1 00:00:18,984 --> 00:00:21,328 DISTANCE GROUNDING FACTOR 2 00:00:21,875 --> 00:00:31,171 Numeric distance protection relays use various algorithms, based on measured current and voltage, to calculate fault impedance 3 00:00:31,563 --> 00:00:37,969 The calculated impedances differ under certain conditions, such as single-phase-to-ground faults 4 00:00:38,281 --> 00:00:48,671 Generally, three methods are commonly used for calculating impedance in phase-to-ground faults: Type A, Type B, and Type C 5 00:00:48,828 --> 00:00:55,312 Here, a single-phase-to-ground fault (Phase E1-L) has been applied to three relays with different algorithms 6 00:00:55,625 --> 00:01:00,781 The voltage and current measured by each relay are displayed as shown. 7 00:01:01,094 --> 00:01:06,015 The line impedances calculated by the distance relays are shown as displayed 8 00:01:06,250 --> 00:01:16,250 The different measured impedance values are due to the varying grounding factors used in the distance relays. Below, these three methods are introduced 9 00:01:16,875 --> 00:01:22,578 As you may know, the distance relay determines the fault location by calculating impedance 10 00:01:23,125 --> 00:01:33,593 The shown diagram represents the equivalent circuit of a double-fed line where a single-phase-to-ground fault has occurred in Phase L1 11 00:01:33,906 --> 00:01:41,796 In this circuit, the relay at point M measures voltage and current and calculates impedance based on Kirchhoff's law 12 00:01:42,500 --> 00:01:52,109 In the written equation, the term RF is considered as zero undefined due to the arc caused by the short circuit 13 00:01:52,266 --> 00:02:00,625 Therefore, by making certain assumptions to simplify this equation, the relay calculates the voltage at point M 14 00:02:01,021 --> 00:02:10,552 In the equations, RF is assumed to be zero, and IE.ZE are determined using the grounding factor. 15 00:02:11,099 --> 00:02:21,177 The grounding factor (K) is used in phase-to-ground faults and relates to line parameters, defined as the ratio of ground impedance to line impedance 16 00:02:21,412 --> 00:02:28,208 . The diagram shows the equivalent circuit for a phase-to-ground fault, assuming RF = 0 17 00:02:28,678 --> 00:02:41,490 where the total impedance ZS is divided into line impedance ZL and ground impedance ZE. With these assumptions, we have the equations as shown. 18 00:02:41,959 --> 00:02:53,521 In the displayed equations, Z0s and Z1s represent the positive sequence and zero sequence impedances of the source, respectively 19 00:03:00,865 --> 00:03:08,911 In general, there are three methods for expressing the grounding factor (K), which are convertible to one another 20 00:03:09,381 --> 00:03:16,490 The first method is the ratio of ground impedance to line impedance, which is a complex number 21 00:03:16,881 --> 00:03:24,068 The second method is the division of zero-sequence impedance by positive-sequence impedance. 22 00:03:24,537 --> 00:03:33,755 The third method represents the grounding factor as a pair of real numbers. Depending on what information about the grounding factor is available 23 00:03:34,068 --> 00:03:43,755 it can be independently entered in the Object Test window, Distance Block, Factor Grounding section of the Vebko software 24 00:03:44,693 --> 00:03:55,474 The Factor Grounding section in the Parameters Protection Distance window allows for inputting the grounding factor and selecting the relay's algorithm 25 00:03:55,865 --> 00:04:05,693 Using the Mode dropdown menu, the method of entering the factor (RL/RE or KL K, K0) can be chosen without affecting the relay's algorithm. 26 00:04:07,178 --> 00:04:14,052 As mentioned, there are equations for converting different types of grounding factors into each other 27 00:04:14,209 --> 00:04:21,396 The relationship between the KL factor and other grounding-related factors is shown. 28 00:04:27,724 --> 00:04:33,505 Distance Protection Relay Algorithm Type A, ‘KL Complex’: 29 00:04:33,974 --> 00:04:39,599 The distance relay with Type A algorithm uses the KL factor, as shown 30 00:04:39,912 --> 00:04:43,505 for calculating impedance in a phase-to-ground fault. 31 00:04:43,896 --> 00:04:50,927 In the shown equation, assuming that the first-phase current, ground current, and fault current are equal (-=1IL=IIF=IE ) 32 00:04:51,240 --> 00:04:56,240 , and with V as the voltage measured by the relay during the fault 33 00:04:56,474 --> 00:05:08,896 the impedance measured by the relay is calculated as shown. Distance Protection Relay Algorithm Type B, ‘XL/XE, RL/RE’: 34 00:05:11,084 --> 00:05:22,490 The distance relay with Type B algorithm calculates impedance for a phase-to-ground fault using the complex grounding factors KrKr and KxKx, as displayed. 