How to Choose CRGO Grades for Transformer Cores

CRGO grade selection starts with the efficiency class, not the price list. A lower-loss grade reduces no-load loss but costs more per tonne and can be less forgiving in a core line that is not set up for thin material.

Start with the loss budget

Calculate the allowed no-load loss from the transformer rating and the target efficiency class. Then add the building factor — the increase in loss caused by cutting, stacking and joints. A 10–15% building factor is common, but it depends on the core design and line quality.

Match thickness to the process

Thinner material lowers loss but increases handling difficulty. If the slitting and cutting line is not equipped for 0.23 mm strip, a 0.27–0.30 mm grade may deliver a better real-world result even though its datasheet loss is higher.

Check the coating and annealing route

C5 coating is standard for most oil-immersed cores. If the core will be stress-relief annealed, confirm that the coating and the annealing temperature are compatible. For wound cores, the annealing contract matters as much as the steel grade.

Document the choice

Record the grade, mill certificate, measured core loss and building factor assumption in the design file. When a type test or a customer audit arrives, that record is the difference between a quick answer and a week of searching.