Title of Invention

"COMBINED NOZZLE CUM THROTTLE GOVERNING SYSTEM FOR STEAM TURBINE"

Abstract

This invention relates to a combined nozzle-cum-throttle governing device for steam turbines to regulate steam at steady speed with change in load comprising a hydraulic speed controller (1) for nozzle mode and an electro-hydraulic controller (2) for nozzle-cum-throttle mode, the said hydraulic speed controller is connected to the hydraulic amplifier (5), MIN logic (Minimum Logic) (6) and hydraulic actuation means (7) to adjust me control valve (9) being connected to the turbine and the said electro hydraulic conn-oiler is connected in parallel to EH-converter (Electro-Hydraulic Converter), hydraulic throttle (3) and EH converter hydraulic nozzle (4) and connected to said M3N logic and said hydraulic actuation means to adjust said control valve, a changeover unit (10) ia connected to valve lift controller nozzle (12) for change over from throttle to nozzle and vice versa.

Full Text

The invention relates to a combined nozzle-cum-throttle governing system for steam turbines to regulate steam flow at steady speed with change in load. The main function of governing system of Turbo Set is to regulate the steam flow with change in load maintaining steady speed within a specified limit Turbine Governing system is also required to ensure the operation of Turbo Set without exceeding the thermal stresses in Turbine components during start-up, rolling, load change and load shedding. The steam entry is realized either in Throttle control mode or in Nozzle control mode. Throttle Governing system ensures simultaneous opening of all HP control valves depending on steam throughput to HP Turbine, However, in Nozzle Governing system sequential opening of valves takes place depending on load requirement The existing governing system used with steam turbines is available in single mode only i.e. Throttle Control mode or Nozzle Control mode. There are disadvantages associated with the present system of Nozzle Control mode is that the start up of me machine takes place in partial arc steam admission instead at mil arc periphery of the turbine inlet portion. This leads to non-uniform heating of the turbine inlet portion. Another disadvantage associated with the present system of Throttle Control mode is that the steam turbine operation is inefficient during part load operation. Therefore, the main object of the present invention is to provide simple and efficient governing system for steam turbines. An object of the present invention of the governing system for steam turbines is that start up of the turbo set is possible in foil arc admission mode by selecting throttle mode. Full arc admission helps in uniform heating for turbines and thereby reduces stresses during startup. Another object of the present invention of the governing system for steam turbines is that optimum efficiency of the steam turbine is achieved during part load operation by selecting the system in nozzle mode. Further object of the present invention of the governing system for steam turbines is that smooth change over is possible from throttle mode to nozzle mode and vice versa. According to this invention there is provided a combined nozzle-cum-throttle governing device for steam turbines to regulate steam at steady speed with change in load comprising a hydraulic speed controller (1) for nozzle mode and an electro-hydraulic controller (2) for nozzle-cum-throttle mode, the said hydraulic speed controller is connected to the hydraulic amplifier (5), MIN logic (Minimum Logic) (6) and hydraulic actuation means (7) to adjust the control valve (9) being connected to the turbine and the said electro hydraulic controller is connected in parallel to EH-converter (Electro-Hydraulic Converter), hydraulic throttle (3) and EH converter hydraulic nozzle (4) and connected to said MIN logic and said hydraulic actuation means to adjust said control valve, a changeover unit (10) is connected to valve lift controller nozzle (12) for change over from throttle to nozzle and vice versa. The nature of the invention, its objective and further disadvantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings. Fig. 1 shows schemetically the structure of turbine controller system Fig. 2 shows a block diagram for nozzle-cum-throttle Fig3 shows a block diagram of changeover scheme. In accordance with the present invention, the combined-nozzle-throttle governing system facilitates operation of The turbo set in both modes viz. nozzle as weli as throttle. The steam turbine is started in throttle mode (i.e. full arc admission) and after attaining a block load value, the set is put in nozzle mode (i.e. partial arc admission). Full arc admission helps in uniform heating of turbine and thereby reduces stresses during start up. It also takes care of stability of film formation in bearing. The system comprises of a Hydraulic Speed Controller (for Nozzle mode) (1) and an Electro-Hydraulic Controller (2) for Nozzle (4) as well as Throttle (3) (mode). The Hydraulic Speed Controller (1) adjusts the control valves (9) by way of Hydraulic Amplifier (5) whilst me Electro-Hydraulic Controller (2,3,4) acts on the control valves (9) by way of Electro-Hydraulic converter (3,4). Change in speed is sensed electrically by speed load Controller (21) through Hall Generator (15). Speed/load Controller (21) further processes the signal (16) based on load/speed demand and transmits valve-opening signal (17,18) to Electro Hydraulic Converter (3,4) which is equipped with six follow-up-pistons. Four follow-up pistons generator Secondary oil for HP control valve servomotors (22) and remaining two follow-up pistons generate secondary oil for IP control valve servomotors (23). The integer Hall generator stated herein is a probe used to measure operational speed of the Steam Turbines using hall effect principle. It generates voltage pulse corresponding to speed and transmits the same to the electronic processing circuit Change in speed is also sensed hydraulically with the help of varying oil pressure, which is directly proportional to square of speed, generated through Hydraulic Speed Transmitter (14). Hydraulic Amplifier (5) is operated in a pre-defined fashion with the help of