Understanding Power Quality
Understanding Power Quality ECE 528
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Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 19 Universityofldaho Today Harmonics fundamentals Harmonic phase sequence Triplen harmonics Harmonic sources Locating harmonic sources References39 1 Fundamentals of Electric Power Qualityquot by Surya Santoso Lecture i9 Universityofldaho From last time power factor relationships 0 Distortion Power Factor PFdist 0 Displacement Power Factor PFdisp 0 True Power Factor PF PFdist39PFdisp PF Lecture la 3 Universityofldaho Harmonic phase sequence 0 Remember unbalanced 60Hz voltages can be broken down into positive negative and zerosequence components 0 Harmonic voltages and currents even if perfectly balanced are also classi ed as either positive negative or zero sequence Lecture la 4 Universityofidaho Harmonic phase sequence 0 Harmonic phase sequence becomes important for motors and on grounded wye systems 3 f rah A i i Lecture i9 5 l Universityofidaho Harmonic phase sequence Positive Lecture i9 E Universtyafldaho Triplen Harmonics Odd multiples of the third harmonic balanced fundarnenia currents sum to ii balanced third harmonic currents coincide fining I 139 NM i quot3 i 1 1 II t E l l I Hiquot ll I a I an V gs 1 N HI My 15 3 Neutral current contains no if fundamental but is 300 of the third 1 n e harmonic phase current From 1 with modifications to text Lecture 19 7 Universtyafldaho Triplen harmonics W l a ll ill All figures from 1 Balanced triplen harmonic currents are blocked by delta transformer windings Unbalanced harmonic currents and voltages may not produce the same effects as their balanced counterparts Unbalanced harmonic voltages and currents can be broken down into a set of positive negative and zero sequence harmonic symmetrical components more complex analysis Lecture 19 8 Universityorldaho Harmonic sources Commercial loads 0 Singlephase power supplies Older power supplies stepped down AC supply first with a transformer then rectified it o What are the advantages and disadvantages of this approach Now most electronic devices use switched mode power supplies 0 Advantages and disadvantages Lecture 19 9 Universityoldaho Switchmode power supplies Lecture 1 9 10 Universityofldaho Swntchmode power supply harmonic spectrum ian A sum mm mm mm 5on2 ssnz 7m anus 1U2EI6116mb125mb138D515DD5152D5176D5185U7198D721UD7222D8236D8 Fiewencie Hz Lecture19 11 Universityofldaho Other commercralload Issues magnetic and electronic ballasts u l l k l l s Emu g 501 39 E 02 gt u 1 0 37 Tzrgie msl an 4 01A y y quot 1 DUE i v nos E 003 gum l l 5 gum 002 l l m IIIII 2 D 450 720 QED 12 u 600 1 00 500 240 300 1 Frequency 1H1 h Frequencymz Lecture19 12 All figures from 1 Universityofldaho Other commercialload issues 0 Efficiency is driving the use of ASDs in HVAC systems 0 Harmonic issues need to be considered in building electrical systems Could be a significant problem when older buildings become home to computers and modern lighting systems Lecture la la Universityofldaho Industrial loads 0 Threephase power converters Variable speed drives AC or DC employing sixpulse rectifiers are generally the most common source of harmonics in industrial facilities Triplen harmonics not a problem three phase drives don t produce them PWM ASD is the most popular Lecture la l4 Universityofidaho Harmonic sources Variable speed drive Event DetailsWavefnms Lecture i9 i5 Universityafidaho Harmonic sources variable speed drive Waveform harmonics A iHamE iHamC Harm Lecture ia iE Universityofldaho Locating harmonic sources 0 Method described in the text Follow the current downstream to the load 1719 Lecture 19 i7 Universityofidaho Another way to find harmonic sources Waveform harmonics Hm HUB HEB Hm H12 H16 H16 H18 Hzn APHarm EPHarm CPHarm Lecture 19 18 Next time 0 System response 0 Effects of harmonic distortion 0 Interharmonics Lecture 19 Universityofldaho Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 20 Universityofldaho Today Harmonic phase sequence from waveforms System response Parallel resonance Effects of harmonic distortion Interharmonics Lecture 2D 2 Universityofldaho Harmonic phase sequence clarification o A graphical example of harmonic phase sequence Threephase fundamental and 2quotd harmonic waveforms Sequence is ABC for fundamental A08 for 2nd harmonic 5 7 R Leclure 20 3 Universityofldaho Triplen harmonics on three phase systems 0 Triplen harmonics in a threephase system Threephase fundamental and 3rd harmonic waveforms Third harmonic waveforms are in phase they add in the neutral Leclure 20 4 Universityofldaho System response to harmonics o The most signi cant issue is that one of the resonant frequencies of the system will coincide with a common harmonic frequency 0 Utility system capacitors generally create parallel resonances with the system s impedance Lecture 2D 5 Universityofldaho Parallel resonance There can be multiple resonant frequencies Ih c 7 c2 7 15y 1 1 i Lsys 39cl Lsys 39CZ Lecture In E Universityofldaho Series resonance Created by series combination of transformer and capacitor May affect customers with no nonlinear load May damage utility capacitors near customers with nonlinear loads g T Lecture 2D 7 Universityofldaho A realworld example Haiwwk Lecture In E Universityofldaho Effects of harmonic distortion 0 Capacitors Overheating Blown fuses May provide a path to the neutral for triplen harmonics 0 Transformers Harmonic current and voltage distortion will contribute to transformer heating Lecture 2D Universityofldaho Derating transformers serving nonlinear loads Note corrections to PSQ text 0 p213 table 52 should be table 65 p275 0 Also eq 530 is wrong Kfactor is not the same as FHL Harmonic Loss Factor See FPQ eq 665 and 669 for correct definitions Transformer losses due to harmonic currents 0 IR losses increased RMS currentmore losses 0 EddyCurrent Losses increase with the square of the current frequency Lecture 2D Universityofldaho Derating transformers serving nonlinear loads FPQ pg 216222 0 Total load losses heating is eq 653 PLL PIZR PEc POSL We llthe othersiray IOSSe 0 At rated full load current IR P P LLiR 2 PEC7R I RiR The R indicates rated conditions Lecture In M Universityofldaho Derating transformers serving nonlinear oads FPQ pg 216222 0 We ll switch to perunit analysis with a base of P IZR R o The loss equation becomes PLL7Rpu 1 PEC7Rpu o The perunit eddy current loss factor is a constant that we can get from tables or the transformer manufacturer See table 64 p 219 Lecture 2D 12 Universityofldaho Derating transformers serving nonlinear loads FPQ pg 216222 0 Changes to losses with harmonics I 2 The summation is a factor that h increases the RMS value ofthe P 2 P 2 currentinthe IZR losses based I R I RiR o IR harmonic content IR is rated h current 0 In perunit P 2 pu ZIh2pu I R h Lecture 2D 13 Universityofldaho Derating transformers serving nonlinear loads FPQ pg 216222 0 Changes to losses with harmonics 1h 2 2 The summation is a factor that increases the eddy current 1EC 1EC7R Z I h losses by the square of the h R 39equency causing the losses 0 In perunit PECltpugt PECRltpugtZIhltpugt2h2 h Lecture In M Universityofldaho Derating transformers serving nonlinear loads FPQ pg 216222 0 A little rearranging PLLQm PIZRQm PEcpu PLLpu ZIh2pquot PEchp 39ZIhpu239h2 h h zi1hltvugti2h2i I LLW ZIh2pquot39 1 PEGRWm39h z h zilh M h Lecture 2D is Universityofldaho Derating transformers serving nonlinear loads FPQ pg 216222 FHL the harmonic loss factor for eddy currents Z1hpu2h2 See other forms ofthis equation in h eq 660 p 218 F zinfwi h Lecture 