Distribution transformers for Nigeria

Nominal voltages in the NERC Distribution Code

Distribution companies (DisCos) are licensed to distribute on networks from 240 V up to 33 kV. The Rural Electrification Agency’s technical standards give the system frequency as 50 Hz ± 1 %.

What the REA standards say about distribution transformers

The Rural Electrification Agency (REA) harmonised technical standards, version 2.0 of July 2025, state for distribution transformers:

• New equipment only; the minimum rating for a distribution transformer is 200 kVA
• Single-phase or three-phase; three-phase units use vector group Dyn11
• Transformer windings of copper
• Transformers approved as ISO compliant
• 11 kV / 400 V and 33 kV / 400 V substations are both described

NEMSA inspection before the installation is energised

The Nigerian Electricity Management Services Agency (NEMSA, NEMSA Act 2015) states that no electrical installation may be put into use or connected to the public supply network unless it has been tested, inspected and certified by a NEMSA electrical inspector.

In practice the transformer is inspected as part of the installation. Ask your DisCo or contractor which factory test reports the inspector wants to see, and include that in your enquiry.

SONCAP: Product Certificate and SONCAP Certificate

• SONCAP is the Standards Organisation of Nigeria (SON) conformity assessment programme for regulated imports. The SONCAP Certificate (SC) is a mandatory customs clearance document, and the Product Certificate is needed to open Form M.
• Route A (Product Certificate 1, unregistered): valid for one shipment only. Route B (Product Certificate 2, registered) and Route C (Product Certificate 3, licensed): valid for one year.
• The Product Certificate is issued after testing and assessment by a SON-appointed accredited firm. The firm issues a Certificate of Conformity, and SON then issues the SONCAP Certificate for that shipment.
• The SC is issued per consignment, so the process repeats for every shipment. Test reports from an ISO/IEC 17025 accredited laboratory are accepted for Route A.
• Non-conforming goods attract a SONCAP default charge of 20 % of CIF value or ₦2 million, whichever is higher.
• Check with your clearing agent or SON whether your transformer’s tariff heading is on the SONCAP regulated list before you fix the delivery plan.

What our published ratings cover

• Oil-immersed S11, 10 / 11 kV class (IEC 60076, 50 Hz): 415 V is among the published low-voltage options; Dyn11 is a published vector group; tapping ±2 × 2.5 %; ratings from 30 to 4,500 kVA. Nigeria’s 50 Hz is the frequency of the loss values published on this site.
• 33 kV: compact substations (YBW, 50–2,500 kVA, 11 and 33 kV among the published voltages, 415 V among the published low-voltage options). Loss tables for 33 kV oil-immersed distribution transformers are not published here; they are quoted on request.
• 33 kV / 11 kV substation transformers: the power transformer line lists 33 kV primary and 11 kV secondary, 5,000–31,500 kVA. Vector group is on request.
• SONCAP certificates and the test reports your inspector needs: on request, per order.

Send with your enquiry

• DisCo or project, site location, and whether NEMSA inspection is already scheduled
• Rated power (kVA), HV (11 or 33 kV) and LV (415 V), vector group, tapping range
• Type: oil-immersed, compact substation or dry-type; pole, pad or indoor
• SONCAP route (A, B or C) and the tariff heading shown on your Form M, if you have it
• Quantity and required delivery date