Power transformers. Electricity transmission. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power transformers. Electricity transmission. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric power supply

Consumers of electricity are everywhere. It is produced in relatively few places close to sources of fuel and water resources. Therefore, it becomes necessary to transmit electricity over distances sometimes reaching hundreds of kilometers.

But the transmission of electricity over long distances is associated with significant losses. The fact is that, flowing through power lines, the current heats them. In accordance with the Joule-Lenz law, the energy spent on heating the wires of the line is determined by the formula

where R is the line resistance.

With a long line, power transmission can become generally uneconomical. To reduce losses, you can, of course, follow the path of reducing the resistance R of the line by increasing the cross-sectional area of \u100b\u100bthe wires. But to reduce R, for example, by a factor of XNUMX, the mass of the wire must also be increased by a factor of XNUMX. It is clear that such a large expenditure of expensive non-ferrous metal cannot be allowed, not to mention the difficulties of fixing heavy wires on high masts, etc.

Therefore, energy losses in the line are reduced in another way: decrease in current in the line.

Example. Reducing the current by a factor of 10 reduces the amount of heat released in the conductors by a factor of 100, i.e., the same effect is achieved as from a hundredfold weighting of the wire.

Since the current power is proportional to the product of the current strength and voltage, in order to maintain the transmitted power, it is necessary to increase the voltage in the transmission line. In addition, the longer the transmission line, the more advantageous it is to use a higher voltage. So, in long transmission lines (for example, in the high-voltage transmission line Volzhskaya HPP - Moscow), a voltage of 500 kV is used.

Meanwhile, alternating current generators are built for voltages not exceeding 16-20 kV, since a higher voltage would require more complex special measures to isolate the windings and other parts of the generators.

Therefore, at large power plants they put step-up transformers. The transformer increases the voltage in the line as much as it reduces the current. The power loss in this case is small.

For the direct use of electricity in the motors of the electric drive of machine tools, in the lighting network and for other purposes, the voltage at the ends of the line must be reduced. This is achieved using step-down transformers.

Moreover, usually a decrease in voltage and, accordingly, an increase in current strength occurs in several stages. At each stage, the voltage is getting smaller, and the area covered by the electrical network is getting wider.

Author: Koryakin-Chernyak S.L.

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