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
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

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 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

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

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

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 8DJ Typical Application Examples

12. Thank you very much for your attention!