# How to simulate 3 phase (symmetrical ) circuits on LTspice?

#### babaliaris

Joined Nov 19, 2019
115

I can't find any guides on the internet so I tried to figure it out myself. I tried using 3 sin voltage sources with time delays of 0, -120, -240 each. In class, these values are in degrees and not seconds so I'm confused If I'm using the correct value in LTspice.

The simulation does not seem to work. Ic should be furthermore delayed than Ib and not be on top of each other.

What am I doing wrong, and what is the proper way to simulate 3 phase systems in LTSpice?

Thank you!

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#### ericgibbs

Joined Jan 29, 2010
15,735
hi baba,
You don't use delays.
I will post an example for you..
E

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Last edited:

#### crutschow

Joined Mar 14, 2008
30,127
As Eric said you don't use delays, you use the phase [Ph(deg) below] of 0, 120, and 240.

#### babaliaris

Joined Nov 19, 2019
115
Thanks! I did not know Phi stands for phase. Didn't notice the [deg] as well.
Also, I noticed that you use +120 and +240. I'm not sure if this is a regional difference
but I'm from Greece (Europe) and we use -120 for the second phase and -240(or +120) for the third phase.
So why?
Thank you again!

#### babaliaris

Joined Nov 19, 2019
115
Also, can I somehow plot the phases (in degrees) of each current? Can I do it with an expression or something like that?
Thank you!

#### crutschow

Joined Mar 14, 2008
30,127
I'm from Greece (Europe) and we use -120 for the second phase and -240(or +120) for the third phase.
So why?
As long as you generate the 3 phases with 120° difference, then it makes no difference how they are specified.
Also, can I somehow plot the phases (in degrees) of each current?
To plot the current just click on the voltage source or load after the simulation has run.

#### ericgibbs

Joined Jan 29, 2010
15,735
hi baba,
Simple example.
E

#### babaliaris

Joined Nov 19, 2019
115

#### MrAl

Joined Jun 17, 2014
9,191
Thanks! I did not know Phi stands for phase. Didn't notice the [deg] as well.
Also, I noticed that you use +120 and +240. I'm not sure if this is a regional difference
but I'm from Greece (Europe) and we use -120 for the second phase and -240(or +120) for the third phase.
So why?
Thank you again!
Hello,

You also need to specify the phase rotation. There are different rotations for 3 phase systems.
You should look at the time domain plot of the three phases to make sure you have the phase rotation you need.

Also, if you do a delta instead of a wye you can sometimes get away with using just two sine sources because the third phase is always going to be the difference of the first two. Again you have to look at the phase rotation to make sure you end up with what you really want.