Harmonics

Chapter 1

Introduction

1.1 Motivation:

The primary motivation behind the study of Power System Harmonics is

the power quality in a power system has become an important issue nowadays

with significant development of power electronics technology application of

power electronic equipments and nonlinear loads in recent years lead to harmonic

interference problems in a power system. The loads are nonlinear and harmonic

currents generated by the loads will cause a voltage drop across source impedance

which causes decrease in power quality.

Power System may also contain sensitive loads such as computers or

electronic controllers which consume less power are connected in parallel with

nonlinear loads. The harmonics generated by these nonlinear loads may be

harmful to sensitive loads and could even damage the sensitive loads.

1.2 Background:

A good assumption for most utilities in the United States is that sine-wave

voltage generated in central power stations is very good. In most areas, the

voltage found on distortion system typically has much less than 1.0 percent

distortion. However, the distortion increases closer to the load. At some loads, the

current waveform barely resembles a sine wave. Electronics power converters can

chop the current into seemingly arbitrary waveforms.

While there are a few cases where the distortion is random, most distortion

is periodic, or an integer multiple of the power system fundamental frequency.

When electronics power converters first became commonplace in the late

1970s, many utility engineers became quite concerned about the ability of the

power system to accommodate the harmonic distortion. Many dire predictions

were made about the fate of power system if these devices were permitted to

exist. While some of these concerns were probably overstate, the field of power

quality analysis owes a great debt of gratitude to these people because their

concern over “new” problem of harmonics sparked the research that has

eventually led too much of the knowledge about all aspect of power quality.

Presence of harmonics has been a lot since the 1990’s and has led to

deterioration in the quality of power. Moreover, there has also been an increase in

use of devices and equipments in power system also including the nonlinear loads

and electronic loads used in residential areas there by loading the transmission

and the distribution systems. This is because they operate at very low power

factors which increases the losses in line and also causes poor regulation in

voltage further leading the power plants to supply more power. Also, some

nonlinear loads and electronics equipment are such that instead of drawing current

sinusoidally they tend to draw current in short pulses thus creating harmonics.

Some of the examples of nonlinear loads would be rectifiers, inverters, etc. Some

of the examples of electronics equipments would be computers, scanners, printers,

etc.

Chapter 2

Cause of Power Quality Deterioration

2.1 Introduction:

As always, the main objective of the power system would be generation of

electrical energy to the end user. Also, associated with power system generation

is the term power quality. So much emphasis has been given to power quality that

it is considered as a separate area of power engineering. There are many reasons

for the importance given to the power quality. One of the main reasons is, the

consumers are well informed about the power quality issues like interruptions,

sagging and switching transients. Also, many power systems are internally

connected into a network. Due to this integration if a failure exists in any one of

the internal network it would result into unfavorable consequences to the whole

power system. In addition to all this, with the microprocessor based controls,

protective devices become more sensitive towards power quality variation than

were the past generation protective devices.

Following are some of the disturbances which are common in affecting the

power system.

1.) Transients

2.) Sagging

3.) Variations in voltage

4.) Harmonics

2.2 Transients:

In terms of power system, the transients can be defined as an action or a

situation in power system with variations in power system and which is not

desirable in nature. A general understanding of transient is considered to be an

oscillatory transient who is damped due to the RLC network. A person who is

new to the power system also uses the term “surge” to define transient. A surge

may be analyzed as a transient who is resulting from the stroke of lightening

where protection is done by using a surge arrester. A person who is more

groomed in the field of power engineering would avoid using the term “surge”

unless it is specified as to what exactly

2.3 Variations in Voltage:There are two types of variations in the voltages.

Short duration voltage variations

Long duration voltage variations.

2.3.1 Short Duration Voltage Variations:Short duration voltage variations are usually caused by faults in the power

system. Short duration voltage variations consist of sags which are caused

depending on the system conditions and faults that are caused in the power

system. It really depends on what kind of fault is caused in the power system

under what condition which may lead to voltage drops, voltage rise and even

interruptions in certain conditions. When such faults take place, protective

devices are used in order to clear the fault. But, the impact of voltage during such

faulty conditions is of short-duration variation.

