Construction site use of mechanical equipment, the vast majority of electricity as an energy source, with the increase in the level of mechanization of construction, the use of electric machinery, contact with electrical equipment more and more people, and the safety of these people's knowledge of electricity and the level of skills and relatively low, can not recognize the hazards and dangers in the event of an electric accident and the lack of timely and effective first aid measures, so in the process of installation and use of electrical equipment prone to electrocution casualties. After the electric shock accident and the lack of timely and effective first aid measures, so in the process of installing and using electrical equipment is prone to electric shock casualties. According to statistics each year due to electrocution deaths accounted for more than 7% of all accidental deaths, economic losses are greater, to strengthen the construction site safety of electricity, to prevent the occurrence of electrocution accidents can not be delayed.
The author engaged in construction site safety management for many years, on-site inspection found that a lot of electrical equipment, facilities, working environment is very poor, often dealing with water, slurry, due to maintenance is not timely, damage, aging, resulting in the use of electrical equipment, facilities, insulation degradation, and the site electrician of these electrical equipment, facilities can not be regularly insulated resistance test, if this type of electrical equipment, If the performance of the protection device of such electric equipment and facilities is poor, it is very easy for the operator to cause direct electric shock in the process of work. Therefore, good insulation is to ensure the normal operation of equipment and lines of the necessary conditions, but also to prevent electrocution is an important measure of casualties.
Here I talk about how to test the insulation resistance of electrical equipment and facilities at the construction site.
A test content
Construction site mainly test electrical equipment, facilities and power, lighting lines insulation resistance.
Second, the test instrument
The insulation resistance of the test equipment or line must use megohmmeter (shaking table), can not use a multimeter to test. Megohmmeter is a high voltage and easy to use test large resistance indicator. Its scale unit is megohm, expressed in ΜΩ. In practice, according to the object to be measured to select different voltage levels and resistance measurement range of the meter. The megohmmeter measurement range selection principle is: the measurement range can not be too much beyond the measured insulation resistance value, to avoid large errors. On the construction site is generally measured below 500V electrical equipment or line insulation resistance. Therefore, most of the selection of 500V, resistance measurement range 0----250ΜΩ megohmmeter. Megohmmeter has three terminals: L (line), E (ground), G (shielding), these three terminals according to the measurement of different objects to choose.
Three, test methods
1, lighting, power line insulation resistance test method
Line insulation resistance in the test can be relative to the phase, relative to the ground six sets of data. First of all, cut off the power supply, connected to the line, according to the clockwise direction of the megohmmeter generator crank, so that the generator rotor voltage for the measurement of the use of the rotor. Crank speed should be from slow to fast, to be governor sliding, to ensure that the speed is uniform and stable, not fast and slow, so as to avoid inaccurate measurements. General megohmmeter speed up to about 120 revolutions per minute, the generator will reach the rated output voltage. When the generator speed is stabilized, the pointer on the dial is also stabilized, then the pointer reading is the insulation resistance value measured.
Measurement of the insulation resistance of the cable, in order to eliminate the core insulation surface leakage caused by the measurement error, the wiring method in addition to the use of "L" and "E" terminal, but also need to use the shielding terminals. G". Connect the "G" terminal to the cable insulation paper.
2, electrical equipment, facilities, insulation resistance test method
First disconnect the power supply, the three-phase asynchronous motor stator winding measurement of the three-phase winding on the shell (i.e., relative to the ground) and three-phase winding insulation resistance between. Shake the three-phase asynchronous motor rotor winding measured relative phase. When measuring the relative ground "E" test line connected to the motor shell, "L" test line connected to the three-phase winding. That is, the three-phase winding to the shell of a shake into; if not qualified, then dismantle the single-phase shaking test respectively; the relative phase measurement, the phase should be removed from the joint piece.
Four, insulation resistance value test standards
1, the site of the newly installed low-voltage lines and overhaul of the insulation resistance of the electrical equipment should be not less than 0.5 ΜΩ.
2, the line in operation, the requirements can be reduced to not less than 1,000 Ω per volt.
3, the three-phase squirrel-cage asynchronous motor insulation resistance shall not be less than 0.5 Μ Ω.
4, three-phase wire-wound asynchronous motor stator insulation resistance value should be greater than 0.5 ΜΩ, cold state should be greater than 2 ΜΩ, rotor insulation resistance value should be greater than 0.15 ΜΩ, cold state should be greater than 0.8 Μ Ω.
5, hand-held power tools with electric parts and the shell of the insulation between the value of resistance: Ⅰ hand-held power tools should be greater than 2 Μ Ω, Ⅱ hand-held power tools should be greater than 7 ΜΩ, Class III hand-held power tools should be greater than 1 ΜΩ.
6, transformer, between the secondary windings and the core of the insulation resistance value should be greater than 2 ΜΩ.
V. Need to test the insulation resistance value of several cases
1, the new installation of the power equipment before putting into operation;
2, long unused equipment or out of service for more than 3 months before being used again.
3, the motor after overhaul or failure;
4, mobile power equipment (such as: stone grinding machine, submersible pumps, tampers, flat vibration machine, hose vibration machine, etc.) in the field before the first time to use;
5, hand-held power tools in addition to the first time before the use of the test, and then every period of time regular test;
6, safety Isolation transformer (eg: traveling light transformer) before use.
6, insulation resistance value test should pay attention to the problem
1, measure the insulation resistance of electrical equipment, cut off the power supply, and then the equipment will be fully discharged.
2, the instrument should be placed in a horizontal position.
3, megohmmeter measurement leads should be used well-insulated single wire, and should be sufficiently separated from the other parts of the equipment to be measured shall not be contacted.
4, the measurement of large electric capacity of the motor, cable, transformer and capacitor should have a certain charging time, shaking a minute after reading, after the test will be discharged after the equipment.
5, can not use two different voltage levels of megohmmeter to measure the same insulator, because any insulator with different voltages, resulting in different physical changes in the insulator, so that the leakage current within the insulator is different, thus affecting the measured resistance of the insulator is different.
6, the test should be carried out in good weather, the surrounding ambient temperature of not less than 5 ℃ is appropriate.
Seven, concluding remarks
Building construction site is always in a dynamic, changing, the site of temporary electricity is no exception. Due to the inconsistency of electricity equipment, facilities in and out of the field time, to the temporary power management has brought some difficulty, so the construction site must establish a temporary power safety inspection system, strengthen the safety of electricity knowledge of the operating personnel education, on-site electrician for the system of electrical professional training, to master the basic knowledge of safe electricity and the performance of a variety of electrical machinery and equipment, familiar with the "construction site of temporary power safety specifications," and other provisions of electricity. It is familiar with the "Safety Technical Code for Temporary Electricity Use at Construction Sites" and other regulations on electricity use. The site of serious hidden dangers, do not meet the safety requirements of the electricity equipment, facilities should be eliminated resolutely, in a timely manner to update, renovate the electricity equipment, facilities, to achieve its essential safety, to ensure that the site of the temporary use of electricity safety.
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