1、E 4862593 ObOS9b 87 E I NT ER NAT I O N AL TE LEC O M M U N I CAT I O N U N I ON DIRECTIVES concerning the protection of telecommunication lines against harmful effects from electric power and electrified railway lines Volume V Inducing currents and voltages in power transmission and distribution sy
2、stems ITU-T TE LEC0 MMU N I CATI ON STANDARD i ZAT I O N SECTOR OF ITU 1999 INTERNATIONAL TELECOMMUNICATION UNION DIRECTIVES concerning the protection of telecommunication lines against harmful effects from electric power and electrified railway lines Volume V Inducing currents and voltages in power
3、 transmission and distribution systems ITU-T TELECOM M UN 1 CATI ON STAN DARD I Z AT I O N SECTOR OF ITU 1999 o ITU 1999 Ail rights reserved. No part of this publication may be reproduced or utili - to scientists and researchers who need a reference book with the most recent findings; - to students
4、who require a textbook with which to become acquainted with electromagnetic coupling phenomena; - to Administrations which need to have a basis to form national regulations and standards. The Directives have been prepared as a result of close collaboration between many members of ITU-T, CIGRE and th
5、e UIC. They therefore describe technical methods for solving mutual problems which are recognized by these international organizations and which should facilitate coordination between member organizations in user coun- tries. The principal object of the Directives is to describe ways in which advers
6、e effects from power transmission and distribution lines or from electrified railway lines onto telecommunication lines can be reduced or avoided. Such effects may result in danger to personnel, damage to telecommunication equipment, deterioration of telecommunication transmission quality or to dist
7、urbance of signalling. Although the advice given in the Directives has been described for public telecommunication networks, the basic principles have a more general application, and owners of other networks should decide whether they can be adapted to their own needs. Volume V - Chap. 1 1 48b25L Ob
8、80603 847 1.2 Structure of he Directives 1.2.1 Content of inividual volumes The new Directives are divided into 9 volumes, each dealing with a separate part of the overall subject matter. The series is made up as follows: Volume I “Design, construction and operational principles of telecommunication
9、, power and electrified railway facilities” describes these systems and shows why conditions for their mutual coexistence must be established. Volume II “Calculating induced voltages and currents in practical cases” describes the methods for evaluating voltages and currents resulting from capacitive
10、, inductive and conductive coupling in a variety of com- monly-encountered situations. Volume Il “Capacitive, inductive and conductive coupling: physical theory and calculation methods” gives an account of the physical laws governing the relevant phenomena together with mathematical models, and intr
11、oduces a precise calculation method to evaluate voltages and currents resulting from couplings. Volume IV “Inducing currents and voltages in electrified railway systems” describes traction systems using d.c. and ac. at various frequencies (16 2/3 Hz, 50 Hz, 60 Hz etc.) in normal operation and under
12、fault conditions. Volume V “Inducing currents and voltages in power transmission and distribution systems” describes unbalanced and balanced power systems in normal operation and under fault conditions. Volume VI “Danger and disturbance” considers the risk to both equipment and people. Volume W “Pro
13、tective measures and safety precautions” describes methods which are commoniy used to ensure satisfactoq working and operating conditions. Volume WI Protective devices” gives the latest information on devices which may be used to improve safety stan- dards or reduce disturbance of telecommunication
14、systems. Volume M Testing methods and measuring apparatus” describes the methods and apparatus used to determine parameten required for coupling calculations, and to verify the satisfactory operation of protective measures. In addition it deals with testing methods raking into account modem practice
15、s in other fields of electromagnetic compatibility (e.g. lightning, high frequency disturbances). The volumes overlap to some extent deliberately. This limits the need to consult several volumes simultaneously when resolving practical problems. Calculation methods for evaluating voltages and current
16、s induced into lines are given in both VolumesII andIiI. In VolumeII simplified formulae are given for each type of coupling with graphs and data for stepby-step calculation. The method covers the usual cases which arise in practice and requires access only to calculators or small computers. It is u
17、seful to those seeking a simple procedure where some approximations have to be made. In Volume III, a rigorous calculation method is given, strictly associated with the theory of coupling which is also treated in the volume. The method deals with a wide range of situations and assumes that access is
18、 avaiable to adequate computing facilities. The volume is intended to be used by those who require a precise evaluation of the coupling results. 2 Volume v - chap. 1 4b25L ObOb04 783 1.2.2 Use of the Directives 1.2.2.1 When stuying coupling processes in general - For a broad understanding of telecom
19、munication, power and electrified railway facilities and their mutual coupling effects, consult Volume I. - For further information on inducing installations in power or electrified railway systems, consult Volume N (railway systems) or Volume V (power systems). - For detailed study of coupling phen
20、omena and calculation methods, consult Volumes II and . - To understand the effects of induced voltages and currents, i.e. danger and disturbance, and the limiting values which are recommended. consult Volume VI. - For advice on protective components or complex protective devices, consult Volume WI.
