Types of tests and measurements of electrical equipment. Types of testing of electrical equipment
Checking, testing and adjustment of electrical equipment.
General information. Before carrying out measurements related to the adjustment or testing of devices, a set of preparatory measures must be performed:
a thorough examination of the tested object in order to identify and eliminate defects;
study of the electrical circuit and the establishment of standards for test voltages and currents
drawing up a measurement scheme indicating the necessary devices, their class, measurement limit, permissible insulation resistance, etc .;
providing the necessary conditions for measuring (temperature, humidity, surface cleanliness, lighting, etc.) and safe work performance;
preparation of the workplace and the necessary equipment in accordance with the measurement scheme.
When making high voltage measurements, special attention must be paid to the quality of the equipment connection to the ground loop, checking it visually or with an ohmmeter.
All work should be carried out in strict compliance with safety regulations.
Choice of instruments. Measuring instruments, depending on their purpose, scope and working conditions, should be selected according to the following basic principles:
it should be possible to measure the physical quantity under study;
the measurement limits of the instrument should cover all possible values of the measured quantity. With a large range of changes in the latter, it is advisable to use multi-limit devices;
the device must provide the required measurement accuracy. Therefore, attention should be paid not only to the class of the selected device, but also to factors affecting the additional measurement error (non-sinusoidality of currents and voltages, deviation of the position of the device when it is installed in a position other than normal, influence nie external magnetic and electric fields, etc.);
when carrying out some measurements, an important role is played by the efficiency (consumption) of the measuring device, its mass, dimensions, location of controls, uniformity of the scale, the ability to read readings directly on the scale, speed, etc .;
connecting the device should not significantly affect the operation of the device under study, therefore, when choosing devices, their internal resistance should be taken into account. When the measuring instrument is connected to matched circuits, the input or output resistances must be of the required nominal value;
the device must meet the general technical requirements for safety in the production of measurements, established (GOST 22261-76), as well as technical conditions or private standards;
it is not allowed to use devices: with obvious defects in the measuring system, case, etc.; expired verification; non-standard or not certified by the departmental metrological service; voltages that do not correspond to the insulation class to which the device is connected.
Determination of measurement error. The deviation of the measurement result from the true value of the measured quantity is called the measurement error.
The error inherent in the measuring instrument, which is under normal conditions of use (GOST 22261-76), is the main one. If one of the influencing quantities deviates beyond the limits set for the normal value or the range of normal values, additional errors appear. The limits of permissible basic and additional errors of measuring instruments are established in the form of absolute, reduced, relative errors or in the form of a certain number of divisions.
The absolute measurement error Δ is expressed in units of the measured quantity and is defined as the difference between the measured Hism. and the true values of the measured value X, i.e. Δ = Hizm. — X.
Due to the fact that the true value of the measured quantity is unknown, in practice they use the actual value of the quantity found experimentally and as close as possible to the true value.
The most complete measurement quality is characterized by a relative measurement error δ, equal to the ratio of the absolute measurement error to the true (actual) value of the measured quantity, X:
For a comparative assessment of the accuracy of pointer instruments, they use the concept of the reduced instrument error γ,% - the ratio of the absolute error to the limit value of the scale:
The value of Xk is taken equal to: the final value of the scale - for devices with a one-sided scale; the sum of the end values of the scale of the device - for devices with a two-sided scale; the difference between the final and initial values of the range - for devices with a non-zero scale; the length of the scale, if the scale has sharply tapering divisions.
Measuring instruments, the limits of permissible errors of which are expressed in the form of relative or reduced errors, (according to GOST 13600-68) are assigned accuracy classes selected from a series of numbers (1; 1.5; 2; 2.5; 3 ; 4; 5; 6).
For pointer devices, the accuracy class determines the maximum allowable value of the basic reduced measurement error. Knowing the accuracy class of the device, it is possible to determine the limit of the relative measurement error:
Often the value of the desired value A is determined indirectly from the results of several measurements related to the desired value by known dependencies. In this case, the relative error is determined as follows:
δ l \u003d (| A δa | + | B δv | + | C δc | + ..-) / L, where δ a, δv, δc are the relative errors in measuring the quantities B, C, B;
TYPES OF TESTING ELECTRICAL EQUIPMENT.
In the process of installation and after its completion, as well as under operating conditions, electrical equipment of electrical installations is checked, tested and adjusted.
Electrical equipment may be damaged during transport and installation. During operation, it may be damaged due to natural wear and tear, as well as structural defects.
Regulated requirements are imposed on the adjustment of electrical equipment, for compliance with which the following tests are carried out:
typical in accordance with the current GOSTs;
acceptance in accordance with the PUE, and in some cases with the instructions of the Ministry of Energy;
preventive and others in accordance with the Rules for the technical operation of power plants and networks (PTE), the scope and standards for testing electrical equipment and instructions for individual elements of electrical equipment.
Typical tests are carried out at manufacturing plants according to the programs and with the volumes specified in the standards and specifications, but in part they can be carried out at the installation site of electrical installations. During type tests, the compliance of electrical equipment with the requirements that are imposed on it by standards is checked.
Acceptance tests are carried out in newly constructed and reconstructed installations up to 500 kV. During tests, the compliance of the installed equipment with the project is revealed, the necessary characteristics are taken, and a certain amount of measurements are performed. After reviewing the test results, a conclusion is made on the suitability of the equipment for operation.
