Broken neutral on unbalanced 3 phase system

[alhambra]

Three 277volt single phase resistive loads 20ohm 40ohm and 60ohm are powered from a 480volt Y 4 wire supply. What would be the phase voltages on the three loads if the supply neutral to ground connection was interrupted. What would be the neutral voltage.

 

[jim dungar]

This sounds like a question on a test?

What answers have you come up with so far? What area are you having trouble with?

 

[dbuckley]

Is part of that question not a 'trick' question...?

 

[charlie b]

. . . if the supply neutral to ground connection was interrupted. What would be the neutral voltage.

(1) Interrupted in what way?

(2) What do you mean by "neutral voltage" (i.e., voltage from what point to what other point?

(3) Have you ever worked with the analytical technique called "Symmetrical Components"?

 

[alhambra]

This is not a trick question but from a practical utility test. This situation arises when the connection between the utility transformer neutral to the ground electrode is broken and so the neutral is floating. The neutral bonding at the consumer is also broken. Because the loads are unbalanced at least one of the phase voltages experiences a voltage rise that can be as high as line voltage and the neutral is no longer at zero volts. The question is how to quantify that voltage rise and neutral voltage.I am familiar with symmetrical components but the only application I know is to short circuits. I have never seen a sequence diagram for such a situation.