If the regulatory tap setting on a single-phase transformer shifts from 100% to 97.5%, what happens to the secondary voltage?

If the regulatory tap setting on a single-phase transformer shifts from 100% to 97.5%, what happens to the secondary voltage?

• A. It will remain the same and available power will decrease
• B. It will increase
• C. It will decrease
• D. It will remain the same and available power increases

Answer: (B)

A regulator tap changes the effective number of turns on a winding, altering the voltage relationship between primary and secondary. For a transformer, the secondary voltage is Vs = (Ns/Np) × Vp. Moving the primary tap from 100% to 97.5% reduces the number of primary turns (Np decreases). With the same applied primary voltage, the turns ratio Ns/Np increases, so the secondary voltage rises. In short, lowering the tap raises the secondary voltage. The transformer’s kVA rating doesn’t change with tap settings; only the voltage changes.

A regulator tap changes the effective number of turns on a winding, altering the voltage relationship between primary and secondary. For a transformer, the secondary voltage is Vs = (Ns/Np) × Vp. Moving the primary tap from 100% to 97.5% reduces the number of primary turns (Np decreases). With the same applied primary voltage, the turns ratio Ns/Np increases, so the secondary voltage rises. In short, lowering the tap raises the secondary voltage. The transformer’s kVA rating doesn’t change with tap settings; only the voltage changes.