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Power QualityPower Quality

EKT 451EKT 451CHAPTER 8CHAPTER 8

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IntroductionIntroduction

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.

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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, ).

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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.

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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

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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.

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Voltage FlickerVoltage Flicker

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

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

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

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TransientsTransients

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

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

Frequently this transient is called a voltage Frequently this transient is called a voltage "Spike." "Spike."

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Transients - sources Transients - sources

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

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

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

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Transients - solutions Transients - solutions

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

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

Wiring solutions include using special circuit and Wiring solutions include using special circuit and grounding practices.grounding practices.

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

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Harmonics/Voltage Distortion

because of the increased popularity of electronic and other non-linear loads, these waveforms quite often become distorted.

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

The distorted waveform repeats itself with some basic The distorted waveform repeats itself with some basic frequency.frequency.

The sine wave associated with this frequency, which is The sine wave associated with this frequency, which is usually 60 Hz, is called the fundamental.usually 60 Hz, is called the fundamental.

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

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Harmonics Distortion

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

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Power Quality IssuePower Quality Issue

Residential areaResidential area Heavy Heavy

Commercial Commercial IndustryIndustry

Light Commercial Light Commercial IndustryIndustry

AgricultureAgriculture

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Power Quality IssuePower Quality Issue

Residential areaResidential area

Damaged Equipment             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.

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Power Quality SolutionPower Quality Solution

Solutions to power quality problems fall Solutions to power quality problems fall into two categories; into two categories;

i) wiring solutions i) wiring solutions Wiring solutions include the use of special Wiring solutions include the use of special

circuit and grounding practicescircuit and grounding practices ii) equipment solutions. ii) equipment solutions.

surge suppressorssurge suppressors power conditioners power conditioners battery backupsbattery backups emergency power generators emergency power generators voltage regulatorsvoltage regulators