1. EXPERIMENTAL STUDY AND COMPARATIVE ANALYSIS OF TRANSFORMER HARMONIC BEHAVIOUR UNDER LINEAR AND NONLINEAR LOAD CONDITIONS

2. Overview Practical Results Introduction Transformer Harmonic
Conclusions

3. Introduction increases the losses of power transformers,
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 :
increases the losses of power transformers,
cause extra heat of transformer,
can affect the insulation lifetime and
It can also cause reduced power factor, lower productivity, efficiency, capacity and lack of system performance

4. Objective: investigation in harmonic problems and their effects on power transformers and other power systems.

5. TRANSFORMERS

6. Power Transformer
A transformer is a static device that transfers electrical energy from one circuit to another by electromagnetic induction..

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.

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

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

10. HARMONIC

11. Harmonics
Harmonic distortion is caused by the introduction of waveforms at frequencies in multiplies of the fundamental frequency.

12. Harmonic Analysis
Figure 1: Fundamental with two harmonics

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:
there phase diode rectifier
Converters
Control circuits
Motors

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.

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

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

17. Practical RESULTS

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.

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

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
The Y-Y Connection in Three-Phase Systems

21. The Y-Y Connection in Three-Phase Systems in transformer
FIGURE 2: Y-Y transformer connections

22. open circuit parameters (Primary)
open circuit parameters (Secondary)

23. short circuit parameters (Primary)

24. Transformer Data

25. Figure 5: Linear Load Condition
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

26. Figure 4: Linear load V, I waveforms and harmonic
Experiments 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,
Figure 4: Linear load V, I waveforms and harmonic

27. Figure : indivisual harmonic components

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

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 .

30. Experiments Nonlinear inductive load Condition
Figure 5: Nonlinear inductive load Condition
Figure 6: Nonlinear load V, I waveforms and harmonic

31. Figure : indivisual harmonic components

32. 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 .

33. Experiments Nonlinear Capacitive Loads Condition
Figure 7: Nonlinear Capacitive load
Figure 8: Nonlinear load V, I waveforms and harmonic

34. Figure : indivisual harmonic components

35. This figure shows the primary and secondary current and voltage
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%

36. I I Transformer losses and efficiency (Practical) 1 5.5 156 79 5.4 183
Linear Load
Inductive
Nonlinear Load
Capacitive NO I
Power losses
efficiency
Efficiency 1
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
38.9
244
92.35
37.9
230
92.66
mean
250.8 86
201.6
86.414
184.4
88.72
Transformer losses and efficiency (Theoretical) NO I
Power losses
efficiency
Efficiency 1
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
mean
224
85.682
213.4
85.1
217.55
84.08 36

37. Linear and nonlinear load Condition, current harmonic
Nonlinear inductive load Condition
Nonlinear Capacitive load Condition
Harmonic Order
Difference % 3
0.03A
0.15A
0.7
0.83A
5.6 5
0.17A
3.71A
19.9
9.41A
64.9 7
0.13A
2.24A
11.9
6.12A
42.3 9
0.01A -
0.41A
2.8 11
1.38A
7.7
0.37A
2.6 13
1.22A
6.2
0.95A
6.1

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

39. Figure 9 MATLAB/SIMULINK

40. Transformer losses and efficiency using MATLAB
Linear Load
Inductive
Nonlinear Load
Capacitive NO I
Power losses
efficiency
Efficiency 1
5.2
15.3
96.4
5.4
15.2
96.2
5.3 15 96 2
14.5 23 98 24
97.9 14
97.8 3 36 39 37
97.88 4 32 58
97.6 33 60
97.5 54
97.7 5 79
97.4
38.9 80
97.2 38 75
97.3
mean
42.26
43.6
40.8

41. CONCLUSIONS

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.

43. THANK YOU