In considering the status of the synchroscope pointer as shown in figure "B" of the illustration, at what point should the circuit breaker for the incoming machine be closed if paralleling manually? See illustration EL-0053.
• Synchroscope pointer position in relation to phase angle (12:00 vs 6:00 = what does that mean electrically?) • Effect of pointer speed and direction on frequency difference between bus and incoming generator • Requirement for voltage, frequency, and phase to match closely when closing the breaker while paralleling generators
• When the two machines are in phase (their voltage peaks line up), where should the synchroscope pointer be on the dial? • If the incoming machine is just slightly faster than the bus, how will the pointer move, and why is a slow movement preferred to a rapid one? • What mechanical and electrical stresses could occur if you close the breaker when the phase angle error is large or changing very quickly?
• Identify which clock position represents zero phase-angle error between bus and incoming machine on the synchroscope face • Determine which pointer motion (fast vs slow, direction) indicates a small, safe frequency difference just before closing • Eliminate any choices that involve closing the breaker with the pointer near maximum phase error (180° out of phase) or rotating very rapidly
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