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What Is An Uninterruptible Power Supply? IT Fundamentals

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What is a UPS

The worst thing about a power failure is that you have no idea when it’s going to come. And even worse, if will take your server and network systems offline, usually for a few minutes. When you’re working on some important project this can be really frustrating, especially if you’re in the middle of something big. That’s why most businesses use an Uninterruptible Power Supply also known as a UPS. Not every power outage can be predicted so having a UPS ensures these systems will remain online and running smoothly through any situation.

Types Of UPS

Standby (offline)

A standby UPS provides protection against power surges and, in the event of a power outage, acts as a battery backup to provide continuous power to connected devices. The unit is typically installed near the load or on the same circuit as critical equipment, such as computers and networking equipment. The device can be configured for rack mount or desktop use and includes an internal battery that’s charged during normal operation. In the event of a power failure, AC power passes through the unit under normal conditions and switches to battery mode when a power failure is detected.


Line-interactive UPSs provide consistent power by regulating the output voltage of the power supply unit (PSU) with an internal inverter. They can protect against sags as well as surges and outages. The PSUs in line-interactive UPSs have low impedance and high frequency ratings, so they can handle the high current demands that occur during startup of large loads like motors or air conditioners. Line-interactive units also have their own battery backup systems that kick in when there’s a loss of external AC power.

Online (double-conversion)

An online double conversion UPS is a type of uninterruptible power supply that uses several batteries in parallel to provide backup battery power. Online double conversion UPS systems are typically used in data centers and other facilities with a large amount of equipment that requires continuous power. The system uses a battery charger and inverter to convert incoming AC power from the utility grid into DC power, which is then converted back into AC to provide electricity to connected devices.

What Can A UPS Protect Against?

Common types of power interruptions include spike, surge, sag and brownout. The following is an explanation of each type:

Blackout: A total loss of electricity to an area due to failure of equipment or other causes, such as lightning strikes or trees falling on wires.

Spike: A spike is a sudden increase in voltage that lasts for less than a second and may cause damage to computer equipment. It usually occurs when demand on the grid increases or when there is a fault in the grid’s transmission system.

Surge: A surge is similar to a spike except it lasts longer — up to several seconds — and may result in permanent damage to equipment with sensitive electronics such as televisions or computers. Surges can also happen when lightning strikes near power lines or substations.

Sag/Brownout: A sag is a temporary reduction in voltage that lasts for several minutes and usually occurs during periods of high demand on the grid when there aren’t enough generating units available to meet this demand

Swell: The opposite of a brownout. A swell is a period of increased voltage that lasts for seconds to a minute.

Line noise:

Radio frequency interference (RFI) – The electromagnetic radiation emitted by radio transmitters that causes interference with other devices in close proximity to the transmitter’s antenna.

Electromagnetic interference (EMI) – The interference caused by electric motors, neon lights and other electrical equipment operating near sensitive electronics such as computers or televisions.

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