9. Organization of Diagnostics for Power Industry Facilities

9.1 General Principles of Diagnostic Monitoring of Electrical Equipment

The main regulatory and legal issues of diagnostic monitoring of high-voltage electrical equipment can be resolved on the basis of the existing GOST 27.002-89 “Diagnosing of products. General requirements”. To carry out diagnostic measures, in accordance with the Rules for Technical Operation of Consumer Electrical Installations, the following should be developed as legal documents: a summary of normative parameters and a summary of criterion parameters.

The development of diagnostic monitoring measures must necessarily be an integral part of the development of electrical equipment. The question of the nature of diagnostic measures and the methods of their implementation necessarily arises either during operation - for equipment in an unsatisfactory condition, or upon completion of the service life. Under the current economic conditions, the problem of extending the service life of equipment that has exhausted its designated service life has become urgent. Properly planned diagnostic measures can significantly increase the actual service life of equipment, which will certainly be reflected in reduced costs.

Each of the states (serviceable, faulty, operable, inoperable) is characterized by a set of values of parameters describing the state of the object, as well as by qualitative characteristics for which quantitative estimates are not applied. The list of these parameters and characteristics, as well as the limits of their permissible changes, are established in normative-technical and (or) design (project) documentation.

An operable object, unlike a serviceable one, need only satisfy those requirements of the normative-technical and (or) design (project) documentation whose fulfillment ensures the normal use of the object for its intended purpose.

For complex objects, partially operable states can be distinguished, in which the object is capable of partially performing the required functions or performing functions with reduced performance indicators.

Upon reaching the limiting state, the object must be withdrawn from operation, sent for medium or major overhaul, decommissioned, destroyed, or transferred for use not for its intended purpose.

The operating time of an individual object, its service life, etc. can be determined only after a failure has occurred or the limiting state has been reached. Until these events occur, one can only speak of predicting these values with greater or lesser reliability. Medium and major overhaul allow partial or complete restoration of the service life, returning the apparatus to an operable state.

The ultimate object of activity in the field of electrical engineering is the electrical apparatus. Therefore, the question of service life must be tied to the electrical apparatus as a unit of electrical engineering complexes. An electrical apparatus consists of a number of assemblies, each of which has its own service life. The exhaustion of the service life of an individual assembly can bring the entire apparatus to a limiting state if the limiting state of this assembly affects the operability of the apparatus as a whole.

The generalized specified function of electrical equipment as a complex of electrical apparatuses is the transmission and distribution of electrical energy of specified parameters. Thus, a switching apparatus must ensure the interruption of current with specified parameters, a transformer must convert one set of specified electrical energy parameters into another, etc.

From the standpoint of the terms adopted, the goal of diagnostic measures is to determine the "predicted residual service life", i.e., the remaining ability of the apparatus to perform its specified functions. If, for some parameter designated as a criterion of the limiting state, permissible boundaries are established (the initial and final value of the limiting-state criterion), then for this parameter a predicted residual service life can be established as the position of the current value of this parameter within the established boundaries. In a number of cases, especially when the change in a given parameter is not a monotonic function of the apparatus's operation, one has to limit oneself to stating the fact that the limiting state has been reached, which corresponds to the complete exhaustion of the service life with respect to this parameter, effectively answering the question "yes - no": there is service life remaining - there is no service life remaining.

Thus, to resolve the question of the serviceability and operability of an apparatus, it is necessary to have the corresponding technical requirements of normative-technical and (or) design (project) documentation.

The main object of diagnostic attention and the element common to all electrical apparatuses is the electrical insulation. But the interests of diagnostics are much broader, taking into account the purpose of each of the apparatuses and the assemblies included in it. The main task of diagnostics of electrical apparatuses is to determine their state and predict their operability, and to determine ways and means of extending or restoring their operability.

The main goal of diagnostic monitoring of electrical equipment is, based on determining the state of the electrical equipment, to maximize the use of the actual service life of the equipment and to prevent an emergency failure of the equipment.

The main methods of achieving this goal are:

1) establishing frequent or continuous monitoring for potentially unreliable, defective equipment, the operation of which is nevertheless possible for an indefinite continued period of time, with the purpose of its timely disconnection upon reaching the established limits of the monitored parameters;

2) timely withdrawal of equipment from operation for preventive repair carried out not according to a plan, but according to objective readings, with the purpose of complete or partial restoration of the service life.

