Southern Taiwan University of Science and Technology

1. Southern Taiwan University of Science and Technology Dertermining Optimal Surge Arrester's Location In Distribution Network Accounting For Several Influence Elements Presented by: Nguyen Phan Thanh

2. Objective • To protect the distribution substation from lightning overvoltage, the lightning arrester is installed at the high voltage side of transformers.  • If the lightning arrester is installed at the terminals of transformers, the transformer will be protected safety. • However, lightning arrester must to protect for all insulation of the substation’s components. • Thus, the determination of reasonable distance between lightning arrester and terminals transformer to protect efficiency the transformer and switching devices of the substation is very necessary.

3. Objective • This project presents a new method for calculating the separated distance and the Mean Time Between Failure (MTBF) of the transformer with different configurations to make sure that the life of transformer according to first requirement, considering the affected factors such as the shielding factor of the object, areas ground flash density, the inductance value of connected wires.  • The OPSOLA program is built to help the users easily determine the appropriate installed position of lightning arrester and check MTBF for the existing configuration of substation.

4. Content • The previous protection methods • The proposed protection method • The OPSOLA Program • Result

5. I. The previous protection methods The maximum distance: • The simple protection method (Với: D = a + b) Table 1. BIL and Up a : The maximum separation between J and pole-mounted transformer, m b : Distance between J and surge arrester, m Ut : Arrester residual voltage, kV C: Velocity of wave propagation, C = 300 m/s. BIL: Basic Insulation Level of Transformer (KV)

6. D I. The previous protection methods 2. The improved protection method (J. R. Lucas Method) O : Point of lightning stroke S0 : Rate of rise at O, kV/µs I0 : Lightning stroke current , kA X :Distance in which a surge with an infinite slope will decay to slope SA at A, m SA : Rate of rise of surge voltage at A, kV/µs   : Reflection coefficient at transformer Et : Peak surge voltage at transformer, kV Sf : Shielding factor (0,3 ÷ 0,5) N : The number of direct stroke into line, times/100km/year h : Height of nearby objects, m b : Horizontal span between outermost conductors, m Ng: Number of stroke per km2 per year LF: Lifetime of transformer, year FR: Failure rate of transformer, % Nf :Number of lightning surges arriving at A /year, with slope higher SA T : Wave front time, s k : Corona damping constant, kV.km/s .

7. D I. The previous protection methods 2. The improved protection method (J. R. Lucas Method) O : Point of lightning stroke S0 : Rate of rise at O, kV/µs I0 : Lightning stroke current , kA X :Distance in which a surge with an infinite slope will decay to slope SA at A, m SA : Rate of rise of surge voltage at A, kV/µs   : Reflection coefficient at transformer Et : Peak surge voltage at transformer, kV Sf : Shielding factor (0,3 ÷ 0,5) N : The number of direct stroke into line, times/100km/year h : Height of nearby objects, m b : Horizontal span between outermost conductors, m Ng: Number of stroke per km2 per year LF: Lifetime of transformer, year FR: Failure rate of transformer, % Nf :Number of lightning surges arriving at A /year, with slope higher SA T : Wave front time, s k : Corona damping constant, kV.km/s .

8. I. The previous protection methods • The previous methods: • Accounting for influence elements with some experiment parameters • Just considered to single transformer substation • The proposed method: • Determining surge arrester‘s location for 3-line, 2-transfomer substation based on: • IEEE Std C62.22.2009 • Influence elements (can be calculated) • Mean Time Between Failure (MTBF) of Transformer

9. II. The proposed protection method The proposed protection method based on IEEE Std C62.22.2009 (3-line , 2 - transformer substation) S.1.Eliminate 1 transformer and determine the line which the lightning wave transmitted into. S.2.Define the following parameters: - J, the common point between transformer, surge arrester and the line identified in step 01. - D1, distance from J to pole-mounted transformer - D2, distance from arrester to ground d2 = A, B, C: Line A, B, C. T1,T2 : Transformer T1 and T2 D1: Separate distance between T1 and line, m. D2: Separate distance between T2 and line, m. Ntt: Number of identified lines S.3.Eliminate all line connected to D1 S.4.Calculate SJ , kA/s

10. II. The proposed protection method The proposed method based on IEEE Std C62.22.2009 S.5.Distance : stroke - substation , km with: B: insulation equipments. d1: distance between line and arrester , m. D2: distance between arrester and ground, m. S : slope wave, kA/s. MTBF: mean time between failure, year FR: acceptable failure rate, % N : number of stroke into line, times /100 km/year Kc: corona damping constant , kV.km/s Va: Mức bảo vệ đầu sóng của chống sét van tại 0,5s, kV Z : line impedance,  L : Inductance, H. S.6. Voltage of Arrester

11. II. The proposed protection method The proposed protection method based on IEEE Std C62.22.2009 S.7. Determine D1 and D2: D1 = min (D1_T1_Line A ; D1_T1_Line B ; D1_T1_Line C) D2 = min (D2_T2_Line A ; D2_T2_Line B ; D2_T2_Line C)

12. II. The proposed protection method Shielding Factor Object ‘s Height Nonlinear regression technique Curve Fitting Matlab (Sf) Build 16 relationships Sf, H và DO SfL: S.F at left side SfR: S.F at right side Sf = SfL + SfR Distance from objects to line (DO = x), m H = 10m: Sf = 5,013.10 - 7.x3 – 6,051.10-5.x2 – 0,003655.x + 0,4813 H = 14m: Sf = – 6,047.10 - 12.x5 + 1,452.10 - 8.x4 – 3,332.10 - 6.x3 +0,3459.10 - 3.x2 – 0,0247.x + 0,9982

13. II. The proposed protection method The number of stroke into line , times/100km/year The inductance line which connect to surge arrester - The inductance at line (length 1 m) , H/m Which: , m - The inductance line which connect to surge arrester , H

14. (3) (1) II. The proposed protection method Check MTBF of transformer Nonlinear regression technique Curve Fitting Matlab MTBF (year) Build 6 relationships Sf, H và DO Ng (times/km2.year)