Power Quality - 4. Flicker case study. Content. Course. Ljubljana, Slovenia 2013/14. Prof. dr. Igor Papič

Transcription

1 Course ower Quality - 4 Ljubljana, Slovenia 2013/14 rof. dr. Igor apič igor.papic@fe.uni-lj.si Flicker case udy Content Session 1 Session 2 Session 3 Session 4 1 day 2nd day 3rd day 4th day 5th day Flicker case udy Harmonics Introduction to Harmonics - design calculation of Interruptions definitions ower Quality of power factor flicker spreading definitions calculations what is Q correction devices in radial network reliability indices non-linear loads economic value resonance points variation of improving harmonic responsibilities filter design network reliability sequences parameters Basic terms and Flicker - basic Consequences of definitions ropagation of oltage sags terms inadequate power voltage quality harmonics definitions voltage variation quality continuity of sources characteriics flicker frequency voltage quality supply consequences types sources interruptions commercial cancellation causes flickermeter cos quality ropagation of Modern Harmonics - Flicker spreading voltage sags compensation Q andards resonances in radial network transformer devices EN network mashed network connections active and hybrid other andards parallel simulation equipment compensators limit values resonance examples sensitivity series and shunt series resonance mitigation compensators Harmonics case Other voltage Flicker mitigation Conclusions Q monitoring udy variations syem solutions Q improvement measurements calculation of unbalance network and cos Q analyzers frequency voltage enforcement definition of data analyses impedance transients compensation optimal solutions characteriics overvoltages ower Quality, Ljubljana, 2013/14 3 1

2 flicker spreading in a radial network transfer coefficient of flicker in a radial network between point and (diurbing load) TC ( ) = ( ) ( ) = TC ( ) ower Quality, Ljubljana, 2013/14 4 flicker spreading in a radial network example of supply network data for calculation network equivalent short-circuit power S sc = 3700 M rated voltage U H =110 k ower Quality, Ljubljana, 2013/14 5 flicker spreading in a radial network example of supply network data for calculation transformer 1 110/35 k short-circuit voltage u sc1 = 7,69 % rated power rated voltage S TR1 = 40 M U H 110 k; U = 35 k = M ower Quality, Ljubljana, 2013/14 6 2

3 flicker spreading in a radial network example of supply network data for calculation transformer 2 110/35 k short-circuit voltage u sc2 =10 % rated power rated voltage S TR 2 = 60 M U H 110 k; U = 35 k = M ower Quality, Ljubljana, 2013/14 7 flicker spreading in a radial network example of supply network data for calculation series reactor rated voltage = 35 k U M reactive power rated current = 8,3 Mr Q L = 0,7 k I L ower Quality, Ljubljana, 2013/14 8 flicker spreading in a radial network example of supply network data for calculation furnace transformer 35k/L short-circuit voltage = 4 % u scf rated power rated primary voltage S TRf U M = 38 M = 35 k ower Quality, Ljubljana, 2013/14 9 3

4 flicker spreading in a radial network example of supply network calculation of parameters (the same voltage level U M ) network equivalent X Z sc SC 2 M U = S X sc sc = 0,33 Ω ower Quality, Ljubljana, 2013/14 10 flicker spreading in a radial network example of supply network calculation of parameters (the same voltage level U M ) transformer 1 X Z TR1 TR1 U = S X 2 M TR1 TR1 usc 1 = 2,36 Ω 100 ower Quality, Ljubljana, 2013/14 11 flicker spreading in a radial network example of supply network calculation of parameters (the same voltage level U M ) transformer 2 X Z TR 2 TR2 U = S X 2 M TR2 TR2 usc2 = 2,04 Ω 100 ower Quality, Ljubljana, 2013/

5 flicker spreading in a radial network example of supply network calculation of parameters (the same voltage level U M ) series reactor Q X = = 5,65 Ω Z L L L 3I 2 L X L ower Quality, Ljubljana, 2013/14 13 flicker spreading in a radial network example of supply network calculation of parameters (the same voltage level U M ) furnace transformer X Z TRf TRf U = S X 2 M TRf TRf uscf = 1,29 Ω 100 ower Quality, Ljubljana, 2013/14 14 flicker spreading in a radial network case reference load flicker value () = 8,5 Z Z Z = X = sc; Z X TR1 ower Quality, Ljubljana, 2013/