Objects of diagnostic monitoring are determined mainly by the functional significance of the electrical apparatus in the power supply system. The most complete, comprehensive diagnostic monitoring is supposed to be carried out on repairable products, since restoring their operability through repair can repeatedly extend the time of their actual operation.

Diagnostic monitoring begins from the moment the equipment is created. Acceptance tests are in fact a diagnostic measure aimed at determining the further operability of the equipment according to the established technical requirements. But the concept of diagnostic monitoring applies fully to equipment that is already operating and in service, and the task of such diagnostic investigation includes either determining the possibility of trouble-free completion of the designated service life, or, upon its completion, determining the possibilities for further trouble-free operation of the equipment. At present, monitoring measures are carried out in three ways: inspections, diagnostic tests, and monitoring.

Inspection is a traditional preventive measure for maintaining the operability of equipment. Carrying out inspections is associated with large expenses and with the involvement of specially trained personnel to work in a hazardous and, quite often, remote work zone. Inspection, while being a diagnostic measure in essence, practically does not solve diagnostic tasks (in their current understanding), since with its help it is impossible to prevent an emergency failure, it is impossible to make a prediction about the operability of the apparatus, and the condition of the apparatus can only be assessed by external, accessible manifestations. And yet, equipment requires constant observation. The contradiction between the need for more thorough monitoring than can be achieved by means of inspection, the need to remove personnel from the work zone, and the need to reduce expenses on preventive measures while simultaneously increasing the objectivity and reliability of monitoring can be resolved by creating automatic systems for continuous monitoring of equipment condition. In reality, this is exactly what is happening. Moreover, the development of automatic monitoring and control systems leads to a differentiation of the monitoring function: part of the monitoring functions is assigned to automation and electronics, freeing personnel from routine tracking of normative parameters, while the monitoring measures remaining with personnel acquire an increasingly diagnostic slant, i.e., they are effectively implemented as diagnostic tests. The performance of monitoring measures by personnel is now usually carried out not so much to maintain any established parameters, but rather with the purpose of predicting the further behavior of the equipment in terms of its operability, i.e., the main orientation of monitoring measures is the diagnostics of the equipment's condition: establishing deviations in functioning and their causes with the purpose of predicting the ability of the apparatus to perform the functions assigned to it and of preventing an unexpected failure. At the same time, automatic monitoring systems are also being assigned an increasing number of diagnostic functions: a continuous tracking system must not only state the current value of the observed parameter, but, using accumulated knowledge, form a scientific prediction about the operability of the equipment for the future.

Thus, the tasks of diagnostic monitoring of equipment condition are solved in two ways:

- by means of episodic determination of the most important parameters - by means of diagnostics;

- by means of continuous tracking of the most informative parameters - by means of monitoring.

Diagnostics, consisting of a set of diagnostic tests, is divided into two stages: operational diagnostics and diagnostic inspection.

Diagnostic measures can be carried out both on operating equipment (energized) and on non-operating equipment (de-energized). In the latter case, in addition to the general task of diagnostics (carried out in the form of a comprehensive diagnostic inspection), an equally important task is added: determining the ability of the insulation to withstand loads when energized and during the transient period when reaching operating modes. If in the first case we are talking about the resource indicators of the equipment, then in the second, in addition to this, the readiness of the equipment for energizing must be assessed by direct correspondence of the established parameters: when the equipment is commissioned, all current characteristics must be within the permitted limits or brought to this state before voltage is applied.

The operational diagnostics performed first involves the use of non-destructive testing methods, i.e., methods that do not lead to the expenditure of service life, and is carried out simultaneously with the electrical apparatus performing its main functions. These are methods of physico-chemical diagnostics, thermal imaging technology, methods of acoustic monitoring, and certain methods of electrical monitoring. Obviously, operational diagnostics is used during operation wherever it is unambiguously recognized as expedient and reliable (for example, thermal imagers for monitoring heat release, chromatographic analysis for monitoring the oil insulation of transformers and bushings, acoustic monitoring of electrical discharges).

