Why must long-distance power transmission apply ultra-high voltage transmission?
Electricity generated from the power plant’s generators is only 1 kilovolt to more than 20 kilovolts. During the transmission of electricity, it is necessary to first use a booster transformer which applies voltage up to several hundred kilovolts before connecting to the transmission grid. When going to the locality to use electricity, use a voltage reducing transformer to lower the voltage each level to the required voltage. Why must we apply the ultra-high voltage transmission method in the power transmission process?
The main purpose of adopting ultra-high voltage transmission is to reduce wastage of electricity on the transmission lines. We know that the electricity flowing through the electric stove generates heat because when the current passes through the wire the resistance converts electricity into heat. With the same principle, the electric transmission line also has a certain resistance value. Although using aluminum or copper with very small resistivity to make wires, but because the wires used for long-distance transmission are very long, its resistance cannot be ignored. Then, the amount of electricity converted to heat on the load line will become a relatively significant number. This part of electricity is completely wasted in the transmission of electricity.
You might think, is there a way to reduce or eliminate the resistance of the wire? The solution is there, but it’s not economical. The simplest way to reduce the electrical resistance of a transmission wire is to increase its cross-sectional area. If so, not only will the amount of material needed to make the wire increase a lot, but the wires because it will be heavier, the electric poles and wire towers to support the wire must also be reinforced, costly for the whole Power transmission lines will be very large. Scientists have discovered that when the temperature of some materials drops to a certain value, their resistance is completely lost, that is, superconductivity occurs. But so far, superconducting materials have the highest critical temperature detected by humans, down to – 10077 ° C for resistance to disappear. So using superconducting materials to load electricity is far from practical applications.
Knowledge of physics tells us: under constant resistance, its power dissipation is proportional to the square of the current. Therefore, reducing current is another way to reduce transmission waste. But how can the current be reduced? Since the transmission capacity is equal to the product of current and voltage, under constant transmission power conditions, it is possible to use high voltage increase to achieve the purpose of reducing current and minimizing transmission waste. Electrical Power. For example, if you want to transmit electricity with a capacity of 200 kW, if you use 2 kV electricity for transmission, the current in the wire will be 100 amperes. Again assume that the resistance of the conductor is 10 ohms. Then the power lost on the transmission line will be 100 kW, which is half of the total transmission capacity. If the transmission voltage is 100 times higher, reaching 200 kV, the current in the wire is only 1 amp. At that time, the lost power on the transmission line was only 10 kW, equivalent to 1/10000 of the lost energy using 2 kV for transmission.
Raising transmission voltage can reduce transmission wastage, so can unlimited transmission voltage increase? Since raising the transmission voltage can bring other problems, for example, the air between the power cord and the wire gets pierced, an arcing occurs during a sudden power failure …, at present, The super high voltage used in long distance power transmission is 500 – 1000 kV. If you want to increase the load voltage more than that, there are many technical difficulties that need to be solved.
In the suburbs, you can see the tall steel towers that support electrical wires with many insulating porcelain strings. They are made for the super high voltage electrical loads. The designers not only have to ensure the safety of the power transmission lines, but also consider the aesthetic appearance.