🔍 Key Concepts

• Parallel operation of alternators and how they share load based on prime mover input (mechanical power) • What happens to an alternator’s kW (real power) output when its driving torque is reduced while frequency and voltage are held by the bus • The difference between an alternator generating power vs motorizing (acting as a synchronous motor) when its mechanical input is too low

💭 Think About

• Think about what keeps an alternator in step with the other machines when they are all tied to the same bus. Can its speed (frequency) change much on its own? • If you keep the alternator connected to the switchboard, and you reduce the mechanical power from its prime mover, where does the electrical power to keep it spinning at system frequency come from? • At the moment where its mechanical input is less than its electrical output, is the alternator pushing power to the bus or is the bus pushing power into the machine?

✅ Before You Answer

• Verify that on a common bus, frequency and speed are effectively fixed by the system, not by one machine whose power is reduced • Check which option correctly describes a machine that is still synchronized to the bus but now has insufficient mechanical input, and what naturally happens in protection terms • Eliminate any option that implies the alternator can freely change speed/frequency while it remains connected in parallel to the other alternators