What is an automatic transfer switch and what is it used for

What is an automatic transfer switch and what is it used for

A transfer switch is an electrical switch that switches a load between two sources. An automatic transfer switch monitors the utility power continuously and in case of the utility power failure the transfer switch will send the signal to generator so there will be continuous power supply and when the generator has reached the proper operating speed with the correct frequency and voltage levels the transfer switch will disconnect the utility source and connects the generator. ATS are devices which can automatically switch from 2-3 sources of power to improve the reliability of the electrical supply to a connected load. It automatically switches when it senses one of the sources has lost or gained power. It manages the control without manual intervention and ensures back feeding. When the utility power is restored the automatic power switch returns the load to the grid. Then the generator cool down will take place and after this cool-down period generator will shut down automatically and then the transfer switch will go back to the monitory mode and checks for next power outage. ATS also makes test run cycles to make sure the standby generator is ready when we need it.

How does an automatic transfer switch work

The automatic transfer switch can transfer load from one power source to another, it senses when the mains supply is interrupted and starts up a secondary supply ATS is also known as a generator transfer switch. ATS has additional circuit components which are mostly in the form of a computer and it can monitor the incoming power supply, voltage sags, power surges, and power spikes. ATS is connected to multiple power supply sources and supplies the load with power from only one of the sources at any particular instant of time. ATS links the load and main supply and this enables the use of either main supply or alternative source when there is outrage on the main source. ATS can maintain a proper supply of the power to the load by automatically activating the generator when there is a need.

What is the difference between an ATS and AMF

The auto main failure is an (AMF) electronic module that can automatically control a standby generator, it can be described as a programmable device which have certain parameters that can be helpful to detect the main failure and can restore the mains too. ATS and AMF have some similarities as both of them can be used to detect the failure and restore the mains. If the AMF controller is in the auto mode of operation then it does the whole control of the engine and generator. ATS doesn’t have the features to monitor the whole parameters of the engine but it does the switching in a safe way the load to the mains or generator.

What are the practical consideration that must be taken while using an ATS

Voltage regulation of the back-up source should be between the permissible ranges and it could be fulfilled by using an automatic voltage regulator unit to control the excitation of the generator. The frequency of the generator is determined by the speed of the driving engine which is provided by a closed-loop speed control system to supply the electrical loads with the standard frequency. While using more than one backup source, synchronization conditions must be considered such as the same voltage, frequency, phase sequence, and phase shift and only after checking this the power transferring is done through ATS.

What are the types of ATS transition

Open transition

Open transition is also called a break before make transfer switch, a break before make contact switch breaks contact with one source of power before it makes contact with the other. It will prevent the back feeding from an emergency generator back into the utility line. Back feeding occurs when electric power is being induced in the power grid. Power flows in the opposite direction.

Closed transition

A closed transition transfer switch is called a make before break transfer switch, make break before the transfer switch makes contact with another source before it breaks contact with the interrupted source. In some cases, loads are even affected by the slightest loss of power and there also some operational conditions in which the loads need to be transferred with zero interruption of power when conditions permit and for these conditions closed transition transfer switch can be used.

Delayed transition

Delayed transition switch is used in which large inductive loads result in large inrush currents, delayed transition allows the magnetic field to collapse completely before reconnection. There will be a time delay between the opening of the closed contacts and the closing of the open contacts and this will allow large motor loads to demagnetize before transfer. This will prevent the severe bump which is caused by switching a rotating motor from one source to another source which is not in synchronism.

What are the applications of ATS

  • ATS can be used for facilities with a standby power system and a single utility feed, so if any problem occurs for utility feed ATS will transfer the load
  • It can also be used in redundant utility feeds with no standby generator so if one utility feed fails then the load will be connected to the other one.
  • It is also used in systems where multiple on-site generators are used so if one of the generators fails the load will be transferred to the other
  • Continuous power to the load is possible by using the ATS
  • It is used in places where constant and reliable sources of power are needed
  • Manpower is not needed for starting the generator and changing power supply from one source to another.