05012013144403 power quality disturbances

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POWER QUALITY-DISTURBANCES AND MONITORING SEMINAR

POWER QUALITY

DISTURBANCES AND

MONITORING

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ABSTRACT

Power quality is a concept, limited mostly to conversations among utility engineers but as

electronic appliances take over the home, it may become a residential issue as well. The

increasing use of equipments sensitive to power quality disturbances, the related economic

aspects and the increasing awareness of power quality issues have created a need for

extensive monitoring of power quality.

This paper gives a consistent set of definitions for different types of power quality

disturbances. Power quality monitors which form an indispensable part of power quality

monitoring systems are also described. Categories of power quality monitors that are used

to measure power quality disturbances are identified. The paper also discusses about the

real time monitoring system and the analysis tools for processing measurement data.

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CONTENTS

TOPICS PAGE NO:

INTRODUCTION . 1

INCREASED INTEREST IN POWER QUALITY .. 2

POWER QUALITY DEFINITION . 3

POWER QUALITY DISTURBANCES

CAUSES . 5

STEADY STATE VARIATIONS 6

EVENTS . 8

VOLTAGE MAGNITUDE EVENTS .. 1

POWER QUALITY MONITORING

MONITORING OB!ECTIVES .. 11

POWER QUALITY MONITORS .. 12

REAL TIME MONITORING SYSTEM 15

ANALYSIS OF POWER QUALITY MEASUREMENTS . 1"

BENEFITS OF POWER QUALITY MONITORING . 1#

CONCLUSION . 2

REFERENCES .. 21

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INTRODUCTION

The aim of the power system has always been to supply electrical energy to customers.

"arlier the consumers of electrical energy were mere acceptors. #nterruptions and other

voltage disturbances were part of the deal. $ut today electric power is viewed as a product

with certain characteristics which can be measured, predicted, guaranteed, improved etc.

%oreover it has become an integral part of our life. The term &power quality' emerged as a

result of this new emphasis placed on the customer utility relationship.

The fact that power quality has become an issue recently does not mean that it was not

important in the past. (tilities all over the world have for decades worked on the

improvement of what is now known as power quality. #n the recent years, users of electric

power have detected an increasing number of drawbacks caused by electric power quality

variations. These variations already existed on the electrical system but only recently they

are causing serious problems. This is because of the fact that end use equipments have

become more sensitive to disturbances that arise both on the supplier as well as the utility

side. "nd use equipments are more interconnected in networks and industrial processes,

that the impact of a problem with any piece of equipment is much more severe. To

improve power quality with adequate solutions, it is necessary to know what kinds of

disturbances occurred. ) power quality monitoring system that is able to automatically

detect, characteri*e and classify disturbances on electrical lines is therefore required.

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INCREASED INTEREST IN POWER QUALITY

Power quality is an increasingly important issue for all business. ) recent study by #$%

showed that power quality problems cost ( business more than - billion a year. The

increased interest in power quality has resulted in significant advances in monitoring

equipments that can be used to characteri*e disturbances and power quality variations. The

recent increased interest in power quality can be explained in a number of ways.

Equipments have become more sensitive to voltage disturbances

The electronic and power electronic equipments have especially become much more

sensitive to voltage disturbances than their counterparts 0 or !0years ago.

Equipments cause voltage disturbances

%odern electronic and power electronic equipments are not only sensitive to voltage

disturbances but also cause disturbances for other customers. ".g. /onsinusoidal

current drawn by rectifiers and inverters.

Technical challenge taen up b! utilities

1esigning a system with a high reliability of supply at a limited cost is a technical

challenge which appealed to many in the power industry and hopefully still does in the

future.

Po"er qualit! can be measured#

The availability of electronic equipments to measure and show wave forms has

certainly contributed to the interest in power quality.



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POWER QUALITY$ DEFINITION

The definition of power quality given in the #""" dictionary is as follows

3Power quality is the set of parameters defining the properties of the power supply as

delivered to the user in normal operating conditions in terms of the continuity of voltage

and voltage characteristics4.

