The Evolution of Switchgear and Purpose / Function
Basic function of MV switchgear
- Carry normal loads, including permissible overloads.
- Protect electrical network equipment downstream. (e.g. cables. transformers, electrical motors) Protection equipment will measure and if required give a signal to the MV switch gear to interrupt the electrical circuit to the load or fault.
- This interruption must be done to ensure the following:
- Maximum human safety (both operators and public)
- To prevent damage to electrical equipment, (trip on overload, trip on Earth fault)
- In-case of serious fault minimizes damage to electrical equipment, (damage to MV underground cable or overhead line.)
- Provide enough segmentation of the medium-voltage networks so that in the event of outages, limited equipment and or users will be affected.
- For working on equipment (e.g. Maintenance) ensure a safe environment for the Maintenance personnel to work safely on sections of the MV network. Alway remember (lock-out and Tag-out)
Evolution of switchgear
- MV Switch gear started with using Air as the Insulation medium and MV Fuses for fault interruption.
- In the early 1950 the industry starts to use Oil as an interruption medium
- In 1980 Vacuum, and SF6 interrupters was developed and SF6 was also used as insulation medium
Total Air insulated switchgear or switching systems.
The first disconnection equipment for electrical networks was based on total air insulated equipment.
- Equipment was huge
- Normally housed in cages for human safety and segmentation
- Fault interruption was based on fuse technology with
- Off load links/blade disconnectors.
