Should transformers be included in a data centre thermography survey?

Yes, the parts that can be safely seen under load. That means the LV cable box and tails, the busbar or cable link to the main switchboard, and the outside of the tank or enclosure. HV compartments are not opened live, and thermography does not replace oil analysis or the transformer’s own protection checks. Readings are taken at normal load and compared like for like.

Why transformers belong in scope

Every critical path in a data centre starts at a transformer. A survey that begins at the LV main switchboard leaves out the connections that carry the full load of that side of the site: the LV tails or busbar link from the transformer to the incomer. Those joints are as much a part of the power path as anything in the switch room (see whole power path, intake to rack).

What can be imaged live

LV cable box and tails, where the site’s authorised person can open the cover safely, or through an infrared window if one is fitted.
The busbar link or cable run from the transformer to the LV main switchboard incomer.
The outside of the tank, radiators and fins on oil-filled units, looking for an uneven pattern from one side or section to another.
Cast resin (dry-type) units, through the enclosure’s viewing points or mesh where the site permits, without opening the enclosure live.
Auxiliary supplies: cooling fan controls, marshalling boxes and the small boards around the transformer.

What stays outside the survey

HV cable boxes and HV switchgear compartments are not opened under load. Where the transformer belongs to the network operator, it is their equipment and their access rules apply. Thermography also does not tell you what is happening inside the windings or the oil. A tank surface reading is a surface reading, not an internal temperature, and it is reported that way. Oil sampling and the transformer’s temperature and protection devices are separate checks carried out by the HV specialist.

Traps a good thermographer avoids

A transformer runs warm by design. A warm tank is not a finding. What matters is a difference between matching parts: phase to phase on the LV tails, one radiator section against the next.
Sun and weather on outdoor units. Solar gain on one face of a tank can look like a hot spot. Outdoor transformers are best imaged after dark or on an overcast day (see outdoor equipment in UK weather).
Shiny metal and enclosure panels reflect heat from elsewhere. Readings are taken on painted or oxidised surfaces, and any reading on bare metal is noted as a limitation.
Light load. On a 2N site each transformer may carry well under its rating. The report records the load at the time so the next survey can be compared fairly (see enough load on a 2N site).

What the report gives you

A same-day report that locates each finding by transformer, termination and phase, with the measured temperature, where it was taken, the difference in °C from the matching reference and the load at the time. Ti inspects and reports. The site’s HV or electrical contractor investigates any finding with the equipment isolated and carries out the work.

Proof from the same power path

Joints downstream of the transformer are where load shows up problems. On a London data centre build, commissioning thermography by our team found 16 busbar sections reading above 80 °C under test load, the highest 103.5 °C at a tap-off unit, all located and imaged before handover (see busbar thermography at commissioning).

Frequently asked questions

Does the transformer need to be switched off for the survey?

No. Thermography needs it energised and on load. Only parts that can be safely seen live are imaged.

Can thermography replace oil analysis?

No. They look at different things. Thermography shows heat at connections and surfaces; oil analysis looks at the condition inside the tank.

How often should transformers be surveyed?

Most sites include them in the annual survey of the critical power path, and again after a significant load increase.