im Journal of JET v°iume 9 (2016) p.p. 57-67 Issue 4, December 2016 Type of article 1.01 Technology www.fe.um.si/en/jet.html ANALYSIS OF THE OPPOSITE REACTIVE POWER DIRECTION PHENOMENON ON TWO PARALLEL OVERHEAD TRANSMISSION LINES ANALIZA POJAVA NASPROTNE JALOVE MOČI NA DVEH VZPOREDNIH NADZEMNIH VODIH Ivan TolicR, Robert Nad1, Ivana Hartmann Tolic2 Keywords: reactive power, transmission line, measurement Abstract This paper presents an analysis of the opposite reactive power direction phenomenon on two parallel overhead transmission lines. Measurements are performed on transmission lines, recorded using energy meters. Superficial reasoning leads to the conclusion that the measurement system is not trustworthy. In addition, more detailed theoretical analysis shows that the phenomenon is possible and it is not the result of the incorrect measurement, but it is the result of reactive power distribution along the respective transmission lines. Povzetek V članku je predstavljena analiza pojava nasprotne jalove moč na dveh vzporednih nadzemnih vodih. Najprej so meritve opravljene na realnem daljnovodu in pojav je posnete z merilniki električne energije. Površno razmišljanje nas pripelje do zaključka, da je sistem merjenja dvomljiva. R Corresponding author: Ivan Tolic, Croatian Transmission System Operator Ltd., Measurement Department, Kupska 4, 10000 Zagreb, Tel.: +385 91 217 7128, E-mail address: Ivan.Tolic@hops.hr 1 Croatian Transmission System Operator Ltd., Measurement Department, Kupska 4, 10000 Zagreb 2 Faculty of Electrical Engineering, Computer Science and Information Technology Osijek, Department of Software Engineering, Kneza Trpimira 2B, HR-31000 Osijek JET 57 Ivan Tolič, Robert Nad, Ivana Hartmann Tolič JET Vol. 9 (2016) Issue 4 Podrobnejša teoretična analiza pa pokaže, da je ta pojav mogoč in ni posledica nepravilnega merjenja. Vendar je rezultat porazdelitve jalove moči vzdolž posameznih prenosnih vodov. 1 INTRODUCTION In current power systems, transmission system operators (TSO) are associated with larger organizations in order to satisfy increasing requirements for energy exchange in the competitive market environment. TSOs in Europe are joined to the European Network of Transmission System Operators for electricity (ENTSO-E), [1], where the rights and obligations are defined according to REGULATION (EC) No 714/2009 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL, [2], Transmission lines are one of the key unique components of electricity transmission, [3], The rapidly increasing needs for technical and economic compromises in the competitive market environment emphasizes the importance of accurate energy measurements. Therefore, metering points are equipped with modern equipment (accuracy class 0.2) in order to meet all requirements for reliable and accurate measurement, which is the fundamental requirement for the functioning of the TSO in the above-mentioned market environment, [4]. 2 THE DESCRIPTION OF OPPOSITE REACTIVE POWER DIRECTION PHENOMENON 2.1 The architecture of metering point Current metering points in the high voltage power system consist of instrument transformers (voltage and current), an energy meter, and connection equipment (see Fig. 1.). The purpose of the metering point is to provide information about the measurand (measured value, i.e. the quantity of interest), [5, 6], 110 kV Figure 1: The principal scheme of metering point 58 JET Analysis of the opposite reactive power direction phenomenon on two parallel overhead transmission lines For more details about the requirements for the instrument transformers and energy meters, the reader is referred to [7-10]. In this paper, two parallel 110 kV overhead transmission lines (OTL) are observed (see Fig. 2). Both lines have their own independent metering point, as presented in Fig. 1. Figure 2: Two parallel 110 kV overhead transmission lines Energy meters, such those as described in [11,12], measure active and reactive power and energy in two directions. In some measuring periods, the opposite reactive power direction is measured. At first glance, this phenomenon sounds ambiguous. Superficial reasoning leads to the conclusion that the quality of the measurement system is doubtful. However, more detailed analysis is necessary. Additional testing shows the correctness of the measuring system components, and the efforts are directed to an analysis of the electrical conditions