What electricity is and how it reaches you

Everything around you is made of atoms. Atoms are incredibly small. They are the building blocks of every material: the screen you are reading this on, the air you are breathing, the wires in your walls. Each atom has a centre (called the nucleus) surrounded by even tinier particles called electrons.

Electricity is the movement of electrons through a material. When electrons flow along a wire, that flow carries energy. Think of it like water flowing through a pipe. The water itself is not the energy, but the movement of the water can turn a wheel or push something. In the same way, moving electrons can power a light bulb, charge your phone, or run a hospital.

Some materials let electrons flow easily. We call these conductors. Copper and aluminium are good conductors, which is why most electrical wires are made from them. Other materials block electrons. We call these insulators. Rubber and plastic are insulators, which is why wires are coated in plastic to stop the electricity leaking out or shocking you.

To make electrons flow, you need a push. That push is called voltage. A battery provides a small voltage. A generator at a power station produces a comparatively modest voltage, which a step-up transformer then raises to a very high voltage before the electricity joins the transmission network. The higher the voltage, the harder the push, and the further the electricity can travel without losing too much energy along the way.

Most electricity is made by spinning a magnet inside coils of wire. When a magnet spins near a wire, it pushes the electrons in the wire and creates a flow of electricity. This is called a generator. The question is: what spins the magnet?

In a gas-fired power station, burning natural gas heats water to make steam. The steam pushes a turbine (like a very large fan), and the turbine spins the generator. In a coal power station, burning coal does the same thing. In a nuclear power station, a nuclear reaction produces heat, which makes steam, which spins a turbine.

Wind turbines skip the steam step entirely. The wind pushes the blades directly, and those blades spin the generator. Solar panels work differently again: they use sunlight to knock electrons loose inside special materials (called semiconductors) without any spinning parts at all.

The key point is that all of these sources produce the same thing: a flow of electrons that can travel along wires to where it is needed. It does not matter whether the electrons started moving because of gas, wind, or sunlight. Once electricity is on the network, it all looks the same.

Power stations are often far from the cities and towns that need the electricity. Offshore wind farms are out at sea. Nuclear stations are in remote coastal areas. The electricity they generate needs to travel long distances to reach homes and businesses.

This is where the transmission network comes in. Think of it as the motorway system for electricity. Just as a motorway carries large volumes of traffic at high speed over long distances, the transmission network carries large amounts of electricity at very high voltages (275,000 or 400,000 volts) across the country.

The voltage is kept extremely high for a practical reason. When electricity travels a long distance, some energy is lost as heat in the wires, and that heating loss grows with the square of the current. For the same amount of power delivered, doubling the voltage halves the current, and halving the current cuts the heating loss to a quarter. So the transmission network uses very high voltage to keep the current low and move power efficiently over hundreds of miles. For example, delivering the same power at double the voltage needs only half the current, so the energy wasted as heat falls to a quarter of what it would have been.

In Great Britain, the wires and substations of the transmission network are owned and maintained by separate transmission owners. The National Energy System Operator (NESO), which replaced National Grid ESO in 2024, does not own the network; it operates the electricity system, making sure that the amount of electricity being generated at any moment matches the amount being used. If those two numbers drift apart, the system frequency changes, and things start going wrong, exactly as happened in the 2019 blackout.

Electricity at 400,000 volts is far too powerful to plug into your toaster. Before it reaches your home, the voltage needs to be reduced in stages. This is the job of the distribution network.

If the transmission network is the motorway, the distribution network is the local road system. It takes electricity from the transmission network, steps the voltage down through a series of substations, and delivers it at a safe level (230 volts in the UK) to homes, shops, schools, and hospitals.

A typical journey looks like this:

• 400,000 V or 275,000 V on the transmission network (the motorway).
• 132,000 V at a grid supply point, where the electricity leaves the transmission network and enters the distribution network.
• 33,000 V on the primary distribution network (the A-roads).
• 11,000 V on the secondary distribution network (the B-roads).
• 230 V at your wall socket (the street outside your house).

Each step down happens at a substation, which contains a transformer. A transformer is a device that changes the voltage of electricity. It does not create or destroy energy; it simply converts high-voltage, low-current electricity into lower-voltage, higher-current electricity (or the reverse).

In England, Scotland, and Wales, 14 licensed distribution network operators (DNOs) manage this local network. Each one is responsible for a geographical area. The company we will follow in this course, London Grid Distribution, is a fictional DNO that manages the electricity distribution network across Greater London.

Electricity networks are not passive pipes. They are active, constantly balanced systems. Grid electricity does not flow in one direction like water; it is alternating current, meaning it reverses direction 50 times a second in Great Britain, which is what "50 hertz" means. Every generator connected to the network spins in step with that same 50 hertz rhythm, like dancers keeping the same beat. At every moment, the total amount of electricity being generated must match the total amount being used. If generation drops (because a power station trips) or demand spikes (because millions of kettles switch on at half-time), the generators slow down very slightly and the system frequency starts to drift away from 50 hertz. Frequency is, in effect, the grid's heartbeat: a steady 50 hertz means generation and demand are balanced, and a falling frequency means the system is losing that balance.

When frequency drops too low, automatic protection systems disconnect parts of the network to prevent damage to generators and equipment. This is called load shedding. It is a deliberate, controlled action: sacrifice some customers now to save the rest of the system from a total collapse (a blackout).

The 2019 event showed what happens when coordination between the different parts of the system is not fast enough. The generators, the transmission operator, and the distribution networks all had their own protection rules, but those rules did not work together smoothly enough to contain the problem before it spread.

This is not just an engineering problem. It is an information problem, a communication problem, and an organisational problem. Different companies own different parts of the system. They use different computer systems, different data formats, and different decision processes. Getting them to act together in real time is enormously difficult.

That difficulty is exactly why this course exists. Enterprise architecture is a discipline for making complex organisations work coherently across their systems, data, and processes. Before we get to that discipline, we need to understand the physical system it will be applied to. The next module introduces the fictional company that runs part of this network.