Overview

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

2. Overview • Introduction • Transformer • Harmonic • Practical Results • Conclusions

3. 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 : • 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 • Wyeto Delta • Wyeto 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

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. ExperimentsLinear Load Condition Figure 5: 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.

26. ExperimentsLinear 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. 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. Transformer losses and efficiency (Practical) Transformer losses and efficiency (Theoretical) 36

37. Linear and nonlinear load Condition, current harmonic

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

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