The present invention relates to a method of reduction of throttling losses in a turbomachine at off design conditions. Particularly, the present invention relates to a method of reduction of throttling losses in a turbomachine at overload conditions through modification of the layout design of a turbomachine.
BACKGROUND OF THE INVENTION:
Traditionally, during the times of extreme weather conditions and with the need to draw the power output not below the design condition, a process of injection of working fluid more than the design volumetric flow into later stages of a turbomachine is introduced. Typically, for example, the operational parameters of a turbomachine are as follows:
Inlet pressure at nozzle chest 250 bar
Inlet Temperature at nozzle chest 600oc
Exit pressure at end of LP module/Inlet 0.08 bar
pressure at condenser
Exit temperature at end of LP 42oc
module/Inlet temperature at condenser
Mass flow rate 100 Kg/Sec
Speed of rotor 3000 rpm
Power Output 160MW
In summer, the atmospheric temperature may go up to 50oc. The temperature of the water may be at 47oc or above. It is established principle that pressure is directly proportional to temperature. So, it is not possible to drop pressure of working fluid up to a pressure of 0.08 bar having a corresponding temperature of 42oc as it will hinder the function of a condenser in transferring heat from working fluid to the water. Therefore, it is possible to drop pressure of working fluid only up to a pressure of 0.16 bar having a corresponding temperature of 55oc or so which ultimately results in the drop of designed power output of 160MW. But, the customer requirement is to

produce the power not less than the designed power output of 160 MW irrespective of weather conditions. At this juncture, the principle of injecting the working fluid more than the design volumetric flow came in to play to produce at least the designed power output irrespective of weather conditions.
Typically, the turbomachine designed with a provision to inject the working fluid more than the design volumetric flow has the capacity to produce more power than the designed power output in winter conditions depending on the volumetric flow.
Figure 1 illustrates a thermodynamic cycle layout of a high pressure turbine at peak load conditions.
Typically, any turbomachine will be designed at a particular design condition subjecting to various design requirements and design constraints. At off design conditions (i.e.,120-130% of design volumetric flow), a nozzle chest/inner casing (NC/IC) of a high pressure turbine (HP) would not be able to accommodate steam of higher mass flow rate due to space constraints which ultimately results in choking, recirculation and loss of efficiency. So, a part of steam at high pressure (for example at 250 bar) before entering the nozzle chest/inner casing (NC/IC) of the high pressure turbine (HP) at an inlet (I) is admitted through a bypass throttle valve (TV) and the steam at low pressure (for example at 180 bar) after throttling is injected into later stage of the high pressure turbine (HP). But, the process of throttling involves loss of energy without being captured in terms of pressure reduction of steam.
Generally, reduction of throttle valve losses at inlet of a nozzle chest of a turbomachine is common in prior art but capturing of energy lost in throttling at a bypass throttle valve of a turbomachine is no where found in the prior art.
Some techniques have been disclosed in the prior art for reduction of throttle valve losses in turbomachines.
US Patent no. 4178763 filed on March 24th, 1978 titled “System for minimizing valve throttling losses in a steam turbine power plant” discloses a means for rendering the valve positions of a plurality of steam admission valves to a selected state of a

plurality of predetermined steam admission valve position states by adjusting the value of a boiler throttle pressure as a function of the selected state, the each predetermined state substantially corresponding to a minimum of valve throttling losses. The granted patent teaches about different optimized valve positioning states for minimizing the throttle valve losses but the granted patent is silent on capturing the lost energy in the throttling process.
US Patent no. 4811565 filed on February 5th, 1988 titled “Steam Turbine Valve Management System” discloses a valve control system provided with separate adjustments for unison and sequential operation modes. A valve operation mode is selected from among the unison and sequential operation modes for reduction of throttle valve losses. The granted patent describes about a valve management system through sequential opening/closing of valves and thereby reducing the throttle valve losses but the granted patent is silent on capturing the lost energy in the throttling process.
Therefore, there is felt a need for development of a method to reduce enthalpy lost at a bypass throttle valve of a turbomachine to overcome the drawbacks of the prior art and thereby capture more power output and achieve more thermodynamic cycle efficiency.
OBJECTS OF THE INVENTION:
An object of the present invention is to provide a method to reduce throttle valve losses at a bypass throttle valve of a turbomachine in cases of high volumetric flow.
Another object of the present invention is to capture enthalpy lost in throttling process at a bypass throttle valve of a turbomachine.
One more object of the present invention is to improve thermodynamic cycle efficiency of a turbomachine.