As a rule, physicochemical methods form the basis of operational equipment diagnostic methods. Energy exposure of the insulation of electrical devices leads to changes at the molecular level, regardless of the type of insulation, culminating in chemical reactions with the formation of new chemical compounds. The formation of new chemical compounds is the ideological basis of physicochemical diagnostics, while determining the quantity of newly formed characteristic components and the rate of their formation forms the basis for determining the condition of the insulation and the extent of energy exposure it has undergone.

The main purpose of operational diagnostics is to determine the type of defect, its hazard level, and rate of development. In the absence of monitoring, the main diagnostic function of ensuring safe operation falls on operational diagnostics, and based on its readings a decision is made regarding the need for a more thorough, fundamental diagnostic examination in order to make a final decision on the fate of the unit.

A diagnostic examination is carried out on de-energized equipment, i.e. with the main function suspended based on the readings of operational diagnostics or monitoring. Here, the full power of all available methods can be applied for a detailed study of the condition of all elements ensuring operability: physical, chemical, electrical, technical, and mechanical methods - in accordance with the developers' instructions, regardless of their significance and complexity.

Monitoring, like operational diagnostics, involves the use of non-destructive testing methods, i.e. methods that do not consume the equipment's service life, and is carried out simultaneously with the electrical apparatus performing its main functions. If a monitoring system is present, the signal indicating the need for a more thorough diagnostic examination should come from it.

The main method of eliminating defects is repair (preventive, minor, medium, and major overhaul). Therefore, the ultimate goal of a diagnostic examination, as the final stage of diagnostic monitoring, is to determine the type and scope of repair needed to increase the remaining service life or to restore an operable condition.

Regardless of the path taken by the diagnostic examination, in order to resolve questions of service life and operability, the developer of the diagnostic monitoring methods must first of all develop limit state criteria if these are absent from the regulatory-technical and design (project) documentation. Ultimately, to carry out diagnostic measures, the following must be presented as legal documents: a summary of normative parameters and a summary of criterion parameters. The former - the basic technical requirements of the regulatory-technical and design (project) documentation - are intended for classifying the condition of equipment into the categories "serviceable - unserviceable," while the latter - requirements characterizing the apparatus exclusively from the standpoint of its ability to perform its assigned functions - are for classification into the categories "operable - partially operable - inoperable." These classification summaries form the basis of computer diagnostic programs, both for diagnostic examination and for monitoring.

A rejection criterion is a set of values of diagnostic parameters and other indicators sufficient to assess the condition of the object under inspection and to classify it as having damage (defects). The ultimate purpose of such a classification is to predict the operability of the equipment.

The rejection criterion is taken to be the deviation of the values of the monitored parameters beyond established limits. It is taken into account that the same changes in a parameter's value may be caused by different defects, whose development poses unequal risks of object failure.

9.2. Development of a methodology for diagnosing and forecasting the service life of electrical equipment

Using the "Approximate Procedure for Technical Diagnostics of Consumer Electrical Installations" set out in the Technical Operating Rules for Consumer Electrical Installations, along with existing standard diagnostic methodologies for similar objects - for example, RAO "UES of Russia" has developed thermal imaging diagnostic methodologies for practically all types of electrical equipment - a methodology is being developed for the technical diagnostics and service-life assessment of the object under consideration, which should include:

1 Objectives of technical diagnostics:

• determination of the type of technical condition;
• locating the site of a failure or faults;
• forecasting the technical condition.

1. Conditions for technical diagnostics:

• establish diagnostic indicators and characteristics;
• ensure the electrical installation's suitability for technical diagnostics;
• develop and implement diagnostic provisioning.

1. Indicators and characteristics of technical diagnostics.
   1. The following diagnostic indicators are established:

• indicators of diagnostic accuracy and reliability;
• technical-and-economic indicators.

Indicators of diagnostic accuracy and reliability are given in Table 2.1.

Technical-and-economic indicators include:

- combined material and labor costs;

- duration of diagnostics;

- frequency of diagnostics.

1. The following diagnostic characteristics are established:

- the range of electrical installation parameters that make it possible to determine its technical condition;

• the depth of the search for the site of a failure or fault, determined by the level of structural complexity of the constituent parts or by the list of elements to whose precision the site of the failure or fault must be determined;
• the range of product parameters that make it possible to forecast its technical condition.

