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Lab 5 - 3-Phase Power
Problem
To study the behaviour of 3-phase power with balanced and unbalanced loads.
Prelab
- Using the circuit diagram below, calculate the current in each phase and the neutral. (Each phase is about 120V RMS.)
- Add a 40 μf capacitor in series with the phase 3 load. Calculate the current in each phase and the neutral.
Measurement Schematics
Procedure
- Set up the circuit as follows
- (Note: ammeter is a clamp-on meter and not wired in.)
- Measure and record the voltage and current in each phase as well as the neutral.
NOTE: Make sure the power is turned off while changing the circuit below.
- Disconnect the third phase
- Be careful not to short the circuit with the loose wire.
- Measure and record the voltage and current in each phase as well as the neutral.
- Disconnect the second and third phases. Measure and record the voltage and current in each phase as well as the neutral.
- Reconnect all 3 resistors and add the 40 μf capacitor in series with the phase 3 load. Measure and record the voltage and current in each phase and the resistor with the capacitor as well as the neutral.
- Insert the two power meters in the circuit as shown below without the 40 μf capacitor. Record the values measured by each.
- Insert the 40 μf capacitor and measure the total power shown on the power meters.
- Does the voltage and current in each phase agree with your calculated values? Explain any differences.
- What effect does disconnecting two phases have on these values?
- Is it what you expected? Why or why not?
- Does the total power agree with the power calculated above?
- What effect does adding a capacitor have on these values? Explain
- Compare the total power to the sum of the V * I for each resistor.
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