The recent upgrade of a data centre in Nigeria required a custom-engineered dry-type transformer solution designed to manage high levels of voltage fluctuations.

In addition, the high level of total harmonic distortion related to data centres meant the transformer had to be designed according to K-factor 13 to ensure maximum reliability and to compensate for the additional heat caused by the harmonics, as well as the associated voltage distortion.

“In the context of an unstable power supply, this application required an unusual but effective solution,” explained Trafo Power Solutions MD David Claassen. “The challenge is that the voltage of the electrical supply in this area often fluctuates between plus and minus 10% of nominal voltage, so we designed our transformers to include an automatic on-load tap changer (OLTC).”

The fully integrated OLTC is installed on the transformer feet allowing voltage fluctuations to be sensed automatically. The secondary voltage of the transformer is adjusted accordingly by the OLTC, which ensures a stable secondary voltage reaches the data centre’s critical equipment. The design is intended to allow the transformer to correct up to 10% under-voltage and up to 10% over-voltage in the power supply in four equal steps.

“It is important to realise that this level of fluctuation – if not corrected – would be extremely detrimental to electrical infrastructure,” Claassen continues. “In fact, some equipment would experience catastrophic failure under these conditions.”

Included in the project scope was the control and protection of both the transformer and tap changer, as well as an automatic voltage regulator. The transformer supplied by Trafo Power Solutions is a 2 000 kVA unit which will step down the incoming voltage from 11 kV to 400 V. The company is also responsible for commissioning the solution on site.

“Cooling will be achieved in an air natural configuration, but fans have been included on the transformers to allow them to carry a 25% higher load, if necessary,” says Claassen. “The cooling aspect of the design is important in this context, as the higher harmonics can also lead to raised temperatures in the transformer.”

An electrostatic shield is included between the primary and secondary windings in this type of design to arrest any stray current that could be caused by the harmonic distortion.

Claassen adds that the company also offers modular solutions for data centres, allowing customers to gradually build up medium voltage infrastructure.