Today, human life is very uncomfortable without electrical appliances. And all devices, as you know, are powered by electrical networks. In order for the devices to work perfectly, they must measure the insulation resistance.
Content
- Electrical resistance tests
- Insulation resistance measurements
- Control process
Measurements are carried out not only in old houses, but also in new buildings. This work prevents an accident that can occur due to deteriorated material.
Electrical resistance tests
Workers who test electrical resistance in cable insulation have certain skills and experience that allow them to carry out such measurements competently and in a short time. To make the necessary measurements, be sure to turn off the power in the networks and remove the load from them. Insulation resistance test is carried out alternately between all transmitter threads.
If the readings are low, remedial action is taken immediately. Malfunctions can occur for various reasons:
- violation of wire insulation;
- breakage of the cable;
- poor insulation of cable glands in the ground;
- violation of insulation with screws;
- installation error.
Only enterprises that have the appropriate documents from the electrical laboratory (ETL) for admission to work of increased danger have the right to engage in such work. The devices used for research are necessarily verified in the centers of standardization.
Insulation resistance measurements
The terms for diagnosing the insulating resistance are established by the Rules for the technical operation of electrical installations of consumers (PTEEP).
Once a year:
- in more dangerous places;
- lifting mechanisms of elevators and electric hoists;
- fixed electric stoves.
1 time in 3 years:
- in other cases.
In healthcare organizations, the terms are set by GOST, which was approved by the Federal Agency for Technical Regulation and Metrology of December 27, 2006 No. 413.
Once a year:
- emergency power supply;
- insulation resistance;
- phase "zero";
- visual inspection of electrical installations;
- the structure of balancing the capabilities of the charges;
- measurements in AC circuit breakers;
- measuring electric current in devices of the Department of Education (schools, kindergartens, nurseries, etc.).
1 time in 3 years:
- a system for balancing the potentials and capabilities of charges;
- measurement of electricity leakage in transformers of a medical structure.
Control process
Other studies of cable resistance are determined by the PPR system - scheduled preventive maintenance, established by the Rules for Technical Electrical Operation by Consumers (PTEEP). In the process of monitoring, they measure the resistance of the cable insulation, draw up an act of measuring the electrical resistance of the insulation, which is stored in the electrical laboratory for 5 years.
With constant measurements of electrical resistance, it is easy to identify faults in the insulation and make timely corrections in the power line. By checking the resistance of the insulating layer, deviations from the norms can be determined. Immediate correction of faults helps to avoid short circuits in the electrical circuit and, as a result, fire in buildings. Prompt actions will be able to prevent the negative consequences of the accident and save the health and lives of people.
To measure large values of resistance in cables, a device is used megohmmeter. Such a device generates from 100 to 2500 volts. The old-style megohmmeter works on the principle of a dynamo. Modern cars, on the other hand, are electronic devices and run on batteries. Most often, the measurement of the insulation resistance with a megohmmeter is carried out at a high resistance.
To carry out studies of insulation resistance with a megohmmeter, a permit for special work is required. Measurements of the electrical resistance of the insulating layer are made by highly qualified personnel from a special-purpose electrical laboratory.
Carrying out measurements is the connection of the terminals of the megohmmeter to the strands of cables with the supply of high currents.
When investigations are carried out in cables or wires, the loads must be disconnected. The electrical resistance of the insulation is determined according to Ohm's law. But the electrical resistance of insulation cannot be called a stable measure. To a greater extent, this depends on the temperature and humidity in the air or in the ground. Measurement of the electrical resistance of the insulating layer of wires running in the ground must be carried out during the highest soil moisture. The norms are specified in PTEEP and PUE.
A megohmmeter is used to measure the electrical resistance of the insulating properties of cables exposed to the external environment. Due to its influence, the operation in electrical appliances deteriorates, therefore a short circuit may occur. The megohmmeter is arranged as follows:
-
electric generator; - indicator;
- toggle switch;
- resistance;
- checking the integrity of the motor electrical winding.
An accurate determination of all existing defects in the wiring is possible only after a certain time has elapsed from the beginning of the study. Before starting the test, the required voltage is set on the megohmmeter and the test begins. Check the chain and the unit itself.
