Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Patent
1997-11-19
1999-07-27
Regan, Maura
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
702 35, G01R 3102
Patent
active
059296429
DESCRIPTION:
BRIEF SUMMARY
It is general knowledge that a predetermined region of an electric power transmission line system, e.g., a section of a three-phase power transmission line, can be monitored for faults by providing a protective device at each end of the section of electric power transmission line. Each protective device is generally provided with a fault detector circuit that delivers a signal to activate the respective protective device when a fault occurs.
It is also known ("New accurate transmission line fault location equipment," IEE Conf. Publ. 302, 1989, pages 1-5) that currents and voltages can be stored at each end of a section of a multiphase electric power transmission line to be monitored in a method of locating a fault, where this is accomplished by determining values immediately before and during the occurrence of a fault. The stored values are sampled and processed further in different ways, depending on whether they are assigned to values stored before or during a fault.
As also stated in IEE Proceedings, vol. 137, pt. C, no. 6, November 1990, pages 395-402, for accurate location of a fault in a three-phase power transmission line by this known method, variables obtained by using the known Clarke transformation in the transition to modal values or functions are taken into account. At each end of a section of an electric power transmission line to be monitored, first the sampled values obtained from currents and voltages stored immediately before a fault occurs are taken into account, and measured precursor fault vector values of one aerial mode are formed from these sample values. The aerial mode is a mode which, in addition to another aerial mode and a ground-based mode is characteristic of the Clarke transformation. Using the measured precursor fault vector values, a phase angle is determined on the basis of asynchronous sampling at the two ends of the section of the power transmission line to be monitored between the measured precursor fault vector values. In the known method, which takes into account sample values calculated from currents and voltages stored during the fault, fault vector voltage values are calculated using the measured precursor fault vector values, with intermediate calculation of differential measured vector values; these fault vector voltage values are measured values indicating the voltage at the fault location, as considered in relation to both ends of the section of electric power transmission line to be monitored. Since the fault vector voltage values determined from both sides for the same fault location must be the same, this yields the possibility of calculating the location of the fault with a relatively high accuracy. However, the prerequisite is that the phases of the two fault vector voltage values must match. Since this is not the case with the known method, the phase angle is determined with the measured precursor fault vector values and a corresponding measured phase angle value is formed. This measured value is used for synchronization of the fault vector voltage values and only then is the location of the fault determined from the fault vector voltage values.
The known method is subject to some uncertainty in locating a fault inasmuch as complete diagonalization is impossible with a Clarke transformation. This is where the invention begins, by formulating the object of providing a method of locating a fault in a predetermined region of a multiphase electric power transmission line system with an especially high measurement accuracy.
This object is achieved according to this invention in a method of locating a fault in a predetermined monitoring region of a multiphase electric power transmission line system with the detection of voltages and currents of the phase conductors at the ends of the monitoring region, where measured values that are proportional to the currents and voltages and occur immediately before and during the fault at the ends of each monitoring region are stored; measured precursor fault vector values of one aerial mode and another aerial mode are for
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"New Accurate Transmission Line Fault Location Equipment", IEE Proceedings, Fourth Int'l Conference on Developments in Power System Protection, vol. 137, Pt. C, No. 5, Nov. 1990.
Chen Zhihong
Philippot Luc
Regan Maura
Siemens Aktiengesellschaft
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