Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2003-09-29
2004-11-23
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S527000, C324S532000, C702S059000, C361S081000
Reexamination Certificate
active
06822457
ABSTRACT:
TECHNICAL FIELD
The disclosed invention relates to a method and system for identifying faults on an electrical transmission system, and more particularly to a method of precisely determining the location of a fault on an electric transmission line by detecting and monitoring high frequency bursts produced by faults and also using a system of high frequency transmitter and receiver combinations to monitor and detect high frequency bursts produced by the transmitters, said system including memory to store high frequency data before and after a detected fault, and algorithm capability to analyze said stored data.
BACKGROUND
A common occurrence in the power distribution industry is an arcing or electrical discharge in the transmission and distribution grid system. Such faults commonly are caused by such as insulation breakdown, physical damage to the transmission line, moisture ingress etc., or a combination thereof, and it is noted, characteristics of an arcing or discharge fault vary widely. For instance, a fault may manifest as a relatively high impedance transient event which lasts for only microseconds, or as a low impedance sustained fault that eventually leads to rupture of network protection devices, (eg. a fuse or circuit breaker or the operation of a circuit breaking relay).
It is to be understood that even minor occurrences of transient discharge in cables can eventually lead to more catastrophic problems because successive discharge events degrade the quality of the cable. Early detection and location of transient fault events, leading to their correction, can therefore result in economic benefits such as increased overall network quality and customer satisfaction because of reduced outages.
Important to the presently disclosed invention is that a consistent characteristic of an arcing or discharge fault event is, at the time of discharge, the generation of a burst of electrical energy or noise which comprises high frequency components. And, it is also important to understand that voltage and/or current waveforms generated by the arcing or discharge fault event travel away from the fault site in both directions in the transmission system. This phenomenon has been disclosed in a number of patents. For instance Biskeborn, U.S. Pat. No. 2,493,800, 1950, Weintraub, U.S. Pat. No. 2,717,992, 1955, Biskip, U.S. Pat. No. 3,462,681, 1969, disclose fault location systems that:
Detect the electrical wave associated with a discharge, partial discharge, arcing fault or lightning strike that travels to each end of the cable or transmission system from the fault point.
Collect time data associated with the traveling wave caused by the fault or event passing a sensor or coupling point at each end of the transmission system.
Calculate distance to fault by centrally processing the time delay data via an RP communications link, or some other data transmission link.
Said Patents describe systems for application to high voltage overhead transmission lines, and assume a velocity of propagation of the traveling wave.
The Biskeborn 800 Patent describes an application to shorter cable lengths, but requires access to each end of the cable at a common point.
The Pardis, U.S. Pat. No. 3,609,533, 1971, describes a fault location system which utilizes a high energy pulse transmitted on the network under test to provide a reference for time and/or delay measurements to determine distance to fault, (rather than use of an RP link or other transmission media). The 533 Patent generally:
Is applied to high voltage overhead transmission lines;
Is designed for massive insulation breakdown or lightning strike, and provides 500 to 1,000 feet of accuracy; and
Assumes velocity of propagation of the traveling wave.
A Patent to Maureira, U.S. Pat. No. 5,416,418, 1995, describes application in lover voltage, (ie. 6 kV to 33 kV), distribution cables, and focuses on partial discharge events using a pulse transmission technique as a reference/timing signal. The general characteristics of the Maureira invention are:
It is designed for application on shorter power distribution networks than is the Pardis 533 Patent system;
It detects much smaller partial discharge or corona discharge faults, (partial discharge faults are periodic, non-catastrophic corona discharge events), that don't necessarily trip circuit breakers or destroy the cable, but do degrade the cable over time;
It requires the cable to be isolated from the distribution network;
It requires a high voltage source to stress the cable into partial discharge activity; and
It assumes velocity of propagation or uses a VOP established during test setup.
Considering previous disclosures and the economic benefit associated with locating faults in a proactive manner, it is apparent that clear commercial advantage can result from application of new technology which provides low cost, accurate fault location methods and apparatus, thereby providing improvement over previously disclosed systems. Characteristics of such a method and apparatus, as disclosed in this Specification include:
It monitors and stores the established phenomenon of a traveling wave emanating from an arcing or discharge fault in the time domain,
It co-ordinates the monitoring invention(s) in a manner that allows ratio-metric time to distance calculations versus a known distance between the monitoring systems based on traveling wave time delay measurements and initiating signals,
It improves upon Biskeborn, Weintraub, Biskip, and Pardis, by providing more accurate, higher resolution timing measurements, which, in turn, increase the accuracy of distance to fault calculations,
It improves upon Maureira by allowing the transmission system to remain In service for fault locating,
Unlike the Maureira 418 Patent system, there is no requirement that an external, (other than that intrinsic to the distribution system), high voltage be applied to sufficiently stress the transmission system to cause discharge.
A Patent to Bjorklund, 5,903,155 describes the same fundamental process that Biskeborn, Weintraub, Biskip, Pardis and Maureira use, namely:
Detecting the traveling wave produced by a fault by at least two receivers on each end of the transmission system;
Synchronize the timing of the traveling wave reception via some method so distance to fault calculations can be made.
The specific claims of the Bjorklund patent are:
It specifies High Voltage DC transmission system in the claims;
It uses synchronous clocks at each receiver; and
It detects current associated with the traveling wave using a DC transformer and a Rogovski (AC) coil. Previous patents also detect the current.
A Patent to Wright et al 4,499,417 describes a single ended system that uses the disturbance created by the fault and subsequent reflections. In summary;
It detects the first instance of a disturbance created by a fault in either voltage or current;
It identifies and labels that particular event using either voltage or current characteristics;
It continues to analyze the transmission line comparing subsequent events to the first using the characteristics as above or predicted characteristics based on knowledge of the transmission line;
It measures time taken for the disturbance to travel from initial characterization, travel to the fault and back as a reflection;
It determines distance to the fault based on time measurement data; and
Distance to Fault calculations are based on a signal propagation velocity constant determined by the type of transmission line.
A Patent to Bunch 4,570,231 describes the same fundamental process that Biskeborn, Weintraub, Biskip, Pardis and Maureira uses, namely:
It detects the traveling wave produced by a fault by at least two receivers on each end of the transmission system;
It synchronizes the timing of the traveling wave reception via some method so distance to fault calculations can be made;
The specific claims of the Bunch patent are:
It comprises a fault finder for locating fault on a high voltage transmission line;
It provides improved filtering to reject background noise to allow easier ident
Borchert Marshall B.
Hartzell Douglas A.
Deb Anjan K.
Welch James D.
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