11 kV or 33 kV Supply? What Nigerian Businesses Should Know Before Applying to Their DisCo

Once a business outgrows a low-voltage connection, the next step is to take supply at medium voltage through its own transformer. In Nigeria that usually means 11 kV or 33 kV from the local distribution company (DisCo). The choice affects your equipment cost, your reliability and how easily you can expand later. Here is what to think about before you apply.

Who needs a medium-voltage supply?

Factories, large commercial buildings, hospitals, hotels and estates usually need more power than a low-voltage service can provide. With their own transformer, they take supply at 11 kV or 33 kV and step it down to 415 V on site. They then own and maintain the substation equipment on their side of the connection.

11 kV vs 33 kV: how they compare

Load size

11 kV suits most commercial buildings, estates and medium factories. Larger industrial loads, or sites planning major growth, may be better served at 33 kV, which carries more power on the same current.

Availability at your location

What matters most in practice is which network is near your site and how much spare capacity it has. Ask your DisCo early which feeder can supply you, at which voltage, and how reliable that feeder has been.

Reliability

Feeders differ widely. A dedicated or less heavily loaded feeder can give far better supply hours than a busy shared one. For critical sites, ask about a second supply or plan for generator backup sized to your essential load.

Equipment cost

33 kV switchgear, cables and transformers generally cost more than 11 kV equivalents, and need greater clearances. That extra cost can be justified for large loads or when 11 kV capacity is not available.

Future expansion

Size the transformer, switchgear and cables with your growth plans in mind. Upgrading a substation later is far more expensive than allowing spare capacity now.

What to prepare before you apply

• A load assessment showing current and future demand. See why load assessment matters.
• A single-line diagram of the proposed substation: incoming switchgear or RMU, transformer, LV switchboard and metering.
• Equipment specifications for the transformer, switchgear and cables.
• Substation location and access, with space for safe clearances and maintenance.
• An earthing design for the substation.

Requirements and procedures vary between DisCos, so confirm what documents, inspections and approvals your DisCo needs before you buy equipment.

Typical customer substation

• An RMU or VCB panel to connect to the DisCo feeder and protect the transformer
• A distribution transformer, for example 11/0.415 kV or 33/0.415 kV
• An LV main switchboard with incomer ACB and outgoing feeders
• A changeover or ATS for generator backup
• Metering as required by the DisCo

Commissioning matters

Before energising, the switchgear, transformer and cables should be tested: insulation resistance, pressure or VLF testing of cables, transformer ratio and winding tests, and protection relay injection. Read more in our guide to planning HV switchgear installations.

Talk to Corustar

Corustar Technological Services is an electrical engineering contractor based in Ikeja, Lagos, working across Nigeria. See our HV/LV Switchgear Maintenance & Commissioning service, request a quote, or call +234 816 976 9672. For outages and faults, call our 24/7 emergency line on 0705 739 9297.