Abstract: The residual phase currents for each selected winding of a transformer are first determined and then summed to provide a value designated I.sub.X. The neutral current for the transformer is also determined, with the neutral current being designated I.sub.Y. A directional element calculates a torque value T according to the following formula: T=R.sub.e (I.sub.X .multidot.I.sub.Y *). This torque value will be negative for an external (reverse) fault, and positive for an internal (forward) fault. The quantity of the torque is compared against threshold values before a forward or reverse fault for the transformer is declared.

Abstract: A transformer over-voltage protection circuit shuts down a resonant inverter when high voltages occur at the output of a transformer. The high voltages can be caused by a broken or removed display tube. The system is designed to be used in display system, such as, an active matrix liquid crystal display (AMLCD). The system senses the voltage at the output of the transformer by utilizing a tickler or a tertiary winding. The signal from the tertiary winding is rectified and compared to a threshold. If the signal from the tertiary winding is greater than the threshold, the inverter is shut down for a period of time.

Abstract: There is provided at least one pressure detector for detecting a change in pressure of an insulating medium, a vibration detector for detecting vibration of an oil-filled electric equipment, and a determination processor for determining, based on information detected by the pressure detector and the vibration detector, whether an internal short circuit has occurred in the oil-filled electrical equipment.

Abstract: A fault protection device incorporated in a transformer having a primary winding and at least two secondary windings connected to ground, and having a sensing coil to sense the fluxes generated by each of the secondary windings and generating a flux signal when an imbalance in the fluxes in the secondaries is detected and in which the sensing coil is in the form of at least two sensing coil portions, the sensing coil portions being positioned near but spaced from the sides of the secondary windings, the flux signal being constituted by a voltage induced in the sensing coil by fluxes produced by the secondary windings, and a switch connected to the sensing coil and connected in series with a power supply and at least one terminal of the primary winding, the switch being conditioned to an open condition in response to the flux signal to isolate the primary winding from the power supply.

Abstract: A power converter protective apparatus for protecting an AC-DC converter against an excess fault current by preventing the fault current of a power system from flowing into the AC-DC converter. The protective apparatus comprises a series transformer, whose primary winding is connected in series with a power system and whose secondary winding is connected to a voltage-type AC-DC converter, first current bypass means of a normally open-type connected in parallel with the primary winding, a current transformer for detecting a fault current in the power system, and a control unit for outputting a bypass control signal to the first current bypass means when the current transformer detects the fault current, whereby when the fault in the power system is detected, a fault current flowing through the primary winding is bypassed by the first current bypass means.

Abstract: A current differential protection arrangement for an electric power supply unit with a measured value pre-processing device and an analysis device that checks on the basis of a predefined dependence of a differential current on a stabilizing current (response characteristic curve) to determine whether the differential and stabilizing current values thus formed are in a blocking range or a triggering range, where an additional stabilization range is present in the blocking range. To avoid fixed-time blocking after an external fault with transformer saturation with such a protection arrangement, the analysis device in a stabilizing circuit contains a testing arrangement which checks the current values thus formed to determine whether they describe a point in the additional stabilization range. If this is the case, a blocking signal is produced, which activates the blocking device downstream from the testing arrangement.

Abstract: A differential current protective device for a transformer arranged in a multi-phase power supply system and having at least one star-connected winding arrangement with a grounded star point. The differential current protective device receives currents proportional to the system currents via current transformers provided on the high and low voltage sides of the transformer. A computing circuit of the protective device determines a differential phase-related current from the currents measured, taking into account a current parameter that corresponds to the zero system current based on the phase and whose intensity is monitored. The differential current protective device includes an auxiliary current transformer having its primary winding in the connection between the star point and ground. The computing circuit processes the secondary current of the auxiliary current transformer as the current parameter corresponding to the zero system current.

Abstract: A preprocessing circuit receives signals representative of a current circulating in a primary winding and of a current circulating in a secondary winding of a transformer. The signals representative of currents are used to calculate the values of a through current and a differential current. The preprocessing circuit performs a spectral analysis and provides a neural network with signals representative of the fundamental component of the through current, of the fundamental component of the differential current, of the second harmonic and of the fifth harmonic of the differential current. The neural network identifies fault conditions and normal operation states, and supplies a triggering and/or alarm signal to an output when a fault condition is detected.

