Power System Blockset

Transient Performance for a Fault at Bus B2

The configuration of the substation circuit breakers normally allows to clear a bus fault without losing lines or transformers. You will now modify your case1 circuit in order to perform a three-cycle, three-phase-to-ground fault at bus B2 as shown on Figure 2-9:

1. Disconnect the 3-Phase Fault block and reconnect it as shown on Figure 2-9 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 checked
   Transition times :[2/60 5/60]
   Transition status [1, 0, 1...]: (0/1)
   

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 checked
   Switching of Phase B: not checked
   Switching of Phase C: not checked
   

The circuit breakers will not be switched anymore. They will 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 its Elements parameter to 1. This will allow you to see clearly the phase A voltage on the scope.
5. You will now add blocks to read the flux and the magnetization current of the saturable transformer connected at bus B2.

Copy the Multimeter block from the Measurement library into your case1 circuit. 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 on OK.

6. You have now two signals available at the output of the Multimeter block. Use a Demux block to send these two signals on a two trace scope (See Figure 2-9).
7. In the Simulation/Parameters menu, change the stop time to 0.5. This longer simulation time will allow you to observe the expected low frequency modes (9 Hz). Start the simulation.

Waveforms of interest are plotted on Figure 2-8.

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 9Hz 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.

Figure 2-9: S Series Compensated Network Used for a Fault at Bus B2

Frequency Analysis

Chopper-Fed DC Motor Drive