Gas Turbine-Generator system has proximity to zero level due to absence of condenser. Therefore, Generator should have Terminal Bushings at the top of the Stator Frame. This avoids digging of tunnel / trench for routing Bus Duct and also avoids accumulation of gases from safety point of view. It was decided to develop a module THRI 108/44 for application with Gas Turbine.
2. DESIGN CHALLENGES :
Since, bar type design of THRI 108/44 module for GTG application is not available. Hence the same had to be designed afresh taking the following major design challenges into consideration:
2.1.Shifting Terminal bushings for tapping power from bottom to top.
2.2.Location, number and size of coolers and cooler ducts in stator Frame to accommodate connections between Bus Bar and Terminal Bushings.
2.3.Proven ventilation scheme inside stator frame for cooling of stator core, windings and its overhangs.
2.4.Provision of static excitation system by providing slip ring shaft.
2.5.Position of Barring Gear on Exciter End (non drive end) requiring Slip Ring shaft rotor having a matching coupling with generator rotor on one side and barring gear on other side.
2.6.Provision of routing of piping emanating from bottom of stator and end shield in the foundation.
2.7. Routing of connections between bus bar and terminal bushings maintaining required electrical connections
2.8.Use of existing components as far as possible for inventory and variety reduction.
2.9.Mechanical and Electrical calculations for soundness of design.
3. ACTION PLAN :
3.1.Identification of assemblies for fresh designing - 34 numbers design groups out of 125 groups were identified to be designed afresh. (Annexure-1)
3.2.Carrying out Exhaustive Electromagnetic, Mechanical, Ventilation & Heat Transfer calculations.
3.3.Development of detailed design documents, scrutiny by technology, incorporating the changes suggested and release of documents (drawings and CBOM).
3.4.Verification of design by Internal design groups – Internal design groups of experts were formed and Changes suggested by different groups were incorporated in the documents.
3.5.Strength of stator frame under various load conditions, its natural frequency and rotor dynamics to be carried out by Corporate R & D to validate the design.
4. INNOVATIVE SOLUTIONS AND ITS DETAILS :
4.1.Electromagnetic calculations were carried out and design data sheet issued for preparation of design documents. 4.2.Since the Terminal Bushings are to be mounted at the top, there was no space available to accommodate 4 Nos. Hydrogen cooler ducts (400 x 570 mm), as provided in conventional THRI design (ref. Fig.1). Therefore, it was decided to use two nos Twin-coolers (ref Fig. 2&3). This concept has 2 nos. twin coolers placed in two separate cooler ducts. Operating conditions of one cooler out of operation apply here also as in case of conventional 4 Nos. separate coolers. 4.3.Changes in size of cooler and cooler ducts (550 x 650 mm) and duct location resulted in increase of width of stator body to 4200 mm from 4000 mm and height 4550 mm. Accordingly, stator body was redesigned completely maintaining routings of ribs, plates etc to follow the ventilation scheme of existing machine. Full length Foundation Support has been provided on stator in line with conventional GTGs.
4.4.Due to the above mentioned increased dimensions of stator body, the generator is not suitable for rail transport (limit up to 4040 mm). Thus the generator stator shall have to be transported by road only. A dragging fixture has been designed and shall be welded to the bottom of stator frame to place it directly on the road trailer without requiring any additional fixture. It will also help placing the stator at any location without any support or can be dragged at power station for erection, if required. 4.5.It was proposed to use common Core Assembly...