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

Evolution of Medium-Voltage Switchgear Source: ABB Local installation Workshop manufacture Factory-assembled, type-tested Factory-assembled, compact Factory-assembled, SF6-insulated non type tested type tested Air-insulated Air/solid-insulated Cast-resin insulated Gas-insulated Year until 1950 until 1970 since 1970 since 1980 since 1982 Building 83 m3 47 m3 29 m3 24 m3 8 m3 Panel 19 m3 14.5 m3 8.7 m3 5.8 m3 2.2 m3

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)

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

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

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

Situation with Gas-Insulated Switchgear Today’s state of the art is 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

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

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

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

Switchgear Type 8DJ Typical Application Examples

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