Choosing a generator for data centre power protection

Following a power outage, a UPS system with true online topology will be able to supply all the protection required - even for the largest, most critical loads, if sized correctly. The UPS dual power conversion technology is designed to filter out mains-borne disturbances, while the batteries maintain power during the initial blackout period. However, a UPS alone will not be sufficient if the blackouts are likely to protract and extend beyond the battery autonomy of the UPS. Extending battery autonomy to hours rather than minutes can be prohibitively expensive, especially as there is little value in powering a critical load but not its cooling system.

UPSs and generators working together

In some applications, it may be acceptable to use the battery autonomy to gradually reduce the load if the blackout time is extended. However, for critical applications that must remain up and running through power blackouts of any length, a matched UPS-generator arrangement becomes the only practical solution. To ensure continuity of power throughout a blackout event, UPS, generator and an Automatic Mains Failure (AMF) Detection panel are needed to work together. When the mains initially fail, the UPS batteries support the load during a pre-set AMF delay time. If this period expires, the generator starts up and the UPS detects the generator power, using it to feed the load and recharge the depleted batteries. The generator runs until mains power is restored and stabilised, and is then shut down under AMF control while the UPS reverts to mains. UPS battery power covers the short power interruption during this transfer.

A backup generator set comprises a stored energy source, an engine, an alternator, a control panel and the AMF panel. Although both gas and diesel-powered engines are available, standby generators are normally diesel-powered. Engine suppliers include John Deere, Volvo and Mitsubishi, for which different control panels with varying capabilities are available. Standard types provide automatic and manual generator control while providing the basic indication of operational parameters, which includes voltage, frequency, coolant temperature, oil pressure and battery voltage, plus alarm and fault indication. More advanced panels offer more sophisticated user interface displays and enhanced diagnostic capabilities. Remote monitoring and control via Ethernet, RS485 or USB ports as well as fault-finding and alarm diagnostics are also possible.

Whichever configuration is chosen, generators must be compatible with the UPS and all other power equipment to guarantee an uninterrupted power supply. Ensuring compatibility can be considerably simplified by sourcing UPS and generator from a single supplier, who offers proven, matched generator/UPS sets. An issue can be the generator output frequency. If its range is outside the UPSÂ’s tolerance, the UPS cannot synchronise with the generator without endangering its load.