What is the purpose of the synchronizing check and which instruments are used?

• A. To align voltage, frequency, and phase before closing a breaker; instruments include voltmeter, wattmeter, and synchroscope (or synchronizing relay).
• B. To test performance under overload conditions; instruments include ammeter, voltmeter, wattmeter.
• C. To check rotor speed stability under dynamic load.
• D. To measure insulation resistance before operation.

Answer: (B)

Synchronizing check is done to ensure the generator is in step with the system before closing the breaker. You want the generator’s voltage to match the bus voltage, the frequency to match the system frequency, and the phase angle to be aligned. If these aren’t in sync, closing the breaker can cause a heavy circulating current and mechanical strain.

To perform this check, you use a voltmeter to compare voltages, a synchroscope (or a synchronizing relay) to observe and control the phase relationship, and a wattmeter to help confirm the correct power-flow relationship or assist with frequency indication. This combination—voltmeter, wattmeter, and synchroscope (or synchronizing relay)—is the standard set for synchronization.

The other descriptions don’t fit the purpose: testing under overload conditions uses current measurements and power readings to assess performance under high load, not the moment of connection; checking rotor speed stability under dynamic load focuses on governor response during transient events; and measuring insulation resistance is a safety/pre-start test, not part of synchronizing.