AC Synchronous Machine Characterization

1. Turn on the low-power DC power supply with a short circuit across its terminals.
   1. Limit the current on the low-power DC power supply to 1.8 A.
   2. Turn off the supply and disconnect the short circuit.
2. Connect the supply terminals across ports 1 and 4 of the synchronous motor.
   1. Turn on the supply and measure the DC voltage and current. Vary the voltage as needed to reach a current of 1.8 A.
   2. Turn off the supply, then repeat the previous two steps for ports 2 and 5 and ports 3 and 6.
3. Disconnect the low-power DC power supply.

2. Synchronous Machine Start-up

1. Make sure the three-phase disconnect switch, synchronous motor switch, and DC motor switch are all off.
   1. Check that the VARIAC is at 0%.
   2. Wire the VARIAC to the three-phase outlet, and connect the setup shown in Fig. 1.
   3. Remember to set the 1 to 1000 scaling of the digital power meter current probe.
2. Check that the "Start/Run" switch is in the "Start" position.
3. Turn on the three-phase disconnect switch.
4. Quickly increase the VARIAC output until the digital power meter reads around 115 V.
5. Measure the armature current I_AC1, armature voltage V_AC1, real power, and power factor.
6. Remember that the phase (line-to-neutral) voltage and phase current on phase "a" are being measured, so the power factor measurement on the power meter is correctly reflecting the per-phase power factor.
7. Measure the torque and speed of the machine.
8. Turn on the 125 V DC power supply. Make sure all connections are clear from the supply terminals.
   1. Press the supply "Start" button and set the supply output to 125 V.
9. Flip the "Start/Run" switch to the "Run" position. Pay attention to how the machine sound changes. The machine sound becomes smoother as the rotor magnetic field locks to the stator rotating magnetic field.
   1. Record the armature current I_AC1, armature voltage V_AC1, real power, power factor, and the field voltage and current from the DC power supply display.
   2. Measure and record the torque and speed of the machine.
10. Turn off the DC power supply, flip the "Start/Run" switch to the "Start" position, and set the VARIAC back to 0%.
11. Turn off the three-phase disconnect switch. Leave the rest of the circuit intact.

Figure 1: A schematic of the setup to start the synchronous motor. Please click here to view a larger version of this figure.

3. Effect of Load on Torque Angle

1. Make sure the three-phase disconnect switch, synchronous motor switch "S₁," and DC motor switch "S₂" are all off.
   1. Note that while "S₁"is on the synchronous motor side, it is used to connect/disconnect the "RL" load across the DC machine terminals.
   2. Check that the VARIAC is at 0%.
2. Connect the setup shown in Fig. 2 and set "R_L" to 200 Ω.
3. Check that the "Start/Run" switch is in the "Start" position.
4. Turn on the three-phase disconnect switch.
5. Quickly increase the VARIAC output until the digital power meter reads around 115 V.
6. Turn on the 125 V DC power supply. Make sure all connections are clear from the supply terminals.
7. Press the supply start button and set the supply output to 125 V.
8. Flip the "Start/Run" switch to the "Run" position.
9. Record the armature current I_AC1, armature voltage V_AC1, real power, power factor, and field voltage and current from the DC power supply display.
10. Measure and record the torque and speed of the machine.
11. Keep the strobe light on near the shaft and measure the initial angle δ_o.
    1. To set up the strobe light, plug it into a regular power outlet and turn it on.
    2. With the Coarse knob, adjust the speed reading on the strobe light to be close enough to 1,800 RPM, which is the synchronous speed of 1 four-pole 60 Hz machine. Synchronous speed is calculated in rounds per minute (RPM) as n=120xf/P where f is the frequency and P is the number of poles.
    3. Place the strobe light to face the motor shaft's edge, and adjust the Fine knob until the shaft appears stationary. The human eye is tricked to see the shaft as stationary by having the strobe light frequency (or speed reading) match the shaft speed.
12. Turn on "S₁" and repeat steps 3.9 to 3.11, but measure the new angle as δ₁.
13. Turn on "S₂" and repeat steps 3.9 to 3.11, but measure the new angle as δ₂.
14. Turn off "S₂" and change "R_L" to 100 Ω.
15. Turn on "S₂" and repeat steps 3.9 to 3.11, but measure the new angle as δ₃.
16. Turn off the DC power supply, flip the "Start/Run" switch to the "Start" position, turn off "S₁"and "S2," and set the VARIAC back to 0%.
17. Turn off the three-phase disconnect switch. Leave the rest of the circuit intact.

Figure 2: A schematic of the setup to study the effect of load on torque angle. Please click here to view a larger version of this figure.

4. Effect of Field Current on Power Factor

This section investigates one side of the V-Curve.

1. Make sure the three-phase disconnect switch, synchronous motor switch S₁, and DC motor switch S₂ are all off.
2. Check that the VARIAC is at 0%.
3. Connect the setup shown in Fig. 3, which is only different from Fig. 2 by adding the series field resistor "R_F," and set "R_L" to 200 Ω.
4. Set "R_F" to the 10 Ω position. "R_F" does not require measurement for this experiment, since the goal is to vary field current only.
5. Check that the "Start/Run" switch is in the "Start" position.
6. Turn on the three-phase disconnect switch.
7. Quickly increase the VARIAC output until the digital power meter reads 115 V.
8. Turn on the 125 V DC power supply. Make sure all connections are clear from the supply terminals.
9. Press the supply start button and set the supply output to 125 V.
10. Flip the "Start/Run" switch to the "Run" position.
11. For "R_F" = 10, 6, 3, and 1, record the armature current I_AC1, armature voltage V_AC1, real power, power factor, field voltage and current from the DC power supply display.
12. Measure and record the torque and speed of the machine.
13. Reset "R_F" to 10 Ω.
14. Turn on "S₁," and repeat steps 4.11 to 4.13.
15. Turn on "S₂," and repeat steps 4.11 to 4.13.
16. Turn off "S₂" and change "R_L" to 100 Ω.
17. Turn on "S₂," and repeat steps 4.11 to 4.13.
18. Turn off the DC power supply, flip the "Start/Run" switch to the "Start" position, and set the VARIAC back to 0%.
19. Turn off the three-phase disconnect switch and disconnect the setup.

Figure 3: A schematic of the setup to study the effect of changing the field current. Please click here to view a larger version of this figure.