Still another object of the present invention is to provide an optimum thermodynamic cycle layout at overload conditions.
Further another object of the present invention is to increase power output of a turbomachine than the designed power output at overload conditions.
Yet another object of the present invention is to provide a method for maximum utilization of working fluid.
SUMMARY OF THE INVENTION:
In accordance with the present invention a method to eliminate throttling losses in a turbomachine during overload conditions is provided, the method comprising the steps of:
(i) placing a turbine (200) in connection with an inlet (I) of a nozzle
chest/inner casing (NC/IC) and a high pressure turbine (HP); and
(ii) adapting a part of working fluid to flow through the turbine (200) to
capture enthalpy lost in the working fluid before injection into the high pressure turbine (HP).
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:
Figure 1 illustrates a thermodynamic cycle layout of a high pressure turbine at peak load conditions according to the prior art; and
Figure 2 illustrates a thermodynamic cycle layout of a high pressure turbine at peak load conditions in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A preferred embodiment will now be described in detail with reference to accompanying drawings. The preferred embodiment does not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.
Figure 2 illustrates a thermodynamic cycle layout of a high pressure turbine at over load conditions.
In accordance with the present invention, there is provided a thermodynamic cycle layout 100 of a high pressure turbine HP comprising a turbine 200 provided in between an inlet I of a nozzle chest/inner casing NC/IC and the high pressure turbine HP. A part of high pressure steam (for example at 250bar) is adapted to pass through the turbine 200 to capture the enthalpy lost due to throttling in the prior art method and the steam at comparatively low pressure (for example at 180 bar) is adapted to inject into a later stage of the high pressure turbine HP.
Typically, the turbine 200 is placed in the position of a bypass throttle valve TV of the figure 1.
Typically, the thermodynamic cycle layout 100 and the introduction of the turbine 200 in the layout find its application only in conditions of very high pressure steam inlet and high volumetric flow.
TECHNICAL ADVANCEMENTS:
A method to reduce throttling losses in a turbomachine during overload conditions has several technical advantages including but not limited to the realization of:
• a method to reduce throttle valve losses at a bypass throttle valve of a turbomachine in cases of high volumetric flow;
• a method to capture enthalpy lost in throttling process at a bypass throttle valve of a turbomachine;

• a method to improve thermodynamic cycle efficiency of a turbomachine;
• a method to provide an optimum thermodynamic cycle layout at overload conditions;
• a method to increase power output of a turbomachine than the designed power output at overload conditions; and
• a method for maximum utilization of working fluid.
Although the invention has been described herein above with reference to the embodiments of the invention, the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.

We claim:
1) A method to eliminate throttling losses in a turbomachine during
overload conditions, said method comprising the steps of :
a) placing a turbine (200) in connection with an inlet (I) of a nozzle chest/inner casing (NC/IC) and a high pressure turbine (HP); and
b) adapting a part of working fluid to flow through said turbine (200) to capture enthalpy lost in the working fluid before injection into said high pressure turbine (HP).

2) A method to eliminate throttling losses in a turbomachine during overload conditions as claimed in claim 1, wherein said turbine (200) is placed in the position of a bypass throttle valve (TV).
3) A method to eliminate throttling losses in a turbomachine during overload conditions as claimed in claim 1, wherein introduction of said turbine (200) in a thermodynamic cycle layout of said high pressure turbine (HP) find its application in conditions of high pressure inlet and high volumetric flow.