Abstract: Integrated Services Digital Network (ISDN) terminal equipments (TEs) are remotely powered from a central source via line interface circuits. One function of the line interface circuit is that of conducting energizing direct current for the associated telecommunications terminal equipment while providing effective overcurrent protection in spite of widely variable load current requirements which occasionally may mimic a faulty over current condition.

Abstract: A constant power circuit for causing a constant power level to be dissipated by a load when an overpower condition is detected. The overpower condition is detected by measuring the voltage across and current drawn by the load in accordance with a programmed load value and determining whether the sum of the measured current and voltage exceeds the power limit for the load. In a preferred embodiment, the sum of the voltage and current is compared to a linear piecewise approximation of a constant power curve in the current-voltage plane, the curve representing the power limit for the load for the range of current and voltage magnitudes in which the load circuit may safely operate. When an overpower condition is detected, the power is dissipated by the load at a constant power level defined by the constant power limit by oscillating the power level within a hysteresis band about the constant power limit.

Abstract: A circuit breaker having the overcurrent tripping characteristic, which is capable of detecting an overcurrent flowing through main circuit between an ac source and a load. The circuit breaker comprises a pre-alarm circuit having a pre-alarm characteristic, a pre-alarm signal output circuit for producing an alarm in response to the output of the pre-alarm circuit and a photocoupler for controlling the data transmission between the circuits. The circuit breaker can detect the main circuit current before it becomes an overcurrent and generate the alarm accurately.

Abstract: Device for detecting the quenching of part a superconducting element comprising two identical superconducting conductors electrically connected in parallel is provided with means (104, 105, 109, 110) of detecting a difference in intensity or phase between the currents flowing in the conductors. An application to a superconducting current limiter is described.

Abstract: A differential protection circuit includes a pair of current transformers each having a secondary winding and each being inductively coupled to a power conductor at a different location. The secondary windings of these transformers are electrically connected in series with each other in a loop in a bucking arrangement. A resistor is connected in parallel with the secondary winding of each transformer. Control circuits are connected to sense a voltage signal appearing across the resistor and to take appropriate action when the sensed voltage reaches a predetermined level. An additional winding on one of the transformers provides isolation between the loop and one of the control circuits to prevent false tripping of the differential protection circuit.

Abstract: The invention relates to a protective circuit for the induction coil of a magnetically inductive type flow meter. If the leads of a flow meter used in an explosive environment are cut there can occur a high voltage and resulting sparking which could cause an explosion. The invention provides a circuit in which a short circuit path is provided for the induction coil if the leads thereof are severed to prevent the development of a high voltage which could cause dangerous sparking.

Abstract: A current sensing buffer 26 for driving a digital signal line of a unit under test 12 is composed of current mirror circuits in series with output switching transistors supplying test signals to the digital signal line. The current mirror circuits 66, 72 and 80, 84 generate sample currents corresponding to the magnitude of current through the respective drivers 68 and 78 to detect drive faults caused by bus or component failures. In buses comprised of several digital signal lines, one current sensing buffer 26 is used per line, and each curent sensing buffer 26 is controlled by a programmable circuit tester 10. The current sensing buffer 26 can be incorporated into an interface pod 14 which is substituted for a control component of a unit under test 12.

Abstract: An electric motor controller comprises a circuit for selecting between driving and braking an electric motor in accordance with the health or otherwise of a pair of main electric motor control switches (14 and 16). In a preferred embodiment the health of the switch is determined by the voltage (A) between the switches. The controller also comprises apparatus for detecting the sense of movement of the motor. In the event that the motor is moving in a sense opposite to that selected, the apparatus increase field current to reduce the armature current thereby increasing the braking effect of the motor. Also in the controller are apparatus for changing from armature to field current control and vice versa, in response to a given magnitude of control signal. In order to provide an unambiguous change-over, a lockout circuit is provided to inhibit change-over in a transition region. The lockout circuit maintains the mode of control to above/beneath the change-over level when changing from one level to another.

