Fault Analysis and Circuit Breakers Selection for Electrical Lines Protection: Case of Electrical Line from Lutchurukuru to Kindu (D.R. Congo)

International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No.3/4/5, October 2025 DOI : 10.5121/ijcsea.2025.15502 21 FAULT ANALYSIS AND CIRCUIT BREAKERS SELECTION FOR ELECTRICAL LINES PROTECTION: CASE OF ELECTRICAL LINE FROM LUTCHURUKURU TO KINDU (D.R. CONGO) M N Audry 1, H Shabani 1,2, J Fisher 2 and J Ngondo 1,3 1 Electrical Engineering, MAPON University, Kindu-Maniema, Democratic Republic of Congo (D.R. Congo) 2 School of Electrical and Communications Engineering, Papua New Guinea University of Technology (Unitech), Lae 411, Morobe Province, Papua New Guinea 3 North China Electric Power University, 02, Beinong Lu, Changping, Beijing, China ABSTRACT Consumption of electrical energy has steadily increased due to industrial, commercial and demographic growth. In order to deliver constant power to consumers, reliability is an important factor that power companies must take into account. Common disturbances on transmission lines resulting from various faults such as line to line, single line to earth, double line to earth and faults between three lines affect the stability of the electric supply. This paper seeks to demonstrate the behavior of transmission line signals due to disturbances caused by different types of faults and to identify the effect of faults on transmission lines as well as on the bus assembly. Simscape Power tool available in MATLAB/Simulink environment was used to model the 33 kV, 105 km transmission line. Its simulation made it possible to obtain the voltage and the current wave forms in the transmission network during the occurrence of different fault types. The electrical faults cause down time equipment damage and, thus, present a high risk to the integrity of the power grid. After various fault analysis of the power line from Lutchurukuru to Kindu, the circuit breakers to be placed at the transmitting and receiving ends of this power line were selected with the aim of reinforcing the power line protection system. Hence, the circuit breakers at the transmitting end (Bus 2) of the line must have a breaking capacity of 4.376 MA, a voltage of 34.5 kV, a number of cycles for the fault interruption time of 5 and a sub transient fault current of 49.15 A, while the ones placed at the receiving end (Bus 7) of the line must have a breaking capacity of 497.5 kA, a voltage of 34.5 kV, 5 number of cycles for fault interruption and a sub transient fault current of 5.6 A. KEYWORDS Transmission lines, reliability, faults, Circuit breaker, MATLAB/Simulink 1. I NTRODUCTION For the transmission and distribution of electrical energy, the lines are the vital links to ensure the continuity of services to users, the latter are exposed to atmospheric and natural conditions which increase the probability of appearance of any type of faults [1]. Faults in power lines occur in unusual conditions due to climate (Lightning, strong Wind, tremors, weight of ice on conductors, trees, contaminated or broken insulators, corona not controlled, aircraft and cars hitting lines and structures) [2] and human errors. The analysis of faults forms an important step on the study of electrical system; the problem consists of determining the bus voltages International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 22 and the line current during the appearance of different types of faults. Faults on electrical equipment are subdivided into two categories including balanced three phase faults and unbalanced faults (single phase fault, two phase fault, fault between two phases and earth) [3]. The information obtained after fault analysis is necessary for the parametrization and coordination to obtain the nominal values of the protective equipment [4]. However, the electrical line from Lutchurukuru to Kindu requires reinforcement in its protection system, along this line it is found certain protective devices such as fuse holder disconnectors (already defective and replaced by bare wires in the open air), Lightning arrestors, but there are no circuit breakers at both ends of this line or a relay for faults detection and isolation of defective areas. Maniema is supplied with electricity by the Lutchurukuru power station via a 105 km power line [5]. This paper analysesvarious faults that may appear in this line during operation which will make it possible to make a good choice of protection devices and to configure the monitoring device to thus, protect this line and to guarantee residents of the town of Kindu with continuous and reliable power supply. The main goal is to present the behaviour of bus voltage and line currents during normal and faulty operating conditions. The following steps were undertaken before circuit breaker selection to ensure the protection of the Lutchurukuru Kindu line by:  Modelling of Lutchurukuru-Kindu Power Network;  Simulating the network, under normal conditions;  Simulating various types of faults in the power line;  Selecting appropriate circuit breakers for the power line protection. The above simulations were carried out on the Simulink environment. 2. F AULTS IN P OWER S YSTEMS In general, the balanced systems only exist in theory, in reality many systems are almost unbalanced and for practical reasons they can be analysed as balanced. However, there are emergency conditions (open conductors, unbalanced loads…) where the degree of unbalance can no longer be neglected. To protect the system against such eventualities, it is necessary to size protection devices such as fuses, circuit breakers and to adjust protection relays [6]. To do this the voltage and currents in the system during unbalanced faults must be known in advance. Faults in electrical lines can be classified into two type, series faults (open conductors) and shunt faults (short circuit). Series faults are easily identified by observing the value of each phase voltage [7]. If the fault voltage value is zero it indicates that fault has occurred, in case current value increases it means a shunt fault has occurred. Short circuit faults may be asymmetrical (line to ground, line-to-line, double line to ground) or symmetrical (triple line and triple line to ground) [1], [8]. On Fig. 1 we observe the classification of faults in overhead transmission lines where A, B, C and G indicate respectively the three phases and the ground. International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 23 Figure 1. Faults classification [7]. 