2D 16 Derating transformers serving nonlinear loads FPQ pg 216222 Remember we re trying to keep the heating due to harmonics at or below the heating we get at Universityofldaho rated load without harmonics ZIh2pul PEC7RpuFHL g 1 PEC7Rpu h Perunit losses with harmonics Rated perunit losses without harmoni Lecture 2D Universityofldaho Derating transformers serving nonlinear loads 0 More rearranging of equations Also taking the square root of each side to get the perunit RMS current give us the Derating Factor DeratingiFactor Imagpu 1 PEciR 1 t FHL39PEciR RMS current in perunit mm 2 Ilium h Lecture 2D Universityofldaho Derating transformers serving nonlinear loads Example from FPQ p 219 From table 64 PEciR 015 From table 66 99114 F 621 HL 1596 HL Lecture 2D Universityofldaho Derating transformers serving nonlinear loads 0 The result 1 PEC R Deratin g 1 FHL39PEciR Derating 07716 The allowable current calculation in PU translates directly to a derating factor For a current with the harmonic spectrum described in table 65 the transformer should be derated to 7716 of its nameplate capacity Lecture 2D Universityofldaho Derating transformers serving nonlinear loads 0 Another way The K factor FPQ p 221 2013112 Kfactor h 2 IR 0 Using K factor we compute the Kfactorfor a given current and select a Krated transformer accordingly 0 Note Kfactor depends on the magnitude of the current we can reduce K by reducing overall loading in effect derating the transformer Lecture 2D 21 Universityofldaho Other impacts 0 MOtOl S For motors the impact of harmonic voltages is similar to that of negative sequence fundamental frequency voltages heating 0 Telecommunication systems Higher frequency currents on the power system will more easily couple to nearby communication circuits Lecture 2D 22 Universityofldaho Interharmonics PSQ only IEC100021 definition Between the harmonics of the power frequency voltage and current further frequencies can be observed which are not an integer of the fundamental They can appear as discrete frequencies or as a wideband spectrumquot ntaharmomcs in 36 OSCIRED W6 2 I c Lecture ZEI Universityafldaho Interharmonics PSQ only 0 Issues Measurement requires multiple fundamental cycles Heating similar to regular harmonic currents Light flicker Lowfrequency interharmonics can create noticeable light flicker Lecture ZEI Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 34 Universityofidaho Today 0 Finish DGDR issues Transformer connections Protective relaying Lecture 34 2 Universityofldaho DG transformer connections and power quality The transformer configuration used to connect the DG to the distribution system can have a significant impact on power quality and reliability There are several options Grounded wyewye Deltawye Deltadelta or ungrounded wyedelta Grounded wyedelta 0 Note All connections are in systemgenerator order Lecture 34 Universityofldaho Grounded wyewye transformer connection J o Most common transformer connection in the US Lecture 34 Universityofldaho Grounded wyewye transformer connection 0 Advantages Standard utility transformer replacements available if needed No voltage phase shift simpler relaying and fault detection Ferroresonance is not much of an issue Lecture 34 5 Universityofldaho Grounded wyewye transformer connection 0 Disadvantages DG can feed any type of primary system fault Passes zerosequence currents 0 Solutions A reactor in the neutral will limit the DG contribution to a ground fault and will also reduce zerosequence current flow between the DG and the distribution system Lecture 34 E Universityofldaho Deltawye transformer connection 0 Second most common transformer connection in US 0 Most common transformer connection in Europe Lecture 34 7 Universityofldaho Deltawye transformer connection 0 Advantages Low DG contribution to ground faults Zero sequence harmonics from the DG are blocked Primary single linetoground faults do not have as severe an impact on the secondary voltages Lecture 34 E Universityofldaho Deltawye transformer connection 0 Disadvantages May be difficult for generator protection to detect single linetoground faults on primary system Triplen harmonics from DG may circulate in lowimpedance secondary neutral Possible ferroresonance and the need for threephase switches on the primary side of the transformer Lecture 34 a Universityofldaho Deltadelta or ungrounded wyedelta transformer connection 0 Uncommon connections but used in some industrial facilities to reduce impact of SLG faults on the primary system Lecture 34 in Universityofldaho Deltadelta or ungrounded wyedelta transformer connection 0 Advantages Primary SLG faults do not affect the load Minimizes DG contribution to ground faults Some inverters may require an ungrounded connection Could centertap oneleg of delta secondary to provide single and threephase service Lecture 34 ii Universityofldaho Deltadelta or ungrounded wyedelta transformer connection 0 Disadvantages Ferroresonance issues may require three phase switches and protection on primary side Detection of primary single linetoground faults is difficult Nonstandard equipment for most utilities Lecture 34 i2 Universityofldaho Grounded wyedelta transformer connection o Usual connection for substation transformers and central station generators Lecture 34 i3 Universityofldaho Grounded wyedelta transformer connection 0 Advantages Primary system faults are easily detected by the generator s interconnection protection system Blocks triplen harmonics from the generator Protection scheme is standardized based on utilityowned generator protection systems Lecture 34 i4 Universityofldaho Grounded wyedelta transformer connection 0 Disadvantages Acts as a source for ground fault current May interfere with existing protection systems 0 May cause sympathetic tripping of other feeders during ground faults 0 May make fuse saving impossible Transformer may overheat clue to zero sequence currents Lecture 34 Universityofldaho Protective relaying for distributed generation Purpose of protective relaying Protect the generator 0 Detect abnormal operation 0 Block unsynchmnized paralleling Prevent unintentional islands 0 Detect primary system faults o Detect conditions indicating islanding In any of these events the relays and control system initiates a trip of the generator a contactor or circuit breaker or prevents the contactor or circuit breaker from closing Lecture 34 Universityafldaho Protective relaying for distributed generation 0 Small generators Overunder voltage Overunder frequency 0 Large generators same as above plus Overunder current Negative sequence voltage and current Synchronizing Many other relays may be used depending on the generator and the particular installation Lecture 34 17 Universityafldaho DG relay example 0 Single device incorporates Undervoltage Overvoltage Underover frequency Negative sequence voltage Directional power From Schwenzer Engineering Synchronism check Laboratories SEL547 Lecture 34 18 Universityofldaho Next time 0 Start wiring and grounding Chapter 10 Seven lectures scheduled Lecture 34 19 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 37 Universityofldaho Today 0 Wiring and grounding problems Locating extra neutraltoground bonds Missing or incorrectly isolated grounds Ground loops Correctly Isolated grounds Lecture 37 2 Universityofldaho Specific wiring and grounding problems 0 Missing equipment grounding conductor PSQ page 442 fig 102 Issues 0 Return path impedance for groundfault current is high sometimes very hig 0 Equipment case may become energized 0 Without a GFCI groundfault current may not trip circuit breaker