Abstract: Plastic mold heater moisture detection and dry out apparatus for detecting the presence of moisture in the plastic molding heaters and for drying out the heaters. The plastic mold heater moisture detection and dry out apparatus includes a heater leakage current sensor, an analog to digital converter, a microprocessor, and a triac that are operatively connected to a heater temperature sensor and the heaters. The plastic mold heater moisture detection and dry out apparatus monitors the heater leakage current that is due to moisture or the like present in the heaters and depending upon the value of this leakage current either permits normal heater operation, dries out the heaters or shuts off power if an unsafe ground fault situation exists. In drying out the heaters a series of increasing voltages are applied to the heaters during successive loops or passes to avoid heater electrical arcing that could damage and degrade the heaters.

Abstract: An insulating substrate has a U-shaped conductive layer which produces a magnetic field when a current flows therethrough as indicated by arrows. The substrate also includes a conductive layer on which a power semiconductor element is mounted through its main electrode. A current detector such as Hall effect elements is located inside the U-shaped conductive layer. When a load current flows through the semiconductor element, it flows through the conductive layer to produce the magnetic field since the other main electrode of the semiconductor element is electrically connected to one end of the conductive member through a metal wire. Accordingly, the load current flowing through the semiconductor element will be effectively detected by the current detector without connecting a resistor or current transformer to external terminals of a power semiconductor device, thereby providing a composite semiconductor device with a compact structure used for inverters for driving three-phase motors, etc.

Abstract: In this power control apparatus, a current flowing in a main current (201) is detected by a current transformer (202) and a zero-phase current transformer (203), provided in the main circuit. A value of this current is provided to a CPU (214) included in an intelligent controller (207). A maximum peak value and the like are evaluated by the CPU to be compared with predetermined set values. If those values are equal to or higher than the set values, an excitation signal is applied to a tripping device (205) to release a latch by a latch scheme (206) and thus to trip the circuit breaker. The CPU alters the set value when supplied with a setting alteration instruction from a central monitor (40), and causes the circuit breaker to be tripped when supplied with a stop instruction therefrom.

Abstract: A power source unit for an image recording apparatus having a CPU which controls an operation sequence of a load, includes a current sensor and a relay. The current sensor senses a load current. The relay is connected to a supply path to the load. The relay is operated to interrupt the supply path to the load when the CPU determines that the load current sensed by the current sensor exceeds a current limit value which is determined in advance for every operation cycle of the unit.

Abstract: In a method and device for limiting the starting current of a DC converter, at least one buffer capacitor is initially charged through a load resistor. The current going through the load resistor is measured with a monitor. The monitor switches on a DC converter and bridges the load resistor once a switching threshold is reached. A predetermined minimum current is used as the switching threshold.

Abstract: A lamp output protective circuit for an electronic controller having a first npn transistor connected to an output terminal through which a lamp is supplied with electric power, a resistor connected between the emitter of said first npn transistor and the ground, and a second npn transistor having its collector connected to the base of the first npn transistor, its emitter to the ground and its base to a point between the emitter of the first npn transistor and the resistor. The base of the first npn transistor and the collector of the second npn transistor are connected to a signal line of the electronic controller connected to a power source.

Abstract: Energy sensing and monitoring apparatus is disclosed which can sense a plurality of energy levels in a conductor, and provide an indication when any of such energy levels is improper. The energy sensing apparatus includes an inductive device for sensing an energy level in a conductor and for providing an input signal indicative of the energy level; a comparator for receiving the input signal, comparing the input signal to a plurality of predetermined level ranges, and providing an output signal when the input signal does not fall within at least one of the predetermined level ranges; and a power source for supplying power to the comparator.

Abstract: The output terminals (15, 16) of an analog sensor (14) are monitored by a microprocessor (17). The microprocessor is DC coupled to a main analog ground terminal (16) of the sensor, while also separately being connected to a main power ground terminal (13) at which ground reference potential is provided to the microprocessor. A resistor (38), a semiconductor switch (36) and a printed circuit board metalization trace (35) provide a normal low resistance connection between the main analog sensor ground terminals (20) and the main power ground terminal (13). Current sensing circuitry (33) limits the current passed through the low resistance connection and thereby prevents excessive current from damaging printed circuit board metalization paths (34, 35) connecting the sensor analog ground terminal (16) to the main power ground terminal (13).

