What is a UPS?
UPS is an abbreviation for Uninterruptible Power Supply. In simply terms it provides protection against power outages and brown outs. They are used to protect computers, servers, network equipment, and security systems where an unexpected power outage would cause serious disruption, or even injuries and fatalities, such as medical facilities.
The primary role of a UPS is to provide short term power when the input power fails, often working together with backup generators to bridge the gap during generator start up. They also provide varying degrees of power correction and protection, such as;
- Over and Under voltage protection
- Filtering of line noise that can damage sensitive equipment
- Providing stable output frequency
- Harmonic distortion correction
Types of UPS
Standby UPS
This is the most common type and is generally used for personal computers and workstations.
The transfer switch is set to choose the filtered AC input as the primary power source (solid line path), and switches to the battery/inverter as the backup source should the primary source fail. When that happens, the transfer switch must operate to switch the load over to the battery/inverter backup power source (dashed path). The inverter only starts when the power fails, hence the name “Standby.”
Line Interactive
The Line Interactive UPS, is the most common design used for small business, web, and servers. In this design, the 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 yields reduced switching transients when compared with the Standby UPS topology.
Double Conversion
These are usually the UPS system of choice when dealing with higher voltage scenarios, and they feature a configuration similar to those of standby units, but with a primary power path focused on the inverter rather than the AC main. This configuration offers excellent efficiency as the AC current simultaneously charges the backup battery, but there is a risk of long term wear on certain components with a double conversion.
Maintenance
UPS systems generally provide emergency power to essential services, therefore a correct maintenance plan is essential to ensure the correct operation when required. Maintenance procedures vary between manufactures, with inspection frequencies dependent of how critical the system is. Generally inspections will be undertaken annually.
General maintenance may include;
- Testing of line and load side parameters
- Visual inspection
- Thermal Imaging
- Battery condition check
- Simulated fault (Turn line power off and check output parameters)
- Run time under full load
If you need advice on selecting or maintaining a UPS system, feel free to contact us.
More Information/References
http://www.apc.com/us/en/faqs/FA157448/
http://powershield.com.au/what-types-of-ups-uninterruptible-power-supply-are-there/
http://www.datacenterexperts.com/resources/white-papers/datacenter-power/188-3-types-of-ups-s.html