FIELD OF INVENTION:
The invention in general relates the gas turbines used in power generating plants, oil refineries, pump and compressor drives. The invention teaches about an arrangement of control ring (45) bracket required to modulate the IGV’s in the gas turbines in order to control the airflow at varying load conditions.
BACKGROUND OF THE INVENTION:
Gas turbines, also known as internal combustion engines, are common prime movers for many applications. They have been utilized widely in stand by and peaking applications where their relatively low installed cost outweighs other factors.
A typical gas turbine core has three modules, namely, the compressor, combustion system and the turbine. Air enters the compressor through the inlet system and is pressurized to a level of 8 to 10 times that of the entering air. The compressed air then passes into the combustor where fuel is introduced and ignited, producing high temperatures in the machine. The hot gases are then directed to the turbine, from where they are expanded to the atmospheric pressure and in turn provide power to run the compressor and the driven equipment such as a generator.
Combustion gas turbines are usually used in conjunction with a heat recovery steam generator (HRSG) for improved cycle efficiency. In such a configuration increasing the exhaust temperatures in part load conditions improve the cycle efficiency. This increase in exhaust temperature is made possible by modulation of inlet guide vane (IGV).
This is achieved by rotating the IGV there by varying the flow area between the IGV’s. The rotation of the IGV is modulated by a pre-programmed control mechanism operated by an assembly of the following key parts.
A. Control ring (45)
B. Actuator
C. Actuator linkage
D. Rack and gear assembly

The location of IGV and related parts in a gas turbine is shown in figure-2-5. The IGV’s are attached to the stator casing with provision for rotation through holes provided on the casing. The projected part of the IGV (or shank) is connected to a small pinion, which in turn is in mesh with ring gear. The rack is free to rotate on the inlet casing about engine axis centre. The rack is connected to a control ring through friction. The control ring is connected to an actuator assembly.
Based on load conditions, the actuator (cylinder-piston assembly) is commanded by machine control system to open or close by moving the piston. This movement then rotates the control ring and there by rotates the IGV’s through rack-pinion arrangement as described previously.
The assembly shown in figure 2 can be seen in several gas turbines of ~25MW rating. The position of the actuator (4) and the control ring arm (7) are located under the inlet casing. This particular arrangement imposes great difficulty in assembling the parts and in carrying out inspection, monitoring and repair works in-situ due to less accessibility and poor visibility. The prior art deficiency is due to the control ring actuator being confined between the front support plate and inlet plenum aft walls. Added to the disadvantage of the control ring (6) and actuator location, the area is surrounded by number of pipelines and auxiliary equipment that are required for the safe operation of the gas turbine.
The requirement was repositioning of the control ring (6) and actuator system to a maintenance friendly location.
OBJECTS OF THE INVENTION:
It is therefore an object of the present invention to propose a bracket to the control ring which eliminates the disadvantages caused by the prior art.
Another object of the present invention is to propose arrangement of control ring that provides easy access to monitor/set the IGV angle in the assembled machine.
Another object of the present invention is to propose positioning of the control ring that aids in avoiding errors due to poor visibility while performing maintenance.
A still further object of the invention is to provide maintenance friendly system to enable maintenance without disturbing the adjacent equipment.

SUMMARY OF THE INVENTION:
The invention provides a bracket to the control ring that is connected to the rack and gear assembly for facilitating the rotation of IGV at determined angles based on load conditions. The required rotation angle is calculated based on exhaust temperature requirement and the linkage movement is initiated by the actuator system, which is connected to the control ring. The control ring is in contact with the rack and gear assembly, which in turn is connected to the IGV shank.
The actuator is connected to the lever of the control ring which is at the bottom of the control ring (at 6 O’clock position viewing aft looking front). The connection is in place by using connecting hardware. The control ring–actuator connection then falls in the closed space formed by the inlet plenum wall (1) (in Figure 3) of the GT. For any maintenance, correction in settings of the IGV angle the technical personal has to pass through a very constrained space to access the area.
The invention attains significance in the following areas, viz. accessibility and easy maintenance. By the present invention, the actuator can be accessed with adequate visibility and ease there by avoiding human fatigue while working in this region. In addition, repair and maintenance work can be carried out without disturbing the adjacent equipment hardware.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is made with reference to the accompanying figures. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
Figure 1 shows location of IGV control ring in a Gas turbine.
Figure 2 and 3 shows IGV control ring-actuator assembly in accordance to the invention.
Figure 4 and 5 shows schematic of improved, maintenance friendly design of ergonomic control ring- actuator assembly in accordance to the invention.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS:
Figure 2 presents the prior art actuator and control ring (6) arrangement in a gas turbine. The location of the connecting point between control ring (6) arm (7) and actuator (4) lies at 6 O’clock position of the machine which is close to the base of the machine (1). Referring to Figure 1 and Figure 2, it can be seen that the assembly point can be accessed only from the side. For a typical gas turbine, the repair at the IGV control ring (6) region asks for adjusting the LVDT (11) and connected hardware. So, for a technician it becomes difficult to access these parts due to poor visibility and accessibility.
The schematic of improved, maintenance friendly ergonomic design of the control ring (45) is shown in Figure 4 and 5. According to the invention, the system now comprises of
a. Modified Control ring (45)
b. New designed bracket
c. Actuator assembly
d. Actuator linkage
e. Rack and Gear assembly
The prior art deficiencies are overcome in the new arrangement. The schematic arrangement of the new design is shown in Figure 4. In the new art (Figure 4) a linkage (49) is designed to connect the modified control ring (45) and the actuator (44). The assembly is arranged, so that connecting point between (49) and (44) comes at 3’O clock position (viewing from aft towards front). The new art creates improved accessibility, as the parts (2), (3), (4), (9) and (10) of the assembly are positioned away at the sides of the gas turbine. By improving the accessibility to these parts, the down time and ease in repair or diagnosing the machine problems related to IGV becomes easy.

WE CLAIM:
1. A new bracket arrangement for an inlet guide vane (IGV) control ring (45)
system of a gas turbine that comprises:
- a turbine base (41) on which an actuator piston (44) is mounted;
- a linkage (49) coupled to the actuator piston (44);
- a control ring (45) affixed to the linkage (49) to form a 3’0 clock position from the turbine base (41).

2. The new bracket arrangement as claimed in claim 1, wherein the hydraulic actuator assembly (43) holds the actuator (44).
3. A new bracket arrangement for an inlet guide vane (IGV) control ring (45) system of a gas turbine as substantially described and illustrated herein with reference to the accompanying drawings.