Interruptions:

When there are reductions in the voltage or current supply interruptions

take place. Interruptions may occur due to various reasons, some of them being

faults in the power system, failures in the equipment, etc.

Sagging:

A short duration voltage variation is often referred to as sagging. When

there is a decrease between 0.1 to 0.9pu in rms voltage sagging takes place. There

are many ways to obtain the magnitude of sagging from the rms voltages. Most

of the times lowest value obtained during the event are considered. Sagging

normally has constant rms value during the deep part of the sag. Thus, lowest

value is an acceptable approximate value

2.3.2 Long Duration Voltage Variations:

Long duration voltage variations are comprised of over voltages as well as

under voltages conditions. These under voltage and over voltage conditions are

caused by variations in the power system and not necessarily due to the faults in

the system. The long duration voltage variations refer to the steady state

condition of the rms voltage of the power system. The long duration voltage

variations are further divided into three different categories i.e. interruptions, over

voltage and under voltage.

Under Voltage :

There are many reasons for the under voltage conditions in the power

system. When there is a decrease in the rms ac voltage to less than 90% of a

power system for some amount of time then under voltage condition exists. Load

switching on or switching off of a capacitor bank can also cause under voltage

condition. Also, when a power system is overloaded it may result into under

voltage condition.

Over Voltage:

Compared to the under voltage condition, over voltage is an increase in

the rms ac voltage to greater than 110% of the power system for some amount of

time. Unlike under voltage condition, load switching off or capacitor bank getting

energized are main reasons for the over voltage conditions.

2.4 Harmonics:

Harmonics are one of the major concerns in a power system. Harmonics

cause distortion in current and voltage waveforms resulting into deterioration of

the power system. The first step for harmonic analysis is the harmonics from

non-linear loads. The results of such analysis are complex. Over many years,

much importance is given to the methods of analysis and control of harmonics.

Harmonics present in power system also has non-integer multiples of the

fundamental frequency and have periodic waveform. The harmonics are

generated in a power system from two distinct types of loads.

First category of loads is described as linear loads. The linear time-

invariant loads are characterized such that application of sinusoidal voltage results

in sinusoidal flow of current. A constant steady-impedance is displayed from

these loads during the applied sinusoidal voltage. As the voltage and current are

directly proportional to each other, if voltage is increased it will also result into

increase in the current. An example of such a load is incandescent lighting. Even

if the flux wave in air gap of rotating machine is not sinusoidal, under normal

loading conditions transformers and rotation machines pretty much meet this

definition. Also, in a transformer the current contains odd and even harmonics

including a dc component. More and more use of magnetic circuits over a period

of time may get saturated and result into generation of harmonics. In power

systems, synchronous generators produce sinusoidal voltages and the loads draw

sinusoidal currents. In this case, the harmonic distortion is produced because of

the linear load types for sinusoidal voltage is small.

Non-linear loads are considered as the second category of loads. The

application of sinusoidal voltage does not result in a sinusoidal flow applied

sinusoidal voltage for non-linear devices. The non-linear loads draw a current

that may be discontinuous. Harmonic current is isolated by using harmonic filters

in order to protect the electrical equipment from getting damaged due to harmonic

voltage distortion. They can also be used to improve the power factor. The

harmful and damaging effects of harmonic distortion can be evident in many

different ways such as electronics miss-timings, increased heating effect in

electrical equipments, capacitor overloads, etc. There can be two types of filters

that are used in order to reduce the harmonic distortion i.e. the active filters and

the passive filters. Active harmonic filters are electronic devices that eliminate

the undesirable harmonics on the network by inserting negative harmonics into

the network. The active filters are normally available for low voltage networks.

