🔍 Key Concepts

• Paralleling AC generators and matching conditions (voltage, frequency, phase) • Effect of slight frequency difference between the incoming machine and the bus on power flow direction • What happens if the incoming generator frequency is higher or lower than the bus at the instant of closing the breaker

💭 Think About

• Think about which way real power will initially flow if the incoming generator’s speed/frequency is slightly higher or lower than the bus when you close the breaker. • Consider what condition you want at the instant of closing the breaker: do you want the incoming machine to immediately pick up load, lag behind, or bang into the system? • How would ‘much greater’ or ‘much less’ frequency affect mechanical and electrical stress when synchronizing?

✅ Before You Answer

• Make sure you understand that bus frequency is the frequency of the already-running online generators. • Recall that for proper synchronizing you generally want same voltage, same frequency, and phase alignment just before closing the breaker. • Eliminate any options that would clearly cause a large power surge or mechanical shock when the breaker is closed.