EXPERIMENTAL STUDY AND COMPARATIVE ANALYSIS OF
TRANSFORMER HARMONIC BEHAVIOUR UNDER LINEAR
AND NONLINEAR LOAD
Overview
Introduction
Transformer
Harmonic
Practical Results
Conclusions
Introduction
Harmonics and distortion in power system current and
voltage waveforms have been present for decades. However, today the number of harmonic producing devices is
increasing rapidly. The transformer designed to operate at rated frequency has had its loads gradually replaced with non-linear loads that inject harmonic currents. The flow of harmonic currents :
1. increases the losses of power transformers, 2. cause extra heat of transformer,
3. can affect the insulation lifetime and
Objective:
investigation in harmonic problems and their effects on
power transformers and other power systems.
TRANSFORMERS
Power Transformer
A transformer is a static device that transfers
electrical energy from one circuit to another by
electromagnetic induction..
Transformer terminology
The primary winding is the winding of the transformer which is connected to the source of power. It may be either the high- or the low voltage winding, depending upon the application of the transformer
The secondary winding is the winding of the transformer which delivers power to the load. It may be either the
high- or the low-voltage winding, depending upon the
application of the transformer.
Three Phase Transformer
A three phase transformer is constructed by winding three single phase transformers on a single core. These
transformers are put into an enclosure which is then filled with dielectric oil, Since it is a dielectric, a nonconductor of electricity, it provides electrical insulation between the windings and the case. It is also used to help provide
cooling
Three-Phase Transformer Connections
Four types of connections of three phase transformers can be found:
Delta to Delta
Delta to Wye
Wye to Delta
Wye to Wye
HARMONIC
Harmonics
Harmonic distortion is caused by the introduction of waveforms at frequencies in multiplies of the
fundamental frequency.
Harmonic Analysis
Figure 1: Fundamental with two harmonics
Source of Harmonic
The main source of the harmonics is the non-linear loads that produce the voltage harmonics and current harmonic
In general, harmonic sources are given below:
1.
there phase diode rectifier
2.Converters
3.
Control circuits
4.Motors
Total Harmonic Distortion (THD)
The total harmonic distortion of a signal is a measurement of the harmonic distortion present.
It is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.
1
2
V
V
ThD V
n
n n
2%
2I
I
ThD I
n
n n
2%
Transformer losses
Transformer losses are generally classified into no load or core losses and load losses.
The loses of transformer in the case of harmonics are given below
2 2 2
2 2
h
s p p Lh
L s
cu a
R R a I
R R I
P
Effect of power system harmonics on transformers
Increase the no load and full load losses of transformer
Overheating of transformer
Increase the RMS value of the transformer current
Practical RESULTS
Parameter Transformer
Our experiment was established to determine the
harmonics and losses cause by the harmonics in three phase transformer.
The transformer was a three phase transformer 415/47
with power of 8 KVA under 50 HZ.
equipments
Three variac to control voltage
Fuses to ensure the security during the experiment
Resistor elements, capacitors, inductors
Three phase bridge rectifier
Power quality analyses
In our experiment we used the Y-Y connection for the
next reasons
The Y-Y Connection in Three-Phase Systems
Each phase is transformed through a set of primary and secondary windings connected phase-to-neutral
in Figure.1 shows the physical winding connections as three separate two-winding transformers.
Both the primary and secondary windings of each of
these transformers are connected between one phases
The Y-Y Connection in Three-Phase
Systems in transformer
open circuit parameters (Primary)
open circuit parameters (Secondary)
short circuit parameters (Primary)
Transformer Data
Experiments Linear Load Condition
The first experiment includes the measurement of power and losses in addition to its efficiency under linear load condition, resistive and inductive load
Figure 5: Linear Load Condition
as seen in fig4 the load current is purely sinusoidal and in phase with the voltage. As shown the voltage and current of secondary in the case of linear load, the active and
reactive power,
Experiments Linear Load Condition
Figure 4: Linear load V, I waveforms and harmonic
Experiments Nonlinear load Condition
In the second stage, anon linear load composed of 3 phase bridge rectifier with inductive DC load and capacitive load were implemented and
experimented the result
Experiments Nonlinear inductive load Condition
This figure shows the primary and secondary current and voltage. We can notice that the primary current THD was less than the secondary THD, that is due to the
transformer which isolate the load current from the grid current.
