How does an MV substation project come together?
Every decision depends on the one before. The load estimate sets the number and size of transformers. Their size sets the RMU transformer feeders (fuse or breaker), the LV fault level and the LV board rating. The ring capacity the utility wants sets the MV cable size. The equipment sets the room size, ventilation and access, and the room and approvals usually set the date the building gets power. Running these together, instead of in separate silos, is what keeps a project on time.
PractitionerFreeze the substation location and room size early with the architect and the utility. Track long-lead items (transformers, RMUs, LV boards) from the first design stage, and get the utility's ring cable size and route before the civil design is fixed.
What goes into the cost?
- Equipment: RMU, transformers, LV main board, MV and LV cables and terminations.
- Civil and building works: room, trench, plinths, doors, louvres, fire rating.
- Earthing, testing and commissioning.
- Utility connection charges and fees, which are often a large share and set by the utility.
ExpertAdd the cost of losses (MV-504) to the transformer comparison. Over 25 years, the present value of losses for a large transformer can be similar to its purchase price, which often justifies a lower-loss unit.
Regional notes
GCC
Utilities often supply and install the RMU and transformers, so the developer's BOQ may cover only the room, LV board and connection charges. Check the utility's scope split.
Australia and New Zealand
Contestable works may be built by accredited contractors and handed over, so the developer's scope can include the MV equipment and cables.
Asia
Scope splits and charges vary by utility. Check whether the utility or the developer supplies the switchgear and transformers.