The active filters consist of active components such as IGBT-transistors and

eliminate many different harmonic frequencies. The signal types can be single

phase AC, three phases AC. On the other hand, passive harmonic filters consist

of passive components such as resistors, inductors and capacitors. Unlike the

active filters which are used only for low voltages, the passive filters are

commonly used and are available for different voltage levels

Chapter 3

Fundamentals Of Harmonics

3.1 General:

When we talk about ac we are talking about alternating current. The

voltage pushing that current through the load circuit is described in terms of

frequency and amplitude. The frequency of the current will be identical to the

frequency of the voltage as long as the load resistance/impedance does not

change. In a linear load, like a resistor, capacitor or inductor, current and voltage

will have the same frequency. As long as the characteristics of the load

components do not change, the frequency component of the current will not

change. When we deal with non-linear loads such as switching power supplies,

transformers which saturate, capacitors which charge to the peak of the supply

voltage, and converters used in drives, the characteristics of the load are dynamic.

As the amplitude of the voltage changes and the load impedance changes, the

frequency of the current will change. That changing current and resulting complex

waveform is a result of: these load changes. The complex current waveform can

be described by defining each component of the waveform. The component of

any waveform can be defined in terms of dc, and all frequencies from 0 to

infinity. The frequencies that are normally dealt with using drives are 50 and 60

Hertz. By definition, these frequencies are termed fundamental in their respective

distribution systems.

3.2 Definition:

The Fourier theorem states that all non-sinusoidal periodic functions can

be represented as the sum of terms (i.e. a series) made up of:

1. Sinusoidal term at the fundamental frequency

2. Sinusoidal terms (harmonics) whose frequencies are whole multiples of the

fundamental frequency

3. DC component, where applicable

The nth order harmonic (commonly referred to as simply the nth

harmonic) in a signal is the sinusoidal component with a frequency that is n times

the fundamental frequency.

The equation for the harmonic expansion of a periodic function is presented below:

y ( t )=Y0+∑n=1

∞

Yn√2sin (nωt-φn)

Where:

Yo: value of the DC component, generally zero and considered as such here in

after

Yn: rms value of the nth harmonic

ω: angular frequency of the fundamental frequency

ϕn: displacement of the harmonic component at t = 0.

Example of signals (current and voltage waves) on the French electrical

distribution System:

The value of the fundamental frequency (or first order harmonic) is 60 hertz (Hz)

The third harmonic has a frequency of 180 Hz

The fifth harmonic has a frequency of 300 Hz

The seventh harmonic has a frequency of 420 Hz

etc.

A distorted signal is the sum of a number of superimposed harmonics

Fig 3.2 Voltage waveform showing the effect of harmonics

3.3 Representation of harmonics: the frequency spectrum

The frequency spectrum is a practical graphical means of representing the

harmonics contained in a periodic signal.

The graph indicates the amplitude of each harmonic order.

This type of representation is also referred to as spectral analysis.

The frequency spectrum indicates which harmonics are present and their relative

importance.

Fig 3.3 Graph of Harmonics Spectrum

3.4 Triplen Harmonics:

The triplen harmonics are defined as the odd multiples of the 3rd

harmonic (ex. 3rd, 9th, 15th, 21st etc.).They deserve special consideration

because the system response is often considerarably different for triplens than

for rest of harmonics.The normal mode for tripplen harmonics is to be zero

sequence. During imbalances, triplen harmonics may have positive or negative

sequence components.

Chapter 4

Harmonic indices

The two most commonly used indices for measuring the harmonic content

ofa waveform are the total harmonics distortion(THD) and the total demand

distortion. Both are measures of the effective value of waveform and may be

applied to eitger voltage or current.

4.1 Total Harmonic Distortion

Total harmonics distortion is the ratio between the RMS value of sum of

harmonics to the RMS value of the fundamental.

