1 00:00:18,959 --> 00:00:21,123 Capacitive Voltage Transformers 2 00:00:21,148 --> 00:00:25,468 Voltage transformers are composed of a core, two windings, and insulation. 3 00:00:25,493 --> 00:00:33,007 VTs convert the high voltage of the primary side to low voltage on their secondary winding with the turn ratio written on their plate. 4 00:00:33,032 --> 00:00:41,210 Because of the internal casualties such as copper and iron casualties, the vector of the secondary voltage is different from the primary voltage. 5 00:00:41,258 --> 00:00:47,140 Moreover, the connected burden is capable of affecting the turn ratio error and phase displacement. 6 00:00:47,165 --> 00:00:53,687 If the actual amplitude of the secondary voltage is lower than nominal secondary voltage, the amplitude error is negative. 7 00:00:53,712 --> 00:00:59,740 Also, if the secondary vector is lagging in relation to the primary vector, the phase error is negative. 8 00:00:59,765 --> 00:01:05,968 To compensate for the turn ratio error, sometimes manufacturers adjust the number of primary or secondary turns. 9 00:01:05,993 --> 00:01:14,023 Nowadays, most of the VTs that are used in the industry are either inductive VTs or capacitive VTs which are called “CVT”. 10 00:01:14,048 --> 00:01:21,445 CVTs are composed of an inductive VT, a high-voltage capacitive divider and a compensator reactor. 11 00:01:21,470 --> 00:01:30,865 In the IEC standard, the title CVT is used for this equipment but in the ANSI standard, this equipment is called CCVT. 12 00:01:30,897 --> 00:01:38,107 The compensator rector is designed in a way that it can compensate for the phase displacement caused by the capacitive divider. 13 00:01:38,132 --> 00:01:45,068 All CVTs can be used for measurement purposes but only certain types of this equipment are suitable for protection purposes 14 00:01:45,093 --> 00:01:51,570 Dual-purpose CVTs (measurement and protection) must be in accordance with all of the considered descriptions and the current standards. 15 00:01:51,595 --> 00:01:54,125 According to the maximum allowed error percentage, 16 00:01:54,158 --> 00:02:04,523 the accuracy class of the protection CVTs is considered to be from 5 percent of the nominal voltage to a coefficient of the nominal voltage (Rated Voltage Factor) and after its value, the letter P is used. 17 00:02:04,548 --> 00:02:09,015 3P and 6P are the standard accuracy classes for protection CVTs. 18 00:02:09,040 --> 00:02:13,851 For example, 3P accuracy class means that the maximum allowed error is 3 percent. 19 00:02:13,876 --> 00:02:22,428 Moreover, in IEC standard, three classes of T1, T2 and T3 are considered for the function of CVT in transient state. 20 00:02:22,453 --> 00:02:31,295 For example, 3PT2 class indicates that the function of the 3P class is for protection purposes and T2 class is for transient states. 21 00:02:31,320 --> 00:02:35,742 Classes related to the transient response are a defined in the following table: 22 00:02:35,767 --> 00:02:37,046 In the above relation, 23 00:02:37,071 --> 00:02:40,671 Us (t) is the response for the transient secondary voltage. 24 00:02:40,703 --> 00:02:51,530 For example, for the 3PT2 class, the relation of the transient voltage to the nominal voltage peak in the range of from 10 ms to 90 ms after the beginning of the transient state, 25 00:02:51,595 --> 00:02:56,640 It should decreas and be in the range of less than 25 times to 0.2. 26 00:02:56,665 --> 00:03:00,203 In this regard, it is necessary to pay attention to several points: 27 00:03:00,228 --> 00:03:07,789 CVTs need a damping piece of equipment for the 6PT3 and 3PT3 transient response classes. 28 00:03:07,814 --> 00:03:15,328 By agreement between the manufacturer company and the customer, it is possible to consider different values for the turn ratio and Ts time. 29 00:03:15,353 --> 00:03:20,320 Selecting the transient response class depends on the characteristics of the protection relays. 30 00:03:20,345 --> 00:03:29,101 About Measuring CVTs, the accuracy class is defined based on the highest allowed error percentage in the nominal voltage with the nominal burden. 31 00:03:29,126 --> 00:03:37,156 The standard accuracy classes for single-phase Measuring CVTs are considered to be 0.2, 0.5, 1.0 and 3.0. 