35 00:05:22,708 --> 00:05:30,129 In the given equation, it is assumed that the first-phase current, ground current, and fault current are equal (i.e., IL1=I=IF=IEIL1=I=IF=IE). 36 00:05:30,521 --> 00:05:40,599 Additionally, V represents the voltage measured by the relay during the fault. Based on this, the impedance measured by the relay is calculated as shown. 37 00:05:41,459 --> 00:05:49,583 Type C distance relays use an algorithm similar to Type B for calculating the imaginary part of the fault impedance X. 38 00:05:49,896 --> 00:05:55,286 However, they calculate the real part of the fault impedance R differently. 39 00:05:55,599 --> 00:06:04,114 This algorithm considers the arc resistance (RF arc) by assuming that the fault current IF is equal to the line current. 40 00:06:04,428 --> 00:06:11,302 The main concept in this algorithm is to combine arc resistance with line resistance 41 00:06:11,537 --> 00:06:19,818 In other words, the real part of the ground impedance is subtracted from the real part of the phase-to-ground fault impedance (ground-fault loop). 42 00:06:20,131 --> 00:06:30,365 The ground resistance value can then be determined from the calculated XL as a function of the factor Kr and the line angle. 43 00:06:41,615 --> 00:06:45,755 Interpretation of Results for Different Algorithms 44 00:06:45,990 --> 00:06:50,599 Simplifying (IE=−IF=IL1IE=−IF=IL1) allows for comparing the obtained results 45 00:06:51,459 --> 00:06:58,802 The displayed table shows the line impedance calculated by different distance protection algorithms. 46 00:06:59,896 --> 00:07:03,958 The displayed table shows a key result of the analysis 47 00:07:04,193 --> 00:07:13,177 The measured impedance (Zmeas = Rmeas +j xmeas) by the distance relay includes the line impedance ( Z_L) along with a portion of the arc resistance. 48 00:07:13,568 --> 00:07:21,693 The amount of added RF arc resistance to the line impedance depends on the distance protection algorithm used. 49 00:07:22,709 --> 00:07:26,068 As shown in the table, in Type A relays 50 00:07:26,303 --> 00:07:34,115 the grounding factor or KL impacts both the real and imaginary parts of the impedance as a complex value. 51 00:07:34,271 --> 00:07:40,443 In this case, the arc effect from a short circuit is considered an inductive and resistive phenomenon 52 00:07:40,678 --> 00:07:46,224 represented as a complex impedance. In Type B algorithms, 53 00:07:46,693 --> 00:07:57,240 the relays reduce the arc resistance ( RF ) by a factor of 1 /(1+Kr) in the real part 54 00:07:57,474 --> 00:08:05,911 . In Type C algorithms, relays measure impedance without any compensation factor for arc resistance ( RF) 55 00:08:06,303 --> 00:08:14,661 Distance relays of Types A, B, and C define measured impedance differently. Consequently: 56 00:08:14,818 --> 00:08:27,865 Scaling on the impedance plane changes and will no longer depend solely on ( X ) and (R). The relevant axes scaling is illustrated in the accompanying diagrams. 57 00:08:28,568 --> 00:08:36,536 Measured impedances from different relay types are not directly comparable on the same impedance plane. 58 00:08:36,849 --> 00:08:46,693 All distance protection algorithms produce the same ( R_L ) and ( X_L ) results at the line angle or when RF = 0. 59 00:08:46,928 --> 00:08:55,990 Outside the line angle, depending on the fault's location on the impedance plane, the arc resistance is added to the line impedance 60 00:08:57,630 --> 00:09:07,318 All distance protection algorithms function correctly; however, grounding factors must be considered when setting zones and testing relays. 61 00:09:08,646 --> 00:09:11,771 Considering Grounding Factors During Testing 62 00:09:12,162 --> 00:09:19,974 The Vebko software, including the Test and Stable versions, implements all mentioned distance protection algorithms. 63 00:09:20,359 --> 00:09:25,515 As discussed, depending on the available grounding factor data 64 00:09:26,063 --> 00:09:33,641 it can be entered independently according to the equations in the Vebko software’s Object Test window 65 00:09:33,875 --> 00:09:37,468 within the Distance Block under the Factor Grounding section. 66 00:09:37,938 --> 00:09:44,656 You can also select any of the mentioned algorithms to calculate current and voltage. 67 00:09:45,125 --> 00:09:51,843 It’s crucial that both the testing software and the relay use the same algorithm during testing 68 00:09:52,078 --> 00:09:56,609 otherwise, this may result in inaccurate test outcomes. 69 00:09:56,844 --> 00:10:03,484 The choice of distance protection algorithm is selected by checking boxes, as shown in the figure. 70 00:10:03,953 --> 00:10:09,968 For the algorithms used by distance protection relays, refer to the relevant manuals and documentation 71 00:10:10,125 --> 00:10:21,218 Since algorithms are not always publicly available, some common examples are listed in the displayed table.