Automatic Transfer Switches

How an Automatic Transfer Switch (ATS) works:

The ATS has a supply monitoring relay which monitors for a utility (mains) failure or a failure in one of the individual power cables (phases).

When a failure is detected the ATS sends a signal to the generator instructing it to start (Remote Start Signal).

Once the generator is running at its required speed and voltage the ATS switches the mains supply off and simultaneously switches the generator supply on.

The generator will now supply the electricity to your building.

When the mains is restored, the supply monitoring relay senses this and switches the generator supply off whilst simultaneously switching the mains supply on.

The generator will continue to run for a preset time period known as the cool down period and then the whole system waits for the next mains failure.

To prevent the generator starting when the mains is interrupted  for small time intervals e.g. 2 seconds, time delay relays are built into the ATS to prevent a remote start signal being sent to the generator. Similar relays are also supplied to prevent the reverse happening i.e. the generator stopping and transferring  load to the mains when the mains is only restored temporarily.