1. Characteristics of the range of diagnostic parameters.

4.1 The range of diagnostic parameters must meet the requirements of completeness, informativeness, and measurement accessibility at the lowest cost of time and implementation expense.

4.2 Diagnostic parameters may be characterized by providing data on nominal and permissible values, test points, etc.

5 Method of technical diagnostics.

5.1 Diagnostic model of the electrical installation. The electrical installation subjected to diagnostics is specified in the form of a tabular diagnostic chart (in vector, graphical, or other form).

5.2 Rules for determining structural (defining) parameters. This parameter directly and substantially characterizes a property of the electrical installation or its unit. Several structural parameters may be present. Priority is given to the parameter(s) that satisfy the requirements for determining the true technical condition of the given electrical installation (unit) for the specified operating conditions.

5.3 Rules for measuring diagnostic parameters. This subsection includes the basic requirements for measuring diagnostic parameters and the relevant specific requirements that apply.

5.4 Diagnostic algorithm and software.

5.4.1 Diagnostic algorithm. A description is given of the list of elementary checks of the object under diagnosis. An elementary check is defined by the working or test stimulus applied to the object, as well as by the set of indicators (parameters) forming the object's response to the corresponding stimulus. The specific values of the indicators (parameters) obtained during diagnostics are the results of the elementary checks or the values of the object's response.

5.4.2 The need for software, for the development of both specific diagnostic software products and other software products to ensure the functioning of the technical diagnostics system as a whole, is determined by the Consumer.

5.5 Rules for analyzing and making decisions based on diagnostic information.

5.5.1 Composition of diagnostic information:

a) rated (nameplate) data of the electrical installation;

b) data on the technical condition of the electrical installation at the initial moment of operation;

c) data on the current technical condition, including the results of measurements and examinations;

d) data including the results of calculations, assessments, preliminary forecasts, and conclusions;

e) generalized data on the electrical installation.

Diagnostic information is entered into the industry-wide database (if one exists) and into the Consumer's database in the appropriate format and information storage structure. Methodological and practical guidance is provided by the superior organization and the specialized organization.

5.5.2 The user's guide describes the sequence and procedure for analyzing the diagnostic information obtained, comparing and correlating the parameters and indicators obtained after measurements and tests; recommendations and approaches for making decisions on the use of diagnostic information.

6 Technical diagnostic equipment.

6.1 Technical diagnostic equipment must ensure the determination (measurement) or monitoring of diagnostic parameters in the operating modes of the electrical installation established in the operational documentation or adopted at the given enterprise under specific operating conditions.

6.2 The equipment and instrumentation used to monitor diagnostic parameters must allow for reliable determination of the measured parameters. Oversight of the technical diagnostic equipment must be carried out by the metrological services of the corresponding levels of the technical diagnostics system's operation, in accordance with the regulation on the metrological service. The list of equipment, instruments, and apparatus required for technical diagnostics is established in accordance with the type of electrical installation being diagnosed.

7 Rules of technical diagnostics.

7.1 Sequence of diagnostic operations. A description is given of the sequence for performing the relevant measurements and expert assessments across the entire set of diagnostic parameters and characteristics established for the given electrical installation and presented in the diagnostic chart. The content of the diagnostic chart is determined by the type of electrical installation.

7.2 Technical requirements for performing diagnostic operations. When performing diagnostic operations, it is necessary to comply with all requirements and instructions of the PUE (Electrical Installation Rules), these Rules, the Inter-Industry Labor Protection Rules (safety rules) for the operation of electrical installations, other industry documents, as well as GOSTs on diagnostics and reliability. Specific references must be made in the working documents.

7.3 Instructions on the electrical installation's operating mode during diagnostics. The operating mode of the electrical installation during the diagnostic process is indicated. The diagnostic process may take place while the electrical installation is operating, in which case this is functional technical diagnostics. Diagnostics may also be performed in shutdown mode. Diagnostics may also be performed under a forced operating mode of the electrical installation.

7.4 Safety requirements for the diagnostic processes and other requirements in accordance with the specifics of the electrical installation's operation. |The general and the main safety requirements for diagnostics that pertain to a particular electrical installation are indicated; in doing so, the relevant sections and clauses of the applicable rules and directive materials must be specifically listed.

