DIgSILENT Pacific PowerFactory Users’ Conference 2011 Lightning Insulation Coordination Study Presenter: Nguyen Dong Hai Le DIgSILENT Pacific DIgSILENT Pacific PowerFactory Users’ Conference 2011 1 Presentation Outline Introduction • Network Components Model • Stroke Current Model • Case Studies and Results • Conclusions • DIgSILENT Pacific PowerFactory Users’ Conference 2011 2 1
Introduction – Lightning Insulation Coordination Insulation Coordination is required to ensure Equipment’s insulation shall withstand voltage stress caused by • lightning strike. Efficient discharge of over voltages due to lighting strike. • DIgSILENT Pacific PowerFactory Users’ Conference 2011 3 Network Component Models Transmission Line Model • Equipment's Stray Capacitance • Surge Arrester. • Current Dependant Characteristic of Tower Footing Resistance • Tower Surge Impedance. • Time Dependant Characteristic of Insulator Strength. • Stroke Current Model. • Determination of Critical Stroke Current’s Parameters. • DIgSILENT Pacific PowerFactory Users’ Conference 2011 4 2
Network Component Models – Transmission Line Individual tower model • Separated circuit of Earth Wire(s) • Ph+E coupling capacitance due to string insulator • DIgSILENT Pacific PowerFactory Users’ Conference 2011 5 Network Component Models – Equipment’s Stray Capacitance Typical data of equipment's stray capacitance Equipment Capacitance to Ground Capacitive Potential Transformer 6000pF Magnetic Potential Transformer 600pF Current Transformer 350pF Disconnector 120pF Circuit breaker 150pF Bus Support Insulator 100pF 70MVA Transformer HV 2700pF 60MVA Transformer LV 2350pF 10MVA Transformer TV 2000pF Between Transformer winding 30pF DIgSILENT Pacific PowerFactory Users’ Conference 2011 6 3
Network Component Models – Surge Arrester Model Typical Discharge Current vs Residual Voltage Characteristic of 220kV Surge Arrester. Discharge Max Residual Current(kA) Voltage(kV) 0.1 527.9 0.4 558.4 1 582.0 2 602.4 5 643.0 10 676.8 12 791.9 13 832.5 15 900.0 DIgSILENT Pacific PowerFactory Users’ Conference 2011 7 Network Component Models – String Insulator Model V B 1 . 39 = 0 . 58 + CFO t where V B : the breakdown, flash over, or crest voltage, t : the time to breakdown or flash over CFO : Critical Flash Overvoltage in kV. (CFO implies the voltage level that result in a 50% probability of flash over if applied to the insulation.) DIgSILENT Pacific PowerFactory Users’ Conference 2011 8 4
Network Component Models – Tower Surge Impedance Conical Tower (Sargenet A.M.) Cylindrical tower (Sargenet A.M.) 2 2 h = Z 60 ln Z T = 60 ln 2 − 60 T sin θ r where θ is the sine of the half angle of the cone where h and r are the height and radius of the cylinder, respectively DIgSILENT Pacific PowerFactory Users’ Conference 2011 9 Network Component Models – Tower Footing Resistance(1) Current to initiate sufficient soil ionization • ρ E 1 0 I g = 2 2 π R 0 Tower Footing Resistance • R = 0 R i + 1 I / I R g where R : Surge tower footing resistance i is assumed to be low current R = 100 Ω 0 resistance for transmission tower footing resistance and for earth resistance R = 10 Ω 0 inside substation (worst case). : assumed soil ionization E 0 = 400 kV / m gradient I : lightning current through the footing R impedance ρ : soil resistivity. DIgSILENT Pacific PowerFactory Users’ Conference 2011 10 10 5
Network Component Models – Tower Footing Resistance(2) Current to initiate sufficient soil ionization • ρ 1 E 0 I g = π 2 2 R 0 Tower Footing Resistance • R R = 0 i 1 + I / I R g DIgSILENT Pacific PowerFactory Users’ Conference 2011 11 11 Stroke Current Model – Heidler Function Mathematical Model / Heidler function DIgSILENT Pacific PowerFactory Users’ Conference 2011 12 12 6
