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§ 9. Terms and standards for testing electrical equipment
Every phase electrical wires, busbars, cables, windings and contacts of electrical devices must be carefully insulated from one another and from grounding structures. However, over time, during the operation of electrical equipment, the dielectric characteristics of the insulation change. The aging of insulation is affected by the heating temperature of the conductors and the outside air, room humidity, switching overvoltages that occur in electrical circuits with inductive and capacitive elements, duration of operation, etc. Such insulation sometimes does not withstand even rated voltages, as a result of which electrical breakdown occurs.
Therefore, in order to ensure that electrical equipment and devices do not fail due to the fact that their insulation resistance is lower permissible norm, and also to electrical networks no short circuits occurred due to electrical breakdowns of insulation, all types of insulation are checked and tested within certain periods in accordance with the "Rules technical operation power stations and networks."
These tests are carried out, as a rule, at current and major repairs electrical equipment. In addition, between-repairs, i.e., preventive tests are carried out, which make it possible to identify problems that have arisen during the installation or operation of equipment or cable lines defects, which makes it possible to eliminate these defects in a timely manner, prevent an accident or prevent a reduction in the supply of electricity to consumers.
For each equipment, devices and networks, there are insulation resistance standards, which are established by the “Rules for Electrical Installations”.
To determine the insulation condition, two methods are used: measuring the resistance of a given section of an electrical installation or apparatus using a megohmmeter or checking the insulation condition with an increased, strictly standardized voltage.
Rice. 46. Megaohmmeter:
A - general form, b- simplified diagram: 1
- frame, 2
- inductor
When measuring insulation resistance with a megaohmmeter (Fig. 46), the arrow on its scale shows the insulation resistance of the device or section or circuit being tested. Framework 1
magnetoelectric system is powered by current from an inductor 2
, rotated by hand. When the clamps X1 And X2 open, current passes only through the frame with the additional resistor R2 and the moving part of the magnetoelectric system is installed in one of its extreme positions with the sign , which indicates an infinitely large resistance. If you close the clamps X1 And X2, the current will flow through the second frame with an additional resistor R1. In this case, the moving system will be installed in another extreme position, marked “0” on the scale, i.e., the measured resistance will be zero. When connecting the measured resistance Rx to the clamps X1 And X2 the moving system will be installed in an intermediate position between and 0 and the arrow on the scale will indicate the value of this resistance. The megohmmeter scale is calibrated in kiloohms and megohms: 1 kOhm = 1000 Ohms; 1 MΩ = 1000 kΩ. Inductor DC generators with manual drive from the handle.
The voltage at the external terminals of the generator depends on the speed of rotation of the handle. To smooth out oscillations during rotation, a centrifugal regulator is built into the drive.
The rated rotation speed of the megohmmeter generator is 2 rpm or 120 rpm.
To connect the megohmmeter, use PVL connecting wires with moisture-resistant insulation, otherwise the megohmmeter readings may be significantly distorted.
Megaohmmeters are produced with rated terminal voltages: Ml 101M - 500 and 1000 V, MS-05 - 2500 V.
When measuring the insulation resistance of long cable lines and windings electric machines and transformers, the megohmmeter readings at the beginning of the rotation of the handle decrease sharply. This is explained by the presence of significant capacity in cable lines and electrical machines through which the charging current passes. Therefore, in such cases, when using a megohmmeter to measure insulation resistance, the device readings are taken only after 60 s. from the moment the handle begins to rotate.
Touching the circuit being measured while rotating the handle of a megohmmeter connected to the circuit is dangerous and may result in electric shock. Therefore, when taking measurements, the necessary safety measures are taken to prevent people from touching electrical circuits.
In large capacity installations (long cable lines, transformers high power) the measured circuit can acquire significant electric charge. Therefore, after removing the voltage from the megohmmeter, such circuits are discharged using a flexible copper wire to ground using an insulating rod to connect to each of its phases. In installations with voltages above 1000 V, cables and large machines are discharged in dielectric gloves and galoshes.
For insulation testing increased voltage use various devices for straightening and alternating current.
Most often, when testing insulation, a kenotron installation is used, circuit diagram which is shown in Fig. 47, a. It is mounted in the body of a car and has its own source of electricity. The positive pole of the kenotron lamp (anode) is grounded, and the negative pole (cathode) is connected to one of the phases of the electrical installation under test (for example, a cable), while the other two phases and the shell are grounded (Fig. 47, b).