2.1. Fault Effects Heavy short circuit may cause damage to equipment or any other element of the power system due to overheating or flashover, different phenomenon may be observed [9], [10];  There may be reduction in the supply voltage of the healthy feeders, resulting in the loss of industrial loads.  Short circuit may cause the unbalance of the supply voltages and currents, thereby heating rotating machines.  There may be a loss of the power stability  The faults may cause an interruption of the supply to consumers; Thoughtful result of the uncleared faults, is fire which may not destroy only the equipment of its origin but also may spread within the system and cause total failure. 2.2. Faults types in Transmission Lines Normally a power system operates under balanced conditions. When the system is unbalanced due to the insulation failures at any point or due to the contact of live wires, a short circuit or fault is said to occur [1]. Faults that occur in transmission lines are classified into two groups as:  Symmetrical faults  Asymmetrical faults. 1. Symmetrical faults.It is a fault which appears when all three phase conductors are short circuited, the latter gives balanced faults currents. Three phase to ground fault is shown in the following Fig. 2. International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 24 Figure 2. Symmetrical faults. For this type of fault, it should be noted that:  Symmetrical faults rarely appear in practice since the majority of faults are nonsymmetrical.  The symmetrical fault is the most dangerous since it imposes a large fault current on the circuit breakers. 1. Asymmetrical faults.These faults lead to unequal currents with unequal phase shifts in a three-phase system. This may occur by natural disturbances or by human errors with open conductors or short circuit [11]. As presented in the Fig. 3, asymmetrical faults are generally classified as:  Single line to ground fault (L – G fault)  Double line fault (L – L fault)  Double line to ground fault (L – L – G fault) Figure 3. Asymmetrical faults. The single line to ground (L – G fault) is the most current fault (60 to 75% of occurrence). They appear when a conductor of transmission line falls to earth or during contact between the latter and the neutral conductor [1]. A fault between two phases appears in an electrical line when two conductors are short circuited (L – L fault). The occurrence frequency rate of this fault type fluctuates between 5 to 15%. The fault between two phases and earth in transmission line appears when two conductors fall and are connected together across the neutral (L – L – G fault). The occurrence frequency rate of this fault type fluctuates between 15 to 25% [12]. A fault study comprises the following [3]:  Determination of the maximum and minimum three phase short-circuit currents;  Determination of asymmetrical fault currents;  Rating evaluation of required circuit breakers;  Investigation of schemes of protective relaying;  Determination of voltage levels at strategic points during faults. International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 25 3. T RANSMISSION L INE P ROTECTIVE D EVICES Transmission system must be protected from short circuit currents, which can endanger personnel and cause permanent damages to critical equipment [13]. To guarantee a safely isolation of the system faulty parts, the fault current must not exceed the capacity of the circuit capacity device [14]. Various types of protection devices in transmission systems as shown in Fig. 4. Figure 4. Various protective devices. The purpose of protective device is to detect abnormal signals in the power transmission system [2]. A protection system consists of a set of devices intended for fault and abnormal situation detection in networks in order to control the triggering of cutting elements. The functional chain of a protection system includes one part for fault detection and another part for fault elimination [12], [15]. As presented in Fig. 5, whatsoever the technology, the protection system is made up of the following three fundamental parts [16]:  Sensors or measuring reducers which lower the values to be monitored (current, voltage) to levels usable by the protection;  Protective relays;  Switching equipment (one or more circuit breakers). Figure 5. Fundamental elements of protective systems. At the receiving end of the line there is a similar protection system, in the event of a fault the circuit breaker opens and the line is taken out of service [16]. 3.1. Fault Location Different techniques and methods have been introduced on fault location estimation; among them impedance-based faults location methods are the most used by utilities [17]. Based on the input data (voltage and current) of fault location algorithm, the algorithms can be categorized as: International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 26  One end algorithm method which is economic and simple but subjected to different errors such as the uncertainty of transmission lines, unbalanced load flow, the accuracy of transmission line model [18], and measurement errors. With this method the location of fault is based on the impedance from one end of a transmission line [19].  Two end algorithm method which estimates the location of fault using voltage and current from both ends of a transmission line [20]. 