Basics of parametric modeling of turbogenerators

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Basics of parametric modeling of turbogenerators

Tretiak Oleksii

Candidate of Technical Sciences (Ph. D.), SE “Plant “Electrotyazhmash ”, Deputy Head of Department, Senior Lecturer of Aerospace Thermal Engineering Department, National Aerospace University named after N. Ye. Zhukovsky "KhAI"

Kobzar Kostyantyn

Candidate of Technical Sciences (Ph. D.) SE “Plant“Electrotyazhmash”, Chief Designer on Turbogenerators

Gakal Pavlo

Doctor of Technical Sciences, Assistant professor, Head of the Aerospace Thermal Engineering Department National Aerospace University after N.Ye. Zhukovsky, "KhAI,



Summary

The analysis of the methods of modernization of Turbogenerators of a classical design is made on the basis of requirements to reliability. Existing designs of Turbogenerators are studied and their strength margins, as well as reliability characteristics of their main units, are determined. The optimal method is chosen namely the method of parameterization of Turbogenerators design. It is proposed to use parameterization for designing of serial Turbogenerators of low power.

Key words: Turbogenerator, parametric modeling.



Introduction

There are several world schools of generator building. As a rule, many of them rely on the experience of using their design decisions, and each high- power machine is unique.

Due to the fact that when designing of new electric power plants, the period between designing and commissioning is significantly shortened, it became necessary to search for new methods for reducing the construction time.

At that it is necessary to provide reliability of design at more high level.

In this connection, there is a need to find new concepts for the designing and calculations of Turbogenerators.

Based on the analysis of the existing designs of Turbogenerators, we can say that they all repeat each other as a whole.

In [1,2] it is described the development of Turbogenerators of Western firms. If we emphasize the typical designs, then we can assume that these designs can be parameterized and in the preparation of TCP (Technical-Commercial Proposals) it is possible to consider parametric models for one series. In the near future, we are waiting for the transition to air cooling, and this means that there shall be a need to create highly-used machines.



Purpose of the Work

The Tasks of Studying:

To analyze the ways of modernization of Turbogenerators of classical design.

Select the optimal method of parameterization of the design of Turbogenerators.

Consider the existing designs of Turbogenerators, determine the strength margins, as well as the reliability characteristics of the main units.

Propose a parameterization of the design for serial Turbogenerators.

Propose a series of Turbogenerators based on parametric modeling.

Basics of Parametric Modeling.

Parametric designing and modeling.

One of the main promising directions of technical objects designing is increasing of efficiency due to the creation of parametric design by different methods. The parametric design model allows significantly reduce the time required for the designer to make changes to the original data or after carrying out of the verification calculation [3].

Parametric modeling (parameterization) is modeling (design) using the parameters of model elements and the relationships between these parameters. Parametric modeling is significantly different from the usual two-dimensional drawing or three-dimensional modeling. The designer in the case of parametric design develops a mathematical model of objects, with parameters that change the configuration of the part, the mutual movement of parts in assembly.

The basic types of parameterization include:

Tabular parameterization consists in creating of a table of parameters for typical parts. Developing of a new part sample is done by selecting from the table of standard sizes. The possibilities of tabular parameterization are very limited, since it is usually impossible to specify arbitrary new parameter values and geometric relationships.

Hierarchical parameterization (parameterization based on the history of constructions) consists in the fact that during the construction of the model the entire construction sequence is displayed in a separate window in the form of a "tree of construction". It lists all the auxiliary elements existing in the model, sketches and performed operations in the order of their creation.

In addition to the "tree of construction" of the model, the system remembers not only the order of its formation, but also the hierarchy of its elements (relationships between elements). Parameterization based on the history of constructions is present in all CAD systems using three-dimensional solid-state parametric modeling. Usually this type of parametric modeling is combined with variational and / or geometric parameterization.

Variational or dimensional parameterization is based on the construction of sketches (with overlapping of various parametric links on the sketch objects) and the imposition of constraints by the user in the form of a system of equations that determine the relationships between the parameters.

Variation parameterization allows you to easily change the shape of the sketch or the size of the parameters of operations, which makes it convenient to modify the three-dimensional model. Geometric parameterization is parametric modeling, in which the geometry of each parametric object is recalculated depending on the position of the parent objects, its parameters and variables.

