Automatic Changeover Unit (ACU)
Industry-leading power changeover unit specifically designed for the Australian railway industry
Intelligently switches between two independent supplies to maintain power to critical high current loads
● Consistent, predictable, and settable changeover times
● Switching decisions based on multi-input SmartELogic incorporating inputs from:
– Mains voltage, current, frequency and phase
– Standby (emergency supply) voltage level
– Current State and situation
Hotspot detector for ‘high resistance’ faults
● Watchdog feature to detect failures
● Remote monitoring
● Manual operation for servicing/maintenance
Why is an ACU needed?
The power supplies of all electrically-operated railway signalling systems are prone to disruption, whether by lightning strike, electrical system failure or supply disruption. Uninterruptible Power Supplies (UPS) don’t provide cost-effective protection given that the loading of a signalling system will typically exceed 40kVA, and outages may last days. Many railway authorities opt for supplying their signalling systems primarily from nearby street Mains services, while backing-up using a Standby supply, often derived from their own traction supply system.
In the past, Mains and Standby sources would have been monitored by an electro-mechanical changeover system (also known as an ECO panel) which switched the Standby supply into service after the street Mains supply had gone down. Presently-deployed electro-mechanical changeover schemes typically aren’t quick enough to prevent connected systems from responding to a break in supply that would result from such a changeover. Typical connected signalling equipment and relays require a break of no more than 70ms in order to maintain function. ECO switching time will vary depending on the nature of the power failure and can’t guarantee the 70ms minimum holdover time that typical connected relays or other signalling equipment can sustain. In a suburban commuter network for instance, the resulting dropping-out of such relays would restore cleared signals back to red which would in turn cause approach-locking requirements to impose delays before the affected route could be re-cleared.