Abstract: This invention concerns a circuit arrangement for current limiting for a.c. machines with phase gating control by solid-state devices, aimed at achieving a smooth start by arresting the steady decrease in the ignition angles upon the attainment of a predetermined limiting current value. For use with single-phase measurement of the load current, a circuit is provided for measuring the instantaneous value of the magnitude of the load current, such as a threshold-value detector, which is actuated by a single-phase full-wave rectified load current. The output of this threshold-value detector is applied to a monostable digital device.

Abstract: A microprocessor based circuit breaker has a removable rating plug which provides a reference for the current rating of the breaker. The removable rating plug also has an EEPROM to which the microcomputer of the circuit breaker writes for storage, the number of operations of the circuit breaker operating mechanism and a trip history of the breaker in the form of a count of the number of trips weighted by the magnitude of the trip current. The rating plug is periodically removed and plugged into a portable programmer which selectively displays the number of operations and operating history of the circuit breaker. The programmer clears this operating data when recorded and can write into the EEPROM the style and serial number of the circuit breaker with which the rating plug is to be used.

Abstract: A device to locate internal faults in a high-voltage capacitor battery that has a plurality of symmetrically parallel and series-coupled capacitor banks arranged in parallel branches coupled by shunt branches. The phase angles of the shunt currents flowing in the shunt branches relative to the total current flowing in the parallel branches are determined. A fault is located in one of the capacitor banks based upon these determined phase angles.

Abstract: A circuit arrangement for protection against fault currents in power supplies, having an energy storage means, such as frequency converters for the operation of three-phase motors. The arrangement comprises two identical detector windings in the supply lines leading to the power supply so that a differential current detector winding connected with such detector windings causes a circuit breaker device to be actuated when a given value is exceeded. This circuit breaker device interrupts all the supply lines between the power supply and a load connected therewith by means of switching paths. This ensures that despite the energy stored in the power supply there is rapid and reliable switching off of the load should a fault current occur.

Abstract: A hoist for raising and lowering objects with an apparatus for detecting mechanical overload of the hoist. The system provides a hoist having an alternating current motor connected to an alternating current power supply. The level of current of the power supplied to the motor is compared to a level of power indicative of a mechanical overload condition. If the current signal representative of the actual motor current level equals or exceeds the mechanical overload reference current then an overload output signal is provided.

Abstract: So that internal faults (7) on high-voltage lines (4), generators (5), transformers (6) and other objects to be protected are more reliably detected even with saturated current transformers (3,8) and a tripping of protective measures such as, for example, an opening of switches (2,9) is reliably prevented in the case of external faults and short circuits (10), alternating current measurement signals (I.sub.1 ',I.sub.2 '), which are proportional to the alternating currents (I.sub.1, I.sub.2) flowing into the object to be protected, are detected by means of the current transformers (3,8). The alternating current measurement signals are then supplied via a low-pass filter (12), a transformer (13), a channel selection device (14), an analog/digital converter (15) to a microcomputer (16) for analysis. In the case of a fault, the microcomputer (16) provides a protective tripping signal (F=1) to switches (2,9) which open and thus isolate the object to be protected (4-6) from high-voltage lines (1,11).

Abstract: A current sense circuit (100) includes a semiconductor power switch such as a MOSFET (102) having a source metallization contact pad (14) with a conductor jumper bond wire (106) directly connected thereto in the MOSFET module housing (104), which bond wire is connected to a source terminal lead frame within the module, which lead frame extends externally of the module for connection to a load (22) and load voltage (24). The current sense circuitry includes amplifier circuitry (150, 168) having first and second inputs (122, 124) connected to the source bond wire (106) at spaced points (126, 128) along the bond wire within the module housing (104) without insertion of additional series shunt resistance in the bond wire (106) between such points (126, 128), and sensing current flow through the bond wire (106) by sensing voltage between such points (126, 128) and amplifying such voltage.

