Which statement best describes the ventilation openings calculation for transformers rated over 50 kVA?

Which statement best describes the ventilation openings calculation for transformers rated over 50 kVA?

• A. Square inches per kVA less the area for grates
• B. Square inches per kVA plus the area for grates
• C. Square centimeters per kVA minus the area
• D. Square inches per kV

Answer: (A)

Ventilation openings for transformers above 50 kVA are based on the transformer's rating in kVA, using a standard square inches per kVA requirement, but you must subtract the area taken up by grates to get the actual open area available for air flow. In other words, you compute the gross required opening as square inches per kVA times the kVA rating, then reduce that by the grate area to get the net ventilation area. The option that states square inches per kVA minus the area for grates reflects this net calculation. Using plus would overstate the requirement, using square centimeters per kVA uses a different unit, and per kV refers to voltage rather than kVA rating.

Ventilation openings for transformers above 50 kVA are based on the transformer's rating in kVA, using a standard square inches per kVA requirement, but you must subtract the area taken up by grates to get the actual open area available for air flow. In other words, you compute the gross required opening as square inches per kVA times the kVA rating, then reduce that by the grate area to get the net ventilation area. The option that states square inches per kVA minus the area for grates reflects this net calculation. Using plus would overstate the requirement, using square centimeters per kVA uses a different unit, and per kV refers to voltage rather than kVA rating.