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Lab 1 - Phasors in AC Circuits
Prelab (done in lab)
- Using circuit 1.1 calculate the following phasor quantities (magnitude and phase). Use the applied voltage as the reference phasor.
- Vs
- Is
- VR1
- I1
- VR2
- I2
- You might want to simulate the circuit in PSpice to obtain the values.
- Using the above values calculate:
- The power dissipated in the each resistor
- The power dissipated or supplied to the entire circuit
Problem
To study phasor concepts in single phase AC circuits.
Introduction
Your introduction should mention:
- What phasors represent, and how they are added, multiplied, and divided.
- The difference between resistance, reactance, and impedance (the triangle representation is a good aid)
- The difference between real, apparent, and complex power (the triangle representation is a good aid)
- How power is dissipated in resistors vs capacitors & inductors.
Equipment & Components
Resistors: R1 & R2 = 500Ω, RSH = 0.5Ω
Capacitor: XC = 40μf
Inductor: XL = 1H
Power meter
Digital Multimeter
Oscilloscope w/ two 10:1 probes
Isolation Transformer
Variable Transformer
Circuit 1.1
Procedure
Part 1: Voltage Measurement
- Use the DMM (Digital Multimeter) to measure the voltages.
- Vs
- Is
- VR1
- I1
- VR2
- I2
- VRSH
- VL
- VC
- Measure the phases using the oscilloscope where:
- Channel 1 shows probes 1 and 2 ADDed.
- Channel 2 shows probe 2 INVERTed.
- Measure across a and d as shown in Circuit 1.1.
Part 2: Power Measurement
- Insert a wattmeter into the circuit and remove RSH as in circuit 1.2.
- Record the power delivered to the circuit
- As a check, calculate the power dissipated by each resistor.
Circuit 1.2
Results
Part 1: Voltage
- Verify Kirchoff’s Laws by drawing a phasor diagram for each of the two meshes.
Part 2: Power
- Does power dissipated = power supplied?
- Explain any differences.
- Is power dissipated anywhere else not accounted for?
- Do the energy storage elements (inductor or capacitor) dissipate any average power?
- From the wattmeter reading, determine the power factor.
- pf = cos( θV - θI ) = P/VI
- From this, determine the angle of IS .
- Is this the same as the theoretical value?
Part 3: Impedance
- Using the power measurement obtained in part 3, determine the equivalent impedance of the circuit.
- |Zeq| = Vs / Is
- Req = P / Is2
- Xeq2 = Zeq2 - Req2
- How does this compare with the calculated value? Explain any differences.
Questions
- Why does the calculated value for VR1 not match the prelab calculation as closely as VR2 does?
- What is the sum of voltages across the resistors? Why does it exceed the source voltage?
- Explain why purely resistive components dissipate power, whereas purely reactive components don't.
- What type of power (Apparent, Real, Reactive) do Wattmeters measure?
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