# Answer Question

### 3 phase rms value calculation

I was trying to justify the derivation done by PSCAD for calculating RMS quantity for a 3-phase, input voltage waveform. PSCAD is converting the signal into :

where, V AB = V A -V B, V Bc = V B -V C, V CA = V C -V A, and feeding this input signal to the rms meter which uses the formula as below for a analog rms meter (For digital rms meter the same formula is done with sampled values and quantified with the discrete signal),

where x=INPUT signal and T=time period of signal.

To my understanding PSCAD is trying to convert 3 phase signal to an equivalent 1 phase signal and taking line to line voltages to calculate the same and then using the rms formula to compute 3 phase rms voltage. But still I'm a bit doubtful on this derivation how are you squaring the input signal again in the rms function. Can you please help?

where, V AB = V A -V B, V Bc = V B -V C, V CA = V C -V A, and feeding this input signal to the rms meter which uses the formula as below for a analog rms meter (For digital rms meter the same formula is done with sampled values and quantified with the discrete signal),

where x=INPUT signal and T=time period of signal.

To my understanding PSCAD is trying to convert 3 phase signal to an equivalent 1 phase signal and taking line to line voltages to calculate the same and then using the rms formula to compute 3 phase rms voltage. But still I'm a bit doubtful on this derivation how are you squaring the input signal again in the rms function. Can you please help?