Kenotron insulation tester KII-70 is a unit consisting of a mobile control panel and a kenotron attachment. It is designed for testing solid liquid dielectrics with DC voltages up to 70 kV. The test voltage is changed from 0 to 70 kV using a regulator with an additional winding to power the signal lamp circuit.
The kenotron attachment consists of a transformer and a kenotron placed in a bakelite cylinder filled with transformer oil. At the top of the console there is a three-limit microammeter with a scale of 200, 1000 and 5000 μA and a limit switch designed to measure leakage currents. The attachment has terminals for connecting high-voltage DC circuits and the object being tested. In addition, the device is equipped with an overcurrent protection device with two settings: coarse and sensitive. 
Rice. 47. Schemes of kenotron installation:
A- principled, b- testing cables with lead sheath; 1
- kenotron lamp, 2
- filament transformer, 3
- heat switch, 4
- power switch, 5
- power switch, 6
- control transformer, 7
- contactor, 8
- test transformer, 9
- cable cores, 10
- cable sheath
on the higher voltage side of the tester, while it does not operate in the minute power mode at a voltage of 50 kV.
A sensitive setting switches off the device when short circuit on the high voltage side of the transformer. In this case, the protection should not operate at a voltage of 70 kV and secondary current 5 mA.
On the cover of the tester's control panel there is an overcurrent protection device and a switch maximum protection, signal lamp, kilovoltmeter.
For direct current testing, the kenotron attachment is installed on the hinged door of the control panel and the tested object is connected to it. Using a regulator, voltage is supplied to the control panel, gradually increasing it to the test value. The voltage is controlled on the scale of the device, calibrated in kilovolts (maximum). At the last minute of the test time, the leakage current is measured using a microammeter.
Testing with alternating current of industrial frequency is carried out by connecting the test object to the alternating current terminal, after which the voltage is raised by the regulator to the test voltage. Voltage control is carried out on a kilovoltmeter scale, calibrated in kilovolts.
During testing, the voltage is gradually raised to the test voltage and maintained unchanged throughout the entire test period. The test time is determined by the “Rules for the technical operation of consumer electrical installations and safety rules for the operation of consumer electrical installations” for each type of equipment, apparatus and networks and ranges from 1 to 10 minutes.
During a major overhaul distribution devices voltage up to 1 kV, which is carried out once every 3 years, the insulation resistance of elements of drives of switches, disconnectors, secondary circuits of equipment, power and lighting wiring is tested with an industrial frequency voltage of 1 kV for 1 min or with a megohmmeter with a voltage of 1000 V. When measuring the insulation resistance in electrical receivers, devices and devices must be turned off in power circuits, and in lighting networks- lamps are turned out, disconnected plug sockets switches, group panels from electrical receivers.
Smallest valid values The insulation resistance of secondary control circuits, protection, alarm relay circuits, power and lighting wiring, switchgears, switchboards and conductors with voltages up to 1000 V is 0.5 MOhm, and the operating current buses and voltage circuit buses on the control panel are 10 MOhm.
An increased voltage of 1000 V is tested for 1 min. secondary circuits protection, control, alarm circuits with all connected devices (drive coils, automatic machines, magnetic starters, contactors, relays, etc.). The insulation resistance of the battery after its installation must be no less than:
Measurement of loads and voltage at control points of the lighting network is carried out once a year; insulation resistance of portable transformers with secondary voltage 12 - 42 V are tested once every 3 months, and stationary - once a year.
Switches, disconnectors, grounding blades, short circuits, separators and their drives are tested at least once every 3 years, simultaneously with major repairs. The lowest permissible resistance values of the supporting insulation, measured with a megohmmeter for a voltage of 2.5 kV, at rated voltage up to 15 kV are 1000 MOhm and over 20 kV - 5000 MOhm. Testing of this insulation of switches with voltages up to 35 kV with increased voltage of industrial frequency is carried out within 1 minute. Contact resistance is measured at the same time DC, which is for: VMG-133 (1000 A) - 75 μOhm; VMP-10 (1000 A) - 40 μOhm; VMP-10 (1500 A) - 30 μOhm; VMP-10 (600 A) - 55 μOhm.
