Three Phase System problem ... please help

[afesheir]

hi people ...
I have attached a problem that I tried to solve, but I want to make sure that my solution is true, also there is a mistake but I can't catch it.

The problem is in GIF format, so you can view it using ACDSee

 

[Nigel Goodwin]

At first glance (with no maths) I would assume they are both the same - and it's been FAR too long for me to even consider working it out!

 

[Gaston]

i would have to agree with nigel, it looks like there would be no difference

 

[afesheir]

thx

hay people ... someother body has solved this problem but instead of verifying the larger voltage drop, she verified the larger power and found that L2 will be brighter ...? but I think I should arrive the same result when verifing the voltage drop ... so where is the bug ?

 

[Sceadwian]

Something to do with the phase lag between the capacitor and the inductors and the natural phase of the system?

 

[afesheir]

there is no inductor, which one are you speaking about?

 

[Sceadwian]

Sorry, that's just my inability to read the diagram. I saw L1 and L2 and just asumed they were inductors. The capacitor is still going to cause a phase shift that's not going to be equal across the other two purely resistive phases.

 

[ClydeCrashKop]

I agree.
From an Onan book "The inductive reactance always causes the current to lag behind the voltage by 90 degrees." I seem to remember that capacitance is just the opposite.

 

[Sceadwian]

Exactly, my math SUCKS and so does my basic diagram reading skills, but that's what I was trying to get at =) Just to confirm I ran a simulation.

I ran a basic simulation with a three phase AC source each phase 120 degree out of phase A B C 0 120 240. A 10u capacitor on the A lead, and two 10 ohm resistors on each of the B and C leads, and the C phase drew more power because of the capacitive reactance.

 

[afesheir]

ok, but I am still asking about the bug in my solution, the two voltage drops are equal ... the phase shift is in opposite sign, but the phase shift doesn't affect the brightness on the lamp ... am I right ...?