Design of MO Surge Arresters with Polymeric Housings

Transcription

1 Design of MO Surge Arresters with Polymeric Housings Kai Steinfeld (Director R&D Surge Arresters) High Voltage Surge Arrester s

2 Voltages in Electric Power Systems Voltage Limiting Effect of Surge Arresters Magnitude of voltage (p.u.) and above Overvoltage without arrester Withstand voltage of equipment Voltage limited by surge arresters 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>

3 Nonlinear V-I characteristic of MO surge arrester Rating for nominal system voltage 110 kv 300 Nominal discharge current 10 ka 8/20 µs Line to ground peak voltage (kv) Lightning impulse protection level (U res ) = 245 kv Leakage MCOV = 240 µa Rated volt. U r = 96 kv * 2 = 136 kv MCOV U c = 77 kv * 2 = 109 kv Highest volt. for equipment U m = 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>

4 Tube, Cage and Wrapped Design Design Principles Tube design silicone housing MOV fibre glass cloth impregnated with epoxi resin MOV supporting rod pressure relief and sealing system FRP tube silicone housing Cage design (Direct moulding) Wrapped design MOV supporting rod silicone housing end fitting terminal PTD H 4 <Dateiname hier eingeben>

5 Cage vs. Wrapped Design Moisture Ingress into Wrapped Design SA 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 Penetration SR tube SR sheds end cap Countermeasures: Reliable sealing system (e.g. end caps) on end face Long term stable, void-free bonding of all interfaces Diffusion SR tube SR shed Sophisticated technology and material needed in order to avoid moisture ingress FRP cloth wrapped around MOV stack PTD H 4 <Dateiname hier eingeben>

6 Cage vs. Wrapped Design Moisture Ingress into Cage Design SA 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 Penetration Cage design arresters are inherently resistant Diffusion to moisture ingress show very low internal leakage current in moist ambient conditions (Kari Lahti, Research into Performance of MV Arresters under Different Climatic Conditions INMR World Conference 2003, p. 53) PTD H 4 <Dateiname hier eingeben>

7 Cage Design Surge Arresters Crimping vs. Cone Elements 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>

8 Mechanical Resistance of Different Designs High Voltage Property Design System voltage in kv Static cantilever strength in knm Length in m Headload in kn Deflection in mm Tube Design Cage Design Wrapped Design n.a. Typical mechanical properties of different high voltage polymer surge arrester designs PTD H 4 <Dateiname hier eingeben>

9 Silicone Rubber (SR) vs. EPDM Chemical structure and bonding strength CH 3 CH 3 - Si - O - Si - O - CH 3 CH 3 Polydimethylsiloxane (PDMS)- Silicone Rubber (SR) - (CH 2 - CH 2 )x - (CH - CH 2 )y - CH - CH 2 - CH 2 CH = CH - CH 3 Ethylene Propylene Hexadiene Monomer (EPDM) Chemical bond -Si -O - (Silicone rubber backbone) Energy (kj per mole) 445 -C -H C -C - (EPDM and Epoxies backbone) 348 -Si-C 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>

10 Silicone Rubber (SR) vs. EPDM Burning Behaviour 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>

11 Cage Design Surge Arresters Short Circuit Behaviour 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>

12 Application of Cage Design Surge Arresters Horizontal Installation 1240 mm 2480 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/s 2 * 1,24 m = residual cantilever strength residual headload 2.8 knm 0,9 knm 1.9 knm kn PTD H 4 <Dateiname hier eingeben>

13 Application of Cage Design Surge Arresters Line Surge Arrester 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>

14 High Voltage Surge Arresters PTD H 4 <Dateiname hier eingeben>