Transmission and Distribution of Electricity in Hong Kong

When you plug in and switch on an electrical appliance, you are actually drawing electrical energy from power stations that may be very far away. The electrical energy from power stations reaches your home because of an extensive network of conducting cables that forms the electricity transmission and distribution systems of Hong Kong. The system transmits electrical power from a few power stations to almost every home in Hong Kong, from the city centres to the remote areas.
Fig. 1 Thomas Edison’s greatest contribution was perhaps his economically viable model for generating and distributing electric power. Fig. 2 The fantastic night view of Hong Kong is made possible by an effective electrical transmission and distribution system (Photo courtesy of HEC).
In Hong Kong, electricity is transmitted mainly through overhead lines or underground cables. Due to the resistance of the transmission wires, there is always some loss of power through the heating effect of current. The electricity transmission systems must be designed in ways which reduce this loss as much as possible.
High transmission voltage
Fig. 3 High voltage transmission lines on a transmission substation
To reduce energy loss, electricity generated in power stations is raised to a very high voltage for transmission. A high transmission voltage means only a relatively small current flows through the transmission cables. As you know, current produces heating effect when flowing through the cables with resistance. When the current used for transmission is small, energy loss due to heating effect on the cables is reduced, enabling more electrical power to be transferred to the users.
Low resistance transmission wires
As the heating effect occurs when a current flows through cables with resistance, reducing the resistance of the transmission cables will reduce energy loss. How do engineers design a transmission wire that is low in resistance and at the same time economical?
The first consideration is the choice of material. Metals are good conductors with low resistance. Copper and aluminium are the most commonly used metals in transmission wires. They are very good conductors, cheap, resistant to corrosion, and strong. The resistance of the transmission wire is lowered by making the wire thicker. Thicker wires have larger cross-sectional area and therefore lower resistance.
Even though the cables are carefully designed to reduce resistance, as the length of the cables required in a transmission system is very long, the total resistance of the cables is still quite significant. In the following activity, you will observe how long resistive wires affect the transmission of electricity.

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