THD can be used to describe voltage or current distortion and is calculated as

follows:

THD=√∑ of squares of amplitudesof all harmonicssquare of amplitude of fundamental

× 100

The THD is very useful quantity for many applications, but its limitation

must be realized. It can provide a good idea of how much extra heat will be

realized when distorted voltage is applies across a resistive load. It can give an

idea about the additional losses caused by the current flowing through a

conductor.

4.2 Total Demand Distortion

Current distortion levels can be characterized by a THD value, as has been

described, but this can often be misleading. A small current have a high THD but

not be a significant threat to the system.

Some analysts have attempted to avoid this difficulty by referring THD to

the fundamental of peak demand load current rather than to the fundamental of

the peak demand load current rather than the fundamental of present sample. This

is called total demand distortion and serves as the basis for the guidelines in IEEE

standard 519-1192

TDD=∑h=2

hmax

I h2

I L

IL is the peak, or maximum, demand load current at the funamental

frequency component measured at the point of common coupliing

Chapter 5

Sourecs of Harmonics

Devices causing harmonics are present in all industrial, commercial and

residential installations. Non-linear equipment or components in the power system

cause distortion of the current and to a lesser extent of the voltage.

5.1 Non-linear loads

5.1.1 Definition:

A load is said to be non-linear when the current it draws does not have the same

wave form as the supply voltage.

Fig 5.1.1 Current waveform in non-linear load

5.1.2 Harmonics in non-linear load:

DC Bus will only charge when the AC sine wave voltage is greater than

the DC capacitor voltage, this results current draw only at the peaks of the sine

waves instead of the whole sine wave

Fig 5.1.2 Common Single Phase Bridge Rectifier Circuit and waveform

5.2 Types of equipment that generate harmonics

Harmonic load currents are generated by all non-linear loads. These include:

Single phase loads, e.g.

Switched mode power supplies (SMPS)

Electronic fluorescent lighting ballasts

Small uninterruptible power supplies (UPS) units

Three phase loads, e.g.

Variable speed drives

Large UPS units

5.2.1 Single phase loads

Switched mode power supplies (SMPS):

The majority of modern electronic units use switched mode power

supplies (SMPS). These differ from older units in that the traditional step-down

transformer and rectifier is replaced by direct controlled rectification of the supply

to charge a reservoir capacitor from which the direct current for the load is

derived by a method appropriate to the output voltage and current required. The

advantage to the equipment manufacturer is that the size, cost and weight is

significantly reduced and the power unit can be made in almost any required form

factor. The disadvantage to everyone else is that, rather than drawing continuous

current from the supply, the power supply unit draws pulses of current which

contain large amounts of third and higher harmonics and significant high

frequency components. A simple filter is fitted at the supply input to bypass the

high frequency components from line and neutral to ground but it has no effect on

the harmonic currents that flow back to the supply. Single phase UPS units exhibit

very similar characteristics to SMPS.For high power units there has been a recent

trend towards so-called power factor corrected inputs. The aim is to make the

power supply load look like a resistive load so that the input current appears

sinusoidal and in phase with the applied voltage. It is achieved by drawing input

current as a high frequency triangular waveform that is averaged by the input

filter to a sinusoid.

Fig 5.2.1 a. Harmonic spectrum of a typical PC

Fluorescent lighting ballasts

Electronic lighting ballasts have become popular in recent years following

claims for improved efficiency. Overall they are only a little more efficient

than the best magnetic ballasts and in fact, most of the gain is attributable to

the lamp being more efficient when driven at high frequency rather than to

the electronic ballast itself. Their chief advantage is that the light level can be

maintained over an extended lifetime by feedback control of the running

current a practice that reduces the overall lifetime efficiency. Their great

disadvantage is that they generate harmonics in the supply current. So called

power-factor corrected types are available at higher ratings that

reduce the harmonic problems, but at a cost penalty. Smaller units are

usually uncorrected. Compact fluorescent lamps (CFL) are now being sold as

replacements for tungsten filament bulbs. Miniature electronic ballast, housed

in the connector casing, controls a folded 8mm diameter fluorescent tube.