Abstract: A sneak current protection device is disclosed including a series connected fuse, resistor and inductor for limiting the rate of current rise through the protective fuse whereby the fuse operates in compliance with all industry accepted standards for fire hazard and circuit protection.

Abstract: An adaptable current regulating system provides a regulated current in accordance with both the actual characteristics of a system under control and the actual measured period of an AC supply. The system constantly monitors its status, and provides a master controller with the status of the system, and is programmed to provide control in accordance with information received from the master controller.

Abstract: A method and apparatus in a control system for an electromagnetic contactor for reducing multiple re-ignitions incorporates a regulated source of electrical power coupled to a contactor actuating coil through a controllable switch. The switch is used to regulate coil current to a desired value whereby opening time of the contactor can be determined within a defined range. Alternating current through tips of the contactor is monitored and each zero crossing of the current wave form is determined. The control system responds to a command to open the contactor tips by coordinating such opening with the zero crossings of the current wave form whereby the contact tips separate within a predetermined phase angle prior to a zero crossing. The system also includes apparatus for detecting a fault current of the alternating current in the contact tips and for inhibiting operation of the contact tips for a predetermined time interval in order to allow fuses to clear the fault prior to opening the contactor.

Abstract: A method for protecting the gate unit for a GTO thyristor includes predetermining a characteristic curve as a time function adapted both to the maximum load capacity possible for a brief time and to the long-term load capacity of a controllable electronic switch of the gate unit connected to the GTO thyristor. The voltage dropping at the electronic switch is detected and compared with the predetermined characteristic curve. The electronic switch is blocked as soon as the detected switching voltage exceeds the predetermined characteristic curve. An erase pulse switches off the GTO thyristor with the controllable electronic switch.

Abstract: A protection circuit for a switched mode power supply has a reference voltage applied through a resistor to a first input terminal of a comparator. The second input terminal of the comparator is supplied with an indicating voltage that is a function of the magnitude of input current to the supply. A capacitor precludes rapid changes in the voltage applied to the second input terminal. When a trip level is reached, the comparator operates a latch for disabling the pulse width modulator of the supply. A diode is coupled between the high capacity voltage output of the supply and the first input terminal of the comparator for rapidly changing the voltage applied to the first input terminal to operate the latch, in response to a significant decrease in voltage at the high capacity output.

Abstract: A method and apparatus for controlling the consumption of electrical current exceeding the total generating capability of an electrical system and for monitoring the charge of a storage battery between maximum and minimum levels and for disconnecting electrical loads in response to the level reaching the minimum.

Abstract: A single or multiple phase directional harmonic overcurrent relay device suitable for simultaneously monitoring overcurrents at either of two harmonic frequencies in an electric power system is provided which comprises current and voltage input means, upper and lower harmonic current and voltage filters, a trip means which can enable an appropriate protective or diagnostic device when a condition of harmonic overcurrent exists, and a phase detection means which receives signals from the voltage and current filters and transmits a signal to the trip means only when the phase angle between the harmonic voltage and harmonic current is within a specified range. The two harmonics that are to be monitored simultaneously, such as the 5th and 7th harmonics, can be selected by means of a series of simple filter cards which can be inserted into a card cage in an apparatus housing the relay of the present invention.

Abstract: Apparatus for the supervision of a sudden pressure relay (SPR) system which protects a power system network transformer having a plurality of windings associated with each phase of the power system network. This apparatus overcomes the difficulties associated with previous overcurrent supervision of the SPR system for multiple-winding transformers. The apparatus utilizes a maximum restraint signal selection network which offers a discriminating differentiation between high and low current levels in all of the transformer windings and accomplishes this in one embodiment with a single measuring unit per phase of the power system network. For each phase, when the selected maximum restraint signal exceeds a predetermined level, the supervisory unit blocks the SPR from operating the breakers which isolate the power transformer from the power system network. This blocking condition is relieved after a predetermined time period from when the selected restraint signal falls below the predetermined level.

Abstract: A power controller system for providing electrical power to a multiplicity of loads at outputs thereof under direction of a plurality of input controllers operating a corresponding plurality of output energization means with the controllers capable of having different output states in response to differnt system input signals, the controller having selected common components for forcing selected ones of said input controllers to terminate power to corresponding loads. Current sensing means upsetting current balances in bipolar transistors are used to sense beyond-limit currents.