the THD value of the load currents is between 24 and 30.8 and
The power factor was decreased from one to about 95%
in this case
The losses in the transformer were increased due to
Experiments Nonlinear inductive load Condition
Figure 5: Nonlinear inductive load Condition
Figure 6: Nonlinear load V, I waveforms and harmonic
Experiments Nonlinear Capacitive Loads Condition
The THD of current wave forms arrive the value of 79.0%
The power factor was decreased from one to about 95% in this case
The losses in the transformer were increased due to existence of harmonics
The efficiency of the transformer was 92% at
37% of the transformer power .
Experiments Nonlinear Capacitive Loads Condition
Figure 7: Nonlinear Capacitive load
Figure : indivisual harmonic components
This figure shows the primary and secondary current and voltage. We can notice that the
primary current THD was less than the secondary
THD, that is due to the transformer which isolate
the load current from the grid. The primary current
THD was 57.9%, and the secondary current THD
was 79.0%
Transformer losses and efficiency (Practical)
NO
I
Power losses efficiencyI
Power losses efficiencyI
Power losses Efficiency1 5.5 156 79 5.4 183 72.18 8 142.9 73.76
2 15.5 171 88.6 14.4 198 85.54 13.5 160 84.60
3 23 250 89 23.3 199 90 24.7 188 89.82
4 33.5 323 88 31.2 184 92 33.8 201 91.8
5 42 354 90 38.9 244 92.35 37.9 230 92.66
mean 250.8 86 201.6 86.414 184.4 88.72
Linear Load Inductive
Nonlinear Load Capacitive Nonlinear Load
NO
I
Power losses efficiencyI
Power losses efficiencyI
Power losses Efficiency1 5.5 165.7 72.35 5.4 188.78 68.733 8 215.4 68.5
2 15.5 193.8 85.19 14.4 192 85.44 13.5 181.16 81.14
3 23 220.5 88.05 23.3 215.84 89.23 24.7 210 88.63
4 33.5 239 90.91 31.2 228.34 91.20 33.8 238.5 90.93
5 42 301 91.91 38.9 249.6 92.09 37.9 242.7 91.16
Transformer losses and efficiency (Theoretical)
Linear and nonlinear load Condition, current harmonic
Linear Load
Condition Nonlinear inductive
load Condition Nonlinear Capacitive load Condition
Harmon ic
Order
Harmoni
c Order Differen
ce % Harmoni
c Order Differenc
e %
3 0.03A 3 0.15A 0.7 3 0.83A 5.6
5 0.17A 5 3.71A 19.9 5 9.41A 64.9 7 0.13A 7 2.24A 11.9 7 6.12A 42.3
9 0.01A 9 - - 9 0.41A 2.8
Transformer losses and efficiency using MATLAB
The studied system was designed and simulated in
MATLAB as shown in the figure (9) the results of
simulation was presented in the table
Transformer losses and efficiency using MATLAB
NO
I
Power losses efficiencyI
Power losses efficiencyI
Power losses Efficiency1 5.2 15.3 96.4 5.4 15.2 96.2 5.3 15 96
2 14.5 23 98 15.3 24 97.9 14 23 97.8
3 23 36 98 24 39 97.9 24 37 97.88
4 32 58 97.6 33 60 97.5 32 54 97.7
5 39 79 97.4 38.9 80 97.2 38 75 97.3
mean 42.26 43.6 40.8
Linear Load Inductive
Nonlinear Load Capacitive Nonlinear Load
CONCLUSIONS
In this thesis focused on the study of harmonics and their effects on the power losses in power transformers. The
analysis of three phase transformer and its equivalent circuit was applied using the conventional methods. The study of theoretical losses in the case of linear load based on the equivalent circuit parameters was investigated. Another
analysis based on the same equivalent circuit with non-linear loads and harmonic currents was also established in order to be compared with the linear ones.
