voltage class - conditional term, which allows to break the equipment for structural and operational features in the group.
From the history of the question
The history of development of transmission lines briefly considered in the review of the two-pole machines, but try to "run Europe "to readers comprehended the cause of the need to divide the classes of equipment voltage. The first in the history of transmitted direct current from the dynamo grams. Three-quarters of a mile current sent an inventor named equipment. It happened at the Vienna exhibition in 1873. First there was already Telegraph (with lines of up to 20 km), but ate a cell or from a static generator, the topic has little to do.
Then transfer the current over long distances is not mentioned need. It was used by the local oscillators. For example, for the supply of lighthouses in England and France. They all straightened current, as if on purpose, replicating modern high-voltage line HVDC. New significant event occurred in 1882 when Oskar von Miller hired Frenchman Marcel Deprez pass voltage 2 kV at a distance of about 60 km. It has become obvious achievements, but the recipient has reached a quarter of the initial potential difference.
Then between Edison and Tesla occurred conflict ended at the end of the 80s the creation of new equipment designed for alternating current. Nose to the wind kept Dolivo-Dobrovolsky, immediately developed a three-phase motor power system. Patent of the Russian citizen was not given because of the counter-arguments of Nikola Tesla, but the battle led to the current observation: "The use of a transformer allows to significantly reduce the loss of line."
And that turned out to be immediately used. In 1891 he transferred to the voltage of 15 kV by as much as 180 km with an efficiency of 75%. Edison rest! Since that time, the AC advantages become apparent, the low voltage causes high losses in the line. This is the main reason why in the modern world there is a need to share equipment for voltage classes.
Already in 1912 reached 110 kV voltage, ten years later, it was 220. The rate of voltage increase showed exponential dependence of the passing years. Then designed line 380, 765 (750) and 1200 kV.
Meanwhile in Russia
Russia lagged in development. Whether the Party cell of the first secret revolutionary forces took away from the state, or bad luck prevented the country to keep pace with the times, the fact remains - catch up with and surpass the West could not be the only high-voltage line has been broken except for Kazakhstan from the Russian Federation to the coup 90 years.
World energy consumption is growing every ten years doubled for the period of the first oil crisis. By the early 80's the first line of EHV built:
- 1150 kV AC.
- 1500 kV DC.
On 1980 70 power plants operated in the Soviet Union, who gave the country more than 1 GW of power. Between 1960 and 1990, length of the lines of the Soviet state has increased from 0.22 to 5.1 million. km. At the end of the "perestroika" the emphasis is on the 220 kV voltage class. Almost twice increased length of the lines from 330 to 750 kV for the past few years. The apogee of the Soviet policy considered Siberia-line Ekibastuz-Urals, where the highest potentials applied, the marked text.
Kilometer line even at that time cost 10 - 100 thousand rubles. The numbers can increase manifold when laying special conditions. This also applies to superhigh voltage. To raise the voltage at high flow rates is acceptable, the costs for the construction of transmission lines, transformers and equipment pay off savings on leaks. DC lines are almost not form the corona discharges, because the voltage was able to raise up to 1.5 MW, significantly reducing power loss on the ohmic resistance of copper conductors.
In the development of any class of electrical invariably there is a need to increase the transmit power. Most effective way to increase the voltage of the network. With increasing current abruptly going uphill heat energy losses due to the ohmic resistance of the wire. As a result, there are other requirements for insulation. If its home circuit test current clamp with a prefix of 500 V, for equipment of 6.6 kV or 110 it looks serious.
For example, oil transformers known to withstand more stress than usual, because the conditions for the emergence of an arc created deliberately disadvantageous. Therefore, in transformers key feature of the transition to the new class becomes the introduction of oil insulation. A similar spoken about the cables, and push-button stations measure indicates otherwise - go in search of equipment, for use in hazardous areas.
New challenges make engineers and inventors to seek fresh solutions. And in each case, a special task. You can not create a single list of all voltage classes for the list of equipment available in the industry. Obviously, the appliances for voltage class divide does not make sense, but the gradation remains. For example, the AC power system voltage below 50 V DC and - 120 relate to safe, acceptable to use in bathrooms, washrooms, kitchens.
voltage classes present in the art is quite palpable. Manage to find the net documents with similar content:
- SRT 56947007-184.108.40.206 Typical specifications for switchgear (complete distributed devices) classes 6-35 kV.
