Automatic Transfer Switch

Automatic Transfer Switch

An automatic transfer switch is an integral component of an emergency power supply system (EPSS). This transfer switch allows safe switching from utility power to standby generator power while maintaining isolation of each source from the other. The main goal is to provide electrical power to the facility loads (during a power outage) from the standby generator without backfeeding that can damage utility equipment and hurt (or kill) utility workers. Automatic transfer switches safeguard data and telecommunication networks, industrial processes and critical installations such as health care facilities and financial transaction centers.

Transfer Switch Components

Automatic transfer switches continually monitor the incoming utility power. If the normal power source, often the utility, fails or exhibits some anomalies such as voltage sags, spikes or surges, these switches detect this loss of power (or anomaly) and send a start signal to the standby generator. The switches connect the generator to the facility loads when the generator has achieved proper frequency and voltage. When utility power returns or no anomalies have occurred for a set time, the transfer switch will then transfer back to utility power. It will instruct (command) the generator to turn off, after a specified amount of "cool down" time with no load on the generator. Electrical power to a facility's loads will be lost for a period of approximately 10 seconds while the generator set starts-unless there is an uninterruptible power supply (UPS) serving loads in the system to bridge the power gap while the generator set starts.

Power system specialists can set up a transfer switch to provide power only to critical circuits or entire electrical (sub) panels. Some transfer switches allow for load shedding or prioritization of optional circuits, such as heating and cooling equipment.

There exist three different ways in which a transfer switch can provide power-switching operation:

  • Open Transition - Break-before-Make operation
  • Closed Transition - Make-before-Break operation
  • Closed Transition Soft Load - Both sources are paralleled

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

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

Transfer Switch

Power system specialists should test automatic transfer switches on a monthly basis for EPSS in accordance with NFPA (National Fire Protection Association) Code 110. This standard also requires a monthly generator run. There are two main steps for such testing: 1) automatic generator start that is initiated by the transfer switch, 2) automatic transfer of facility load onto the standby generator. During the test, the specialists should also take appropriate action when power interruption to the facility load is a matter of concern.

Existing Facilities

For existing facilities, the engineer must determine the loads that may actually suffer negative impact from monthly interruptions in power. One solution for this is to use UPS for protection from these negative impacts. Also, engineers can replace existing open transition switches with closed transition switches.

The testing of a transfer switch establishes the following:

  • The switch is not going to fail during a transfer
  • Moving parts will continue to operate smoothly
  • Transferring capacity to the standby generator will be very smooth

How Prime Power can help you with different automatic transfer switch related services
We at Prime Power provide the installation, testing, troubleshooting, and maintenance of your automatic transfer switch. You can rest assured of the quality of the automatic transfer switches that we offer. They are safe, reliable, rugged, versatile, and compact assemblies for transferring essential loads and electrical distribution systems from one power source to another. Prime Power can deliver transfer switches in separate enclosures for stand-alone applications, or as an integral component of other equipments such as switchgear.

If your business relies on safeguarding data on telecommunications networks, industrial processes and critical installations such as health care facilities and financial transaction centers, we can help your business by installing high-quality automatic transfer switches for your EPSS.

Prime Power's automatic transfer switches are characterized by:

  • Fewer moving parts resulting in higher reliability
  • Inherent double-throw operation
  • Silver alloy main contacts (highly conductive) and arcing contacts (resistant to heat)
  • Repeatable fast transfer operation
  • Safe manual operation under load (without opening door)
  • Slow switch operation for maintenance and adjustment.
  • UL listing with "any breaker

Prime Power also provides high-quality services such as:

  • Engineering, design, and service responsibility, all under one roof
  • Staffed service centers that operate 24/7. Service vans that are stocked with parts and not dependent upon supply from other manufacturers

We understand that automatic transfer switches require regular maintenance including preventive maintenance in the form of testing. Our engineers are highly experienced to carry out testing of automatic transfer switches to see you and your business prepared for a power-outage emergency.