6 flicker spreading in a radial network case ( ) = 8,5 ( ) = ( ) TC = ( ) = ( ) ( ) = 1, 05 Z Z + Z X sc X sc + X TR1 ower Quality, Ljubljana, 2013/14 16 flicker spreading in radial network case B reference load flicker value () = 8,5 between point and B is H transformer (TCB = 0,8) B Z = X sc TR B ; Z = X 1 ; TC = 0,8 ower Quality, Ljubljana, 2013/14 17 flicker spreading in radial network case B B ( ) = 8,5 ( ) = ( ) = ( ) ( B) = ( ) TC = 0, 84 Z Z + Z B X sc X + X sc TR1 = 1,05 ower Quality, Ljubljana, 2013/

7 flicker spreading in a radial network case C bigger transformer (60 M) reference load flicker value () = 8,5 Z = X = sc; Z X TR2 ower Quality, Ljubljana, 2013/14 19 flicker spreading in a radial network case C ( ) = 8,5 ( ) = ( ) TC = ( ) = ( ) ( ) = 1, 19 Z Z + Z X sc X sc + X TR2 ower Quality, Ljubljana, 2013/14 20 flicker spreading in a radial network case C1 correction of load reference flicker vale (ronger network) ( ) X sc + X = 8,5 X + X ( ) = ( ) TC = ( ) = ( ) ( ) = 1, 09 sc TR2 TR1 + X + X TRf TRf = 7,83 Z + Z Z X sc X + X sc TR2 ower Quality, Ljubljana, 2013/

8 flicker spreading in radial network case D reference load flicker value () = 8,5 TR1 and series connected reactor B Z = X ; Z = X 1 ; Z = X sc B TR B L ower Quality, Ljubljana, 2013/14 22 flicker spreading in radial network case D B ( ) = 8,5 B ( B) = ( ) = ( ) = 2,74 sc ( ) = ( ) = ( ) = 0, 34 Z + Z Z + Z Z B Z + Z B + Z + Z B B X sc + X TR1 X + X + X sc sc TR1 X X + X TR1 L + X L ower Quality, Ljubljana, 2013/14 23 flicker spreading in radial network case D1 correction of load reference flicker vale (weaker network) ( ) X sc + X TR1 + X L + X = 8,5 X + X + X = 20,57 B ( B) = ( ) = ( ) = 6,63 sc ( ) = ( ) = ( ) = 0, 82 sc TR1 Z + Z Z + Z Z B Z + Z B + Z + Z TRf B B TRf X sc + X TR1 X + X + X sc sc TR1 X X + X TR1 L + X L ower Quality, Ljubljana, 2013/

9 oltage sags definitions Content Session 1 Session 2 Session 3 Session 4 1 day 2nd day 3rd day 4th day 5th day Flicker case udy Harmonics Introduction to Harmonics - design calculation of Interruptions definitions ower Quality of power factor flicker spreading definitions calculations what is Q correction devices in radial network reliability indices non-linear loads economic value resonance points variation of improving harmonic responsibilities filter design network reliability sequences parameters Basic terms and Flicker - basic Consequences of definitions ropagation of oltage sags terms inadequate power voltage quality harmonics definitions voltage variation quality continuity of sources characteriics flicker frequency voltage quality supply consequences types sources interruptions commercial cancellation causes flickermeter cos quality ropagation of Modern Harmonics - Flicker spreading voltage sags compensation Q andards resonances in radial network transformer devices EN network mashed network connections active and hybrid other andards parallel simulation equipment compensators limit values resonance examples sensitivity series and shunt series resonance mitigation compensators Harmonics case Other voltage Flicker mitigation Conclusions Q monitoring udy variations syem solutions Q improvement measurements calculation of unbalance network and cos Q analyzers frequency voltage enforcement definition of data analyses impedance transients compensation optimal solutions characteriics overvoltages ower Quality, Ljubljana, 2013/14 26 oltage sags voltage sag magnitude voltage sag duration phase-angle jumps types of three-phase unbalanced sags short-circuit fault, load connection, transformer winding connection other characteriics point-on-wave missing voltage causes of voltage sags ower Quality, Ljubljana, 2013/

