Power Transmission and Distribution
Design of MO Surge Arresters
with Polymeric Housings
Kai Steinfeld (Director R&D Surge Arresters)
High Voltage • Surge Arrester
s
Power Transmission and Distribution
Voltages in Electric Power Systems
Voltage Limiting Effect of Surge Arresters
High Voltage
6
Overvoltage
without arrester
Withstand voltage
of equipment
Voltage limited by
surge arresters
Magnitude of voltage (p.u.)
and above
5
4
3
2
1
0
Lightning
overvoltage
(Microseconds)
Switching
overvoltage
(Milliseconds)
Temporary
overvoltage
(Seconds)
Highest voltage
for equipment
(continuosly)
Type and duration of voltage
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 2
Power Transmission and Distribution
Nonlinear V-I characteristic of MO surge arrester
Rating for nominal system voltage 110 kV
High Voltage
300
Line to ground peak voltage (kV)
Nominal discharge current 10 kA 8/20 µs
Lightning impulse protection level (Ures) = 245 kV
200
Leakage current @ MCOV = 240 µA
Rated volt. Ur = 96 kV * √2 = 136 kV
100
MCOV Uc = 77 kV * √2 = 109 kV
Highest volt. for equipment Um = 71 kV * √2 = 100 kV
0
1E-05
1E-03
1E-01
1E+01
1E+03
1E+05
Current (A)
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 3
Power Transmission and Distribution
Tube, Cage and Wrapped Design
Design Principles
High Voltage
Tube design
silicone housing
MOV
fibre glass cloth
impregnated
with epoxi resin
MOV
supporting rod
pressure relief
and sealing system
Wrapped design
MOV
supporting rod
FRP tube
silicone housing
silicone housing
end fitting
Cage design
(Direct moulding)
terminal
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 4
Power Transmission and Distribution
Cage vs. Wrapped Design
Moisture Ingress into Wrapped Design SA
High Voltage
Moisture ingress into wrapped design surge arrester possible by
„
Penetration into end face
„
Diffusion through housing
„
Accumulation of water in interfaces and voids
„
MOV – FRP wrap
„
FRP wrap – SR tube
„
SR tube – SR sheds
Penetration
end cap
Countermeasures:
„
Reliable sealing system
(e.g. end caps) on end face
„
Long term stable, void-free
bonding of all interfaces
Î
Sophisticated technology and
material needed in order to
avoid moisture ingress
SR tube
Diffusion
SR shed
FRP cloth
wrapped around
MOV stack
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 5
Power Transmission and Distribution
Cage vs. Wrapped Design
Moisture Ingress into Cage Design SA
High Voltage
Moisture ingress into cage design surge arrester only possible by
„
Diffusion through housing
But
„
No penetration into end face
due to hermetically tight end fitting
„
No accumulation of moisture
due to strong, void-free bonding
of all interfaces by direct moulding
of silicone rubber onto FRP rods and MOV
Î
Cage design arresters
Î are inherently resistant
Diffusion
to moisture ingress
Î show very low internal leakage current
in moist ambient conditions
Penetration
(Kari Lahti,
“Research into Performance of MV Arresters
under Different Climatic Conditions
INMR World Conference 2003, p. 53)
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 6
Power Transmission and Distribution
Cage Design Surge Arresters
Crimping vs. Cone Elements
High Voltage
Prestress of rods and MOV 5 kN
Static cantilever strength 350 Nm
Design suitable for MV
supporting rod
bores
MOV
end fitting with
crimp impression
Prestress of rods and MOV 100 kN
Static cantilever strength 2.8 kNm
Design suitable for HV
cone element
conical bore
end fitting
supporting rod
MOV
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 7
Power Transmission and Distribution
Mechanical Resistance of Different Designs
High Voltage
Design
Tube Design
Cage Design
Wrapped
Design
System voltage
in kV
170
170
170
Static cantilever
strength in kNm
14.7
2.8
0.8
Length
in m
1.76
1.77
1.56
Headload
in kN
8.4
1.6
0.5
Deflection
in mm
44
173
n.a.
Property
Typical mechanical properties of different
high voltage polymer surge arrester designs
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 8
Power Transmission and Distribution
Silicone Rubber (SR) vs. EPDM
Chemical structure and bonding strength
High Voltage
CH3
CH3
- (CH2 - CH2)x - (CH - CH2)y - CH - CH2 CH2
- Si - O - Si - O CH3
CH3
CH = CH - CH3
Polydimethylsiloxane (PDMS)Silicone Rubber (SR)
Ethylene Propylene Hexadiene Monomer (EPDM)
Chemical bond
Energy
(kJ per mole)
- Si - O (Silicone rubber
backbone)
445
-C-H-
414
-C-C(EPDM and Epoxies
backbone)
348
- Si - C -
318
Energy of UV
radiation (300 nm)
398
„
„
„
-Si-O- Backbone of SR has
higher bonding energy as
–C-C- backbone of EPDM
SR has lower carbon
proportion as EPDM
Consequently, SR has
inherently better chemical
and physical resistance, UV
resistance and lower
flammability as EPDM
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 9
Power Transmission and Distribution
Silicone Rubber (SR) vs. EPDM
Burning Behaviour
High Voltage
Siemens 3EK7 surge arrester cage design
with SR housing
MV surge arrester wrapped design
with EPDM housing
Cage design MV surge arresters with silicone rubber and EPDM tested
with AC current 40 A for 30 min
(Simulation of arrester failure in compensated MV power systems)
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 10
Power Transmission and Distribution
Cage Design Surge Arresters
Short Circuit Behaviour
High Voltage
High voltage cage design surge arrester after short circuit test 65 kA:
„ Arc burns through silicone rubber housing in between FRP rods
„ No internal pressure built up since there is no hermetic enclosure
„ No pressure relief system needed
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 11
Power Transmission and Distribution
Application of Cage Design Surge Arresters
Horizontal Installation
High Voltage
2480 mm
1240 mm
intrinsic
force
700 N
residual
headload
780 N
static cantilever strength
arrester mass 71.4 kg
intrinsic bending moment 71.4 kg * 9,81 m/s2 * 1,24 m =
2.8 kNm
residual cantilever strength
residual headload
1.9 kNm
0.780 kN
0,9 kNm
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 12
Power Transmission and Distribution
Application of Cage Design Surge Arresters
Line Surge Arrester
High Voltage
Cage design surge arrester
used as line surge arresters
in 245 kV overhead power line
(REN S.A., Portugal)
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 13
Power Transmission and Distribution
High Voltage
Surge Arresters
PTD H 4 · <Dateiname hier eingeben> · 05.08.2004 14