1 00:00:23,745 --> 00:00:23,809 E 2 00:00:23,810 --> 00:00:23,875 Ex 3 00:00:23,876 --> 00:00:23,940 Exc 4 00:00:23,941 --> 00:00:24,005 Exci 5 00:00:24,006 --> 00:00:24,070 Excit 6 00:00:24,071 --> 00:00:24,135 Excita 7 00:00:24,136 --> 00:00:24,200 Excitat 8 00:00:24,201 --> 00:00:24,265 Excitati 9 00:00:24,266 --> 00:00:24,330 Excitatio 10 00:00:24,331 --> 00:00:24,395 Excitation 11 00:00:24,396 --> 00:00:24,460 Excitation 12 00:00:24,461 --> 00:00:24,526 Excitation t 13 00:00:24,527 --> 00:00:24,591 Excitation te 14 00:00:24,592 --> 00:00:24,656 Excitation tes 15 00:00:24,657 --> 00:00:24,721 Excitation test 16 00:00:24,722 --> 00:00:24,786 Excitation test 17 00:00:24,787 --> 00:00:24,851 Excitation test o 18 00:00:24,852 --> 00:00:24,916 Excitation test of 19 00:00:24,917 --> 00:00:24,981 Excitation test of 20 00:00:24,982 --> 00:00:25,046 Excitation test of C 21 00:00:25,047 --> 00:00:25,111 Excitation test of CT 22 00:00:25,112 --> 00:00:25,177 Excitation test of CT, 23 00:00:25,178 --> 00:00:25,242 Excitation test of CT, 24 00:00:25,243 --> 00:00:25,307 Excitation test of CT, P 25 00:00:25,308 --> 00:00:25,372 Excitation test of CT, Pa 26 00:00:25,373 --> 00:00:25,437 Excitation test of CT, Par 27 00:00:25,438 --> 00:00:25,502 Excitation test of CT, Part 28 00:00:25,503 --> 00:00:25,567 Excitation test of CT, Part 29 00:00:25,568 --> 00:00:25,632 Excitation test of CT, Part I 30 00:00:25,633 --> 00:00:25,697 Excitation test of CT, Part I: 31 00:00:25,698 --> 00:00:26,198 Excitation test of CT, Part I: 32 00:00:26,223 --> 00:00:26,280 T 33 00:00:26,281 --> 00:00:26,338 Tr 34 00:00:26,339 --> 00:00:26,396 Tra 35 00:00:26,397 --> 00:00:26,454 Tran 36 00:00:26,455 --> 00:00:26,512 Trans 37 00:00:26,513 --> 00:00:26,570 Transf 38 00:00:26,571 --> 00:00:26,628 Transfo 39 00:00:26,629 --> 00:00:26,686 Transfor 40 00:00:26,687 --> 00:00:26,710 Transform 41 00:00:26,745 --> 00:00:26,802 Transforme 42 00:00:26,803 --> 00:00:26,859 Transformer 43 00:00:26,860 --> 00:00:26,917 Transformer 44 00:00:26,918 --> 00:00:26,975 Transformer a 45 00:00:26,976 --> 00:00:27,033 Transformer an 46 00:00:27,034 --> 00:00:27,091 Transformer and 47 00:00:27,092 --> 00:00:27,149 Transformer and 48 00:00:27,150 --> 00:00:27,207 Transformer and i 49 00:00:27,208 --> 00:00:27,265 Transformer and it 50 00:00:27,266 --> 00:00:27,323 Transformer and its 51 00:00:27,324 --> 00:00:27,381 Transformer and its 52 00:00:27,382 --> 00:00:27,439 Transformer and its s 53 00:00:27,440 --> 00:00:27,497 Transformer and its sa 54 00:00:27,498 --> 00:00:27,555 Transformer and its sat 55 00:00:27,556 --> 00:00:27,613 Transformer and its satu 56 00:00:27,614 --> 00:00:27,670 Transformer and its satur 57 00:00:27,671 --> 00:00:27,728 Transformer and its satura 58 00:00:27,729 --> 00:00:27,786 Transformer and its saturat 59 00:00:27,787 --> 00:00:27,844 Transformer and its saturati 60 00:00:27,845 --> 00:00:27,902 Transformer and its saturatio 61 00:00:27,903 --> 00:00:27,960 Transformer and its saturation 62 00:00:27,961 --> 00:00:28,018 Transformer and its saturation: 63 00:00:28,019 --> 00:00:28,419 Transformer and its saturation: 64 00:00:28,444 --> 00:00:30,991 Before talking about the Excitation test, 65 00:00:31,016 --> 00:00:41,383 it is necessary to review some important and useful subjects related to analyzing behavior of transformers including equivalent circuit and some electric and electromagnetic analyses. 66 00:00:41,408 --> 00:00:44,601 You can see a transformer equivalent circuit in the figure. 67 00:00:44,626 --> 00:00:54,223 In this circuit, “Rp” and “Rs” refer to the primary and secondary coils resistance respectively which occur as heat loss and increase in the temperature of the coil. 68 00:00:54,248 --> 00:01:02,158 “XP” and “XS”, on the other hand, indicate a part of the flux whose path is through air and is known as “leakage Flux”. 69 00:01:02,183 --> 00:01:12,104 In the parallel branch, “Rc” is the indicator of core loss including eddy current and Hysteresis losses which occur as increase in the temperature of the core. 70 00:01:12,136 --> 00:01:19,547 The reason for parallelism of “Rc” is that the losses caused by it are in accordance with the square of the input voltage. 