SimPowerSystems

Transient Performance for a Fault at Bus B2

The configuration of the substation circuit breakers normally allows clearing a fault at the bus without losing the lines or the transformers. You now modify your case1 model in order to perform a three-cycle, three-phase-to-ground fault at bus B2:

1. Disconnect the 3-Phase Fault block and reconnect it so that the fault is now applied on bus B2.
2. Open the 3-Phase Fault dialog box and make the following modifications:

• Phase A, Phase B, Phase C, Ground Faults : all selected
  Transition times : [2/60 5/60]
  Transition status [1, 0, 1...]: (0/1)
  

1. You have now programmed a three-phase-to-ground fault applied at t = 1 cycle.

3. Open the dialog boxes of circuit breakers CB1 and CB2 and make the following modifications:

• Switching of Phase A: not selected
  Switching of Phase B: not selected
  Switching of Phase C: not selected
  

1. The circuit breakers are not switched anymore. They stay at their initial state (closed).

4. Insert a Selector block (from the Simulink Signals & Systems library) in the Vabc output of bus B2 connected to the scope. Set the Elements parameter to 1. This allows you to see the phase A voltage clearly on the scope.
5. You now add blocks to read the flux and the magnetization current of the saturable transformer connected at bus B2.

1. Copy the Multimeter block from the Measurements library into your case1 model. Open the Transformer dialog box. In the Measurements pop-up menu, select Flux and magnetization Current. Open the Multimeter block. Verify that you have six signals available. Select flux and magnetization current on phase A, and click OK.

6. You now have two signals available at the output of the Multimeter block. Use a Demux block to send these two signals on a two-trace scope.
7. In the Simulation --> Simulation parameters dialog, change the stop time to 0.5. This longer simulation time allows you to observe the expected low-frequency modes (9 Hz). Start the simulation.

Waveforms of interest are plotted here:

Figure 2-8: Simulation Results for a 3-Cycle 3-Phase-to-Ground Fault at Bus B2

The 9 Hz subsynchronous mode excited at fault clearing is clearly seen on the phase A voltage at bus B2 (trace 1) and capacitor voltage (trace 3). The 9 Hz voltage component appearing at bus B2 drives the transformer into saturation, as shown on the transformer magnetizing current (trace 4). The flux in phase A of the transformer is plotted on trace 5. At fault application the voltage at transformer terminals drops to zero and the flux stays constant during the fault.

At fault clearing, when the voltage recovers, the transformer is driven into saturation as a result of the flux offset created by the 60 Hz and 9 Hz voltage components. The pulses of the transformer magnetizing current appear when the flux exceeds its saturation level. This current contains a 60 Hz reactive component modulated at 9 Hz.

Frequency Analysis

Chopper-Fed DC Motor Drive