Substations
Secondary substations
The point where a distribution network steps medium voltage down to the low voltage that buildings and sites use, whatever physical form it takes.
At a glance
- Role
- medium voltage to low voltagethe last transformation before the consumer
- Forms
- prefabricated, walk in, package, in buildingset by the site
- Ownership
- network operator or customerdecides whose standard applies
- Standards
- IEC 62271-202 when prefabricatedIEC 61936-1 for the installation
Secondary substation describes a role in the network rather than a product. It is the node where medium voltage is transformed to low voltage and distributed to the consumers around it. It can be a prefabricated compact station, a walk in station, a package substation or a room in a building.
Who will own and operate it matters as much as its form. A secondary substation that the network operator adopts is built to that operator's standard, and the operator's specification decides the switchgear, the transformer and often the enclosure. A customer owned station follows the customer's specification within the operator's connection conditions.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Ownership | Network operator or customer | Whether the operator adopts the station |
| Physical form | Prefabricated, walk in, package or in building | Space, access and operating practice |
| Transformer | Rating and voltage pair | The load of the area or site supplied |
| Medium voltage | Ring main unit or panels | The network arrangement |
| Low voltage | Number and rating of outgoing ways | The consumers supplied |
| Earthing | Earthing arrangement and earth electrode design | The network and local rules |
Typical options are the ones buyers most often specify. They are not a list of what is available, which is confirmed per enquiry.
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 62271-202 | AC prefabricated substations up to and including 52 kV, where the station is prefabricated |
| IEC 61936-1 | Power installations exceeding 1 kV AC, for the design and erection of the installation. It does not cover the design of prefabricated, type tested switchgear or prefabricated substations |
| IEC 62271-200 | Metal enclosed switchgear above 1 kV up to and including 52 kV |
| IEC 61439-1 and IEC 61439-2 | Low voltage switchgear assemblies |
The distinction in IEC 61936-1 matters in specifications: the station you buy is proven by its manufacturer to IEC 62271-202, while the installation around it is designed to IEC 61936-1.
Documents normally requested
| Document | What it evidences |
|---|---|
| Technical datasheet and single line diagram | Ratings, panel functions and the arrangement offered |
| General arrangement drawing | Footprint, height, cable entry and floor fixings |
| Type test report | The design has passed the type tests of its standard, including internal arc where claimed |
| Routine test report | The individual assembly's tests before dispatch |
| Schematic and wiring diagrams | Control, protection and interlocking circuits |
| Operating and maintenance manual | Operation, interlocks and maintenance |
An internal arc classification is only as good as the type test behind it, and it applies to the tested configuration. Ask for the report that matches the arrangement offered.
What we need to quote accurately
| 01 | Whether the station will be adopted by the network operator, and the operator's name |
| 02 | Transformer rating and the primary and secondary voltage |
| 03 | Medium voltage configuration: ring main unit functions or panel schedule |
| 04 | Low voltage distribution: incomer rating, number and size of outgoing ways |
| 05 | Enclosure type and whether it is operated from outside or from an internal aisle |
| 06 | Site access for delivery and lifting, and the foundation arrangement |
| 07 | Metering position and any network operator requirement |
| 08 | Quantity, destination, required delivery date and acceptable condition |
Delivery and logistics
Distribution equipment is heavy, and a delivery date is only real once the site is ready for it. The dimensions and weight of the unit offered decide the vehicle, the lifting equipment and the route to the foundation, and they come from the manufacturer's drawing rather than from the rating.
Liquid immersed transformers are usually shipped filled, which affects transport rules and the handling on arrival. Anything crossing a border also carries customs documentation, and where the destination applies its own conformity or energy efficiency rules the paperwork has to match that market rather than the country of manufacture.
Lead times vary widely with rating, specification and manufacturer loading. We state a delivery basis in each quotation for the specific unit offered and do not publish a general lead time we cannot hold.
Related
Request a quote for this equipment
Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.