Standby generators are engine-driven generators that start by themselves when the grid fails and supply power to a building until the grid returns. Hospitals, offices, apartment blocks, mobile towers and data centres use them. In India, most are diesel generators, called gensets, and some run on gas. A genset is sold by its rating in kVA, from about 5 kVA for a small shop to several thousand kVA for a data centre.
The key part is the automatic transfer switch. It watches the grid voltage all the time. When the voltage drops, the switch signals the engine to start. It waits until the generator has reached the right voltage and frequency. Then it disconnects the building from the grid and connects it to the generator. This usually takes 10 to 30 seconds. When the grid returns, the switch moves the building back and the engine stops. The switch must never join the building to both at once, since the grid and the generator would then work against each other.
Imagine a private hospital in Lucknow with a six-hour power cut. At 2 am the grid fails. The generator starts in about ten seconds. The operation theatre and the intensive care unit have a small battery supply for those ten seconds. After that, the generator carries the load. A diesel tank of a few thousand litres lasts the night.
A generator that is rarely used may fail when it is needed. So the owner runs it on a test schedule, usually once a week, and keeps the fuel and the battery fresh. Diesel gensets in India must also meet noise and emission limits set by the pollution control authorities.
Standby generators are being connected to software. A maker can see from far away whether the engine will start, how much fuel remains and when service is due. The generator is used with a smart electrical panel, which decides which circuits to feed. In large buildings the building automation system can start it on a test schedule. Data centres need it as part of their power and cooling. A battery storage system can replace a generator where noise and diesel are a problem. The company named below, Generac, sells mainly home standby generators in the United States. It also sells larger generators for offices, factories and data centres.