When selecting a transformer, a customer needs to understand very clearly the issues relating to the load that the transformer will supply or be supplied by.
Unfortunately, with today’s modern grid there is no such thing as a perfect load. Power electronics, as well as many other switching electronics, have contributed to non-sinusoidal waveforms, and hence harmonics. The Total Harmonic Distortion (THD(i)) that a transformer encounters significantly influences the design of that transformer.
For instance, a transformer designed for standard distribution loads allows for a THD(i) of no more than 5%. A THD(i) of ≤5% is appropriate for today’s general distribution loads. When the rating becomes closer to ≤1%, the transformer is effectively being rated for an ideal grid solution.
The THD(i) of a transformer can have a significant impact on the overall price of the transformer. This is due to differences in construction such as core designs, electrostatic shield and winding construction.
The effects of harmonic distortion on a transformer is additional heat hot spots within the core caused by eddy currents. This can lead to insulation breakdowns between the core laminates and eventually the complete failure of the transformer.
The windings can also be expected to see additional heating as well as encounter higher peak voltages, which could lead to interturn winding failures if the insulation system is not appropriate.
This is further exacerbated by loads, such as data centres and supplies and such as solar, which can have extremely high harmonic distortions, sometimes as high as 73%.