o How would you locate this problem Lecture 37 3 Universityofldaho Specific wiring and grounding problems 0 Locating missing grounds Visual inspection Measure neutralto ground voltage at receptacles Use a receptacle tester Measure voltage between points that should be bonded together Lecture 37 4 Universityofldaho Specific wiring and grounding problems 0 Another missing ground L Lecture 37 5 Universityofldaho Wiring and grounding problems 0 Incorrectly isolated grounds ungrounded equipment Sometimes called a clean ground Occasionally found on CNC machines and other sensitive industrial equipment Perception is that this avoids noise on the grounding system wrong Lecture 37 E Universtyufldaho Wiring and grounding problems Ungrounded equipment Ser Ice panel equirgment I I Hot A HotLine 1 39 I I I I I Ground d Hot I C ndu t I I 39 Neutral I I I I Bonding Jumper g I A 4 Grounding gt x J Lecture 37 7 Ul liVEFStjfofldEh Wiring and grounding problems Ungrounded equipment NEC violation Unlikely to resolve interference problems May result in high touch potentials even without a fault due to capacitive coupling inside the equipment Ground fault in the equipment is unlikely to trip some upstream protective device Lecture 37 8 Universityofldaho Additional ground rods 0 The wrong way Ground rods not all connected to the neutral toground bond at the service entrance Ground rods distributed in such a way that lightning transients will flow through the facility grounding system Lecture 37 a Universityofldaho Additional ground rods 0 The right way Connect all ground rods to the facility grounding system ideally at one point Additional ground rods reduce the overall impedance to earth Low impedance to earth at the service entrance reduces voltages between grounded equipment and the earth Lecture 37 in Universityofldaho Ground loops 0 An electrical connection usually in a communication circuit between two or more devices that are connected to different ground references Lecture 37 ii Universityofldaho Ground loops Causes equalizing current flow between devices on communication circuits Where it s a problem Communication circuits with ground connections at both ends 0 Serial cables including USB 0 Parallel cables 0 Some remote transducer signal cables 0 Most audiovideo signal cables Ever wonder why it s hard to find a 50 parallel printer cable or USB cable Lecture 37 i2 Universityoldaho Ground loops Symptoms Data errors Remote sensing errors Audible hum in audio systems Bars on video screens What about flat panel displays Damaged equipment Lecture 37 13 Universityoldaho Ground loops 0 Solutions Establish a single nearb ground point for interconnected devices Use a groundoo isolator d sh k essentally a hlgh requency From ra 10 ac com isolation transformer Use differential mode communications systems with appropriate surge suppression at both ends of the circuit Use optical isolation fiberoptic cables this is becoming easier From apocom Lecture 37 14 Universityofldaho Isolated grounds the right way Isolated can be misleading Dedicated or Insulated might have been better terms An isolated equipment grounding conductor is a separate additional grounding conductor It is only connected to the grounding system at the ground bus in the main service panel or a separately derived system It is insulated as it passes through downstream panels to some end device where it is used as that device s equipment grounding conductor Lecture 37 15 Universityofldaho Isolated grounds the right way Isolated grounds are used to reduce noise on the equipment grounding conductor associated with other loads on the system Covered in the 2005 NEC in article 25096 Usually used for computers or other sensitive equipment Receptacles are colorcoded orange 6 From Lewes com Lecture 37 16 Universityofldaho Isolated grounds the right way 0 Where does the noise come from Translormer Lecture 37 i7 Universityafldaho Coming up 0 More wiring and grounding Neutral sizing Separately derived systems Signal reference grounding Lecture 37 i8 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 32 Universityofldaho Today 0 Distributed Generation Power Quality and Reliability PQ Issues Operating conflicts Lecture 32 2 Universityofldaho PQ issues with DGDR o Sustained interruptions How DG may help 0 Individual customers can run on DG during the interruption 0 Portable DG can be used for critical loads during planned outages How DG may hurt o If the utility relies on DG for base capacity and the DG becomes unavailable load shedding may be required Lecture 32 3 Universityofldaho PQ issues with DGDR 0 Voltage Regulation Active voltage regulation not permitted IEEE 1547 How DG may help 0 If the DG reduces load fluctuations on a feeder by responding to a large variable load it will also reduce voltage fluctuations How DG may hurt 0 Following a fault DG may not reconnect for up to 5 minutes or until system voltage is in ANSI C841 range B IEEE1547 Lecture 32 4 Universityofldaho PQ issues with DGDR Harmonics Harmonic current injection is limited by IEEE 519 and 1547 How DG may help 0 To the extent that DG increases system capacity at a location the voltage distortion due to distorted load current t ere will e lower How DG may hurt 0 DG oonnected through an inverter may inject some harmonic current 0 Switching frequencies may correspond to system resonances o Capacitors may cause resonanoes Lecture 32 5 Universityofldaho PQ issues with DGDR 0 Voltage Sags How DG may help 0 Rotating machines including DG can help support system voltage during a voltage sag How DG may hurt 0 DG is required by IEEE1547 to trip during certain voltage sags Loss of generation may result in a more severe sag or an interruption Lecture 32 E Universityofldaho Operating conflicts 0 Distribution systems are normally designed for radial singlesource operation 0 DG may change the direction of power ow and impact the response of the distribution system to faults 0 Reverse power flow may impact the operation of voltage regulators Lecture 32 7 Universityofldaho Operating conflicts o Reclosing Issues 0 Reclosing on rotating generators can damage them 0 DG can feed a fault and prevent it from clearing Solution Rules 0 DG is required IEEE1547 to disconnect from the Area EPS during faults on the Area EPS and prior to reclose by the Area EPS Lecture 32 E Universityofldaho Operating conflicts DG interruption requirements per IEEE1547 voltage at the PCC V lt 50 016 seconds 50 S V lt 88 200 seconds 110 lt V lt 120 100 second 120 S V 016 seconds Universityofldaho Operating conflicts o Interference with relaying Reduction of reach Solutions g 0 Adjust relay to increase reach 0 Add recloser to add another protection zone 0 Minimize DG contribution to ground faults Lecture 32 in Operating conflicts o Interfering with relaying sympathetic tripping 0 Issues May make nding faults dif cult Increases area affected by 0 Solutions Directional relays Changes to circuit breaker settings Lecture 32 Universityofldaho Operating conflicts o Interference with relaying Defeat of fuse saving 0 Issue Universityofldaho Fuse ooordinate with recloser fasttrip varies with DG ope t 0 Solutions 6 Larger fuss r a Do without fuse saving Minimize DG oontribution to ground faults Lecture 32 Universityofldaho Operating conflicts 0 Voltage regulation IEEE1547 limits individual DG to 5 or less voltage fluctuation at the PCC when paralleling IEEE1547 requires DG to disconnect during relaying but impact on distribution system is not addressed in the standard LTC transformers and regulators adjusted for the load with the DG may be set too low without the DG Lecture 