10 oltage sag characteriics voltage sag magnitude voltage sag due to a short circuit fault one phase in time domain ower Quality, Ljubljana, 2013/14 28 oltage sag characteriics voltage sag magnitude one-cycle (20 ms) rms voltage oltage (pu) rms 1 N 2 vi N i = 1 = ower Quality, Ljubljana, 2013/14 29 oltage sag characteriics voltage sag magnitude half-cycle (10 ms) rms voltage oltage (pu) ower Quality, Ljubljana, 2013/

11 oltage sag characteriics voltage sag magnitude fundamental component in one cycle (20 ms) oltage (pu) t 2 j 0 fund () t = v( ) e d T ωτ τ t T τ ower Quality, Ljubljana, 2013/14 31 oltage sag characteriics voltage sag magnitude peak voltage in one cycle (20 ms) oltage (pu) peak max = v( t τ ) 0 < τ < T ower Quality, Ljubljana, 2013/14 32 oltage sag characteriics voltage sag duration the rms value (or number of cycles) is below 90 % short sags oltage (pu) ower Quality, Ljubljana, 2013/

12 oltage sag characteriics voltage sag duration long po-fault component sags with longer duration rms voltage (pu) ower Quality, Ljubljana, 2013/14 34 oltage sag characteriics phase-angle jumps sag with a magnitude of 70 % phase-angle jump -45º oltage (pu) ower Quality, Ljubljana, 2013/14 35 oltage sag characteriics Z S1 Z F1 I1 unbalanced voltage sags three-phase syem use of symmetrical components positive sequence negative sequence zero sequence + E _ Z S2 + 1 _ + 2 _ Z F2 I 2 ZS0 Z F0 I L1 2 S = 1 1 a a = L a a L3 a = e a = e j120 2 j _ ower Quality, Ljubljana, 2013/

13 oltage sag characteriics unbalanced voltage sags three-phase syem L3 three-phase fault L1 L2 L3 L1 single-phase fault -3Z S1 / Z L2 ower Quality, Ljubljana, 2013/14 37 oltage sag characteriics unbalanced voltage sags three-phase syem phase-to-phase fault (a 2 -a)z S1 / Z L3 L2 L1 (1-a)Z n / D (a 2 -a)z n / D L3 two-phase-to-ground fault L2 L1 ower Quality, Ljubljana, 2013/14 38 oltage sag characteriics types of three-phase unbalanced sags load connection ar connected load delta connected load transformer winding connection 1. transformers that do not change anything to the voltage (YNyn) T = ower Quality, Ljubljana, 2013/

14 oltage sag characteriics types of three-phase unbalanced sags transformer winding connection 2. transformers that remove zero sequence component (Yny, Yyn, Dd, Dz) T = transformers that swap line and phase voltages (Dy, Yd, Yz) j T = ower Quality, Ljubljana, 2013/14 40 oltage sag characteriics types of three-phase unbalanced sags type of short-circuit fault type of load connection type of transformer winding connection seven characteriic types of voltage sags type type B type C type D type E type F type G ower Quality, Ljubljana, 2013/14 41 oltage sag characteriics characteriic types of three-phase unbalanced sags type L3 L2 L1 L1 = 1 1 L2 = j L3 = + j ower Quality, Ljubljana, 2013/

15 oltage sag characteriics characteriic types of three-phase unbalanced sags type B L3 B L1 L1 L2 L3 = 1 1 = j = + j L2 ower Quality, Ljubljana, 2013/14 43 oltage sag characteriics characteriic types of three-phase unbalanced sags type C L3 C L1 L1 L2 L3 = = j = + j L2 ower Quality, Ljubljana, 2013/14 44 oltage sag characteriics characteriic types of three-phase unbalanced sags type D L3 D L1 L1 = 1 1 L2 = j L3 = + j L2 ower Quality, Ljubljana, 2013/

