Question 1

What is a K-factor transformer, and does my plant need one?

Accepted Answer

A K-factor transformer is rated for the additional heating caused by harmonic-rich, non-sinusoidal loads — such as VFDs, servo drives, and other electronic equipment — on a scale from K-4 to K-50. If non-linear loads make up more than 20–25% of your facility's total load, you should specify at least a K-13 rated transformer; heavier concentrations of drives and rectifier equipment often call for a higher rating.

Question 2

What K-rating do I need for VFD-heavy loads?

Accepted Answer

It depends on what share of your total load is non-linear. As a general guideline, facilities with non-linear loads above 20–25% of total load should specify K-13 or higher; heavy industrial sites with extensive VFD, servo, and rectifier equipment often require ratings further up the K-4 to K-50 range. Talk to our engineering team about your specific load profile.

Question 3

Dry-type vs. oil-filled for factories?

Accepted Answer

Dry-type (cast-resin/VPI) construction is the standard choice for indoor plant distribution — it removes oil handling and its associated fire and maintenance burden from the plant floor, while offering low-maintenance operation suited to a continuous production environment.

Question 4

How do harmonics affect transformer sizing?

Accepted Answer

Non-linear loads like VFDs, servo drives, and rectifiers draw current in non-sinusoidal pulses rich in 5th, 7th, 11th, and 13th harmonics, which increases eddy-current losses in the windings and core beyond what a standard-duty transformer is designed to dissipate. Sizing must account for K-factor rating and, per UL 1561, an oversized neutral conductor (200% of full-load current) to handle harmonic neutral currents from single-phase electronic loads.

Question 5

Indoor vs. outdoor for plant distribution?

Accepted Answer

Indoor plant floor distribution is typically handled with dry-type transformers for their oil-free, low-maintenance profile. Outdoor site-level and substation distribution for larger industrial campuses uses pad-mounted or high-voltage power transformers, depending on site scale and voltage requirements.

Industrial Transformers | Manufacturing Plants | Seatrust