Mention is made of the need for the organization performing diagnostic work to have the appropriate permits. Before starting diagnostic work, the personnel involved must obtain a work permit for carrying out the work. This section must formulate safety requirements for functional diagnostics and diagnostics under forced operating mode of the electrical installation. Any specific requirements that the given Consumer has for the particular operating conditions of this electrical installation must also be indicated.

8 Processing of technical diagnostics results.

8.1 Instructions for recording diagnostic results. The procedure for recording the results of diagnostics, measurements, and tests is indicated, and forms of protocols and reports are provided.

8.2 Instructions and recommendations for issuing a conclusion.

Instructions and recommendations are given for processing the results of inspections, measurements, and tests, for analyzing and comparing the obtained results with previous ones, and for issuing a conclusion, a diagnosis. Recommendations are given for carrying out repair and restoration work.

1. Metrological support and processing of technical diagnostics results

The results of any measurement differ from the true value of the measured quantity by some amount, which depends on the accuracy of the instruments and the measurement method, the operator's qualification, and the conditions under which the measurement is performed. The deviation of the measurement result from the true value of the measured quantity is called the measurement error. Measurement errors determine the zone of uncertainty of the measurement result. Mathematical processing of measurement results and knowledge of the metrological characteristics of the measuring instruments make it possible to present the final measurement result as a value of the measured quantity together with accuracy indicators.

The effectiveness of technical diagnostics of objects largely depends on the reliability of the measurement information obtained and its reproducibility, and this cannot be ensured without calibration of the diagnostic equipment. The use of uncalibrated diagnostic equipment leads to a situation where inspection carried out by the manufacturer at product acceptance and by the consumer at incoming inspection (using diagnostic equipment of the same type and the same procedure) can produce diametrically opposite results, which leads to significant material costs. Improving product quality also depends on the degree of metrological support of production.

A low level of inspection operations, caused by insufficient or incorrectly assessed measurement accuracy or insufficient and unstable sensitivity of the diagnostic equipment, leads to a decrease in the reliability and reproducibility of the obtained information on the monitored parameters of the object, which, as a rule, leads to a decrease in the reliability of the diagnostic results. Consequently, in order to ensure reliable information is obtained as a result of inspection operations, it is necessary to improve the quality of metrological support of diagnostic equipment, one form of which is the calibration of diagnostic equipment.

During calibration, the first thing to determine is whether the technical and metrological characteristics of the diagnostic equipment comply with the requirements of the regulatory and technical documentation (RTD). For the calibration of diagnostic equipment intended for general use, the RTD are the state standards for calibration procedures or the methodological guidelines of Gosstandart of Russia for calibration. In the absence of state standards or methodological guidelines of Gosstandart of Russia for the calibration of diagnostic equipment intended for use within a single department, departments may apply their own methodological guidelines for calibration. If there is a need to reflect the specifics of the calibration conditions of diagnostic equipment, departmental methodological guidelines are sometimes applied even when state standards or methodological guidelines of Gosstandart of Russia for calibration exist, but provided that the main requirements established therein are observed.

For the calibration of non-standardized diagnostic equipment manufactured and used at a single enterprise, methodological guidelines for calibration developed at the enterprise are used.

The development of new and the revision of existing state standards for calibration procedures and methodological guidelines for calibration is carried out by the standardization and metrology centers of Gosstandart of Russia according to their specialization, as well as by the organizations that develop diagnostic equipment or the leading (base) organizations of the metrological services of the ministry (department) that are developers of diagnostic equipment.

Methodological guidelines of metrological institutes for calibration are developed by organizations submitting diagnostic equipment for state acceptance testing.

The procedure for developing, coordinating, approving, formalizing, registering, and issuing departmental methodological guidelines for calibration and enterprise methodological guidelines is established by the ministry (department) to which the organization developing the RTD for calibration belongs.