The parametric model, in the case of geometric parameterization, consists of construction elements and image elements. Elements of construction (design lines) define parametric connections. Elements of an image include image lines (with which designer lines are drawn), as well as design elements (sizes, inscriptions, hatchings, e.t.c.)

Some elements of the construction may depend from other elements of the construction. Elements of construction may contain parameters (for example, the radius of a circle or the angle of a straight line). When one of the model elements changes, all the elements that depend on it are rebuilt in accordance with their parameters and the ways they are assigned.

Geometric parameterization allows for more flexible correction of the model. If it is necessary to make an unplanned change to the geometry of the model, it is not necessary to delete the original construction lines (this can lead to loss of associative relationships between the model elements); you can draw a new line of construction and transfer the image line to it. For the parameterization, different tools are used [6, 7].

The methods of turbogenerators designing

In order to correctly consider the possibility of parameterization of Turbogenerators design, it is proposed to determine the strength margins for one type of Turbogenerators, taking into account existing methods at the time of commissioning of the unit, taking into account possible correction for refinement for finite element methods (or three-dimensional modeling).

At that, the failure of large units can be considered in the context of the rules of "Technical Operation of Electric Power Stations and Networks".

According to the results got in the work of Mr. Kobzar K. A. [8], the modernization of constructions was carried out by increasing of power by 10%. Consequently, it can be concluded that the strength margins have been reduced, provided that the reliability indices are saved and maintained at the same level.

The concept of performing calculations by the methods of mathematical modeling in a three-dimensional formulation was developed by Mr. Tretyak A. V., including:

The analysis of the general design of the unit.

The causes of failure by three-dimensional modeling are considered.

Correlation of the existing methods with the data obtained in p. (2).

Optimization of the design taking into account the maximum zones of strength margins.

Choice of optimal design.

In order to determine optimal parameters of designing it is necessary to consider the basic stages of designing preparation which include:

development of designing task, sketch design project;

manufacturing and testing prototype sample;

designing of the technical project, working project;

manufacturing and testing of items from experimental lots;

the development of the design according to the test results;

specifying of the working project and its registration;

transfer of the working project and its registration;

transfer of the working project to the bodies of technological preparation of production.

The initial for designing of new products is the design (technical) task, which is compiled by the Customer (Enterprise) or on his behalf by the designing organization.

Based on the analysis of the customer's design task and the comparison of various versions for possible product decisions, a comparative evaluation of decisions, taking into account the design and operational features of the developed and existing products, as well as patent materials, a technical proposal is prepared namely a set of design documents containing technical and technical and economic grounds for the further development of the project.

One of the most advanced and most innovative, combining the experience of generations and the indefatigable ardor of youth in it-self was the school of Mr. Gruboi Alexander Petrovych.

It was he, who laid the basic principles of the possibility of transition from two-dimensional modeling to three-dimensional. And a qualitative leap was achieved by combining the leading experts of the "old school" and "the youth". At that, the basic dogmas laid down by Mr. Stanislavsky L. Ya. have been preserved, but rather even toughened. The best criterion for determining of quality was time. The characteristic feature of the machines was reliability.

In the 60-`s of the 20th century, the design team of SE "PLANT "ELECTROTYAZHMASH" under the guidance of Mr. L. Ya. Stanislavsky the tests were carried out at Turbogenerators rated 200 MW and 300 MW with hydrogen and hydrogen-water cooling at SDPP.

It was established by the tests carrying out that the design requires partial refinement that is why the following changes were made:

The norms for gas-tightness of welded structures and generator assemblies were toughened (the stator casing, the ducts, the shields, the end terminals, e.t.c.)

The oil shaft seals were modernized in order to reduce oil leaks into the generator, which reduced the consumption of hydrogen. Corrosion resistance of the working surfaces of the casings was improved.

The design of a current lead of a closed type rotor the design of Mr. Khlopkov O.N. was put in to practice.

In order to eliminate the hydrogen ingress into the bearing No. 6 of the shields in the parts:

Cooling of the structural elements of the shield in the area of the casing of the 6-th bearing was improved.

