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November 19, 2012 -
Power & Communication
Today's tip is to consider online uninterruptible power supplies (UPS) to protect data centers. Generators can offer long-term protection from interrupted service, but only a UPS can protect against many common faults in power systems.
An online UPS has three components: a charger/rectifier, storage batteries, and a power inverter. Incoming alternating current from the utility enters the charger/rectifier, which converts it to direct current. This direct current charges the batteries and supplies power to the inverter, which converts the direct current back to alternating current. In systems that provide power for loads in extended outages, a generator typically is connected to the batteries.
The UPS supplies power to the loads continuously, no matter what happens to the utility power. But taking alternating current from the utility, converting it to direct current and back to alternating current also eliminates most power disturbances, including noise, transients, and voltage fluctuations.
Passive-standby systems provide the lowest level of protection and are the least expensive of the three. These off-line systems monitor incoming power and switch to a battery source when an interruption occurs. This transfer takes place in milliseconds and is acceptable for some computer-based applications. But the loss of power during the transfer can disrupt some sensitive electronic equipment. These UPS also do not filter power-line noise or voltage spikes or sags, so their use is limited largely to desktops or similar systems not performing critical tasks.
Line-interactive systems insert a transformer or an inductor between the power source and the connected equipment, and a bank of batteries helps condition and filter incoming power. The systems offer more protection than passive-standby but do not offer enough protection for mission-critical operations, such as data centers.
Double-conversion systems are true online UPS. They eliminate the momentary loss of power found in the other two types of UPS by using a bank of batteries connected to the direct-current part of the system. They fully isolate protected equipment from the power source, thereby eliminating most power disturbances. Run times range from 15 minutes to as long as the generator's fuel lasts.