What is a UPS System?
Uninterruptible Power Supply Systems
Uninterruptible Power Supply (UPS) are used predominantly to support mission-critical applications where a loss of power could damage or disrupt business continuity or jeopardise safety.
Uninterruptible Power Supply Systems
An Uninterruptable Power Supply picks up the load of critical equipment if it senses and imminent power failure and provides power from its battery systems. A UPS therefore ensures the uninterrupted operation of mission-critical electrical systems can continue without disruption.
A UPS is usually only employed as a short-term measure, however with enough batteries, a UPS can support a load for as long as required. For power interruptions that last longer than a few minutes, a generator is the preferable option. Each have their own place in data centre infrastructure management.
What will a UPS System protect against?
The main power events a UPS system can protect against are:
Power Outage
A power cut to a data centre or comms room for example could mean data corruption, a lapse in business continuity and ultimately, loss of revenue. Supporting your facility with back up UPS systems will significantly increase resilience and prevent down time.
Under-voltage
An under-voltage scenario is a temporary decrease in power. The power used by the sudden addition of an electrical load can cause a significant voltage drop on the rest of the circuit. Undersized or overloaded utility or facility transformers will increase the likelihood of this occurring.
Over-voltage
Overvoltage swells are the opposite of undervoltage. Common causes of overvoltage are sudden load reductions, insulation failures or addition of intermittent supply to the local grid.
Power Surges
Typically caused by something like a lightning strike, a power surge can cause devastating damage to server room equipment.
UPS systems can completely isolate your equipment from all power quality issues.
Types of UPS systems
There are four common elements to most UPS systems. The Rectifier (converts AC-DC), the batteries (store energy), inverter (converts DC-AC) and the transfer switch (used to switch the load from mains to battery backup). The flow of power through these key elements determines the type of UPS.
Stand by UPS
These UPS systems simply switch to back up power from the batteries using the transfer switch in the event of a power outage. Most stand by UPS configurations include a surge protector and a power quality filter on the incoming line. The batteries are trickle charged to ensure they are ready for and power outage. These systems are low cost and efficient.
Line Interactive
In this design, the battery-to-AC power converter (inverter) is always connected to the output of the UPS. Operating the inverter in reverse during times when the input AC power is normal provides battery charging. When the input power fails, the transfer switch opens and the power flows from the battery to the UPS output. With the inverter always on and connected to the output, this design provides additional filtering and reduces switching times when compared with the standby UPS topology.
Double Conversion
The double conversion design allows power to flow into the rectifier where it is converted to DC, a fraction of this DC current charges the batteries, the rest in converted back to AC through the inverter to support the load, hence the name double conversion. During a power failure, DC power is drawn from the batteries through the inverter to power the critical load. This design removes any transfer time as the inverter is already fully engage and supporting the load. It also provides the best isolation for the critical load from power quality issues however it is not as efficient as other methods.
Other types of UPS exist that include, to a varying degree, some of the technologies mentioned above. One example of such is Schneider Electrics new ECOnversion or older Delta-Conversion technologies. It is important to note that different modes on UPS systems can affect what ‘type of UPS’ a UPS is operating as. High efficiency ‘Eco’ modes usually convert a Double Conversion UPS into a Stand by UPS system at the cost of resilience.
To find out more about the different types of Uninterruptible Power Supply Systems download this White Paper.
