Electrical Power Systems

An electrical power system is the network that generates electricity and delivers it to consumers. It spans power stations, transmission lines that carry energy over long distances at high voltage, distribution networks that bring it to towns and buildings, and the loads that finally use it. To move large amounts of power efficiently, the system operates at high voltage and low current on transmission lines, because lower current means smaller losses in the conductors. Transforming voltages up and down at the right points is therefore central to the design.

Substations are the nodes where this transformation and switching takes place. A substation contains transformers that step the voltage up or down, along with circuit breakers, isolators, busbars and protective relays that route power and disconnect faulty sections. Step-up substations near generators raise the voltage for transmission, while step-down substations near consumers lower it to safer distribution levels. Substations also house instruments for monitoring current, voltage and power, and equipment to protect the network against faults and lightning surges.

Many loads, especially motors and transformers, draw reactive power as well as the real power they consume. Reactive power does no useful work but increases the current flowing in the system, raising losses and reducing capacity. The ratio of real power to the total apparent power is the power factor. To improve a poor power factor, capacitor banks or other correction networks are connected to supply the reactive power locally, so the network carries less current. This power-factor correction lowers losses, frees up capacity and can reduce charges that utilities apply for low power factor.

Frequently asked questions

Why is power transmitted at high voltage?

Transmitting the same power at higher voltage means lower current, which reduces resistive losses in the conductors, making long-distance transmission far more efficient.

What does a substation do?

It transforms voltage up or down and switches and protects sections of the network using transformers, breakers, isolators and protective relays.

What is power factor correction?

Adding equipment such as capacitor banks to supply reactive power locally, which raises the power factor, lowers current and reduces losses in the supply network.