Modern power supply networks have two main characteristics:
- electricity generation, regardless of the type of power plant (thermal, hydro, wind), occurs in one place;
- most electricity consumers are located in completely different places.
The generated electricity is delivered through power transmission lines, and to minimize the inevitable losses voltage is increased to the maximum possible value, gradually decreasing as it approaches the terminal distribution nodes.
Risks from power lines for a person
For reasons of ensuring the highest technical and economic efficiency, electricity transmission carried out mainly via overhead lines and only in cities they are replaced by cable lines.
The high operating voltage of power lines carries a potential danger to humans, which is determined by:
- the final risks of breakdown of the air gap and electric shock to a person;
- harmful influence of electric field strength even without direct breakdown
Taking into account this feature, the current norms prohibit approaching power lines closer than a certain distance, which depends on the operating voltage. It ranges from 0.6 m for overhead lines with a voltage of not more than 1000 V and gradually increases to 5 - 8 m in relation to power lines with an operating voltage of 750 and 1150 kV.
There is not always a pronounced security zone around power lines. Further, the external design features are considered that allow you to immediately determine the operating stress.
Low voltage distribution networks
The unique characteristics of the most common 400-volt bare wire distribution networks are:
- five wires (three phase wires, which are supplemented by a neutral wire and an additional phase of street lamps);
- Small-sized white porcelain or transparent glass insulators in pin design.
Various types of supports are used to implement the lines. Figure 1 shows an example of a pole support.
Sometimes 400-volt lines are implemented on insulated wires. Then such lines look as shown in Figure 2.
Medium voltage lines
Medium voltage transmission lines include lines with an operating voltage of up to 35 kV.
Their main characteristic features:
- larger also porcelain and glass insulators;
- three-wire implementation scheme.
Suspended insulators are sometimes used on corner (rotary) supports. Figure 3 shows a diagram of the suspension of wires on such a support.
35-, 110 and 220-kilovolt power lines
The lines of this working stress are characterized by more massive supports, which are usually made of concrete or openwork steel. They are implemented in a three-wire circuit. The main difference is the design of insulators: 3-element in the first case, 6-element in the second, multi-element in the third.
The number of separate plates of insulators in 110-kilovolt lines, which belong to high voltage transmission lines, can reach four dozen. An example of insulators for suspending phase conductors of a line of this type is shown in Figure 4.