Electrical insulation is the most important means to ensure the safety of working with electrical installations and their smooth operation. The action of alternating current, not exceeding 0.5 mA, is almost imperceptible to the human body. According to current standards, an alternating current with a frequency of fifty hertz, flowing through the human body, should not exceed the value of 03 mA. Therefore, the systematic measurement of insulation resistance is a necessary measure designed to ensure electrical safety when working with high voltage equipment.
The most important characteristic of the insulation coating in this aspect is the indicator of its electrical resistance. In high voltage electrical installations, several different types of insulation are used. The working cover is designed to ensure the normal functioning of the unit. It is selected taking into account the technical features of each electrical installation. Therefore, regular measurement of insulation resistance of this type is necessary to control the integrity of the coating, which ensures the normal performance of the equipment.
Additional insulation, performing a purely protective function, is intended to exclude even the slightest likelihood of electric shock in the event of any damage to the main coating. Measurement of insulation resistance of this type is key in terms of safe operation with electrical installations.
In addition, some types of electrical equipment use double insulation, which is a combination of the above two types of coating. A feature of this combination is that the parts of the unit that are accessible to touch will not get dangerous voltage even if one of the insulating layers (working or additional) is damaged. Measurement of the insulation resistance of this type is reduced to monitoring the overall integrity of the shell and each of its components separately.
The need for regular monitoring and control measures is due to factors that worsen the condition of the insulation coating and contribute to its degradation. Such detrimental factors are, first of all, injuries of an electrical and mechanical nature; the influence of aggressive chemical compounds, which is not uncommon in industrial production; thermal damage.
A device for measuring insulation resistance is called a megaohmmeter. This device is intended not only for measuring the resistance of an insulating material, but also for checking its electrical strength (in other words, a test for the absence of electrical breakdowns). Before testing, electrical equipment must be de-energized. The very method of measuring the insulation resistance of electrical installations consists in the formation in the bowels of the device through a special built-in electromechanical DC generator of a certain control voltage, which is applied to the test object. In this case, the measuring voltage must exceed a similar indicator of the electrical network.