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Tretiak Oleksii, Candidate of Technical Sciences (Ph. D.), SE "Plant "Electrotyazhmash", Deputy Head of Department on Mechanical Calculations, Senior Lecturer of Aerospace Thermal Engineering Department, National Aerospace University named after N. Ye. Zhukovsky "KHAI"
E-mail: alex3tretjak@ukr.net
Kobzar Kostyantyn, Candidate of Technical Sciences (Ph. D.), SE "Plant"Electrotyazhmash", Cheef Designer on Turbogenerators, E-mail: kk7@ukr.net
Shut' Oleksandr, SE "Plant"Electrotyazhmash", Deputy Head of Department on Hydrogenerators and LDCM
E-mail: alekspetm@gmail.com Poliienko Vladyslav, Design Engineer, SE "Plant"Electrotyazhmash", Master Student, National Aerospace University named after N. Ye. Zhukovsky "KHAI" E-mail: vlad_polienko@outlook.com.
Gakal Pavlo, Doctor of Technical Sciences, Docent, National Aerospace University, Associate Professor at the Department of Thermal Engineering Aerospace, E-mail: pavlo.gakal@gmail.com
PECULIARITIES OF THREE-DIMENSIONAL CALCULATION OF LARGE UNITS OF GENERATORS BY FINITE ELEMENT METHODS
Abstract: The scientific work presents the basic designing principles of large units of Turbogenerators using the example of pressing down flanges. Peculiarities of mechanical calculations of welds are considered.
Keywords: Turbogenerator, stresses, finite element method, pressing down flange.
Introduction norms of mechanical strength: resource units and
In the present time in generators-building, non-resource units. there are two types of units and parts regarding the
Obviously, the approach to calculations and designing for all the above mentioned details can only be determined in its group.
Consequently, assumptions that we could consider inside from a non-resource group cannot be transferred to resource and vice versa.
According to generally accepted standards for designing, for all types of units, stresses shall not exceed the yield strength limit, and the limiting factor
shall be the fatigue limit, which shall be determining for the parts that shall work for more than 30 years, with possibility of further extension of the resource.
However before the calculation designing it is necessary to consider in details the design of existing generators.
Design Peculiarities of the Stator of Turbogenerators Manufactured at SE "Plant "electro-tyazhmash"
Figure 1. Turbogenerator
The general view of Turbogenerator is submitted in (Figure 1) [1]. The stator casing is double: namely external and internal. The external casing is welded, combined of three parts, provided with jointing rings and fasteners set. Welding, annealing, machining and hydro-tightness tests shall be carried out separately for each part. Assembly of the casing parts between each other shall be carried out on to the guiding fingers. The parts shall be fastened with bolts with consequent welding from outside with gas-tight weld. The casing shall be carried out of cylindrical shape. From the turbine end in the bottom part of the stator casing the gas coolers duct is arranged in which along the longitudinal axis of Turbogenerator three gas coolers are arranged. The stator casing is light-weighted due to thickness decreasing of the shielding, ribs, beams
and other parts. Inside the stator casing at the flat spring suspension the internal casing is suspended. In the internal casing there is the stacked up core. The internal casing (namely the stator core frame) is welded, cylindrical, consisting of the forcing rings, longitudinal beams, tightening ribs, prisms, shielding, face end and intermediate ring frames. One side of springs of suspension is fixed to the thrust rings of the internal casing with the help of cylindrical eye-bolts and fasteners. The second side is fastened to the annular ribs with the help of T-shaped straps and pair rings. The stator core consists of the died and insulated with high-quality varnish of hot drying laminated segments manufactured of cold rolled electrical sheet steel with decreased specific losses. The core has the axial cooling system of the back and teeth for which purpose the core segments are
provided with holes. The packages are pressed in axial direction with the help of the pressing down flanges from the both ends of the stator. The installation of power accumulators, five rows of springs of the suspension and manufacturing of prisms of steel with improved characteristics provides effective suppression of vibration of the stator core and maintains a stable force of the core pressing in operation. The stator core is cooled with hydrogen which under gauge pressure the stator casing is filled with. The stator casing from the face ends is tightly closed with the external shields. The modernized design of the external shields, thrust bearings, seals provides easiness of assembly and maintenance of these units.
