Title of Invention

AN IMPROVED SHAFT SEALING DEVICE FOR HYDRO TURBINES OPERATING PARTICULARLY IN WATER CONTAINING HARD SLIT PARTICLES

Abstract

The invention relates to an improved shaft sealing device for hydro turbines operating in particular, in water containing hard slit particles, the hydro turbine having a rotating sleeve (2) fixed to a shaft (1) of the turbine (T); a top cover (4); a plurality of radial holes (7) to supply clean water through the turbine body; and an inlet (8) configured in the form of a passage for ingress or outgress of silty water, the device comprising atleast two main working seals (3) formed of moulded rubber nitrate, and each having a horizontal limb (3a) and a vertical limb (3b) forming an angle of 110° with each other; and a spring-loaded seal (6) provided underneath the atleast two main working seals (3) which maintains an uniform gap with the rotating sleeve (2), the gap acting as a labyrinth to reduce the presence of water including the velocity of silt particles directed to the main seals (3). The horizontal limb (3a) is fixed to a plate on the top cover (4), the vertical limb (3b) forming a line-contact with the rotating sleeve (2) and causing the atleast two main working seals (3) pressed firmly to the rotating sleeve (2) during operation of the turbine (T) so that the inlet (8) of silt-water is blocked to prevent entry of the silt particles. {FIGURE 5}

