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Abstract

Сontents

Introduction

In our days at modern domestic and foreign power plants and in electric networks a significant amount of worn-out electric equipment is operated. For example, in the USA as of 1997 about 65 % of power transformers fulfilled more than 25 years, in Russia wear of fixed assets of power industry makes about 50 %. As of the end of 2005 the average term of electric equipment operation of Ukraine already exceeds a half design that leads to decrease in reliability of its functioning and accident rate increasing. The economic situation, and also total of capital equipment don't allow to make its replacement in the next years. In this regard more and more actual there is a problem of extension of service life and an assessment of possibility of further operation of such electric equipment in systems of power supply industrial, residential and public buildings.

For transition to service system of power transformers on actual state the most complex challenge is determination of current state of the transformer.

The purpose of this service system is increasing of reliability and decreasing in operational costs.

1. Service system of power transformers on actual state

As this service system (SS) understand process of tracking a condition object in continuous on-line a mode. Basis of such look SS is the technical diagnosing (TD) and forecasting of a condition of object. By means of means of TD (monitoring) carry out continuous control of parameters of a state. Continuous control, allows the operational personnel to watch deterioration of parameters and to their approach to limit values. Approach of parameters to limit values, testifies to functioning violation. Limit values of parameters systems are installed by experts in existing criteria and brought in a database. These values define inadmissible conditions of the equipment and allow to warn in due time the personnel about need of certain actions on preservation of transformers resourse.

Main purposes of transition to service on actual state:

• increasing of efficiency of operation of the transformer equipment and reduction of cases of failures of power supply because of equipment failure due to identification of an initial stage of development of defect and/or preemergency and emergency operation in the controlled equipment;

• reduction of investment expenses for unreasonable updating of the equipment;

• decreasing in expenses on carrying out repairs as a result of the organization of repairs for a real condition of the equipment instead of the calendar;

• reduction of labor costs of the personnel as a result of introduction of the automated control methods and diagnostics;

• increasing in time of operation of the equipment on the basis of the actual values of critical parameters of the transformer equipment;

• decreasing in risks of causing ecological damage because of failure of the transformer equipment;

• reduction of expenses by insurance.

Earlier it was told that damages of windings, inputs and switches of branches to devices of voltage regulation under load are the main reasons of long-term refusals. Therefore it is very important to control a condition of these transformer nodes.

Systems of monitoring are differently by the variety. Practically all companies which make electric equipment, offer also monitoring systems. Various systems of monitoring allow to trace various measured sizes in real time. However use of all their range can be inexpedient. Therefore the set of sensors has to be developed taking into account specific requirements to this transformer, depending on its age and a state [10].

The important element of SS on actual state is the service of technical diagnostic. Its tasks include performance of inspections of the equipment, participation in equipment acceptance from repair, and also issue of recommendations about prevention of refusals. Staff of service has to be trained in application of diagnostic aids and results. Therefore the requirement to monitoring system from the user is one of the main possibility of simple and safe access to all necessary information on a condition of the installed equipment [5].

Access to information provides the Internet on the basis of Web. Thanks to connection of the server of monitoring with the Internet network, all departments of the power enterprise can receive necessary information. Protection by the password allows to get access to information to only those users who have the right of the admission.

In figure 1.1 the typical structure of monitoring system is presented. Sensors and the sensors covering the main knots of the transformer, cables of communication of sensors belong to basic elements with knot of collecting and information transfer, the communication line with the equipment on a control panel where the reception and reformative equipment with the central server is directly placed.

Typical structure of monitoring system

Figure 1.1 – typical structure of monitoring system

(animation: 9 frames, 5 cycles, 234 kilobytes)

In general the structure of monitoring consists of three levels.

The level I consists of sensors and measuring systems (sensors of temperature, moisture content of oil, etc.).

The level II – the monitoring block. Represents set of controllers which provide collecting and processing of the signals received from sensors of level I. Also this level carries out information exchange with the III level.

The level III is executed in the form of uniform centralized programmatically – a technical complex for all transformer equipment and intended for:

• mathematical processing;

• it is settlement – analytical tasks;

• remote configuration and check of serviceability of the equipment of the bottom levels.

The level III also provides visualization of a condition of controlled and counted parameters of the transformer equipment, display of signals of operation of the alarm and precautionary system, accumulation of databases of parameters, and also allows to carry out work with the saved-up archives and magazines and allows to make transfer on remote top levels of management.

Communication between devices II and III levels is carried out by means of digital channels with use wire (twisted couple in the screen) or optical communication lines [7].

Advantages. Application of given SS allows:

• to find malfunctions at the time of their emergence and to warn or reduce consequences of defects;

• to carry out continuous supervision over working conditions and a condition of the transformer;

• to make service on the basis of a state;

• to provide optimization of management by the transformer, i.e. an assessment of the remained service life, service life extension, a replacement delay, etc.;

• to carry out the careful analysis of the reasons of defect;

• to increase safety of people and to improve environment protection;

• to control real current technical condition of mechanisms;

• to control quality of production, adjustment and installation when commissioning;

• to control quality of the performed repair and adjustment work;

• technically reasonably to plan terms and the content of repair and adjustment work;

• to plan terms of acquisition of spare parts in process of their need;

• to reduce need for spare parts, materials and their stocks in a warehouse;

• to raise a resource and reliability of the equipment, to prolong the between – repairs period and service life;

• to increase the general culture of production and qualification of the personnel;

• to lower costs of service by 75 %,

• to reduce quantity of service by 50 %,

• decrease in number of refusals for 70 % for the first year of work [3].