CFLs rated at 11 watt are sold as replacements for a 60 watt filament lamp

and have a life expectancy of 8000 hours. The harmonic current spectrum is

shown in Figure. These lamps are being widely used to replace filament bulbs

in domestic properties and especially in hotels where serious harmonic

problems are suddenly becoming common.

Fig 5.2.1 a. Harmonic spectrum of a typical CFL

5.2.2 Three Phase load

Variable speed controllers, UPS units and DC converters in general are

usually based on the three-phase bridge, also known as the six-pulse bridge

because there are six pulses per cycle (one per half cycle per phase) on the DC

output. The six pulse bridge produces harmonics at 6n +/- 1, i.e. at one more and

one less than each multiple of six. In theory, the magnitude of each harmonic is

the reciprocal of the harmonic number, so there would be 20 % fifth harmonic and

9 % eleventh harmonic, etc.

Fig 5.2.2 Harmonic spectrum of a typical 6-pulse bridge

Chapter 6

Effect of Harmonics

The effects of three-phase harmonics on circuits are similar to the effects

of stress and high blood pressure on the human body. High levels of stress or

harmonic distortion can lead to problems for the utility's distribution system, plant

distribution system and any other equipment serviced by that distribution system.

Effects can range from spurious operation of equipment to a shutdown of

important plant equipment, such as machines or assembly lines. Harmonics can

lead to power system inefficiency. Some of the negative ways that harmonics may

affect plant equipment are listed below:

6.1 Current Harmonics

These important non-linear circuits produce current harmonics. Current

Harmonics do have an effect on the electrical equipment supplying harmonic

current to the device (transformers, conductors). Current Harmonics can cause

issues with distribution equipment with has to handle the current from the utility

transformer all the way down to the device, but generally don’t affect other

equipment connected to the electrical system. Harmonic currents can cause

excessive heating to transformers. For electrical systems feeding single phase

loads the third harmonic has gained attention in design consideration and

transformer selection for causing the neutral conductor to draw excessive current.

6.2 Voltage Harmonics

Voltage Harmonics can affects sensitive equipment throughout your

facility. Voltage Harmonics arise when Current Harmonics are able to create sags

in the voltage supply. When any device draws current it creates a voltage dip

which is required for current to flow. This voltage dip is visible with larger loads

when turning on a hair dryer or a table saw and seeing the lights dim down. The

amount of sag depends on many factors like transformer impedance wire size.

Current Harmonics create Voltage Harmonics, but the magnitude of the Voltage

Harmonics depends on the “Stiffness” of your electrical distribution’s “System

Impedance”.

6.3 Effect of Harmonics Conductor overheating: a function of the square rms current per unit volume of

the conductor. Harmonic currents on undersized conductors or cables can cause a

“skin effect”, which increases with frequency and is similar to a centrifugal force.

Capacitors: can be affected by heat rise increases due to power loss and reduced

life on the capacitors. If a capacitor is tuned to one of the characteristic harmonics

such as the 5th or 7th, overvoltage and resonance can cause dielectric failure or

rupture the capacitor.

Fuses and Circuit Breakers: harmonics can cause false or spurious operations

and trips, damaging or blowing components for no apparent reason.

Transformers: have increased iron and copper losses or eddy currents due to

stray flux losses. This causes excessive overheating in the transformer windings.

Typically, the use of appropriate “K factor” rated units is recommended for non-

linear loads.

Generators: have similar problems to transformers. Sizing and coordination is

critical to the operation of the voltage regulator and controls. Excessive harmonic

voltage distortion will cause multiple zero crossings of the current waveform.

Multiple zero crossings affect the timing of the voltage regulator, causing

interference and operation instability.

Utility Meters: may record measurements incorrectly, result in higher billings

to consumers.