16 oltage sag characteriics characteriic types of three-phase unbalanced sags type E L3 E L1 L1 = L2 = j L3 = + j L2 ower Quality, Ljubljana, 2013/14 46 oltage sag characteriics characteriic types of three-phase unbalanced sags type F L3 F L1 L1 = L2 = j 3 j L3 =+ j 3 + j L2 ower Quality, Ljubljana, 2013/14 47 oltage sag characteriics characteriic types of three-phase unbalanced sags type G L3 L2 G L1 2 1 L1 = L2 = j L3 = + j ower Quality, Ljubljana, 2013/

17 oltage sag characteriics types of three-phase unbalanced sags origin of voltage sags Fault type Star-connected load Delta-connected load Three-phase type type Two-phase-to-ground type E type F hase-to-phase type C type D Single-phase type B type C transformation of voltage sags to lower voltage level Transformer Sag on primary side connection type type B type C type D type E type F type G YNyn B C D E F G Yy, Dd, Dz D C D G F G Yd, Dy, Yz C D C F G F ower Quality, Ljubljana, 2013/14 49 oltage sag characteriics other characteriics point-on-wave point-on-wave of sag initiation - the phase angle of the voltage at the moment the voltage waveform shows a significant drop compared to its normal waveform (The phase angle is measured with respect to the la upward zero-crossing of the voltage waveform.) point-on-wave of sag recovery - the phase angle of the voltage at the moment the voltage waveform shows a significant recovery missing voltage the difference between the actual voltage during the event and the voltage as it would have been if the event had not taken place ower Quality, Ljubljana, 2013/14 50 oltage sag characteriics other characteriics complex missing voltage a complex number which represents the missing voltage of a voltage sag in one phase difference in the complex plane between the pre- event voltage and the voltage during the sag ower Quality, Ljubljana, 2013/

18 Causes of voltage sags power syem faults lightning, wind, ice, contamination of insulators, animal contact, transportation/conruction accidents the mo common is single-phase fault (over 70 %) the mo severe is three-phase fault arting of large induction motors transformer energizing asymmetrical sags - different inrush currents in the three phases associated with large 2nd and 4th harmonic diortion load changes ower Quality, Ljubljana, 2013/14 52 ropagation of voltage sags Content Session 1 Session 2 Session 3 Session 4 1 day 2nd day 3rd day 4th day 5th day Flicker case udy Harmonics Introduction to Harmonics - design calculation of Interruptions definitions ower Quality of power factor flicker spreading definitions calculations what is Q correction devices in radial network reliability indices non-linear loads economic value resonance points variation of improving harmonic responsibilities filter design network reliability sequences parameters Basic terms and Flicker - basic Consequences of definitions ropagation of oltage sags terms inadequate power voltage quality harmonics definitions voltage variation quality continuity of sources characteriics flicker frequency voltage quality supply consequences types sources interruptions commercial cancellation causes flickermeter cos quality ropagation of Modern Harmonics - Flicker spreading voltage sags compensation Q andards resonances in radial network transformer devices EN network mashed network connections active and hybrid other andards parallel simulation equipment compensators limit values resonance examples sensitivity series and shunt series resonance mitigation compensators Harmonics case Other voltage Flicker mitigation Conclusions Q monitoring udy variations syem solutions Q improvement measurements calculation of unbalance network and cos Q analyzers frequency voltage enforcement definition of data analyses impedance transients compensation optimal solutions characteriics overvoltages ower Quality, Ljubljana, 2013/

