ECG 440L
EXPERIMENT # 1
MEASUREMENT OF POWER QUANTITIES
A. SINGLE-PHASE CIRCUITS:
Select R = 150Ω, L = 0.4H, C = 20μF, and V = 120V for the single-phase circuits
shown.
1. Parallel R-L Circuit: Connect the circuit in Fig. l(a). Measure the supply voltage
VS, the source current IS, current through the resistive element IR, current through
the inductive element IL, and real power supplied by source.
2. Shunt Compensation: Add a shunt capacitor to the circuit as shown in Fig. l(b).
Repeat all the measurements listed in 1 above in addition to current through the
capacitor IC.
3. Series Compensation: Add a series capacitor to the circuit as shown in Fig. l(c).
Repeat all the measurements listed in 1 above in addition to voltage across the load
VL.
B. THREE-PHASE CIRCUITS:
B1. Balanced 3Ф 4-wire Load:
Connected the three-phase R-L load as shown in Fig. l(d) with L = 0.4H and R =
300Ω.
1. Measure the current in phases a, b, and c, and total real and reactive powers
supplied by the three-phase source.
2. Measure the line-to-neutral voltages Vbn, Vcn, and Van, and the line-to-line voltages
(a-b, b-c, c-a).
3. Measure the phase angle of Vbn, Vcn, Vab, Vbc and Vca with respect to Van.
4. Measure the neutral current In.
B2. Unbalanced 3Ф 4-wire Load:
Connect the unbalanced circuit in Fig. l(e) with L = 0.4H and R = 300Ω, and C =
20μF. Then repeat steps 1 and 4 above.
B3. Unbalanced 3Ф 3-wire Load:
Now disconnect the connection between the neutral of the source and the neutral of
the circuit in Fig. l(e).
1. Measure the current in phases a, b, and c, and total real and reactive powers
supplied by the three-phase source.
2. Measure the line-to-neutral voltages VbN, VcN, and VaN (where N is the neutral point
of the load). Also measure the magnitude and phase angle (with respect to Van) of
VNn, i.e., the voltage across the neutral of the load and the neutral of the source.
QUESTIONS:
Single-phase circuit:
1. Consider the circuit in Fig. 1(a). From the given L and R values and measured
source voltage, calculate the source current, current flow though the resistive and
inductive elements, and real power supplied by the source. Compare these values
to measured one and state the various sources or error.
2. Draw a phasor diagram showing all voltages and currents.
3. Repeat 1 and 2 for Fig 1(b).
4. Repeat 1 and 2 for Fig 1(c).
5. Calculate the capacitor values in Fig. l(b) and l(c) that result in unity power factor.
Three-phase balanced circuit:
1. Draw a phasor diagram of the source voltages (both phase-to-neutral and
line-to-line). Use Van as reference. How close is the source to a balanced one?
2. Calculate the line current and power factor (from the measured phase voltage and
load impedance values), and real and reactive power supplied by each phase.
Compare these calculated values with the measured one.
2. It is desirable to improve the Y-connected load power factor of the circuit in Fig 1(d)
to 0.95 (lag) by placing a delta-connected capacitor bank. Calculate the capacitor
size of each branch of the delta circuit.
Three-phase unbalanced circuits:
1. Repeat items 2 above for the 3-phase 4-wire unbalanced circuit in Fig. 1(e).
2. Without the neutral connection, calculate the line currents, the phase-to-Neural
voltages, and Neutral-to-neutral voltage from the measure source voltages and load
impedance values. Compare your results with the measured one. Then draw a new
phasor diagram showing all voltages (i.e., Van , Vbn, Vcn, Vab, Vbc and Vca , VaN. VbN,
VcN, VNn, Vbc)
IS
+
VS
IL
jXL
IR
R
R
IC
-jXC
jXL
IR
R
Fig. 1(a)
IS
+
VS
IL
jXL IR
Fig. 1(b)
IS
-jXC
+
+
VS
VL
-
Fig. 1(c)
IL
Va
Ia
R
Vb
jXL
R
jXL
R
jXL
R
Ib
jXL
Vc
Ic
In
Fig. 1(d)
Va
Ia
R
Vb
Ib
-jXC
R
Vc
Ic
In
Fig. 1(e)
Va
Ia
R
jXL
Vb
R
Ib
-jXC
R
Vc
Ic
In
Fig. 1(e)