Drives/Power Supplies: can be affected by misoperation due to multiple zero

crossings. Harmonics can cause failure of the commutation circuits, found in DC

drives and AC drives with silicon controlled rectifiers (SCRs).

Chapter 7

Power and Harmonics

7.1 Active Power

The active power P of a signal distorted by harmonics is the sum of the

active powers corresponding to the voltages and currents in the same frequency

order. The expansion of the voltage and current into their harmonic components

may be written as:

P=∑h=1

∞

V h I h cosφh

Where ϕ h is the displacement between voltage and current of harmonic order h.

Note:

it is assumed that the signal does not contain a DC component, i.e. V0= I0 = 0

When the signal is not distorted by harmonics, the equation P = V1 I1 cos ϕ1

again applies, indicating the power of a sinusoidal signal, where cos ϕ1 is equal

to "cos ϕ").

7.2 Reactive Power

Reactive power applies exclusively to the fundamental and is defined by

the equation:

Q=V 1 I 1sin φ 1

7.3 Distortion Power

Consider the apparent power S:

S=VrmsIrms

In the presence of harmonics, the equation becomes:

S2=(∑h=1

∞

V h)(∑h=1

∞

I h)Consequently, in the presence of harmonics, the equation S2=P2+Q2 is no longer

valid. The distortion power D is defined as S2=P2+Q2+D2, i.e.:

D=√S2−P2−Q2

7.4 Power factor in presence of harmonics

There are two different types of power factor that must be considered

when voltage and current waveforms are not perfectly sinusoidal.

Input Displacement Factor (IDF) =which refers to the cosine of the angle

between the 50/60 Hz voltage and current waveforms.

Distortion Factor (DF) is defined as follows:

DF= 1

√1+THD2

Total Power Factor (PF) = Product of the Input Displacement Factor and the

Distortion Factor as follows:

PF=IDF × DF

Chapter 8

Harmonics Reduction Techniques

8.1 Genral Tecniques

Following techiques are use to reduce the effect of harmonics

Grouping the disturbing loads

Separating the sources

Using transformers with special connections

Installing inductors

8.1.1 Grouping the disturbing loads:

When preparing the single-line diagram, separate where possible the

disturbing equipment from the other loads. Practically speaking, the different

types of loads should be supplied by different bus bars.

By grouping the disturbing loads, the possibilities of angular

recomposition are increased. The reason is that the vector sum of the harmonic

currents is lower than their algebraic sum.

An effort should also be made to avoid the flow of harmonic currents in

the cables, thus limiting voltage drops and temperature rise in the cables.

Fig 8.1.1 Grouping of non-linear loads and supply as far upstream as possible

8.1.2 Separating the sources

In efforts to attenuate harmonics, an additional improvement may be

obtained by supplying the different loads via different transformers, as indicated

in the simplified diagram below

Fig 8.1.2 Supply of the disturbing loads via a separate transformer

This disadvantage of this solution is the increase in the cost of the installation.

8.1.3 Using transformers with special connections

Special types of connection may be used in transformers to eliminate

certain harmonic orders.

The harmonic orders eliminated depend on the type of connection implemented:

A delta-star-delta connection eliminates harmonic orders 5 and 7

A delta-star connection eliminates harmonic order 3 (the harmonics flow

in each of the phases and loop back via the transformer neutral)

A delta-zigzag connection eliminates harmonic order 5 (loop back via the

magnetic circuit).

Fig 8.1.3 A delta-star-delta transformer prevents propagation of harmonic orders 5 and 7

upstream in the distribution system.

8.1.4 Installing inductors

In installations comprising variable-speed drives, the current can be

smoothed by installing line inductors. By increasing the impedance of the supply

circuit, the harmonic current is limited.

Use of harmonic inductors on capacitor banks is a means of increasing the

impedance of the inductor and capacitor assembly, for harmonics with high

frequencies.

