In a transformer, the VA rating on the primary is equal to the VA rating on the secondary.

In a transformer, the VA rating on the primary is equal to the VA rating on the secondary.

• A. False
• B. True
• C. Sometimes
• D. Not applicable

Answer: (B)

A transformer's rated apparent power is the same on both windings because the same VA is transferred from the primary to the secondary during rated operation. In an ideal transformer, Vp × Ip equals Vs × Is, since Vs = Vp × (Ns/Np) and Is = Ip × (Np/Ns). When you multiply voltage and current for each side, you get Vp × Ip = Vs × Is, so the VA rating matches on primary and secondary. In real transformers there are losses (copper, core), so efficiency is not 100%, but the nameplate VA rating is the maximum each winding can safely handle, meaning both windings are designed for the same apparent power.

A transformer's rated apparent power is the same on both windings because the same VA is transferred from the primary to the secondary during rated operation. In an ideal transformer, Vp × Ip equals Vs × Is, since Vs = Vp × (Ns/Np) and Is = Ip × (Np/Ns). When you multiply voltage and current for each side, you get Vp × Ip = Vs × Is, so the VA rating matches on primary and secondary. In real transformers there are losses (copper, core), so efficiency is not 100%, but the nameplate VA rating is the maximum each winding can safely handle, meaning both windings are designed for the same apparent power.