When paralleling two alternators the synchronizing lamps grow dim and are totally darkened as the synchroscope pointer approaches the 0° position. What does this indicate?
• Paralleling alternators – voltage, frequency, and phase relationship • How synchronizing lamps behave when two voltages are in phase vs out of phase • What the synchroscope pointer at 0° actually represents
• Think about what it means electrically when all three lamps go dark at the same instant as the pointer reaches 0°. • Consider the relationship between relative phase angle and brightness of the lamps: when are they bright and when are they dark? • Ask yourself: what condition must exist between the incoming alternator and the bus for the synchroscope pointer to be steady at 0° with no lamp flicker?
• Verify what 0° on the synchroscope indicates about the phase relationship between the incoming machine and the bus. • Confirm what dark lamps (all simultaneously) indicate about the phase difference between the two voltages. • Make sure the condition described matches safe paralleling conditions: correct voltage, frequency, and phase sequence.
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