32 is Universityofldaho Operating conflicts 0 Voltage regulation solutions Limit the DG on a feeder Increase regulator step speed Disconnect load when DG disconnects Allow DG to reconnect more quickly Lecture 32 M Universityofldaho Operating conflicts o Harmonics Issues 0 Linecommutated thyristorbased inverters generated significant harmonics 0 Some synchronous generators can generate large zerosequence currents Solutions 0 Newer PWM inverters have lower current distortion 0 Use nonresonant switching frequencies 0 Use reactors in the neutral or generators with a 23 coil winding pitch Lecture 32 15 Universityofldaho Wind generation versus load Note vertical scales are not the same l ll l l j fill l l ill l ll39 il l i la n Milli l UU UU AM 39 3 00 days 39 ens200 1200 00 AM Lecture 32 will l 200 W Universityofldaho Next time o More DGDR issues Islanding Location issues For another perspective on coil pitch in synchronous generators Generator Winding Pitch and Harmonics from Caterpillar Inc Lecture 32 i7 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 31 Universityofldaho Today 0 Distributed Generation Power Quality and Reliability What is it The interested parties Some general big picture issues Lecture 3i Universityofldaho Definitions Distributed Resources DR Sources of electric power including generators and energy storage systems that are not directly connected to a bulk power transmission system Distributed Generation DG A subset of DR Electric generators connected to a distribution system through a PCC I IEEE 1547 2003 IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems Lecture 3i Universityofldaho What is it Common technologies 0 Reciprocating Engine Genset Uses gas or diesel generator with synchronous or induction generator Used to produce electrical energy and heat from methane produced in landfills and anaerobic digesters Waste heat can be used for onsite space and water heating and for heating the digester Lecture 3i Universityofldaho Common technologies Gas turbines Used as peaking generators Popular where heat is needed 0 Generating both electrical energy and heat increases ciency Connected through synchronous generator to the distribution system Microturbines 0 Generally 25kW to a few hundred kW 0 Replacement for reciprocating engine 0 Connected through an inverter to the distribution system Lecture Si Universityofldaho Common technologies 0 Fuel cells Expensive but clean and quiet 0 Can be used indoors 0 Operation is similar to batteries hydrogen in an anode combines with Oxygen cathode in an electrochemical reaction producing water and electrical energy Popular for remote locations with small critical loads Lecture Si Universityofldaho Common technologies 0 Wind turbines Becoming costcompetitive in some areas May require inverter interface to power system Generally require remote locations away from significant loads Nondispatchable Requires energy storage for standalone operation Lecture Si 7 Universityofldaho Common technologies 0 Photovoltaic solar panels Expensive Requires inverter interface Requires energy storage for standalone operation Nondispatchable Lecture Si 8 Universityofldaho Energy storage 0 Storage offers a way to bank generation for emergencies or flatten the daily load profile 0 Allows generators to run at maximum ef ciency 0 Similar to hybrid vehicles but for the power system 0 Can reduce generation and transmission requirements Lecture 3i Universityofldaho Typical daily load profile I l quot T w i w 2 If i E innitquot v 150 7 1 7 7 Time Lecture 3i Universityofldaho Energy storage technologies 0 SMES 0 Batteries 0 Compressed Air 0 Pumped hydro o Flywheels o Capacitors 0 Heated fluids Lecture Si ii Universityofldaho The DGDR distribution system interface 0 Synchronous machine May support islands May interfere with protection systems High source impedance changes system response when operating off grid 0 Reduced fault current 0 Increased harmonic voltage distortion 0 Increased severity of voltage sags Lecture Si 12 Universityoildaho The DGDR distribution system interface Induction machine Reduced islanding risk Simpler synchronizing with the power system Often requires capacitors o Capacitors may create resonant problems 0 May selfexcite if islanded 0 May feed faults and interfere with protection systems Lecture 31 Universityofldaho The DGDR distribution system interface 0 Electronic inverter Harmonics in newer PWM inverters is less of a concern than in older inverters 0 IEEE 519 and IEEE 1547 describe the limits Indiu39dnal 11 lt 11 11 g 1 lt 17 17 s l lt 13 13 s 1 lt 35 35 g h flewquot order 1 odd rhsroruou harmonicsquot TDD Percent 1a 40 20 13 06 03 50 a 1 lhe genie omie Local EPS maximum load mm em miegmred demand 15 or 30 minutes whim me DR mm V munchies are liuuted to 25 of ihe odd harmonic limits above PCC hEVen Lecture 31 Universityofldaho The DGDR distribution system interface 0 Electronic inverter continued Islanding is less of an issue 0 Inverter can quickly detect and separate from the system May feed faults briefly 0 Electronic controls can quickly detect abnormal conditions and disconnect the inverter from the system Lecture 3i i5 Universityofldaho Operating conflicts o Interference with relaying Reduction of reach Solutions g 0 Adjust relay to increase reach 0 Add recloser to add another protection zone 0 Minimize DG contribution to ground faults Lecture 3i iE Universityofldaho Operating conflicts o Interfering with relaying sympathetic tripping 0 Issues May make nding faults dif cult Increases area affected by 0 Solutions Directional relays Changes to circuit breaker settings Lecture Si Universityofldaho Operating conflicts o Interference with relaying Defeat of fuse saving 0 Issue Fuse ooordinate with recloser fasttrip varies with DG ope t 0 Solutions 6 Larger fuss r a Do without fuse saving Minimize DG oontribution to ground faults Lecture Si Next time Universityofldaho o More on speci c power quality issues Sustained interruptions Voltage regulation Harmonics Voltage sags Lecture 31 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 4 Universityofldaho Today 0 Power electronics review 0 Common devices and topologies o The Power Quality perspective on power electronics Lecture 4 2 Universityofldaho What are Power Electronics 0 Power electronics refers to devices employing semiconductors to convert and control electrical energy 0 Types of conversions magnitude Frequency Number of phases Lecture 4 Universityofldaho Why are power electronics important to PQ 0 They cause harmonic distortion 0 The presence of harmonic distortion from power electronics can affect the power system and other loads 0 Power electronic devices have particular vulnerabilities when it comes to PQ o The use of power electronic devices is increasing Lecture 4 Universityofldaho How power electronics create harmonics Generally a power electronic device draws current in pulses from the power system Current waveform for a desktop computer 39 W F Lecture 4 5 Universityafldaho Nonlinear current harmonics As we learned with the Fourier Series the nonlinear current can be assembled from sinusoids Harmonic spectrum of the computer current High 3rd 5th and 7th I harmonics Lecture 4 E Universityofldaho Why is the current drawn in pulses The basic rectifier filter capacitor combination VWC Lecture 4 Universityafldaho Controlling the output A regulated linear DC power supply We want the dc output voltage to be nearly constant despite load variations and supply voltage Transistur tputre ul variations H t t mu 3 inn Ca lm we Transistor operated in active region as a variable resistor