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