computer science

Uninterruptible power supply

Uninterruptible power supply is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Uninterruptible power supply rather than just read about it. In short: An uninterruptible power supply (UPS) or uninterruptible power source is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywhe…

Key takeaways

Uninterruptible power supply belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Uninterruptible power supply to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Uninterruptible power supply from memory before moving on to harder problems.

Reference excerpt

An uninterruptible power supply (UPS) or uninterruptible power source is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery run-time of most uninterruptible power sources is relatively short (typically ranging from 5 to 15 minutes) but sufficient to start a standby power source or properly shut down the protected equipment. It is a type of continual power system. A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 volt-ampere rating) to large units powering entire data centers or buildings.

Common power problems 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:

Voltage spike or sustained overvoltage Momentary or sustained reduction in input voltage Voltage sag Noise, defined as a high frequency transient or oscillation, usually injected into the line by nearby equipment Instability of the mains frequency Harmonic distortion, defined as a departure from the ideal sinusoidal waveform expected on the line Some manufacturers of UPS units categorize their products in accordance with the number of power-related problems they address. A UPS unit may also introduce problems with electric power quality. To prevent this, a UPS should be selected not only by capacity but also by the quality of power that is required by the equipment that is being supplied.

Technologies The three general categories of modern UPS systems are on-line, line-interactive and standby:

An online UPS uses a "double conversion" method of accepting AC input, rectifying to DC for passing through the rechargeable battery (or battery strings), then inverting back to 120 V/230 V AC for powering the protected equipment. A line-interactive UPS maintains the inverter in line and redirects the battery's DC current path from the normal charging mode to supplying current when power is lost. In a standby ("off-line") system the load is powered directly by the input power and the backup power circuitry is only invoked when the utility power fails. UPSs are given a power rating in volt-amperes (VA) that range from 300 VA to 5,000 kVA. Most UPS below one kilovolt-ampere (1 kVA) are of the line-interactive or standby variety which are usually less expensive. For large power units, dynamic uninterruptible power supplies (DUPS) are sometimes used. A synchronous motor/alternator is connected on the mains via a choke. Energy is stored in a flywheel. When the mains power fails, an eddy-current regulation maintains the power on the load as long as the flywheel's energy is not exhausted. DUPS are sometimes combined or integrated with a diesel generator that is turned on after a brief delay, forming a diesel rotary uninterruptible power supply (DRUPS).

Offline/standby

The offline/standby UPS offers only the most basic features, providing surge protection and battery backup. The protected equipment is normally connected directly to incoming utility power. When the incoming voltage falls below or rises above a predetermined level the UPS turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. The UPS then mechanically switches the connected equipment onto its DC-AC inverter output. The switch-over time can be as long as 25 milliseconds depending on the amount of time it takes the standby UPS to detect the lost utility voltage. The UPS will be designed to power certain equipment, such as a personal computer, without any objectionable dip or brownout to that device.

Line-interactive

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Uninterruptible power supply

Start with the simplest possible case. Write down what Uninterruptible power supply claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Uninterruptible power supply before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Uninterruptible power supply ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Uninterruptible power supply

In research: Uninterruptible power supply appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Uninterruptible power supply in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Uninterruptible power supply is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer security hardware, Data center technology, Electric power systems components, so understanding it makes those chapters shorter.
In everyday life: Look for Uninterruptible power supply outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Uninterruptible power supply in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Uninterruptible power supply means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Uninterruptible power supply out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Uninterruptible power supply in simple terms?

Why does Uninterruptible power supply matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Uninterruptible power supply?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Uninterruptible power supply.