IEEE Std 776-1987 IEEE Guide for Inductive Coordination of Electric Supply and Communication Lines.pdf

ANSI/IEEE Std 776-1987 Approved September 18.1987 American National Standards lnslllule :EEE Guide for Inductive Coordination of 3lectric Supply and Communication Lines H W w II! Published by The Institute of Electrical and Electronics Engineers, Inc 345 East 47th Street, New York, NY 10017, USA Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 11:09:08 UTC from IEEE Xplore. Restrictions apply. n Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 11:09:08 UTC from IEEE Xplore. Restrictions apply. IEEE Guide for Inductive Coordination of Electric Supply and Communication Lines 1. Scope This guide addresses the inductive environ- ment that exists in the vicinity of electric power and wire line telecommunications systems and the interfering effects that may be produced thereby; guidance is offered for the control or modification of the environment and the sus- ceptibility of the affected systems in order to maintain an acceptable level of interference. To aid the user of this guide in calculating induction between power and telecommunica- tion lines, the concept of an interface is devel- oped. This guide permits either party, without need to involve the other, to verify the induction at the interface by use of a probe wire. This guide does not apply to railway signal circuits. 2. References The following publications shall be used in conjunction with this standard: l ANSIIIEEE Std 81-1983, IEEE Guide for Measuring Earth Resistivity, Ground Imped- ance, and Earth Surface Potentials of a Ground s ys tem . 2 ANSI/IEEE Std 487-1980, IEEE Guide for the Protection of Wire-Line Communication Facili- ties Serving Electric Power Stations. 3 ANSI/IEEE Std 820-1984, IEEE Standard Telephone Loop Performance Characteristics. 4 IEEE Std 367-1987, IEEE Recommended Practice for Determining the Electric Power Sta- tion Ground Potential Rise and Induced Voltage from a Power Fault.2 ANSI / IEEE publications can be obtained from the Sales Department, American National Standards Institute, 1430 Broadway, New York, NY 10018. IEEE publications can be obtained from the Service Cen- ter, The Institute of Electrical and Electronics Engineers, 445 Hoes Lane, PO Box 1331, Piscataway, NJ 08855-1331. 3. General 3.1 Inductive Interference. An effect, arising from the characteristics and inductive relations of electric supply and telecommunication sys- tems, of such character and magnitude as would prevent the telecommunication circuits from rendering service satisfactorily and economi- cally if methods of inductive coordination were not applied. Inductive interference is produced by the simultaneous coexistence of three factors: (1) An inductive influence, (2) A coupling mechanism between two elec- trical systems or circuits, one of which produces the influence, and (3) A susceptibility of the second system or circuit to interference. While inductive interference may occur at any time the above conditions are satisfied, the ma- jority of cases and the principal concern of this guide involve interference in telecommunication systems as a result of their proximity to electric power systems. Therefore, subsequent discussion is limited to that general case, although the prin- ciples and practices may apply to other cases as well. 3.1.1 Inductive Influence (Electric Supply Circuit with its Associated Apparatus). Those characteristics that determine the char- acter and intensity of the inductive field that it produces. The voltages and currents present on an op- erating power system produce electric and mag- netic fields in the vicinity of the system. The character and intensity of those fields determine the inductive influence. Character is related pri- marily to the frequencies present, while inten- sity is related to the magnitudes of voltages and currents modified by line configuration, current distribution, and any shielding structures in the immediate vicinity, excluding the shield of a telecommunications cable. 3.1.2 Coupling. The effect of an interfering source on a signal transmission. 7 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 11:09:08 UTC from IEEE Xplore. Restrictions apply. IEEE Std 776-1987 IEEE GUIDE FOR INDUCTIVE COORDINATION OF For the inductive influence of a power system to affect another system or circuit, there must be coupling between the two. The coupling mech- anism consists of the mutual impedance between circuits in proximity to each other. This has re- sistive, capacitive, and inductive components. Electric induction, via capacitive coupling, may be consequential when the exposed circuit is composed of unshielded conductors above ground. However, when the exposed circuit con- ductors are enclosed in a grounded metallic sheath or shield, capacitive coupling generally may be considered negligible compared to the magnetic induction via inductive coupling. Therefore, the coupling mechanism of primary concern will generally be the mutual inductance between an electric supply circuit or circuits and telecommunications. The primary factors af- fecting coupling are separation of the systems, frequency of the magnetic field, and earth re- sistivity. 