# Three-Phase angle adjustment to get line-line voltage

Hello! Thanks for amazing project. Right now we have an IotaWatt reading 3-phase voltage using custom made transformes of 254V:9VAC sensing Phase + Neutral. It has been working as expected but we would like to have the Line-Line voltage, as Va-b, Vb-c, Vc-a.

I understand that IotaWatt can sense phase adjustments, I would like to get the angle data so I can correctly approximate Line-Line voltage. Is this possible?

A workaround we are investigating is to transform Line-Line as 440V:9V but would lose detail of current by phase.

Short answer is yes. The devil is in the details. This is not well documented at all because if I understand you correctly, you are using the direct reference method. What you are looking to do is use derived reference for a phase-phase circuit.

The derived reference for a phase-phase circuit is developed by both shifting the phase angle, and increasing the basis phase-ground voltage by a factor of \sqrt{3} =1.732.

Fortunately, direct and derived reference are not mutually exclusive. For any input, there is a reference voltage. For any configuration where there is only one VT configured, that is the implied reference voltage for all inputs and is not a parameter during setup.

When you configure more than one VT, as you imply for your setup, an additional VRef parameter is used to specify which VT is to be used as reference. It defaults to the VT on Input_0, but any of the configured VTs can be selected.

When you check “Enable derived three-phase” in the inputs setup display, another parameter is added to each individual input setup. That parameter is phase and determines the phase angle and voltage multiplier to be applied to the selected VRef. It looks like this:
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You can see the phase angle shift that will be applied to the voltage reference specified in VRef.

Most of the time, with direct reference, you will accept the default A - no shift and no change to the voltage. Remember, this is not which of your three phases that you want to use, but rather what phase you want to derive from the specified VRef.

So, you are interested in the phase-phase selections A-B and C-A. IoTaWatt will shift the specified VRef voltage by the indicated phase angle and also increase the voltage by \sqrt{3}.

When configuring a phase-phase circuit, you will have a CT on one of the conductors. Assign the VRef that corresponds to that CT. The two possible choices for phase-phase will be A_B and C_A depending on your phase rotation. You will probably need to determine that through trial and error.