Len McGanity, product manager at ABB, explains how a new approach to Automatic Transfer Switches (ATSs) can enhance operation of mission-critical power supplies.
What is an ATS?
ATSs play an essential role in data centres and other facilities where continuity of power is critical. They detect when power is lost on the main supply and then automatically power switch loads over to a secondary supply, as well as powering up backup generators.
Outages affect all sites at some point, even those with ‘five nine’ reliability of 99.999%. When they happen, ATSs ensure constant uninterrupted power to supply servers and other critical equipment.
What is important in an ATS?
Until recently, ATS installations could have as many as 30 connection points between the ATS controller and switch to carry signals for services such as metering, sensors and PLCs. However, every electronic connection is a potential source of failure – therefore by opting for an ATS with minimal connectors, operators will benefit from higher inherent reliability.
Another benefit of such simplicity is more straightforward installation and maintenance. Simplicity of an ATS unit can be further enhanced by reducing the number of external components and accessories. Instead, such accessories can be integrated into the ATS, for example metering or communications modules that slot into defined space inside the ATS.
This reduces the amount of installation and wiring, as well as the space required elsewhere in the cabinet. While this also saves installation, it also helps control costs and reduce complexity as panel builders can use standardised panels, even when the data centre operator has specific requirements for their installation.
Modular accessories also help from a maintenance perspective, as modules can be swapped easily when required, reducing downtime and service costs.
One important feature with any mission-critical equipment is that it should operate reliably in the most unexpected of conditions. While the data centre environment is well protected from extremes of temperature and vibration, ATS units should be reliable to switch seamlessly even after being exposed to fault-level voltages during a short circuit.
How can ATS units integrate into monitoring systems?
As more operators are turning to condition-based monitoring, remote diagnostics and remote control to manage their assets, they are asking for electrical equipment to be digitally enabled. That is why the latest generation of ATSs can be sourced with modules for in-built intelligence and digital communication, as well as metering.
At the most simple level, this allows in-built condition and temperature monitoring. This provides peace of mind so that operational staff know that their ATSs are always ready at a moment’s notice. It will also raise an alert when the units require maintenance, meaning that operators will only need to maintain kit when it is needed, rather than using the conventional approach of time-based maintenance.
More sophisticated services such as automatic load shedding are also possible, by combining the capabilities of intelligent software, metering and communication modules. This is valuable for sites where the backup generators are only sized to provide power for critical loads.
When load shedding is enabled, an intelligent algorithm in the ATS will compare the generator’s capacity with the power consumption. It will then review a list of low-priority loads and automatically switch off the most appropriate ones. This decision-making is based on the priority of a load and the power drawn, as well as ‘respect time’. This is the minimum period that a load must remain connected or disconnected – and this feature is designed to support long-term reliability.
Once mains power has returned, the ATS will then reverse the process, switching loads back over to the main supply and switching low-priority loads back on while powering down the genset safely.
The communication interface is also valuable during installation and commissioning, particularly. It enables remote programming, configuration and testing, which is a major advantage when working on a project where multiple ATS units will protect multiple circuits.
With many SCADA and Building Management Systems in operation in the data centre sector, it’s important that the communication interface is compatible with existing technology as well as having capacity for future-proofing.
As such, the latest generation of equipment, such as ABB’s TruONE ATS, can communicate using two standards at once from the seven most common protocols: Modbus, Profibus, DeviceNet, Modbus TCP, Profinet, EtherNet/IP and Open ADR, as well as IEC 61850.
What to look for in ATS technology
ATSs are used around the world in facilities where uninterrupted power is essential. Existing ATS technology was based on combining switches, controllers, sensors and interfaces.
One drawback of this was that these arrangements were often complex and time consuming to install, with multiple connectors being potential points of failure. Some also require special arrangements during maintenance.
As a result, ABB developed the TruONE ATS to package the switch and controller into a package connected by a single digital connector to enable straightforward operation. Ergonomic studies have found that this method reduces installation by 80% and cuts time required for cabling and commissioning by up to 90%.
Being a digital connection, the controller or Human Machine Interface (HMI) can be mounted on the outside of a panel door and completely isolated from line voltage to ensure safe operation for site-based maintenance staff.
Integrating the digital communication interface will help data centre operators future-proof their operations and streamline operations with remote and cloud-based monitoring via digital platform systems.
When selecting a suitable ATS for your facility it is also essential that it provides continuous operation so that generator use during business hours goes unnoticed, resulting in minimal disruption.
Additionally, safety and protection should always be top of the agenda, it is beneficial if your chosen ATS unit enables both emergency and manual operation – even under load – without opening the panel door when the HMI is mounted to the ATS frame.
This way, the HMI can be detached from the frame for door mounting, offering more flexibility for the panel designer. Additionally, regardless of the HMI installation method, there’s no need to connect dangerous line voltages to the door, mitigating the risk of operator injury due to equipment malfunction.