High-voltage transmission is a key step in large-scale power transmission. Generally high-voltage transmission is a long-distance transmission. So, why use dangerous high voltage lines to transmit electricity? In fact, the core purpose of using high voltage is to reduce unnecessary losses in long-distance power transmission.
Principle of High-Voltage Transmission
Normally, the generator output of a power plant is only 5 to 18 kV. When it is connected to the transmission grid, however, the voltage is first raised to 220 kV or 330 kV. In the long-distance power transmission, the loss of transmission power is great. In order to reduce the loss of power transmission, the smaller the DC resistance of the transmission cable, the better.
There are two ways to reduce power transmission losses. One is to increase the cross-sectional area of the conductor. However, when the cable radius is thickened, its weight increases and so does the overall cost.
Another method is to increase the line transmission voltage. With the increase in transmission voltage, the transmission current can be significantly reduced, thus making the loss on the transmission line is greatly reduced. According to the electric power formula, the transmission power is equal to the product of voltage and current. In the case of equal power, the higher the transmission voltage, the smaller the transmission current. In addition, the losses on the transmission cable are proportional to the transmission current and inversely proportional to the transmission voltage.
Currently, some power plants have increased their transmission voltage to the ultra-high voltage level of 500 kV – 1000 kV. In this way, the transmission power can be increased exponentially on the cables of the same diameter, reducing the loss of power during transmission.
Why Do Most High-Voltage Transmission Use Overhead Cables?
Currently, no effective insulation material can be found for the outer skin insulation of electric wires for ultra-high voltage transmission. Usually UHV cables are bare and they use air as insulation.
In addition, underground cables are more complex than overhead cables. To avoid external damage, underground cables usually require armor layers.
In general, underground cables are technically demanding and more difficult to manufacture and lay. The cost of an underground cable of the same voltage level can be several or even tens of times higher than that of an overhead line of cable.
If all high-voltage transmission lines are replaced with underground cables, especially for long-distance transmission through complex terrain, the cost and technical requirements will skyrocket.
Why Does Electricity Need to Be Transmitted Over Long Distances?
The long-distance transmission of electricity is related to the source of power generation. Common power generation sources include thermal power, hydroelectric power, nuclear power, wind power, solar power, etc.
Due to the different distribution of natural resources in different regions, the power generation capacity varies greatly. Therefore, most of the electricity needs to be transmitted over long distances to reach different regions.
And in the process of long-distance transmission of electricity will produce huge losses. Therefore, only by increasing the voltage can we increase the effectiveness of long-distance transmission as much as possible. High-voltage transmission is to increase the voltage and then send it to the destination, and the distance to the destination is not required to use electricity.