12 Dec UNDERGROUND CABLE FAULT DETECTION UNDER ESTEEM By entering the distance between the manholes, via the propagation. 2 Apr A distance fault locator for an underground cable for calculating .. A report of this work is described in the paper entitled “An Advanced. ACKNOWLEDGEMENT Accomplishment of this project report is a result of my and on-line fault detection and location system for underground distribution power cable. the fault current to be used in locating the fault distance from the control room. . 9 ii) The overall cost of the locator unit can be much higher than the.

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The correlation process used by the controller 30 is shown in the flow chart of FIG. These measured values are low pass filtered and then converted from an analog to an instantaneous digitized current and voltage values. The reflected pulse spectrum of FIG. A fault distance locator as claimed in claim 1, further comprising means for low pass filtering said fault-current occurrence signal to generate an analog filtered current signal. At predetermined intervals, such as every 15 to 30 minutes, as previously explained, the controller 30 will inject periodically the high frequency pulse in FIGS.

A fault distance locator as claimed in claim 1, wherein said injection means is comprised of a pulse generator unit which generates the reference pulse signal at a frequency range between 0. This prior art system is typically quite heavy and is mounted on a special van or truck and must be operated by specially-trained crewmen on site after the testing has been performed on the de-energized cable.

Aside from these prior art patents, there are also known heretofore the use of microprocessor-based relays by electric utilities for protecting transmission systems against overcurrents and for locating faults. With particular reference to FIG. Thus, this method requires additional time and labor expense which is a slow undergeound tedious process. After the steps of determining of an existence of a cable fault and determining the approximate location of such fault, linemen or repairmen later return in several days to find the exact and locwtor location of the fault so that the appropriate repairs can be made in order to restore the circuits to their previous normal operation.

This paper also stated generally that one of the methods for measuring the distance to a fault point on a transmission line is to set off pulses when a fault occurs and the pulse return time from the fault point is utilized to determine the location of the fault point. United States Patent In block all of the times to reflection calculated from the data sets are averaged to produce the most accurate value of the reflection time. What is claimed is: This will allow sufficient time for a reflection to return from a discontinuity on a cable length of 50, feet.

Accordingly, it is a general object of the present invention to provide an improved fault distance locator for underground cable circuits which is relatively simple and economical to manufacture and assemble, but yet overcomes the disadvantages of the oocator art fault-location systems.


This propagation speed will also be stored and subsequently used in calculating the distance to the fault.

An inverse Fast Fourier Transform is performed on the correlation spectrum in block so as to distannce the same back to the time domain for a frequency band between 0. In blockthe ratio of the reflected pulse data set truncated from the spectrum of FIG.

One end of the resistor R1 is joined to the center conductor 18 at node A, and the other end of the resistor R1 is joined to one end of the resistor R2 at node B. A set of 4, to 5, data points will be sampled and stored in the random-access memory, and the controller will calculate the time to the reflection from the end of the cable.

With this information, the fault cable section can then be “switched out” or isolated so as to become a new open-loop point. This is because the pulse data will furnish the most recent value of the actual pre-fault surge impedance of the cable, which is changeable from cable environment.

The distance between the measuring point and the fault point is computed on the basis of the measured values and the parameters of the section. The pulses are injected by the pulse generator unit into the conductor 18 of the underground cable 16 shortly after a cable fault has been determined to exist, as will be explained more fully hereinafter. A linecrew will be sent to inspect the FCI in the transformer and switchgear box at each switch location to determine the last FCI unit tripped to indicate the passage of a fault current.

To this end, electric utilities have constructed access points which are generally provided at pedestals or towers that are located at spaced apart positions along the underground cables. Since the pulse duration may be longer than 3 to 10 mS, it may mask a short reflection a close fault that occurs in less than the pulse length.

Fault distance locator for underground cable circuits – Dipl.-Ing H. Horstmann GmbH

In this manner, the faulted cable section can be located. This filtered current signal is then passed through an amplifier 60 to a second input of the multiplexer 46 via line Description of the Prior Art As is generally known to those in the electric utility industry, buried underground cables utilized in the United States are typically formed with a center conductor surrounded by an outer polymeric insulation and a concentric neutral disposed over the polymeric insulation.

When a fault does occur, the computer controller 30 will initiate the injection into the cable a series of chirped pulse streams or bursts every few hundred microseconds until the cable is cleared. Further, prior to the fault locating step the cable is to be de-energized, tested for potential, and grounded so as to remove the charge due to the cable capacitance.

The time delay between the sending pulses and their associated reflected pulse signals are monitored for approximately to microseconds after each burst and the corresponding data is stored in the random-access memory of the controller for processing after the fault has been cleared. This invention relates generally to fault-location systems for determining the distance to a fault point and more particularly, it relates to a fault distance locator for underground cable circuits and a method for the same for calculating more accurately the location of a cable fault from a source-connected monitoring location in an efficient and effective manner.


The controller device includes correlation means for correlating the reflected pulse signals to the reference pulse signal to determine delay times between the pulse signals sent on the faulted cable and the reflected pulse signals therefrom so as to calculate the distance to the location of the cable fault. Typically, the pulse stream will be in the form of a chirped pulse stream of six to seven symmetrical pulses with a frequency between 0.

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Further, the pulse stream of the single frequency can be made to have a changing amplitude. Preferably, the pulses will have an average period of approximately nanoseconds 2.

In addition, the shape of the pulses may not only be square but can also be sinusoidal or triangular in form. A fault distance locator as claimed in claim 8, further comprising a high voltage capacitor interconnected between said pulse generator unit and said cable. The current of the underground cable 16 involved is detected or monitored by a current transformer 24 C.

Field of the Invention This invention relates generally to fault-location systems for determining the distance to a fault point and more particularly, it relates to a fault distance locator for underground cable circuits and a method for the same for calculating more accurately the location of a cable fault from a source-connected monitoring location in an efficient and effective manner.

Lodator method for calculating the location of a cable fault as claimed in claim projwct, wherein said correlation step further includes the step of converting by an inverse fast Fourier transform said frequency spectrum back into a time domain to produce a major spike signal indicative of the delay time between the sending pulse signal and the reflected pulse signal which is used to determine the distance to the cable fault.

The most current of the pulse signals will be stored in the random-access memory to be used and defining a reference pulse signal for calculating distance when a fault occurs. Reed issued on Sep. Search Expert Search Quick Search. The delay times between the reflected pulse signals and the sending pulse signals are obtained by a disatnce process which is specifically designed to eliminate the effect of noise caused by arcing voltage and thus provides a basis to calculate accurately the cable fault distance.