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What is a UPS?

Everything you need to know about a UPS explained by the experts at Metartec


What is a UPS?


UPS stands for Uninterruptible Power Supply. It is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and or by means of diesel generators and flywheels for high power users. The on-battery runtime of most uninterruptible power sources is relatively short, 5–15 minutes being typical for smaller units, but sufficient to allow time to bring an auxiliary power source on line, or to properly shut down the protected equipment.

While not limited to protecting any particular type of equipment, a UPS is typically used to protect computers, data centres, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption and/or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 VA rating) to large units powering entire data centres, buildings, or even cities.

UPS Applications


The primary role of any UPS is to provide short-term power when the input power source fails. However, most UPS units are also capable, in varying degrees, of correcting common utility power problems:

  1. Power failure: defined as a total loss of input voltage.
  2. Surge: defined as a momentary or sustained increase in the mains voltage.
  3. Sag: defined as a momentary or sustained reduction in input voltage.
  4. Spikes, defined as a brief high voltage excursion.
  5. Noise, defined as a high frequency transient or oscillation, usually injected into the line by nearby equipment.
  6. Frequency instability: defined as temporary changes in the mains frequency.
  7. Harmonic distortion: defined as a departure from the ideal sinusoidal waveform expected on the line.

UPS units are divided into categories based on which of the above problems they address, and some manufacturers categorize their products in accordance with the number of power related problems they address.


How can a UPS help?


A UPS has internal batteries to guarantee that continuous power is provided to the equipment even if the power source stops providing power. Of course the UPS can only provide power for a while, typically a few minutes, but that is often enough to ride out power company glitches or short outages. Even if the outage is longer than the battery lifetime of the UPS, this provides the opportunity to execute an orderly shutdown of the equipment.

Advantages:

  1. Computer jobs don't stop because the power fails.
  2. Users are not inconvenienced by the computer system shutting down.
  3. Equipment does not incur the stress of another (hard) power cycle.
  4. Data isn't lost because a machine shut down without doing a "sync" or equivalent to flush cached or real time data.

 

What type of functions can a UPS perform?


A UPS traditionally can perform the following functions:

  1. Absorb relatively small power surges.
  2. Smooth out noisy power sources.
  3. Continue to provide power to equipment during line sags.
  4. Provide power for some time after a blackout has occurred.

In addition, some UPS or UPS/software combinations provide the following functions:

  1. Automatic shutdown of equipment during long power outages.
  2. Monitoring and logging of the status of the power supply.
  3. Display the Voltage/Current draw of the equipment.
  4. Restart equipment after a long power outage.
  5. Display the voltage currently on the line.
  6. Provide alarms on certain error conditions.
  7. Provide short circuit protection.

How long can the equipment supported by a UPS keep running after the power is interrupted?


This depends on how large the UPS unit is and what kind of equipment it is protecting. For most typical computer workstations, one might have a UPS that was rated to keep the machine alive through a 15 minute power loss.