Detecting Phase sequence with light bulbs/ Short circuit voltage

[ESSVE]

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.

 

[NascentOxygen]

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.