The insulation resistance of suspended and multi-element insulators is measured with a megohmmeter for a voltage of 2.5 kV only at positive ambient temperatures, and the insulation resistance of each suspended insulator or element of a pin insulator must be at least 300 MOhm.
Testing with increased power frequency voltage of newly installed multi-element support and suspension insulators is carried out with a voltage of 50 kV. Each element of a ceramic insulator is tested for 1 minute, of organic material - 5 minutes. Support single-element insulators of internal and outdoor installations tested at the increased voltage indicated in table. 24, for 1 min.
Table 4. Test voltage of support single-element insulators, kV
Pin insulators of bus bridges with a voltage of 6 - 10 kV, support and suspension porcelain disc insulators, as well as contact connections of busbars and connections to equipment in the absence of temperature indicators are tested once every 3 years. Testing the insulation resistance of bushings and bushings is carried out with a megohmmeter at a voltage of 1000 - 2500 V for bushings with paper-oil insulation. The insulation resistance must be at least 1000 MOhm. Insulators of bushings and bushings with voltages up to 35 kV are tested with increased voltage, the value of which is indicated in table. 5.
Measuring the insulation resistance of moving and guiding parts made of organic materials, oil switches of all voltage classes are made with a megohmmeter for a voltage of 2500 V. Moreover, the lowest permissible insulation resistance must be no less than: for voltages up to 10 kV - 1000 MOhm, from 15 to 150 kV - 3000 MOhm.
Table 5. Test voltage of bushings and bushings
Testing the insulation of oil switches with voltages up to 35 kV at high power frequency voltage is carried out within 1 minute. The test voltage is taken in accordance with the data in table. 6.
Table 6. Test voltage of external insulation of oil switches
The DC resistance of oil switch contacts should not differ from the manufacturer's data.
When testing oil switches, their speed and time characteristics are also subject to verification. These measurements are made for switches of all voltage classes. The measured characteristics must correspond to the manufacturer's data.
After repair, winding insulation power transformers together with the inputs, they are subjected to tests with increased alternating current voltage with an industrial frequency of 50 Hz. The test voltage depends on the type of repair and the scope of work (with or without changing the transformer windings).
The insulation of each winding, not electrically connected to the other, is tested separately.
The test voltage values at an industrial current frequency of 50 Hz are indicated in table. 7.
Table 7. Test voltage of insulation of windings together with inputs, kV
The test results are recorded in the protocol. This data is necessary to compare the results obtained with the results of previous tests carried out at various times before this repair.
Tests of transformers after repair are carried out throughout the entire program and to the extent provided for by the current rules and regulations.
During preventive tests, the insulation of the windings of power transformers is tested with increased power frequency voltage in accordance with Table. 8 for 1 min.
Table 8. Test voltages internal insulation oil-filled transformers
The DC winding resistance is measured on all branches and may differ by no more than 2% from the manufacturer's data.
The transformation ratio of the transformer is checked at all switching stages. Permissible deviations may be no more than 2% of the values obtained on the same branch on other phases, or from the manufacturer’s data.
The minimum breakdown voltage of the oil, determined in a standard vessel before pouring into transformers and insulators, for voltages up to 15 kV should be 30 kV, and from 15 to 35 kV - 35 kV.
For fresh oil, before filling a newly commissioned transformer, a complete chemical analysis is carried out according to a special program.
Measurement of the insulation resistance of leads and rods made of organic materials is carried out with a megohmmeter for a voltage of 2500 V. Minimum permissible resistance insulation from organic materials at a rated voltage of up to 10 kV should be 1000 MOhm, at a voltage from 15 to 150 kV - 3000 MOhm.
The insulation resistance of the primary windings of instrument transformers is measured with a megohmmeter for a voltage of 2500 V, and of the secondary windings - for 500 or 1000 V. The insulation resistance of the primary winding is not standardized, and the resistance of the secondary winding together with the circuits connected to it must be at least 1 MOhm.
Depending on the insulation resistance of the primary windings of current and voltage transformers up to 35 kV, the test is carried out at the following test voltage values. If the insulation resistance is designed for a voltage of 6 kV, the test voltage is taken equal to 28.8 kV, for a voltage of 10 kV - 37.8 kV, for a voltage of 20 kV - 58.5 kV.
The duration of application of the test voltage for the primary windings of instrument transformers is 1 min. Only for current transformers with insulation made of hard ceramic materials or cable masses, the duration of application of the test voltage is 5 minutes.