Varies VOItage drop t0 Line Frequency regulate output voltage quot3mm Lecture 4 Universityofldaho Losses in the linear dc supply 0 V0 lt Vdc output voltage lt capacitor voltage 0 The power dissipated in the load is VoIo o The power dissipated in the transistor is Pswitch0ldcVoIo o If Vo 12 Vdc then Pswitch12VdcIo o The switch mode supply reduces losses significantly Lecture 4 a Universityofldaho Controlling the output Switch mode power supplies The transistor is operated as Switchmode pQWer SUPP39Y a switch either fully on or equwalent Circwt fuy off oAdvantages Reclucecl losses and weight More tolerant of input voltage variations oDisadvantages High switching frequency interference Need for special high frequency transformers etc Lecture 4 in Universityofldaho Topologies of converters o The general switch mode power supply ReC l er ACDC High Energy storage Frequency amp Flller Transrormer Lecture 4 ll Universityofldaho Topologies of converters The variable speed drive ASD VSD VFD Rectifier Energy Storage amp Filler See PSQ pages 184 194 or FPQ pages 203210 Lecture 4 12 Universityofldaho Where are power electronics 0 Almost everywhere Industrial systems 0 Motors 0 Control systems Lighting 0 Electronic ballasts in fluorescent lights 0 Dimming systems Generation 0 ggnvert DC from solar or AC from Wind to 60Hz Lecture 4 is Universityofldaho Where are power electronics HRRM II I c5 I 5 9 131721252933374I4549 Lecture 4 M Universityofldaho Some PQ issues with power electronics Impact on line voltage flattopping reduces ride through time of electronic loads during Current voltage sags Distorted voltage results in distorted current even in linear loads Voltage Lecture 4 is Universityafldaho Some PQ issues with power electronics Other lineside issues Higher frequencies associated with harmonics and high switching frequencies can increase capacitive coupling Line voltage notching if rectifier uses thyristors Lecture 4 16 Universityofldaho Power electronics vulnerabilities o Flattopped voltage reduces dc bus voltage reducing stored energy for voltage sag ridethrough o Capacitor switching What will happen when this voltage waveform passes through the rectifier and into the dc bus capacitor Lecture 4 Universityafldaho Loadside issues 0 Primary issue is the fact that the ac output from a converter contains high frequency components 0 Voltage output of a small UPS Lecture 4 Universityofldaho Load side issues Short rise time may affect load the same way a transient would If the rise time here represents 14 cycle what would the frequency be Lecture 4 la Universityafldaho Special problem with PWM drives 0 A Pulse Width Modulated VFD can effectively vary both the voltage and frequency of its output signal 0 This is done by varying the width of output voltage pulses 0 Rise time can be 01 micro second 0 If the motor leads are long voltage reflections can lead to increased voltages at the motor terminals Lecture 4 2D Universityafldaho Voltage reflections in PWM drives Normal leading edge Leading edge of PWM of PWM voltage pulse VOItage PUISe With reflected voltage Lecture 4 Problems for the investigator Universityafldaho o In some cases handheld meters may give misleading readings 0 Average responding meters may read values significantly higher or lower than the TrueRMS values of voltage and current depending on the wave shape 0 Some problems such as high frequency voltage reflections may require oscilloscopes or other more specialized monitoring equipment Lecture 4 Universityofldaho Next time o Terminology Read chapter 2 in FPQ and PSQ if you haven t 0 Investigation planning Lecture 4 23 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 30 Universityofldaho Today 0 Power quality and reliability benchmarking Statistics Dealing with real world data Harmonic indices Lecture 3D 2 Universityofldaho Statistics Cumulative probability or frequency Many standards including IEEE 5191992 and EN50160 allow the measured THD voltage frequency etc to fall outside the steadystate limits for short periods of time Cumulative probability 0 The sum of the probabilities of values above below or between speci c points depending on the limit in question CP95 o The point at which the cumulative probabilityquot equals 95 Lecture 3D 3 Universityofldaho A CP95 example thzhll y Dens y Lecture 3D 4 Universitycfldaho A CP95 example Probability Density h m A nu In m H5 ma mi 225 mu Lecture 30 5 Universitycfldaho Realworld benchmarking EN50160 report application of CP95 EN50160 COMPLIANCE REPORT sue ECE 523 class 30a Week 7 palm2006 06 45 08 o to 03092006 06 4s 05 0 Numlnal Voltage Un 277 v Power Frequency Range Threshold Compliance 60 Hz 1M 98 5 100 0 PASSED 60 Hz em75 mu 0 ma 0 PASSED Supply Voltage Variations Cum Iinnce Range Threshold CHA CHE CHC 277 V 10MD 95 0 100 0 100 0 IOU 0 PASSED 277 V 10MS IDU 0 00 0 WED 0 IOU 0 PASSED Rapid Vollage Changes Nol available Flicker Compliance Range Threshold CHA CHE CHC lt1 95 0 E17 5 SB 5 S7 5 PASSED Supply Voltage Unbalance Range Threshold Compliance 072 950 mu 0 PASSED Lecture 30 6 Universityofldaho Realworld data issues 0 Voltage THD may not be the same on all three phases General approach is to average the voltage THD o Simpler reporting one number 0 May mask high values on one phase Lecture 3D Universityofldaho Harmonic indices 0 STHD95 System Total Harmonic Distortion CP95 Example use 0 Compaan VTHD between different substations Calculation o For mch substation the CP95 value of the VTHD reoorded at the substation is weighted based on connected KV The STHD95 is the net CP95 value of all of the individual weighted CP95 values for individual substations Lecture 3D Universityofldaho Harmonic indices 0 SATHD System Average Total Harmonic Distortion An average of averages Example use 0 Similar to STHD95 find the mean THD of a group of feeders or substations Calculation 0 Sum the kVAweighted average THDs and divide by the total system kVA Lecture an a Universityofldaho Use of harmonic indices STHD95 and SATHD describe the overall voltage THD on a system but not the voltage THD experienced by individual customers Benchmarks may be chosen for these indices to help prioritize system improvements The data used to calculate STHD95 and SATHD can help identify areas of high and low distortion within a system Lecture 3D in LJniversityofldaho Including Power Quality and reliability in distribution planning the concept 0 Additional utility system costs will be offset by reduced customer costs More frequent treetrimming Shorter spans Longer crossarms Increased animal guards Recloserssectionalizersfuses Designing for higher windloading Lecture 3D ii Universityofldaho Including Power Quality and reliability in distribution planning dif culties 0 Accurate customer costs are very difficult to obtain Labor to respond to events Production quantity and quality Equipment damage Disposal of waste Failure to meet delivery obligations and more Reduced customer costs do not automatically translate a e to increased utility construction and mainten nc Significant utility system upgrades or modifications may be reqUIred to resolve an issue that is only a Significant problem for one customer or a small group of customers Normal statistical variation can mask the true impact of system changes in the short term Lecture 3D i2 Universityofldaho Including Power Quality and reliability in distribution planning contracts 0 In the case of power quality contracts costs are assigned to specific events 0 Utility can analyze the cost of power quality events accurately and select improvements accordingly 0 Offsetting utility costs in the form of contract