Technique of definition of the optimal variant of replacement of electric equipment

Abstract

The scale of the use of electrical equipment in agriculture in Ukraine is constantly expanding.  The number, nomenclature, complexity and responsibility of the functions that it performs are growing. Therefore, the requirements for the reliability of the electrification facilities and the cost-effectiveness of their use are increasing. The solution of this problem is connected with the increase of the efficiency of operation of the electrical equipment, and optimization of its terms of operation.

Determination of optimum terms of work of electrotechnical means is a difficult technical and economic task. It is necessary to consider the reached level and the directions of development of technical means, stocks and rates of use of resources, regularities of operation of the equipment and a state and the prospects of development of economy.

The complexity of accounting of the specified factors induces to application of the approximate calculation focused on definition of an average, economically the most expedient, the term of operation of the electrotechnical equipment.

Optimization of service life of electric equipment used in agriculture even on the simplified models has specific difficulties, it, first of all, accounting of uncertain factors: change in time of properties of electric equipment, costs of operation, losses are caused by refusals.

Therefore for the solution of problems of optimization of terms of replacement of electric equipment, it is expedient to apply decision-making methods in the conditions of uncertainty.

Research objective is development of a technique of definition of an optimal variant and term of replacement of electric equipment in the conditions of uncertainty of operation.

In order to restore the performance of the electrical equipment, the maintenance staff should take one of two decisions: to write off and replace it with new ones or to carry out major repairs and to continue operation. After the re-failure of this equipment again, two possible solutions are possible: write-off or overhaul, and so on.

In practice the same equipment is capitally repaired by no more than three times. Therefore the problem of replacement of electric equipment has four versions of the decision: replacement new after each failure; replacement new after the first capital repairs; replacement new after the second capital repairs; replacement after the third capital repairs.

Representation of the whole set of output data, including uncertain factors, as system states, and variants of substitution - as  variants of solutions, we get the typical task of choosing strategies in conditions of uncertainty.

For its decision it is necessary to enter criterion of efficiency and to calculate its value for each pair situation: a state - the decision. All these values in total form a matrix which allows to choose an optimal solution.

But these principles have a significant disadvantage, because the optimal solution is formed regardless of the actual state of the system.

The quality of the choice can be improved by a zoning method which at a small number of possible decisions, allows to define that each option of replacement will be optimum for some zone of basic data.

The essence of a method consists in splitting a large number of basic data into zones in which one of options better than others. For this purpose for each version of decisions consists the equations of criterion of efficiency and consistently find required zones, investigating their pair borders. At the same time it is possible to define the best option of replacement and optimum service life of electric equipment.

In tasks of definition of optimum service life economic criterion of efficiency is total costs of electric equipment operating time unit for all the operation period.

Dependent dependencies are defined to determine those aggregates of output data, in which each of the options will be optimal.

We will accept operating costs constants, then they will be identical to all options therefore we can consider them.

Service life in zero option is equal to one period of no-failure operation, in the first - to two, in the second - we rub and so on. At the same time the second and the subsequent periods is less than first.

In specifications it is specified capital repairs of asynchronous electric motors that indicators of their reliability after repair have to be not less than 80% of values of indicators of new electric motors.

For the considered concrete situation the second option - replacement of the engine after two capital repairs will be optimum. At the same time optimum service life will equal 5 years.

The analytical solution of a problem of the replacement of electric equipment connected with the choice of option consists in definiteness of borders of zones of the output data in which the considered options are optimum.

To choose replacement option, it is necessary to compare the valid service life before the first capital repairs to settlement.

Having technical and economic indicators on the operation of electrical equipment in a particular enterprise and using a PC for their processing, it is possible to plan measures for the organization of technical service with minimal tim