As the electromagnetic field influences the person
The electromagnetic field of extra-high voltages negatively influences the human body. Medical examination of personnel, is long VL of extra-high voltage working close, showed that the electromagnetic field of industrial frequency causes increased fatigue, lowering of arterial pressure, falling of pulse rate in the person; in heart there are sharp pains which are followed by heartbeat and arrhythmia.
Harmful effects of the electric field on the human body which is close VL are defined by two factors:
- biological influence of electro-magnetic radiations and emergence of electric discharges between the person and current carrying parts;
- between the person and the metal designs having different potentials.
Current up to 50 mk does not exert noticeable impact on the human body.
At the current exceeding 50 mk it is necessary, performing works near VL, to use the special shielding suits or the stationary portable shielding devices.
The size of the current proceeding through the person is directly proportional to the potential of electric field in the location of the person. In turn, the potential of electric field depends on electric unit tension, on distance between the person and the current carrying part. Obviously, than tension of the electric unit is higher and than closer the person is to the current carrying part, especially potential will be high and bigger force current will pass through the person. Potential under VL is determined at the height of 1,7 m from the earth (average height of the person). The greatest values of currents fall on the middle of intermediate flight of VL at distance of 1-3 m from the projection of the extreme phase wire to the earth. Depending on increase in tension of VL current intensity increases. At the voltage of 110 kV, 220 kV, 500 kV and 750 kV current intensity will be according to 10 mk, 38 mk, 113 mk, 200 mk.
When moving the person under the extreme phase from the middle of flight to the VL support current intensity decreases up to 3 mk at the voltage of VL of 110 kV and up to 60 mk — at 750 kV. Under the average phase wire and between phase wires of VL current decreases by 25 — 50%. Potentials of dangerous size are as well by machines and different mechanisms if they are near VL. Therefore all machines and mechanisms on rubber to the course, the influences of electric field used in the zone, have to be supplied with the metallic circuit connected to the chassis or the body. Before entrance to the influence zone the chain should be lowered to the earth.
Measurements of currents under VL at the height of 1,7 m from the earth allowed to draw the conclusion that at the voltage of VL higher than 220 kV the current passing through the person considerably exceeds the tolerance limit therefore finding of the person under the operating VL without the corresponding protection is undesirable. The person can is long to be about VL without use of protective equipment if the distance from the place of production of works to the projection of the extreme wire to the earth makes (not less): at VL of 110 kV — 5 m, VL of 220 kV — 10 m, VL of 330 kV — 20 m, VL of 500 kV — 30 m, VL of 750 kV — 40 m, VL of 1150 kV — 55 m.
The size of the current proceeding through the person when it is in the zone of influence of VL depends not only on tension of the last, but also on weather conditions. During wet weather the current passing through the person increases (at dry footwear). Usually animals feel concern and try to leave the zone of influence of VL.
Maximum permissible levels of electric field intensity should not exceed the following sizes:
- in the territory of the residential zone, kitchen gardens, gardens — 5 sq.m;
- in residential buildings — 0,5 sq.m.
At strength higher than 1 sq.m it is necessary to take the measures excluding impact on the person of the notable electric discharges and currents which are flowing down on the earth. Treat such measures:
- the organization of the sanitary protection zone of the territory along the route VL where strength does not exceed 1 sq.m. For VL of different tension of distance from the projection to the earth of extreme phase wires before constructions or the person have to be the following: at the voltage of 330 kV — 20 m, at 500 kV — 30 m, at 750 kV — 40 m and at 1150 kV — not less than 55 m;
- removal of inhabited construction from VL or use of the shielding devices.
Availability of residential buildings and performance of work within the sanitary protection zone are inadmissible.
Indirectly the person himself without application of measuring apparatuses can define the electric field intensity which is not exceeding 5 sq.m. At such tension most of people does not feel impact of electric discharges, touching with the hand back the grass or the bush. If necessary to cross VL of extra-high voltage it is not necessary to put on synthetic clothes and footwear as there can be the spark discharge between the person and the earth or the grass, and fabric will be burned. It is in that case better to take off footwear and to pass under VL barefoot.
- In the sanitary protection zone of VL of 330 kV and it is forbidden to perform any handworks above, to put haystacks, ricks of bread, the stack of peat, firewood, etc.
- Stay in the sanitary protection zone of VL, even short-term, children and teenagers up to 18 years is inadmissible.
- Within the sanitary protection zone of VL it is forbidden to make fire. It is impossible to approach VL during the thunderstorm, holding at the same time over the braid head, the pitchfork.