Introduction Utilities transmit electricity over power lines into

home as an alternating current (AC) wave. This is how power travels through wiring and

passes into appliances.

Sometimes, interference in the supply of electricity affects how the equipment runs.

Many appliances, such as personal computers, microwave ovens and sophisticated stereo systems, have sensitive electronics that can be disrupted or damaged.

Electric systems experience disturbances from natural or man-made (e.g., lightning, wind, cars hitting power poles, falling tree branches, ).

Power Interruptions

Power interruptions are zero-voltage events on one or more phases and are typically short duration events, the vast majority of power interruptions are less than 30 seconds.

Interruptions can be caused by weather, equipment malfunction, recloser operations, or transmission outages.

Electric supply interruptions are almost always caused by circumstances external to the customer's facility.

The leading causes are lightning strikes, damage to lines usually encountered during inclement weather, overloaded power lines, and power line contacts such as birds and trees.

If working on computer, a momentary interruption can lose data. Avoid this by using a UPS/battery backup.

Interruptions - sources

Short-term Variations

Voltage sags

Sags are a short-term reduction in voltage, and can cause interruptions to sensitive equipment.

Voltage sags typically are non-repetitive, or repeat only a few times.

causes of sags are the switching on of large loads, or short circuits on the power line.

They are also caused by temporary heavy demand for electricity that exceeds the utilities capability to meet it.

Voltage Flicker

Voltage flicker is rapidly occurring voltage sags caused by sudden and large increases in load current.

Voltage flicker is most commonly caused by rapidly varying loads that require a large amount of reactive power such as welders.

It can cause visible flicker in lights and cause other processes to shut down or malfunction.

Transients

A transient is a "momentary change in the voltage or current over a very short time.

More often, transients are measured in microseconds rather than milliseconds.

Frequently this transient is called a voltage "Spike."

Transients - sources

Lightning is one of the leading causes of transients on utility power lines.

The surge currents associated with lightning strikes interact with the distribution system's impedance creating voltage transients.

Lightning can also induce voltages on power lines without even hitting them. The large electric fields generated during a discharge can couple into the power system, creating induced transients.

Transients - solutions

The solution to transients problems is the installation of surge protection equipment.

While some utilities install surge suppression equipment on their distribution lines it is still necessary for the customer to install equipment in their home or business.

Wiring solutions include using special circuit and grounding practices.

Properly designed transmission towers and other distribution system components can minimize lightning-generated transients.

Harmonics/Voltage Distortion

Harmonic is an integer multiple of the fundamental frequency (60 Hz).

So, the 2nd harmonic has a frequency of 120 Hz, the 3rd is at 180 Hz, the 4th at 240 Hz, and so on.

Voltage distortion is any deviation from the nominal sine waveform of the AC line voltage.

Because of the increased popularity of electronic

and other non-linear loads, these waveforms quite often become distorted.

Harmonics Distortion

Many solid-state motor controls and computer power supplies can cause the supply voltage to other equipment to become so distorted that sensitive electronics will either fail to operate or operate intermittently.

Power Quality Issue Residential area Heavy Commercial Industry Light Commercial Industry Agriculture

Power Quality Issue Residential area Electronic equipment and motors are two of the most common items damaged in a home. Computers, TVs, and stereos can be damaged by short bursts of high voltage known as surges. Motors like air conditioner compressors and pumps can be damaged by high voltage surges or long periods of very low voltage. Low voltage will cause the motor to slowly burn up.

Power Quality Solution Solutions to power quality problems fall into two

categories; i) wiring solutions

use of special circuit grounding practices

ii) equipment solutions. surge suppressors power conditioners battery backups emergency power generators voltage regulators