Abstract: The reliability of transformer differential relays is enhanced by providing a method and apparatus which enable improved discrimination between transformer current differentials due to transformer inrush current and current differentials due the occurrence of an internal fault. This improvement in discrimination is provided by generating a first signal representative of currents flowing in at least two windings of the transformer, a second signal representative of a positive portion of the first signal, and a third signal representative of a negative portions of the first signal. A first output signal is generated when the magnitude of the second signal exceeds a first predetermined value, and a second output signal is generated when the magnitude of the third signal exceeds a second predetermined value. A trip signal is generated upon coincidence of the first and second output signals.

Abstract: A protective circuit is used in conjunction with a switching power source for protecting the latter from overload and from short circuits. It is detected whether the current at the primary winding current of a switching power source transformer, the load current of the switching power source, or both exceed predetermined reference voltages. If so, supply of power to the switching power source is interrupted for a predetermined period of time, thereby bringing the switching power source into inoperable condition in this duration.

Abstract: A protective DC link circuit connecting a motor to a power supply. The motor has a stationary assembly and a rotatable assembly in magnetic coupling relation thereto and includes windings adapted to be commutated in at least one preselected sequence. The motor also has power switches for selectively providing power to the windings in the preselected sequence by switching the power supply in connection with the windings whereby an electromagnetic field is produced for rotating the rotatable assembly. The DC link circuit connects the power supply to the power switches. The DC link circuit includes a link capacitor connected in parallel with the power supply wherein a voltage across the link capacitor defines a DC link voltage.

Abstract: A monitoring apparatus for a tuned harmonic filter is provided to prevent electrical system and filter damage. A tuned harmonic filter is provided in an electrical system to prevent overheating, motor damage, flickering lights, capacitor failure, etc. The present invention provides a sensing device in conjunction with the filter reactor to provide a signal indicative of the true operating condition of the filter. A monitoring circuit compares the signal with normal operating conditions of the filter to determine if a "fault" is occurring. Timing devices provide for a delay or rapid disconnection of the filter and/or electrical system. Indicator devices are provided to aid in diagnostic analysis of an electrical system. A remote indicator device may be included.

Abstract: A transformer ground fault protector is provided and includes sensing means in the form of at least one conductive plate adjacent but spaced from the output of each secondary winding in a transformer having its secondary windings connected in series and at the midpoint of the series circuit to ground. The at least one conductive plate forms a capacitive circuit with the windings and provides an output voltage when the secondary windings are energized and unbalanced. The output voltage generated by the at least one conductive plate in normal operation of the transformer, is substantially equal to zero volts. However, when a fault occurs in the transformer, the output voltage induced in the at least one conductive plate has a magnitude greater than zero. The resultant voltage in turn is conveyed to a comparator which compares the magnitude of the resultant voltage with a predetermined threshold voltage.

Abstract: A method and system of transformer protection in which parallel admittance currents indicative of the apparent excitation state of a transformer to be protected are evaluated from the transformer terminal voltages and currents sampled at a proper interval, and discrimination between an internal defect and excitation inrush is made in response to a magnitude of the parallel admittance current, and a breaker opening command is issued in response to a judgement of internal defect. The method and system enables high-accuracy and high-sensitivity fault detection through a simple computation.

Abstract: An apparatus for monitoring phased currents in a first winding and a second winding of a transformer and for disconnecting the transformer from a power source supplying the transformer when a difference between the magnitude of the current in the first winding and the magnitude of the current in the second winding exceeds a predetermined amount to indicate a fault condition is disclosed. The apparatus is used in combination with circuitry for generating first and second current signals each having a phase and magnitude which is a function of the phase and magnitude of the phased currents in the first and second windings, respectively.

Abstract: A device for use in connection with electricity meters incorporating current transformers is disclosed. The device detects saturation incidents of the magnetic cores of the transformers, thereby reducing measurement errors.

Abstract: In a transformer protection system, data of voltages and currents detected at individual terminals of a transformer connected to an electric power system are supplied to a computer. The computer computes driving point admittances or shunt admittances of the transformer on the basis of the voltage and current data and predetermined transfer admittances of the transformer and decides that an internal fault has occurred in the transformer when the values of the driving point admittances or shunt admittances deviate from pre-set reference values, thereby disconnecting the transformer from the electric power system.

Abstract: It is desirable to provide remote digital protection of distribution transformers. This specification discloses a protection system able to measure and compare increases in both negative and positive phase reference currents on a distribution cable feeding a transformer and to trigger a circuit breaker to isolate the cable only if the negative sequence current increase exceeds a predetermined proportion of any simultaneous positive sequence current increase. Consequently, engergizing with a 12.5% unbalance current has been found possible without false tripping.

