What condition is required when connecting multiple generating facilities in parallel?

What condition is required when connecting multiple generating facilities in parallel?

• A. The load currents must be in phase
• B. The frequencies must be in sync
• C. The voltage must be equal
• D. The angle of rotation must be in unison

Answer: (D)

When connecting multiple generating units in parallel, they must act as one source through synchronization. The key part is aligning their internal voltages so they share the same instantaneous phase, which means the rotor angles of the machines are in step with each other. If the angles aren’t in unison, circulating power flows between the machines instead of delivering power to the load, causing mechanical stress and potential instability. Keeping the rotor angles synchronized ensures the machines share load smoothly and run at the same speed, with voltages and frequencies matched. That alignment—the angle of rotation being in unison—is the essential condition for safe parallel operation.

When connecting multiple generating units in parallel, they must act as one source through synchronization. The key part is aligning their internal voltages so they share the same instantaneous phase, which means the rotor angles of the machines are in step with each other. If the angles aren’t in unison, circulating power flows between the machines instead of delivering power to the load, causing mechanical stress and potential instability. Keeping the rotor angles synchronized ensures the machines share load smoothly and run at the same speed, with voltages and frequencies matched. That alignment—the angle of rotation being in unison—is the essential condition for safe parallel operation.