Full Text

FIELD OF INVENTION The present invention generally relates to shaft sealing device for hydro turbine applications operating sustainability in water containing hard and abrasive silt particles. More particularly, the invention relates to an improved shaft sealing device which provides longevity to the shaft sealing arrangement particularly for those hydro turbines, which operate in water containing hard silt particles, which erodes the underwater parts of turbine. BACKGROUND OF INVENTION Shaft seal is an essential device of a hydraulic turbine, which serves to prevent the entry of water from the low-pressure zone above runner crown to the top cover and prevents flooding. There are various types of shaft seals adopted by turbine manufacturers in the world, including the lip type rubber seal. Hydro turbine shaft sealing device is located at a place where the turbine shaft passes through a hole in the lower plate of the top-cover. Conventional lip type shaft seal has two rubber sheets, cut circularly in shape, working as the main sealing element which are mounted on the lower plate fixed with the turbine top cover. The shaft seals press against a rotating sleeve mounted on the flange of the shaft, thus forming a surface contact. Technically clean water at a pressure of 3 to 4 atmospheres is fed through a plurality of radial holes in a bath formed in the body between these two rubber rings. This water presses one of the two rubber rings against the sleeve and thus prevents entry of the dirty and silty water. The clean water serves for the cooling and lubrication of the rubber rings. The sealing rings when required can be replaced only through the turbine top cover without dismantling the guide bearing, and without dewatering the turbine, but by providing a maintenance seal on temporary basis. Now, in case of the hydro turbines operating in water having substantial amount of hard and abrasive silt particles, erosion of under-water parts is a common problem. These silt particles also erode the surface of the rotating shaft sleeve and damage the rubber seals, thus making way for the water to leak past the seal through the surface contact. The leaked water accumulating in the top-cover require frequent pumping out the water. Ultimately, the failure of the seals takes place which causes shut-down of the unit necessitating replacement of the seals. SUMMARY OF INVENTION The deficiency of the sealing device of prior art have been technically analysed and to minimize the problem, a new design of seal has been developed by using moulded nitrile rubber instead of rubber sheets. The device of the invention accomplishes the goal of reducing frequency of failure of conventional lip type shaft seal in silt laden water. According to the invention, the shaft sealing device makes line contact with the rotating sleeve and is flexible enough to maintain the contact undiminished in case of any erosion in the rotating sleeve. The improved device shall not only minimizes the leakage of water and flooding of the top-cover which eventually force turbine shut-down. The device further reduces volumetric losses in turbine discharge. The new seal forms a line contact with the rotating sleeve and since the line contact is more effective than a surface contact, this solves the problem of water leakage to the hydro turbines operating in silty water. Accordingly, there is provided an improved shaft sealing device for hydro turbines operating in particular, in water containing hard slit particles. The hydro turbine having a rotating sleeve fixed to a shaft of the turbine; a top cover; a plurality of radial holes to supply clean water through the turbine body. An inlet is configured in the form of a passage for ingress or outgress of silty water. The device comprises atleast two main working seals formed of moulded rubber nitrate, and each having a horizontal limb and a vertical limb forming an angle of 110° with each other. A spring-loaded seal is provided underneath the atleast two main working seals which maintains an uniform gap with the rotating sleeve, the gap acting as a labyrinth to reduce the presence of water including the velocity of silt particles directed to the main seals (3). The horizontal limb (3a) is fixed to a plate on the top cover (4), the vertical limb (3b) forming a line-contact with the rotating sleeve (2) and causing the atleast two main working seals (3) pressed firmly to the rotating sleeve (2) during operation of the turbine (T) so that the inlet (8) of silt-water is blocked to prevent entry of the silt particles. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS OF INVENTION Figure 1- Lip Type Rubber Sealing (Conventional Design): Figure 2- Enlarged View of Conventional Type Sealing: Figure 3- Shows an improved shaft sealing (device according to the invention. Figure 4- Shows an enlarged view of the shaft sealing device of Figure 3 Figure 5- Shows a cross-sectional view of the main seals of the device according to the invention DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT OF INVENTION The conventional type arrangement of turbine shaft sealing is shown in Figure 1. Enlarged view of this type of seal is shown in Fig. 2. Figure 2 clearly shows the two conventional type main working seals (3) making a surface contact with the rotating sleeve (2). The main working seals (3) are generally made of rubber sheets. The top-cover (4) of the turbine (T) accommodates the seals (3). A seals (3) make a surface contact with the rotating sleeve (2) mounted on the turbine shaft (1). A maintenance seal (5) is further provided. Figure 4 shows the improved shaft sealing device in which the main working seals (3) making a line contact with the rotating sleeve (2). A spring-loaded solid rubber seal (6) acting, as labyrinth is located below the main working seal (3). It maintains a uniform gap of 1 millimeter with the rotating sleeve (2). This gap works as a labyrinth, which reduces the pressure of water in the vicinity of the main working seal (3) and velocity of silt particles rushing to the main seals (3). Reduction in velocity of silt particles helps in combating silt erosion of rotating sleeve. Figure 5 shows the cross-section of the improved shaft sealing device having a L-shaped moulded rubber working seal with the two limbs (3a,3b) at an angle of 110° to each other. According to the present invention, the improved device comprises atleast two main working seal (3) made of moulded nitrile rubber in the form of a ring and having L-shaped cross-section (see Fig. 5) with its two limbs (3a,3b) forming 110° with each other. The horizontal limb (3a) is fixed with a plate on the top-cover (4) with fasteners and the inclined limb (3b) forms a line contact with the stainless steel rotating sleeve (2) fixed to the turbine shaft (1). The two working seals (3) press firmly against the rotating sleeve (2) (see Fig. 4) blocking entry passage (8) of dirty and silty water from below. In addition to this, a spring loaded solid rubber seal (6) is also provided below the two main working seals (3), which maintains a uniform gap of 1 millimeter with the rotating sleeve (2). This gap works as a labyrinth, which reduces the pressure of water in the vicinity of the main working seal (3) and velocity of silt particles rushing to the main seals (3). Arrangement for technically clean water supply is provided at pressure of 3 to 4 atmospheres through a plurality of radial holes (7) in a bath formed in the body of the turbine between these two rubber rings (3). This water presses the two rubber rings (3) against the sleeve (2) and blocks the passage (8) for entry of the dirty and silty water from coming up. The clean water also serves for the cooling and lubrication of the rubber rings (3). Sealing rings (3) can be replaced through turbine top cover (4) without dismantling the guide bearing and dewatering the turbine (T) with the help of a jacking type maintenance seal (5). Now, in case of erosion of the rotating sleeve (2) and wearing of the rubber seals (3) due to abrasive silt particles, the line contact of the moving and fixed parts (3b, 3a) shall always remain intact because of the flexibility of the moulded rubber rings (3) and effectiveness of the line contact. That means any damage on the surface of the rotating sleeve (2) due to erosion will least affect the capability of the sealing device. This invention greatly helps in overcoming the problem of failure of turbine seal in silty water condition thus reducing operation of top-cover drainage pumps and ultimately powerhouse drainage pumps. Frequency of shut-down of generating units is also greatly reduced increasing availability of machines on bars. ADVANTAGES OF THE INVENTION ■ Problem of turbine seal failure in case of the turbines operating in silty water got minimized to a great extent. Maintenance work reduced. ■ Shutdown of unit in case of excessive leakage past seal reduced hence better availability of machines on bars. ■ Less operation of top-cover drainage pumps, hence increase in life of pump-motor sets. ■ No fear of flooding of the power station. ■ Uninterrupted operation of the units during monsoon season. ■ Less frequent operation of station drainage pumps, hence increase in life of pump-motor sets. ■ Saving in electricity cost. ■ Satisfactory operation of turbine guide bearing as possibility of mixing of water with oil is ruled out. ■ Better goodwill and satisfaction of powerhouse owner. We Claim: 1. An improved shaft sealing device for hydro turbines operating in particular, in water containing hard silt particles, the hydro turbine having a rotating sleeve (2) fixed to a shaft (1) of the turbine (T); a top cover (4); a plurality of radial holes (7) to supply clean water through the turbine body; and an inlet (8) configured in the form of a passage for ingress or outgress of silty water, the device comprising: - atleast two main working seals (3) formed of moulded rubber nitrate, and each having a horizontal limb (3a) and a vertical limb (3b) forming an angle of 110° with each other; and - a spring-loaded seal (6) provided underneath the atleast two main working seals (3) which maintains an uniform gap with the rotating sleeve (2), the gap acting as a labyrinth to reduce the presence of water including the velocity of silt particles directed to the main seals (3), characterized in that the horizontal limb (3a) is fixed to a plate on the top cover (4), the vertical limb (3b) forming a line contact with the rotating sleeve (2) and causing the atleast two main working seals (3) pressed firmly to the rotating sleeve (2) during operation of the turbine (T) so that the inlet (8) of silt-water is blocked to prevent entry of the silt particles. 2. The device as claimed in claim 1, wherein the spring-loaded seal (6) comprises solid rubber. 3. The device as claimed in any of the preceding claims, wherein the plurality of radial holes (7) are configured in the turbine body between the atleast two main working seals (3). Dated This 20th day of November 2006 (P.D.GU^TA) / OF LS.DAVAR & CO/ APPLICANTS' AGENT ABSTRACT TITLE "AN IMPROVED SHAFT SEALING DEVICE FOR HYDRO TURBINES OPERATING PARTICULARLY IN WATER CONTAINING HARD SLIT PARTICLES" The invention relates to an improved shaft sealing device for hydro turbines operating in particular, in water containing hard slit particles, the hydro turbine having a rotating sleeve (2) fixed to a shaft (1) of the turbine (T); a top cover (4); a plurality of radial holes (7) to supply clean water through the turbine body; and an inlet (8) configured in the form of a passage for ingress or outgress of silty water, the device comprising atleast two main working seals (3) formed of moulded rubber nitrate, and each having a horizontal limb (3a) and a vertical limb (3b) forming an angle of 110° with each other; and a spring-loaded seal (6) provided underneath the atleast two main working seals (3) which maintains an uniform gap with the rotating sleeve (2), the gap acting as a labyrinth to reduce the presence of water including the velocity of silt particles directed to the main seals (3). The horizontal limb (3a) is fixed to a plate on the top cover (4), the vertical limb (3b) forming a line-contact with the rotating sleeve (2) and causing the atleast two main working seals (3) pressed firmly to the rotating sleeve (2) during operation of the turbine (T) so that the inlet (8) of silt-water is blocked to prevent entry of the silt particles. {FIGURE 5}

