Functionality of Transformers Voltage Regulation - Essay Example

Electronics Lab 2 0 Aim This experiment was set up to determine the functionality of transformers voltage regulation. It focused on measuring the impedance of the high frequency transformers and demonstrating the characteristics of the voltage (V) by the use of the voltage waveforms. The experiment finally showcased the efficiency of low frequency transformers. 2.0 introduction The reason behind conducting this practical was to comprehend the use of transformers, principles and how they are applied in our modern world. A transformer can be defined as a static machine which is used in many energy transformations and is composed of two or more electronic circuits that are linked using one magnetic circuit. Transformers generally consist of two windings; primary and secondary as shown in the diagram below. If the primary windings consist of more turns than the secondary windings, the transformer is a step down transformer as the one shown below. Transformers with greater amounts of secondary windings than primary windings are known as step up transformers. Step down transformers are more common in industries where they are connected from the power grid to the households Figure 2.1: a depiction of an ideal transfomer Transformers are also divided into two; high frequency and low frequency transformers. The low frequency transformers work best at 50/60 Hz while the high frequency transformers work best at 100 kHz. Each set of the devices posse’s advantages over the other in some situations. The low frequency transformer has low eddy current lose, lower stray capacitances and comparatively low antenna losses. On the other hand, the high frequency transformer has a lower magnetizing current meaning that it needs less inductance so that fewer turns fiord a larger gauge of copper wire. This minimizes copper losses. Deciding the best transformer relies on the costs and efficiency. Overall, the high frequency transformer is efficient while the low frequency transformer is less costly. Table 1.1 illustrates the difference between ideal and practical transformer. From the outset, it is conclusive that the ideal transformer doesn’t account for the losses in the circuit while the practical transformer does. 3.2 Design calculations The experiment included a single design calculation to determine the resistor needed for the power resistor. In the calculation, it was found that the value of the power resistor must exceed 30Ω. This meant that the best resistor for the experiment was the 33Ω power resistor. The first lab question was about the meaning of load regulation. From research it was determined that voltage regulation is the measure of the ability of a transformer to maintain constant secondary voltage in case it is supplied with constant primary voltage. Low percentages show that the secondary voltage is stable. The second question was on the behavior of the transformer with the primary connection and no secondary connection. Transformers will show a behavior similar to the BH curve shown below. The BH curve illustrates the relationship between the magnetic flux density (B) and the magnetic field intensity (H). Consequently, the transformer exhibits the BH curve when there is no secondary load. Figure 3.1: ?Ideal transformers BH curve 3.3 Theory The first part of the experiment was set to determine the equivalent circuit of the transformer from the open and short circuit. This is achieved by calculating the impedance values within the frequency levels. The open circuit was used to calculate the parameters of the shunt branch of an equivalent circuit. The shunt branch is illustrated in the figure 3.2, is composed of a parallel connection of a resistor and an inductor. The test was set by putting no load on one end and using the other end to measure the impedance. The LCR meter was deployed to determine the accurate figures of the parameters in the equivalent circuit. An estimation of the parameters in the equivalent circuit is calculated as shown in equation 1. The short circuit test is almost the same as the open circuit but it is connected in short circuit. Load loss and leakage impedance is calculated from the short circuit. The LCR meter is deployed to find the parameters. However, estimates of the values can be calculated from equation 2. The second section involved the calculation of the voltage ratios and the winding turn ratio. Turn ratio is calculated as follows Tratio = where T1 is the primary side while T2 is the secondary side The voltage ratio on the other hand is calculated as Vratio = where T1is the primary side while T2 is the secondary side The third section was on drawing the equivalent circuit. The circuit is drawn in figure 3.4 The final section was on testing the voltage regulation and the efficiency. Voltage regulation is calculated by the equation 5. Inn the equation VNL denotes voltage with no load and VL denotes the voltage with load, for the power resistor and the inductor. ∆V= X 100% The last part of the equation is the efficiency test. It determines how much the transformer is efficient. The equation marked 6 illustrates how efficiency is determined. The Pout variable is used to show the difference of power from the two connections i.e. when no load is connected and when the