To the question about electromagnetic compatibility and electrical installation resources

Самарский Государственный Технический Университет Технический Университет

Рассматриваются вопросы научного обоснования связи обеспечения электромагнитной совместимости, теории надежности и ресурсов при создании и эксплуатации электротехнических комплексов в электрических сетях и системах энергоснабжения.

Ключевые слова: электромагнитная совместимость, надежность, ресурсы, электротехнические комплексы, системы электроснабжения, электроустановки.

The main text

The foreground tendencies of the electrical power engineering development for the next decade are assurance of electromagnetic compatibility (EMC) and consequently the rise of reliability of electrical installations (EI) and electrical equipment [1,4]. The achieved level of scientific and technological progress already now allows to create highly reliable electrical complexes and systems (ETCS) in electrical engineering and, above all, in the energy supply [5, 6]. Complex of measures used on the stages of projection, manufacturing, assembling and operation works as a basis for it. At the stage of projection it is a choice of modern electrical equipment, rational structural schemes and materials, the proper calculation of normal and emergency conditions taking into account all the impacts that may occur during the process of operation. At stages of assembling and construction of electric power facilities it is thorough control of the accessory, appliances, plants and materials.

In addition, high level of organization and control of technological processes, the intermediate control tests of elements, nodes and blocks of ETCS, proven system of acceptance tests should be provided. Removal of hidden faults on the stages of start-up testing and putting into the operation, use of the maintenance that includes the complex of diagnostic and plan-prophilactic actions of ETCS allow to minimize the probability of violation of EMC and the rise of electrical equipment refusal during the operation.

Resource and durability are the most important properties that characterize the EMC and determine the longevity of the definite EI and complexes. [3] The requirements indexes of longevity are assigned on the early stages of the ETCS elaboration in the field of electrical power engineering. Resource in time and parametric definition is an essential characteristic of EMC. In essence it gives the idea of ETCS stock ability to resist various internal and external the electromagnetic effects (EME). This resistance is provided by both natural means of internal durability of the object and special safety means and systems. Note that there should be equally estimated EME which are directed from the environment at the object and vice versa.

Present state of applied and calculus mathematics, electrophysics, electromagnetic processes, electro material science and mechanics allow to predict the longevity indexes on the stage of projection with the use of loading diagrams that are as much is possible close to the working conditions of produced object, system or EI and etc. based on the attraction of mathematical and physics modeling methods. The theoty of EMS and reliability of ETCS in electro power engineering gives the opportunity to estimate the effect of varied factors on the average resource and the dispersion of resource and also in common with methods and means of technical diagnostics allow to estimate the residual resource of EI.

Practical significance of the ETCS resource problem in the electro power engineering is rather high. Although at the present rate of scientific and technological progress the obsolescence of EI happens faster than in previous years, in many fields of electro power engineering actual resource does not correspond to optimal values from the economic point of view.

The increase in resource of electrical equipment gives the considerable economy saving of investment and cost of materials, energy and labour costs that goes for replenishment of the EI fleet and their maintenance. The solution to the problem of the individual resource prediction as the time of the managed maintenance of EMC is also of the outmost importance. It is based on the evaluation of its current conditions by the up-to-date means of “spare” diagnostics and control during the process of operation.

Technical resource (next as a resource) it is the value that characterize the reserve of its possible running time. According to GOST 27.002-89 total running time from the beginning of operation or resumption of it after repair to the transition to the marginal state is called as the resource. Depends on the start time, operation duration units and marginal state the notion of resource has different meaning. electromagnetic electrical power network

As the measure of duration can be chosen any crescent parameter which characterize the duration of object operation. Speaking about generators, transformers and autotransformers, electric motors and other power facilities the running time in hours works as the measure of resource, as for switching unit it is the number of normal and emergency commutations, as for protective devices it is the number of liquidated and bounded dangerous EME. In case the running time is measured by the number of production cycles the resource will take discrete values.

The units of resource measurement are chosen with the reference to particular field and particular class of EI individually. In the view of theory and general EMC methodology, EI life-cycle and resources the normal functioning time is considered to be the best and most universal characteristic.

Firstly, the EI operation time generally includes not only the time of useful functioning but also breaks while the total running time does not increase. Meanwhile, during such breaks EI are affected by environment, loads which occurred during transportation and etc. In addition, during the breaks in functioning the properties of materials might be changed. Thus, material obsolescence and electrical insulation in particularly causes the decrease of the common resource.

Secondly, the resource is closely connected with the life time defined as calendar duration of EI operation till its transition to a marginal state which is measured in time units. The life time from the beginning of the life circle to the EI write-off (planned, normative life time) connected with the rate of science and technical progress in electrical power engineering to a considerable extent. The use of economic-mathematical models for normalization of resource requires the resource measurement in units of running time, time and etc.