Documents:

01245-kol-2006 abstract.pdf

01245-kol-2006 claims.pdf

01245-kol-2006 correspondence others.pdf

01245-kol-2006 description(complete).pdf

01245-kol-2006 drawings.pdf

01245-kol-2006 form-1.pdf

01245-kol-2006 form-2.pdf

01245-kol-2006 form-3.pdf

01245-kol-2006 gpa.pdf

1245-KOL-2006-ABSTRACT-1.1.pdf

1245-KOL-2006-ABSTRACT.pdf

1245-kol-2006-CANCELLED PAGES.pdf

1245-KOL-2006-CLAIMS-1.1.pdf

1245-KOL-2006-CLAIMS.pdf

1245-KOL-2006-CORRESPONDENCE-1.1.pdf

1245-kol-2006-CORRESPONDENCE.pdf

1245-KOL-2006-DESCRIPTION COMPLETE-1.1.pdf

1245-KOL-2006-DESCRIPTION COPLETE.pdf

1245-KOL-2006-DRAWINGS.pdf

1245-kol-2006-EXAMINATION REPORT.pdf

1245-KOL-2006-FORM 1-1.1.pdf

1245-KOL-2006-FORM 1.pdf

1245-KOL-2006-FORM 13.pdf

1245-kol-2006-FORM 18.pdf

1245-KOL-2006-FORM 2-1.1.pdf

1245-KOL-2006-FORM 2.pdf

1245-KOL-2006-FORM 5.pdf

1245-kol-2006-GPA.pdf

1245-kol-2006-GRANTED-ABSTRACT.pdf

1245-kol-2006-GRANTED-CLAIMS.pdf

1245-kol-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

1245-kol-2006-GRANTED-DRAWINGS.pdf

1245-kol-2006-GRANTED-FORM 1.pdf

1245-kol-2006-GRANTED-FORM 2.pdf

1245-kol-2006-GRANTED-FORM 3.pdf

1245-kol-2006-GRANTED-FORM 5.pdf

1245-kol-2006-GRANTED-SPECIFICATION-COMPLETE.pdf

1245-KOL-2006-OTHERS.pdf

1245-KOL-2006-REPLY TO EXAMINATION REPORT-1.1.pdf

1245-KOL-2006-REPLY TO EXAMINATION REPORT.pdf

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