32 00:03:37,181 --> 00:03:38,468 Test Object tab 33 00:03:38,493 --> 00:03:44,187 To perform a test, every module needs a set of information about the equipment which is entered in “Test Object”. 34 00:03:44,212 --> 00:03:51,296 In this tab, the general characteristics of the “CVT” and its information for performing the test and adding to the report are specified. 35 00:03:51,329 --> 00:04:01,359 In “Data” section, information such as serial number, model, the manufacturer company and the installation location of the “CVT” are entered to be added to the report. 36 00:04:01,384 --> 00:04:09,703 In “Winding Material” field in “Temperature Correction” section, the conductor type of the windings is selected from among “Copper” and “Aluminum”. 37 00:04:09,728 --> 00:04:22,718 In “Winding Temp.” field the current temperature of the windings and in “Reference Temp.” field, the reference temperature for measuring the resistance of the windings are entered so that they can be used to correct the values measured in different temperatures. 38 00:04:22,743 --> 00:04:30,968 Usually, the reference temperature which is 75 degrees is written in front of the secondary winding resistance on the plate of the “CVT”. 39 00:04:30,993 --> 00:04:42,953 In “Correction Factor” field which is uneditable, the temperature correction factor is calculated by the software in accordance with the current ambient temperature as well as the reference temperature and the winding material. 40 00:04:42,978 --> 00:04:48,976 It is possible to view the relation used for calculating this factor, by holding the cursor on its field. 41 00:04:49,001 --> 00:04:54,453 The „RMS“ value of every parameter is calculated based on the average of several time periods. 42 00:04:54,478 --> 00:05:03,054 As the number of these time periods increases, it takes longer to make the calculations but also the accuracy increases and there will be fewer fluctuations. 43 00:05:03,079 --> 00:05:08,257 The number of these time periods is entered in „Averaging“ field in „Noise Suppression“ section. 44 00:05:08,282 --> 00:05:13,226 This field is the same as „No. of period“ field in „Setting“ in „Signal View“ window. 45 00:05:13,251 --> 00:05:23,546 In “Date” field in “Extra Data” section, the date of performing the test is entered in AD and the information about the performer of the test is entered in “Tested By” field. 46 00:05:23,571 --> 00:05:28,281 Also, the information about the supervisor is entered in “Approved By” field. 47 00:05:28,306 --> 00:05:35,234 In “Data Table”, the characteristics of every core and tap are entered in every row in accordance with the characteristics plate. 48 00:05:35,259 --> 00:05:40,750 The core number and the tap number are entered in “Core Number” and “Tap Number” fields, respectively. 49 00:05:40,775 --> 00:05:50,851 The primary parameters are entered in “Vprimary” and “Primary Factor” fields while the secondary characteristics are entered in “Vsecondary” and “Secondary Factor” fields. 50 00:05:50,890 --> 00:06:00,585 The burden is specified in “VA” field and in “CLP” and “CLM” fields, the Protection Core and Measuring of the transformer are entered, respectively. 51 00:06:00,610 --> 00:06:08,078 Likewise, the information related to the two other taps of the CVT that are being used is specified. 52 00:06:08,103 --> 00:06:18,397 Also, if the characteristics of the “VT resistance” are available, it is possible to check “Show Resistance Column” option to add the related column to the table. 53 00:06:18,422 --> 00:06:26,311 By checking this option, some changes are made in the “DC Resistance” test table which will be thoroughly explained in its related video. 54 00:06:26,336 --> 00:06:37,772 Also, by pressing the „Add to Report“ option in the box at the bottom, this information is added to the output report and a message stating „The Report was added to the list“ is displayed. 55 00:06:37,876 --> 00:06:43,850 It is possible to view the report by selecting „Report“ window from the bar at the right. 56 00:06:43,875 --> 00:06:50,420 By clicking on „Delete Report“ option in „Delete From Repor“ window, the added report is removed. 57 00:06:50,445 --> 00:06:52,787 If „Set as default“ option is checked, 58 00:06:52,812 --> 00:07:01,990 the entered information is saved as default and every time, by opening the „Capacitor Voltage Transformer(CVT)“ room this information is displayed.