Electricity: measuring and testing – Conductor identification or location
Reexamination Certificate
1999-03-11
2001-12-25
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Conductor identification or location
Reexamination Certificate
active
06333625
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fault localizing and identifying device for electric systems. The device comprises a primary unit and a secondary unit, the primary unit comprising a first connection which is connectible to a first conductor or earth connection in the electric system, and a second connection which is connectible to a second conductor in the electric system. The secondary unit is connectible to corresponding conductors at a distance from the primary unit.
BACKGROUND ART
Prior-art fault localizing and identifying devices of the type mentioned above are used to localize, for instance, short circuits or earth faults or to follow a conductor through the system. It should be mentioned that the term electric system includes, inter alia, systems of transmission lines, fire alarm systems and house electric mains. The known devices are made up of two units having a transducer/detector or transceiver configuration. As a rule, one part is connected to a line at one end thereof, for instance, in a switch cabinet, whereupon the actual fault localizing or identification is carried out by means of the other unit at a distance from the first unit. The distance can be considerable and may, in some cases, amount to ten, twenty or more kilometers.
A known device is disclosed in DE-44 29 310. This device is used to localize earth faults in three-phase networks. It comprises a primary unit in the form of a pulse generator emitting pulses on the phase conductors via an earth coil and a secondary unit in the form of a detector detecting induced current changes at the beginning of the pulses. The change is an increase if the conductor portion between the coil and the detector is correct, but a decrease if the earth fault is located along said conductor portion.
Another prior-art device is disclosed in U.S. Pat. No. 4,642,556. This device is used to identify conductors in a power distribution network. It comprises a primary unit in the form of a transmitter which transmits current pulses in the conductor that is to be identified in the network and a detector which inductively detects the electromagnetic field generated by the current pulses around the conductor.
There are also known devices comprising a primary unit which is connected to one end of a line and which comprises resistors with different values, which are connected to the conductors, and a secondary unit which is connected to the other end of the line and which detects the resistance in the various conductors as well as the resistances in the primary unit.
A common feature of the known devices is that they are usable to a limited extent, either for a specific task, such as the two tasks first described, or for a small number of tasks, such as the last-mentioned type. They do not manage a combination of, for instance, detecting earth faults and short circuit faults in a pure main circuit and identifying a conductor in a system with connected resistive loads, such as a street lighting system.
SUMMARY OF THE INVENTION
A general object of the invention is to provide a device for localizing faults and identification in electric mains, which is usable for a larger number of various tasks than the known devices.
A special object of the invention is to provide a device for localizing faults and identification in electric mains, which is usable for localizing faults and identification in mains with connected resistive loads.
The objects are achieved by a fault localizing and identifying device according to the invention as defined in claim 1.
The primary unit of the device produces a varying resistance between the two conductors. This resistance variation is easily detectable by means of the secondary unit in some other place in the mains. An advantage of the device is that it is also usable in mains with connected resistive loads, such as lamps, since their resistance is small in relation to the high-impedance state, which means that the shift between the states can be perceived also when the number of loads connected between the primary and the secondary unit is great.
Provided that the first connection is connected to the earth conductor, it is also possible to easily detect an earth fault and also to localize the earth fault. The resistance variation is in fact detectable when the secondary unit is connected between the primary unit and the earth fault, but not when it is connected in such manner that the earth fault is positioned between the primary and the secondary unit. This means that in any case it is easy to define the position of the fault to be within two test points which can be close to each other.
REFERENCES:
patent: 5760591, 19980600
patent: 5796258, 19980800
Browdy and Neimark
Kerveros J
Metjahic Safet
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