AC Synchronous Machine Synchronization

1. Prime-Mover Initialization

The prime-mover in this experiment is the dynamometer, which operates as a motor that spins the generator rotor (field).

1. Make sure the three-phase disconnect switch, synchronous motor switch, and DC motor switch are all off.
2. Check that the VARIAC is at 0%.
3. Wire the VARIAC to the three-phase outlet and connect the setup shown in Fig. 1.
   1. Use the three-phase switch on the synchronous machine side as "S₁."
   2. Note that "S₁" and the three-lamp setup are in parallel.
   3. Also note the polarities of the digital power meter probes.
   4. Check that the "Start/Run" switch is in the "Start" position.
4. Set "R_F" to maximum resistance.
5. Leave the VARIAC at 0% and leave "S₁" off.
6. Turn on the three-phase disconnect switch.
   1. Turn on the high voltage DC power supply.
   2. Make sure all connections are clear from the supply terminals.
   3. Press the "V/I DIS" button on the supply to display the voltage and current operating points. Adjust the voltage knob to 15 V.
   4. Press "Start" on the DC supply panel. The dynamometer should have a large transient current drawn from the DC supply. If its "OCT" light turns on, increase the over-current limit.
7. The machine should spin slowly.
   1. Increase the DC supply output voltage to around 160 V.
   2. Measure the shaft rotational speed.
   3. Adjust the supply voltage in order to achieve 1800 RPM rotational speed.
   4. Record the DC current and voltage on the supply display.
8. Leave the setup intact and do not turn off any of the equipment.

Figure 1: A schematic setup for the three-phase synchronous generator experiment. Please click here to view a larger version of this figure.

2. Synchronizing the Synchronous Generator with the Grid

1. Switch the Start/Run switch on the synchronous machine side to "Run". The three lamps should now turn on.
   1. Adjust "R_F" and the supply voltage iteratively to achieve V_G=120 V, and adjust the frequency of the V_G on the digital power meter to 60 Hz. Values within +/- 2% are acceptable.
   2. Slightly increase the VARIAC output to achieve V_AC1=120 V.
2. At this stage, the grid is providing 120 V at a frequency of 60 Hz.
   1. Record voltage, current, and power readings on both power meters. Do not ignore +/- signs in front of any number on the meters.
3. The lamps should change their lighting pattern.
   1. If the lamps all go bright and dim at the same time, then the generator and the grid have the same phase sequence. Call it a-b-c for the three-phase sequence in use.
   2. If the lamps cycle, like Christmas tree lights, then the generator and the grid have different phase sequences, where one is a-b-c and the other is a-c-b across the set of lamps.
      1. In this case, turn the VARIAC back to 0%.
      2. Press "Stop" on the power supply panel.
      3. Reduce the DC voltage setting back to 15 V.
      4. Switch phases "b" and "c" on the VARIAC side.
      5. Repeat all the above steps, starting at Step 2.1.
4. This step requires quick action: At the instant that all the lights turn off, turn on "S₁." The lights should all remain off, since "S₁" is now acting as a short circuit across their terminals.
5. The generator is now synchronized with the grid. Record the voltage, current, and power readings on both power meters. Do not ignore signs.
6. Leave the setup intact.

3. Effect of Field Current variation

1. Adjust "R_F" in about five steps from its maximum position to minimum position, and record the following for each step: Shaft speed; Shaft torque and sign; Voltage, current, and power readings on both power meters; Voltage and current readings on the DC supply.
2. If this "R_F" variation provides the same sign for all power readings:
   1. Slightly adjust the DC supply output to achieve a reverse power flow from/into the synchronous machine.
   2. Remember that negative power means the machine is generating electrical power.
3. Adjust the DC power supply voltage in five steps without exceeding a total DC current on the supply display of 3.5 A. Record the following for each step: Shaft speed; Shaft torque and sign; Voltage, current, and power readings on both power meters; Voltage and current readings on the DC supply.
4. Keep the setup intact.

4. Disassembling the Setup

The following sequence should be followed before disassembling the setup:

1. Turn the VARIAC back to 0%.
2. Turn off the power supply output by pressing "Stop".
3. When the machines stop rotating, flip the "Start/Run" switch to the "Start" position, and switch off "S₁."
4. Turn off the three-phase disconnect switch.
5. Disassemble the setup.