RU2818190C1 - Method of testing for seismic resistance of electric cable - Google Patents

Abstract

FIELD: cable industry.

SUBSTANCE: invention relates to the cable industry and concerns earthquake resistance testing of electric cables. Method consists in the fact that seismic resistance of electric cable products is checked in accordance with specified modes of action. During the tests, the parameters of the validity criteria are monitored: functioning before, during and after the tests (absence of wire breakage); preservation of integrity of the shell after tests (absence of visible external damages, ruptures or cracks); resistance of insulation to effect of test voltage after tests (absence of insulation breakdown); insulation resistance before and after tests (if necessary). According to the disclosed method, a sequence of modes is set for the vibration table, which includes frequency, amplitude and duration of exposure at each frequency of at least one minute, depending on the required service life of the cable. A sample of the tested cable is obtained and fixed in the tooling of the vibration table so that a section of the cable with a length of at least one meter is subjected to tests, wherein the tooling is made in the form of an angular structure with an angle between planes of 90°±10°, providing attachment to it by clamps of tested section of cable with two straight sections perpendicular to each other, which makes it possible to take into account the effect of longitudinal and transverse waves. Further, the sample is exposed to a given sequence of operating modes of the vibration table and the validity criteria are monitored after the tests, the values of which are used to make a conclusion on the validity of the cable.

EFFECT: possibility of checking electrical cable products for effect of earthquakes.

4 cl, 1 dwg

Description

State of the art

From the state of the art, methods for testing optical cables for seismic resistance are known, disclosed in MI 16.00-186-2012 and three patents: RF patent No. 2617638; RF patent No. 2607729; RF patent No. 2617793.

These methods focus specifically on testing optical cable products with optical fibers as a transmitting element. These methods are not suitable for cables that have a copper conductor as a current-carrying core, due to the fact that optical fibers have worse mechanical properties and require a more careful approach to monitoring the parameters of suitability criteria during operation and testing. Moreover, methods for installing cables with copper conductors are simpler and do not require such complex options for installing cable products during seismic testing as in optical communication cables.

The essence of the invention

The invention solves the problem of simplifying the testing of cable products for resistance to seismic influences.

The invention provides the following technical results: increasing the simplicity and creating a universal method for testing the seismic resistance of cable products of any type with current-carrying conductors.

The specified technical results are achieved by the fact that the method of testing the seismic resistance of an electric cable is as follows:

- as acceptance criteria, the values of the following parameters are taken: preservation of the functionality of the sample, integrity of the sample shell, resistance of the sample insulation, electrical resistance of the sample insulation;

- set a sequence of modes for the vibration stand, including frequency, amplitude and duration of exposure at each frequency of at least one minute, depending on the required service life of the cable;

- obtain a sample of the cable being tested and fix it in the vibration stand equipment so that a cable section with a length of at least one meter is subjected to testing, while providing a test cable section with two straight sections perpendicular to each other;

- influence the sample with a given sequence of operating modes of the vibration stand;

- monitor the suitability criteria after completion of the tests, based on the values of which conclusions are drawn about the suitability of the cable.

Parts of the cable sample being tested on opposite sides of the vibration stand are wound into coils or wound onto drums with an internal diameter of at least 20 times the nominal outer diameter of the cable.

They provide the vibration stand operating mode using the swing frequency method in one direction.

They provide the vibration stand operating mode using the fixed frequency method.

A distinctive feature of this method is that seismic resistance tests are carried out using special equipment, which allows one to take into account the effects of longitudinal and transverse waves characteristic of an earthquake.

List of drawing figures

Figure 1 shows a diagram of fastening a cable sample in the equipment for testing for seismic resistance

Carrying out the invention

The following set of parameters is accepted as criteria for the suitability of the cable under test: functioning before, during and after testing (no wire breakage); maintaining the integrity of the shell after testing (no visible external damage, ruptures or cracks); insulation resistance to test voltage after testing (no insulation breakdown); insulation resistance before and after testing (values in accordance with the technical specifications and normative documents for specific cable products, if necessary and additionally agreed upon).

Tests simulating the conditions of exposure to seismic waves under various cable laying conditions consist of a vibration stand platform, equipment for testing seismic resistance with an angle between planes of 90°± 10°.

The diagram for fastening the cable sample in the equipment for testing for seismic resistance is shown in Figure 1, which shows:

1 – Equipment for seismic resistance tests (angle between planes 90°± 10°); 2 – Sample of the cable product under test; 3 – Vibration stand platform; 4 – Clamps (cable ties); 5 – Connector; 6 – Control equipment (multimeter).

The effects created by the vibration stand simulate seismic conditions for laying cables under the influence of an earthquake with an intensity of 9 points according to MSK-64 at an installation level above the zero mark of up to 70 m in accordance with GOST 30546.1-98.

Set a sequence of modes for the vibration stand, including frequency, amplitude and duration of exposure at each frequency of at least one minute, depending on the required service life of the cable.

For cables with a service life of at least 60 years, it is advisable to adhere to the values of the setting modes of vibration stands for testing the seismic effects of cable products indicated in the table below.

Frequency Hz. 5 6 7 8 9 10 12.5 16 20 25 thirty Oscillation acceleration amplitude, m/s ² 6.88 6.88 6.88 6.88 6.88 6.88 6.19 5.5 4.68 3.44 2.75

For cables with a service life of at least 50 years for the same frequency sequence, the amplitude values should be reduced by 8-10 percent.

A sample of the cable being tested is obtained and secured in the vibration stand equipment so that a cable section with a length of at least one meter is subjected to testing, while providing a test cable section with two straight sections perpendicular to each other.

The equipment is placed on the vibration stand platform so that the cable laying plane (two sections connected at right angles) is perpendicular to the vibration stand platform.

Next, the sample is exposed to a given sequence of operating modes of the vibration stand and the validity criteria are monitored after completion of the tests, based on the values of which conclusions are drawn about the suitability of the cable.

The cable is considered to have passed the seismic resistance test if:

- during testing, the functioning of the cable is not disrupted;

- after the impacts, during external examination, no visible damage, ruptures or cracks were found on the surface of the samples;

- there is no insulation breakdown when testing with alternating test voltage;

- the insulation resistance value corresponds to the value given in the specifications for the specific cable products being tested.

Claims (8)

1. A method for testing the seismic resistance of an electric cable, which consists in taking the values of the following parameters as acceptance criteria: maintaining the functionality of the sample, the integrity of the sample shell, the resistance of the sample insulation, the electrical resistance of the sample insulation; - set a sequence of modes for the vibration stand, including frequency, amplitude and duration of exposure at each frequency of at least one minute, depending on the required service life of the cable; - obtain a sample of the cable under test and fix it in the vibration stand equipment so that a cable section with a length of at least one meter is subjected to testing, while the equipment is made in the form of an angular structure with an angle between the planes of 90°±10°, ensuring that the tested cable section is attached to it with clamps with two straight sections perpendicular to each other, which allows taking into account the effects of longitudinal and transverse waves, - influence the sample with a given sequence of operating modes of the vibration stand; - monitor the suitability criteria after completion of the tests, based on the values of which conclusions are drawn about the suitability of the cable. 2. The method according to claim 1, characterized in that parts of the cable sample being tested on opposite sides of the vibration stand are wound into coils or wound onto drums with an internal diameter of at least 20 nominal outer diameters of the cable. 3. The method according to claim 1, characterized in that the vibration stand operates using the swing frequency method in one direction. 4. The method according to claim 1, characterized in that the vibration stand operates using the fixed frequency method.