Medium-Voltage Switchgear - Then and Now -

1. Medium-Voltage Switchgear - Then and Now - Hans-Joachim Müller

2. Evolution of Medium-Voltage Switchgear Source: ABB Local installation Workshop manufacture Factory-assembled, type-tested Factory-assembled, compact Factory-assembled, SF6-insulated type tested non type tested Gas-insulated Cast-resin insulated Air/solid-insulated Air-insulated

3. Situation in the Past Yesterday,switchgear were air, oil or cast-resin insulated with the following features: • Huge dimensions • Dependent on pollution and climate • Maintenance at regular intervals • Human failure during maintenance • High fire risk • Not arc-fault tested This means: • High investment for buildings • High costs for maintenance staff and system transfer in the network • Breakdown of the network (longer downtimes)

4. Restricted Availability and Reliability of Supply After short circuit at the rear side of an epoxy-resin insulated switchgear Burned-out 10 kV substation: Fire after short circuit in an epoxy-resin insulated ring-main unit

5. Objectives for the Development of New Switchgear Requirements for development: • Personal safety • Reliability of supply • Maintenance-free design • Suitability for all switching duties • Sufficient power reserves • Low fire risk • Small, light design Concept options for new switchgear due to availability of the following equipment: • Maintenance-free switching devices • Shockproof cable plugs and bar connections • Electronic measuring and protection devices

6. Implementation of the Development Tasks Constructional implementation: • Solid insulation is replaced by insulating gas with constant properties • Sealed enclosure of primary part • Installation of fixed-mounted, maintenance-free switching devices:- Vacuum circuit-breaker- Three-position switch- SF6-switch-disconnector • Shockproof cable plugs • Use of current and voltage transformers with low susceptibility to faults • Verification of safe isolation from supply with capacitive voltage dividers • Maintenance-free and reliable operating elements with few parts inside the enclosure • Easiest operation • Pressure-resistant enclosure with defined pressure relief

7. Situation with Gas-Insulated Switchgear Today’s state of the artis gas-insulated switchgear with the following main benefits: • Small, compact dimensions • Independent of environmental effects and climate • Widely maintenance-free • Maximum safety for staff • Low fire risk • Arc-fault tested Advantages: • Low invest for buildings due to compact dimensions and climate-independent design • Maximized power supply reliability • Maximum personal safety • Lowest life cycle costs • Reduced operational costs - no additional maintenance costs

8. First SIEMENS Gas-Insulated Medium-Voltage Switchgear (April 1982) • Kulmbach / Germany • 8DA10 • 16 panels • 24 kV / 16 kA (3s) / 1250 A

9. Site altitude: 3000 – 5000 m Applications Today • Tibet / China • 8DA10 • 205 panels • 40.5 kV / 31.5 kA (3s) / 1250 A

10. First SIEMENS Gas-Insulated Medium-Voltage Ring-Main Unit (April 1982) • Stadtwerke Lambrecht / Pfalz, Germany • Project: Municipal power supply • Electrical data: 24 kV, 16 kA, 630 A • Typicals: 8DJ10, scheme 10

11. Switchgear Type 8DJTypical Application Examples

12. Thank you very much for your attention!