3.2. Circuit Breaker Selection When a fault appears the protection devices are activated (relay and circuit breaker). A short time called tripping time elapsing before the protection relay detects the overcurrent and launches the tripping pulse to the circuit breaker [21]. For the circuit breaker to open, another time called opening time passes. The circuit breaker opening is accompanied with an arc which is extinguished after a duration called arc time. The time from which the tripping pulse is launched until the arc is extinguishing is called interruption time. The speed of the circuit breaker will therefore be recognized according to the time which elapses between the appearance of the fault and extinction of the arc [22]. The selection of circuit breakers is based on the following factors [1]:  Class of the voltage considered (nominal effective voltage level);  The load current that the circuit breaker must withstand in the normal or emergency condition;  The short circuit current that the circuit breaker must withstand;  The speed of interruption of the short circuit (the latter depends on the number of interruption cycles and the network frequency. The load current in normal operation can be found by studying the power flow of the circuit to be protected [23]. The short circuit data determines the selection of the circuit breaker by taking into account the operating voltage [24]. In general, the quicker the circuit breaker interrupts a fault, the better it is for the system because there is a reduction in the risk of damage devices [25], [26]. 4. D ESCRIPTION OF L UTCHURUKURU – K INDU N ETWORK TheFig. 6 illustrates the single power line diagram of Lutchurukuru to Kindu network. The Lutchurukuru power plant is designed with 3 turbo alternator groups of 2700 kVA each, but currently only one remains working with a power production of around 500 kW. The output voltage is 6.6 kV. The transformer station is located at the outlet of the power plant where two 2 MVA transformers are placed in parallel which raise the voltage up to 33 kV for its transport to the town of Kindu located approximately at 105 km where the overhead line stays on pillars of 10 m in height. It is a three-phase line with one terminal, its phase conductors have a diameter of 50 mm. International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 27 Figure 6. Single power line diagram: Lutchurukuru to Kindu network 5. E LECTRICAL NETWORK DESIGN SIMULATION MODEL The Lutchurukuru – Kindu electrical network was modelled and simulated in the MATLAB/Simulink platform as shown in the figure 7. Figure 7. Single power line diagram: Lutchurukuru to Kindu network The generator produces a voltage of 6.6 kV that is raised to 33 kV at the level of power point (Lutchurukuru power plant) then transported at a distance of 105 km. Along the power line two transplants are made simultaneously over 100 and 103 km at different nodes as given in table 1. Table 1. Load power at different nodes. Location Node P (kW) Q (kVAR) Alunguli 4 80 60 Kama 2 6 80 60 Kindu 8 80 52.5 Kindu 9 100 75 Kindu 10 120 90 The power line will be protected by two circuit breakers, one at the transmitting end of the line (Bus 2 at Lutchurukuru) and the other at the other at the receiving end (Bus 7 at Kindu), it has been split into two parts (with a total length of 100 km) to allow faults to be simulated at different positions along the line using fault simulator block. The electrical power is generated by a three-phase power source, which is transmitted to the various loads thought transmission lines, whose parameters are shown in the table 2. International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 28 Table 2. Transmission line parameters of the 𝜋model Specifications Values Unit Length 100, 2 et 3 km Positive Sequence Resistance 0.512 Ω/km Homopolar Resistance 0.371 Ω/km Positive Sequence Inductance 2.29 mH/km Homopolar Inductance 10.154 mH/km Positive Sequence Capacitance 4.4 nF/km Homopolar Capacitance 9.56 nF/km 6. S IMULATION RESULTS AND CIRCUIT BREAKER SELECTION For the analysis and evaluation of Lutchurukuru-Kindu power line network, the following faults were simulated:  Three phase faults;  Single line to ground faults;  Fault between two phases: without earth and with earth. 6.1. Normal Operating Conditions In the absence of the power line fault, the system is sinusoidal and balanced. The existence of the voltages and currents at the two ends of the line (on buses 2 and 7) is shown in the Fig. 8. (a) At Bus Bar 2 (b) At Bus Bar 7 Figure 8. Voltage and current transmission under normal conditions International Journal of Computer Science, Engineering and Applications (IJCSEA) Vol. 15, No. 3/4/5, October 2025 29 6.2. Three Phase Faults The Fig. 9 presents the voltage and current simulations for a three-phase fault at 25 km from Lutchurukuru. Thus, it is noticed an abrupt voltage decrease and a sudden current increase after 0.1 sec run when the fault appeared. (a) At Bus Bar 2 (b) At Bus Bar 7 Figure 9. Voltage and current transmission under three phase faults Referring to the radial configuration (Single Power Line Diagram in Fig.6), the following observations are made:  The fault closer to the sources (Bus 2) will be the most dangerous because it presents a very large fault current.  As the fault moves away from transmitting end (Bus 2), both the voltage and the current decrease during the fault occurrence. Table 3 presents the measured data collected at the transmitting end (Bus 2) and the receivingend (Bus 7)across various locations. Table 3.Data measured at different locations. Bus 2 Bus 7 Location Voltage (kV) Current (A) Voltage (kV) Current (A) km 0.0667 49.15 0.006 0.13 1 0.0664 47.26 0.003 0.024 0.0669 48.5 0.009 0.104 1.5917 45.2441 0.01013 0.27 25 1.5905 45.178 0.0688 0.05 1.5908 45.2455 0.02 0.21 3.052 43.25 0.011 0.32 50 3.051 43.25 0.05 0.0655 3.051 43.25 0.017 0.2586 4.4011 41.49 0.087 O.39 75 4.401 41.498 0.042 0.08 4.40 41.498 0.013 0.31 5.41 40.18 0.04 0.46 95 5.41 40.18 0.02 0.099 5.40 40.19 0.06 0.326