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4.1 Objective

The objective of this exercise is to understand and analyze the response of the power system to the following perturbations:

• Part 1: A three-phase short circuit on bus 1, the generator does not have rotor damper windings (D = 0).

• Part 2: A three-phase short circuit on bus 1, the generator has rotor damper windings.

• Part 3: A three-phase short circuit on bus 3, the generator does not have rotor damper windings (D = 0).

Simulations are first run in phasor mode, then in time-domain mode.

4.2 Initializing the Setup

Once the simulator is started in phasor mode, the steady state power flow values are displayed in the “Measurements” section. These values must correspond to the values obtained in the preliminary calculations.

4.3 Exercise

4.3.1 Part1: Short-circuit in BUS 1 Without Damping Windings

a.     Enter the duration of the fault on bus 1 in the “Duration of the fault 1” field in the main panel (in the field below switch ).

b.     Go to the “Display 1” tab and click on switch to activate the signals on the rotor oscillation frequency.

c.      Go to the “Display 2” tab and click on switch to set the oscilloscopes to record signals for a period of 6 seconds. The first oscilloscope displays the generator rotor’s mechanical angle on bus 4 and the second displays the voltage Va on the bus. Signal data is also saved in MATLAB (Note: if you do not want to overwrite the previous saved data, remember to change the file numbers in the “delta_file” and “voltage_file” fields, for each fault before saving). The panel is completely deactivated during the recording and the “Recording” light turns to red. You must wait for the light to return to green before proceeding to the next exercises. The data files are saved in the following location:

C:\OPAL-RT\TestDrive\v2.9.0.16\Models\TransientStabilityTD_Model\TransientStabilityTD_Model_SM_Master\OpNTtarget

d.     Click on switch to start a fault on bus 1.

e.     In the “Display 1” tab, observe the waveforms displayed on the “generator mechanical angle” and “BUS 4 magnitude voltage” oscilloscopes. There are potentiometers to the left of oscilloscope 1 to adjust the signals.

f.       In the “Display 2” tab, the oscilloscopes display the system response 6 seconds after the fault insertion. Use the potentiometers to the left to find the maximum rotor angle value. Use the data recorded in MATLAB to more accurately determine the value for this angle.

g.     Click on the PSS switch to damp system oscillations. During the stabilization, the “PSS” indicator turns green. It is imperative to wait until the indicator returns to off (gray) before continuing to the next exercises.

Note about the PSS: To damp the generator rotor oscillations, we can control its inductor current (excitation current) to instantly produce an adequately resistant torque component. The PSS detects the power oscillations and sends a signal to adjust the voltage controller setpoint in the generator’s field current. In the model implemented on the simulator, the PSS can be used to damp power oscillations. Once properly damped, the PSS automatically deactivates.

h.     Wait until power oscillations stop (the “Oscillations” indicator will turn off).

i.       Determine the critical clearance time for the fault by repeating procedures from steps a) to h) with fault durations as close as possible to analytically determined values.

4.3.2 Part 2: Short-circuit in BUS 1 With Damping Windings

a.     Click on switch to activate the damper windings in the rotor of the generator.

b.     Repeat steps a) to f) from Part 1. Note that PSS use is not needed. Comment.

c.      Find the maximum duration that the system can support before becoming unstable by repeating procedures from steps a) to h) from Part 1 with fault duration as close as possible to analytically determined values.

d.     When the exercise is complete, deactivate switch to reset the synchronous generator damper to zero.

4.3.3 Part 3: Short-circuit in BUS 3 Without Damping Windings

a.     Enter the fault duration for bus 3 in the “Duration of the fault 3” field in the main panel (in the field below switch ).

b.     Go to the “Display1” tab, click on switch to activate the signal on the rotor’s oscillation frequency.

c.      Go to the “Display2” tab, click on switch to set the oscilloscopes to record the 4 signals for 6 seconds.

d.     Click on switch to start the fault on bus 3.

e.     Observe the waveforms displayed in the “Display1” tab oscilloscopes: “Generator mechanical angle” and “BUS 4 magnitude voltage”. Use potentiometers on the left to adjust oscilloscope 1.

f.       In the “Display 2” tab, the oscilloscopes display the system response 6 seconds after fault insertion. Use the potentiometers to the left to find the maximum rotor angle value. Use the data recorded in MATLAB to more accurately determine the value for this angle.

g.     Click on switch to close circuit breakers D1 and D2. This reconnects the line between buses 1 and 3, and between buses 3 and 2.

h.     Click on switch to damp system oscillations.

i.       Wait until oscillations stop; the “Oscillations” indicator will turn off.

j.       Find the maximum duration that the system can support before becoming unstable by repeating procedures from steps a) to i) from Part 1 with fault duration as close as possible to analytically determined values.

4.3.4 Part 4: Time-Domain Simulation

a.     Using the saved data files (see Section 4.3.1), repeat parts 1 to 3 in time-domain mode.

b.     Do the results correspond to results from phasor mode simulation? Comment.