The effect of the static synchronous compensator (STATCOM) on distance protection of a high-voltage transmission line is studied in this article. To carry out the research stated in the topic of the paper, an experimental scheme was developed, equipment was selected, the operation settings of the 3 stages of distance protection were calculated and quad characteristics were built on their basis. All listed above, as well as further experiments, were carried out by the real time digital simulator. The STATCOM model was integrated in the scheme and set next. A series of experiments was carried out: two-phase and three-phase short circuits in various nodes of the scheme with and without the compensator and in various connection nodes. After all the experiments were carried out, appropriate conclusions were made about the impact of FACTS devices on the operation of distance protection. Possible ways to solve detected problems were also proposed

Andreev, Nikita

Bay, Yuly Dmitrievich

Razzhivin, Igor Andreevich

Ruban, Nikolay Yurievich

English

Electronic archive of Tomsk Polytechnic University

978-1-7281-2896-2/19/$31.00 ©2019 IEEE Studies of the Impact of FACTS Devices on the Operation of Transmission Line Protection  Nikolay Yu. Ruban, Nikita S. Andreev, Yuly D. Bay, Igor A. Razzhivin Division for Power and Electrical Engineering Tomsk Polytechnic University Tomsk, Russia rubanny@tpu.ruAbstract—The effect of the static synchronous compensator (STATCOM) on distance protection of a high-voltage transmission line is studied in this article. To carry out the research stated in the topic of the paper, an experimental scheme was developed, equipment was selected, the operation settings of the 3 stages of distance protection were calculated and quad characteristics were built on their basis. All listed above, as well as further experiments, were carried out by the real time digital simulator. The STATCOM model was integrated in the scheme and set next. A series of experiments was carried out: two-phase and three-phase short circuits in various nodes of the scheme with and without the compensator and in various connection nodes. After all the experiments were carried out, appropriate conclusions were made about the impact of FACTS devices on the operation of distance protection. Possible ways to solve detected problems were also proposed. Keywords—FACTS, STATCOM, Distance Protection, Relay Protection, Transmission Line. I. INTRODUCTION Currently, flexible alternating current transmission systems (FACTS) – a set of technical and information tools for automatic control of transmission line parameters – are widely spread and developed [1]. Many problems are solved with the help of these devices: increasing the transmission capacity of power lines; ensuring the stable operation of the power system under various disturbances; improving the reliability of energy saving of consumers; reduction of losses in electrical networks. One of such devices is a static synchronous compensator (STATCOM). As with the putting of any new element into the system, it is necessary to study the effect of STATCOM on network operation in various modes, including faults. The role of automatic devices that detect faults and disconnect equipment or inform personnel and dispatchers about the appearance of an abnormal mode, is performed by relay protection and automation. One of the most widely used basic protection of 110-220 kV lines is distance protection (DP), the principle of this one is to calculate the resistance based on measured voltages and currents. There are guidelines for calculating and configuring relay protection for various equipment and different network modes [2]. Besides each protection manufacturer provides its own recommendations for setting up its own devices. The regulatory documents used in Russia for setting up distance protection do not contain any recommendations for their operation in networks with FACTS devices. Perhaps this is due to the low prevalence of FACTS in Russia, but recently such devices have been shared quite actively. Thus, there is a question about the qualitative and quantitative influence of FACTS devices on functioning now elements, including the relay protection of transmission lines, as well as the question of taking them into account when calculating the settings and configuring the protection. In the paper a study of the effect of a second-generation FACTS device — a static synchronous compensator — on the distance protection of a 220 kV transmission line was conducted, since it has several advantages over similar compensation devices and is widely used now and also an effective device in terms of its use for maintaining voltage levels or controlling power flows [1, 3, 4]. At the same time, there is a problem of the behavior of FACTS in case of faults, particularly their influence on the operation of relay protection [5-9]. The purpose of the study is to answer the question about the necessity of taking into account the impact of a particular device on a distance protection in Russian networks. Production companies are interested in the results in terms of improving the quality and accuracy of recommendations for protection setting up. II. STUDY CASE To carry out the study, a circuit in which there is a 220 kV transmission line with a three-stage distance protection installed is required. According to the [2], the first stage is adjusted from the own resistance of the protected line, the second stage is adjusted from the first stage of the previous line, the third stage is adjusted to ensure reliable coverage of the previous line. It is also possible to set from the short-circuit on the low voltage side of the transformer at the end of the protected line. Due to the above, it was decided to use the experimental power grid presented in Fig. 1. All the equipment shown in the diagram is made in Russia and its parameters are selected in accordance with [10].  