Power Quality Issues, Problems and Related Standards Avinas Panwar1,ASSISTANT PROFESSOR, MADHAV UNIVERSITY ABU ROAD INDIA 1 apanwar84@gmail.com, Summary: Te growt in power electronics as impacted many loads tat traditionally were considered linear in nature. As a result, te number of nonlinear loads as increased and is expected to increase dramatically in te years aead. Wit increasing quantities of non-linear loads being added to electrical systems, it as become necessary to establis criteria for limiting problems from system voltage degradation. Tis paper presents te power quality problems, issues and related international standards. Te presentation is done wit giving a toroug knowledge of armonics, power quality indices, parameters effecting electric power etc. Latest researc work in giving different international standards for different type of power quality problems is also been given. Tis is important for design engineers and researcers in power quality to know te international standards used for power quality. INTRODUCTION Te paper and te tecnology on wic it is grounded are largely motivated by te power quality issues. Te term power quality is rater general concept. Broadly, it may be defined as provision of voltages and system design so tat user of electric power can utilized electric energy from te distribution system successfully, witout interference on interruption. Utilities may want to define power quality as reliability. Equipment manufacturers, in turn may define it as a power tat enables te equipment to work properly. In oter words power quality can be defined as, Any power problem manifested in voltage, current or frequency deviations tat results in failure of or disoperation of customer equipment. From te utility perspective, Power Quality as been defined as te parameters of te voltage tat affect te customer s supersensitive equipment. From te power user perspective, Power Quality may be defined as any electrical parameter or connection tat affects te operation of te equipment. Tis included all electrical parameters, connections and grounds, weter te source from te utility, local equipment or oter users. From te Power Quality market or industry perspective, it is any product or service tat is supplied to users or utilities to measure, treat, remedy, educate engineers or prevent Power Quality issues, problems and related items [6] Tis paper critically discusses about te power quality problems, issues and related standards wit giving a toroug knowledge of armonics, power quality indices, parameters effecting electric power etc. Te above said areas are discussed under te following eads: 1. Power quality problems & issues. Harmonics and armonics sequences 3. Power quality indices 4. Power quality standards 1. Power Quality Problems & Issues: Voltage sags are considered te most common Power Quality problem. Tese can be caused by te utility or by customer loads. Wen sourced from te utility, tey are most commonly caused by faults on te distribution system. Tese sags will be from 3 to 30 cycles and can be single or tree pase. Depending on te design of te distribution system, a ground fault on 1 www.ijltemas.in Page 53
pase can cause a simultaneous swell on anoter pase. A recent survey of Power Quality experts in Arizona indicates tat 50% of all Power Quality problems are related to grounding, ground bonds, and neutral to ground voltages, ground loops, ground current or oter ground associated issues. Electrically operated or connected equipment is affected by Power Quality [10, 1, 15, 16]. Determining te exact problems requires sopisticated electronic test equipment. Te following symptoms are indicators of Power Quality problems: 1. Piece of equipment misoperates at te same time of day.. Circuit breakers trip witout being overloaded. 3. Equipment fails during a tunderstorm. 4. Automated systems stop for no apparent reason. 5. Electronic systems fail or fail to operate on a frequent basis. 