His study is a description of basic quality parameters of
voltage with discussing basic requirements that must be
complied with by generator installations connected to electroenergetic
networks. The requirements for wind power stations
have been particularly included, cooperating with SN electroenergetic
network SN 15 kV-20 kV

Bugaj, Andrzej

Cebulski, Włodzimierz

Ryszard, Nawrowski

English

University of West Bohemia Digital Library

Acceptance test of voltage quality of wind farms connected to SN network

DSpace at University of West Bohemia

V-1Acceptance test of voltage quality of wind farmsconnected to SN networkNawrowski Ryszard1, Andrzej Bugaj2, Włodzimierz Cebulski31 Politechnika Poznańska, ul. Piotrowo 3A 60-965 Poznań,Polska e-mail: Ryszard.Nawrowski@put.poznan.pl2 ENERGA-OPERATOR S.A. Oddział w Kaliszu, 62-800 Kalisz, Al. Wolności, Polska e-mail: Andrzej.Bugaj@kalisz.energa.pl3 PBG S.A. 61-082 Wysogotowo ul. Skórzewska 35, Polska, e-mail: wlodzimierz.cebulski@pbg-sa.plKeywords  wind power station, generator, electric energy qualityAbstractHis  study  is  a  description  of  basic  quality  parameters  ofvoltage with discussing basic requirements that must becomplied with by generator installations connected to electro-energetic networks. The requirements for wind power stationshave been particularly included, cooperating with SN electro-energetic network SN 15 kV-20 kV.I. INTRODUCTIONThe necessity of Poland’s fulfillment from acceptedobligations towards EU concerning specific percentage ofrenewable sources in total volume of produced electricenergy,  caused  very  dynamic  growth  of  this  field  ofenergetics. In our direct neighbourhood, distributedsources of electric energy have been created such as windfarms and bio-gas co-generators. Big part of theseinstallations  from  500  kW  to  5  MW  is  connected  to  theexisting electro-energetic networks of medium voltageSN 15 kV-20 kV. Considering the fact that the Operatorof Distributive System is obliged to provide receivers withelectric energy of parameters specified in EN-PN 50 160standard EN-PN 50 160 each time before connecting nextunits to distributive network, researches and analyses ofquality parameters of energy produced by these sources,shall be carried out.II. BASIC PARAMETERS OF VOLTAGE WITHREQUIREMENTS FOR WIND FARMSA. HarmonicsThe measure of distortion that has been commonlyaccepted are harmonic values. Harmonics include currentsor voltages, which frequency is a total multiplicity ofvoltage basic frequency. Multiplicity of basic frequencyspecifies the so called harmonic number. By superpositionof harmonic components (according to Fourier series) ofdifferent frequencies and amplitudes, an optional distortedperiod course is achieved. Common phase displacementof individual harmonic components decides also aboutform of course. Voltage or current distortions in electro-energetic networks is expressed by total distortion ratio –THD, which is calculated according to the followingdependence:%100UUTHD2402n )1()n(u å= ÷÷øöççèæ=                      (1)The upper limit of summing up values is usually value40, and sometimes 50. Relative distortion ratio is alsodefined for h harmonic - HR, calculated according to thefollowing dependence:1UUHR h=                   (2)where:U 1 – effective value of basic harmonic,Uh – effective value of h harmonic.The main sources of harmonics in electro-energeticsystem are three groups of installations: devices withmagnetic cores (e.g. transformers, engines, generators,etc.), arc devices (e.g.: discharge furnaces, discharge lightsources, welding devices, etc.) and electronic and energo-electronic devices. Permissible level of harmonics in SNnetwork is THDU 8% value.[1]B. Voltage fluctuations and deviationsThese are voltage changes of different duration, in therange of amplitudes from 90% to 110% value of nominalvoltage Un.With relation to a dynamics and reason of describedvoltage change, voltage deviation (usually fall) withconstant value in time or voltage fluctuations. Voltagefluctuations defined as series of changes of effective valueof envelope of time course (temporary values), wherespeed of voltage changes is bigger than 1% Un per second.Basic parameters of voltage fluctuations are:1. amplitude of fluctuations – specified as adifference between adjacent effective values ofvoltage21'ekseks UUV -=d                     (3)where: 1eksU  i 2eksU  - next extreme effective values ofvoltage in the moment 1t  and 2t  = tt D+1Moreover, also average frequency of amplitudesoccurrence of voltage fluctuations Vd is calculated intime T and it is number m of fluctuations amplitudes intime T per time unit and specified in the followingformula:Tmf v =                               (4)Frequency of voltage fluctuations amplitude ismeasured by a number of fluctuations per second (1/s) orrelatively (1/m), (1/h).In order to evaluate level of voltage fluctuations ratiosof short-term