WAMS-based Hierarchical Active Power Differential Signal Algorithm for Backup Protection of a FACTS Compensated Transmission Network

POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER WAMS-based Hierarchical Active Power Differential Signal Algorithm for Backup Protection of a FACTS Compensated Transmission Network Sreelekha VENUGOPAL1, Prince ASOK 1, Sabha Raj ARYA2 1Department of Electrical Engineering, Rajiv Gandhi Institute of Technology, APJ Abdul Kalam Technological University, Alathara Rd, 695016 Kerala, India 2Department of Electrical Engineering, Sardar Vallabhbhai National Institute of Technology, Ichchhanath, Surat, 395007 Gujrat, India [email protected], [email protected], sabhara[email protected] DOI: 10.15598/aeee.v20i4.4512 Article history: Received Mar 22, 2022; Revised Jul 20, 2022; Accepted Jul 27, 2022; Published Dec 31, 2022. This is an open access article under the BY-CC license. Abstract. This paper proposes a hierarchical active power differential signal-based generalized backup protection algorithm using Wide Area Measurement System (WAMS) data for Flexible AC Transmission System (FACTS)-compensated transmission networks. The proposed algorithm can be used for backup protection of transmission systems with any shunt and series-type FACTS devices. The increased number of FACT compensators affects the reliable operation of primary and backup protection of the transmission lines. Both shunt and series compensated lines cause malfunctioning of existing backup protection schemes. The proposed algorithm utilizes the sequence components of bus voltages and active power differential signals of lines to identify the faulty line. The algorithm is validated on a modified 9-bus system under MATLAB/SIMULINK platform. It is observed that the algorithm is suitable for identifying a faulty line in transmission systems containing both uncompensated and compensated lines with series or shunt-type FACTS controllers. This algorithm has the advantage that it uses a generalized backup protection logic and can be used for the accurate identification of a faulty line irrespective of the type of compensation devices. Keywords Backup protection, FACTS devices, faulty line identification, PMU, Power differential protection, Superimposed power component, WAMS. 1. Introduction As the power demand goes on increasing with industrial developments and commercial activities, the power transmission system is being modified. Due to environmental reasons and right-of-way restrictions, construction and the addition of a completely new transmission path may be difficult and impossible. The efficient utilization of the existing power transmission system by including Flexible AC Transmission System (FACTS) devices is a preferred alternative for the problem, which increases the power transmission capability of lines with improved stability margins and control of power [1]. FACTS compensators alter the magnitude and phase angle of the apparent line impedance and line current, as seen by the protection devices. The existing relays are designed for uncompensated lines and their settings do not consider the presence of compensating devices and the variation of line impedance or current values due to their compensating actions. Hence the incorporation of FACTS devices in transmission systems causes the malfunctioning of distance relays, ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 390 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER introduces problems in the operation of the existing protection system, and affects the reliable operation of primary and backup protection [2] and [3]. Both shunt and series compensated lines cause problems in existing protection schemes. In the present scenario, it is necessary to develop a generalized protection scheme that can take care of the protection issues caused by the compensated lines also. The development of a secured remote backup protection scheme using wide-area measurement systembased data for the present-day transmission system is very essential for secure operation [4]. Several transmission line protection algorithms have been developed using different techniques for relaying applications. Traveling wave-based and transient componentbased fault detection schemes need higher sampling rates for the capture of details in the signals [6], [7], [8] and [9]. Differential current-based techniques [10], [11], [12], [13] and [14] and impedance-based estimation techniques [15], [16] and [17] are also well described in the literature. But these techniques cannot be used as generalized algorithms in the presence of compensating devices. Various techniques are proposed by the researchers for the backup protection of uncompensated lines using Wide Area Measurement System (WAMS)-based data. By estimating and analyzing the distribution of sequence components of fault voltage the faulty bus can be identified [17]. Positive sequence voltage magnitude and absolute angle difference of positive sequence current angle are effective in identifying the faulty bus and the faulty line in a system with uncompensated lines [18]. In [19], the faulty region is identified using differential currents, and the faulty line is determined by a fault correlation factor calculated using the steady-state components of voltage and current. An active power differential-based logic is effective for the primary and backup protection schemes of uncompensated lines utilizing Phasor Measurement Unit (PMU) data [20]. A synchrophasor-based state estimator can be used for the backup protection of transmission lines [21]. But these algorithms do not consider the effects of compensating devices. FACTS devices help to improve the steady-state and transient performance of the system. But the presence of these controllers poses many problems in the operation of the protective relays due to the fast control actions, impedance changes of the line, voltage and current injected from the control devices, and the transients produced by the control actions. When the device is included in the fault loop, it affects the apparent impedance seen by the distance relay causing its maloperation. The type of FACTS device has also its effect on the apparent impedance seen by the relay and trip boundary. A backup protection scheme for series compensated lines based on the magnitudes and angles of positive and negative sequence voltages and currents is found more effective to avoid the malfunctioning of the relay in the presence of series compensation [22]. The modified impedance method for series compensated lines requires the measurement or estimation of voltage across the compensating device [23]. Spectral energy calculations based differential protection scheme using the Discrete Wavelet Transform (DWT) technique are proposed in [24] for SVC compensated lines. Fault detection in Fixed Series Capacitor (FSC) compensated lines can be achieved using differential admittance [25]. Sequence and superimposed components-based logic can be used for fault detection in the presence of Unified Power Flow Controller (UPFC) compensated lines [26] and [27]. Impedance-based techniques and differential apparent power-based techniques are also developed to avoid the malfunctioning of relays in the presence of UPFC [28], [29] and [30]. But these algorithms developed for compensated systems have considered only one type of device and its effects at a time and cannot be generalized. This work attempts to develop a generalized backup protection scheme based on WAMS-based data which utilizes the power differential value to identify the faulty line. It utilizes sequence components of bus voltages to identify the buses near a fault and the hierarchical magnitudes of differential active power signals to identify the faulty line. The proposed algorithm successfully detects the symmetrical and unsymmetrical fault conditions in a transmission system and the faulty line as well. The algorithm is validated in a modified WSCC 9 bus system incorporating FACTS devices and gives a reliable performance during different fault conditions and different line loading conditions. This paper is organized as follows. In Sec. 2. description of the power differential concept is given. The proposed algorithm is explained in detail in Sec. 3. Simulation results are discussed in Sec. 4. The conclusion is presented in Sec. 5. 