Transformer ventilation openings for transformers rated over 50 kVA are calculated at how many square inches per kVA, less the area for grates?

Transformer ventilation openings for transformers rated over 50 kVA are calculated at how many square inches per kVA, less the area for grates?

• A. 2 sq in per kVA
• B. 4 sq in per kVA
• C. 3 sq in per kVA
• D. 1 sq in per kVA

Answer: (C)

Ventilation openings for transformers over 50 kVA are sized by the transformer's rating, using 3 square inches of opening per kVA to ensure adequate cooling. Any grate or screen reduces the actual free opening, so you subtract its area from the total calculated opening to get the net vent area. For example, a 75 kVA transformer would require 225 square inches of opening (3 × 75). If the grates occupy 40 square inches, the net ventilation area is 225 − 40 = 185 square inches. This is why 3 square inches per kVA, less the area for grates, is the correct approach.

Ventilation openings for transformers over 50 kVA are sized by the transformer's rating, using 3 square inches of opening per kVA to ensure adequate cooling. Any grate or screen reduces the actual free opening, so you subtract its area from the total calculated opening to get the net vent area.

For example, a 75 kVA transformer would require 225 square inches of opening (3 × 75). If the grates occupy 40 square inches, the net ventilation area is 225 − 40 = 185 square inches. This is why 3 square inches per kVA, less the area for grates, is the correct approach.