For dry reactors, the insulation resistance of the windings relative to the fastening bolts is measured with a megohmmeter for a voltage of 1000 - 2500 V. Its value must be at least 0.5 MOhm.
Porcelain insulation of the reactor, as well as fuses above 1000 V, is tested with increased power frequency voltage for 1 minute with the following test voltage values: at a rated voltage of 6 kV - 32 kV, at 10 kV - 42 kV, at 20 kV - 65 kV.
The insulation resistance of power cable lines is measured with a megohmmeter for a voltage of 2500 V. In Fig. Figure 48 shows a diagram for connecting a megohmmeter when measuring cable resistance. For power cable lines with voltages up to 1000 V, the insulation resistance must be at least 0.5 MOhm, and for voltages above 1000 V, the insulation resistance is not standardized. Measurements with a megohmmeter should be made before and after testing the cable with increased voltage. Power cables voltages above 1000 V are tested with increased rectified current voltage.
Test voltages and the duration of their application are given in table. 9.
Data from all tests and measurements are recorded in the electrical equipment test log and in test and measurement reports.
Table 9. Rectified current test voltages for power cables
Rice. 48. Diagram for connecting a megohmmeter when measuring cable resistance
A- circuit for measuring insulation relative to ground, b- circuit in the presence of surface leakage currents, V- measurement of insulation between cores, 1 2 - cable
This data is used for comparison in subsequent tests and measurements. They make it possible to analyze the condition and performance of equipment, plan the time for necessary repairs to increase the insulation resistance or reduce leakage currents and thus increase the operating time of the equipment in trouble-free mode.
Today, electrical equipment testing is one of the important parts checks modern production- industrial facility.
The frequency of testing electrical equipment depends on the power of the device, its features, purpose, and level of wear during operation. In most cases, the frequency is set depending on the power - the more powerful device, the more often it is necessary to check it for operability and absence of breakdowns.
Electrical equipment testing, which occurs every few years, includes a whole range of activities, several tests, each of which is designed to check one or a group of parameters.
Types of electrical equipment inspections
Modern types of electrical equipment testing include:
- check temperature regime, compliance of real indicators with maximum permissible standards;
- checking for breakdowns or malfunctions;
- high voltage testing, which can be used to identify even minor defects, which only in the future can develop into major breakdowns;
- checks may differ in other parameters.
Other parameters include a check that is carried out in connection with the device undergoing repairs, or during the first start-up (commissioning).
The electrical testing program may vary significantly depending on the type of test itself. For example, checking the insulation integrity does not imply any work other than testing the device in this area.
At the same time, testing and inspection using a thermal imager will allow you to detect defects both in the device itself and in the cables connected to it.
Tests and measurements of electrical equipment vary, so if the owner begins to doubt the serviceability of his device, he should determine the type of failure in order to order necessary tests. But in most cases, specialists called to the site are themselves able to determine what kind of breakdown there may be and what method it can be installed and identified.
Testing times for electrical equipment
In terms of speed, electrical testing times vary depending on the type of device being tested and the test method chosen. For example, measurements taken during a malfunction take longer than regular, scheduled, periodic ones.
The time frame for checking electrical equipment at an enterprise is usually very tight, since the inspectors themselves have a good idea of what the downtime of an industrial facility threatens, and that is why specialists try to complete their work as quickly as possible.
Who to contact for quality testing of electrical equipment
If you need to find people who offer to carry out preventive testing of electrical equipment up to 1000 V or higher, then you should contact specialized companies for which the provision of such services is their main focus. But before you turn to a company for a service, you should make sure that it has the right to perform such checks.
If a logical question arises - who grants permission to test electrical equipment, then the easiest way is to request the relevant documents from the testing company itself. The potential customer must be presented with permits from Rostechnadzor, as well as employee certificates of professional certification.
If there are no such documents, then any operational tests of electrical equipment, as well as preventive ones, will be considered invalid, and the results of such testing government agencies will not be taken into account. Consequently, the owner of the equipment will have to look for a new contractor who can carry out the inspection, this time issuing the necessary documents.
"StandardService" has all permissions to provide such services. These include preventive and regular testing of electrical equipment.
We offer inter-repair testing of electrical equipment, and can also carry out direct repairs, having previously identified faults.
We offer our customers high-voltage testing of electrical equipment, testing, and much more.