%odern electronic and power electronic devices are not only sensitive to voltage

disturbances5 it also causes disturbances for other customers. These devices become the

source and victims of power quality problems. )s such the term power quality is used to

define the interaction of electronic equipments within the electrical environment.

1ifferent parameters of power quality are6

$oltage qualit!

7oltage quality concerns with the deviation of the voltage from the ideal

characteristics. The ideal voltage is a single frequency sine wave of constant frequency

and constant magnitude.

Current qualit!

Current quality concerns with the deviation of the current from the ideal

characteristics. The ideal current is again a single frequency sine wave of constant

magnitude and frequency. )n additional requirement is that the sine wave should be in

phase with the supply voltage.



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Po"er qualit!

Power quality is the combination of voltage quality and current quality. Thus power

quality is concerned with the deviations of voltage and8or current from the ideal

characteristics.

POWER QUALITY$ P%ENOMENA&DISTURBANCES

Power quality is concerned with the deviation of the voltage from the ideal waveform or

the deviation of the current from the ideal waveform. uch a deviation is called a power

quality phenomena or disturbances. #t is important to first understand the kinds of power

quality disturbances that can cause problems with the sensitive loads. Categories of these

disturbances must be developed with a consistent set of definitions, so that the

measurement equipments can be designed in a consistent manner. Power quality

phenomena can be divided into two basis categories.

Stead! state variations

) characteristic of voltage or current is never exactly equal to its nominal or desired

value. The small deviations from the desired value are called voltage or current

variations. ) property of any variation is that it has value at any moment in time.

%onitoring of variations thus has to take place continuously.

Events

9ccasionally, the voltage or current deviates significantly from the nominal or ideal

wave shape. These sudden deviations are called events. %onitoring of events take

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place by using a triggering mechanism where recording of voltage or current starts the

moment, a threshold is exceeded.

C'()*) +, -+*/ 0('4 -/+*)

The causes of power quality problems can be many. #t is often difficult to point an exact

cause for a specific problem. Power quality monitoring equipments comes to aid in such

situations. %ost of the causes of power quality problem can be divided into two categories

. Internal causes

)pproximately ;0< of electrical problems originate within a business facility.

Potential culprits may include large equipments start or shut down, improper

wiring and grounding, overloaded circuits or harmonics.

%# E&ternal causes

)bout !0< of power quality problems originate with the utility transmission and

distribution system .The most common cause is a lightning strike5 other

possibilities include equipments failure, vehicle accidents, weather conditions,

neighboring business and even normal operation of utility equipments.

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STEADY STATE VARIATIONS

This category includes voltage and current variations which are relatively small deviations

of voltage and current characteristics around their nominal or ideal values. The two basic

characteristics are magnitude and frequency. 9n average voltage magnitude and voltage

frequency are equal to their nominal value but they are never exactly equal. 7ariations

must be measured by sampling the voltage and current over time. #nformation is best

presented as a trend of the quantity over time and then analy*ed using statistical methods.

)n overview of voltage and current variations are given below6

V+'7* ,(('+9

The fast changes or swings in the steady state voltage magnitude are called voltage

fluctuation. The change in voltage magnitude can be due to variations of total load of a

distribution system, action of transformer tap changers, switching of capacitor banks.

#f the variations are large enough or in a certain critical frequency range, the

performance

of the equipment can be affected.

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V+'7* '9: (//*9 (9''9*

(nbalance or + phase unbalance is the phenomenon in a + phase system in which the

>% values of voltages and phase angles between consecutive phases are not equal.

The primary source of voltage unbalance is the unbalanced load. This can be due to an

uneven spread of low voltage customers over the three phases but more commonly

unbalance is due to a large single phase load.

%'/+9 ;+'7* '9: (//*9 :)+/+9

The voltage waveform is never exactly a single frequency sine wave. The phenomenon

of having periodic steady state distortions of sine wave due to equipment generating a

frequency other than the standard 0 ?* frequency is called harmonic distortion. The

non fundamental components present is called &harmonics'. ?armonic distortion of

voltage and current result, from the operation of nonlinear loads and devices in the

power system.

