Phase angle shift

[rg1]

This question I found in Chapman. I think the question is wrong? It should be -Line Voltage on Primary side lags the Line Voltages of Secondary? As comments?

 

[TNPE]

No, it's correct.  You're dealing with voltages here, not currents.  Now, had it been worded in terms of asking for proving the currents, then it would be lagging. Draw it out and it'll make sense.   

Use this to get started:

VAB=VA-VB 

Plug and chug along and make substitutions and simplifications where needed (ideally, convert VB angle to (-1/2 + j(sqrt3/2))and you will find it to be:

(sqrt 3)V/_+30