3.1.3 Inductive Susceptiveness (Telecom- munication Circuit with its Associated Ap- paratus). Those characteristics that determine, so far as such characteristics are able to deter- mine, the extent to which the service rendered by the circuit can be adversely affected by a given inductive field. The existence of an inductive field and cou- pling with a metallic telecommunication circuit will cause longitudinal voltages to be induced in the telecommunication circuit. However, inter- ference does not occur unless the circuit is sus- ceptible to being adversely affected by the induced voltages and resulting currents. One kind of interference is the introduction of an unwanted signal (noise) into the circuit. The sus- ceptiveness of the circuit to noise depends upon the cable shield, the amplitude and the fre- quency of the signal normally transmitted, cir- cuit impedances, and the longitudinal balance of the circuit and its associated equipment. Lon- gitudinal balance determines the extent to which longitudinal (common-mode) voltages are converted to metallic (differential-mode) volt- ages. Interference may also be manifested as a malfunction in the operation of the circuit. The malfunction may be caused by electrical or ther- mal overstress of a circuit component by the induced voltage or resulting current. 3.2 Need for Coordination. The continued suc- cessful coexistence of systems for the transmis- sion, distribution, and utilization of electric power and wire line telecommunications de- - pends upon the ability of their operators to re- solve problems of interference between the systems. The need for coordination between op- erators of electric supply and telecommunica- tions lines has existed since the early days of the industries. At various times, cooperative studies have been undertaken, resulting in the production and dissemination of a large body of technical information on the subject. This in- formation continues to grow with the expansion of these industries and the introduction of new technology. However, this growth and change introduces new concerns that should be ad- dressed if continued compatibility of the systems is to be accomplished. Some of those concerns are as follows: (1) Extension of services to more customers, leading to longer lengths of serving facilities. (2) Ecological considerations, which encourage the concentration of facilities on joint or adja- cent rights-of-way. (3) Higher capacity power systems serving larger loads and more nonlinear loads. (4) The deployment of more susceptible elec- tronic devices and equipment for telecommuni- cation and signaling systems along tele- communication lines, thus exposing them to the effects of the inductive environment. These concerns emphasize the need for con- tinued cooperative inductive coordination to avoid interference where possible and to reduce it to an acceptable level whenever it occurs. 3.3 Mutual Responsibility of Parties In- volved. Inductive coordination is defined as the location, design, construction, operation, and maintenance in conformity with harmoniously adjusted methods that will prevent inductive in- terference. Historically, inductive coordination has been accomplished through the cooperative efforts of the industries involved, without regulatory in- tercession. This cooperative effort best meets the service needs of the public and resolves inter- ference problems in the most equitable and ec- onomical manner. However, for such a cooperative effort to succeed, all parties involved should recognize and be willing to discharge a mutual responsibility for the handling of all in- Failure to do so may result in regulatory au- thority action to protect the public interest. ductive coordination problems that may arise. - 8 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 11:09:08 UTC from IEEE Xplore. Restrictions apply. ELECTRIC SUPPLY AND COMMUNICATION LINES IEEE Std 776-1987 - 4. The Inductive Environment 4.1 Guidelines for an Acceptable Environ- ment. This portion of the guide will address the following: (1) Areas of concern (2) Threshold considerations (3) Suggestion of a classification system (4) Definition of the interface (5) Establishment of an acceptable environ- mental threshold for positive action (6) Susceptiveness criteria for telecommuni- cations plant. 