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A fresh approach for automatic transfer switches

Author : Len McGanity, Product Manager at ABB

01 May 2018

According to this piece, a new breed of automatic transfer switches (ATS/s) has simplified communication between the switch and its controller to save installers time and effort, as well as improve capabilities, in critical power and fire safety systems for the connected and IoT age.

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The role of an ATS is to seamlessly transfer power from mains to a secondary supply in the case of an outage. Such switches have existed for many years, but the technology is changing. This reflects the growing sophistication of digital communication for condition monitoring and fire safety testing, as well as new load-shedding services.

Why are ATS units particularly important now?

Even highly-reliable power supplies will experience an outage at some point: there is still room for loss of power even in systems with ‘five nines-level’ (99.999%) availability, such as data centres, hospitals and telecoms sites, as well as commercial and industrial sites, where loss of power can have significant costs.

However, the same is true for any building that requires constant and uninterrupted power for fire-critical equipment, such as pumps for sprinkler systems, smoke extractor units, emergency lighting and fire lifts. Tall buildings are a particular area of focus, following the Grenfell Tower tragedy, which highlighted the importance of fire safety and emergency systems in high-rise residential blocks, as well as other buildings (such as offices, sports arenas and entertainment venues).

Today, ATSs are installed in almost all buildings higher than three storeys, to meet the BS 8519 fire safety standard, which was published in 2010.

How is the role of ATSs changing?

The most basic role of an ATS is to switch the connected loads to a secondary power supply or a UPS. However, an ATS may also control the start-up of a backup generator, only switching loads over once it is up and running. Once mains power has returned, the ATS will then automatically return to the original supply and power down the generator.

Today, expectations are growing in terms of ATS capabilities, which could include the integration of units into building management systems (BMS), the adoption of condition-based monitoring to optimise maintenance budgets, and the enablement of sophisticated load-shedding schemes.

Even straightforward installations have traditionally required a complex arrangement, with integration of external sensors and controllers. The latest generation of ATSs, however, includes straightforward design for ease of installation with modular accessories and communication capabilities for remote monitoring.

What features are important in an ATS?

Given that the ATS is the piece of kit that handles the mechanics of switching in an outage, high reliability is essential – and the more straightforward the design, the better the reliability. Some ATSs have as many as 30 individual electronic connections between the switch and its controller. The latest ATSs use digital communication over a single wire connector.

Ease of installation and maintenance are also important, especially for facilities where multiple units have been installed. Some ATSs have a self-contained design that integrates modules for accessories and communications.

This minimises the need to install external components. Once in service, simple replacement of modules during servicing also reduces downtime and service costs. The modular approach also eliminates the need to make space for components and wiring elsewhere in the panel.

This enables a more compact installation and it also helps panel builders to offer standard cabinets, even for projects where the customer’s specification calls for additional capabilities. 

The ATS is most likely to be needed when a site is faced with extreme or unexpected conditions, so it is important that it should be proven to operate reliably in extreme temperatures, voltages – and after exposure to mechanical shock or vibration. The latest generation of ATSs has built-in temperature and condition monitoring to ensure they are ready if the operator needs to switch to backup power at short notice. What type of communication interface is important?

Communication is becoming increasingly important to all types of electrical equipment and in every phase of an asset’s lifecycle. With Industry 4.0 and the Internet of Things becoming more influential, facility managers now expect equipment like the ATS to be compatible with remote monitoring and control, either through existing SCADA or BMS systems, or via cloud-based monitoring and control systems. These are becoming more important for facility managers who want to operate a fleet of assets and access operational information from a connected device.

The latest ATSs feature built-in metering, diagnostics and the ability to interface with external control systems. They are also compatible with the most common communications protocols and are even able to manage communication with multiple systems at one time. These include Modbus, Profibus, DeviceNet, Modbus TCP, Profinet, EtherNet/IP and Open ADR, as well as the IEC 61850 smart grid communication protocol. This ensures that the ATS is compatible with a facility’s existing technology, as well as with future upgrades.

An intelligent communication interface is also important during the installation and commissioning phase: it enables remote programming, configuration and testing. This feature allows installers to connect with multiple ATS units on different circuits and save time, which would otherwise be required for programming each one individually.

Do ATSs have any other capabilities?

Modern state-of-the-art ATSs can also enable load-shedding. This is helpful for sites where backup generators produce enough power only for essential equipment. In such a case, an ATS can be equipped with metering sensors, communication and intelligent software to automatically switch off low priority loads, so that the loads match the output of the emergency generators. Once the software detects that mains power has returned, the ATS will then automatically reconnect the loads, either individually or in groups.

How is the TruONE ATS different to other switches?

Existing ATS technology has been developed by combining controllers and switches with a variety of sensors and interfaces, depending on the requirements of the installation and the relevant standards. Feedback from the industry suggested that such switches are time-consuming and complex to install. ABB, in response, developed the TruONE ATS to be the first unit that combines the switch and controller in a single package that is compatible with the multiple standards used around the world.

Because it replaces multiple individual electronic connections with a single digital connector, ergonomic studies have found that the new switch will speed up installation by 80%, as well as reduce the time required for cabling and commissioning by up to 90%.

Another important difference is the ability to operate the switch manually under load. This means that an operator can restore power immediately if required. In comparison, some ATSs must be isolated before manual operation – which may even require the building to be evacuated. Because it has just one simple connector, it is possible to mount the human-machine interface (HMI) on the outside of a panel door. This means that users can safely operate the switch manually without opening the cabinet door, therefore protecting operators from any possible exposure to live conductors.

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