How Standby Generators Work

The first generators required a team of engineers to keep them working. They kept the steam engines running that provided the mechanical power for the generator, and made constant adjustments to the generator to regulate the power production. As the technology matured, the need for constant supervision gradually declined until generators were able to operate on their own. As cost declined and reliability increased, systems designed to provide backup power were brought to market. They are called Standby Generators because they are always standing by, ready to supply power whenever needed, without operator intervention.


Guardian 20kW Home Backup Generator

Guardian 20kW Home Backup Generator

A standby generator system is permanently installed outside the residence or business and is connected to a long-term supply of fuel to eliminate frequent refueling. Residential and commercial systems usually run on natural gas or LP gas. An automatic transfer switch connects the generator to the building’s electrical system.

When a power outage is detected, the engine starts automatically and turns the power generating unit which is called an alternator. The alternator converts the mechanical energy of the internal combustion engine into electrical energy. After a few seconds, the engine speed and electrical output stabilize and the transfer switch begins supplying power from the generator to the home or business.

Automatic Transfer Switch

Cummins Onan Home Standby Generator

Generator System With Automatic Transfer Switch

The automatic transfer switch makes the generator a permanently installed solution to power outages. Depending on the model, it may have it’s own circuit breakers or control a load center, which may include the main service panel for some models. Some provide power management capabilities for 240-volt, high-current loads.

The transfer switch isolates the standby generator from the utility power lines. When an outage occurs, it automatically disconnects the utility service and connects the generator as soon as it is ready to supply power. A typical switchover takes less than a minute from startup to transfer.

When the utility restores power, the transfer switch disconnects the generator and reconnects the utility supply.

Power Management

When high-voltage devices all try to operate at the same time, the generator may not be able to handle the full load. With a power management option, the high-voltage loads are only allowed to run when the generator can supply them with power. Some homes or businesses have multiple loads that need management while running on standby power, including air conditioners, hot water heaters, and well pumps. With the right power management option, these loads each get their share of power as necessary to keep the appliances operating during an outage.

Generator Controller

At the heart of the generator is the controller. It handles all standby generator functions from start to shutdown, and also monitors the generator for problems. Some models handle the power outage detection, others rely on the transfer switch to detect an outage. In either case, a short delay of a few seconds is allowed to ensure the outage was not momentary. The engine is started and allowed to warm up for about five seconds which also gives the alternator output time to stabilize at full voltage.

After power is restored, the controller runs the engine in a cool-down cycle, usually for about a minute, and then shuts the generator down. To keep the standby generator lubricated and ready to run, the controller will also exercise the generator on a set schedule. It starts the unit, lets it run for a short period, then shuts it down again.

Standby Generator System

Manufacturers design transfer switches and generator controllers to work together as a unit and provide more features than using separately designed and manufactured switches and generators. This eliminates compatibility issues, simplifies installation, and reduces the cost of installation while improving reliability. A standby generator system is often called a ‘Genset’ for generator set. The set includes the generator and the transfer switch, and any optional electrical equipment necessary, such as power management devices.

The modern standby generator system is always ready to supply power during an outage to keep homes safe and businesses operating.

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