2. Active Power Differential of a Transmission Line A power difference exists between the two terminals of a transmission line, due to the losses in the transmission line, which increase with the load. Figure 1 shows πmodel of a transmission line. Vx,Vyare the voltages Ix,Iyare the line currents at bus Xand bus Y.ZL, Zxg and Zyg are the parameters of the πequivalent model of the line. The sources Esand Erwith source impedances Zsand Zrare connected to the transmission line at Xand Y. The apparent power at terminal Xand Ybe Sxand Syrespectively. The differential ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 391 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER active power P dxy is the real part of the differential apparent power (Sx−Sy). P dxy =R(Sx−Sy,(1) Sx=Vx×Ix,(2) Sy=Vy×Iy.(3) VxVy Vf IsIx Ixg Iyg IyF Ir If Zs Zxg Zyg Zf X L Y EsEr Zr (a) During external fault. Vf mZL (1-m)ZL If F Er Zr Zyg Zf Zs Zxg Es Vy IyIr Y Ixg Iyg Vx IsIx X (b) During internal fault. Fig. 1: Equivalent circuit of line. The expression for this differential power is different when there is a fault within the line and when there is a fault outside. Case 1. Differential power for an external fault. In Fig. 1(a) an external fault occurs at point Foutside the line. The differential apparent power: S1−S2= Vx 2−Vy 2 zg!+ Vx 2−Vy 2 zL!.(4) Case 2. Differential power for internal faults. For an internal fault at Fas shown in Fig. 1(b), the expression for line terminal currents can be written as follows. mis the distance of fault point from bus X expressed as a fraction of the distance between bus X and Y. The differential apparent power: Sx−Sy=Vx 2−Vy 2 zg +Vx 2 mzLzf −Vy 2 (1 −m)zLzf .(5) Comparing Eq. (4) and Eq. (5), it can be observed that the differential apparent power value is considerably large in the case of internal faults. During faults, the real part of the differential power is large because of the high value of fault currents. Hence it can be used to identify a fault in a line. In the case of FACTS compensated lines, this differential active power during normal operation of the line includes the normal losses of the device in its operating range. FACTS devices can inject or absorb reactive power into the system, but cannot produce active power on their own unless they are connected to a source that can supply active power. During abnormal conditions, these devices get bypassed by their protection circuits. So, the active power differential can be effectively used for the detection of a fault in the compensated lines also. 3. Hierarchial Active Power Differential Relaying Signal Based Backup Protection Algorithm A WAMS-based differential power protection scheme for transmission systems containing a FACTS compensated line is proposed in this section. As shown in Fig. 2, the information from different substations of the protected area is collected at the PDC. The proposed algorithm utilizes the sequence components derived from bus voltages, taking advantage of the fact that the voltage of the bus near the fault location deviates the most, to identify the faulty bus. The faulty line is identified using a power differential criterion based on the three-phase differential power. 3.1. Fault Detection and Fault Area Identification Unbalanced faults occurring in a system can be detected using the negative or zero sequence voltage components of bus voltages [22]. The faulty situation can be identified using the following criteria. Vb2≥K2VNor Vb0≥K0VN,(6) where Vb2and Vb0are the negative and zero sequence components of bth bus respectively in a B-bus system and is the rated voltage magnitude of the bus K2and K0are the thresholds whose values are selected such that all unbalanced faults in the system can be detected reliably. The occurrence of balanced faults can be identified by positive sequence components of the bus voltages using the criterion given below: Vb1≤K1VN,(7) where Vb1is the positive sequence component of bth bus and K1is the threshold, whose value is appropriately set to identify balanced faults in the system. The values of thresholds K1,K2and K0range between 0 and 1. During fault conditions and normal switching ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 392 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER Bus voltage magnitudes Bus Voltage and Line current magnitudes Fault detection and faulty bus identification logic Faulty bus Faulty bus and line Faulty line identification logic Sequence voltages and currents from the protected area Check whether any of the negative sequence and zero sequence bus voltage magnitudes indicate unsymmetric fault Check whether any of the