Some transformer problems look like load issues. Others look like insulation fatigue. But underneath both, the real cause may sit quietly in the background: poor power factor.
Many industrial units run well below nameplate load yet show signs of heating. The mismatch often comes from reactive power inflating the current draw.
This wears down transformers in ways that are slow, silent, and easy to miss until failure hits.
Here’s how poor power factor changes transformer stress patterns (and what that means for long-term reliability).
Transformers serve both active and reactive power. So, when the power factor drops, total current rises, even if the useful power stays the same.
The effect shows up as extra current flow through windings, leading to unnecessary I²R losses.
This additional heating creates subtle but repeated strain on the insulation near terminals and leads.
Unlike a surge or overload, this doesn’t trip alarms. But you’ll notice higher surface temperatures and uneven ageing across coils. Over time, this raises the risk of partial discharge or tap changer wear.
Low power factor can distort the transformer’s thermal profile. The increased current doesn’t spread evenly. Some windings absorb more heat than others, depending on the coil design and how the current flows.
In many field inspections, the earliest signs show up as varnish discolouration or dry-band tracking near neutral points. These patches become hotspots under fluctuating load.
If left unchecked, the transformer develops uneven ageing across its phases, even when the apparent load looks balanced on paper.
When power factor stays low, you start using up transformer capacity faster than expected. Even moderate loads draw higher current, pushing the unit closer to its thermal and dielectric limits.
This often causes teams to assume they need a larger unit or more frequent cooling interventions. But the underlying issue is reactive current eating into the usable margin.
Instead of overbuilding, fixing the power factor helps recover capacity that’s already there, just underutilized due to poor correction.
Power factor problems creep into the maintenance cycle. Higher current flow increases contact stress at bushings and tap changers. Pressure relief devices may activate more frequently due to oil expansion.
In capacitor-supported systems, a mismatch between load profile and correction capacity can result in switching surges. These impact both the transformer and the correction unit itself.
Most of these symptoms are manageable, but only if teams notice the pattern. Otherwise, they get logged as unrelated issues.
Power factor may look like a billing issue on the surface, but it tells a deeper story inside the transformer.
Many of the service cases we’ve handled for overheating or derating have had low correction ratios behind them.
Our field teams routinely evaluate these patterns during transformer upgrades or rental deployments. When current levels appear high for the load served, power factor correction becomes part of the discussion.
You can always reach out to us if you're seeing heating patterns that don't match your actual load. It might be time to look past the numbers and check the power quality behind them.