Thirdly, the prediction goals of residual resource of EI functioning are the random process and time usually works as an argument. Thus, the running time gains the meaning of random time function. Resource calculation in time units allows to set the prediction goals in the most general form that is why next it will be possible to use for resource measurement without breaking the generality time units considering them as a continuous independent variable. It is sometimes possible to use discrete time, for example, the number of EME in the form of overvoltage, current overload and etc. If you know the distribution according the duration of EME and also the duration of breaks between them, then it is not difficult to convert to calendar time.

While calculation of resource and the life time on the stage of projection the time of putting into the operation (or more exactly, the time of its useful functioning) is usually taken for start time. As for the objects in operation it is possible to take as a start time the moment of the last inspection, preventive action or the operation resumption after the thorough repairs. It also might be an arbitrary moment in time when the question of further operation or reconstruction was put. The EI transition to the marginal state as an object of EME involves temporary or permanent stopping in operation.

The reasons for the stopping in operation:

- physical deterioration of obsolescence;

- excessive loss of efficiency resulted in economically inexpedient further operation;

- a decline in safety below the permitted level.

It is not always possible to define exact indications and parameters that EI conditions should be classified as a marginal state. Sharp rise of failure rate, standing periods or repair expenses compared with the same indexes of similar EI are usually reasons for electrical equipment write-off. As for once recoverable electrical equipment objects the resource before the intermediate or thorough repairs and a full resource are distinguished and as for repeatedly recoverable resources beside these the overhaul repair is distinguished. Marginal states which correspond to these values of the resource might be different. Criteria of the marginal state of each electrical equipment type might be established in normative and technical, design or operational documentation.

Let us consider the notion of normative resource and normative life time. The choice of these indicators is the economic and technical problem that is to be solved on the stage of preliminary design elaboration. It is also necessary to take into the account the modern technical conditions, the global level and speed of science and technical progress in the particular field, accepted at these days the standard values of economic efficiency indicators, limits on the cost of materials, componentry and elements, limits of its delivery time, targets, technical and economic predictions and etc. The task of designers, estimators and creators is to select materials, design forms, sizes and technological processes that provides with the normative values of parameters for the designed object.

When the object is not created, on the projection stage the calculation including the assessment of the resource is done on the basis of analytical models which used the statistics of materials, componentry and elements, overloads, EME and conditions of similar EI operations while there is not enough statistics it is possible to use the expert assessment.

The notion of resource might be interpreted in different ways for the explotable objects of electrical equipment. An individual residual resource (the duration of operation from the given time point to the marginal state) is the basic definition. During the operation the overhaul repair is set individually according to technical conditions that defines the notion of individual resource to the nearest medium or thorough repair. Individual terms for other preventive measures are set in the same way.

Technical objects resource (EI, appliances, insulation constructions, linear and substation constructions) is not only technical but economic characteristic. According to the modern speed of the progress in science and engineering the generations of series of machines should be changed approximately every ten years, as for electrical power engineering, control and computer engineering even more often. The actual resource needs to be adjusted with best values of the life time. Unfortunately, in the most fields the resource does not reach values which are optimal from the economic point of view and for a number of installations an average actual resource is below the level of the normative resource. A well-known example is electrical equipment of oil-and-gas production field. Its insufficient reliability (or durability) especially in conditions of the North lead to poor quality of projection, production, maintenance and storing.

In the present conditions of science and technology the significant increase in the EI resource is possible (up to the values corresponding to its obsolescence). Some measures of resource increasing require more proper approach to calculations and projection, maintenance and operation while others are connected with usage of new materials, constructive solutions and technological processes [3].

The resource increase represents a serious reserve of saving money, energy, materials and working expenses. Thus, according to well-known information of B.I. Kudrin [6] the resource increase in some fleet of electric motors on average of 10 % is approximately equivalent to a 10 % economy in the production of new electric motors or introduction of new relevant industrial capacities. Resource to a considerable extent depends on overloads which affects elements of EI or other constructions.

The correct choice of materials and proper calculation are main resources of rise in the resource. Development of prediction methods should be considered as one of the essential parts of the general resource problem because prediction of the resource includes the establishment of dependence from its internal and external factors.

The prediction of resource occupies the special place on the stage of operation. In contrast to the projection stage prediction on the stage of operation is done for specific existing objects. During this prediction the residual resource and (or) residual life time are estimated.

