What is an Offline UPS?
An Offline UPS, under normal conditions (mains present), supplies the load with mains power. Only when there is an interruption in the mains supply, or the mains supply voltage goes out of spec, (mains fail), does the UPS switch the load to inverter power with a short break. The Offline topology is relatively inexpensive, however it provides very little or no filtering of noise that is present on the mains supply and there is a short break in supply, (approx 4ms), when the inverter is switched in.
What is a Line Interactive UPS?
A Line Interactive UPS, under normal conditions (mains present), supplies the load with mains power while using the inverter to charge the battery. When the mains supply fails the power reverses out of the battery and supplies the load. The line interactive topology provides more filtering and regulation than the offline topology and eliminates the break in supply to the load inherent with the offline topology.
What is an On Line UP?
An On Line UPS, under normal conditions (mains present), supplies the load with mains power from the inverter. This type of topology normally provides better filtering and regulation and ensures that there is never a break in supply to the load. Most good On Line UPS’s topologies use double conversion techniques to provide superior performance and these UPS’s are used on critical loads.
What is Double Conversion?
Double Conversion refers to the two conversion stages needed to convert the AC supply to DC and then back to AC to supply the load. The DC link provides two important advantages over other topologies:
a). It provides very good filtering of mains noise, thus ensuring that the load is supplied with clean power.
b). The battery is always connected to the input of the inverter ensuring that there is no switch over time when there is a loss in mains supply.
What are Sags and Surges when referring to the AC mains supply?
A sag is when the AC voltage drops below a certain percentage for one cycle or more, (normally 10% of the nominal value). Sags can cause system crashes as well as damage hardware. A surge is defined as the AC voltage rising above a certain value for one cycle or more, (normally 10% of the nominal value). Surges can damage hardware.
What is noise in the context of a power supply?
Noise is high frequency oscillations superimposed on the 50Hz mains supply. Can cause incorrect data transfer and corruption, program crashes and software and hardware failures.
What are spikes in the context of a power supply?
Spikes are high voltage surges lasting less than a cycle, normally less than 1ms in duration. Spikes can have a magnitude in excess of 100% of the supplies nominal voltage. Can cause incorrect data transfer and corruption, program crashes and software and hardware failures.
How is power factor defined with respect to a UPS?
Power Factor in the context of a UPS is defined as the ratio of real power output to apparent power output. Most computer loads have a power factor of 0.6 to 0.7, therefore if a UPS is supplying a 1000VA 0.7 pf computer load, it must be capable of supplying real power of 700 watts and apparent power of 1000VA. Looked at in another way, the lower the power factor of a UPS the lower the real power it is capable of supplying.
Does a UPS provide lightning protection for equipment?
A UPS does not provide adequate lightning protection for sensitive electronic equipment. For lightning protection to be effective a well designed and installed protection system must be installed upstream from the UPS.
What is an AGM battery?
An Amalgamated Glass Matt, (AGM), battery is constructed using fiberglass separators between the plates. The high porosity of these separators is used to contain the quantity of electrolyte necessary for cell operation, but without any free electrolyte.
What are the common types of batteries used in UPS system?
Vented Lead Acid, sometimes used in large UPS installations, require special rooms. Valve Regulated Lead Acid (AGM) batteries are available in 3 - 5 year and 8 –10 year design life. No special room is required as recombination technology provides for low gas emissions. Valve Regulated Lead Acid (flooded) batteries are available in 5 year design life. Unlike the AGM battery these batteries have flooded electrolyte. They have gas recombination technology making them suitable for UPS application especially in countries with high ambient temperatures.
What is the design life of a battery?
The design life must not be confused with the actual life span of the battery. The design life is the time it will take for the battery to lose 20% of its capacity when operated strictly in accordance with the manufacturer’s specifications. The actual service life of a battery is determined mainly by temperature, ripple current and number of discharges.