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POWER QUALITY 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 qu ality issues have created a need for extensive monitoring of power quality.
This This paper paper gives gives a consis consisten tentt set of defini definitio tions ns for differ different ent types types of power power quality quality disturbanc disturbances. es. Power quality monitors monitors which form an indispensab indispensable le 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 PAGE NO:
INTRODUCTION …………………………………… ………………………………………………. ………….
1
INCREASED INTEREST IN POWER QUALITY …………..
2
POWER QUALITY DEFINITION …………………………….
3
POWER QUALITY DISTURBANCES CAUSES ………………………………… …………………………………………………. ………………. STEADY STATE STATE VARIATIONS ARIATIONS ……………………… ………… ……………
5 6
EVENTS …………………………………… …………………………………………………. …………….
8
VOLT VOLTAGE – MAGNITUDE EVENTS ………………..
1
POWER QUALITY MONITORING MONITORING OB!ECTIVES ………………………..
11
POWER QUALITY MONITORS ……………………..
12
REAL TIME MONITORING SYSTEM ………………………
15
ANALYSIS 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. $ut today electric power is viewed as a product with certain characteristi characteristics cs which can be measured, measured, predicted, guaranteed, guaranteed, improved improved etc. %oreover it has become an integral part of our life. The term &power quality' emerged as a result of this new emphasis placed on the customer utility relationship. The fact that power quality has become an issue recently does not mean that it was not impo import rtan antt in the the past. past. (til (tilit itie iess all all over over the the worl world d have have for for decad decades es work worked ed on the the improvement of what is now known as power quality. #n the recent years, users of electric power have detected an increasing number of drawbacks caused by electric power quality variations. These variations already existed on the electrical system but only recently they are causing serious problems. This is because of the fact that end use equipments have become more sensitive to disturbances that arise both on the supplier as well as the utility side. "nd use equipments are more interconnected in networks and industrial processes, that the impact of a problem with any piece of equipment is much more severe. To improve power quality with adequate solutions, it is necessary to know what kinds of disturbances occurred. ) power quality monitoring system that is able to automatically detect, characteri*e and classify disturbances on electrical lines is therefore required.
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INCREASED INTEREST IN POWER QUALITY Power quality is an increasingl increasingly y important important issue for all business. business. ) recent study by #$% 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 have become more sensitive sensitive to voltage disturbances 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 cause voltage disturbances disturbances
%odern electronic and power electronic equipments are not only sensitive to voltage disturbance disturbancess but also cause disturbanc disturbances es for other customers. customers. ".g. /onsinusoi /onsinusoidal dal 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 can be measured#
The availa availabil bility ity of electr electroni onicc equipm equipment entss to measur measuree and sho show w wave wave forms forms has certainly contributed to the interest in power quality. www.seminarsToi!s.!om 2
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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. %ode %o dern rn elec electr tron onic ic and and power power elec electr tron onic ic devi device cess are are not not only only sens sensit itiv ivee to volta voltage ge 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 $oltage qualit! qualit !
7oltag ltagee qual qualit ity y conc concer erns ns with with the the devi deviat atio ion n of the the volt voltag agee from from the the idea ideall characteristics. The ideal voltage is a single frequency sine wave of constant frequency and constant magnitude. Current qualit!
Curr Curren entt qual qualit ity y conc concer erns ns with with the the devi deviat atio ion n of the the curr curren entt from from the the idea ideall characteristics. The ideal current is again a single frequency sine wave of constant magnitude and frequency. )n additional requirement is that the sine wave should be in phase with the supply voltage.
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Po"er qualit!
Power quality is the combination of voltage quality and current quality. Thus power quality quality is concer concerned ned with with the deviati deviations ons of voltag voltagee and8or and8or curren currentt from from the ideal ideal characteristics.