6. Electronic systems work in one location but not in anoter location. Te commonly used terms tose describe te parameters of electrical power tat describe or measure power quality are Voltage sags, Voltage variations, Interruptions Swells, Brownouts, Blackouts, Voltage imbalance, Distortion, Harmonics, Harmonic resonance, Interarmonics, Notcing, Noise, Impulse, Spikes (Voltage), Ground noise, Common mode noise, Critical load, Crest factor, Electromagnetic compatibility, Dropout, Fault, Flicker, Ground, Raw power, Clean ground, Ground loops, Voltage fluctuations, Transient, Dirty power, Momentary interruption, Over voltage, Under voltage, Non-linear load, THD, Triplens, Voltage dip, Voltage regulation, Blink, Oscillatory transient etc [4, 1, 15]. Power Quality as been an issue since electrical power was invented. It as only become a well publised issue in recent years because of te loads it affects. If your favorite TV program is interrupted by te local sewage pump operating on a Variable Speed drive interfering wit it, you are aware of a Power Quality problem. Wen te ligts blink and your PC reboots, you are aware of a Power Quality problem. Te electrical loads get more sensitive [6]. Tere are undreds of manufacturers making tousands of different Power Quality solutions today [7]. Te categories of tese solutions are: Utility based solutions for te substation level. User based solution for wole facility protection. User load level solutions for specific loads Designed in solutions, built in by te equipment manufacturer to reduce te sensitivity to Power Quality problems. Te issue of electric power quality is gaining importance because of several reasons: 1. Te society is becoming increasingly dependent on te electrical supply. A small power outage as a great economical impact on te industrial consumers. A longer interruption arms practically all operations of a modern society.. New equipments are more sensitive to power quality variations. 3. Te advent of new power electronic equipment, suc as variable speed drives and switced mode power supplies, as brougt new disturbances into te supply system. 4. Deregulation is resulting in structural canges in te utility industry (Traditionally, te generation, transmission, distribution and retail services ave been bundled into one regulated company te task of wic, among te oters, was to be responsible for te quality of power. In a deregulated environment, it is wortwile to ask, www.ijltemas.in Page 54
wo will be responsible for te power quality? 5. Te deregulated environment may reduce te maintenance of and investments into te power system and, ence, reduce te margins in te system. 6. Emerging of distributed generation (known also as embedded and dispersed generation) as a side effect of te deregulation. Distributed generation canges te way ow te utility grid is operated and introduces new power quality callenges. Te end users awareness in power quality issues as increased. Te nature of electricity as a product is special. Similar to te conventional products its caracteristics affect its usefulness to te customer. Different from te conventional products te application of it is one of te main factors tat ave an influence on its caracteristics. Te current tat te customer s appliance draws from te supply network flows troug te impedances of te supply system and causes a voltage drop, wic affects te voltage tat is delivered to te customer. Hence, bot te voltage quality and te current quality are important. It is rater natural to split up te responsibilities so tat te power distribution supplier is responsible for te voltage quality and te customer is accountable for te quality of current tat e or se is taking from te utility.. Harmonics and Harmonics Sequences: In power systems armonics appear as a waveform distortion of te voltage or te current. Te armonics are generated by nonlinear loads. Te sinusoidal voltage applied to te nonlinear load does not result in a sinusoidal current. Furter, tis nonsinusoidal current will produce a nonsinusoidal voltage drop wile flowing troug te finite source impedance, and, ence, cause armonic voltages. Alongside wit te armonics, interarmonics and dccomponent may distort te waveform. Te spectral component wit frequency of f is Harmonic; If f = nf fund, were n is an integer > 0 DC-component; If f = 0 (f = nf fund, were n = 0) Interarmonic; If f = nf fund, were n is an integer > 0 Subarmonic; If f > 0 and f < f fund, were f fund is te fundamental power system frequency. Te interarmonics and subarmonics are also referenced in IEC Std 60050-551-0 (001). In power systems te armonics ave an interesting property called te sequence. Natural sequences are sown in Table. Te sequence indicates te pase sequence of te pase quantities. Te fundamental component is of positive sequence, meaning tat pase a is leading pase b, wic is leading pase c. Te pase order is ten a-b-c. Te pase order of a negative sequence component is a-c-b. Wit zero-sequence components all pase quantities are similar and te pase order can not be defined. If a space-vector is constructed from a armonic sequence it is noticed tat positive sequence components rotate into te positive direction and negative sequence components into te negative direction. Te zero-sequence component does not contribute to te space-vector at all [4,6,9]. Table 1: Natural sequences of caracteristic current armonics of converters www.ijltemas.in Page 55
