Abstract: A switching device is provided for alternating current parallel remote feed for the automatic disconnection of a faulty section and connection of a fault-free section of a remote feed field. The switching apparatus enables safe continued operation in case of a field fault. To this end, the switching apparatus contains switches for disconnecting the remote feed current paths and for connecting a d.c. voltage source to the section of the remote field facing away from the alternating voltage source. The switches are controllable by the direct current emitted by the d.c. voltage source and by the alternating currents flowing in the remote feed current paths.

Abstract: A circuit interrupter includes a microprocessor based trip unit having a plurality of output control lines and a power supply for providing operating power to said trip unit. Interlock means are provided to maintain the output control lines in a predetermined inactive status for a predetermined time period following energization of the power supply to allow time for operating power to rise to a level sufficient to enable the microcomputer to assert positive control over the status of the control lines. An automatic reset circuit is provided to reset the microcomputer program counter to an initialization routine unless a pulse pattern produced by proper execution of the microcomputer instructions is received by the automatic reset circuitry.

Abstract: A high reliability electrical power system is provided with a microprocessor-based control unit which maintains power output and performs control functions for the system which is driven by the power system. A self locking feature prevents the transmission of potentially erroneous control signals if a component of the system being controlled or the control unit fails. The control unit conducts a series of self-test routines which result in the generation of digital key words. If the correct key words are generated and the other circuits of the control unit are operating properly, the control unit output remains operative. If the self test routines detect a failure in the system being controlled or the control unit or if a failure occurs in one of the control unit output circuits, the control unit output is locked into a predetermined state.

Abstract: A protective relay system for providing pilot protection for two and three terminal alternating current transmission lines, which system does not require a continuous metallic circuit between the relaying points. The evaluation circuit develops operating and restraining quantities, modified by a predetermined constant which determines the operating characteristic of the relay system.

Abstract: Phase line currents of a polyphase power supply are rectified and applied to a common input terminal of a sine wave detector circuit to sense the presence of a signal current that is injected from a low voltage DC source into any time gaps that are formed between phase currents only when one or more phase line failures occur. Failure of the DC source disables the detector circuit.

Abstract: In a protection apparatus for a feeder (H) of an electric power transmission system compensation for mutual coupling between the feeder and another feeder (G) is controlled in dependence on the ratio of the zero sequence currents (I.sub.M, I.sub.N) in the two feeders. The mutual coupling compensation signal (I.sub.M Z.sub.M ') is arranged to be proportional to the zero sequence current (I.sub.M) in the other feeder when the ratio of the zero sequence currents is below a predetermined value, and to be limited to a value proportional to the protected feeder zero sequence current (I.sub.N) when said ratio is above the predetermined value. The arrangement reduces the possibility of maloperation of the feeder protection due to faults on the other feeder.

Abstract: In a selective safety device for the protection of successive power levels in a power distribution system, a current limiting switch is provided in each of the power levels and includes a current-limiting quick-switching contact which is so positioned at the power supply side in each one of the different power levels such that the current limiting switch immediately in front of a fault is switched off upon occurrence of a fault. A resistor is connected across each of the quick-switching contacts and is serially connected in the interrupted circuit upon the opening action of the quick-switching contact. Additionally, a slow-switching contact is serially connected with each of the quick-switching contacts to be opened after opening of the quick-switching contact with a presettable delay time, which is dependent upon the power levels in which the slow-switching contact is connected.

Abstract: A circuit interrupter includes a microcomputer-based trip unit, and a display and control panel comprising a numeric display device and a plurality of legends associated with light-emitting diodes. The trip unit presents a sequential display of numeric values of associated circuit electrical parameters and time-current trip characteristic setting values, with the currently visible numeric quantity being identified by an energized light emitting diode and associated legend. The control panel also includes a test switch for initiating a test operation and a potentiometer for selecting a desired simulated fault current value for the test operation. The test capability is provided simultaneously with normal circuit breaker operation which maintains full protection of the associated circuit. A short-delay feature is provided having a selectable i.sup.2 t characteristic with adjustment of both pick-up and time parameters.

Abstract: A power-distribution network for the energization of a multiplicity of loads comprises a two-conductor trunk extending from a DC supply, a plurality of parallel primary branches connected to the trunk via respective first overload-responsive circuit breakers, and a plurality of parallel secondary branches connected to each primary branch via respective second overload-responsive circuit breakers. Each secondary branch terminates at one or more DC/AC converters feeding associated loads, the converter frequencies being suppressed in the supply network by filters included in the second circuit breakers. Each circuit breaker further includes at least one capacitor which, in the event of a short circuit in a parallel branch, supplies the associated loads for a time long enough to let the supply voltage substantially recover its normal value.

Abstract: A high voltage d.c. power transmission system utilizes a metallic return conductor for carrying return current between converters at opposite ends of the system. The return conductor is connected to earth ground at one end of the system and is otherwise insulated from earth ground so that its opposite end is floating with respect to d.c. The return conductor has no capacitor connected from earth ground thereto of a size capable of limiting the voltage thereon. But connected between said opposite end of the return conductor and earth ground is a valve-type surge arrestor having a primarily zinc-oxide valve element and no gap in series therewith. This surge arrestor has a protective level that is reached by the overvoltages produced by the normal operating transients of the system, such as those produced by system start-up and commutation failures.

Abstract: In a protective relaying device comprising first and second potential transformer circuits for transforming voltages of an electric power system, first and second relaying elements are further provided for receiving the output voltages of the first and second potential transformer circuits, respectively so that each of the relaying elements delivers an output of a particular logic state when it operates. When the outputs of the first and second relaying elements coincide with each other, a logic circuit receiving the outputs delivers a tripping signal to a circuit breaker.

Abstract: A network protector relay produces a close signal entirely from sequence components based on the magnitude and phase relationships between the positive sequence component of the phase-to-ground voltages on the network side of the protector and the positive sequence component of the phasing voltages. The close signal may be inhibited by either the presence of the negative sequence component of the phase-to-ground voltages on the network side of the protector or if a trip contact is closed. The trip contact will be closed under certain specified conditions which make it advantageous to prevent manual closing of the contacts.

Abstract: In an arrangement for level and sequence detection in a directional wave detector, which has a three-phase directional wave detector with two inputs per phase and three single phase and one three-phase tripping output and one three-phase blocking output, with a level detector with one partial detector for each of the single-phase tripping outputs and the three-phase blocking output, the level detector is provided with a further partial detector which is connected to the three-phase tripping output of the wave detector and the two partial detectors which are connected to the three-phase outputs of the wave detector have a lower reference level than the other partial detectors which are connected to the single-phase tripping outputs of the wave detector.