19 ropagation across transformers simulation of voltage sag propagation te network voltage levels: 400 k, 110 k, 20 k and 0.4 k TM T1 T2 #2 # #1 #3 #1 # [MW] 30 [MR] 80.0 T3 14 [MW] 4 [MR] BC->G BC->G #1 #2 I [MW] 0.2 [MR] ower Quality, Ljubljana, 2013/14 55 ropagation across transformers simulation of voltage sag propagation te network T1 T2 T3 Un (k) 400/110/31,5 110/20/10,5 20/0,4 Sn (M) ,630 usc (prim-sec.) (%) 12,78 10,13 5 connection YNyd Yyd Dyn Comment Grounded neutral (80 Ω) transformer data TM Un (k) 400 Ssc'' (M) Rtm/Xtm 0,1 Xtm 0,05 H Rtm 1,5 Ω network equivalent ower Quality, Ljubljana, 2013/14 56 ropagation across transformers simulation of voltage sag propagation single-phase fault on 400 k level rms voltage values U (p.u.) U (p.u.) U (p.u.) 400_L1 400_L2 400_L k _L1 110_L2 110_L k _L1 20_L2 20_L k ower Quality, Ljubljana, 2013/

20 ropagation across transformers simulation of voltage sag propagation single-phase fault on 400 k level voltage phase angles fi (.) fi (.) fi (.) 400_L1 400_L2 400_L k _L1 110_L2 110_L k _L1 20_L2 20_L k ower Quality, Ljubljana, 2013/14 58 ropagation across transformers simulation of voltage sag propagation single-phase fault on 400 k level inantaneous voltage values U (k) U (k) U (k) 400_L1 400_L2 400_L k _L1 110_L2 110_L k _L1 20_L2 20_L k ower Quality, Ljubljana, 2013/14 59 ropagation across transformers simulation of voltage sag propagation single-phase fault on 20 k level rms voltage values U (p.u.) U (p.u.) U (p.u.) 400_L1 400_L2 400_L k _L1 110_L2 110_L k _L1 20_L2 20_L k ower Quality, Ljubljana, 2013/

21 ropagation across transformers simulation of voltage sag propagation single-phase fault on 20 k level voltage phase angles fi (.) fi (.) fi (.) 400_L1 400_L2 400_L k _L1 110_L2 110_L k _L1 20_L2 20_L k ower Quality, Ljubljana, 2013/14 61 ropagation across transformers simulation of voltage sag propagation single-phase fault on 20 k level inantaneous voltage values U (k) U (k) 400_L1 400_L2 400_L k _L1 110_L2 110_L k _L1 20_L2 20_L3 30 U (k) k ower Quality, Ljubljana, 2013/14 62 ropagation across transformers simulation of voltage sag propagation single-phase fault on 20 k level inantaneous currents and voltages values on 0.4 k level 04_L1 04_L2 04_L no transfer of diurbance on k level U (k) I (k) I04_L1 I04_L2 I04_L ower Quality, Ljubljana, 2013/

22 Equipment sensitivity sensitivity curves Computer Business Equipment Manufacturers ssociation - CBEM ower Quality, Ljubljana, 2013/14 64 Equipment sensitivity sensitivity curves Information Technology Indury Council - ITIC ower Quality, Ljubljana, 2013/14 65 Equipment sensitivity sensitivity curves Semiconductor Equipment and Materials International - SEMI ower Quality, Ljubljana, 2013/

23 Equipment sensitivity sensitivity curves comparison of different sensitivity curves CBEMs / ITIC / SEMI ower Quality, Ljubljana, 2013/14 67 Equipment sensitivity sensitivity curves new voltage sag sensitivity curves example of generic ac contactor sensitivity curve (University of Mancheer) ower Quality, Ljubljana, 2013/14 68 Mitigation measures methods reducing the number of short-circuit faults reducing the fault clearing time changing the syem such that the short-circuit faults results in less severe events at the equipment terminals or at the cuomer interface connecting mitigation equipment between the sensitive equipment and the supply ower Quality, Ljubljana, 2013/

24 Mitigation measures methods improving the immunity of the equipment ower Quality, Ljubljana, 2013/14 70 Mitigation measures methods ower Quality, Ljubljana, 2013/14 71 Mitigation measures reducing the number of short-circuit faults replace overhead lines by underground cables use covered wires for overhead lines implement rict policy of tree trimming inall additional shielding wires (lighting) increase the insulation level increase maintenance and inspection frequencies ower Quality, Ljubljana, 2013/

