US 3588611 A
Description (OCR text may contain errors)
United States Patent Inventors Joseph F. Lambden Randallstown; John E. Thompson, Glen Burnie, Md. App]. No. 872,894 Filed Oct. 31, 1 969 Patented June 28, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.
TRANSMISSION LINE ARC DETECTION AND LOCATION SYSTEM 11 Claims, 3 Drawing Figs.
US. Cl. 317/31, 317/50, 324/52, 324/585, 340/253 Int. Cl 1102b 3/20, GOlr 31/08 Field of Search 324/52,
58.5 (B), (inquired); 317/31, 50; 340/253 r INDICATOR 2 COUNTER FILTER 3O 2O DETE CTOR  References Cited UNITED STATES PATENTS I 2,717,992 9/1955 Weintraub 2,931,975 4/1960 Bechtel 3,281,674 10/1966 Landgraf.....
3,300,715 1/1967 Tresselt 3,364,421 1/1968 Bullwinkel 3,470,331 9/1969 Barash et a1.
Primary ExaminerJames D. Trammeil Attorneys- F. 1-1. Henson and E. P. Klipfe] ABSTRACT: Detection of an are along a transmission line and location of the point along the line at which the arc,was ignited is achieved by detecting and counting peaks of the standing wave that moves with, and precedes, the are as the arc travels backward toward the source of power carried by the transmission line.
TRANSMISSION LINE ARC DETECTION AND LOCATION SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the detection of faults, or causes of failure, on transmission lines. In particular, the invention resides in methods and systems for detecting the existence of arcing on high power transmission lines and for locating the position at which the arc occurs.
2. Description of the Prior Art Transmission lines, whether of the open wire, multiwire cable, coaxial, or waveguide types, are subject to physical breakdowns which increase the loading or apparent loading at points where such breakdowns occur. Accordingly, each breakdown reduces the amount of energy which will ultimately be transferred from the generator, or source of energy for frequently results in an are which can travel along the line back toward the source of power and cause extensive damage to system components. Typically, it has heretofore been the practice to utilize a plurality of sensors along the line as a means for locating the point of ignition of the arc, but such a technique has not proven capable of accurately pinpointing the origin of the are because it only provides an indication that an arc has reached a particular sensor. Since the sensors are usually widely separated, one can merely deduce that the oint of ignition is somewhere between the first sensor indicating arrival of the arc and the sensor immediately preceding it toward the load. The are can be extinguished by simply removing power from the line, but this renders the line useless for further power transmission because as soon as power is reapplied recognition of the arc will occur, unless the fault is located and repaired.
It is apparent, then, that a method for detecting and accurately locating the origin of arcs along transmission lines is highly desirable, and it is the principal object of the present invention to provide such a method and to provide a system for practicing the method.
SUMMARY OF THE INVENTION Briefly, according to the present invention, peaks of the standing wave that results from reflection of energy transmitted along the line at the point of the arc, are detected as the standing wave moves with the movement of the arc backward toward the source of energy, preceding the arc front. Ignition of an arc is accompanied by a sharp increase in reflected energy and this phenomenon alone may be detected to indicate the the wave moves along the line, at a preselected point where means are provided to couple energy from the line without normally appreciably disturbing the energy transmission along the line. Distance from this point to the origin of the arc is equal to the number of wavelengths of the standing wave passing the point from original detection of the arc to loss of detector output upon passage of the standing wavebeyond that point. The loss of detector output is utilized to initate turning off of the source of energy, to extinguish the arc and thereby prevent damage to system components.
BRIEF DESCRIPTION OF THE DRAWINGS In describing an exemplary embodiment of the invention in detail, reference will be made to the accompanying drawing, in which:
FIG. 1 is an overall schematic diagram of a transmission line and of an embodiment of the arc detection and location system used therewith;
FIG. 2 is a block diagram of an embodiment of a portion of the detection and location system of FIG. 1; and
FIG. 3 is a wave diagram useful in explaining the operation of the system in locating the point at which the arc originated.
DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the accompanying drawing, the arc detector and locator of the present invention is utilized in conjunction with a transmission line 10 having a source of power, designated by generator 12, connected to the transmitting end of the line and a utilization system, designated by load 14, connected to the receiving end of the line. Transmission line 10 must be capable of carrying high power from source 12 to load 14, but apart from that requirement and the capability to cooperate with the source and the load as input and output devices, the specific type of transmission line utilized is immaterial to the practice of the invention. For the sake of example, however, let it be assumed that transmission line 10 is a waveguide utilized between a transmitter and a high gain antenna.