Preventive tests are carried out during the operation of the equipment, which allows you to expand the possibilities of detecting defects for the purpose of timely repair or replacement of equipment.
Test types
Acceptance tests carried out during the commissioning of equipment after installation or repair at the installation site. For electrical installations, they consist in setting up electrical equipment. Industrial production is distinguished by a variety of electrical installations that use modern automated electric drives with control stations, transformer substations, overhead and cable power lines, etc. Therefore, the scope and standards of acceptance tests provide for the necessary checks, measurements and tests for various types of electrical equipment that make up electrical installations, and determine the main criteria for the suitability of electrical equipment for operation.
These criteria can be divided into two types: absolute and relative.
Absolute the criteria clearly define the signs during verification and the values of physical quantities during measurements or tests, by which one can judge the suitability (or unsuitability) of the electrical equipment under test for operation.
The standards also provide absolute criteria for the state of insulation, contact connections, permissible temperatures of current-carrying parts and windings of electrical machines and apparatus, time characteristics of switches, etc.
relative criteria for the state of the equipment under test are based on the comparison of measurement data of certain electrical quantities during commissioning tests with measurement data of the same quantities obtained earlier, for example, during factory tests or based on a comparison of measurement data performed during commissioning on the same type of equipment.
Such criteria often have to be used when analyzing the characteristics of electrical machines, transformers, as well as when measuring insulation resistance.
The final conclusion on the possibility of putting the electrical installation into operation is given on the basis of its comprehensive testing in operation. When carrying out these tests, it is possible to identify and repair weakened parts of electrical equipment in a timely manner.
Preventive testing are carried out during the operation of electrical equipment according to the PPR schedule. Their volume and frequency are established by local regulations, depending on the conditions and mode of operation of the electrical equipment. Regular preventive tests prevent the occurrence of sudden damage and thus prevent possible interruptions in the continuity of the power supply. Thanks to the introduction of preventive tests, the accident rate of electrical equipment has been sharply reduced. Preventive tests allow you to more fully assess the condition of electrical equipment and its main elements: the mechanical part, the magnetic system, current-carrying parts with their contact connections and insulation.
Rejection tests - This is a fault finding of electrical equipment before repair.
operational tests, or inter-operational control (MOC), is carried out in the process of repairing electrical equipment.
Control tests performed after repair, regardless of its volume. The purpose of these tests is to establish the compliance of the technical data of electrical equipment and automation equipment produced after repair with passport data, repair specifications, standards, etc.
Type tests are carried out when changing the design, materials or manufacturing technology, if these changes can affect the characteristics of the machine and transformer, and, as a rule, include verification of the relevant parameters according to the acceptance test program.
These tests are intended to establish whether the actual data characterizing the design of the machine correspond to the data laid down during the design or obtained as a result of development studies.
The purpose of testing electrical equipment- checking compliance with the required technical characteristics, establishing the absence of defects, obtaining initial data for subsequent preventive tests, as well as studying the operation of the equipment. There are the following types of tests:
1) typical;
2) control;
3) acceptance;
4) operational;
5) special.
Type testing of new equipment, which differs from the existing design, materials or technological process adopted during its manufacture, are carried out by the manufacturer in order to verify compliance with all the requirements for this type of equipment by standards or specifications.
control tests each product (machine, apparatus, device, etc.) is subjected to upon release from the manufacturer to verify that the manufactured product complies with the basic technical requirements. Control tests are carried out according to a shortened (compared to standard tests) program.
acceptance tests upon completion of installation, all newly commissioned equipment is subjected to assess its suitability for operation.
Equipment in operation, including equipment that has been repaired, is subject to operational testing, the purpose of which is to check its serviceability. Operational tests are "during major and current repairs and preventive tests that are not related to the withdrawal of equipment for repair.
Special tests conducted for research and other purposes under special programs.
Programs (as well as norms and methods) of type and control tests installed by GOSTs for the corresponding equipment. The volume and norms of acceptance tests are determined by the "Rules for the installation of electrical installations". Operational tests are carried out in accordance with the "Electrical Equipment Testing Standards" and "Rules for the Technical Operation of Consumer Electrical Installations". In the process of acceptance and operational tests, it is necessary to additionally take into account the requirements of factory and departmental instructions.
A certain part of the test work is common when setting up various elements of electrical installations. Such works include checking electrical connection diagrams, checking and testing insulation, etc.
Checking wiring diagrams
Checking the wiring diagrams includes:
1) familiarization with the design switching diagrams, both in principle (complete), and installation, as well as the cable magazine;
2) verification of compliance of the installed equipment and apparatus with the project;
3) inspection and verification of the compliance of the installed wires and cables (brand, material, section, etc.) with the project and the current rules;
4) checking the presence and correctness of the marking on the terminations of wires and cable cores, terminal blocks, terminals of devices;
5) checking the quality of installation (reliability of contact connections, laying wires on panels, laying cables, etc.);
6) checking the correct installation of circuits (continuity);
7) checking the schemes of electric circuits under voltage.
The circuits of primary and secondary switching are checked in full during acceptance tests after the installation of the electrical installation is completed. With preventive tests, the amount of commutation verification is significantly reduced. Installation errors or other deviations from the project found during the verification process are eliminated by adjusters or installers (depending on the volume and nature of the work). Fundamental changes and deviations from the project are allowed only after their coordination with the design organization. All changes must be shown on the drawings.