Detecting Phase sequence with light bulbs/ Short circuit voltage

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Connecting light bulbs in series with a circuit resistor when detecting phase sequence is important to ensure varying brightness, indicating phase differences. In the case of a short circuit in phase "A," the short circuit voltage is typically larger in a four-drive system compared to a three-drive system. The four-drive system is generally more expensive than the three-drive system. Understanding these concepts is crucial for effectively synchronizing a three-phase synchronous motor with the mains. Proper phase detection and circuit design are essential for reliable motor operation.
ESSVE
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Homework Statement


1) If one is using light bulbs to detect phase sequence then it is wise to connect them in series with circuit resistor. Why ?

2) There is short circuit in phase "A". In which case is short circuit voltage larger, in four-drive (?) system or in three-drive (?) system ? Which system is cheaper ?

The Attempt at a Solution



1) Because otherwise light bulbs would have same brightness ?


Any help would be much appreciated.
 
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Hi ESSVE. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

(1) probably is referring to using light bulbs as an indicator of phase difference when trying to synchronize a 3 phase synchronous motor with the 3 phase mains.

(2) probably refers to there being a short-circuit in phase A winding of a motor. But I don't understand the rest of the question.
 
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