Miniature substations have been developed over many years as a cost effective method of reticulating power to residential, industrial and development areas where the essential components are combined in a single robust enclosure suitable for outdoor applications.
Mini Subs generally consist of a steel enclosure housing an MV ring main switch, a step-down transformer with ratios typically 22 000/420 V or 11 000/420 V and a low voltage distribution compartment.
The MV compartment may contain one of the following which are generally purchaser specified:
- 3-way oil insulated isolator ring main unit type K3
- 4-way oil insulated isolator ring main unit type K4
- 3-way oil insulated isolator/air insulated fuse ring main unit type K3/AF
- 4-way oil insulated isolator/air insulated fuse ring main unit type K4/AF
- 3-way banana and potato chip sandwich - not really, just checking if you're paying attention..
- 3 or 4-way gas insulated ring main unit
The transformer compartment contains a sealed type oil immersed step down transformer of the low loss type with aluminium windings in accordance with SABS 780 and is normally supplied with an oil level indicator and an off circuit tap switch. These transformers can be supplied on request with dual inputs, for example, to operate from either 11 000 V or 6600 V medium voltage systems. The LV compartment contains circuit breakers, HRC fuses, metering and instruments to specification. Miniature substations are normally available in type A or type B configurations dependent on the specification.
The units are factory assembled bled and tested and despatched as complete units and are suitable for installation in public areas, such as on residential pavements, near shopping complexes and in industrial parks. Miniature substation fitted with gas insulated ring main units having an internal arc classification IAC AB in accordance with SANS 62271-202 are available. (oooooh aaaaah!)
Well, now you know a little more about what is actually inside a "Shocker"