# Dynamic Load and Programmable Voltage Source

This example shows the use of the 3-Phase Dynamic Load and 3-Phase Programmable Voltage Source blocks ### Description

A dynamic load is connected on a 500 kV, 60 Hz power network. The network is simulated by its Thevenin equivalent (voltage source behind a R-L impedance corresponding to a 3-phase short circuit level of 2000 MVA). The source internal voltage is modulated in order to simulate voltage variation during a power swing. As the dynamic load is a nonlinear model simulated by current sources, it cannot be connected to an inductive network (R-L in series). Therefore, a small resistive load (1 MW) has been added in parallel with the dynamic load.

The dynamic load power is a function of its terminal positive-sequence voltage V. Open the Dynamic Load menu and notice that both exponents np and nq are set to 1 and that the specified minimum voltage Vmin is 0.7 pu. It means that the load active power P and reactive power Q are defined by the following equations:

``` If V > Vmin P = Po*(V/Vo); Q = Qo*(V/Vo) If V < Vmin P = Po*(V/Vo)^2; Q = Qo*(V/Vo)^2```

In other words, as long as voltage is higher than 0.7 pu, the load current is constant. When voltage falls below 0.7 pu the load behaves as a constant impedance.

In order to simulate the variation of P and Q as function of voltage, the source internal voltage is controlled by the 3-Phase Programmable Voltage Source block. Open the source menu and notice that the specified type of amplitude variation is a sinusoidal modulation (Amplitude of the modulation = 0.5 pu, Frequency of the modulation = 1 Hz). Therefore, the source positive-sequence voltage varies between 0.5 pu and 1.5 pu. The initial source voltage is 1 pu. Modulation starts at t = 0.2 s and stops after 1 cycle at t = 1.2 s.