Order Sequence Order Sequence 1 Positive 6 Zero Negative 7 Positive 3 Zero 8 Negative 4 Positive 9 Zero 5 Negative 10 Positive Transients may be impulsive or oscillatory in nature. Impulsive transients are typically caused by ligtnings and ig oscillatory transients as a response of a local system to te impulsive transient. A low frequency oscillatory transient may be a result of a capacitor switcing. Sort duration variations are typically caused by faults or energization of large loads wic require ig starting currents. Long duration underor overvoltages usually result in switcing of large load or generation unit or a capacitor bank. An incorrect transformer tap setting may also be a cause of suc a situation. Voltage unbalance may be caused by excess of poorly balanced single pase loads or blown fuses in one pase of a capacitor bank. Waveform distortions are caused by nonlinear loads in te power systems. A alf-wave rectification may cause dc-offset. Harmonics are originating from many sources, in wic typically power electronics are involved, but may also be produced by nonlinearly magnetizing inductances. Interarmonics are mainly caused by cycloconverters and arcing devices. Notcing is a periodic voltage disturbance typically caused by commutations of power electronic device. Notcing could be regarded as armonics wit ig orders, but is typically considered as a special case. Voltage fluctuation may be caused by rapidly varying loads or generation. Certain voltage fluctuations are often called flicker, because of te visible effect to incandescent lamps. Power frequency variations may be caused by power system faults or disconnection or connection of large load or generation unit. 3. Power Quality Indices: 3.1 General armonic indices A complete description of a given distortion is te spectrum, but it is not very practical for roug comparisons and assessments. Hence, several armonic indices ave been developed to measure and caracterize armonic distortions wit a single figure [4, 6]. Te most common armonic index is te total armonic distortion (THD). max THD 1 (1) 1 is te fundamental wave RMS value and is te RMS value of te armonic component. Typical rule-of-tumb values for acceptable waveforms are a 5% THD for te current and a % THD for te voltage in te customer s point of connection. Tere exists also an alternative definition of te THD, wic is sometimes called distortion index (DIN) DIN= max max 1 max () DIN is frequently used in te European literature but rarely in te United States Te advantage of tis formulation is tat it is always between zero and one. Te THD goes infinitely large as te distortion increases. For small distortions, owever, bot definitions give approximately te same result [4, 6, 8, 9]. Te THD denotes te ratio of te energy content of te armonics to tat of te fundamental component [4]. rms www.ijltemas.in Page 56
THD = (Total Signal Enery- Fundamental Wave Signal Energy) / Fundamental Wave Signal Energy Were te fundamental frequency (and ence also te fundamental wave period) is defined by te power frequency. THD is calculated as: ' rms 1 THD 1 In a periodic case, evidently, THD = THD. In IEC Std 61800-4 (00) THD is called total distortion ratio, and it is noted tat it may be approximated wit THD if interarmonics are disregarded due to teir low amplitude. Furter, it is noted tat assessment of THD and THD lead typically to te same result in case of a voltage, but tere may be significant differences in case of a current. Tis misleading property may be avoided by relating te armonics to te nominal or te maximum current instead of te fundamental wave of te present current waveform. Tis is known as te total demand distortion (TDD). TDD max I n I 4. Power Quality Standards: Power quality is a worldwide issue, and keeping related standards current is a neverending task. It typically takes years to pus canges troug te process. One of te most important developments in te power quality arena is te increased empasis on coordinating IEEE standards wit international standards developed by te International Electrotecnical Committee [1, 3, 5, 8, 14, 15]. Most of te ongoing work by te IEEE in armonic standards development as sifted to modifying Standard 519-199.So let's take a closer look at some of te recent developments witin tese two organizations [8]. Te Power Quality Standards Coordinating Committee, SCC-, sponsored