21、 - For information on relevant testing and measuring techniques, consult Volume E. 1.2.2.2 When establishing srandars or similar regulations - For limiting values of induced voltages and currents, consult Volume VI. - For estimating induced voltages and currents using simplified calculations, consul
22、t Volume II. - For precise calculation of induced voltages and currents, consult Volume iII. To select appropriate protective measures, consult Volume W. - 1.2.2.3 When dealing with danger and disturbance problems in practice - Identify the telecommunication, power and electrified railway lines invo
23、lved and ensure they are described in adequate detail. - Compare the operational and fault conditions in the inducing systems with the actual inducing voltages and currents by consulting Volume IV (railway systems) or Volume V (power systems). - Determine the electrical and geometrical parameters ne
24、eded for calculations in Volume II or Volume Ei using numerical values that are known. - To measure parameters which are not known, consult Volume E. - To estimate the induced voltages or currents using simple calculation methods, consult Volume II. - To calculate induced voltages and currents preci
25、sely, consult Volume i. - To decide whether the predicted induced voltages and currents are acceptable, consult Volume VI. - To select suitable protective measures, consult Volume W. These steps are illustrated in the flowchart in Figure 1/1. Volume V - Chap. 1 3 . Yes 4 Identify power or electrifie
26、d railways and telecommunication faalities involved No Detemine electric and geometrical parameters required to estimate the effeds FIGURE 1/1 Flowchart to be followed when deaUng with danger and disturbance problems in praccc 4 Volume V - Chap. 1 48b2593 ObBObOb 556 6 1.3 Object of Volume V The int
27、ention of Volume V is to give telecommunication engineers an overall view of power system operations, e.g. typical magnitudes of currents and voltages, and principles of calculations, so that they can obtain from power companies the precise information needed to evaluate the effects of these systems
28、 on telecommunication networks. Volume V is not intended to teach power engineers how to calculate fault currents, for instance. Power companies normally have computer programs available to calculate fault current magnitudes. However, Volume V also contains some matter which is not normally needed i
29、n power system technology, and consequently, some parts may be useful to power engineers also. Volume V - Chap. 1 5 1118 4862593 Ob8ObO 492 Themai CHAPTER 2 CURRENTS IN NORMAL OPERATION Natural 2.1 Phase current 20 110 400 Load currents may vary over a wide range even in lines with the same nominal
30、voltage. In the case of short lines, the upper limit of current is determined by economic considerations e.g. by losses, or by the temperature rise of conductors. Consequently, the maximum current depends on conductor cross-section and on the cost of power losses. 3 -10 100 - 300 about 1 about 30 60
31、 - 200 300 - lo00 30 - 50 150 - 250 1ooO-2ooO 1500-3000 500 - 700 700 - lo00 In the case of long lines, the limiting factor is likely to be the voltage drop or the stability of the system. The latter depends to some extent on conductor cross-section but is more dependent on the number of subconducto
32、rs and on the reactive power compensation of the system. A rough estimate is the so-called “naturai power“ (called also the “surge-impedance load“) i.e., the transmitted power at which the reactive power losses in line reactances are equal to the reactive power generation in line capacitances. This
33、is similar to impedance matching of telecommunication lines. The load cuilent in three-phase systems can be calculated from equation: S P I=- $u - .Js u cos p where S is the apparent power, P the active power, U the phase-to-phase voltage and cos cp the power factor. Table 1/2 gives typical ranges o
34、f the thermal limit load and the natural power at 20 kV, 110 kV and 400 kV. TABLE 1/2 Loading capacities of power lines The load current is normally almost symmetrical, i.e., the current magnitudes in the phases are practically equal and their phase-angle difference is 120O. Consequently, the negati
35、ve sequence component (see Chapter 3) is small. An essential part of the loads in low-voltage networks are of single-phase nature, but they are distributed between the phases so that the effective loads of h.v. distribution lines are practically symmeUical. However, some large asymmetrical loads suc