positive sequence bus voltage magnitudes indicate unsymmetric fault Faulty bus identification by sorting bus voltage magnitudes Yes Yes No Calculate power at the line ends Calculate the power differential relay signal Faulty line identification Trip Signal Protected area PMU1PMU2 PMU4 PMU5 PMU6 L2 L3 L4 L5 L6 SS2 SS1 SS6 SS5 SS4 SS3 L1 Fig. 2: Schematic diagram of proposed WAMS-based protection scheme. in of loads Vb1reduces to lower values from rated value. The reduction is higher during faults. The threshold value K1is selected such as to avoid frequent pickup during normal switching of the system. During unsymmetrical fault conditions Vb2and Vb0increases, which are otherwise negligible. Low threshold values of K2and K0are selected such as to improve high impedance fault sensitivity. The faulty area is identified by sorting the buses in the order of sequence component magnitudes. In the case of an unbalanced fault, the buses are sorted in the descending order of negative sequence bus voltage magnitudes. In the case of balanced fault, the buses are sorted in the ascending order of positive sequence bus voltage magnitudes. The bus at the top of the sorted list is identified as a faulty bus. 3.2. Faulty Line Identification For faulty line identification, a new criterion based on the three-phase active power differential value is proposed in this section. The schematic of the active power differential relay is shown in Fig. 3. The threephase differential power of a line connected between buses Xand Yis calculated as: P dxy =|Pxy −Pyx|,(8) where Pxy the three-phase power measured at the line terminal near bus Xand Pyx is the three-phase power measured at the line terminal near bus Y. Bus XBus Y Active Power Differential Relay Fig. 3: Active power differential relay schematic. A high value of differential power P dxy above the normal line losses in a transmission line is an indication of abnormal current flow in the line. It may be due to an overloaded condition or due to the occurrence of a fault. A threshold value P dxyT can be set to detect abnormal conditions. A relaying signal Rxy is obtained using the active power differential value as follows: Rxy =P dxy P rxy ,(9) where P rxy =(|Pxy|+|Pxy|) 2.(10) For the normal operating region considering the line loading and load power factor, the value of relaying signal Rxy is low for all the lines. When a fault occurs in the system, Rxy shoots up to higher values. As the magnitude Rxy depends on the length and line parameters, the normalized value of Rxy each ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 393 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER line is used to identify the faulty line. The normalized value is defined as: Rxy =Rxy RxyT .(11) where RxyT is the threshold value set for the line and its value is taken as the maximum value of Rxy at rated line loading condition considering the normal range of load power factor. The line with the highest Rxy that is connected to the faulty bus is identified as the faulty line. Equation (12) and Eq. (13) are used to compute superimposed components Pxys and Pyxs of the real power flow at terminals Xand Y. It is the difference power between the nth and (n−1)th cycle: Pxys =Pxy[nthcycle]−Pxy[(n−1)th cycle ,(12) Pyxs =Pyx[nthcycle]−Pyx[(n−1)th cycle].(13) A sudden change in the value of Pxys or Pyxs above a threshold PxysT is an indicator of a sudden change in the transmission system and can be used to confirm the occurrence of the fault and to avoid unnecessary pickup at power oscillations. 3.3. Summary of the Proposed WAMS-based Hierarchial Power Differential Algorithm In the proposed algorithm, the changes in the bus sequence magnitudes, the three-phase differential real power of the transmission lines, and superimposed three-phase real power components at the line ends in each cycle are monitored. The changes in real power flow due to the changes in load demand or due to the change in operating modes of the control devices are slower compared to that due to a sudden fault in the system. The device losses can be included in the transmission line losses while calculating the differential power. The value of superimposed components of real power is an indicator of sudden disturbance in the system. The differential real power in a line and superimposed real power components of