light flickering Pst,  defined  in  PN-EN61000-3-3 are used. And long-term light flickering - Plt,V-2They characterize influence of voltage fluctuations on theprocess of view, including time ratio and they aremodified form of energetic voltage dose tP .Difficulty ratio of fluctuations is assigned to time t andspecified by the following formula:dttfGfgdtkP uuttt ),()(3502ò òQ-Q=         (5)where: ),( tfG u - frequency of process spectrum of voltage changesin time t,Q - average interval, including sight effect of differentiationmemory (300 s),k – ratio selected so that tP =1 value matched the level ofoccurring bad sight feeling during light flickering.The basic reason of voltage changes of described nature,is time variation, mainly of passive power of receiversgenerally named current variation receivers. The examplesof such receivers can be wind generators, where variationof generated voltage is mainly caused by windfluctuation.[3] During the acceptance process of windfarms, requirements are met when the above ratios in thepoint of contact with electro-energetic network do notexceed value PLt = 0,35 and PSt = 0,45.[2]C. Power supply dip and short breaksDips are defined as short-term reduction of effectivevalue of voltage in the range between 10% and 90% ofnominal voltage. Un, with duration from 10ms to 1 min(sometimes 3 min are taken). After a given time theeffective value of voltage comes back to previous state.Also, a relative amplitude of dip is defined AUn[%](residual voltage), as minimum difference of effectivevalue during dip and nominal voltage, expressed inpercent.Reducing value of effective voltage below 10% in timerange described above is taken as short-term power supplybreak.The reason of occurring dips and short breaks in powersupply are mainly short circuit in electro-energetic system,causing the flow of big currents, finally significant voltagedrops in electro-energetic network. Relative amplitude ofcreated dip or break depends on place of short circuitoccurrence in respect of power supply sources. The closershort circuit to power supply source, the bigger voltagedrop  is  observed.  Duration  of  such  an  occurrence  isdetermined by speed of protective devices. Many shortcircuits in transfer lines is eliminated in the time from 100to 500ms. In case of generator installations of wind farms,there is a requirements of mounting additionalinstallations, very sensible additional protections, adjustedto cooperation with electro-energetic network e.g. CZIP1E.The results of dips (short breaks) depend on theiramplitude and duration, and also on receivers connectedto electro-energetic network, and more specifically fromcharacteristics of their sensitivity represented by means ofCBEMA or ITIC curve. The exemplary characteristics oftolerance of energy quality in the form of CBEMA curveis presented on picture 1, registered in connection point ofwind farm of 1,5 MW.Pict. 1. CBEMA curve of voltage tolerance.D.  FREQUENCY VARIATIONFrequency of basic component of voltage in electro-energetic network is one of the basic values connectedwith electric energy quality. Quality parametersconcerning voltage frequency include voltage frequencydeviations and voltage frequency fluctuations. Voltagefrequency deviation is expressed by the followingdependancies:Nfff -=D (6)where:f – real frequency voltage basic component of electro-energeticnetwork.fN – voltage nominal frequency of electro-energetic network,Δf – voltage frequency deviation of electro-energetic network.Frequency fluctuations are specified by fluctuationamplitude and frequency of their occurrence according tothe following dependency:21 ekseks fff -=d (7)where :feks1,feks2   – adjoining extreme values of frequency changing in timewith relatively high speed (e.g..: 0,2Hz per second).4. CONCLUSIONSWith relation to a growing number of productiveunits  and  their  variety  not  only  in  terms  of  power,construction, characteristics of exploitation the owners ofdistributive networks must pay special attention tocontinual network’s monitoring with respect to meetingvoltage quality parameters. However, in spite ofecological effect resulting from connecting “green”sources of energy these units can be and very often aresources of electric energy quality parameters disturbances.It results from their particular motor characteristics.LITERATURE[1] PN-EN 50160 Dec 2002: Parameters of feeding voltage in publicdistributive networks[2] Nawrowski Ryszard, Zielińska Maria: Analysis of electric energyquality parameters of wind power station „Chojny“ in Chojne.Poznań 04..2011r.[3]  Kowalski Zbigniew: Quality of electric energy. Lodz PolytechnicPublishing. 2007

http://dspace5.zcu.cz/bitstream/11025/25914/1/Ryszard.pdf

Acceptance test of voltage quality of wind farms connected to SN network

Abstract

Similar works

Full text

Available Versions

University of West Bohemia Digital Library

DSpace at University of West Bohemia