9.4 Safety requirements for diagnostic processes

When performing diagnostic work, as well as in the process of creating experimental setups and conducting research, it is necessary to develop a system of organizational and technical measures and means ensuring the protection of people from the hazardous and harmful effects of electric current, electromagnetic field, radiation, and the harmful substances used. The design of the objects and diagnostic equipment, as well as of experimental setups and the diagnostic tools and systems being developed, must meet the requirements of the Electrical Installation Regulations, and the work on diagnosing electrical networks and electrical equipment and experimental research must be carried out in accordance with the Rules for the Technical Operation of Consumers' Electrical Installations and the Interindustry Labor Safety Rules for the Operation of Electrical Installations.

9.5 Technical and economic performance indicators of the diagnostic system

A significant reduction in the costs of operating power equipment is provided by switching it to condition-based maintenance and repair. To do this, it is necessary to know precisely the condition of the main and auxiliary equipment of the electrical installation and to forecast it for the time needed to prepare for repair. The effectiveness of condition-based maintenance and repair is determined by a reduction in the volume of maintenance and repair work of 30 – 50%, with minimal diagnostic costs. But this reduction alone does not determine the full economic effectiveness of switching to condition-based maintenance and repair of equipment. As shown by studies conducted in a number of Western countries, the reduction in repair costs is only a small (less than 20%) part of the economic effect provided by the reduction in equipment downtime during maintenance and repair.

An analysis by the US Institute of Power Industry Research for 1998 showed that a power plant's specific maintenance costs are $18 per horsepower for run-to-failure operation; $13 per horsepower for scheduled maintenance; and $9 per horsepower for preventive maintenance. The main condition for a successful transition to condition-based maintenance and repair is the active use of various systems for diagnostics and forecasting the service life of machinery and equipment.

Any increase in equipment reliability is achieved through the necessary additional increase in costs. This raises the problem of determining the optimal level of costs at which the technology and production remain profitable. The use of diagnostic systems increases the cost of the product during manufacture and operation; however, their use significantly increases the reliability of the objects, providing an economic gain.

At all stages of the creation and implementation of diagnostic tools and systems, a technical and economic analysis is carried out and the effectiveness of their application is determined. A technical and economic analysis of the application of diagnostic methods and tools makes it possible to justify the most rational directions and sequence for the development or implementation of particular diagnostic systems, to choose the most cost-effective options for creating diagnostic systems and their operating modes, and to determine the social effect of implementing diagnostic systems. The technical and economic justification must contain a brief description of the task at hand and the possible variants of its solution, an assessment of the technical effectiveness of applying the diagnostic system, and the possibility of increasing the reliability of the object being diagnosed.

The formation of effective diagnostic systems must be based on accounting for the useful result of applying the system and the costs of it. The measure of the useful result can be taken as the increase in the reliability of the object being diagnosed, and the mandatory elimination of defects identified by the given system. The economic effect of diagnostic systems is a generalizing indicator characterizing the feasibility of the set of measures for creating and implementing diagnostic systems.

Example of calculating the economic efficiency of a project. Savings in operating costs for equipment repair result from a reduction in the cost of routine, medium, and major repairs due to savings in labor costs and spare parts per repair.

Savings in operating costs (E) are obtained as the difference between the costs of scheduled repairs before (Epl1) and after (Epl2) the implementation of a condition-based repair system based on the results of in-depth diagnostics.

where N - the number of units being diagnosed;

Ccap1,2 - cost of major pump repairs;

Pcap1,2 - specific number of major repairs;

Cmed1,2 - cost of medium repair;

Pmed1,2 - specific number of medium repairs;

Crout1,2 - cost of routine repairs;

Prout1,2 - specific number of routine repairs.

Review Questions

1 What legal documents must be developed for carrying out technical diagnostics of electrical networks and electrical equipment?

2 What is meant by the criteria for the limiting state of electrical equipment?

3 What is meant by the rejection criteria for equipment under inspection?

4 What are the objectives of technical diagnostics?

5 List the indicators and characteristics of technical diagnostics.

6 What is meant by the characteristic of the nomenclature of diagnostic parameters?

7 How is the choice of the method for the technical diagnostics of equipment justified?

6 How is the choice of technical diagnostics tools made?

7 How are the rules for technical diagnostics developed?

8 How is the processing of technical diagnostics results carried out?

9 How is the metrological support of technical diagnostics results carried out?

10 On the basis of which regulatory and technical documents are the safety requirements for diagnostic processes developed?

11 How are the technical and economic performance indicators of the diagnostic system determined?