the line ends are used to confirm the faulty state of the line. The steps to be followed to identify the faulty line (detailed in Sec. 3.1. and Sec. 3.2. ) is summarized below. Step 1: Collect all the time-synchronized bus voltages and line currents through WAMS. Step 2: Calculate the sequence components of all bus voltages. Step 3: Check whether the condition Vb2≥K2VN or Vb0≥K0VNis true. If the condition is satisfied, an unsymmetrical fault is suspected to have occurred in the system and go to step 5 else go to step 4. Step 4: Check whether the condition Vb1≥K1VN is true. If the condition is satisfied, a symmetrical fault is suspected to have occurred in the system. Go to step 6 else go to step 1. Step 5: Sort the negative sequence bus voltages in descending order and find the buses with the highest value of negative sequence voltage magnitude and tag them as the "Faulty/suspicious" buses and go to step 7. Step 6: Sort the positive sequence bus voltages in ascending order and display, find the buses with the lowest value of positive sequence voltage magnitude and tag them as the "Faulty/suspicious" buses. Go to step 7 Step 7: Calculate the differential power P dxy (Eq. (8)), relaying signal, Rxy (Eq. (11)), and the superimposed power component Pxys (Eq. (12)) for all lines connected to the suspicious bus. Step 8: Identify the faulty line using the hierarchical order of the normalized magnitudes of the signal Rxy of the lines in the faulty area. Step 9: Check whether: 1. The magnitude of differential power is greater than the threshold value P dxyT . 2. The magnitude of superimposed power components in the line is greater than the threshold value PsT . 3. The value of falls in the faulty region of the line characteristics (ie Rxy is greater than RxyT ). If all the above conditions are satisfied for any of the lines connected to the "Faulty/suspicious bus" go to step 10, else go to step 1. Step 10: The fault is confirmed, the faulty line number is displayed and appropriate protective actions are initiated. Go to step1. The algorithm is depicted in the flow chart in Fig. 4. 4. Validation of the Proposed Algorithm The proposed WAMS-based algorithm is validated through simulation under MATLAB/SIMULINK environment. Simulation studies are carried out on a modified WSCC 9 bus system incorporating a FACTS device at the midpoint of the line connecting buses 7 and 8 as shown in Fig. 5. ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 394 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER Sort the buses in the ascending order of positive sequence bus voltage magnitude Start Read all bus voltages, line currents and breaker status of all substations Set bus count, b=0 Calculate the positive sequence component Vb1, negative sequence component Vb2 and zero sequence component Vb0 of the bus voltages b=b+1 is b<B is eq(2) true for any of the buses is eq(1) true for any of the buses Sort the buses in the descending order of negative sequence bus voltage magnitude No Yes No No Yes Yes Set buses at the top of the sorted list as the suspecious buses Calculate the differential power Pdxy and relaying signal Rxy and superimposed component Pxys of all the lines Select the line with maximum value of Rxy is Pdxy>PdxyT, Pxys>PxysT and Rxy lies in the faulty region of differential power characteristics of the line Issue signals to initiate appropriate protective actions Select the lines connected to the suspicious buses No Yes B A A B have all lines checked Select the next line with maximum value of Rxy No Yes Fig. 4: Flow chart of the proposed WAMS-based hierarchical active power differential relaying signal-based algorithm. PMU-B7 FACTS DEVICE PMU-B8 PMU-B9 27893 PMU-B5 PMU-B6 1 4 GEN_2 GEN_3 GEN_1 PMU-B4 5 6 LOAD A LOAD B LOAD C Fig. 5: Modified WSCC 9 bus system - single line diagram including FACTS device at the midpoint of line connected between bus 7 and bus 8. The values of thresholds are set as follows K1= 0.6, K2=K0= 0.1. The values of P dxyT and RxyT are set according to the normal value of line losses and power differential characteristics of each line. The system is operated at normal operating conditions and the threshold values P dxyT and RxyT for different lines are identified and shown in Tab. 1. Variation of superimposed components of active power Pxys during the fault is used to