As a consequence of a physical breakdown in line 10, characterized as a fault, an arc may be ignited at a position of the fault, this point being designated by reference numeral 15. The present invention relies on the fact that the position of such a fault appears to the incident wave (transmitted from generator 12) to be a point of poor termination, or impedance mismatch, and that a considerable reflection of the incident power therefore occurs at that point. In actual practice, 25 percent or more of the incident wave may be reflected at the point of ignition of the arc. The combination of the outgoing (incident) wave and the reflected wave traveling in opposite directions on the line creates a standing wave along the line. Moreover, if the arc does not remain stationary but travels backward toward the power source 12, as is typically the situation encountered in practice, the apparent point of poor termination (i.e., of improper loading, differing considerably from the characteristic impedance of the line) moves with the arc. Accordingly, the voltage maxima of the standing wave follows the movement of the arc as it travels back toward the power source. There are two voltage maxima (peaks) each wavelength (of the transmitted energy) ahead of the arc and these maxima maintain their distance ahead of the traveling arc. Thus, the voltage of the standing wave increases and decreases twice each time the arc travels one wavelength of the energy generated by source 12, at any point between the original fault and the source.
According to the present invention, apparatus for coupling energy from transmission line 10 is positioned at a point along the line preferably relatively close to source 12. This coupler 18 should absorb as little of the transmitted energy as possible, so as not to interfere appreciably with power transmission under normal conditions. In the present embodiment a suitable coupler is a directional coupler arranged to accept negligible power from the incident wave but to absorb considerable power from the reflected wave.
A peak detector 20 is connected to coupler 18 to sense the voltage peaks of the standing wave as that wave responds to the movement of the arc toward source 12. The output of the detector 20 is applied to a counter 21 to count the peaks of the standing wave after filtering of the detector output by a wave filter 23 for removing perturbations of a magnitude sufficient to produce erroneous counts, outside the range of frequencies of interest.
the arc is simply The distance, in wavelengths of the transmitted energy, from the position of the coupler 18 to the point of ignition of D=number of peaks/2 By applying the output of counter 21 to a divide-by-two circuit 25, and the resulting signal to an indicator 28 scaled in terms of wavelength, the precise distance of the origin of the are from the coupler 18 (or from any other point along the line, by appropriate scaling of the indicator) is presented in any desired units.
To prevent damage to any components of the system at the source end of the line, or in the detecting apparatus. the loss of detector output which occurs when the standing wave passes the coupler is sensed by logic circuitry 30 which then operates to cut off the power source 12. When source 12 is deenergized the arc is extinguished. The logic circuitry 30 may be implemented as shown in FIG. 2. A monostable, or one-shot, multivibrator 33 is connected to receive an input from the output of peak detector 20. Normally, with the detecting equipment in operation, one-shot 33 is in its stable state and supplies a predetermined voltage level as an output thereof. This voltage level is selected to be adequate to actuate a cutoff switch 35, ordinarily supplying energizing power to source 12, to the off condition in which power is removed from the source. A gate 36 is connected between the output circuit of one-shot 33 and the switch 35 and is normally in the blocking condition to prevent application of the cutoff voltage to switch 35 when one-shot 33 is initially in its stable state. Gate 36 is also connected to receive an input from the output of detector and responds to a voltage level from the detector to switch to a signal-passing condition where it remains latched" until reset by a signal applied to a reset input lead thereto. in contrast, an output voltage emanating from detector 20 triggers one-shot 33 to its quasi-stable state. If the delay time of the monostable multivibrator, i.e., the time interval between assumption of the quasi-stable state and return to the stable state, is set to be greater than one-half wavelength of the energy transmitted from source 12, then one-shot 33 cannot return to its stable state so long as detector 20 continues to produce output pulses at a rate detennined by the passage of peaks of the standing wave at coupler 18.
