Presented by: Nguyen Phan Thanh

Southern Taiwan University of Science and Technology

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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.

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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.

Objective

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The previous protection methods The proposed protection method The OPSOLA Program

Result

ContentContent

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PC BILD . U2.S 1,2

Un kV 17,5 24 36

BIL kV 95 125 170

Up kV 57,2 79,9 117,6

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1. The simple protection methodThe maximum distance:

Table 1. BIL and Up

(Với: D = a + b)

a : The maximum separation between J and pole-mounted transformer, mb : Distance between J and surge arrester, mUt : Arrester residual voltage, kVC: Velocity of wave propagation, C = 300 m/s.BIL: Basic Insulation Level of Transformer (KV)

I. The previous protection methodsI. The previous protection methods

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2. The improved protection method (J. R. Lucas Method)

DO : Point of lightning stroke S0 : Rate of rise at O, kV/µs I0 : Lightning stroke current , kAX :Distance in which a surge with an infinite slope will decay to slope SA at A, mSA : Rate of rise of surge voltage at A, kV/µs   : Reflection coefficient at transformerEt : Peak surge voltage at transformer, kVSf : 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 yearLF: 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, sk : Corona damping constant, kV.km/s .

I. The previous protection methodsI. The previous protection methods

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g f

0,628h bN N 1 S10

AS

7

ycf

FR (%)N

LF

AAS2.T 0,02878 .Z 1 S .k.X

f0

xN N. e .dx

t PA

0,8E U CD , m2S

t pE 2U , kV

DO : Point of lightning stroke S0 : Rate of rise at O, kV/µs I0 : Lightning stroke current , kAX :Distance in which a surge with an infinite slope will decay to slope SA at A, mSA : Rate of rise of surge voltage at A, kV/µs   : Reflection coefficient at transformerEt : Peak surge voltage at transformer, kVSf : 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 yearLF: 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, sk : Corona damping constant, kV.km/s .

2. The improved protection method (J. R. Lucas Method)

I. The previous protection methodsI. The previous protection methods

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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

I. The previous protection methodsI. The previous protection methods

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1m

3m 3m 3m

LineA B

LineC

Line

3m

T12T

D12D Arrester

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

(3-line , 2 - transformer substation) The proposed protection method based on IEEE Std C62.22.2009

S.3. Eliminate all line connected to D1

S.4. Calculate SJ

cJ

mtt tt.

K3 3S S .N 2 d N 2

, kA/s

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

II. II. The proposed protection method

d2 =

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Transformer

Arrester

B

2

1

S

md

D

d

d JS.5. Distance : stroke - substation

m1d =

N(MTBF).100

, km

J Jsa a a o1 2 .

2S 2SV V L. V d + d L .

Z Z

S.6. Voltage of ArresterB: 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, yearFR: acceptable failure rate, %N : number of stroke into line, times /100 km/yearKc: corona damping constant , kV.km/s Va: Mức bảo vệ đầu sóng của chống sét van tại 0,5s, kV Z : line impedance, L : Inductance, H.

with:1MTBF FR(%)

The proposed method based on IEEE Std C62.22.2009

II. II. The proposed protection method

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1m

3m 3m 3m

LineA B

LineC

Line

3m

T12T

D12D Arrester

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)

II. II. The proposed protection method

The proposed protection method based on IEEE Std C62.22.2009

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Shielding Factor

Distance from objects to line (DO = x), m

(Sf)

Object ‘s Height

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

Nonlinear regression technique

Curve Fitting Matlab

Build 16 relationships Sf, H và DO

Sf = SfL + SfRSfL: S.F at left sideSfR: S.F at right side

II. II. The proposed protection method

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The number of stroke into line

g gf fL fR

0,6 0,628h b 28h bN N 1 S N 1 S S10 10

The inductance line which connect to surge arrester

, times/100km/year

- The inductance at line (length 1 m)

7 123o

DL =2.10 .ln

r , H/m

- The inductance line which connect to surge arrester

7 123o1 2 1 2.

DL = d + d L = d + d .2.10 .ln

r , H

Which: 3123 12 23 13D D D D , m

II. II. The proposed protection method

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Check MTBF of transformer

2

a a2 T Ta aJ J T2

2,92.D.V .Z D.V .Z 0,77.L.C.V 1,54.L.V .C5,84.L.D.Z 1,54.C.L S S 0,385.C.V V V 0 ZZ

J

g c f

1000.SMTBF 0,6N .K .(28h b).(1 S )

II. II. The proposed protection method

(1)(3)

Nonlinear regression technique

Curve Fitting Matlab

Build 6 relationships Sf, H và DO

0,9998gMTBF =107,5.N 0,02619

1g MTBF 195,4.N 0,0254 M

TB

F (y

ear)

Ng (times/km2.year)