Interference Of Power Line With Communication System k3d6g

Interference of power line with communication system:When a power and a communication circuit are operated in proximity, the power circuit may produce certain conductive or inductive effects, which may interfere with the normal operation of the communication circuit. These electrical interference effects, which appear as a result of extraneous voltages and currents in the communication circuit, may be minimized by measures that are applicable to either circuit alone, or to both. Such measures provide the basis for the coordination of power and communication circuits to avoid interference. Interference and Coordination Definitions of interference and coordination as adopted by the National Electric Light Association and Bell Telephone System lcs), with slight rephrasing, are: Interference is an effect arising from the characteristics and interrelation of power and communication systems of such character and magnitude as would prevent the communication system from rendering service satisfactorily and economically if methods of coordination were not applied. Coordination is the location, design, construction, operation, and maintenance of power and communication systems in conformity with harmoniously adjusted methods which will prevent interference. The electrical-coordination problem arises principally because two distinct systems are employed, namely, (1) power systems for generation, distribution of electrical energy, and (2) communication systems in which used incidentally for the transmission

types of circuits or transmission, and electrical energy is of signals.

Another important consideration arises from the fact that the of electrical energy is generally also a of electrical communication. For example, power lines for delivering electricity to homes and factories are roughly paralleled by telephone circuits required to give electrical communication for the same places. The coordination problem becomes cumulatively more severe as the power systems supply increasing amounts of load and the communication systems become increasingly sensitive. There is also the complication caused by the introduction of neer uses for electrical energy and for electrical communication. The effects of extraneous voltages and currents on communication systems are varied in character, and include hazard to persons, damage to apparatus, and interference with service.

The damage to the physical plant includes the effects resulting from overheating, from breakdown of insulation in lines and apparatus, and from electrolysis. The interference with service includes such effects as noise and acoustic shock in the telephone circuits, false signaling in telephone, telegraph, and supervisory control circuits, as well as disruption of service. Communication circuits are usually equipped with devices that, when subjected to excessive voltages, provide protection, but in so doing may render the circuit inoperative for communication purposes not only for the duration of the abnormal voltage condition but also until maintenance work can be done. The coordination problem is extremely widespread; practically every type of electrical circuit has interfered with some other type of electrical circuit. For example, power-supply circuits have interfered with audio- and carrier-frequency telephone and telegraph circuits, machine- switching and supervisory-control circuits. Similarly, d-c and a-c railway circuits have interfered with practically every type of communication circuit,. It is an interesting and significant fact that communication circuits interfere with one another, not only in the form of “cross fire” between telegraph circuits but also in the form of “crosstalk” between telephone circuits on the same pole line. Power circuits can interfere with each other. For example, a ground fault on a transmission circuit can impress high induced voltages on a neighboring low-voltage distribution circuit and produce apparatus failure or circuit outage.

Travelling waves:A mechanical wave is a disturbance that is created by a vibrating object and subsequently travels through a medium from one location to another, transporting energy as it moves. The mechanism by which a mechanical wave propagates itself through a medium involves particle interaction; one particle applies a push or pull on its adjacent neighbor, causing a displacement of that neighbor from the equilibrium or rest position. As a wave is observed traveling through a medium, a crest is seen moving along from particle to particle. This crest is followed by a trough that is in turn followed by the next crest. In fact, one would observe a distinct wave pattern (in the form of a sine wave) traveling through the medium. This sine wave pattern

continues to move in uninterrupted fashion until it encounters another wave along the medium or until it encounters a boundary with another medium.. This type of wave pattern that is seen traveling through a medium is sometimes referred to as a traveling wave. raveling waves are observed when a wave is not confined to a given space along the medium. The most commonly observed traveling wave is an ocean wave. If a wave is introduced into an elastic cord with its ends held 3 meters apart, it becomes confined in a small region. Such a wave has only 3 meters along which to travel. The wave will quickly reach the end of the cord, reflect and travel back in the opposite direction. Any reflected portion of the wave will then interfere with the portion of the wave incident towards the fixed end. This interference produces a new shape in the medium that seldom resembles the shape of a sine wave. Subsequently, a traveling wave (a repeating pattern that is observed to move through a medium in uninterrupted fashion) is not observed in the cord. Indeed there are traveling waves in the cord; it is just that they are not easily detectable because of their interference with each other. In such instances, rather than observing the pure shape of a sine wave pattern, a rather irregular and non-repeating pattern is produced in the cord that tends to change appearance over time. This irregular looking shape is the result of the interference of an incident sine wave pattern with a reflected sine wave pattern in a rather non-sequenced and untimely manner. There are two basic types of traveling waves Transverse : Motion of the constituent particles is at right angles to the wave direction, e.g. waves on a string, electromagnetic waves. Longitudinal: Motion of the constituent particles is back and forth in the direction of motion of the wave, e.g. sound waves, the “slinky " spring. The problems of traveling waves on the transmission lines of a power system1 differ considerably from those of traveling waves on telephone or telegraph circuits. The primary object in the case of the former is to know how to protect the system from abnormal voltage disturbances which might damage apparatus or cause discontinuity of service; whereas the object in the case of the latter is the transmission of signals. Attenuation, distortion, wave shape modification, and successive reflections are deliberately sought after on the power system as a means of rendering the surges innocuous, but these effects must be carefully avoided or nullified on the communication circuits so as to preserve the wave shape and transmit the signal with strength, fidelity, and without interference. On the power lines, the surges often originate from unknown causes, or at the point of origin are of unknown magnitude and shape (except from a statistical point of view) ; while on the communication circuits the initial shape and magnitude of the wave train are known with exactness. External fields (due to charged clouds), corona, flashovers, faults, and so on are of great importance with respect to surges ; but are of no concern in the normal functioning of a telephone or

telegraph line. Thus on the power lines surges originate from external or undesirable causes and every effort must be made to withstand or control them; while on communication circuits the transients are the direct means to the end. These differences have led to corresponding differences in the mathematical approach. The power engineer is satisfied with approximations which would be intolerable to the communications engineer, and he is willing to take a license with mathematical rigor which would make any self-respecting mathematician groan. Higher mathematics has found little or no application in the study of surges on power systems. This has been due primarily to the fact that the boundary conditions are not definite enough to justify purely mathematical refinements; particularly since engineering results must be obtained in a short time by men who are not mathematicians. However, there are numerous aspects of the problem which lend themselves to mathematical excursions.