25 Mitigation measures reducing the fault clearing time current limiting fuses atic circuit breaker fault clearing time within one half-cycle ower Quality, Ljubljana, 2013/14 73 Mitigation measures reducing the fault clearing time fault current limiters improved protection schemes number of reclosers grading margins ower Quality, Ljubljana, 2013/14 74 Mitigation measures changing the syem high cos, especially in transmission syem redundant components inall a generator near sensitive loads (CH) split buses or subations in the supply path to limit the number of feeders in the exposed area inall current limiting coils at rategic places in the syem to increase electrical diance to the fault feed the bus with the sensitive equipment from two or more subations ower Quality, Ljubljana, 2013/

26 Mitigation measures inalling mitigation equipment the cuomer has control over the situation Uninterruptible ower Supplies (USs) Motor-generator sets are often depicted as noisy and as needing much maintenance oltage Sourced Converters (SCs) generate sinusoidal voltage with the required magnitude and phase ower Quality, Ljubljana, 2013/14 76 Mitigation measures inalling mitigation equipment parallel connected SC - StatCom U s L s I s I p I L Load Lp voltage sourced converter U dc C ower Quality, Ljubljana, 2013/14 77 Mitigation measures inalling mitigation equipment simulation of voltage sag compensation with StatCom (reactive power) effectiveness depends on the network R/X ratio with StatCom (1 M) oltage (pu) R/X = 0.5 R/X = 3.0 no StatCom Time (s) ower Quality, Ljubljana, 2013/

27 Mitigation measures inalling mitigation equipment simulation of voltage sag compensation with StatCom voltage reference is 0.9 pu reactive vs. active power compensation DStatCom (M) 4,5 4 Q 3,5 3 2,5 2 1,5 1 0,5 0 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 line R/X ower Quality, Ljubljana, 2013/14 79 Mitigation measures inalling mitigation equipment series connected SC - DR U s I s U p I L Load L s voltage sourced converter C U dc ower Quality, Ljubljana, 2013/14 80 Mitigation measures inalling mitigation equipment 2 SCs (Unified ower Quality Conditioner UQC) U s I s U p I L Load L s series F parallel F ower Quality, Ljubljana, 2013/

28 Mitigation measures inalling mitigation equipment voltage sags - DR ower Quality, Ljubljana, 2013/14 82 Mitigation measures improving equipment immunity mo effective solution again equipment trips due to voltage sags unfortunately off-the-shelf equipment the immunity of consumer electronics, computers and control equipment can be significantly improved by connecting more capacitance to the internal dc bus single-phase low power equipment can also be improved by using a more sophiicated dc/dc converters the main source of concern are djuable Speed Drives SDs (adding capacitance to the dc bus) ower Quality, Ljubljana, 2013/14 83 Mitigation measures improving equipment immunity improving the immunity of dc adjuable-speed drives is very difficult (the torque drops very fa) a thorough inspection of the immunity of all contactors, relays, sensors, etc, can significantly improve the process ride-through information about immunity should be obtained from the manufacturer beforehand (immunity requirements should be include in the equipment specification) ower Quality, Ljubljana, 2013/

29 Mitigation measures improving equipment immunity size of the capacitor in the internal dc bus is 10 mf ower Quality, Ljubljana, 2013/14 85 Mitigation measures improving equipment immunity size of the capacitor in the internal dc bus is 220 μf ower Quality, Ljubljana, 2013/14 86 Mitigation measures overview of sags for different events different mitigation rategies apply ower Quality, Ljubljana, 2013/