Let us consider the mechanical calculation of non-resource unit at the e.g. of the pressing down flange of Turbogenerator manufactured by SE "Plant "elec-trotyazhmash". In (Figure 2) the overhang part of the stator casing is submitted [2]. The pressing down device of the stator core in the submitted model of the casing is power accumulator. In figure 2 the stator casing overhang is shown with section in situ of power accumulator installation where indicated: the utmost frame of the casing 1, flange 2, tightening ribs 3, press-
ing down flange 4, tightening prism 5, power accumulator 6, bracket 7, overhang part of the winding 8. Dimensions A and B were indicated by Mr. Minko A. [2] for research of the most optimum design.
As it can be seen the pressing down flange is a part which during the whole operation term of Turbogenerator shall create the load with the value of 2 MPa for provision of the stator normal pressing.
Figure 2. The Stator Overhang
The causes and consequences of reducing of pressing are given in the scientific work of Shtogrin, A. V. [3]. In connection with the above mentioned, it becomes necessary to revise the existing methods for calculating the pressure flange assembly by the finite elements method.
Figure 3. Design of Pressing down Flange
Determining of the Stressed State of the Pressing down Flange
At the present time the classical pressing down flange is manufactured of hot rolled plate by application of welds. See (Figure 2). The material of pressing down flange is high-strength stainless steel.
The existing types of stresses are indicated in (Figure 4). Where: a) are normal stresses (tension -compression), b) are bending ones and c) twisting.
As per the norms of mechanical researches for a pressing down flange in a two-dimensional setting only normal stresses are taken into account, however, as experience shows, there are all three groups hence their total action can be taken into account only in a three-dimensional setting.
^ =
A
a) normal,
M w
T =-
m.
W
c) twisting
b) bending, Figure 4. The Existing Types of Stresses At the present time SE "PLANT "ELECTRO- sue of long term strength is very important when TYAZHMASH" in the part of carrying out of the design element cannot be replaced during the mechanical calculations transferred to three- operation process. In the scientific work [4] the dimensional modeling in the medium of Solid- cases when it is necessary to carry out the mesh Works Simulation. For non-resource parts the is- refinement.
Figure 5. Typical areas in a model where locally refined mesh is required
As applied to the pressing down flange, it is necessary to add peculiarity of the design indicated by welds.
The results of mechanical calculations in SolidWorks Simulation are submitted in (Figure 6).
Figure 6. Mechanical Stresses As per GOST5264-80 for our item the welds
plied both for the basic elements provided that the welds are completely welded.
Figure 7. Types of Welds In Table 1 the strength margins for the press-
were carried out. As per the results of experimental ing down flanges of Turbogenerators TGV series operation for the welds submitted in Figure 7 the manufactured by SE "PLANT "ELECTROTYAZH-rule of admissibility of strength margins can be ap- MASH" of various power range are indicated.
Table 1. - Mechanical stresses
№ Part Mechanical stresses, (M Pa)
TGV-200 TGV-300 TGV -500
1. Pressing down Flange 135 157 133
2. Pressing down Finger 274 344 268
Conclusion
In the present scientific work the main peculiarities of design of the Turbogenerators rated 325 MW manufactured by SE "PLANT "ELECTROTYAZHMASH" are submitted. The main features ofmechanical calcula-
tion carrying out for non-resource units are indicated. The allowable stresses for the welds are shown. The transition from two-dimensional to three-dimensional modeling of parts and units by the finite element method in SolidWorks Simulation is substantiated.
References:
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2. Minko А. N. Optimal geometry and mass and overall dimensions parameters of the bearing and shield units of Turbogenerators with air cooling system / Energetics and Electrification.- 2012.- No. 1.- P. 18-21.
3. Shtogrin А. V. Scientific and technical measures in order to reduce damages of stators of high power Turbogenerators caused by vibration in the overhang zones [Text]: dissertation ... cand. tech. sciencies: 05.09.01 / Shtogrin Alexander Valeriyevich; NTU "KPI" - Kiev, - 2015.- 161 p.
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