Prediction of individual resource provides with additional ways of getting economic benefit. Due to natural dispersion of characteristics and conditions of operation (including the history of operation of each object) the range of individual resource values is rather wide. Thus, coefficients of resource variation of boring electrical equipment, submersible electric motors and other EI in oil-and-gas production range from 0.25 to 0.35 and more [1, 2].

Prediction of individual resource allows to warn all kinds of EME violations, failures or unexpected achievement of the marginal state and to plan more correctly modes of operation, control and supply of spare parts. Moreover, the transition to the individual prediction leads to rise of average EI resource because of reducing of proportion of prematurely taken away for repair work. It also opens the way for making a well-founded choice of the operation period.

In some cases, the revenue producing service might be continued in the conditions of declining overloads. That is why it is possible to consider the prediction of the individual resource as the system of operation process and maintenance control according to V.G. Sazukin's suggestion [5].

The introduction of individual prediction requires for additional costs on: - means of technical diagnostics, -build-in and external appliances for recording the level of overloads and state of EI, - creation of telemechanic and microprocessor-based systems for primary information processing, - development of mathematical methods and software for getting valid conclusions on the basis of collected information.

Today, this problem is of the first priority for objects of two groups. Objects of the first group include EI of distributing electrical networks and systems of power supply. They are characterized by high level of science and technical production, strict requirements to technical and economic parameters which lead to toughening of requirements to both electrical part (mainly isolation, switching, security elements and etc.) and mechanical and construction parts. Moreover, it means high requirements to reliability of impacts appearances (particularly of EME) which are sometimes are beyond of the direct control.

The problem of individual resource prediction is of outmost importance in electric power engineering and especially in power supply. In particular in such fields were firstly used (and still in usage) telemechanical systems of representation and registration of normal modes and malfunctions (including overloads and loads which affect EI during the operation period), as well as various sensors which allow to judge the current and accumulated electromagnetic and other physical effects on electrical equipment. They certainly affect the state of the electrical and mechanical parts of the structure and allow to make opinions about the damage and therefore about the residual resource.

The second group of objects includes specific electric power installations. In oil-producing industry they are immersed electric motors (IEM) and their systems of supply. Being complex and responsible technical objects, they contain components and assemblies which during the accident might be the source of increased danger for humans and environment.

A number of them have already elaborated their calculated resource. They continue to make a significant contribution to solving the main technological challenges of oil production because equipment of electric networks and power supply is still in satisfactory technical state. The question of possibility of further operation without breaks for reconstruction but taking into account the real technical state (according to the results of technical diagnostics) of main elements and EI systems of power supply in compliance with strict regulations of technical maintenance and current repairs.

For making well-founded decisions it is necessary to have sufficient information about EME results and other physical impacts on the main and working in most severe conditions elements during the whole previous period of operation and also about changes in their technical state. When you create new electrical installations of oil production, among which IEM have a special significance, it is necessary to provide its equipment with not only systems of early prevention of failures but means of diagnostics and identification of main components state, registration of loads, information processing and establishment of prediction relative to changes of its technical state.

Resource prediction is the part of the EMC theory and reliability of EI and constructions. EMC support and consequently the reliability of EI means the creation of conditions for doing intended functionality during the particular period or running time by the electrotechnical object. These notions include a number of object properties: faultness, durability, maintainability, shelf life. In the reliability theory one of the main notions if failure. It means an event that consists in violation of operating state of the object. The failure is interpreted as random event taking as one of the main indicators of reliability the possibility of non-failure operation during the particular period or running time.

The EMC support (despite the fact it has many common regulations with the reliability theory) is responsible for wider range of questions not in binary form (for example, yes-no, failure - working conditions and etc.) but rather informative and substantive form. First of all, it concerns the internal properties of EI and its ability to resist internal and external EME which might be changed during the operation period. This is connected with such important definitions as noise immunity and sensibility of disturbances. Besides this, during the process of EMC analysis the emission of noise is estimated with taking into account particular EMC characteristics or by using approximate integral normative assessment known as electromagnetic environment.

Resource and the life time as indicators of durability belong to the fundamental concepts of the EMC theory and reliability. In the simplest situation when the object is exploited till the first failure which is identifiable with the transition of the object to the marginal state, operational safety of the object also characterized the durability. However, the more general case is considered when after the period of burn-in failure rate is reduced to a minimum level. And the system of plan-prophilactic measures and maintenance guarantee the prevention of possible failures of at least its rapid removal without long breaks in operation and other serious consequences. Under such conditions main concepts are resource, the marginal state and the life time. This shift in the opinion is one of features of usage of reliability theory in the given study.