30 Other voltage variations Content Session 1 Session 2 Session 3 Session 4 1 day 2nd day 3rd day 4th day 5th day Flicker case udy Harmonics Introduction to Harmonics - design calculation of Interruptions definitions ower Quality of power factor flicker spreading definitions calculations what is Q correction devices in radial network reliability indices non-linear loads economic value resonance points variation of improving harmonic responsibilities filter design network reliability sequences parameters Basic terms and Flicker - basic Consequences of definitions ropagation of oltage sags terms inadequate power voltage quality harmonics definitions voltage variation quality continuity of sources characteriics flicker frequency voltage quality supply consequences types sources interruptions commercial cancellation causes flickermeter cos quality ropagation of Modern Harmonics - Flicker spreading voltage sags compensation Q andards resonances in radial network transformer devices EN network mashed network connections active and hybrid other andards parallel simulation equipment compensators limit values resonance examples sensitivity series and shunt series resonance mitigation compensators Harmonics case Other voltage Flicker mitigation Conclusions Q monitoring udy variations syem solutions Q improvement measurements calculation of unbalance network and cos Q analyzers frequency voltage enforcement definition of data analyses impedance transients compensation optimal solutions characteriics overvoltages ower Quality, Ljubljana, 2013/14 89 oltage variations voltage unbalance overvoltage undervoltage temporary power frequency overvoltage transient overvoltage non-oscillatory oscillatory notching ower Quality, Ljubljana, 2013/

31 oltage unbalance voltage unbalance a condition in which the three phase voltages differ in magnitude, are displaced from their normal 120º phase relationship, or both magnitude unbalance the maximum deviation among the three phases from the average three phase voltage divided by the average of the three phase voltage phase-angle unbalance the maximum deviation of the angular difference between the three phases divided by 120º ower Quality, Ljubljana, 2013/14 91 oltage unbalance EN definition voltage unbalance is a condition in a three-phase syem in which the rms values of the phase voltages or the phase angles between consecutive phases are not equal (ration between negative and positive sequence) limits according to the EN supply voltage unbalance in L and M networks 95 % of the 10-minute mean rms values of the negative sequence component of the supply voltage sell be up to 2 % of the positive sequence component unbalances up to about 3 % occur ower Quality, Ljubljana, 2013/14 92 oltage unbalance supply voltage unbalance - example ower Quality, Ljubljana, 2013/

32 oltage unbalance - causes untransposed lines in transmission network single phase loads on a three-phase circuits (usually less than 2%) blown fuses in one phase of a three-phase capacitor bank single phase faults (usually greater than 5%) single phase generation (e.g., s) ower Quality, Ljubljana, 2013/14 94 oltage unbalance motor heating some udies showed that for THD 15% and 2/1 3% there is no problem with overheating of motors ower Quality, Ljubljana, 2013/14 95 Overvoltage an increase in the rms value of voltage above 110% for more than 1 min main causes: load switching (switching off large load, energizing capacitor bank) incorrect tap settings on transformers the syem is to weak for the desired voltage regulation or voltage controls are inadequate ower Quality, Ljubljana, 2013/

33 Undervoltage a decrease in the rms value of voltage below 90 % for more than 1 min main causes: load switching (switching on large load, de-energizing capacitor bank) incorrect tap settings on transformers overloaded syems ower Quality, Ljubljana, 2013/14 97 Temporary power frequency overvoltage values according to the EN temporary power frequency overvoltages in L networks may reach the value of the phase-to-phase voltage under certain circumances up to 1,5 k rms temporary power frequency overvoltages in M networks depends on the type of earthing of the syem in solidly or impedance earthed syems up to 1,7 Uc in isolated or resonant earthed syems up to 2 Uc ower Quality, Ljubljana, 2013/14 98 Temporary power frequency overvoltage inantaneous voltage swell caused by single-phase fault ower Quality, Ljubljana, 2013/

34 Temporary power frequency overvoltage clearing of single-phase fault in impedance earthed syem voltage and current of the healthy phase ower Quality, Ljubljana, 2013/ Transient overvoltage non-oscillatory transient overvoltage a sudden, non-power frequency change in the eady ate condition of the waveform of voltage that is unidirectional in polarity (primarily either positive or negative) unidirectional (impulsive) transient ower Quality, Ljubljana, 2013/ Transient overvoltage oscillatory transient overvoltage a sudden, non-power frequency change in the eady ate condition of the waveform of voltage that includes both positive and negative polarity values oscillatory transient ower Quality, Ljubljana, 2013/