Fig. 1 Experimental power grid scheme  Generator G1 rated power is 100 MW. STATCOM rated power is 100 MVAR.  Loads power (SL) is 40 20 MVA+ j . Lines rated voltage is 220 kV. Calculation of distance protection parameters is carried out for a set of line 1 installed at substation 1. The model of the DP measuring body in the real-time digital simulator (RTDS) shows the primary resistance. The values of phase voltages and currents are given to the input; it is possible to monitor phase-to-ground resistances, phase-to-phase Power Engineering and Renewable Energy572resistances, and also resistances of direct, inverse, and zero sequences at the output. In the output locuses during modeling data about line resistance are entered, as well as about calculated characteristics in primary values, using this data, the complex draws quad characteristics. III. QUAD CHARACTERISTICS In general, the quad characteristic of each stage has a form shown in Fig. 2.  Fig. 2 Quad characteristic general form  where setZ  – set point of the stage for which the characteristic is built; 1ϕ  – the angle of maximum sensitivity taken equal to the angle of the set point resistance; 2ϕ  – the angle of the edge 01 inclination taken to be 15− °  for 1 and 2 stages, for 3 stage calculated separately due to [11]; 3ϕ  – the angle of the edge 34 inclination taken to be 115°  due to [11]; setR  – active resistance set point; edge 23 passes through the end of a straight setZ  and is parallel to the axis R . With the help of the measuring body in the RTDS, the phase resistance is found at the specified fault (node 2), it is also own for the LINE1: 781 9.2 43.19 44.159  Ohm°= + = jLINEZ j e . The first stage set point calculation for LINE1: (1) 78 7811 0.85 0.85 44.159 =37.535  Ohm° °= ⋅ = ⋅j jLINEsetZ Z e e . For further calculations LINE2 own resistance is needed. From similar experiment: 782 11.07 51.9 53.067  Ohm°= + = jLINEZ j e . Matching with the previous line. The current distribution coefficient between LINE1 and LINE2 with a short-circuit at the node 2 equals one, since there are no additional sources from the beginning of the first line to the end of the second one. The second stage set point calculation for LINE1 with matching: (2)1 210.660.85= ⋅ +LINE LINEsetcIIZ Z Zk;(2) 78 78 7810.660.85 44.159 + 53.067 =75.56  Ohm1° ° °= ⋅j j jsetZ e e e . The third stage is calculated based on the conditions of reliable coverage of the previous line and the conditions of the required sensitivity. For this, a short-circuit is simulated at the end of the LINE2 (node 3) and the resistance of the is measured by LINE1 protection. The resulting value is: (3)1 22.18 94.4 Ohm= +LINEZ j . Required sensitivity coefficient for the third stage is 1.2=sk . The third stage set point calculation for LINE1: (3) (3) 771 1=1.2 (22.18+j94.4)=116.365e  Ohm°= ⋅ ⋅jsset LINEZ k Z . The angle 2ϕ  is calculated next for the third stage operation characteristic: nommaxmin load maxcos 0.85cos 0.9440.9 1ϕϕ = = =⋅U I; 2 max5 arccos(cos ) 5 arccos(0.944) 24.19ϕ = + ϕ = + = ° , where maxcos ϕ  – cosine in maximum load mode; nomcos ϕ  – cosine in normal load mode; minU  – voltage in maximum load mode, p.u.; load maxI  – current in maximum load mode, p.u. Active resistance set points: 1 13.679 Ohm;=setR 2 19.246 Ohm;=setR  3 26.208 Ohm=setR  IV. STATCOM MODEL The STATCOM model in the RTDS is represented by two blocks. Block 1 (STATCOM) is required for elements that are modeled using a small time-step in the program, while a large time-step is used for the main circuit. This block contains DC sources, rectifiers, a reactor, a filter, a special transformer model for connecting parts with different calculation steps, as well as elements generating a sawtooth signal and firing pulses based on the data received from the control system. Blocks 1 and 2 are shown in Fig. 3.   Fig. 3 Blocks 1, 2  In block 2 (CONTROL) the control system is located. The control uses the pulse width modulation method. Based on the measured power flowing between the system and STATCOM, as well as the voltage at the common coupling point (PCC) and the set point, an angle and modulation factor are generated for the reference signal, which is compared with the carrier sawtooth signal in the firing pulse generator. The set points for Power Engineering and Renewable Energy573voltage and active power are put in the control system (when adjusting reactive power and voltage, the set point for active power is equal to zero) in p.u. Base values are set in the measuring bodies. The installed power of STATCOM is regulated by changing the voltage of the element VDC in block 1. V. RESULTS The following experiments were carried out during the studies: a two-phase short circuit between phases AB and a three-phase short circuit at the end of the protected and previous lines. Using midpoint STATCOM, additional experiments were carried out with a fault for 25% and 75% of the protected line length. The obtained polygonal operational characteristics of the starting relays of distance protection and the locuses of resistance are presented in Fig. 4-10. In the figures, the red line shows the resistance of the protected line. Blue indicates the response of the first stage, green and purple - the characteristics of the second and third stages, respectively. The graphs in Fig. 4, 5 are obtained for the case of connecting STATCOM to node 1, in Fig. 6, 7 for the case of connecting STATCOM to node 2, in Fig. 8-10 for the case of connecting STATCOM to the midpoint of line 1. STATCOM is connected to the node 1.  