# Electrical Power and Machines

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Electrical Power and Machines
Author
Course
Date
2
Introduction........................................................................................................... 2
Results and discussion........................................................................................... 3
PART-1 Phase and line measurement in the power supply.................................3
Part-2 Transmission Lines...................................................................................6
Part-3 3-Phase Power Measurements and Calculations....................................15
Part-4 Voltage, current and power measurements in a delta-connected circuit
......................................................................................................................... 17
Conclusion........................................................................................................... 21
References........................................................................................................... 23
Introduction
Three phase circuits are the basis of every electrical power transmission network
(Zhang, Rehtanz and Pal 2012). Power is usually generated using three phase alternators and
transmitted to the load centers using three phase transmission lines. Long distance
transmission can not be realized using the generated voltages hence transformers are used
throughout the system to increase or decrease the voltage magnitudes (Kalaga and Yenumula
2016). The effective and economic operation of the entire system requires an understanding
of three phase circuits under different configurations. This laboratory exercise was carried out
with the general aim to familiarize with the operation and characteristics of transformers,
transmission lines, and different three phase circuit configurations.
One of the specific objectives of this exercise was to determine the relationship
between phase and line voltages for both wye and delta three phase circuits. It was
established through measurement that for a wye connection, the phase voltage is equivalent to
the line voltage. However, the line current is 3 times the phase current. For a wye
connection, the phase current was shown to be equal to the line current. However, the line
voltage was 3 times the phase voltage. Measurements real, reactive and apparent power in
3
the three phase circuits were also performed. It was established that for a balanced three
phase circuit, the total power in the circuit is the sum of the powers in the independent
phases. Disconnecting one of the lines introduces an imbalance into the system and some
current flows through the neutral conductor.
The second objective was to investigate the current and voltage relationships on
unloaded and loaded transmission lines. The transmission line investigated was the nominal π
model for medium transmission lines. For the unloaded line, there was no current at the
receiving end due to the absence of a load. The line voltage at the receiving end was almost
equal to the phase voltage while a small current was registered at the sending end due to the
capacitance. For the loaded line, a small drop in the currents and voltages in the three phases
was observed.
The third objective was to investigate transformer characteristics by performing the
open circuit test and determining the transformation ratio. The ratio was determined by
measuring the primary and secondary voltages of an unloaded transformer. For capacitively-
loaded transformer, it was observed that the secondary voltage was significantly greater than
the primary voltage compared to when an inductive load was used.
Results and discussion
PART-1 Phase and line measurement in the power supply
The objective of this exercise was to measure the line-to-neutral (phase) and line to line (line)
voltages of a three phase ac power supply.
4
Phase voltages of the three phase supply
V 1N V 2N V 3 N Average value
193 194 193 111.33
Line voltages of the three phase supply
V 12 V 23 V 13 Average value
110 112 112 193.33
5
Average line voltage
Average p h ase voltage = 193.3
111.33 =1.7363 3
Q5
The individually measured phase voltages are approximately equal
Q6
The individual measured line voltages are approximately equal
Q7
The individual measured line currents are approximately equal
Q8
The ratio of the average line voltage to the average phase voltage is 1.7363 which is
approximately equal to 3 .
Q9
The current flowing through the neutral line is approximately equal to zero.
Q11
Since no current flows through the neutral line, disconnecting the neutral line has no effect on
the measured quantities.
Q12
P1=V 1 N × I 1 × PF 1 3.27
P1=V 2 N × I 2 × PF2 3.3
P1=V 3 N × I 3 × PF 3 3.3
6
PT =P1+ P2+ P3 9.87
PT =3 ×V p h ase × I p h ase × PF 9.887
PT = 3× I L ×V L × PF 9.89
Part-2 Transmission Lines
The aim of this task was to measure the variables for the unloaded lines
The settings for the various parameters were,
Resistance at per phase transmission line R=3.6
Inductance at per phase transmission line L=115 mH
Half of the earth capacitance CE
2 =3 ×0.55 μ F
Half of the line capacitance CL
2 =3 ×150 nF

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