Asea Brown Boveri Ab

Asea Aktiebolag

Leif Eriksson

Murari M Saha

Salomon Liberman

Kjell Svensson

Method and device for identifying single ground faults

A method and a device, after a fault has occurred in a power network, for measuring and recreating the phase currents I.sub.B prior to the occurrence of the fault by determining continuously, starting from sampled measured values of the phase currents up to the time of the fault for each phase, the amplitude I and the phase angle .phi. of the phase currents based on two consecutive sampled measured values, whereupon a comparison is made between the last determined value I.sub.k obtained and the rated current I.sub.n of the power network. If I.sub.k is greater than I.sub.n, it is considered that a fault has occurred and the phase currents prior to the fault are indicated as I.sub.B =I.sub.k-1 .multidot.sin (.phi..sub.k-1 +.omega.(t-t.sub.k-1)).

Method and device for measuring and recreating the load current in a

A method and a device for determining the distance from a measuring station to a fault on a transmission line based on a fault model of a transmission network while taking into consideration the zero-sequence impedance and, where assuming a fault current, while taking into consideration the feeding of fault current to the fault point from both ends of the transmission line (FIG. 3 ).

Method and a device for determining a fault on a transmission line

A method and a device for determining the fault current which occurs in case of a fault through a short circuit between phases or from phase/phases to ground. A measure of the fault current can be obtained by a linear combination of the sum of measured current samples for each phase at two adjacent points in time and in which each of these sample values is multiplied by a coefficient which is chosen such that the fault current gets into phase with the positive- and negative-sequence current changes.

Fault current filter

A method and a device for phase selection for single-pole tripping of high-impedance ground faults in direct grounded power networks. Starting from the ratio of the negative-sequence voltage to the zero-sequence current (U2/I0) and the ratio of the negative-sequence voltage to the positive-sequence voltage (U2/U1), two criteria with different conditions are formed, each of which indicating a faulted phase, and if both criteria indicate the same phase as faulted, single-pole tripping can take place.

Phase selection for ground fault

A method and a device for preventing overstabilization of longitudinal differential protections in case of internal faults on power lines, which may take place when a fault situation, which is indicated as an external faults, is in reality an internal fault. The invention comprises criteria which finally provide information as to whether the longitudinal differential protection is to enter into operation. The criteria comprise level and directional determination of the currents which are measured in the terminals of the power lines, checking whether these have the same direction, and so on.

Method and device for preventing overstabilization of longitudinal

The invention relates to a method and a device for detecting a flashover between conductors in power transmission lines of different voltage levels suspended from the same towers and wherein the power lines are included in a power network where one of the power lines is stated to be a high-voltage power line (1) and where the other power lines are connected to the high-voltage line via transformers of a known transformer ratio (am) and internal impedance (ZXm) and wherein the line impedances (ZL) are known. Specific to the invention is that the fault current which is caused by a flashover is set to be equal to a detected current change in any of the phases in the high-voltage line. With this assumption an equation system can be set up with the aid of which the relative distance to fault n (0&lt;n&lt;1) can be determined. If the produced value of n lies within the stated region, this is interpreted as if an internal flashover has occurred.

Method and apparatus for detecting flashover between conductors in power

In circuitry for generating tripping and blocking signals for the protection of electrical power supply network components as a result of the occurrence of faults, the blocking signals are selected from each phase of the electrical power supply network to prevent tripping in each phase for faults occurring behind the protected component. A sequence detector includes a partial detector for each phase of the electrical power supply network and includes logic circuitry responsive to respective tripping and blocking signals generated for each phase of the electrical power supply network in dependence on whether the fault lies ahead or behind the protected electrical component, respectively. Each logic circuit includes a gate and a delay circuit responsive to the output of the gate. The output of the delay circuit in the tripping logic circuit is input to the gate in the blocking logic circuit and vice-versa. Each blocking logic circuit includes an additional gate for receiving a blocking input from another protection circuit which is common to all the partial detectors for passing blocking signals and blocking tripping signals.

Multiphase blocking circuitry for electrical power supply networks

In circuitry for generating tripping and blocking signals for the protection of electrical components in an electrical power supply network as a result of the occurrence of faults therein, respective tripping and blocking outputs for each phase of an electrical power supply network are generated such that double or triple pole tripping is prevented unless the presence of an actual second tripping signal is detected subsequent to the detection of a first tripping signal. The respective tripping signals and blocking signals for each phase of the electrical power supply network are generated in dependence on whether the fault lies ahead or behind the electrical component to be protected, respectively, in response to measurement of the voltage and current associated with transient waves generated by faults in each electrical power supply network phase. The presence of a tripping signal resulting from the occurrence of a single phase fault, and the presence of a second tripping signal resulting from the occurrence of a fault in another phase are detected. The functional level of detecting the second tripping signal is modified or adjusted upon detection of the first tripping signal.

Multiphase fault protection circuitry with variable functional level

Circuitry for generating tripping and blocking signals for the protection of electrical components included in electrical power supply networks as a result of the occurrence of faults therein provides multiphase pole tripping in the event that, after a single pole tripping has been executed, a new single phase fault occurs in any of the remaining phases of the electrical power supply network. Respective tripping and blocking signals are generated for each phase of the electrical power supply network in dependence on whether the fault lies ahead or behind the electrical component to be protected, respectively, in response to measurement of the voltae and current associated with transient waves generated by faults associated with each electrical power supply network phase. Multiphase pole tripping signals are generated by undervoltage detector logic circuitry responsive to the generation of the tripping signals upon the occurrence of a single phase fault, and the sensing of an undervoltage in another phase of the electrical power supply network before reclosing of the faulty phase.

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Sala, Sweden

Leif Eriksson