Fastening of the intermediate bush of the outer shields was changed, which made it possible to increase the gas-tightness of the detachable joints.

In order to eliminate getting of compound into the stator connecting busbars, they were reconstructed:

Thermoset insulation instead of compounded insulation was put in to practice (1969, July).

The norms for the rotors balancing in a racing balancing pit were toughened from 30 microns up to 20 microns.

The rotor of the generator was modernized with put in to practice additional milling of the rotor poles in order to reduce its different rigidity.

For the first time, a new design of the brushholders device was put in to practice.

At the basis of the analysis of taken decisions strength margins were determined (Table 1).

Table 1

Strength margins of Turbogenerators of various power.

Cl. Nos.	Description of Parts and Units	TGV-200	TGV-300
		Strength margin	Strength margin
1	Rotor tooth	2.07	2.2
2	Surface of internal boring	1.9	1.78
3	Rotor neck	2.4	1.96
4	Retaining ring	n = 3000	1.9	1.92
		n = 3600	1.19	1.58
5	Wedge of the Rotor Slot	cut	5	5.15
		bend + compression	2.6	2.62
6	Rotor Copper	1.34	1.45
7	Axial Fan	bush	2.02	-
		blade	1.89	-
8	Compressor	wheel	2.75	2.75
		casing	1.53	1.83
		blade	2.07	2.07
9	Spring of suspension	1.38	1.4
10	Pressing down flange	1.16	1.42
11	Pressing down finger	1.25	1.76
12	Foundation bolts	2.12	2.24

Now it is necessary to consider the reliability criteria of Hydrogenerators.

Basic requirements to reliability

Due to the fact that the requirements of normative technical documentation divide constructive elements into resource and non-resource units (Figure 1), the main requirements for Turbogenerator units are given for reliability assessment.

Figure 1 - Types of Turbogenerators units

Turbogenerator shall be connected to the network by the precise synchronization method. At emergency situations elimination at the station or in the power system, it is allowed to switch-on in the network with the self-synchronization method. It is allowed for the whole service life of Turbogenerator to switch-on it in to the network not more than 10,000 (up to 330 starts per a year). At the same time, Turbogenerator shall meet the "Technical requirements for the maneuverability of power units of thermal power plants with condensation turbines" approved by the Ministry of Electrical Engineering, Ministry of Energy and the Ministry of Energy of the USSR dated 01.09.86. It is also allowed to work with variable daily load schedules, including passing maxima not less than twice a day.

Indicators of operational lifetime and reliability include service life that is not less than 30 years, the availability factor shall be not less than 0.995 at failure time shall be not less than 18,000 hours, average time between failures of 12,000 hours and average operational complexity of planned repairs of 2,070 standard hours. The established resource between overhauls is 5 years.

The first repair of Turbogenerator with the rotor withdrawal shall be carried out no later than 8,000 hours after commissioning.

Turbogenerator design shall provide easiness of maintenance, assembly and disassembly of its assembly units and meet the requirements of maintainability, taking into account the minimum complexity of repairs.

Characteristics:

Reliability of Turbogenerator in the conditions and operation modes established by the technical conditions shall be characterized by the following indices:

Readiness factor, p. u. - 0,996;

Time between failures, h- 27000;

Service life at observation of the terms and amounts of planned inspections and repairs, years - 40;

Resource between overhauls, years- 8;

Average operational complexity of planned repairs, norm-hours - 13770.

The failure of Turbogenerator is considered by its condition according to the criteria.

At the same time, the criteria for failures of the main units can be tabularized, presented below.

Criteria for failures of resource units:

The stator core.

Temperature, measured as per individual standard resistance temperature detectors or for their entire group controlling heating of the core, exceeds the maximum permissible value.

Vibration measured with the stationary sensors, above the maximum permissible value,

Removable crushing of the tooth zone.

Removable melting of teeth zone after local short-circuits to the stator casing.

Unscrewing of nuts for fastening of the pressingdown flanges.

The stator winding.

Short-circuit of the winding to the casing.

Phase-to-phase short-circuit.

Turn-to-turn short-circuit.

