# Power (3ph, Instantaneous)

Compute three-phase instantaneous active and reactive
powers

## Library

Control and Measurements/Measurements

## Description

The Power (3ph, Instantaneous) block computes the three-phase
instantaneous active power P (in watts) and reactive power Q (in vars)
associated with a periodic set of three-phase voltages and currents.
These formulas are used to perform the calculations:

$$\begin{array}{l}P={V}_{a}\cdot {I}_{a}+{V}_{b}\cdot {I}_{b}+{V}_{c}\cdot {I}_{c}\\ Q=\frac{1}{\sqrt{3}}\left[({V}_{b}-{V}_{c})\cdot {I}_{a}+({V}_{c}-{V}_{a})\cdot {I}_{b}+({V}_{a}-{V}_{b})\cdot {I}_{c}\right]\end{array}$$

With these formulas, a current flowing into an RL circuit produces
a positive P and a positive Q.

The computed instantaneous reactive power is accurate only for
balanced and harmonic-free three-phase voltages and currents.

## Dialog Box and Parameters

The block has no parameters.

## Inputs and Outputs

`Vabc`

The three-phase voltage signal.

`Iabc`

The three-phase current signal.

`P`

The three-phase instantaneous active power P, in watts.

`Q`

The three-phase instantaneous reactive power Q, in vars.

## Example

The `power_ThreePhasePower`

`power_ThreePhasePower`

model
compares the outputs of the block with the Power (Positive-Sequence)
block and the Power (dq0, Instantaneous) block. It shows that the
Power (3ph, Instantaneous) block gives accurate results when the voltages
and currents are balanced and harmonic free. When the voltage supply
becomes unbalanced, the P output exhibits a ripple, and an error appears
on the Q output.

The model sample time is parameterized by the Ts variable set
to a default value of 50e-6 s. Set Ts to 0 in the command window and
change the **Simulation type** parameter of the Powergui
block to `Continuous`

to simulate the model
in continuous mode.