- GOST 51559 Power transformers 110 and voltage class of 220 kV and 27.5 kV autotransformers voltage for electric railways AC roads.
- GOST 12965 Power transformers, general purpose class 110 and a voltage of 150 kV.
- STO 56947007-29.130.10.077 Typical technical requirements for disconnectors classes 6-750 kV.
- 1516.1 Standard Electric AC voltages from 3 to 500 kV. The requirements for dielectric strength.
From these names can be seen that the stress classes rarely which lists because it As for professionals, they know what requirements must satisfy one or another equipment. Often grading some authors contradict other sources. Probably, the division was made according to different factors. For example, in one case, were taken into account structural features, in another - performance. The aging classification of power lines could look like this:
- To 1 kV - lower voltage.
- Above 1 kV - high voltage.
- 330-500 and 750 kV - EHV.
- Over 1 CF - ultra-high voltage.
There are also a number of other information:
- 380 V or less - a low voltage.
- From 1 to 20 kW - an average second voltage.
- 35 kW - an average first voltage.
- 110 and 220 kV - high voltage.
- 330-500 and 750 - EHT.
- Above 1 MW - ultra-high voltage.
It can be seen that some of the names do not match, so the voltage class, to avoid confusion, give the number. The designation usually appears phase voltage.
From the above it can be concluded that the transmission line structure, individual for each voltage class. For example, high voltage ceramic insulators can break in windy pillar local distribution network 220, if it hangs on each line.
Low-voltage line (see. classification above) are constructed on the single pillars are directly buried in the ground. Here, step voltage does not look too great in the event of an accident, the only measure of protection will be local grounded lightning rod. Lines 20 kV differ only slightly in structure from those described. But the size of the pillars, the distance between the cables, insulators increased. Lightning protection cables are not used, it is not economically justified.
Starting with the 35 kV line, the design is complicated, suspended steel cables lightning protection in areas of intense thunderstorms. It applies a heavy cable, fracture toughness increased column. The increased distance between the wires provide a powerful isolators, fixed on special traverses. Some posts already reminiscent of the high voltage. Composed of individual prefabricated steel sections mounted on the insulating concrete slabs for blocking draining current to the ground in an accident. Above 35 is often used steel-aluminum cables, which carry functions are assigned to a high-strength core.
On power lines to 110 kV voltage class lightning protection cables are suspended already over the entire length, on the lines of 35 kV - only in the area of substations. Line 330 kV resemble the shape of 35, but above the arched columns and more powerful, and insulators navesheno much more to block the electrical arcing and reduce the formation of crown discharges. Lightning protection in the form of wires capable absent in windy areas where overlapping with the line causes a short circuit. The effect is used for protection when working zero sequence relay.
Grounding high-voltage lines are usually held inside the concrete supports to lower the step voltage. In this case, currents flow down immediately into the ground and do not cause such devastating damage bystanders and animals. Starting from 500 kV lightning protection cables and are used for the conductive connection in the form of wire rope with one helix aluminum wires. At these voltages applied digested carried out, which sharply reduces corona discharge losses and decrease the intensity of the electromagnetic field. At the same time decreases the reactance line that allows you to use smaller reactors at substations of performance and size.
Upon cleavage of 500 kV line half bandwidth increases by 21% sodium - 33%. This event is complicated insulating structure and suspension reinforcement supports. Appreciation of lines do not always pay off the resulting economic benefits. The RF line splitting is performed according to the voltage class:
- 330 kV - two.
- 500 kV - sodium.
- 750 kW - 4 or 5 lines.
- 1150 kV - 8 lines.
The wire is distributed by class:
- Pure aluminum or steel - to 20 kV.
- Steel-aluminum wires Group 4 - from 35 to 110 kV.
- Steel-aluminum wires Group 3 - 220 kV and above.
The difference in stress classes
In the example shown the difference of power lines for design stresses classes. At the same time there are performance features - security measures, procedures and maintenance of erection. In each case has unique requirements. Do not be surprised if the wires are broken, voltage classes in the same manner as insulators and lightning protection cables - in another.
It is obvious that the climatic conditions impose some requirements, and physical processes - others. Exactly similarly refers to the electrical equipment, where the division into different voltage classes.