide 50 of 66

51 PG The EG governor consists basically of three separate assemblies: a control box, a speed-adjusting potentiometer, a hydraulic actuator. Slide 51 of 66

52 PG There arc two basic types of EG control boxes: The EGA model (used primarily for generator drive and receives its power supply and speed signal from the generator system) The EGM model (Used primarily for mechanical drive applications and requires a separate power source. The speed signal originates from the electrical impulses generated by a magnetic pickup.) Slide 52 of 66

53 PG Woodward electronic governor. Slide 53 of 66

54 The operation of the EGM governor system PG A magnetic proximity speed pickup is mounted on the turbine to sense speed from a gear mounted on the turbine shaft The pickup is mounted as close to the bearing as possible to reduce speed errors caused by shaft vibration and runout. Slide 54 of 66

55 The operation of the EGM governor system PG The speed reference signal from the pickup is fed into the EGM control box These speed pulses are then converted into a DC voltage proportional to speed This voltage signal is then fed from the control box to the electrohydraulic transducer portion of the governor system Slide 55 of 66

56 PG The EGM consists of a chassis, cover, and two encapsulated printed circuit boards. The chassis internally carries the terminal strips for the input/output connections, transformer, diodes, transistors, potentiometers, etc. The speed-setting potentiometer establishes the reference voltage at the input to the EGM box and thus establishes the set point. Slide 56 of 66

57 The operation of the EGM governor system PG The EGM signal feeds the EGR hydraulic actuator of the system The hydraulic actuator adjusts turbine speed as dictated by the signal produced by the EGM control box The essential element of the EGR actuator is the electrohydraulic transducer that directs oil to and from the power piston or servomotor This servo is remotely mounted on the turbine similar to PG governors on multistage. Slide 57 of 66

58 PG To achieve greater force levels, the Woodward servo is remotely mounted to serve as a prepilot (or slave) to a master pilot that controls the flow of high pressure oil to a large piston This assembly of Woodward servo (prepilot), pilot valve, and piston is called a servomotor. Slide 58 of 66

59 PG Typical steam turbine control system using Woodward PG type governor. Slide 59 of 66

60 PG Steam at constant pressure for process use can be supplied from a steam turbine by adding a pressure-regulating system to the speed control system This combined speed-pressure control system is called extraction control. Slide 60 of 66

61 PG The steam extraction principle: Turbine speed changes; extraction steam demand is constant Slide 61 of 66

62 PG The steam extraction principle: Extraction steam demand reduces; turbine speed is constant Slide 62 of 66

63 Extraction diagram PG Slide 63 of 66

64 PG extraction governor system, load limiting. Slide 64 of 66

65 PG extraction governor system with extraction pressure control. Slide 65 of 66

66 Koniec PG Slide 66 of 66