Unique Features of Metal Encapsulated SF 6. - Insulated Surge Arresters DANIJEL UDOVCIC

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1 Unique Features of Metal Encapsulated SF 6 - Insulated Surge Arresters DANIJEL UDOVCIC

2 Unique Features of Metal Encapsulated SF6-Insulated Surge Arresters Siemens AG, Germany D. Udovcic, R. Göhler siemens.com/energy/arrester

3 Overview Arresters Basics 3-10 Traditional Design Improved Design Type tests Overview Conclusion Seite

4 Magnitude of (over.)voltage / p.u. Fundamentals of Insulation Coordination Possible voltages without arresters Withstand voltage of equipment 2 1 Voltages limited by arresters 0 Lightning overvoltages (Microseconds) Switching overvoltages (Milliseconds) Temporary overvoltages (Seconds) Highest system voltage (Continuously) Seite Time duration of (over-)voltage

5 Factor 2.5 MO Arrester: Voltage-Current-Characteristic 1000 Example: U s = 420 kv, Surge arrester U r = 336kV 20-kA residual voltage = lightning impulse protective level = 850 kv 800 Peak value of voltage / kv Peak value rated voltage: 2 Ur= 475 kv Reference voltage: 490 kv Peak value of COV: 2 Uc = 379 kv Peak value of phase-to-earth voltage: 2 Us / 3 = 343 kv Reference current = 5 ma 0 Leakage current 110 µa 0, ,0001 0,001 0,01 0, Peak value of current / A Seite Nominal discharge current = 20 ka 8 orders of magnitude

6 2,5 m Inductivity of current path 1 µh/m (here: L = 10 µh 3,5 m Protective Zone Voltage at terminals of equipment to be protected higher than protection level of arrester Recommendation: Protection level BIL/1,4 Seite

7 Protective Zone Due to travelling wave effects on the line the protection of the equipment by an arrester can be guaranteed only for short distances between arrester and equipment. Simplified estimation of the protective zone *) : xs protective zone in m BIL basic insulation level in kv Upl protection level of the arrester in kv (BIL / 1.15) - Upl s front steepness of the overvoltage in kv/µs xs = v tw (in the range of 1000 kv/µs) 2 s v tw propagation speed of travelling wave: m/µs (overhead line) (equals "c") m/µs (cable) *) For more detailed information see IEC , IEC and IEC Example : Transmission network, Us = 420 kv, effectively earthed, arrester of Ur = 336 kv: xs = (1425 / 1.15) m = 55.5 m Seite

8 2,5 m 3,5 m Increase of Protection Voltage by Inductive Voltage Drops Example: outdoor arrester U s = 420 kv U r = 336 kv u 20kA, 8/20 µs = 850 kv u 20kA, 1/2 µs = 921 kv Surge current path: Specific inductance 1 µh/m / Length 10 m Inductance L 10 µh u= L di / dt residual voltage 1113 kv 921 kv U / kv I / ka 200 current inductive voltage drop t / µs Additional inductive voltage drop kv Seite

9 Increase of Protection Voltage by Inductive Voltage Drops GIS - Arrester U s = 420kV U r = 336 kv u 20kA, 8/20 µs = 840 kv u 20kA, 1/2 µs = 890 kv Surge current path: Specific inductance 0,3 µh/m / Length 2,5 m Inductance L 0,75 µh u= L di / dt Seite Additional inductive voltage drop 10 kv

10 Advantages of Metal Encapsulated SF 6 -Insulated Surge Arresters Optimum protection for GIS and Transformers. Low protection levels that are especially based on the closeness to the equipment that needs to be protected from overvoltages. Best possible protection against the overvoltages, especially those resulting from steep front impulses due to the lower specific inductance. Seite

11 Application area of SF 6 -Insulated Surge Arresters 145kV 3- phase GIS Arrester with SF 6 -SF 6 bushing 420kV Transformer With Oil-SF 6 Bushing Metal Encapsulated SF 6 -Insulated Surge Arrester for 145kV GIS Seite Metal Encapsulated SF 6 -Insulated Surge Arresters for Transformer protection / 420kV

12 Overview Arresters Basics 3-10 Traditional Design Improved Design Type tests Overview Conclusion Seite

13 Traditional Design of SF 6 -Insulated Surge Arresters 3-phase up to U s = 170kV 1-phase up to U s = 420kV Disadvantages: High voltage tests of the GIS at site: Open up of manhole of the arrester. Gas work required. Dimensions: width, length. Layer of the conductor for the three phase arresters has to be announced in advance. More complicated assembly through the part diversity Accessories kit required at site. Seite

14 Overview Arresters Basics 3-10 Traditional Design Improved Design Type tests Overview Conclusion Seite

15 IMPROVED DESIGN OF SF 6 -INSULATED SURGE ARRESTERS 3 Phase Arresters up to 170kV 1 Phase Arresters up to 420 kv Advantages: Disconnector in the series not required anymore. SF 6 -Volume is reduced up to 60%. Plug and Play solution. Reduced gas work at site. Accessories kit not required. Variable phase position at three phase arrester solution. Monitoring or Remote Control of switching position of arresters. Reducing Diversity of the assembled parts Seite

16 Explanation of contacting Upgraded Design Visual switch position indicator: Switch position On, Closed, I Movement of the contact is limited through the external gear. Because of this limitation it is not possible to overwind or to destroy inner contact or inner parts. Visual switch position indicator: Switch position OFF, Open, 0 Legend: 1. SF6-SF6 bushing 2. Active part 3. Insulating rod 4. SF6- Maintenance flange 5. Pressure relief device 6. Terminal for electrical monitoring devices 7. Integrated isolating device 8. Manual drive mechanism Seite

17 Overview Arresters Basics 3-10 Traditional Design Improved Design Type tests Overview Conclusion Seite

18 TYPE TESTS OVERVIEW Vibration broadcom random, class 2M3 acc. IEC Mechanical endurance tests with 1000 switching operations Insulation withstand tests Shock (half sine), class 2M3 acc. IEC Verification of thermal equivalency Internal partial discharge test Seite

19 Overview Arresters Basics 3-10 Traditional Design Improved Design Type tests Overview Conclusion Seite

20 Conclusion Upgraded design setting a new standard through integrated technology based on decades of experience Upgraded design vs. Traditional Design CHARACTERISTICS Upgraded design Traditional design Electrical / Dielectrical behavior same Mechanical behavior same Housing Without manhole With manhole SF6-SF6 bushing Bottom cover Integrated isolating device Manual / Motorized drive mechanism without opening the arrester. same similar Manually disconnection over the manhole. Manual drive mechanism Based on existing one used in traditional design (single-phase up to 245kV) and Trench CTs and VTs. Motorized drive mechanism MOVs (Metal Oxide blocs) DILO / O-rings Rupture disc assembly Based on existing one used in Trench CTs and VTs. same same same No Seite

21 Contact Danijel Udovcic Project manager GIS Arresters Upgraded Design E T HP AR BA P Nonnendammallee Berlin danijel.udovcic@siemens.com siemens.com/answers Seite