penalties provide incentives to maintain or improve power quality and reliability Lecture 3D is Universityofldaho Next time 0 Start Distributed Generation Distributed Resources and Power Quality Read Chapter 9 Homework 5 due Homework 6 available Lecture an M Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 29 Universityofldaho Today 0 Finish long duration voltage variations Enduser mitigation 0 Power quality and reliability benchmarking Definitions Motivation Issues Trends RMS Voltage variations Lecture 29 2 Universityofldaho Enduser mitigation of Longduration voltage variations 0 Ferroresonant transformers Very constant voltage output over a wide range of voltage input Must be oversized Best for relatively constant load not suitable for motors Inefficient Lecture 29 3 Universityofldaho Enduser mitigation of Longduration voltage variations 0 Electronic tapchanging transformers or regulators Use solidstate switches to quickly switch between taps Can provide voltage in a narrower range than supplied by the utility 0 One example Input 10 to 20 of nominal Output 25 of nominal Lecture 29 4 Universityofldaho Enduser mitigation of Longduration voltage variations 0 UPSs Generally not intended for longterm mitigation 0 Some models incorporate ferroresonant transformers or electronic tapchanging voltage regulators or transformers 0 Provides voltage regulation over a wider range of input without switching to battery Lecture 29 Universityofldaho Enduser mitigation of Longduration voltage variations Magnetic Synthesizers Typically used for larger loads 0 15kW to ZOOkW ratings may be paralleled Similar to ferroresonant transformer 0 Uses saturated reactors and transformers with capacitors to synthesize a lowdistortion wellregulated output voltage Output voltage is relatively constant over a wide range of voltage input 0 Input 40 Output 5 Harmonic benefits 0 Low distortion on output voltage and input current Lecture 29 Universityofldaho Power Quality and Reliability Benchmarking De ning terms PSQ Ch 8 Aggregation Grouping events within a time period or only considering the worst event in the time period Benchmark A standard against which performance is measured Benchmarking The process of evaluating performance against some standard level of performance Uses one or more de ned indices or metrics Lecture 29 7 Universityofldaho Defining terms 0 Index or metric A specific measured parameter c For each index or metric we need to know What is measured and how How often it39s measured The benchmark for that index The target for that index 0 Target Goals for specific indices based on benchmarks local constraints and specific objectives Lecture 29 E Universityofldaho Motivation why benchmark Benchmarking helps drive improvement Underperforming areas can be identified Best practices can be determined Helps ensure factbased decision making The power quality may seem good or bad but is it How good or bad is it specifically Benchmarking helps establish a common set of measurable expectations Regulators utilities and customers can agree to and document indices and benchmarks Lecture 29 Universityofldaho The value of a common set of measurable expectations Energy Energy Consumer Provider Rights amp But 5 1 2 Receivablesamp Received DeliVered Deliverables Produ s G Prod cts 3 amp Services amp Services Rights amp Perceptions 4t Lecture 29 Universityofldaho Motivation Why benchmark o Performancebased ratemaking Links a portion of utility rates and profits to performance against specific benchmarks 0 Power quality contracts Contracts with individual customers that ensure a certain level of power quality and reliability or refunds in exchange for long term contracts V V V Example Sag Score sagscare w o Aggregation interval is 15 min Lecture 29 ii Universityofldaho Benchmarking issues 0 Power quality and reliability are often inversely related 0 Customers do not classify events the same way that utility engineers do 0 Impact of events may vary from customer to customer 0 A single event main contain numerous components and they may be different on different phases Lecture 29 12 Universityofldaho Benchmarking issues 0 Not reasonable to expect the same performance across all transmission and distribution systems Geography Weather System densityfeeder length Undergroundoverhead Protection scheme Animalsvehiclesvegetation Lecture 29 Universityofldaho Trends 0 Standards have been and are being developed which combine power quality and reliability indexes and benchmarks o In Europe EN 50160 Voltage characteristics of electricity supplied by public distribution systems 0 In the US Work is underway to establish Service Quality Indices Lecture 29 Universityofldaho EN50160 pg 292 Sets limits for Frequency Voltage sags Interruptions short and long gt3 min Voltage unbalance Voltage harmonics and more Generally specifies acceptable limits measurement interval length of recording and acceptance percentage Example Voltage sampled every 10 minutes for a week will be within 10 of nominal 95 of the time Lecture 29 is Universityofldaho US Service Quality Benchmarking A Service Quality Index combining power quality and reliability measures has been proposed Not adopted yet Purpose is to reflect customer quality and reliability requirements and expectations EPRI project 1010199 IEEE paper Quantifying Reliability and Service Quality for Distribution Systems by Mark F McGranaghan 2007 Lecture 29 16 Universityofldaho Existing US Power quality indices RMS variation indices SARFIx System Average RMS variation Frequency Index SARFIX ZIZVM T Standard values 0 140 120 and 110 Overvoltage per ITI curve 0 90 80 and 70 Undervoltage per ITI curve 0 CBEMA ITIC SEMI Lecture 29 Universityofldaho Existing US Power quality indices The duration of the RMS variation can be incorporated into the preceding indices SIARFIx 0 System Instantaneous Average RMS Variation Frequency Index SMARFIX 0 System Momentary Average RMS Variation Frequency Index STARle 0 System Temporary Average RMS Variation Frequency Index Lecture 29 Universityofldaho Applications of RMS variation Indices see pg 90 for reliability indices 0 SARFIx STARFIx SMARFIx and STARFIx can be determined for the system and for individual feeders or areas 0 Feeders with belowaverage values can be targeted for improvement 0 Feeders with aboveaverage values can be studied for best practices Lecture 29 Universityofldaho N ext ti me o More power quality and reliability benchmarking Harmonic indices Looking at realworld data 0 Read chapter 8 Lecture 29 Universityafldaho ECE 528 Understanding Power Quality httpwwweceuidahoedueepowerECESZS Paul Ortmann portmannuidahoedu 2087337972 voice 2087363248 fax Lecture 40 Universityofldaho Today 0 Your turn to grade me httpwwwwebsuidahoedustudentevas 0 Wiring for communications 0 Avoiding power systemcommunication system interactions Reference Noise Reduction Techniques in Electronic Systems 2 quot39 Edition by Henry W Ott Lecture 40 2 Universityofldaho Some communications terminology The decibel dB Used to compare power ratios dB1010g Pl Try it 0 Express a 1001 P2P1 power ratio in dB 0 Express a 051 P2P1 power ratio in dB Lecture 40 3 Universityofldaho The decibel in communication circuits 0 Used to measure loss of signal strength 0 Used to measure interference 39om neighboring communication circuits 0 Used to compare different circuit configurations o If voltage or current are measured V2 V2 P 10 A n10 A dB2010g R g g V1 0 Try it V15V V21V what is the ratio in dB Lecture 40 4 Communication circuit problems Revisiting Coupling interference from neighboring power or communication circuits