When paralleling a second generator online, why must the frequency of the oncoming generator be slightly higher than the primary?

When paralleling a second generator online, why must the frequency of the oncoming generator be slightly higher than the primary?

• A. To prevent motorization
• B. To ensure equal load sharing
• C. To avoid backfeed
• D. To stabilize voltage

Answer: (A)

When two generators are put in parallel, they must synchronize in speed, voltage, and phase. If the incoming unit is at a frequency slightly higher than the running unit, it is naturally moving faster and will tend to push power into the bus once connected. The governor then slows it down to match the bus frequency, so power flows from the oncoming generator to the system rather than the system forcing the new generator to run as a motor. This helps prevent the new generator from being driven by the load or the grid, which could cause motorization of the machine. Once synchronized, proper droop sharing and voltage regulation take over to share load and stabilize the system.

When two generators are put in parallel, they must synchronize in speed, voltage, and phase. If the incoming unit is at a frequency slightly higher than the running unit, it is naturally moving faster and will tend to push power into the bus once connected. The governor then slows it down to match the bus frequency, so power flows from the oncoming generator to the system rather than the system forcing the new generator to run as a motor. This helps prevent the new generator from being driven by the load or the grid, which could cause motorization of the machine. Once synchronized, proper droop sharing and voltage regulation take over to share load and stabilize the system.