POWER QUALITY$ 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 dist distur urba banc nces es mu must st be deve develo lope ped d with with a consi consist sten entt set set of defi defini niti tions ons,, so that that the the meas measur urem emen entt equip equipme ment ntss can can be desi designe gned d in a cons consis iste tent nt manne mannerr. Power Power qual qualit ity y phenomena can be divided into two basis categories. Stead! state variations variations
) characteristic of voltage or current is never exactly equal to its nominal or desired value. value. The small deviati deviations ons from from the desire desired d value value are called called voltag voltagee or curren currentt 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 v oltage 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 specific problem. Power quality monitoring monitoring equipments 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. 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 quality problems problems originate with the utility transmissio transmission n and dist distri ribut butio ion n syst system em .The .The mo most st comm common on caus causee is a ligh lightn tnin ing g stri strike5 ke5 othe other r possibilities include equipments failure, vehicle accidents, weather conditions, neighboring business and even normal operation op eration 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 the vari variat atio ions ns are are larg largee enou enough gh or in a cert certai ain n crit critic ical al freq frequen uency cy rang range, e, the 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 frequency other than the standard standard 0 ?* frequency is called called harmonic harmonic distortion. 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 nonperiodic components components in supply voltage can be called called &noise'. &noise'. 1istinguishing 1istinguishing noise from other components is not always simple. )n analysis is needed only in case where where noise noise leads leads to som somee proble problem m with with power power sys system tem or end user equipme equipments nts.. "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 disturbanc disturbances es which can lead to the tripping of equipments, equipments, interruptio interruptions ns 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. *ero. #nterr #nterrupt uption ionss are normal normally ly initi initiate ated d by fault faultss which which sub subseq sequen uently tly trigger trigger protection measures. #nterruptions can be subdivided based on their duration, thus based on the way of restoring the supply. . Sustained These kinds kinds of interr interrupt uption ionss are termin terminate ated d throug through h Sustained Interruptions: Interruptions: These manual restoration or replacement of faulted components. www.seminarsToi!s.!om 0
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%# Temporar! emporar! Interruptions: Interruptions: This refers to interruptions lasting less than ! minutes.
This interruption is terminated
through automatic restoration of preevent situation.
Thes esee inte interr rrupt uptio ions ns are are term termin inat ated ed thro throug ugh h self self '# (ome (oment ntar ar!! Inte Interr rrup upti tion ons: s: Th 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)
Trans Transien ients ts are sub cycle cycle distur disturban bances ces of very very sho short rt durati duration on that that vary vary greatl greatly y 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 electrical system causing problems for equipments equipments down the line. Transi Transients ents can be divided into ! categories6 1. Impulsive Impulsive transient: 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! transient 6 )n oscillatory transient is one where there is a ringing signal
or oscill oscillati ation on follow following ing the initi initial al trans transien ient. t. ".g.6 ".g.6 switch switching ing of power power factor factor correction capacitor is considered the most prevalent type of transient.
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VOLT VOLTAGE – MAGNITUDE M AGNITUDE 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 identify problem conditions before they cause interruptions interruptions or disturbance disturbances. s.
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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 hav ing a system failure is not knowing what caused it. Bith Bith power quality monitoring, power engineers can eliminate some of their troubleshooting troubleshooting headaches4.
POWER QUALITY MONITORING – OB!ECTIVES The obectives of a monitoring program determine the choice of measuring equipments and trigger triggering ing thresh threshold olds, s, the methods methods for collec collecti ting ng data, data, data data storag storagee and analys analysis is requirements and the overall level of effort needed. Deneral classification of obectives for power quality monitoring is explained in the following section. P/+';* '--/+'<= This approach of monitoring is intended to characteri*e the
system performance. ) power producer may find this obective important because this helps to understand the system performance and then be able to match the system performance with customer needs. R*';* '--/+'<= This kind of monitoring is intended to characteri*e a specific
problem. %any services solve power quality problems by performing short term monitoring at specific customers or at different loads.
POWER QUALITY MONITORS The first first step step to troubl troublesh eshoot ooting ing power power quality quality problem problemss is to have a mon monito itorr that that accu accura rate tely ly meas measur ures es volt voltag agee and and curr curren entt wave wavefo form rms. s. Th Thee role role of monit onitor or for for
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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 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.
