SimPowerSystems

DC Line Fault

Disconnect the Step Up & Down block in order to eliminate the step disturbance applied to the reference current. In the DC Fault Timer and Forced Delay blocks of the psbhvdc12pulse model, change the multiplication factor of 100 in the Transition Times to 1, so that a fault is now applied at t = 0.6 s. Open the I_DCfault scope to observe the fault current. Restart the simulation.

Figure 2-34: DC Line Fault on the Rectifier Side

At fault application (t = 0.6 s), the DC current increases to 2.3 p.u. and the DC voltage falls to zero at the rectifier. This DC voltage drop is seen by the Voltage Dependent Current Order Limiter (VDCOL), which reduces the reference current to 0.3 p.u. at the rectifier. A DC current still continues to circulate in the fault. Then, at t = 0.65 s, the rectifier firing angle is forced to 165 degrees when the signal applied to the ForcedAlpha input goes high. This signal would normally be provided by the protection system not simulated here. The rectifier now operates in inverter mode. The DC line voltage becomes negative and the energy stored in the line is returned to the AC network, causing rapid extinction of the fault current at its next zero crossing. Then is released at t = 0.7 s and the normal DC voltage and current recover in approximately 0.5 s.

Response to a Step of Reference Current

AC Line-to-Ground Fault at the Rectifier