Why the transmission of electricity over a distance takes place at increased voltage
Today, the transmission of electrical energy over a distance is always carried out at an increased voltage, which is measured in tens and hundreds of kilovolts. All over the world, power plants of various types generate gigawatts of electricity. This electricity is distributed in cities and villages using wires that we can see for example on highways and railways, where they are invariably fixed on tall poles with long insulators. But why is transmission always high voltage? We'll talk about that later.
Imagine having to transmit electrical energy through wires of at least 1000 watts over a distance of 10 kilometers in the form of alternating current with minimal power losses, a powerful kilowatt floodlight. What are you going to do? Obviously the voltage will have to be converted, reduced or increased in one way or another. using a transformer.
Suppose that a source (a small gasoline generator) produces a voltage of 220 volts, while at your disposal is a two-core copper cable with a cross-section of each core of 35 sq. mm. For 10 kilometers, such a cable will give an active resistance of about 10 ohms.
A 1 kW load has a resistance of about 50 ohms. And what if the transmitted voltage remains at 220 volts? This means that one-sixth of the voltage will (drop) on the transmission wire, which will be at about 36 volts. So about 130 W were lost along the way — they just warmed up the transmitting wires. And on the floodlights we get not 220 volts, but 183 volts. The transmission efficiency turned out to be 87%, and this still ignores the inductive resistance of the transmitting wires.
The fact is that active losses in transmission wires are always directly proportional to the square of the current (see Ohm's Law). Therefore, if the transfer of the same power is carried out at a higher voltage, then the voltage drop on the wires will not be such a detrimental factor.
Let us now assume a different situation. We have the same gasoline generator producing 220 volts, the same 10 kilometers of wire with an active resistance of 10 ohms and the same 1 kW floodlights, but on top of that there are still two kilowatt transformers, the first of which amplifies 220 -22000 volts. Located near the generator and connected to it through a low-voltage coil, and through a high-voltage coil — connected to the transmission wires. And the second transformer, at a distance of 10 kilometers, is a step-down transformer of 22000-220 volts, to the low-voltage coil to which a floodlight is connected, and the high-voltage coil is fed by the transmission wires.
So, with a load power of 1000 watts at a voltage of 22000 volts, the current in the transmitting wire (here you can do without taking into account the reactive component) will be only 45 mA, which means that 36 volts will not fall on it (as it was without transformers), but only 0.45 volts! Losses will no longer be 130 W, but only 20 mW. The efficiency of such transmission at increased voltage will be 99.99%. This is why surge is more effective.
In our example, the situation is considered crudely, and the use of expensive transformers for such a simple household purpose would certainly be an inappropriate solution. But on the scales of countries and even regions, when it comes to distances of hundreds of kilometers and huge transmitted powers, the cost of electricity that can be lost is a thousand times higher than all the costs of transformers. That's why when transmitting electricity over a distance, an increased voltage, measured in hundreds of kilovolts, is always applied — to reduce power losses during transmission.
The continuous growth of electricity consumption, the concentration of production capacity in power plants, the reduction of free areas, the tightening of environmental protection requirements, inflation and the increase in land prices, as well as a number of other factors, strongly dictate the increase in the transmission capacity of electricity transmission lines.
The designs of various power lines are reviewed here: The device of different power lines with different voltage
The interconnection of energy systems, the increase in the capacity of power plants and systems as a whole are accompanied by an increase in the distances and flows of energy transmitted along the power line.Without powerful high-voltage power lines, it is impossible to supply energy from modern large power plants.
Unified energy system allows to ensure the transfer of reserve power to those areas where there is a need for it, related to repair work or emergency conditions, it will be possible to transfer excess power from west to east or vice versa, due to the change of the belt in time.
Thanks to long-distance transmissions, it became possible to build superpower power plants and make full use of their energy.
Investments for transmission of 1 kW of power over a given distance at a voltage of 500 kV are 3.5 times lower than at a voltage of 220 kV, and 30 — 40% lower than at a voltage of 330 — 400 kV.
The costs of transferring 1 kW • h of energy at a voltage of 500 kV are two times lower than at a voltage of 220 kV, and by 33 — 40% lower than at a voltage of 330 or 400 kV. The technical capabilities of 500 kV voltage (natural power, transmission distance) are 2 — 2.5 times higher than those of 330 kV and 1.5 times higher than 400 kV.
A 220 kV line can transmit a power of 200 — 250 MW at a distance of 200 — 250 km, a 330 kV line — a power of 400 — 500 MW at a distance of 500 km, a 400 kV line — a power of 600 — 700 MW at a distance of up to 900 km. The voltage of 500 kV provides power transmission of 750 — 1000 MW through one circuit at a distance of up to 1000 — 1200 km.