on the OTL. 2.2 Measurement results The measurement was performed on a real transmission line under the jurisdiction of the Croatian Transmission System Operator in the period of 2016/10/20 from 00:00-24:00 h. Owing to confidentiality, we are not able to publish the name of the transmission line. - OTL 1 R- - OTL 1 R+ - OTL 2 R- OTL 2 R+ < > ¡12 =11 - 01. (3.14) The lines are connected in parallel, and thus the voltages are equal (3.15) and (3.16) T00*T1=T00*Z2, (3.15) T02*T1 = (h-T01)*T2. (3.16) From (3.16) follows the current 111 at the sending end of the first line by (3.17) uz- (3.17) From (3.14) and (3.17) follows the current ¡¡^ at the sending end of the second line. The apparent powers S0 and S0 at the sending ends of the lines are calculated as (3.19) 50" = 3V100, (3.18) and (3.19) 50" = 300". (3.19) JET 61 Ivan Tolic,Robert Nad, IvanaHartmann Tolic JET Vol. 9 (2016) Issue 4 From Kirchhoff currents law applied at the receiving end of the line, follows (3.20) _ _ _ yields _ _ _ ¡2 = hi + hi -> /22 =¡2- hi. (3.20) The lines are connected parallel, and thus the voltages are equal by (3.21) and (3.22) 727*zl = 722*z2, (3.21) T22*T1 = (j2-T2)*T2. (3.22) From (3.22) follows the current l27 at the receiving end of the first line (3.23) hi = 4^. (3.23) From (3.20) and (3.23) follows the current l22 at the receiving end of the second line. The apparent powers S27 and S22 at the sending ends of the lines are calculated as (3.24) 527 = 3V2l2i, (3.24) and (3.25) 5222 = 3V212,. (3.25) 3.2 Numerical proof of the opposite reactive power phenomenon Owing to confidentiality, we are not able to publish the names of the OTLs, but the measurement results are from a real transmission system. Primary parameters of the OTLs are presented in Table 1. Table 1: Primary parameters of OTLs Parameter OTL 1 OTL 2 Line length l, [km] 4.95 5.64 Resistance R, [Q/km] 0.1388 0.1946 Inductance L, [mH/km] 1.3111 1.3528 Capacitance C, [nF/km] 8.8872 8.5944 The electrical conditions considered for the purposes of a numerical example are at the moment the opposite reactive powers measured using energy meters. The calculation procedure is started for measured quantities at the receiving end of the OTL: U2 = 110^° kV (line voltage) and S2 = p2 + jQ2 = 30 + j2 MVA. Other needed OTL parameters are calculated using equations (3.1) - (3.12), and the results are presented in Table 2. 62 JET Analysis of the opposite reactive power direction phenomenon on two parallel overhead transmission lines Table 2: Calculated parameters of OTLs Parameter OTL 1 OTL 2 Equivalent impedance [0] 2.150^71.38° 2.630z65 33° Total impedance Z [0] 1.180z68 6° Equivalent admittance [S] j1.382*10-5 j1.523*10-5 Total admittance Y [S] j2.905*10-5 Characteristic impedance Zc [0] 201.543z-1047° Propagation constant 0 1.087*10-3 + j5.753*10-3 Attenuation (loss) factor a 1.087*10-3 Phase (velocity) factor 6 5.753*10-3 sh(y • 0 5.855 * 10-3Z72 3° ch(y • i) 0.999z0° Calculation results for the electrical parameters for both OTLs together are presented in Table 3. Table 3: Electrical parameters of both OTLs together Parameter Sending end Receiving end Line voltage U, [kV] U0.161z014° 110z0° Current I, [A] 157.900z-31° 157.810z-381° cosp 0.9984 0.9978 Apparent power 5, [MVA] 30.128z3 24° 30.066z381° Calculation results for the electrical parameters for both OTLs separately are presented in Table 4. Table 4: Electrical parameters of both OTLs separately Parameter Sending end Receiving end OTL 1 OTL2 OTL 1 OTL2 Current I, [A] 87.060z-5 87° 71.061z0 29° 87.01z-658° 71.02z-042° Apparent power 5, [MVA] 16.610z6 00° 13.560z-0148° 16.578Z6S8° 13.530z-042° Active power P, [MW] 16.520 13.560 16.468 13.530 Reactive power Q, [MVAr] 1.736 -0.035 1.899 0.099 JET 63 Ivan Tolič, Robert Nad, Ivana Hartmann Tolič JET Vol. 9 (2016) Issue 4 From the results, it can be observed that the reactive powers Q11 = 1.736 MVAr (sending end of a first OTL) and Q12 = -0.035 MVAr (receiving end of a second OTL) are of the opposite signs. Therefore, the mathematical calculation shows that opposite directions of the reactive power on two parallel OTLs is theoretically possible. 