Question

How Automatic Transfer switch Works? What components used in making of Transfer switch? Explain all the internal working of the components used in making of ATS with single line diagram.

Answer 1

Automatic Transfer switch operation:

• The automatic transfer switch monitors incoming voltage from the utility line, around the clock.
• When utility power is interrupted, the automatic transfer switch immediately senses the problem and signals the generator to start.
• Once the generator is running at proper speed, the automatic transfer switch safely shuts off the utility line and simultaneously opens the generator power line from the generator.
• Within seconds, your generator system begins supplying electricity to the critical emergency circuits of your home or business. The transfer switch continues to monitor the utility line conditions.
• When the automatic transfer switch senses the utility line voltage has returned at a steady state, it re-transfers the electrical load back to the utility line and resumes monitoring for subsequent utility loss. The generator will continue to run for an engine cool-down period of several minutes while the entire system stands ready for the next power outage.

The three (3) functional components of a transfer switch are:

1. Power switching device to shift the load circuits to and from the power source.
2. Transfer Logic Controller to monitor the condition of the power sources and provide the control signals to the power-switching device.
3. Control power source to supply operational power to the controller and switching device.

The details of the automatic transfer system shown in figure.

The automatic transfer logic provides the decision-making for what automatic operations are to happen, and when. It controls the operation of the two transfer circuit breakers, CB-UM and CB-GM, and receives status inputs from those breakers. It also can initiate generator startup for the alternate power source.

Voltage transformers, or VT’s, step the system voltages down to instrumentation levels that can be used by these relays. A user interface allows the adjustment of certain operating parameters of the system, and updates the user on the status of the system.