On the other hand, in the EMC evaluation not only marginal states and failures appear but also temporary lost of EI efficiency with the return to a normal state:

- at the of its own reserves of internal resistance in relation to EME;

- at the expense of functioning of safety equipment and automation devices;

- as a result of the current actions of personnel;

- as a result of current and through repairs;

- finally, when broken-down elements and blocks are replaced or under the process of renovation.

The second feature: EI and constructions in the whole or in the major part correspond to electromagnetic and electromechanical systems. Questions of reliability were first put during the calculations of electromagnetic and electromechanical systems or more precisely in connection with statical interpretation of reserve coefficients and permissible values, energy saturation and intensity of impacts.

However, the basics of the EMC theory in its modern form appeared in 90s during the process of rapid development of electronics and computer technology. Apparatus of EMC theory and reliability of electric objects and power systems to a large extent have been developed mainly in relation with environment impacts on them and vise versa. At the same time various questions, logical circuits, technological, biological and economic aspects of mutual continuation of functioning and preservation of efficiency.

The main task of the EMC theory and reliability in electric power engineering is to assess the reliability indexes according to well-known indicators of individual elements. These elements often correspond to products of mass production which can be tested in sufficient amount for getting trustworthy statical assessment of reliability indexes. From the point of applications of reliability theory the distinguishing feature of objects is that conditions of operation are relatively homogenous, stationary and might be rendered in the conditions of development testing. The EMC theory and reliability of objects was developed in great detail [1, 4]. This theory has become a part of the general theory of large system and it is possible to be named as the system EMC theory and reliability.

Recently, the parametric EMC theory and EI reliability has been developed. In this theory the violation of EMC or a failure is treated like parameters leaving of some limits which characterize the object's efficiency. However, the development of physical failure models in the parametric theory is still at an early stage.

Electromagnetic and electromechanical interaction of elements and EI constructs is more complex. The behavior of these objects depends on their interaction with environment as well as their nature and intensity of operation processes. To predict the behavior of parts of machines and constructions it is necessary to consider processes of: warping, wearing out and damage accumulation, destructions during contemporary loads, temperatures and other external impacts. To assess the faultness and durability of the object it is not enough to know indexes of individual elements. What is more, many machines and constructions are unique or limited - edition, its blocks and assemblies are cumbersome or expensive, that is why, it is impossible to rely on collection of information on the basis of development testing or testing on-location.

In this regard, assessment of indexes of ETCS faultness and durability is done by computational and theoretical methods based on statistics about EI properties, isolation, EME and etc. This is the most significant difference of EMC theory and reliability of EI and ETCS from both system and parametric theories.

The basis for prediction of EMC support and EI resource is conceptual regulations of analysis of electrical equipment of systems and networks functioning with the help of powerful EME which are considered in some publications [1, 3]. In EMC theory and reliability of electrical networks and systems of power supply properties and qualities of EI, structural and isolation materials and impacts are considered to be random that is why the behavior of the object has a random character.

Regulatory requirements and specification of operation impose certain restrictions on parameters. Restrictions might be formulated as a condition of finding a random vector of marginal states of parameters of electrical modes and technical diagnostics. This vector depends on time and characterizes the EI quality in the given area. Failures, intermediate and marginal states correspond to the outputs of random vector on the area of possible values.

Thus, the main problem of the theory of reliability, risks, EMC and resources is the evaluation of possibilities of non-failure and satisfactory (from the point of returns to the up states) work during the given time. This problem is brought to the problem of random processes emissions. Connection between methods of electrical engineering, electrophysics and electric isolation and the theory of random processes is the basis of the theory EMC of electric networks and power supply systems support [1, 4].

Bibliography

1. Electromagnetic compatibility and elaboration of measures for improving of safety from overvoltage of electrical equipment of networks 6 ч 35 kV / F. Chalilov, V. Goldstein, G. Podporkin, V. Stepanov. Moscow: Energoatomizdat, 2009. 344 p.

2. Rise in reliability of electrical equipment and networks 0,4 - 110 kV work during overvoltage in oil production / F. Chalilov, V. Goldstein, A. Gordienko, A. Puchalski. Moscow: Energoatomizdat, 2006. 356 p.

3. Goldstein V., Chrennikov A. Technical diagnostics, fault probability and resources of power and measuring transformers and reactors. Moscow, Electroatomizdat, 2007. 320 p.

4. Electromagnetic compatibility in electro power engineering and electrotechnology / A. Dyakov, B. Maksimov, R. Borisov. Moscow: Electroatomizdat, 2003. 768 p.

5. Sazukin V. The technology of well-ordered functioning of electrotechnical complexes equipment, dissertation, 2001.

6. Kudrin B. Organisation, building and control of electric economy of industrial enterprises on the basis of the theory of large systems, dissertation, d.t.s. MEI, Moscow, 1976.

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