8.2 Solutions when limit values are exceeded8.2.1 Passive Filter

Operating principle: an LC circuit, tuned to each of the harmonic

frequencies requiring filtering, is installed in parallel with the device causing the

harmonic distortion this bypass circuit draws the harmonics, thus avoiding the

flow of harmonics to the power source.

Fig 8.2.1 Operating principle of a passive filter.

Generally speaking, the passive filter is tuned to a harmonic order near the

one to be eliminated. A number of parallel-connected filters may be used when a

significant reduction in distortion over a range of orders is required.

Typical applications:

Industrial installations comprising a set of devices causing harmonics with

a total power rating greater than approximately 200 kVA (variable-speed

drives UPSs, rectifiers, etc.)

installations where power factor correction is required

situations where voltage distortion must be reduced to avoid disturbing

sensitive loads

situations where current distortion must be reduced to avoid overloads

8.2.2 Active filters (active harmonic conditioners)

Operating principle: active filters are systems employing power

electronics, installed in series or in parallel with the non-linear load, to provide

the harmonic currents required by non-linear loads and thereby avoid distortion

on the power system

.

Fig 8.2.2 Operating principle of an active filter.

The active filter injects, in opposite phase, the harmonics drawn by the

load, such that the line current is remains sinusoidal.

Typical applications:

Commercial installations comprising a set of devices causing harmonics with a

total power rating less than 200 kVA (variable-speed drives, UPSs, office

equipment, etc.)

situations where current distortion must be reduced to avoid overloads

8.2.3 Hybrid filters

Operating principle: The two types of filters presented above can be combined in

a single device, thus constituting a hybrid filter. This new filtering solution

combines the advantages of the existing systems and provides a high-performance

solution covering a wide power range.

Fig 8.2.3 Operating principle of a hybrid filter.

Typical applications:

Industrial installations comprising a set of devices causing harmonics with a total

power rating greater than 200 kVA approximately (variable-speed drives, UPSs,

rectifiers, etc.)

installations where power factor correction is required.

situations where voltage distortion must be reduced to avoid disturbing sensitive

loads.

situations where current distortion must be reduced to avoid overloads.

situations where conformity with strict harmonic-emission limits is required.

8.2.4 12-pulse Rectifiers

This is effectively two six-pulse bridges, fed from a star and a delta

transformer winding, providing a 30 degrees phase shift between them.

Fig 8.2.4 12-Pulse Rectifier

Very effective in the elimination of 5th and 7th harmonics. Stops

harmonics at the source. Insensitive to future system changes.

Chapter 9

IEEE Standard 519-1992

IEEE standard 519-1992 is a useful document for understanding harmonics and

applying harmonic limits in power systems. Despite many years of good use there is still

some confusion about how to apply certain aspects of the standard.

Chapter 9

Conclusion

9.1 Conclusion

Virtually all modern electrical and electronic equipment contains a SMPS or

involves some form of power control and so is a non-linear load. Linear loads are

comparatively rare, the fundamental voltage, applied on a non-linear load, cause

harmonic currents (called characteristic harmonics). The main distortion consists of odd

multiples of the fundamental component (50 or 60 Hz). Single phase non-linear loads

have a current distortion, THD, around 120 %. All odd harmonics exist in the current

spectrum. Three phase non-linear loads have a current distortion, THD, up to 200 %. All

odd harmonics exist in the spectrum, except triplen harmonics. As the quantity of

installed equipment rises, and without very strong standards backed

up by rigid enforcement measures, it is likely that harmonic pollution

will continue to increase

References

1. IEEE Std 519-1992, “IEEE Recommended Practices and Requirements for Harmonic

Control in Electric Power Systems,” © Institute of Electrical and Electronics Engineers,

Inc. 1993.

2. Boger C.Dugan, Mark F.McGRANAGHN, Electrical Power System Quality, Tata

McGRAW-Hill

3. en.wikipedia.org/wiki/Harmonics_(electrical power)

4. literature.rockwellautomation.com/idc/groups/.../mvb-wp011_-en-p.pdf

5.