Conductive Capacitive electric field Inductive magnetic field Far field combined electromagnetic field Signal attenuation loss of signal strength between the sending and receiving ends Lecture 40 Universityofldaho The noise path stir M 22293 M All three components are necessary for a noise problem Three possible solutions Suppress the noise at the source Make the receptor immune to the noise Remove or reduce the coupling Lecture 40 Universityofldaho Universityofldaho Conductive coupling Two or more devices sharing conductors so that current on the conductors due to one device results in voltage fluctuations at the other devices This is why isolated grounds are sometimes used as already discussed Lecture 40 7 Universityofldaho Capacitive coupling Produced by the electric field between conductors voltage Directly proportional to Frequency Voltage Conductor length Inversely proportional to Conductor separation Lecture 40 8 Universityofldaho Inductive coupling Produced by the magnetic field between conductors current in aggressor or source Directly proportional to Frequency Current Conductor Length Inversely proportional to Conductor separation Lecture 40 Universityofldaho Overcoming coupling UTP Unshielded Twisted Pair 0 construction Twist ratiosforthis particularcable Cat 5e Cat 5e o24AWG solid 3in copper conductors I I 333in o4 twrsted pairs 4in oVarying lays or 45in twists per inch oNo shield m Lecture 40 Universityofldaho UTP Unshielded twisted pair 0 UTP cable is now widely used as the standard cable for computer networking and industrial control systems Category 5 now 5e cable is a networking cable used in Ethernet and other protocols and designed for frequencies up to 100MHz How does Category 5e cable and the communication systems that use it address capacitive and inductive coupling Lecture 40 11 Universityofldaho Benefit of twisting each pair Capacitive coupling A nearby aggressor circuit is creating an electric field in the area of the twisted pair Twists help prevent differential voltage from developing between conductors in the pair Lecture 40 12 Universityofldaho Benefit of twisting each pair Inductive coupling A nearby aggressor circuit is creating a magnetic field in the area of the twisted pair Twists force induced EMF to be common mode m gt39 if 1 gt 3 W J gt Lecture 40 13 Universityofldaho Differential communication Signal and common mode noise 0 At the receiver the differential signal is extracted 39 l L39 03 IJ l 04 o The common mode noise is cancelled 01 N f 01 Lecture 40 14 cables to other nearby circuits 0 Different twist ratios cable or other nearby cables Lecture 40 Other benefits of twisting the signal pairs 0 Signal cables can be the aggressor too One signal pair could be the aggressor for other signal pairs in the same cable or other nearby signal Twisting the pairs minimizes the capacitive coupling help minimize crosstalk the coupling of signals from one twisted pair to another either in the same Universityofldaho Minimizing crosstalk Same twist ratio Lecture 40 Universityofldaho Universityofldaho Installation issues Delay skew Different twist ratios result in each pair being a slightly different length Signals on one pair may take longer to travel from one end of the cable to the other than signals on another less twisted pair May be an issue with long cables and video signals Lecture 40 17 Universityofldaho Installation issues Maintaining twist ratios Cable bends and terminations can untwist the pairs Some manufacturers are bonding the insulation between pairs together to keep conductor separation to a minimum Bends need to be gradual and twist ratios need to be maintained into connectors Lecture 40 18 Universityofldaho Installation issues Nearby power conductors The NEC requires a minimum spacing of 2 to 4 inches between power and communication circuits Generally avoiding close long parallel runs of power and signal cables is sufficient to avoid problems Lecture 40 19 Universityofldaho Cat 5e cabling terms and limits at 100MHz o Attenuation 04 dB The loss in signal power between the sending and receiving end 0 NEXT Loss 40 dB Near end crosstalk loss the sending end signal power on one pair that appears at the sending end on any other pair in the cable 0 FEXT Loss 35 dB Far end crosstalk loss the sending end signal power on one pair that appears at the receiving end on any other pair in the cable 0 Return Loss 18 dB The amount of sending end signal power that is reflected back on the same pair due to manufacturing variations or flaws in the signal conductors Lecture 40 20 Universityofldaho Next time o More signal wiring Coaxial cables Summarize wiring and grounding Lecture 40 21 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 6 Universityofldaho Today 0 Planning and conducting Power Quality Investigations 0 Premise today s discussion will focus on investigations intended to resolve some existing PQ issue Lecture E 2 Universityofldaho Types of PQ investigations 0 Reactive Resolve a suspected PQ problem 0 Failure or misoperation of customer equipment Vulnerable Power lElectrIcal path E ui ment Quality Disturbance q p Problem 0 Proactive Prevent problems in proposed designs Lecture E 3 Universityofldaho Objectives 0 Resolve the suspected PQ problem Accurately Quickly Economically Lecture E 4 Universityofldaho Preinvestigation steps 0 Find person familiar with problem 0 Check customer s rules for outside workers and electrical safety 0 Agree on expectations Report Presentation Followup Lecture E 5 Universityofldaho General investigation steps H Initial observations and preliminary analysis Hypotheses Predictions and Tests Conclusions Communication U39lIALAJN Lecture E E Universityofldaho Initial observations and preliminary analysis 0 Customer observed problem Initial description is usually incomplete 0 Our computers are rebooting all the time 0 We re having power surges o The factory had another outage yesterday That s the third one this year Lecture E 7 Universityofldaho Initial observations and preliminary analysis Gathering more information Goal is to get a problem description that is as accurate and complete as possible 0 When does the problem occur time frequency 0 Does problem correlate with known power system events 0 What equipment is and is not affected 0 How is the equipment affected 0 Can the problem be predicted How 0 Are neighbors experiencing the same problem 0 What solutions have been tried 0 What is the impact in dollars time etc Lecture E E Universityofldaho Initial observations and preliminary analysis Deciding where to start Lecture E Universityofldaho Initial observations and preliminary analysis Visual observations New or temporary equipment Recent work Nameplate data on problem equipment Locations of panels and equipment Response during problem If suggested by problem description Inspect wiring and panels ControlProtection settings TemperaturesConnections Spot measurements of voltage current etc Lecture E Universityofldaho ObservationsHypotheses Monitoring Advantages Accurate disturbance timestamps Voltagecurrent data during disturbances 0 May be used to determine direction Document normal conditions Disadvantages Requires second trip Collects data unrelated to the problem May require extended recording to catch infrequent problems Lecture E ii Universityofldaho Predictions and Tests Monitoring A log of events during monitoring is essential Event log enables investigator to identify events in recording recorded data often helps form hypotheses and provides data used to test the hypotheses Ideally tests will clearly confirm or eliminate a hypothesis If