Which of the following problems will occur if the circuit breaker of the incoming alternator is closed and it is 180° out of phase with the loaded alternator when paralleling?
• Paralleling alternators: what it means for voltage, frequency, and phase angle to match before closing the breaker • Phase angle difference: what happens electrically when two AC sources are exactly 180° apart • Circulating (cross) currents between alternators when not properly synchronized
• Picture the voltage waveforms of the two alternators: what is the instantaneous voltage of one machine compared to the other when they are 180° out of phase? • If one alternator’s voltage is at a positive peak and the other is at an equal negative peak at the instant you connect them, what must the current between them look like? • Which of the options describes an immediate electrical effect at the moment of closing, rather than a slow or mechanical behavior over time?
• Verify which choice describes very large instantaneous currents due to opposing voltages. • Check which options describe mechanical symptoms (like hunting or stopping) versus a direct electrical fault condition. • Confirm that properly paralleled alternators cannot remain steadily 180° out of phase and still share load in a normal way.
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