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%7< ,/*0(*94 ;+'7* 9+)*

The nonperiodic components in supply voltage can be called &noise'. 1istinguishing

noise from other components is not always simple. )n analysis is needed only in case

where noise leads to some problem with power system or end user equipments.

"lectrical noise can be defined as the high frequency interference caused by a number

of factors like arc welding or operation of electrical motor.

EVENTS

"vents are the phenomena which happen once in a while. Power quality events are the

disturbances which can lead to the tripping of equipments, interruptions of production or

plant operation or endanger power system operation. "vents are measured by a triggering

mechanism. )n overview of various events is given below6

I9*//(-+9)

) supply interruption is a condition in which the voltage at supply terminals is close to

*ero. #nterruptions are normally initiated by faults which subsequently trigger

protection measures. #nterruptions can be subdivided based on their duration, thus

based on the way of restoring the supply.

. Sustained Interruptions: These kinds of interruptions are terminated through

manual restoration or replacement of faulted components.



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%# Temporar! Interruptions: This refers to interruptions lasting less than ! minutes.

This interruption is terminated through automatic restoration of preevent situation.

'# (omentar! Interruptions: These interruptions are terminated through self

restoration. ".g. #nterruption due to transients and other self restoring events.

V+'7* )'7) & )*)

) sag or swell is a decrease or increase in the >% value of voltage ranging from a

half cycle to few seconds. The most likely kind of power quality problem is the voltage

sag. hort duration under voltages is called &voltage sags' whereas, longer duration

under voltages are referred to as &under voltage'. Aikewise over voltages of very short

duration and high magnitude are called &voltage swells'. Aonger duration over voltage

is called as &over voltage'. hort duration voltage variations include variations in the

fundamental frequency voltage that lasts less than minute.



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T/'9)*9)

Transients are sub cycle disturbances of very short duration that vary greatly in

magnitude. Transients are used to refer to fast changes in the system voltage or current

with duration less than . cycles. Transients can be measured by triggering on the

abnormality involved. Bhen transients occur, thousands of voltage can be generated

into the electrical system causing problems for equipments down the line. Transients

can be divided into ! categories6

1. Impulsive transient:Aightning striking a distribution line is normally an impulsive

transient where there is a large deviation of the wave form for a very short duration

in one direction, followed possibly by a couple of much smaller transients in both

directions.

2. Oscillator! transient6 )n oscillatory transient is one where there is a ringing signal

or oscillation following the initial transient. ".g.6 switching of power factor

correction capacitor is considered the most prevalent type of transient.



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VOLTAGE MAGNITUDE EVENTS

The method of classifying events through one magnitude and duration has shown to be

very useful and has resulted in a lot of information and knowledge about power quality.

This classification is aimed at explaining the different types of events.

POWER QUALITY MONITORING

Bith the electrical industry undergoing change, increased attention is being focused on

reliability and power quality. Power providers and users alike are concerned about reliable

power, whether the focus is on interruptions and disturbances or harmonic distortion or

flicker. 9ne of the most critical steps in ensuring reliability is monitoring power quality.

Power quality monitoring can help to identify the cause of power system disturbances and

even help to identify problem conditions before they cause interruptions or disturbances.

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?ence power quality monitoring is a multi pronged approach to identifying, analy*ing, and

correcting power quality problems.

3The only thing worse than having a system failure is not knowing what caused it. Bith

power quality monitoring, power engineers can eliminate some of their troubleshooting

headaches4.

POWER QUALITY MONITORING OB!ECTIVES

The obectives of a monitoring program determine the choice of measuring equipments

and triggering thresholds, the methods for collecting data, data storage and analysis

requirements and the overall level of effort needed. Deneral classification of obectives for

power quality monitoring is explained in the following section.

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troubleshooting power quality problems is undeniable. Power quality monitoring devices

come in a variety of shapes and si*es. Commercially available monitors fall into two

categories6 1>-+/'* +9+/) '9: 2> -*/'9*9 +9+/).