35 Transient overvoltage EN definitions transient overvoltage between live conductors and earth a short duration oscillatory or non-oscillatory overvoltage usually highly damped and with a duration of a few milliseconds or less transient overvoltages are usually caused by lighting, switching or operation of fuses generally will not exceed 6 k in L networks ower Quality, Ljubljana, 2013/ Transient overvoltage causes of transient overvoltages lightning rise time 1.2 μs, decay time to half peak value 50 μs direct roke to phase conductor roke to overhead shielding wire or tower indirect coupling via grounding syem inductive coupling capacitive coupling switching usually expressed as multiple of syem peak voltage inductive / capacitive circuits ower Quality, Ljubljana, 2013/ Transient overvoltage causes of transient overvoltages cable switching (5kHz - 500kHz) capacitor bank energizing 300Hz - 900Hz 1.3 p.u p.u. 0.5 cycles to 3 cycles ferroresonance transformer energizing when transformer is energized simultaneously with F correction capacitor line energizing interruption of magnetizing currents interruption of capacitive currents ower Quality, Ljubljana, 2013/

36 Transient overvoltage low frequency oscillatory transient caused by capacitor bank energization ower Quality, Ljubljana, 2013/ Transient overvoltage capacitor bank energization current and voltage waveforms (6 Mr, 6 k) ower Quality, Ljubljana, 2013/ Transient overvoltage consequences of transient overvoltages flashover of external clearances in air often leads to a short-circuit fault and power-frequency "follow" current arcing damage/burning internal damage to equipment insulation failure - potentially very expensive damage due to surge current & energy (in semiconductors) maloperation of electronic syems (may be temporary but ill coly) ower Quality, Ljubljana, 2013/

37 Transient overvoltage protection of utility equipment rod gaps inexpensive but slow response power follow current lightning arreers non-linear shunt resior absorbs surge energy, limits voltage at terminals, and returns to high-resiance ate typically 65 k discharge capacity for diribution class arreer, 100 k for ation class, min 40 k below 600 shielding & grounding coordination of protective device characteriics with equipment insulation levels ower Quality, Ljubljana, 2013/ Transient overvoltage mitigation methods line reactor in series isolation transformers synchronous" switching (contact closure when syem voltage matches the capacitor voltage) switch with pre-inserted damping resior (0.25 cycle; reduction 10-20%) controlled multiage switching within bank harmonic filter at remote location fit surge arreers at remote location ower Quality, Ljubljana, 2013/ Transient overvoltage mitigation methods synchronous" capacitor switching (controlled switching) simulation results R L Cb Cb ower Quality, Ljubljana, 2013/

38 ul1 ul2 ul3 il1 il3 i ul1 ul2 ul3 il1 il3 i ul1 il1 il3 i Transient overvoltage synchronous" capacitor switching k k k k k u L2 k k k u L3 k k k k i L2 k i L2 k i L2 k k k k k k k t/ms t/ms t/ms ) ) ) ower Quality, Ljubljana, 2013/ Transient overvoltage voltage notching a switching diurbance of the normal power voltage waveform, laing less than a half-cycle which is initially of opposite polarity than the waveform, and is thus subtractive from the normal waveform in terms of the peak value of the diurbance voltage (dependent on firing angle and amount of commutating inductance) problems (due to high d/dt) can cause interference with control circuits communication interference electronic clocks running fa (extra zero crossing) can trigger thyriors and cause conduction ower Quality, Ljubljana, 2013/ Transient overvoltage voltage notching example of voltage notching caused by a three-phase converter oltage () ower Quality, Ljubljana, 2013/

39 Transient overvoltage summary of transient concerns simple surge protective devices can protect mo cuomer equipment from high frequency transients surge suppressors will inject transient currents into the ground syem of the facility lighting is the mo important cause of high frequency transients utility capacitor switching transients can cause nuisance tripping of cuomer electronic equipment ower Quality, Ljubljana, 2013/ Transient overvoltage summary of transient concerns utility capacitor switching kicks off DG, on the other hand varying DG cause excessive capacitor switching capacitor switching transients can be magnified by low voltage power factor correction capacitors capacitor switching controls can limit the transients or cuomers can use filters inead of capacitors ower Quality, Ljubljana, 2013/