Measurement of insulation resistance megohmmeter
The reliability and functionality of the systems for supplying construction objects with electricity is always determined by the quality of the resistance of insulating materials. Every master should know about such important properties of equipment. According to the existing rules for the operation of electrical appliances, from time to time, their verification is necessary. Insulation resistance measurement is always carried out using a megohm meter.
What affects the quality of insulation?
The period of use of electrical cables, as well as their coverage is not infinite. The quality of the insulation can be influenced by factors such as natural light, increased voltage, differences in temperature, difficult to determine damage, as well as the environment in which the wiring is used.
What is it for?
Measurement of insulation resistance by a megohm meter is required for the most accurate determination of possible damage in an electrical circuit.The choice of the rated current depends on the voltage applied to the winding.
Measurement of insulation resistance is needed to test its functionality. As a result of detecting damage to the coating of wires, undesirable malfunctions in the operation of equipment can occur, as well as flammable situations. After the visual identification of insulation wiring defects, you can not call a specialist measurer. If in time to detect the difference in the megohm meter from the set values, you can prevent a variety of accidents, premature wear of equipment, circuits, fire, as well as injuries among service personnel.
The necessary conditions
Measurement of the insulation resistance of the cable is carried out indoors at permissible temperatures from +15 to +35 ° C. At the same time, air humidity should not exceed 80%. These are standard conditions that may vary depending on the technology of manufacturing devices. The data of electrical resistance in measuring circuits must exceed the permissible value by at least 20 times.
What devices are used?
Measurement of electrical insulation resistance can be performed by devices of various configurations.They must be in working order and have documents confirming their quality. Bodies of the State Standard regularly monitor the accuracy of the specified type of equipment. Inside the megohm meters can be placed batteries or integrated generators as power sources.
There are devices with varying degrees of power. 1 kV devices are used when working with wiring, the cross section of which does not exceed 16 mm².
Generally accepted measurement standards
The first measurement of insulation resistance is carried out at the factory after the production of wires. The following testing is carried out at the construction site before the start of installation work and before the activation of energy supply systems. The last check gives you the opportunity to determine the occurrence of problems during installation of electrical appliances.
With the use of this type of device can be measured by any technique of electrical type. Devices with an operating voltage of less than 60 V are not included in this list.
Who can entrust the measurement?
To perform such work requires an appropriate permit. Only qualified specialists who are part of electrical equipment repair teams can take measurements.All of them must be prepared, undergo special training and receive the appropriate certificates determining their professional suitability.
What does the resistance depend on?
Measurement of insulation resistance of cable lines must be carried out before and after their repair. Mainly on the resistance of the insulating sheaths of wires can affect the temperature indicator. The higher the resistance value, the smaller the cable section should be. A variety of material for the manufacture of conductors also plays a role.
If we consider steel wires as an example, then the indicator of their resistance will be greater than in aluminum wire. The humidity of the ambient air can also affect the conductivity of insulating materials. For this reason, when a given value is fluctuated, the attenuation changes.
Method of measurement
In the surveyed network there should be no voltage. It will be necessary to set the maximum possible value at the site before the start. If network elements have a low isolation limit, they must be closed or disconnected. This procedure is carried out using semiconductor installations and capacitors. After that, it is necessary to ensure the grounding of electrical circuits.Measurement of insulation resistance is carried out within a minute. It is necessary to turn the handle of the integrated generator or, if the device is powered from the network, press the "high voltage" button. From the scale of the device must be read. Electric charge is removed from the circuit by grounding after the measurement procedure.
Optimum resistance indicators
The magnitude of these parameters is directly related to what the wiring lines are used for. Resistance of a cable rated for 1 kV should not be higher than 0.5 MΩ. Different devices for monitoring and protection should differ by this value.
Optimum resistance indicators
The size of the insulation sheath should be changed in accordance with the standards and requirements according to the EMP. Resistance should meet the standards for all seasons with a decrease and increase in the required values in accordance with changes in ambient temperature.
How often is the resistance checked?
Standards of time after which it is necessary to carry out planned measurements of certain parameters, as well as the necessary voltage measurement of the insulation resistance are described in more detail in the documentation of ПТЭЭП.Each year, the insulation resistance of lighting devices, crane and elevator wiring is checked. In other cases, this happens every few years. Every six months, portable welding and electrical equipment is checked.
The chance of all sorts of unwanted breakdowns may increase if these requirements are not met. Corresponding sanctions in the form of fines may be imposed on violators. All organizations should plan the dates for such measurements. It should be based on technical inquiries and features that the equipment and each cable line must necessarily correspond to. Measurement of insulation resistance is carried out during operational tests.
It is impossible to start the measurements without making sure that there is no voltage on the objects. Before starting the measurement, you need to ensure that there are no personnel working on those parts of the electrical installation to which the test instrument is connected. Contact with live parts should be prohibited for employees in their immediate vicinity. This is a must check.
Resistance measurement should always be carried out only on discharged current-carrying areas with preliminary grounding, which is removed after the megohmmeter is connected. Special insulating holders serve to protect current-carrying elements while using a megohm meter to measure resistance. It is not allowed to touch the wires while connecting the device. The method of short-term grounding of the current-carrying parts of the residual charge is removed after completion of the work. Measurements should be carried out repeatedly for the entire period of operation of electrical networks. This procedure requires responsibility. An early measurement of the insulation resistance of electrical wiring makes it possible to prevent the occurrence of unforeseen emergency situations at enterprises.
The accompanying act of measuring the insulation resistance of electrical wiring is drawn up before the execution of work. Put the date of measurement. Then the name of the settlement is indicated, in which a team of measurement specialists was involved.Next, you must specify the name of the object or organization where the measurement work was carried out, its address and contact details. Indicate the name of the project, as well as the contract number. All the members of the commission confirm their presence with their signatures and surnames.
The device name, number, class, type and scale are indicated. The field for notes is filled in if necessary. Then the measurement data is given: marking of the wiring according to the drawing, section and number of wires, insulating resistance in relation to the earth and between the wires. Indicate the size and method of withdrawal of the commission, as well as initials, position and all the signatures of its members.
Registration of results
The test results are always recorded in the insulation resistance measurement protocol. A list of certain deficiencies must be submitted to customers in order to take appropriate measures to eliminate them. Documentation in the form of electronic files should be stored in the appropriate databases. Another copy should be printed and placed in the archives of electrical measurement laboratories. Copies of measurement and test reports must be kept for at least three years.
Actions in case of unsatisfactory results
At detection of discrepancies of documentation to the executed works, members of the working commission will not sign the act. The chapter is a corresponding conclusion. After that, the commission draws up a list of identified defects and indicates the name of the organization responsible for their timely elimination, which should fix the inconsistencies within 10 days. Workers are required to deal with the occurrence of faults according to the instructions. They eliminate the damage and do everything according to the rules. Insulating material must be in good condition, not contribute to the occurrence of fire. After that it is necessary to submit the act of the working commission again for re-checking. With full consent, all participants put their signatures.
Megohm meters are very convenient to use. All measurement data will be displayed on a digital display. The ergonomics of modern devices are significantly different from those of the past century. Measurements are simple and easy. Megohm meters are distinguished by their versatility and a fairly wide range of frequencies.
It is recommended to measure the insulation resistance under the same temperature conditions with a difference of no more than 5 ° C in strict compliance with the instructions. Otherwise, it is necessary to re-measure the temperature indicators.