71 00:01:19,572 --> 00:01:25,613 “Xm” indicates magnetizing inductance of the wires wrapped around the core of the transformer. 72 00:01:26,574 --> 00:01:30,956 Transformer Loading and Its Effect on Transformer Saturation 73 00:01:31,166 --> 00:01:36,341 When load is drawn from the transformer, this power causes the secondary current to increase. 74 00:01:36,366 --> 00:01:41,927 When the secondary current increases, the flux caused by the secondary coil increases as well. 75 00:01:42,197 --> 00:01:50,243 Also, after the secondary current increases, the primary current increases as well which leads to an increase in the flux of the primary side. 76 00:01:50,346 --> 00:01:57,657 But since the changes in the secondary side current are bigger, the flux of the secondary side will be more than the primary side. 77 00:01:57,776 --> 00:02:05,928 Because of the influence of the opposite side of these two in the equivalent flux of the transformer core, the flux of the transformer decreases. 78 00:02:05,978 --> 00:02:12,917 As a result, while the load drawn from the terminals of the power transformer increases, the core recedes from the saturation area. 79 00:02:12,942 --> 00:02:21,181 Therefore, in full-load it is possible to use a small core for the transformer, but since transformer is not always used in nominal load, 80 00:02:21,206 --> 00:02:26,908 by reducing the core, the decrease in the load, leads to the saturation of transformer. 81 00:02:26,933 --> 00:02:36,553 So to avoid transformer saturation in light load and change the waveform from sine wave, it is necessary to extend the transformer core. 82 00:02:37,436 --> 00:02:37,505 S 83 00:02:37,506 --> 00:02:37,574 Sa 84 00:02:37,575 --> 00:02:37,643 Sat 85 00:02:37,644 --> 00:02:37,712 Satu 86 00:02:37,713 --> 00:02:37,782 Satur 87 00:02:37,783 --> 00:02:37,851 Satura 88 00:02:37,852 --> 00:02:37,920 Saturat 89 00:02:37,921 --> 00:02:37,989 Saturati 90 00:02:37,990 --> 00:02:38,059 Saturatio 91 00:02:38,060 --> 00:02:38,128 Saturation 92 00:02:38,129 --> 00:02:38,197 Saturation 93 00:02:38,198 --> 00:02:38,266 Saturation C 94 00:02:38,267 --> 00:02:38,336 Saturation Cu 95 00:02:38,337 --> 00:02:38,405 Saturation Cur 96 00:02:38,406 --> 00:02:38,474 Saturation Curv 97 00:02:38,475 --> 00:02:38,543 Saturation Curve 98 00:02:38,544 --> 00:02:38,613 Saturation Curve 99 00:02:38,614 --> 00:02:38,682 Saturation Curve o 100 00:02:38,683 --> 00:02:38,751 Saturation Curve of 101 00:02:38,752 --> 00:02:38,820 Saturation Curve of 102 00:02:38,821 --> 00:02:38,890 Saturation Curve of “ 103 00:02:38,891 --> 00:02:38,959 Saturation Curve of “C 104 00:02:38,960 --> 00:02:39,028 Saturation Curve of “CT 105 00:02:39,029 --> 00:02:39,097 Saturation Curve of “CT” 106 00:02:39,141 --> 00:02:39,541 Saturation Curve of “CT” 107 00:02:39,566 --> 00:02:48,495 As mentioned before, the power transformer recedes from saturation by increasing the current whereas CT gets closer to the saturation area. 108 00:02:48,520 --> 00:02:58,873 The reason for this is related to the voltage of parallel branch where, in the power transformer by increasing the current, voltage of the parallel branch decrease. 109 00:03:01,286 --> 00:03:09,822 But in “CT”, by increasing the current, the voltage of the parallel branch in the secondary side increases and the “CT” saturates. 110 00:03:09,847 --> 00:03:21,220 “CT” saturation in a power system is caused by increase in the primary current because of occurrence of a fault which disables the “CT” to move the fault current to the secondary with the correct ratio. 111 00:03:21,332 --> 00:03:28,079 Since the saturation point of “CT” is related to voltage and parallel branch current, while doing this test, 112 00:03:28,190 --> 00:03:34,029 the secondary voltage increases and the point where by increasing the voltage by 10 percent, 113 00:03:34,172 --> 00:03:38,810 the drawn current increases by 50 percent is considered as the saturation point. 114 00:03:38,835 --> 00:03:44,404 In future videos the ways to enter the values and do the test for different “CT”s will be provided.