power resistor is connected. The sum Pc + Pcu is used to calculate the power when the resistor is connected. It’s obvious that efficiency is calculated as the loss in power divided by the total power. ɳ = = X 100% 4.2 Discussions This lab began with the open circuit test and the short circuit test. The tables provided offer a good glimpse of the different results obtained from the Lm and Ls columns and the Rm and the Rs columns. It is seen that the impedance values are greater in the open circuit than they are in the short circuit test. A frequency of 1 kHZ is an exception to the rule because the transformer used was a high frequency transformer hence the low frequency had a very little impact on the impedance levels in the circuit. Similarly it is noted that the values are not linearly related but some intra winding capacitance can be observed. The value was recorded to demonstrate that there was some capacitance in all of the three scenarios. The next stage of the lab was set up to calculate the voltage ratios between two transformers. Obviously, the ratio was expected to be 10/1 and 27/4. The figures 4.1 and 4.2 together with the tables 4.4 and 4.5 clearly demonstrate this idea. A closer analysis of the ratios reveals that the ratio in table 4.4 is more impacted by the changes in frequency than the ratios in table 4.5 because the transformer used was the 100 kHz transformer as illustrated in figure 4.7. This clearly shows that the conventional HF transformers have there ratios severely distorted when they operate at less than 100 kHz. In contrast, the ratios of the planar transformer remain linear because of the way the transformer has been designed to work best at 100 kHz but work even with varied frequencies. Figure 4.7 this was the transformer used in the experiment The transformers square wave results were also discussed. The square waves are composed of many sine waves such that the transformer fails to convert them accurately so that it forms spikes at the beginning of all of the periods. In the third part of the lab, an equivalent circuit was set up based on the results obtained from the first section. The set up was completed with the results from the 4/40 transformer with the frequency of 25 kHz. The fourth was focused on voltage regulation. Voltage regulation is the measure of the transformers ability to retain the secondary voltage when it is supplied with a constant primary voltage. Lower percentages indicate that the secondary voltage is stable and that the transformer is a good regulator. The lab results showed that the transformer used had a voltage regulation of 10.52% for the power resistor and 0.8% for the inductor. It is known that good transformers have a regulation of below 3%. Additionally, the inductive load is known to create conditions of worse voltage regulation. Consequently, the results were in error. The error could have been caused by human error in connecting the transformers or even malfunctioning equipment. Finally, the transformer’s power efficiency was determined. As was previously shown, the transformers power efficiency ought to be 92%. However, it was determined that the transformer had an efficiency of 78%. The error could have been brought about by temperature, structure of the transformer or even how it was wired for connection. 5.0 Conclusion The sole aim of the experiment was to determine the ideas behind transformers and how they regulate voltage. The sections of the experiment together with the exercises were perfect for doing the same. All the calculations and the results were recorded. The experiment also measured the impedance of the high voltage transformer and obtained its voltage v characteristics. To add on, the voltage waveforms were also gotten together with the determination of the efficiency of the low frequency transformer. From the experiment, it was determined that damaged transformers can give false readings but this error can be reduced by using multiple transformers. Ideal transformer Practical transformer Has100% efficiency Has below 100% efficiency Does not have losses Has losses Made with purely inductive materials Is made up of two purely inductive materials Does not have I2R losses Has I2R losses Doe not have leakage drop Has leakage drop Does not have iron loss Has iron loss Does not have ohmic resistance drop Has ohmic resistance drop Found only in ideal situation Found in practical situation Cannot be used in practical situation Can be used in any practical situation Table 1.1 differences between ideal and practical transformers Even though ideal transformers have an efficiency of 100% this is not possible with practical transformers because of the energy losses and other factors. Practical transformers therefore have an efficiency of below 100%. Both of the transformers have no losses. Whereas ideal transformers have no leakage drop, no iron loss, no I2R loss, no ohmic resistance drop and are made of purely inductive materials the practical transformers have leakage drop, iron loss, I2R loss, ohmic resistance drop and are made of two purely inductive materials. Ideal transformers have ideal conditions whereas practical transformers have practical conditions hence can be used in practical conditions. Ideal transformers do not exist in the first place hence cannot be used. Read More