3.3 Physical interpretation of the results From the point of view of the transmission network, receiving end acts as a consumer of inductive reactive power. Let us consider the sending end to be a referent point for the calculation of energy directions. In this case, the direction of reactive power "R-" means that the sending end sends inductive reactive power while direction "R+" conversely means that the sending end receives inductive reactive power. In the described phenomenon that occurs in certain periods, the sending end in one OTL receives and the second OTL gives the reactive power. Therefore, the reactive powers are in mutually opposite directions. Since the OTLs are relatively short (ca. 5 km) and their capacity against the ground is very small (the contribution of reactive power is about 100 kVAr per OTL), it is to be assumed that the cause of the phenomenon is not in the capacity of the OTLs. This is what makes the phenomenon confused, and at the first moment, the validity of measurements was doubtful. The detailed analysis of the phenomenon leads to an entirely different result. Fig. 5. shows the phasors of the voltage and currents at the sending end of the OTL. It is worth noting that the angle between the currents is independent of load. By changing the load, the angle of current to voltage is proportionally changed. By increasing the load, the angle increases, i.e. approaching the voltage and in the respective moment will cross over. Such an operating condition is shown in Fig. 6. ►-> Figure 5: Currents and voltage at the sending end of the OTL 64 JET phenomenon It is clear that the reactive powers are in the opposite directions. Energy meters register this as the sending end while simultaneously receiving reactive power on one OTL and sending reactive power on the other OTL. From the physical and mathematical point of view, it is obvious that the presented operating condition can be explained independently of the capacity against the ground. This confirms that the reason for the presented phenomenon is not the distribution of capacitive currents along the lines nor incorrect measurement, but this phenomenon comes only due to the distribution of reactive powers along the impedances of the respective OTLs. JET 65 Ivan Tolič, Robert Nad, Ivana Hartmann Tolič JET Vol. 9 (2016) Issue 4 4 CONCLUSION This paper presents an analysis of the opposite reactive power direction on two parallel overhead transmission lines. At the first, the latter phenomenon was measured on the real transmission line using energy meters and seemed ambiguous, i.e. superficial reasoning leads to the conclusion that the quality of the measurement system is doubtful. Additional theoretical analysis was performed. The results show that the phenomenon is theoretically possible and it is independent of the capacities against the ground. Moreover, it is not the result of the incorrect measurement, but it originates only due to the distribution of the reactive powers along the impedances of the transmission lines. References [1] 'European network of transmission system operators for electricity', https://www.entsoe.eu/Pages/default.aspx, accessed April 2016 [2] The European Commission: Regulation (EC) No 714/2009 - on conditions for access to the network for cross-border exchanges in electricity and repealing Regulation (EC), No. 1228/2003 (2009) [3] L. 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Fekete: Determination of Energy Interchanged on the Tie Lines-Some Practical Issues, Journal of Energy and Power Engineering, 2014, iss. 8, pp. 948-956 [6] JCGM: Evaluation of measurement data — Supplement 1 Rv Rhe "Guide Rv Rhe expression vf uncertainty in measurement" — Propagation of distributions using a Monte Carlo method, 2008 [7] IEC 60044-1:1996 Instrument transformers - Part 1: Current transformers, https://webstore.iec.ch/publication/12389, accessed October 2016 [8] IEC 61869-2:2012 Instrument transformers - Part 2: Additional requirements for current transformers, https://webstore.iec.ch/publication/6050, accessed October 2016 [9] IEC 61869-3:2011 - Part 3: Additional requirements for inductive voltage transformers, https://webstore.iec.ch/publication/6051, accessed October 2016 [10] IEC 62053-22:2003 Electricity metering equipment (a.c.) - Particular Requirements - Part 22: Static meters for active energy (classes 0,2 S and 0,5 S), https://webstore.iec.ch/publication/6383, accessed October 2016 [11] Landes&Gyr AG: High Precision Metering ZMQ202/ZFQ202 User Manual, 2005 [12] ISKRAEMECO: Three-phase electronic multi-function meter for industry - Technical Description, 2013 [13] D. 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