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 4. It can also cause reduced
power factor, lower productivity, efficiency, capacity and lack of
system performance 3
Slide 4
Objective: investigation in harmonic problems and their effects
on power transformers and other power systems. 4
Slide 5
TRANSFORMERS 5
Slide 6
Power Transformer A transformer is a static device that
transfers electrical energy from one circuit to another by
electromagnetic induction.. 6
Slide 7
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. 7
Slide 8
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 8
Slide 9
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 9
Slide 10
HARMONIC 10
Slide 11
Harmonics Harmonic distortion is caused by the introduction of
waveforms at frequencies in multiplies of the fundamental
frequency. 11
Slide 12
Harmonic Analysis 12 Figure 1: Fundamental with two
harmonics
Slide 13
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
13
Slide 14
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. 14
Slide 15
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 15
Slide 16
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
16
Slide 17
Practical RESULTS 17
Slide 18
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. 18
Slide 19
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
19
Slide 20
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 20
Slide 21
The Y-Y Connection in Three- Phase Systems in transformer 21
FIGURE 2: Y-Y transformer connections
Slide 22
open circuit parameters (Primary) 22 open circuit parameters
(Secondary)
Slide 23
short circuit parameters (Primary) 23
Slide 24
Transformer Data 24
Slide 25
25 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 were used in the experiment. Figure 5: Linear Load
Condition
Slide 26
26 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
Slide 27
27 Figure : indivisual harmonic components
Slide 28
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 28
Slide 29
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
existence of harmonics The efficiency of the transformer was 92.5%
at 39% of the transformer power. 29
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. 32
Slide 33
Experiments Nonlinear Capacitive Loads Condition 33 Figure 7:
Nonlinear Capacitive load Figure 8: Nonlinear load V, I waveforms
and harmonic
Slide 34
34 Figure : indivisual harmonic components
Slide 35
35 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%
Slide 36
36 Transformer losses and efficiency (Practical) NO I Power
losses efficiency I Power losses efficiency I Power losses
Efficiency 15.5156795.418372.188142.973.76
215.517188.614.419885.5413.516084.60 3232508923.31999024.718889.82
433.53238831.21849233.820191.8 5423549038.924492.3537.923092.66
mean250.886201.6 86.414 184.488.72 36 Linear Load Inductive
Nonlinear Load Capacitive Nonlinear Load NO I Power losses
efficiency I Power losses efficiency I Power losses Efficiency
15.5165.772.355.4188.7868.7338215.468.5
215.5193.885.1914.419285.4413.5181.1681.14
323220.588.0523.3215.8489.2324.721088.63
433.523990.9131.2228.3491.2033.8238.590.93
54230191.9138.9249.692.0937.9242.791.16 mean
22485.682213.485.1217.5584.08 Transformer losses and efficiency
(Theoretical)
Slide 37
Linear and nonlinear load Condition, current harmonic Linear
Load Condition Nonlinear inductive load Condition Nonlinear
Capacitive load Condition Harmonic Order Difference % Harmonic
Order Difference % 30.03A30.15A0.730.83A5.6
50.17A53.71A19.959.41A64.9 70.13A72.24A11.976.12A42.3
90.01A9--90.41A2.8 11- 1.38A7.7110.37A2.6
130.15A131.22A6.2130.95A6.1 37
Slide 38
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 38
Slide 39
39 Figure 9 MATLAB/SIMULINK
Slide 40
Transformer losses and efficiency using MATLAB NO I Power
losses efficiency I Power losses efficiency I Power losses
Efficiency 15.215.396.45.415.296.25.31596
214.5239815.32497.9142397.8 3233698243997.9243797.88
4325897.6336097.5325497.7 5397997.438.98097.2387597.3
mean42.2643.640.8 40 Linear Load Inductive Nonlinear Load
Capacitive Nonlinear Load
Slide 41
CONCLUSIONS 41
Slide 42
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. The
results of experiment show that the increase of harmonic contents
causes extra losses of the transformer. 42