capacitor switching caused the events then the capacitor operating logs will correlate with the event logs Lecture E 12 Universityofldaho Reducing investigation time o For power companies monitor at the service point if possible 0 Install monitors prior to spot measurements 0 Use multiple monitors simultaneously 0 Monitor for as short a time as necessary 0 Photograph or videotape panels equipment etc Lecture E is Universityofldaho Accurate conclusions 0 Avoid speculation 0 Discuss preliminary conclusions with other engineers technicians the customer etc 0 Test preliminary conclusions and recommendations Use models etc to try recommendations on a small scale Avoid shotgun approach make one change at a time Lecture E M Universityofldaho Communicating results Speak to the customer at their level of understanding using analogies where appropriate Engineers tend to write but facetoface meetings are often more effective Show how the data lead to the analysis and how the analysis lead to the conclusions so that the customer can reach the same conclusions on their own Understand and acknowledge the impact of your conclusions on the customer Lecture E is Universityofldaho A realworld example Reported problem Multiple customers on a single distribution feeder reported lights dimming and computers rebooting or switching to UPS More information from discussion with customers Apparently random Not associated with any activities of the customers Lecture E 16 Universityofldaho A real world example continued 0 More information from recording Voltage sags Two to four per day Not associated with customer load at monitored location 0 Analysis Pre and Post sag voltage is different voltage goes up or down about 2 volts Lecture E 17 Universityofldaho A realworld example continued 0 Hypotheses Capacitor switching Regulatorload tap changer stepping o Tests Review capacitor control logs Manually switch capacitors Manually step regulators or load tap changers Lecture E 18 Universityofldaho A realworld example continued 0 Hypotheses Capacitor switching o ruled out no correlation in logs Regulator stepping 0 confirmed manually switched regulator at specific times Customer logged correlating events and monitor recorded event Lecture E l Universityofldaho A realworld example conclusion 0 Communication Customers who had reported events associated with this issue were called It was explained that we had identified a problem with a substation transformer that steps had been taken to prevent any more of these events by transferring the feeders to another transformer and that repairs were scheduled Lecture E Universityafldaho ECE 528 Understanding Power Quality httpwwweceuidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voice 2087363248 fax Lecture 44 Universityofldaho Today Finish Power quality instruments and analyzers Where monitoring fits in a power quality investigation Expert systems Parting comments Lecture 44 2 Universityofldaho Where monitoring fits in a power quality investigation Types of investigations Problem investigation 0 Why is this electrical device malfunctioning Equipment characterization o Harmonics sag vulnerability etc System characterization 0 Typical voltages SAIDI SAIFI THD load pro le IEEE 519 compliance etc Lecture 44 Universityofldaho The role of monitoring in a power quality problem investigation 0 A Power Quality Problemquot Anz gower grabem manifested in voltage current or frequency deviations that results in failure or misogeration of customer eguigment o The power quality equation Power Vulnerable Quality Electrical Path E quoti ment q p Problem Disturbance Lecture 44 Universityofldaho The role of monitoring In a power quality problem investigation The primary question Is there a causal relationship between some electrical disturbance and some equipment malfunction or failure Determining if a causal relationship exists Power quality monitors can collect data useful in making this determination Data must be analyzed to determine if a causal relationship exists Lecture 44 5 Universityofldaho Is there a causal relationship 0 Three necessary factors Time correlation the suspected cause must precede or coincide in time with the effect but time correlation alone is not enough Proximity the suspected cause must result in some change to the electrical environment at the affected equipment Electrical relationship the suspected cause the change to the electrical environment must be capable of producing the effect being studied while following physical laws Lecture 44 6 Universityofldaho Monitors and causal relationships Sometimes it can be just as valuable to not record an electrical disturbance when the equipment malfunctions Be careful though absence of evidence is not evidence of absence Triggering settings monitor location monitor bandwidth and your probes can all affect whether or not an electrical disturbance is recorded Lecture 44 7 Universityofldaho Causal relationships in electrical systems 0 Monitoring at the service point PCC 0 Which voltage sag was caused by something upstream of the FCC and which was caused by something downstream Voltage Current Lecture 44 8 Universityofldaho Expert systems May also be called knowledge based systems 0 Purpose Reduce the time and expertise required to manually analyze large volumes of raw data Help the analyst quickly group similar events Help the analyst separate important data from unimportant data Lecture 44 9 Universityofldaho Expeit systems capabilities and limitations 0 Typical capabilities Classify disturbances General duration sag swell etc Specific capacitor switching arcing Direction System can determine the direction to the source of the problem ie the capacitor that switched the fault or motor starting that caused the voltage sag etc Trend System may make it easier to recognize changes in normal system conditions Lecture 44 10 Universityofldaho Automatic event classification examples armumcs Juurna ingger Drmal iU eryr Automatic Classification O Instantaneous 3919 Events of events allows the user 7 0 39 39 to look at specific types 29 immune 39 of events that are likely to be related to the problem 1 Mild lmpuleeiluEvemei O Mild Arcing 112 Eye 2 Events 39iivr39quot394 a FlatTop 12 2er 1 Evenlsi 7 4 r A nrr Lecture 44 11 Universityofldaho Expert system limitations The expelt system is only as good as the rules the system uses Some problems are ambiguous or are actually combinations of problems In power quality the expert system does not know if a particular disturbance affected a particular device Ultimately it is up to the user to determine if there is a causeandeffect relationship Lecture 44 12 Universityofldaho Expert systems Industry use of expelt systems More popular in permanent monitors 0 Larger data volume 0 Supports automatic noti cation for speci c events Monitor may notify users via phone text message or email that a particular event type magnitude and duration has occurred 0 Provides periodic summary reports of system performance designed for a less technical audience Lecture 44 13 Universityofldaho Parting comments Thank you Lecture 44 14 Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 2 Universityofldaho Review of AC analysis 0 Note In class we will calculate several different values by hand to help us understand their significance In practice many of these values are calculated by the instruments used to collect the data or in software after the date is exported to a computer Having a narrow range of expected values in mind before taking a measurement can be helpful though Lecture 2 2
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