confirm a sudden change in the power flow through the line. PsT = 0.05 pu selected as a common threshold for all lines to confirm the occurrence of a fault. The value Tab. 1: Threshold values selected for different lines. Line P dxyT (pu value on RxyT a common base of 400 MVA) Line 7–8 0.03 0.015 Line 8–9 0.025 0.02 Line 9–6 0.022 0.022 Line 6–4 0.026 0.014 Line 4–5 0.026 0.014 Line 5–7 0.022 0.022 depends on the possible change of power in one cycle during the normal operation of the system. Typical types of faults are simulated at various distances with different fault resistances varying from 1 to 500 Ω. The algorithm is validated by placing SVC, TCSC, SSSC, and STATCOM at the midpoint of line 7–8. Variations of Pxy, and Pxys are shown in Fig. 6. 4.1. Simulation Results for a Fault on Line 7–8 with Different FACTS Devices on Line 7–8 Faults are created at t= 2 s on line 7–8 placing different FACTS devices on the same line. Possible combinations of various FACTS devices with varying fault types, fault distance, and fault resistance are simulated to validate the performance of the proposed ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 395 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER 0 1 2 3 Time (s) 0.4 0.5 0.6 0.7 0.8 0.9 1 Pxy (pu) P78 P87 (a) 0 1 2 3 Time (s) -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 Pxys (pu) P78s P87s (b) 1 2 3 Time (s) -1.5 -1 -0.5 0 0.5 1 1.5 Pxy (pu) P78 P87 (c) 1 2 3 Time (s) -1 0 1 Pxys (pu) P78s P87s (d) Fig. 6: Variation of Pxy, and Pxys signal for a fault in Line 7–8. (a) and (b) LG fault near bus 8 when the line is heavily loaded in the presence of STATCOM. (c) and (d) LLLG fault near bus 8 when the line is lightly loaded in the presence of SSSC. 0 1 2 3 Time (s) 0 0.2 0.4 0.6 0.8 1 Voltage (pu) Vpm5 Vpm6 Vpm7 Vpm8 Vpm9 (a) 0 1 2 3 Time (s) 0 0.2 0.4 0.6 0.8 1 Voltage (pu) Vnm5 Vnm6 Vnm7 Vnm8 Vnm9 (b) 0 1 2 3 Time (s) 0 0.2 0.4 0.6 0.8 1 Voltage (pu) Vzm5 Vzm6 Vzm7 Vzm8 Vzm9 (c) Fig. 7: Case A1: Variation of magnitudes of (a) positive sequence, (b) negative sequence and (c) zero-sequence bus voltages for an LG fault at t= 2 s near bus 8 in line 7–8 containing STATCOM. 0 0.5 1 Power (pu) P78 P87 0 0.5 1 1.5 2 2.5 3 Time (s) (a) -1 -0.5 0 Power (pu) P46 P64 0 0.5 1 1.5 2 2.5 3 Time (s) (b) -1 -0.5 0 Power (pu) P89 P98 0 0.5 1 1.5 2 2.5 3 Time (s) (c) -1 -0.5 0 Power (pu) P45 P54 0 0.5 1 1.5 2 2.5 3 Time (s) (d) 0 0.5 1 1.5 2 2.5 3 Time (s) 0 0.5 1 Power (pu) P96 P69 (e) 0 0.5 1 1.5 2 2.5 3 Time (s) 0 0.5 1 Power (pu) P75 P57 (f) Fig. 8: Case A1: Variation of Pxy in different lines for an LG fault near bus 8 in line 7–8 containing STATCOM. ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 396 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER algorithm. Four typical cases are demonstrated here, namely: •Case A1: Fault Type: LG, FACTS device: STATCOM. •Case A2: Fault Type: LL, FACTS device: TCSC. •Case A3: Fault Type: LLLG, FACTS device: SSSC. •Case A4: Fault Type: LLG, FACTS device: SVC. When the occurrence of a fault is detected in the system, the suspicious bus is selected based on the magnitudes of bus voltage sequence components. The values of P dxy and Rxy are calculated for all the lines connected to the suspicious bus. The line with maximum ˜ Rxy satisfying the threshold conditions is identified as the faulty line. Case A1: Fault Type: LG, FACTS device: STATCOM. An LG fault with ground resistance 10 Ωis simulated at line 7–8 near bus 8. Variation of bus voltage sequence components and line end powers during the simulation periods are shown in Fig. 7 and Fig. 8 respectively. The magnitude of negative sequence bus voltage has the highest value for bus 8, and its value is above the threshold set. This confirms the occurrence of an asymmetrical fault in a line connected to bus 8. The algorithm compares the values of ˜ Rxy of the lines connected to bus 8. The magnitude of ˜ R78 is the highest after the fault as shown in Fig. 9 and line 7–8 is identified as the faulty line. The occurrence of the fault on line 7–8 is confirmed by the change in superimposed components. 