Stroke Current Model – Heidler Function DIgSILENT Mathematical Model / Heidler function 4.00 0.00 -4.00 -8.00 -12.00 -16.00 -5.0000 25.999 56.998 87.998 119.00 [us] 150.00 Direct Stroke: Stroke Current (kA) Lightning Studies Plots Stroke Source Date: 2/23/2011 DIgSILENT Annex: /1 DIgSILENT Pacific PowerFactory Users’ Conference 2011 13 13 Stroke Current Model – Heidler Function DIgSILENT Pacific PowerFactory Users’ Conference 2011 14 14 7
Stroke Current Model – Direct Strokes The maximum shielding failure current I m is calculated by: 1 r b gm I = m A where approximation of r gm is calculated by: ( h + y ) r gm = − γ α 2 ( 1 sin ) h: shielding height(m) y: highest conductor height(m) Geometric Model of Tower for Lightning Study a α = sin 2 2 a + ( h − y ) where a is the horizontal distance between highest phase conductor and shielding wire(m) for h>18m; γ = 444 /( 462 − h ) for h<=18m. γ = 1 (IEEE+1995 Substation Committee, Hileman pp.244, pp.248) DIgSILENT Pacific PowerFactory Users’ Conference 2011 15 15 Stroke Current Model – Back Flashover Rate(BFR) 1 BFR = flashes over per 100km+years d MTBS m where d m is the distance from gantry to the first With any specific MTBS, there exists a critical stroke current I s that the substation insulation may fail under if the first tower suffered from stroke current I>I s 1 P ( I > I ) = S 0 . 6 d N MTBS m L DIgSILENT Pacific PowerFactory Users’ Conference 2011 16 16 8
Stroke Current Model – Critical Stroke Current CIGRE Working Group Report [9] suggests the statistical distribution of all parameters of the flash can be approximated by the lognormal distribution whose probability density function is of the form: 1 1 − Z 2 ( ) = 2 f I e π β 2 I I ln( M ) where Z = β M :probability distribution median and β is the log standard distribution obtained from Berger’s data [1] We have: 1 1 2 ∫ ∞ − Z − > = − 1 P ( I I ) 1 e 2 dZ S 2 π I S 1 1 2 ∫ I − Z S 1 − P ( I > I ) = e 2 dZ S π 2 − ∞ From table of Cumulative Normal Distribution Function, finding the approximate value of Z. The critical stroke current is then calculated: Z β I = Me c DIgSILENT Pacific PowerFactory Users’ Conference 2011 17 17 Stroke Current Model – Front Time Median Front Time Median 0 . 53 t = 0 . 207 I f c (Conditional Lognormal Distributions from Berger’s Data) DIgSILENT Pacific PowerFactory Users’ Conference 2011 18 18 9
Stroke Current Model – Tail Time Median Determining the tail time constant is an iterative process, whereby the following formula is applied in the sequence, as suggested by Bewley (Hilemen pp397): R Z i g = R e + Z 2 R g i R e I = I R S R Iteration no. i R i (2) R e (2) I R (kA) R i (2) 1 10 9.70717 259.054 6.99351 2 7 6.85524 261.35 6.96 E ρ Calculation Example 1 0 = I g π 2 2 R 0 R = 0 R i + 1 I / I R g Z is the surge impedance of earth wire g conductor(s). DIgSILENT Pacific PowerFactory Users’ Conference 2011 19 19 Stroke Current Model – Tail Time Median Tail Time Median Z g T τ = S R i Where T s is to be time travel of surge for the first span length. DIgSILENT Pacific PowerFactory Users’ Conference 2011 20 20 10
Case Studies DIgSILENT Graphic: Brockman Date: 2/23/2011 Project: 2030 Circuit #2 Annex: INSULATION COORDINATION STUDY BROCKMAN SUBSTATION Earth Wire Circuit DIgSILENT P. PowerFactory 14.0.523 Circuit #1 Earth Resistance BRK 33kV Struck Tower Gantry T0002 SA4 Tower SA2 BRK 11kV ~ Lightning Stroke SA1 T0001 SA3 Nodes Branches DIgSILENT Pacific PowerFactory Users’ Conference 2011 21 21 Case Studies – Stroke Current Waveform Summary Current Heidler Function Test Case Waveform T 1 T 2 n η η η η Direct Stroke 20 kA 1.2/50 us 0.98 7.51035E+07 6.8117E+05 8 Ideal First Stroke(AS 1768) 150 kA 4.6/40 us 0.88 3.9549E+06 4.2941E+05 13 250yrs MTBF design 112 kA 2.5/91 us 0.97 1.91343E+06 0.000122304 13 DIgSILENT Pacific PowerFactory Users’ Conference 2011 22 22 11
Recommend
More recommend
