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STANDARDS
• IEC 60099Surge arresters —
Part 1 : Non-linear resistor type gapped surge arresters for a.c. systemsPart 4 : Metal-oxide surge arresters without gaps for a.c. systemsPart 5 : Selection and application recommendations
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Definition
‘‘A protective device for limiting surge voltages on equipment by diverting surge current and returning the device to its original status. It is capable of repeating these functions as specified.’’
[IEEE Standard C.62.11-2005]
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U-I-characteristic of a typical MO arrester in a solidly earthed neutral 420kV system
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Choosing the Continuous Operating Voltage and the Rated Voltage
earthedy effectivel-non
earthedy effectivel 3
05.1
min,
m
m
C
U
U
U
min,1 25.1 Cr UU
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Choosing the Continuous Operating Voltage and the Rated Voltage
FactorStrength eOvervoltagTemporary :
FactorRejection Load :
FactorFault Earth :
2.3
..
rT
L
eC
r
eLmr
T
CUU
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Choosing the Continuous Operating Voltage and the Rated Voltage
min,
2 ,25.1
max Cr
C UU
U
21,max rrr UUU
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Energy Absorption Capability due to Switching
m/µsv
L
LU
resLres
v
LsUU
Z
sUW
300
linelongest oflength :
eovervoltaghighest :
0
)]60/30([)60/30(2
IEC 60099-5 Table 1rU
WW
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Specific energy in kJ/kV of rated voltage dependent on the ratio of switching impulse residual voltage Ua to the r.m.s. value of the rated voltage Ur the arrester.
[Fig. E1 IEC 60099-4]
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Energy Absorption Capability due to Lightning [IEC 60099-5 ]
insulation theof voltageflashover negative The :
s)(300flash lightning a of ofduration equivalent The :
arrester the toconnected lines of No. :
arrester theof level protection impulse lightning The :
))]/2ln(1(2[
fU
lT
N
plU
lplplfplf Z
TUUUNUUW
factor correction Altitude :
gapAir :
700
k
d
f kdU
rU
WW
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Selecting the Housing [IEC 60099-4]
1. Insulation Characteristics
2. Mechanical Characteristics
3. Creepage distance
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Selecting pressure relief class
Porcelain housed arrester after pressure relief test
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Surge Arrester Calculation Protecting Distance
[IEC 60099-5 ]
))(15.1
( fspplrw
P LLUU
A
NL
Urw : Rated lightning impulse withstand voltage
Upl : Lightning impulse protection level of surge arrester
Lf = Ra/r : Length of overhead line in front of the station, which gives a rate of lightingevents equal to the acceptable failure rate
Ra : Acceptable failure rate (number of failures per unit time) for the protected equipment (1/Year)
r : Overhead line outage rate (1/100km.Year)N : Number of lines connected to the substationLsp: Span lengthLp: Protecting distance A : Voltage according to Table2 of IEC60099-5 describing the lighting performance
of the overhead line connected to the station
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Protecting Distance [IEC 60099-5 ]
IEC 60099-5 Table 2 : Factor A for various over head lines
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Protecting Distance [Ministry of Power Standard]
dt
diLLVDSUU CRESp /2
Up : voltage on the terminal of the protected equipment
L : Inductance Of The Conductor Between Line And Effective EarthLc : Maximum Length From Line Conductor To Effective Earth
S : Front Steepness Of Lightning Overvoltage (kV/µS)