PORTABLE MONITORS

?andheld and portable instruments have made great improvements in testing capability in

recent years and are helpful in uncovering small locali*ed problems. $ut these are used for

troubleshooting after an event has taken place. #nstalling a power quality monitor after the

occurrence of the event tells us little about the past. Portable monitors are again subdivided

into two classes6

. $oltage recorders

These instruments record voltage and current strip chart data. Portable monitors are

used for continuous monitoring of steady state voltage variations. These recorders

digiti*e voltage and current signals by taking samples of voltage and current over time.

The most important factor to consider when selecting and using a voltage recorder is

the method of calculation of the >% value of the measured signal.

%# )isturbance anal!*er

1isturbance analy*er and disturbance monitors form a category of instruments which

have been developed specifically for power quality measurements. The analy*ers are

designed to capture events affecting sensitive devices. They typically can measure a

wide variety of system events from very short duration transients to long duration

outages. Thresholds can be set and the instrument is left unattended to record



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disturbances over a long period of time. >ecording starts the moment, a threshold

value is exceeded.

PORTABLEMONITOR

#n the past, measurement equipments were designed to handle either the events or steady

state variations. Bith advances in processing capability, new instruments have become

available that can characteri*e the full range of power quality variations. The new

challenge involves characteri*ing all the data in a convenient form, so that it can be used to

identify and solve problems. This highlights the features of permanent monitors.

PERMANENT MONITORS

Permanently installed full system monitors strategically placed on pieces of equipments

throughout the facility, lets the users know, what happened, where it happened as soon as it

happened. The main feature of these kinds of monitors is that they characteri*e full range

of power quality variations. They record both the triggered and sampled data. Triggering is

based upon the >% thresholds for >% variations and on wave shape for transient

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variation. The simplest monitoring system could be a self contained circuit monitor5

however the real value of monitoring is in automatic data downloading from the measuring

instruments. %onitoring system should fully utili*e the networking infrastructure. ) more

apt term for these efficient monitoring systems would be +real time monitoring s!stems,.

PERMANENTLYINSTALLEDFULLSYSTEMMONITOR

REAL TIME MONITORING SYSTEM CONFIGURATION

>eal time monitoring system contains software and communication facilities for data

collection, processing and result presentation. The software maintains a database of system

performance information which can be accessed. )t the heart we have a server computer

optimi*ed for database management and analysis. $oth the disturbance analy*ers and

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voltage recorders can be integrated into the real time monitoring system. The figure shown

below explains the configuration of a real time monitoring system.

CONFIGURATIONOFREALTIMEMONITORINGSYSTEM

(EAS-.E(ENT INST.-(ENTS:

This involves both the voltage recorder and disturbance analy*ers. There is a trigger circuit

to detect events and a data acquisition board that acquires all the triggered and sampled

data.

(ONITO.ING /O.0STATION:

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This is composed by a trigger circuit that is able to detect events and a data acquisition

board driven by the trigger circuit that acquires all of the detected disturbances.

%onitoring workstation is used to gather all information coming from the measuring

instruments and to periodically send information to a control workstation.

CONT.O1 /O.0STATION:

This station configures the parameters of measuring instruments. This gathers and stores

the data coming from remote monitoring instruments. )gain, control workstation is used

for data analysis and export.

CONT.O1 SO2T/A.E:

This software drives the control workstation. The analysis and processing of data depends

on this software. The algorithms used for processing varies according to the system used.

The algorithms used may be based on wavelet transforms or expert systems or some other

advanced technique.

)ATA3ASE SE.$E.:

The data base management system should provide fast and concurrent access for many

users without critical performance degradation. )t the same time any form of unauthori*ed

access must be avoided.

CO((-NICATION C4ANNE1S:

The selection of communication channel strongly depends on monitoring instruments,

connectivity functions and on their physical locations. ome of the possible channels are

fixed telephone lines by using a modem, mobile communication system by using a D%

modem, telephone lines using 1T%E coding etc.

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DATA ANALYSIS OF POWER QUALITY MEASUREMENTS

The analysis is done by the control software and the method of analysis depends on the

type of disturbance. The main obective of an analy*er is to identify the type of event. Eor

this the analy*er looks for parameters in the measured data to characteri*e the waveform.

