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The Basics of Power Failures and Their Solutions

Session 2 - What Are the Types of Power Outages?

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In the previous session, we looked at how power companies increase the reliability of their power transmission. However, it is impossible to prevent power outages entirely. In this session, let’s learn about power outages and other disturbances.

By the way, did you know that there are various kinds of power failures?
There are, in fact, various “kinds” of outages. Here, as shown in the figure below, we’ll explain the three patterns of power disturbances using the scenario of a lightning strike affecting transmission line A.

How Electricity is Transmitted

Power transmission during an outage

Dips (instantaneous voltage dips, brownout)

Electricity generated at the power plant is first transmitted via dual line then combines into a single line at a substation. Leaving the first substation, the line splits into two then is feed through the next substation. If lightning strikes transmission line A, the voltage on all the A, B, C, D lines receiving power from the same substation drops for a brief moment.
That "moment" is about 0.07 to 2 seconds. Electric utilities typically label such phenomena “dips.”

Interruptions (momentary outage)

After lightning strikes line A causing a dip, the utility will disconnect line A and then, after about a minute, power will regain transmission. This phenomenon, where power transmission on line A is restored following a momentary break in service, is defined by power companies as an “interruption.”
It may be a stretch to merely deem this an interruption on account of it generally taking about a minute to regain transmission. However, as the disruption lasts under a minute, utilities on purpose refrain from calling this a “power outage.”

Power outage

The power company automatically restores power transmission to disconnected line A within a minute. If the voltage doesn’t stabilize even after power is restored, the power transmission on line A is stopped. After that, the utility will investigate the cause of the voltage problem, but line A will stay disconnected until the cause has been eliminated.
This situation, according to the utility, would constitute a “power outage” since the power has been stopped for more than one minute.

As described above, power companies define three types of power disturbances: dips (instantaneous voltage dips), interruptions (momentary outages), and power outages.

I this session, we took a brief look at the types of power outages. These electrical disturbances are not solely caused by the supply side. In the next session, we’ll look at disturbances caused by events on the receiving end where we use electricity.

Revised: 9/29/2016

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