7 Tests Every Nigerian Facility Should Do Before Accepting a New Transformer

A new transformer is a large investment, and it often travels a long way, by sea, by road and over rough site access, before it reaches your substation. Damage in transit, wrong specifications and manufacturing defects all happen. Testing on site before acceptance protects you: if something is wrong, it is found while the supplier is still responsible.

Before testing: inspect on delivery

Check the transformer the day it arrives: rating plate against your order, tank and radiators for dents, bushings for cracks, oil leaks, and any impact recorder fitted for transport. Note any damage on the delivery documents before signing.

1. Insulation resistance (IR) and polarisation index (PI)

Measures the insulation between windings and from windings to earth. Low values can mean moisture got in during transport or storage.

2. Turns ratio (TTR)

Confirms the voltage ratio on every tap position matches the rating plate, and that no turns are shorted.

3. Winding resistance

Measured on every phase and tap. The phases should be balanced. An imbalance points to a loose internal connection or a tap changer problem.

4. Vector group and polarity

Confirms the transformer is connected as specified, for example Dyn11. A wrong vector group causes serious problems if the transformer is ever paralleled with another.

5. Transformer oil tests

Breakdown voltage and moisture content confirm the oil arrived in good condition. A dissolved gas analysis gives a baseline to compare against in future years.

6. Magnetising (no-load) current

Measured at low voltage on each phase. The pattern between phases helps show the core and windings are healthy, and gives a reference for future tests.

7. Protection and accessories

Function-test the Buchholz relay, oil and winding temperature indicators and trips, pressure relief device and any cooling fans. Check that every alarm and trip actually reaches the breaker.

Compare with the factory test report

Every new transformer should come with a factory test report. Site results should be consistent with it. Large differences need an explanation from the supplier before you accept the unit.

Keep the results

Acceptance test results are the baseline for the life of the transformer. When you test again in a year, or after a fault, you compare against them. Read our transformer maintenance and testing guide for what to check after installation.

Talk to Corustar

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