The most common practice in analy*ing the results of monitoring programs is to group the

captured events in a number of classes. These classes are made by comparing the captured

waveforms with ideal waveforms. This classification is called disturbance classification.

ince individual inspection of all wave shapes is not an option due to the large si*e of

databases, a few characteristics are extracted from the measured data typically magnitude

and duration. 1atabases will be filled with a lot of information and recorded data. o

another task of analy*er is to extract only the relevant disturbances.

The root cause of all the power quality problems can be traced to a specific type of

electrical disturbances. "very disturbance has an associated wave form which describes its

characteristics, i.e. a certain type of fault may be accompanied by a certain type of wave

shape &signature'. The wave shape signature from the monitors provides important clues

towards locating the source of electrical problem.

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DATA ANALYSIS

)nalysis tools for processing measured data present the information as individual events

i.e. disturbance wave forms, trends or statistical summaries. $y comparing the captured

events with libraries of typical power quality variation characteristics and correlating with

system events, causes of variations can be determined. The data analysis system should be

flexible enough to handle data from a variety of monitoring equipments and maintain a

database that can be used by many different applications.



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BENEFITS OF POWER QUALITY MONITORING

To improve power quality with adequate solutions, it is necessary to know what kinds of

disturbances occurred. ) power quality monitoring system that is able to automatically

detect, characteri*e and classify disturbances on electrical lines is therefore required. This

brings up advantage for both end users and utility companies. The benefits of power

quality monitoring are many. The following section mentions some of them.

"nsures power system reliability.

#dentify the source and frequency of events.

?elps in the preventive and predictive maintenance.

"valuation of incoming electrical supply and distribution to determine if power

quality disturbances are impacting.

1etermine the need for mitigation equipments.

>eduction of energy expenses and risk avoidances.

Process improvements F monitoring systems allows to identify the most sensitive

equipments and install power conditioning systems where necessary.

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CONCLUSION

Traditional monitoring methods are based on the >% measurements and constrained by

their accuracies. >ecently proposed approaches for automated detection and classification

of power quality disturbances are based on wavelet analysis, artificial neural networks,

hidden %arkov model and bispectra. The use of such advanced techniques makes the

power quality monitoring system more accurate and the power system more reliable.

The configuration complexity of a monitoring system depends primarily upon the number

of instruments used to acquire information and the number of people who need to utili*e it.

The simplest monitoring system could be a self contained circuit monitor built into a

sensitive load. ?owever the real value of monitoring system is in automatic data

downloading from the measuring instruments and hence today, a lot of emphasis is given

on the design of &real time monitoring systems'.

2uture o5 po"er qualit!

#n 0 years time, it may well be that equipment has become fully compatible with the

power supply and does not cause any disturbance to the customers. ?owever, there is no

indication that this will happen soon. o right now the emphasis is on mitigation

equipments and on intelligent power quality monitoring systems which enables the

automatic classification and analysis of the measured data.

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REFERENCES

. P. 1)P9/T",4T>)/#"/T%"T">6 ) 1#T>#$(T"1 %")(>"%"/T

GT"% E9> P9B"> H()A#TG %9/#T9>#/D, #/ #""" T>)/. 9/

P9B"> 1"A#7">G 79A(%" @, )P> !002.

!. #""" B9>I#/D D>9(P P@,4>"C9%%"/1"1 P>)CT#C" E9>

%9/#T9>#/D P9B"> H()A#TG 3, 1>)ET =.

+. C.J.%"A?9>/,4#/T">P>"T)T#9/ 9E P9B"> H()A#TG

%")(>"%"/T4, "A"CT>9T"I C9/C"PT,#/C.

2. (/1">T)/1#/D P9B"> H()A#TG P>9$A"% $G %)T?. ?. J.$9AA"/

. T?" "A"CT>#C P9B"> "/D#/"">#/D ?)/1$99I.

:. www.pqKmonitoring.com

=. www.electrotek.com

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