0123 Time (s) 0 0.5 1 1.5 2 Rxy R78 R89 R96 R64 R45 R57 Fig. 9: Case A1: Variation of Rxy for various lines (R78,R89, R96,R64,R45,R57 ) for an LG fault (Rf= 10 Ω) at t= 2s near bus 7 on line 7–8 with STATCOM in line 7–8. Case A2: Fault Type: LL, FACTS device: TCSC. A line-to-line fault with 0.1 Ωis created at line 7–8 near bus 7 at t= 2 s. Line 7–8 contains TCSC. Bus 7 is identified as the faulty bus as the negative sequence bus voltage of bus 7 satisfies the criterion. The magnitude of ˜ R78 is the highest as in Fig. 10. So, line 7–8 is identified as the faulty line. Case A3: Fault Type: LLLG, FACTS device: SSSC. An LLLG fault with ground resistance of 10 Ωis simulated near bus 8. The occurrence of a symmetrical fault on a line connected to bus 8 is confirmed according to the faulty bus identification steps. The magnitude ˜ R78 is the highest after the fault (Fig. 11) and indicates a fault in line 7–8. Case A4: Fault Type: LLG, FACTS device: SVC. An LLG fault with ground resistance 100 Ωis simulated near bus 7. An asymmetrical fault on a line connected to bus 7 is identified. The magnitude ˜ R78 is the highest after the fault (Fig. 12) and line 7–8 is identified as the faulty one. The results of different cases simulated are summarized in Tab. 2. 0123 Time (s) 0 0.2 0.4 0.6 0.8 1 Rxy R78 R89 R96 R64 R45 R57 Fig. 10: Case A2: Variation of Rxy for various lines (R78,R89 , R96,R64,R45,R57 ) for an LL fault (Rf= 0.1 Ω) at t= 2 s on line 7–8 near bus 8 with TCSC on line 7–8. 0123 Time (s) 0 0.5 1 1.5 2 Rxy R78 R89 R96 R64 R45 R57 Fig. 11: Case A3: Variation of Rxy for various lines (R78,R89 , R96,R64,R45,R57 ) for an LLLG fault (Rf= 10 Ω) at t= 2 s near bus 8 on line 7–8 with SSSC in line 7–8. 4.2. Simulation Results for a Fault on Line Other than Line 7–8 with Different FACTS Devices in Line 7–8 In this case, different FACTS devices are placed on line 7–8. Faults are created on other lines in the system. It is observed that the algorithm identifies the faulty line reliably in these cases also. Four typical cases are demonstrated here, namely: ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 397 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 20 |NUMBER: 4 |2022 |DECEMBER Tab. 2: Performance of the algorithm for a fault on line 7–8. FACTS device in line 7–8 Faulty bus and line Fault type Fault resistance Line and bus identified STATCOM Bus 7 Line 7–8 LG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LL 0.1, 1, 10 Bus 8, Line 7–8 Bus 7, Line 7–8 LLL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LLL 0.1, 1, 10 Bus 8, Line 7–8 SVC Bus 7, Line 7–8 LG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LL 0.1, 1, 10 Bus 8, Line 7–8 Bus 7, Line 7–8 LLL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LLL 0.1, 1, 10 Bus 8, Line 7–8 SSSC Bus 7, Line 7–8 LG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LL 0.1, 1, 10 Bus 8, Line 7–8 Bus 7, Line 7–8 LLL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LLL 0.1, 1, 10 Bus 8, Line 7–8 TCSC Bus 7, Line 7–8 LG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LLLG 1, 10, 100, 500 Bus 7, Line 7–8 Bus 8, Line 7–8 LLLG 1, 10, 100, 500 Bus 8, Line 7–8 Bus 7, Line 7–8 LL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LL 0.1, 1, 10 Bus 8, Line 7–8 Bus 7, Line 7–8 LLL 0.1, 1, 10 Bus 7, Line 7–8 Bus 8, Line 7–8 LLL 0.1, 1, 10 Bus 8, Line 7–8 0 1 2 3 Time (s) 0 0.5 1 1.5 2 Rxy R78 R89 R96 R64 R45 R57 Fig. 12: Case A4: Variation of Rxy for various lines (R78,R89 , R96,R64,R45,R57 ) for an LLG fault (Rf= 100 Ω) at t= 2 s near bus 7 on line 7–8 with SVC in line 7–8. •Case B1: Fault Type: LLL, Line: 8–9 FACTS device: SSSC. •Case B2: Fault Type: LL, Line:6–4 FACTS device: STATCOM. •Case B3: Fault Type: LG, Line: 5–7 FACTS device: SVC. •Case B4: Fault Type: LLG, Line: 9–6 FACTS device: TCSC. Case B1: Fault Type: LLL, Line:8–9 FACTS device: SSSC. Variations of bus voltage sequence components and line end powers during the simulation periods are shown in Fig. 13 and Fig. 14 respectively for an LLL fault, with fault resistance 1 Ω, near bus 9 in Line 8–9. Magnitudes of negative and zero sequence components are negligible for symmetric faults. The magnitude of positive sequence bus voltage is the lowest for bus 9 and is below the threshold value. This indicates the occurrence of a symmetrical fault on a line connected to bus 9. The magnitude of ˜ R89 is the highest after the fault as shown in Fig. 15 and line 7–8 is identified as the faulty line. Case B2: Fault Type and line: LL fault at line 6–4, FACTS device: STATCOM. ©2022 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 398