36、h as arc furnaces and traction feeding transformers do produce a considerable negative sequence component. Previous page is blank. Volume V - Chap. 2 7 As the effects of negative sequence current on telecommunication lines do not deviate from those of positive sequence currents, the negative sequenc
37、e component can usually be ignored in practice. 22 Earth cumnt due to circuit asymmetry 2.2.1 Impedance asymmetry Unless the phase conductor configuration of a three-phase line is an equilateral riangle, the reactances of the phases are not equal. When the impedances of the phases differ from one an
38、other, a part of the load current flows through earth if the neutral points of transformers are earthed. The earth current can be determined using the Thvenin principle as shown in Figure 1/2. If I1 = V+120“, I2 = I/ and I3 = V-120“ when switch s in Figure 1/2 is open, the zero-sequence voltage drop
39、 in the case of a non- transposed single-circuit line is: -jm( in - %: + j 4 in - a23 ) U0= a12 a23 a12 where j =fi = 1/90“, o (= 2zf) the angular frequency, line and au the conductor spacings as shown in Figure U2. the permeability of space, 4rr .lO-7 Wm, L the length of the 2, : Zero-sequence impe
40、dance of the line i, : Total zero-sequence impedance of the circuit FIGURE 112 Determination of earth current caused by asymmetry in phase conductor arrangement 8 Volume V - Chap. 2 I 4862593 Ob8ObO 2b5 I (110 I FIGURE 2/2 Latter symbolr for eonduetor rpuinga FIGURE 3/2 Touer amt.tkir d L the .umpi.
41、r If the conductors are located on a plane, e.g. as in Fig. 3/2, a), so that a12 = a23 and a13 = 2a12, In the case of two parallel lines or a double-circuit line, the effect of the neighbouring circuit should be taken into account (same currents in both circuits). 2 In %l ail a2i a3i ai3 a23 a33 a23
42、 a13 a23 a33 a12 all a2l a31 222 + for and %. see Figure 112) U kV 400 - 400 m 400 400 400 400 400 110 nlll A 700 700 10 700 700 10 2x700 2x700 200 f Hz 50 50 800 50 50 800 50 50 50 - - Figure 312 10 /-9o“ 2/-90“ 10/-90“ low 2/-90“ IS 1-90“ 3/-90“ 15 1-90“ Earth wires mm2 2 x 70Fe 2 x 70Fe 2x7OFe 2x
43、7OFe 2 x 1WSO AiRe 2 x 100150 Alme 2x7OFe 2x7OFe 2xSOFe Pe Rm 100 100 i00 loo00 100 100 100 100 100 2 10 2 2 2 2 2 2 2 Ie A 14 1-175“ 3 1-175“ 0.2 1-173“ 10 1-176“ 11 /-176“ 0.2 1-1 70“ 24 1-173“ 24 1-173 3 /-173 0.02 0.005 0.02 0.015 0.015 0.02 0.015 0.015 0.015 Differences between the phase impeda
44、nces of a transformer or series capacitor may ais0 result in earth-return ! current. The worst case in view of a difference between impedance of the phases is a complete break in one phase due to conductor breakage or biased functioning of a switching device or fuses. I 10 Volume v - chap. 2 I .II 4
45、662591 ObObll 933 = 2.2.2 Capacitance asymmetry The capacitance to earth of individual phases of overhead lines have different values, and as a result, a residual current flows to earth. The earth current is more conveniently determined by calculating charges qi per length of the phase conductors fr
46、om the following equation group (one equation for each phase conductor and earth wire): where the potential coefficients are: where hi is the height of conductor i, ri the radius (or equivalent radius) of conductor i, Aij the distance of conductor i from the image of conductor j, aij the distance of
47、 conductor i from conductor j (Figure u2) and the permittivity of space 8.85.10-l2 F/m. The potentials of the phase conductors in the examples are as follows: and those of the earth wires V4 = V5 = O. it is very cumbersome to solve this group of equations manually. A computer should be used. The cap
48、acitive current flowing to earth (including the earth wires) in the case of a single-circuit line is: where L is the length of the line section. In the case of two parallel lines or a double-circuit line: Table 3/2 illustrates the capacitive current to earth of some typical 400 kV and 110 kV lines.
49、The current magnitude is proportional to the voltage and the frequency. Carrier-frequency coupling capacitors, capacitive voltage transformers, etc., may also cause capacitance unbalance unless they are evenly distributed between the phases. The capacitive current flowing to earth returns to earthed neutral points or circulates between transposition sections of a transposed line. The current through earth is the capacitance asymmetry current multiplied by the screening factor of the earth wires. The remainder of the current flows along the earth