4.1.1 Areas of Concern. Three areas of con- sideration are as follows: (1) Safety from electrical shock due to personal contact with telecommunications conductors. (2) The destruction of plant facilities as a re- sult of dielectric breakdown or energy dissipa- tion. (3) The degradation or interruption of telecom- munications. Each of these considerations is the result of the influencing current of the power system, the coupling between the two systems, and the sus- ceptiveness of the telecommunication system. 4.1.2 Threshold Considerations. The follow- ing is a list of threshold considerations from various standards on the telecommunications system: (1) Safety. 50 V rms continuously induced with respect to ground at 60 Hz on telecommunica- tion facilities has historically been considered an upper threshold in North America by tele- communications companies. Electric power com- panies and railway telecommunications systems have historically used 60 V rms to ground at 60 Hz as their safety threshold. CCITT (tele- phone) also uses the 60 V rms level except for special cases when 150 V rms is accepted. Other higher thresholds have been established in other administrations. (2) Destruction of Cable. ANSVIEEE Std 487- 1980 213 provides a method to obtain the 60 Hz conductor-to-conductor dielectric strength for plastic insulated cable (PIC) typically used in telephone systems: 1.8 kV rms for 19 gauge 1.4 kV rms for 22 gauge 1.2 kV rms for 24 gauge 0.96 kV rms for 26 gauge The numbers in brackets correspond to those of the ref- erences listed in Section 4; when preceded by B, they cor- respond to the bibliography in Section 14. I _ Conductor-to-shield failure may also occur and should be considered. Paper insulated cables re- quire special protection for peak voltages in ex- cess of 1000 V. (3) Destruction of Equipment. An indication of energy dissipation or the product of the current squared and time in line-repeater electronics is typically between 16 and 80 A2 (4) Circuit Degradation. ANSVIEEE Std 820- 1984 4 states that the recommended level of noise to ground is less than or equal to 80 dBrnC. The reference also states that 81-90 dBrnC lev- els are considered acceptable and those in excess of 90 dBrnC are not recommended on telephone voice frequency circuits. s (I2 - t). (5) Circuit Failure (a) the supervision on some voice frequency circuits may be adversely affected when longi- tudinal current exceeds 5 mA. (b) communications carrier systems that are powered over the simplex may be adversely af- fected when the peak ac longitudinal current through the regulating diode approaches the dc powering current. The carrier will fail when the peak ac longitudinal current exceeds the dc pow- ering current through the regulation diode. 4.1.3 Classification System. A method of classifying telecommunication facilities in a given route will allow different environmental criteria. The classification scheme will have four components. The four components are as follows: (1) Circuit sensitivity to power fault conditions (2) Length consideration (3) Ability to inure (accepting an undesirable (4) Fault duration The power system produces two environ- ments: the normal operating condition and the fault condition. Some telecommunication sys- tems and circuits may tolerate interruption dur- ing a fault and others may not. For the purpose of this guide, those that may tolerate a fault- caused interruption will be classified “B”; those that may not are classified “A.” Induced voltage is proportional to the length of the exposure. A length or zone qualifier will preclude an unreasonable economic burden on short exposures. The three zones will be defined as follows: situation) Zone 1 = 0-15 kft Zone 2 = 15-50 kft Zone 3 50 kft 9 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 11:09:08 UTC from IEEE Xplore. Restrictions apply. IEEE Std 776-1987 IEEE GUIDE FOR INDUCTIVE COORDINATION OF The inure classification will be for those fa- cilities where a customer will not have access to conductors and the telecommunications utility is willing to condition these to operate safely at interference levels of 50-100 steady-state V rms to ground. i = inure (50-100 steady-state V rms to ground) c = customer access ( 50 kft (calculation based on 132 kft) When the reference power is 1 mW and the impedance is 600 R (an impedance commonly used in voice band telecommunication practice) the reference voltage is 0.775 V and the unit is dBm (decibel referenced to 1 mW). When the reference power is 1 pW with a 600 R impedance, 11 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 11:09:08 UTC from IEEE Xplore. Restrictions apply. IEEE Std 776-1987 IEEE GUIDE FOR INDUCTIVE COORDINATION OF Table 2 Circuit Degradation (Voltage by Harmonic on the Probe Wire Interface) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200 1260 1320 1380 1440 1500 1560 1620 1680 1740 1800 1860 1920 1980 2040 2100 2160 2220 2280 2340 2400 2460 2520 2580 2640 2700 2760 2820 2880 2940 3000 3060