Fig. 4 Phase-to-phase fault, node 2   Fig. 5 Phase-to-phase fault, node 3  STATCOM is connected to the node 2.  а)  b) Fig. 6 Phase-to-phase (а) and three-phase (b) faults, node 2   а) Power Engineering and Renewable Energy574 b) Fig. 7 Phase-to-phase (а) and three-phase (b) faults, node 3  STATCOM at midpoint of the LINE1.  а)  b) Fig. 8 Phase-to-phase (а) and three-phase (b) faults, 25 % length  а)  b) Fig. 9 Phase-to-phase (а) and three-phase (b) faults, 75 % length   а) Power Engineering and Renewable Energy575 b) Fig. 10 Phase-to-phase (а) and three-phase (b) faults, 100 % length (node 2)  From the results of the performed experiments the fact of the static synchronous compensator influence on the transmission line distance protection operation was established in individual cases. STATCOM does not affect the protection operation if the fault occurs between it and the place where the distance protection is installed, as well as when the compensator is connected at the beginning of the protected line. This is due to the fact that in these cases, the measured current and voltage required to calculate the resistance either do not change or change proportionally. When the STATCOM is located between the distance equipment and the fault place, there is a noticeable influence on the behavior of the protection. For example, the third stage underreaches and does not provide long-distance backup mode with a short circuit at the end of the previous line if the compensator is installed at the end of the protected line, because the locus does not get into the third stage zone of operation. Experiments in which the STATCOM is connected at the midpoint shows that a locus shift relatively to normal operation can lead to the triggering of the second and third stages, when the first and the second ones must operate. This, in turn, leads to a delayed response and may be the result of more serious damage and emergency conditions of the power system. VI. CONCLUSION According to the experiments results, it can be concluded that the compensator increases the measured reactive and active components of the resistance. This fact must be taken into account when calculating the settings for the distance protection of power lines and reflected in the relevant regulatory documents. Thus, it is possible to take this into account using the coefficient, which increases the quad characteristic edges. Another problem solution for protection manufacturers may be to develop an adaptive function. The point is to ensure the exchange of information between distance protection and STATCOM and dynamically change the operation characteristics depending on the mode of the compensator and its installed power. ACKNOWLEDGMENTS  The reported study was funded by RFBR according to the research project № 18-38-00821 REFERENCES [1] Rajive Tiwari, K. R. Niazi, Vikas Gupta, "Optimal location of FACTS devices for improving performance of the power systems", Power and Energy Society General Meeting 2012 IEEE, pp. 1-8, 2012. [2] Hondurov S. A., Ilyukhin E. V., Pirogov M. G., Soloviev A. L., "Step distance protection of 35 - 220 kV transmission lines. The method of calculation", St. Petersburg: PEIPK, 52 p., 2013. [3] Lee C K, Leung S Y, Hui S Y R, et al. "Circuit level comparison of STATCOM technologies. IEEE Trans Power Electronics", vol. 18(4), pp. 1084-1092, 2003. [4] S. Parvathy, K. C. Sindhu Thampatty, T. N. Padmanabhan Nambiar, "Modeling and non linear control of STATCOM for VAR compensation in IEEE 5 bus system", Asia-Pacific Power and Energy Engineering Conference (APPEEC) 2017 IEEE PES, pp. 1-6, 2017. [5] Samkari, H., Allehyani, M., & Johnson, B.K. "Modeling and simulation the impacts of STATCOMs on distance protection", North American Power Symposium (NAPS), Charlotte, NC, USA, 2015. [6] Alam, M.M., Leite, H., Liang, J., & da Silva Carvalho, A. "Effects of VSC based HVDC system on distance protection of transmission lines", International Journal of Electrical Power & Energy Systems, vol. 92, pp. 245-260, 2017. [7] Guan, R., Xue, Y., & Zhang, X.-P., "Advanced RTDS-based studies of the impact of STATCOM on feeder distance protection", The Journal of Engineering, vol. 15, pp. 1038-1042, 2018. [8] Bhaskar, M.A., & Indhirani, A., "Impact of FACTS devices on distance protection in transmission system", 2014 IEEE National Conference on Emerging Trends in New & Renewable Energy Sources and Energy Management (NCET NRES EM), Chennai, India, 2014. [9] Khederzadeh, M., & Ghorbani, A., "STATCOM/SVC impact on the performance of transmission line distance protection", IEEJ transactions on Electrical and Electronic Engineering, vol. 6(6), pp. 525-533, 2014. [10] Neklepaev B.N., Kryuchkov I.P., "Electric part of power plants and substations: Reference materials for course and degree design", BHV-Petersburg, 640 p, 2013. [11] STO 56947007-29.120.70.200-2015. Guidelines for the calculation and selection of settings of microprocessor-based devices for relay protection and automation. - Moscow, 356 p., 2015. Power Engineering and Renewable Energy576

Studies of the Impact of FACTS Devices on the Operation of Transmission Line Protection

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Studies of the Impact of FACTS Devices on the Operation of Transmission Line Protection

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