a task force to pull togeter a list of power quality terms and definitions. However, as te task force began compiling te definitions from various IEEE and IEC standards, tey found many confusing or conflicting terms. Despite tis urdle, tey tried to identify official definitions and provide examples of properly used terms. Accurate comparisons of power quality levels from one facility and system to anoter require consistent metodology. Existing IEEE Standard 1159 provides only general guidelines and definitions, so its group is actively developing more specific procedures for systems monitoring. Standard 1159.3 is actually based on te development of a Power Quality Data Intercange Format (PQDIF). Te format is a means for excanging power quality monitoring information between different applications. It will allow software developers to design applications tat analyze power quality problems independently from te manufacturers of te monitoring equipment [1]. As (4) for te IEC, tere are some specific standards related to te monitoring requirements for eac type of power quality penomena. For example, IEC Standard 61000-4-7 deals wit te requirements for monitoring and measuring armonics, wile IEC Standard 61000-4-15 describes te instrumentation and procedures for monitoring flicker. IEC Standard 61000-4-30 ave some future plans on providing overall recommendations for monitoring all types of power quality penomena wile still referring to oter specific standards were appropriate. IEEE is currently adopting tis standardized approac as well [3]. CONCLUSION www.ijltemas.in Page 57
Tis paper presented a brief and critical discussion about power quality problems, issue and related international standards. Te following recommended standards for equipment is developed to elp preserve voltage integrity by limiting armonic current injection of single-pase loads wic are likely to appear in increasing numbers in power distribution systems. By addressing armonic current distortion at te individual sources, system problems may be avoided. Te armonic current limits establised in te standards are proposed wit te intent of minimizing te impact on existing equipment design. Coordination wit existing industry practices and international armonic standards is also considered in tis paper. Tis paper sould elp researc workers, users and suppliers of electrical power to gain a guideline about te power quality. REFERENCES: [1] IEEE Recommended Practices and requirements for Harmonic Control in Electrical Power Systems, IEEE Std. 519-199. [] Electromagnetic Compatibility, Part 3: Limits- Sect.: Limits for Harmonic Current Emission, IEC 1000-3-, 1 st ed., 1995. [3] Draft Guide for Harmonic Limits for Single-Pase Equipment, An Internet Searc on www. google.com [4] Power Electronics, Moan, Underland and Robbins, Jon Wiley and Sons, 1995. [5] M. McGrangan, Power Quality Standards: an Industry Upadate, An Internet Searc on www. google.com. [6] Antti T., Power Quality Improving wit Virtual Flux-Based Voltage Source Line Converter, An Internet Searc on www. google.com. [7] D.D. Sabin and A. Sundaram, Quality Enances Realiablity, IEEE Spectrum, Vol. 3, No., 1996, pp. 34-41. [8] M. Jovanovic and D.E. Crow, Merits and Limitations of Full-Bridge Rectifier wit LC Filter in Meeting IEC 1000-3- Harmonic-Limit Specifications, in Conf. Rec. of IEEE- APEC 1996, pp. 354-360. [9] T. Key and J.S.Lai, Analysis of Harmonic Mitigation Metods for Building Wiring Systems, IEEE Trans. on Power Systems, PE-086- PWRS--06-1997, July 1997, pp. 1-9. [10] P. W. Hammod, A New Approac to Enance Power Quality for Medium Voltage AC Drives, IEEE Trans. on Ind. Appli, Vol. 33, No. 1, 1997, pp. 0-08. [11] S. Buso, L. Malesani, P.Mattabeli and R. Veronese, Design and Full Digital Control of Parallel Active Filters for Tyristor Rectifiers to Comply wit IEC-1000-3- Standards, IEEE Trans. on Ind. Appli, Vol. 34, No. 3, 1998, pp. 508-517. [1] D.O. Koval, W. u, and J.salmon, Power Quality Carcteristics of Rural Electric Secondary Power Systems, IEEE Trans. on Ind. Appli, Vol. 35, No., 1999, pp. 33-338. [13] J.S.Lai and F.Martzloff, Coordinating Cascaded Surge Protection Devices: Hig-Low Versus Low-Hig, IEEE Trans. on Ind. Appli, Vol. 9, No. 4, 1993, pp. 680-687. [14] T. Key and J.S.Lai, Comparison of Standards Limiting Harmonic Distortion in Power Systems, IEEE Trans. on Ind. Appli, Vol. 9, No. 4, 1993, pp. 688-695. [15] M. B. Huges, J. S. Can, and D. O. Koval, Distribution Customer Power Quality Experience, IEEE Trans. on Ind. Appli, Vol. 9, No. 6, 1993, pp. 104-111. www.ijltemas.in Page 58