Question

A synchronous generator is feeding power to infinite bus bars at unity power factor. Its excitation is now increased. It will feed
1. The same power but at a leading power factor
2. The same power but at a lagging power factor
3. More power at unity power factor
4. Less power at unity power factor

Answer 1

Correct Answer - Option 2 : The same power but at a lagging power factor

• A synchronous generator is feeding power to infinite bus bars at unity power factor. Its excitation is now increased. It indicates that the generated is over-excited.
• An overexcited alternator always supplies lagging current to the connected load, which means that load is of lagging nature.
• Lagging load takes active and reactive power from the supply or alternator. Therefore, reactive power flows outwards from an over-excited alternator.

Important Points:

• Under excited alternator works at the leading power factor
• The normally excited alternator works at the unity power factor
• The overexcited alternator works at lagging power factor

For Synchronous motor its opposite of alternator,

• Under excited synchronous motor works at lagging power factor
• The normal excited synchronous motor works at the unity power factor
• The overexcited synchronous motor works at a leading power factor