Most of us never think about voltage until we need the right voltage batteries to power an appliance, the remote, or a child’s toy. But the correct voltage is critical to the whole power system safely bringing us the electricity we need.

Voltage is a very important concept in operating a power system, and in talking about how the power system works. To understand how voltage influences power system operation, here are some of the key concepts:

  • Electrical energy is carried through conducting material (such as power lines) by electrons. The transmission line’s voltage measures how much potential energy each electron is carrying as it moves along the power line. In other words, voltage is the pressure that pushes current through the electrical supply chain.
  • Electrical current measures how many electrons flow through a particular part of the supply chain in a given amount of time.
  • Voltage combines with current to define how much power flows through the network.

In an AC (alternating current) system, like Australia’s National Electricity Market, voltage and current oscillate together around 50 times a second. This oscillation is the cycle of voltage and current moving quickly between positive and negative values over time. The number of times a second they go through that cycle is called the system’s frequency, measured in Hertz, and the frequency and size of the oscillation is set by different sources of electricity generation.

Voltage is measured in volts (V) – from the 1.5 V battery in the TV remote, to the 230 V wires running from street poles to our houses. At the power system level, where much larger pressure keeps electricity flowing, voltage is measured in thousands of volts, or kilovolts (kV).

We use different voltage levels for different purposes. Generally, it is very high on the biggest power lines coming from large-scale generators or carrying electricity between states, and lower on the lines closer to our homes and businesses. Across Australia, for example, we have power lines supporting as little as 11 kV or as much as 500 kV.

The voltages are different, because bulk power travels better over long distances with high voltages, while our homes and businesses only need a fraction of that power. Voltage is stepped up or down by power transformers that are located either in substations or on the top of poles around the low voltage distribution network.

Like power system frequency, voltage has to be kept within a set range for the power system to work properly and safely. If voltage is too high, equipment can be damaged or “fried”, and if it is too low, equipment can operate poorly or stall. AEMO works with the companies who operate transmission networks to regulate voltage levels so they are where they need to be.

Like managing frequency, regulating voltage is a combination of:

  • Constantly making small adjustments, and
  • Having a reserve of voltage support services to intervene quickly if there is a disturbance in the power system, so the system can keep operating securely and safely.

If voltage goes outside the set range, the first and best options available to adjust power system voltage are:

  • Switching on local sources of voltage support, such as capacitor banks.
  • Changing the transformation ratio of power system transformers.
  • Directing generators to raise their local voltage levels.
  • Using pre-agreed contracts for extra support from transmission networks or generators.

If voltage is still too high or too low, other options as a last line of defence include:

  • Changing power flows by switching parts of the transmission system on or off.
  • As a last resort in an emergency, if frequency is too low, cutting supply to some consumers to avoid more widespread problems.

Have you read our other energy explainers on the important prerequisites of a power system? If not, check them out below.