%# )istur )isturban bance ce anal!* anal!*er 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 outages.. Thresh Threshold oldss can be set and the instru instrumen mentt is left left unatten unattended ded to record record
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disturbances over a long period of time. >ecording starts the moment, a threshold value is exceeded.
PORTABLE MONITOR
#n the past, measurement measurement equipments equipments were designed designed to handle either the events or steady state variations. Bith advances in processing capability, new instruments have become availa available ble that that can charac character teri*e i*e the full full range range of power power quality quality variat variation ions. s. 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 www.seminarsToi!s.!om :
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variat variation ion.. The simple simplest st mon monito itori ring ng syste system m could could be a self self contai contained ned circui circuitt mon monito itor5 r5 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, .
PERMANENTLY INSTALLED FULL SYSTEM MONITOR
REAL TIME MONITORING SYSTEM – CONFIGURATION >eal time monitoring monitoring system contains software and communicati communication on facilities 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 co mputer optimi*ed for database management and analysis. $oth the disturbance analy*ers and
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voltage recorders can be integrated into the real time monitoring system. The figure shown below explains the configuration of a real time monitoring system. system.
CONFIGURATION OF REAL TIME MONITORING SYSTEM
(EAS-.E(EN (EAS-.E(ENT T INST.-(ENT INST.-(ENTS: S:
This involves both the voltage recorder and disturbance analy*ers. There is a trigger circuit to detect events and a data acquisition board that acquires all the triggered and sampled data. (ONITO.ING (ONITO.ING /O.0STA /O.0STATIO TION: N: www.seminarsToi!s.!om ;
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This is composed by a trigger circuit that is able to detect events and a data acquisition board driven by the trigger circuit that acquires all of the detected disturbances. %onitoring workstation is used to gather all information coming from the measuring instruments and to periodically send information to a control workstation. CONT.O1 /O.0STATION:
This station configures the parameters of measuring instruments. This gathers and stores the data coming from remote monitoring instruments. )gain, control workstation is used for data analysis and export. CONT.O1 SO2T/A.E:
This software drives the control workstation. The analysis and processing of data depends on this software. The algorithms used for processing varies according to the system used. The algorithms used may be based on wavelet transforms or expert systems or some other advanced technique. )ATA3A )ATA3ASE SE SE.$E.: SE.$E.:
The data base management system should provide fast and concurrent access for many users without critical performance degradation. )t the same time an y form of unauthori*ed access must be avoided.
CO((-NICATION CO((-NICATION C4ANNE1S:
The selection of communication channel strongly depends de pends 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'. &signature'. The wave shape signature signature from the monitors 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. 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 sens sensit itiv ivee load. load. ?owev ?owever er the the real real valu valuee of mo moni nito tori ring ng syst system em is in auto automa mati ticc data 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 indi indica cati tion on that that this this will will happ happen en soon. soon. o right right now now the the empha emphasi siss is on miti mitigat gatio ion n equipm equipment entss and on intell intellige igent nt power power quality quality mon monito itorin ring g syste systems ms which which enable enabless the automatic classification and analysis of the measured data.
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REFERENCES
. P. 1)P9 1)P9/T /T", ",4T 4T>) >)/# /#"/ "/T% T%"T "T"> ">66 ) 1#T 1#T># >#$( $(T" T"1 1 %" %") )(> (>"% "%"/ "/T T GT GT"% "% E9> P9B" P9B"> > H()A H()A#T #TG G %9/# %9/#T9 T9># >#/D /D,, #/ #""" #""" T>)/ T>)/. . 9/ P9B"> 1"A#7">G 79A(%" @, )P> !002. !. #""" """
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%")(>"%"/T4, "A"CT>9T"I C9/C"PT,#/C. 2. (/1">T) (/1">T)/1#/D /1#/D P9B"> P9B"> H()A#TG H()A#TG P>9$A"% P>9$A"% $G %)T %)T?. ?. J.$9AA"/ J.$9AA"/ . T?" "A"C "A"CT># T>#C C P9B"> P9B"> "/D#/"" "/D#/"">#/ >#/D D ?)/1$9 ?)/1$99I. 9I. :. www.pqKmonitoring.com =. www.electrotek.com
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