From the outside, a substation appears to be a fenced-off heap of industrial metal and gravel varying only by size and location. Like most things in life, despite first impressions, there is more inside the chain-link walls than meets the eye. Every piece of equipment inside a substation fence is a necessary piece of the world’s largest machine, the power grid, and contains some of the earth's most advanced technology.
When a power line is down or in contact with another power line, it is called a ‘fault’. Faults will cause violent damage to expensive equipment if they remain energized for a long time. With electricity, one second is considered a long time. When a fault occurs on a power line, equipment in the substation must respond within milliseconds.
To do this, each substation contains advanced computers known as relays. The relays measure the current and voltage once every 0.13 milliseconds or 7680 times per second (that is 768 times faster than a blink of an eye!). If the relay sees a fault, it responds by turning the power off as fast as possible. Typically, this takes 200 milliseconds. To stop the flow of 3,000 amps at 46,000 volts (185,000 horsepower) the relay cannot just flick a light switch to stop power flow, it must use a breaker.
A substation breaker is a large device capable of opening and closing a circuit carrying massive amounts of power. The breaker’s switch is held inside a tank filled with specially designed gas that prevents arcing. The tanks must remain airtight for years and the breaker must open and close at a moment’s notice when it receives a signal from the relay.
The quick response of a relay and the brute force of a substation breaker allows the substation to respond quickly but what good is this equipment if it does not work when you need it? To ensure the substation is reliable every second of the year, several layers of reliability are built into each substation. The layers include battery banks capable of powering the substation during a power outage, constant monitoring of substation equipment from LPEA’s dispatch center, and a rigorous preventive maintenance plan for all substation equipment.
The next time you see the gravel and galvanized steel in a substation yard, try to imagine the technology that keeps the grid running.