Temperature, measured as per individual standard resistance temperature detectors or for their entire group exceeds the maximum permissible value.

Insulation resistance relatively to the casing lower maximum-permissible value.

Loosening of the bars fastening in the slot part.

Phases DC resistance or the difference between them differs from the maximum permissible values.

The rotor winding.

Short-circuit of the winding to the casing.

Turn-to-turn short-circuit.

Decreasing of the insulation resistance relatively to the casing lower than permissible value.

Temperature, measured as per winding resistance over maximum-permissible value.

Open of circuit.

DC resistance differs from limiting-permissible value.

Criteria for failures of non-resource units:

The stator casing.

Emerge of cracks in the places of welding.

The rotor shaft and retaining ring.

Removable micro-cracks and fractures of teeth.

Formation of colours of tarnishing and microcracks on the fit surfaces of the retaining rings and rotor shaft.

Corrosion of the centering ring of the retaining ring.

The thrust bearing,

Heating over limiting-admissible value.

Melting out of babbitting.

Breakage of the resistance temperature detectors.

Reducing of insulation resistance of the thrust rings of the bearing casing.

So, after considering the basic requirements to designing and steps on technical modernization, you can consider a series of Turbogenerators.

Turbogenerators with Air Cooling

Turbogenerators with indirect air cooling of T2 series were manufactured at SE “PLANT "ELECTROTYAZHMASH" from the middle of the last century. In total, more than 130 Turbogenerators of this series were manufactured.

The design of Turbogenerators of T2 series was improved in developed Turbogenerators series ТА.

In 1998 Turbogenerator ТА-6-2 rated 6 MW with voltage of 6.3 kV, which is successfully in operation at the enterprise "Silur" Ltd. was manufactured.

Since 1999, Turbogenerator TA-12-2 rated 12 MW with a voltage of 10.5 kV is in operation at Zapo- rozhsky Aluminum Plant (ZALK, Ukraine).

In India, at the cement plant in Diamond since 1999, Turbogenerator TA-15-2TV3 rated 15 MW, 3000 rpm, with stator voltage of 11 kV with a brushless excitation system is in operation.

The series of Turbogenerators TA was further improved by the usage of direct air cooling of the rotor winding conductors, at that in the modification the letter "M" is applied.

In 2001, for Mironovskaya TPP (Ukraine), Turbogenerator TA-120-2MU3 with complete air cooling rated 120 MW was designed, which was thoroughly tested at the enterprise stand and is in operation.

In 2006 at SE “PLANT

"ELECTROTYAZHMASH" the head specimen of Turbogenerator type TA-35-2MU3 with air cooling rated 35 MW, with a rotational speed of 3000 rpm was manufactured and tested, and which was installed and successfully operated at the Zaporozhskyi Metallurgical Plant (Ukraine).

Figure 2 - Turbogenerator TA-6-2MU2 rated 6 MW with air cooling

In 2009-2010 the production prototype of Turbogenerator TA-6-2MU2 (Figure 2) with stator voltage of 6.3 kV was tested.

Based on the design of the TA-6-2MU2 Turbogenerators rated 4 MW, 6 MW and 8 MW can be designed with closed or opened air cooling system with parameter adjustment depending on specific environmental conditions and operating conditions.

For low power generators, "Parametric design" can be considered for tabular and geometric parameterization. As a limiting factor, electrical parameters and mechanical parameters were used. In terms of mechanical strength, it is necessary to take into account the increase of the rotor body length, to ensure the necessary vibrational state of the construction at the proper level.

In connection with above mentioned at the basis of parameterization rules and changing of admissible strength margins a series of low power Turbogenerators with air cooling was developed.

Applied parameterization methods allows to develop one project instead of three separate ones, which saves at least a year necessary for the preparation of design and technological documentation.

Conclusion

turbogenerator reliability modeling

In the presented work the main methods of parameterization of complex technical objects are considered. The main ways are indicated which let design highly used Turbogenerators of high power.

The strength margins are calculated of the main design elements and the necessary reliability indices which are characteristic for resource and non-resource assemblies of high-power Turbogenerators.

For the first time a series of Turbogenerators based on parametric modeling of Turbogenerators with air cooling is presented.



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