In an ideal transformer, the VA rating on the primary equals the VA rating on the secondary.

In an ideal transformer, the VA rating on the primary equals the VA rating on the secondary.

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

Answer: (B)

In an ideal transformer, power transfer is lossless, so power in equals power out. The VA rating is simply voltage times current on each winding. With Vp/Vs = Np/Ns and Ip/Is = Ns/Np, multiplying gives Vp·Ip = Vs·Is. That means the apparent power on the primary equals the apparent power on the secondary, so the VA rating is the same on both sides. In real transformers there are losses, but the design assumes the same VA rating for both windings at rated conditions.

In an ideal transformer, power transfer is lossless, so power in equals power out. The VA rating is simply voltage times current on each winding. With Vp/Vs = Np/Ns and Ip/Is = Ns/Np, multiplying gives Vp·Ip = Vs·Is. That means the apparent power on the primary equals the apparent power on the secondary, so the VA rating is the same on both sides. In real transformers there are losses, but the design assumes the same VA rating for both windings at rated conditions.