2. Methods which are necessary for passing to service of power transformers on actual state

Now the most effective remedy for increasing of power transformers reliability is application of methods and means of technical diagnostics.

Generally all modern monitoring systems are aimed at an assessment of a isolation condition as element of the transformer most important and subject to destruction. For this purpose use an assessment transformer, temperature control of the most heated point, determination of moisture content in paper isolation, a tangent angle of dielectric losses definition. Also one of main is control of a condition of the cooling system, at efficiency which an assessment the following parameters are usually used: temperature of the top butter layers, difference of temperatures of oil on an entrance and a cooling system exit, the ambient temperature, a condition of oil pumps and fans. However not control of such parameters as is unimportant: level of partial categories, the characteristic of vibration of a tank of the transformer, currents of electric motors of oil pumps, the speed of streams of oil from an oil pump, current of conductivity, tgδ and capacity of high – voltage inputs, current or power of the electric motor of the voltage regulation under load drive [4].

We will consider most the TD effective methods and estimates of a power transformers condition.

1. Current, voltage and power measurements and control.

Working parameters of the transformer which testify to its loading and serve as entrance sizes for model of thermal and power balance of the transformer [9].

2. Monitoring of moisture content and concentration of the dissolved gases in transformer oil.

The condition of insulating system depends on a condition of oil in a transformer tank in the maximum degree, and so – and reliability of the transformer operation. It is most important to control moisture content in oil. Insulating properties of oil substantially depend on it.

Availability of the dissolved gases in oil usually speaks about existence of defects in the transformer. It too important diagnostic sign. The analysis of combinations of several dissolved gases allows to differentiate type of the defect which has arisen in the transformer.

3. Change of capacity and inputs of tgδ.

Damageability of high – voltage inputs always is, concerning other elements of the transformer, rather high, and according to some information reaches 20 –30 % of total of failures of transformers. Therefore primary sensors and the necessary equipment for measurement of a losses tangent angle are a part of all systems of diagnostic monitoring of the transformer equipment and the capacity of inputs in the on-line mode surely.

The recorded changes testify to malfunction of high – voltage inputs isolation system of the transformer.

4. Monitoring of partial categories in high – voltage inputs and the main isolation of the transformer.

Expeditious diagnostics of a condition of isolation of inputs and transformer windings on level and distribution of partial categories is effective, and especially, highly sensitive to defects at the earliest stages of their development. This method should be included in structure of systems of diagnostic monitoring of the transformer equipment always.

5. Monitoring of thermal operating modes of the transformer and control of the cooling system.

For power transformers of lowering substations measurement of temperature of a tank is obligatory. Data on temperature of a tank of the transformer are necessary in system of diagnostic monitoring for two purposes. First, for identification of change of temperature of a tank, depending on the current technological parameters, and, secondly, for specification of diagnostic inferences for those parameters which have the general trend with a temperature of a tank of the transformer.

6. System of monitoring of a condition of voltage regulation under load of the transformer.

Reliability of work of system of regulation of tension of lowering transformers under loading in many respects defines quality of power supply of consumers. Importance of this parameter significantly increases in modern economic conditions that is caused by toughening of requirements to quality of power supply of industrial and household consumers. For this reason the number of transformers in which monitoring of a condition of voltage regulation under load is conducted grows.

Use of system of diagnostic monitoring of voltage regulation under load for those transformers which work in a mode of automatic maintenance of voltage at the party of connection of the external consumer of electric energy is especially important.

7. Currents of short circuit

Records of processes of currents of SC provide information, first of all, about dynamic loading of windings of the transformer [6].

These methods are effective and allow to reveal defects at an early stage in electric equipment, thereby give opportunity to raise a resource and reliability of the equipment.

Conclusion

Appropriate maintenance, and timely repair are capable to prolong service life of industrial electric equipment significantly. And also to reduce costs of its contents (for example, due to decrease in expenses on elimination of consequences of unplanned stops), to increase the general reliability of work of the enterprise, etc.

For the large enterprises which are especially using the difficult and expensive equipment, questions of transition to service system on an actual state play an extremely important role.

In this work advantages of transition SS on actual state were considered. The main advantages SS are opportunity to cut down operational expenses, and also opportunity it is essential to increase reliability and electric equipment service life.

The basis of technology of transition to service on actual state is made by methods and means of TD which allow to find and identify all potentially dangerous defects at an early stage of their development. Various methods of monitoring which were presented in this work are already developed for possibility of transition on given SS, and also new systems and methods on the basis of modern advanced IT – technologies are developed.

This master's work is not completed yet. Final completion: December 2014. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

References

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