At the same time, we offer our services for affordable prices, we promptly go to sites, carry out testing, inspections and tests in a compressed, record-breaking manner short time, without loss of quality.
It will be convenient for the customer that it is from us, in one company, that you can order inspection and testing of equipment and installations, check the enterprise network, and conduct cable tests.
Our specialists offer their services to both business owners and owners of private, country, or apartment buildings.
Electrical equipment is regularly tested, which pursue the goals of checking compliance with established technical specifications, obtaining data for carrying out the following preventive tests, establishing the absence of defects, as well as for studying the operation of electrical equipment. The following types of tests are distinguished: operational, acceptance, control, standard, special.
Type tests are used for new equipment, which differs from old models in its updated design and device. This type of test is carried out by the manufacturer in order to verify compliance with all requirements and standards that apply to this type equipment or technical conditions.
To check the compliance of the manufactured product with all the main technical requirements, each product is subjected to control tests (apparatus, machine, instrument, etc.). To carry out control tests, as a rule, a reduced work program is used (compared to standard ones).
Acceptance tests used after completion of installation of newly commissioned equipment in order to assess its suitability for operation.
Performance tests are carried out for equipment in operation, including those that have undergone repair. This type of test is used to determine the serviceability of the equipment. Operational tests include tests during current and major repairs, as well as preventive tests that are not related to the removal of equipment for repair.
For research purposes or other special programs, special tests may be carried out.
Some part test work is performed similarly for almost all elements of electrical equipment. These types of work include: testing and checking insulation, monitoring circuits electrical connections.
When checking electrical connection diagrams, the following actions are carried out:
1) familiarization with technical information on the facility - installation and fundamental (complete) switching diagrams, cable log are studied;
2) checking for compliance with the design of real equipment and equipment;
3) checking and inspecting the compliance of cables and wires (section, material, brand, etc.) current rules and the project;
4) control of the correctness and presence of markings on cable cores and wires, device terminals, terminal blocks;
5) installation quality control (cable laying, cable laying on panels, reliability contact connections and so on.);
6) continuity testing (monitoring the correct installation of circuits);
7) reliability test electrical diagrams when submitting .
Most full tests in primary and secondary switching circuits are carried out during acceptance tests after completion of installation of electrical equipment. During maintenance tests, the number of switching control operations is significantly reduced. Installers or adjusters must eliminate deviations from the design or installation errors discovered during the inspection. In order to change or deviate from the project, you must first obtain consent design organization. Any such changes must be provided in the form of drawings.
Before putting an electrical installation or electrical equipment into operation, it is necessary to carry out control tests of the electrical installation, which make it possible to identify possible defects. In addition to identifying defects during control tests, it is possible to obtain data that is necessary for carrying out preventive inspections and for checking the compliance of an installation or equipment with its technical characteristics and standards prescribed in technical regulations approved at the legislative level. Control tests of the electrical installation must be carried out by specialists from an electrical measuring laboratory that has a certificate of registration with Rostekhnadzor.
Control tests of the electrical installation by our electrical laboratory.
Our company has repeatedly carried out control tests of electrical installations and has an accurate measuring equipment and uses modern techniques in his work. This allows our specialists to carry out control tests of electrical installations efficiently and quickly. When our electrical measuring laboratory detects faults and defects, we help control the process and quality of their elimination.
There are certain requirements when conducting control tests. These requirements are specified in the PUE and PTEEP. Among the requirements, it is worth talking separately about established deadlines such tests, since there is an obligation for organizations to conduct control tests of all existing electrical equipment at certain intervals. For example, electrical networks located in particularly hazardous areas are checked at least once a year. Other cases require such tests to be carried out once every 3 years. Elevator equipment and cranes must be inspected annually. Electric stoves are subject to control tests only in a heated state and at least once a year. For other electrical installations and electrical equipment, control tests are carried out within the time limits established technical manager Consumer. depend on the type of equipment being examined.
Control tests of electrical installations are the basis for operational safety.
The safety and reliability of electrical installations and equipment directly depends not only on compliance technical requirements and norms, but also from regular checks. Due to the existence of strict requirements imposed by supervisory authorities, the safest operation of the facility is ensured. To ensure people are protected from injury electric shock, safety of the equipment itself and ensuring fire safety At the facility itself, control tests of insulating materials of current-carrying elements and equipment components should also be regularly carried out.