In operation of the logic circuitry of FIG. 2, the first peak of the standing wave detected by detector 20 results in an output voltage from the detector. Simultaneous application of this voltage to one-shot 33 and to latching gate 36 causes the oneshot to assume the quasi-stable state and to discontinue its output (or to reduce the output level to a value far below that required to actuate switch 35),just as gate 36 is switched from a blocking condition to a passing condition. While peaks of the standing wave continue to pass coupler 18, the one-shot multivibrator is constrained to remain in quasi-stable state because each output pulse of the detector restarts the delay time of the multivibrator and the interval between these output pulses is less than the delay time interval of the multivibrator. However, when the last peak of the standing wave preceding the traveling arc passes coupler l8, detector 20 ceases to produce an output, and at the conclusion of the delay time interval following the last output pulse of the detector, multivibrator 33 reverts to its stable state in which its output voltage is suddenly returned to the aforementioned predetermined level. Gate 36, which remains latched in the passing" condition despite loss of detector output, permits this voltage level to be applied to cutoff switch 35 whereupon the power source 12 is deenergized and the arc is extinguished. The power source may be energized, after repair of the cause of the are using the fault location information obtained from the detection system, but simply applying a reset signal to gate 36 to return the gate to the blocking" condition and thereby to remove the cutoff voltage from switch 35.
The basis of the distance measurement, while it should be quite clear from the preceding description, is further illustrated in FIG. 3. The reflected wave that occurs upon ignition of the arc adds to the incident wave at that point, to produce the standing wave 40. Voltage peaks of the standing wave occur along the line 10 at points x=n M14, where n is an odd integer, from the point of ignition. As the arc moves toward the source of power at the transmitting end of line 10, the impedance mismatch which resulted in standing wave 40 moves with the frontal portion of the arc. Hence, the standing wave is not stationary, but similarly moves with the arc, and its two voltage peaks each wavelength ahead of the arc maintain their distance from the frontal portion of the are as the arc travels backward along the line. Detection of the number of standing wave peaks passing a fixed point along the line is thus tantamount to proportionally detecting the number of wavelengths from that point to the origin of the arc, i.e., to the location of the fault.
It should be apparent that the position of coupler 18 is preferably sufficiently close to source 12 to permit arc detection and location in proximity to the source of power, and yet not so close that insufficient time is available between loss of detector output and arrival of the are at the power source to permit turning off the power source to extinguish the arc and prevent damage to system components.
l. A system for detecting an arc and for locating the point of origination of the are along a transmission line carrying energy between a source and a load, said system comprising:
means for sensing a substantial increase in reflected energy along said line over the amount of reflected energy occurring under normal conditions, as a result of ignition of an arc on the line remote from said source, said sensing means including;
means responsive to movement of said arc backward along said line toward said source, for detecting peaks of the standing wave produced by a combination of said reflected energy and of the outgoing energy from said source, as said standing wave precedes said are in movement therewith backward along said line.
2. The system according to claim 1 further including means responsive to cessation of detection of peaks by said peak detecting means for cutting off said source of energy to extinguish said arc.
3. The system according to claim 1 wherein said sensing means further includes means positioned along said line at a point in proximity to said source of energy for coupling energy from said standing wave to said peak detecting means.
4. The system according to claim 1 wherein said sensing means is positioned at a predetermined point in said line, and wherein is further included means responsive to the number of peaks of said standing wave detected by said peak detecting means for indicating the distance between said predetermined point and the point of origination of said are along said line.
5. The system according to claim 1 wherein said sensing means is located a known distance from said source of energy, and wherein is further provided means for counting the peaks detected by said peak detecting means for determining the distance between said source and the point of ignition of said arc on said line.
6. The system according to claim 5 further including means responsive to the loss of output of said peak detecting means, as an indication of the passage of said arc past the position of said sensing means in said line, for deenergizing said source of energy to extinguish said arc.
7. The system according to claim 6 wherein said sensing means further includes means positioned along said line at said known distance from said source, for coupling energy from said standing wave to said peak detecting means.
8. The method of detecting an are on a transmission line carrying high power from a source to a load, and of locating the point of origination of said are on said line, including the steps of detecting peaks of the standing wave produced by a combination of wave energy reflected from the arc and outgoing wave energy from said source, as said standing wave precedes said arc in movement therewith backward along said line toward said source, at a predetermined point along said line in proximity to said source, and counting the detected peaks as a measure of the distance of the point of origination of said are from said predetermined point at which the peaks are detected. I
9. The method according to claim 8 further including the step of turning ofi said source when peaks tease to be detected, to extinguish said arc.
10. The method according to claim 9 wherein said peak detecting step includes absorbing energy from said standing wave without appreciably disturbing the normal flow of energy along said line toward said load.
11. A transmission line are detection and location system, comprising:
means positioned at a known point on said line for detecting peaks of a moving wave deriving from the addition of the wave incident on an are, if present on said line, and the wave reflected from said arc, said moving wave traveling ahead of said are as it moves toward a source of said energy; and
means responsive to the detected peaks for establishing the location of the ignition point of said are relative to said known point.