# Help on (another) triphasic exercise

Second this week... But was it easy I wouldn't be here...

A problem asked me to identify the diagrams from this picture:

The following are the correct answers, acording to the test developers.

a. The first diagram may represent the voltage over the load of a 4-wire Unbalanced Star.

b. The first diagram may represent the voltage over the load of a 3-wire Balanced Star.

c. The second diagram may represent the voltage over the load of a 3-wire Balanced Star.

d. The second diagram may represent the voltage over the load of an Unbalanced Delta

Again: all the above assertions are to be taken as true

I need help understanding these truths/assertions.

• As far as I know, the line voltage is 30 degrees ahead of the phase voltage on a star connection (a neutral wire enforces this in case one of the impedances is not equal)

This knowledge matches the a. and b., but doesn't seem to my eyes to make sense for c.. How is the assertion c. possible ?

• As far as I know, the line and phase voltages on deltas are equal, with No angle between them. But that wouldn't match assertion d. How is such assertion possible ?

Maybe the trick is in the distinction between load and source...

Who has the patience for this ? If I think any longer I lose my sanity

This is an adaptation of the actual question. The original is longer and not in english. Here, question number 29: https://arquivo.pciconcursos.com.br/provas/21572117/1fc8bd07ea0/tecnico_eletrotecnica.pdf

*I believe the D letter in the diagram is a typo

• show source in references Dec 11, 2019 at 19:44
• If the source of the question is what you mean, I've added now the link at the bottom. Dec 14, 2019 at 22:10
• According to that ...d. (X) Only statements 2 and 4 are correct. or your b),d) Dec 14, 2019 at 22:16
• Not the case. It's hard to see without a translator, but each of the statements (number 2 and 4) from the PDF have two assertions within (total of 4 assertions then). They are badly mixed, and separated only by a comma. In my translation, I've separated in a. b. c. d. (I also changed the order, or else it would be a mess if I simply "carried" the sentences here) Dec 15, 2019 at 2:19
• It's quite a hard question. Maybe because of how it was written, maybe because of my adaptation, which was made with the best of my ability. It's a question taken from a difficult test, meant to be difficult. I called a bounty, but don't burn your brains like I did. Dec 15, 2019 at 2:26