Abstract: A transformer differential relay which includes apparatus for speeding up the detection of a power transformer internal fault condition to initiate breaker action which interrupts current through the transformer is disclosed. Presently, conventional transformer differential relays include a unit for each phase of the power transformer for detecting a potential internal fault in a respective transformer phase winding and for generating a signal to operate a set of breakers. This breaker operation is inhibited for current inrush conditions of the transformer. However, a processing time is associated with the detection of such a current inrush condition. Accordingly, the breaker operating signal must be delayed for at least this processing time in order for the inhibition to be effectuated. For the case in which there is no current inrush condition, the breakers remain delayed in operation from the inception of a true internal fault.

Abstract: A protective relay for a transformer issues a relay tripping command when the differential current that is the difference between currents in the primary and secondary windings of the transformer has a magnitude larger than the specified value and, at the same time, when the differential current includes the fifth harmonic component less than the specified value. Another cause of tripping signal generation is the differential current value processed to have a certain timer characteristics.

Abstract: A current ratio-differential relay for protecting a power system comprises a logical circuit which provides the final output upon determination that the operating force signal is active and the suppressing force signal is inactive. The operating force signal is made active when the scalar quantity of the vector summation of line currents flowing into and out of the bus-bar is larger than a certain value, and the suppressing force signal is made active when the maximum value of scalar quantities of the line currents is larger than the scalar quantity of the vectorially-summed current multiplied by a certain constant. Both signals are supplied to the logical circuit through circuit means having a certain time delay in the restoring operation.

Abstract: A differential protective relay for protecting devices on an ac electrical power system. The protected devices can include a transformer, a generator, or a station bus. The differential protective relay evaluates the current flowing into and out of the protected device only during the period when the current transformers are not saturated. The differential protective relay also detects internal faults accompanying external faults by evaluating the ratio between the current flowing into and out of the protective device. When this ratio exceeds a predetermined limit the protective relay evaluates the difference between the current flowing into and out of the device to determine if this difference is sufficiently large to trip the relay. When a current transformer associated with the differential protective relay is saturated, the differential protective relay produces a restraint signal to restrain tripping.

Abstract: A relay adapted for protection of a transformer and capable of functioning with certainty upon occurrence of any internal fault in the transformer but not functioning in the case of an inrush current which flows therein at the time of non-load energization or the like.

Abstract: Differential protective relay methods and apparatus which include a differential current function supervised by both a harmonic restraint function and a voltage change function. The voltage change function determines whether or not the differential current function requires harmonic restraint supervision, preempting such supervision when it is not required, to enable faster trip decisions to be made by the differential current function.

Abstract: A distribution substation including a transformer module and a feeder module. The transformer module including a tank, a transformer having primary and secondary windings immersed in insulating oil within the tank, a radiator connected to the tank for cooling the oil in the tank, a primary bushing mounted on one of the side walls of the tank at an angle and being connected to the primary of the transformer, a secondary bushing mounted on the top of the tank connected to the secondary winding of the transformer, a primary circuit breaker mounted on the tank in close proximity to the primary bushing, a lightning arrester mounted on the top of the tank in close proximity to the primary bushing. The feeder module including a transition cubicle and a feeder cubicle.

Abstract: A power supply voltage stabilizer comprising a transformer, of which the primary winding is connected to a switching means for controlling power supply to the primary winding. An oscillator circuit is associated with the switching means in order to control on/off operation of the switching means. An abnormal overvoltage and/or overcurrent detection circuit is provided for terminating the oscillation operation of the oscillator circuit when impending overvoltage and/or overcurrent is detected.

Abstract: A transformer differential relay monitors the current flowing through the primary and secondary windings of a power transformer and disconnects the transformer from a power source feeding the transformer whenever the magnitudes of these currents indicate a fault condition in the transformer. First and second current transformer generate primary and secondary winding voltage signals representative of the magnitude of the current flowing through the power transformer primary and secondary windings, respectively. A solid state restraint signal generator is responsive to the primary and secondary winding voltage signals and generates a restraint signal representative of the magnitude of the larger of the primary and secondary winding currents, respectively, at each measurement instant.

Abstract: To detect a d-c component of alternating current in the primary winding of an electric power transformer, a pair of current transducers are provided. Each current transducer has a saturable core adapted to be magnetized by the same current as flows in the transformer primary winding, and bias means associated with both transducers presaturate their respective cores in opposite directions by equal predetermined amounts of magnetomotive force. Secondary windings on the cores of the respective current transducers are connected to means for deriving an output signal in response to voltage induced in one but not both of the secondary windings as a result of alternating current containing a d-c component in the power transformer if such current has sufficient magnitude to unsaturate the core of one of the current transducers, a condition typifying the surge of inrush magnetizing current that flows in the transformer primary when initially energized.