Surge Arrestors Local To Grid Transformer - Assessment Of Required Position
Instructions
1 Enter appropriate figures in blue cells; see notes.
2 Read off total acceptable length for d+d1+d2+dA; see figures.
Notes
N = No. of lines connected to substation (take account of typical outages) 1 line(s) Typically 1 or 2. Line Type Factor A (kV)
A = Lightning performance voltage for the line voltage/type 4500 kV See Table 1. Transmission Single conductor 4500
Urw = Equipment rated lightning impulse withstand voltage (BIL) 550 kV See EE Spec 1/2. Double conductor bundle (twin) 7000
Upl = Arrester Lightning Impulse Level 311 kV See Table 2 or 3. Four conductor bundle (quad) 11000
Lsp = Span length of first span of overhead line 300 m Distribution Unearthed wood pole 2700
Lf = Overhead line section with outage rate equal to acceptable failure rate 50 Earthed construction wood pole 900
Ra = Acceptable failure rate of protected equipment 1 failure in 1000 years 0.001 failures/year Table 1 (taken from EN 60099-5)
r = Line outage rate for first km out 2 fault(s) per 100 km per year/circuit 0.00002 failures/year/m
Arrestor Type Rated Arrestor Rated Discharge Upl (kV)
Lp = arrester protective zone = Lt = total acceptable length d+d1+d2+dA 13.0 m Voltage (kV) Current
ABB type
d
PEXLIMQ132-WV145 132 10kA 311
d
Bowthorpe type
d1
d1 2P4SR132 132 10kA 333
Arrestor dA Bushing dA Arrestor Bushing
Bowthorpe
Metal-oxide gapless
36
45
10kA
10kA
102
123
d2 Table 2
Turret Arrestor Type Rated Arrestor
Voltage (kV)
Rated Discharge Upl (kV)
Current
Gapped to IEC 99-1 132 10kA Heavy-duty 343.2
d2 36 10kA Heavy-duty 100.8
Metal-oxide gapless 132 10kA 303.6-435.6
Transformer to IEC 99-4 36
45
10kA
10kA
82.8-118.8
103.5-148.5
Transformer Table 3
NB Assumes interconnected earth grid.
Calculation method as per EN 60099-5, IEC 99-5 & IEC 71-2:
Eq 1.0 Lp = N/A((Urw/1.15)-Upl)(Lsp+Lf)
Eq 2.0 Lf = Ra/r