signal oil generated from Hydraulic Speed Governor (13). Hydraulic Amplifier (5) is also equipped with six follow-up pistons out of which four follow-up pistons generate secondary oil for HP Control valve Servomotors (22) and two follow-up pistons generate secondary oil for IP Control valve servomotors (23). Hydraulic Amplifier (5) and Electro-Hydraulic Converter (2,3,4) are switched in parallel to form MIN logic (6) as shown in the figure-1. The system not exercising its control at any given time is in its maximum limit position. Speed governing logic of Nozzle cum Throttle Governing system is as per figure-2. A change over unit (10) helps to achieve required opening of control valves (12) for Nozzle Governing operation while switching over from Throttle Governing (11) maintaining the prevailing load condition. Change over unit (10) suitably takes care of characteristic curves for Nozzle Governing as well as Throttle Governing. Secondary oil is the nomenclature for signal oil generated from follow-up pistons and transmitted to control valve (9) servomotors. During Nozzle mode of operation various follow-up pistons generate varying range of secondary oil pressure (for HP valves) depending on control valve cut-in sequence. However, during Throttle mode of operation various follow-up pistons generate similar range of secondary oil pressure. 8 bar control oil system operate control valve servomotors. An increase in secondary oil pressure helps to open control valve further resulting in more steam input to Turbine in commensurate with higher load demand and vice-versa. Change in speed is also sensed electrically by Hall Generator (15) and electrical signal (16) is transmitted to Speed/load Controller (21). Electro Hydraulic Controller further processes the signal based on load/speed demand and transmits valve-opening signal (17,18) to Electro Hydraulic Converter (3,4) which is equipped with six follow-up pistons. Four follow-up pistons generate Secondary oil for HP control valve servomotors ((9) and remaining two follow-up pistons generate secondary oil for IP control valve servomotors. The change over scheme (10) facilitates the change of mode of governing from Throttle to Nozzle or vice-versa even while the turbine is in operation. When the turbine is in Throttle mode of operation, the output of the speed/load controller (21) is connected to the EHC (throttle)(3) and EHC (nozzle)(4) is at its maximum. This means that EHC (nozzle) is ineffective through hydraulic minimum gate. When changeover is selected by operator, the output of EHC (nozzle) is gradually reduced. In this process the four HP valves come under the influence of EHC (nozzle) one by one. When the fourth valve comes under control of EHC (nozzle) , the turbine is in Nozzle mode of operation. The output of EHC (Throtle) (3) is then gradually increased to maximum so that it does not interfere in Nozzle mode of operation. Then the change over process is completed. The mode of operation is selectable by the operator from control desk and change over to other mode can also be initiated. Change over unit (10) suitably takes care of characteristic curves for Nozzle Governing as well as Throtle Governing. The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims. WE CLAIM 1. A combined nozzle-cum-throttle governing device for steam turbines to regulate steam at steady speed with change in load comprising a hydraulic speed controller (1) for nozzle mode and an electro-hydraulic controller (2) for nozzle-cum-throttle mode, the said hydraulic speed controller is connected to the hydraulic amplifier (5), MIN logic (Minimum Logic) (6) and hydraulic actuation means (7) to adjust the control valve (9) being connected to the turbine and the said electro hydraulic controller is connected in parallel to EH-converter (Electro-Hydraulic Converter), hydraulic throttle (3) and EH converter hydraulic nozzle (4) and connected to said MIN logic and said hydraulic actuation means to adjust said control valve, a changeover unit (10) is connected to valve lift controller nozzle (12) for change over from throttle to nozzle and vice versa. 2. The combined nozzle-cum-throttle governing device as claimed in claim 1, wherein the change in speed is sensed electrically by speed/load controller (21) through hall generator (15) and the said signal (16) is processed based on load/speed demand and transmits valve opening signal (17,18) to electro-hydraulic converter (3,4) the said electro-hydraulic converter is equipped with six follow-up pistons out of which four-follow up pistons generate secondary oil for HP control (High Pressure Control) valve servomotors (22) and remaining two follow-up pistons generate secondary oil for IP control (Intermediate Pressure Control) valve servomotors(23). 3. The combined nozzle-cum-throttle governing device as claimed in claim 1 wherein the said change in speed is also sensed hydraulically by hydraulic speed transmitter (14) and the hydraulic pressure signal is fed to hydraulic speed governor (13) which generates a signal oil to operate the hydraulic amplifier (5), the said hydraulic amplifier is also equipped with six follow-up pistons out of which four generate secondary oil for HP control valve (22) and two generate secondary oil for IP control valve servomotors (23). 4. The combined nozzle-cum-throttle governing device as claimed in claim 1, wherein the change over unit (10) provides required opening of control valves (12) for nozzle governing operation while switching over from throttle governing (11) maintaining the prevailing load condition the said change over unit suitably takes care of characteristics curves for nozzle governing as well as throttle governing. 5. The combined nozzle-cum-throttle governing device for steam turbine to regulate steam as steady speed as herein described and illustrated with reference to the accompanying drawings.

Documents:

3334-del-1998-abstract.pdf

3334-del-1998-claims.pdf

3334-del-1998-correspondence-others.pdf

3334-del-1998-correspondence-po.pdf

3334-del-1998-description (complete).pdf

3334-del-1998-drawings.pdf

3334-del-1998-form-1.pdf

3334-del-1998-form-19.pdf

3334-del-1998-form-2.pdf

3334-del-1998-form-3.pdf

3334-del-1998-form-4.pdf

3334-del-1998-gpa.pdf