Abstract: In a direct AC/AC converter, fault protection is performed with a minimal number of fault detecting devices and the rating of such fault detecting devices is reduced while still being able to respond quickly to a fault current. This is achieved by using a current sensor in common to at least all the current lines of one group of switches and by combining the operation of such common current sensor with the operation of one current sensor associated with the related output phase line. In another embodiment, all the current lines connected to a switch, for all the groups of switches, are passed through a common and single current sensor.

Abstract: A method for limiting short circuit current flow in a Field Effect Transistor (FET) to limit the power dissipated therein includes sensing a rise in the drain-to-source voltage of the transistor and clamping the gate-to-source voltage to a predetermined adjustable value thereby reducing the magnitude of the short circuit current flow to within the safe operating characteristics of the device. A comparator switch circuit is responsive to the drain-to-source voltage of the FET exceeding a reference voltage value for clamping the gate-to-source voltage to a predetermined reduced voltage. A trimmable resistive network is connected between the gate and the source electrode of the transistor for adjusting the gate to source clamped voltage potential to compensate for variations in transistor transconductances from one transistor to the next that they may be used in conjunction with the electronic circuitry.

Abstract: An integrated protection unit is a circuit breaker which includes basic overcurrent protection facility along with selective electrical accessories. A molded plastic accessory access cover secured to the integrated protection unit cover protects the accessory components contained within the integrated protection unit cover from the environment. A combined overcurrent trip actuator and multiple accessory unit is either field-installed or factory-installed within the integrated protection unit. One such actuator-accessory unit includes a fast release overcurrent trip circuit.

Abstract: The invention relates to a device for detecting cutoff and short circuit defects in at least one electrical circuit portion. The detecting device (10) is intended to verify a circuit portion (11) connected to the terminals of a source of direct current (T1) and including a passive element (E, r) interposed between two switch devices (P, Q) comprises on the one hand four differential amplifiers (AD1, AD2, AD3 and AD4) each having one of their inputs connected to the common terminal (F) of the passive element (E, r) and to the first switch device (P) and their other input connected to a reference potential (V3 or V.sub.

Abstract: In a thyristor with turn-off facility (AT) and overvoltage protection, the voltage limitation is achieved by a parallel-connected controllable resistor, in particular in the form of a J-FET (JF) which is driven by an overvoltage sensor (OS).The separation of sensor function and bypass function produce advantages for a simple and compact construction.

Abstract: A line current to time interpolator circuit senses the magnitude of current in a power distribution line and develops and AC voltage indicative of the current magnitude. The AC voltage is phase shifted multiple times to produce a number of phase shifted replica AC voltages, and the replica voltages are applied to a multiple input absolute value amplifier to develop a DC voltage indicative of the current magnitude. The DC voltage is applied to a ladder voltage comparator which controls the overall resistance of a discharge path coupled to a charged capacitor. The ladder comparator varies the discharge path resistance in inverse relationship to the DC voltage level to vary the discharge time constant of the capacitor. By controlling operation of a circuit interrupter in accordance with the charge level of the capacitor, the interpolator circuit provides a desired inverse time-current response characteristic.

Abstract: A predetermined unsymmetry of a bipolar waveform is detected by apparatus which includes a circuit which generates a pulse for each zero crossing of the waveform. Each zero crossing pulse triggers a first retriggerable one-shot for a first interval T.sub.1. Timing out of the first one-shot triggers a second retriggerable one-shot for a second interval T.sub.2. If both the first and second one-shots have timed out a third one-shot is triggered for a third interval T.sub.3. The intervals are selected such that twice T.sub.1 plus T.sub.2 is equal to the period of one cycle of the bipolar waverform so that triggering of the third one-shot is an indication of a predetermined unsymmetry determined by relative values of T.sub.1 and T.sub.2 of the bipolar waveform. T.sub.3 is selected such that two symmetrical cycles of the bipolar waveform are required to clear the unsymmetry indication.

Abstract: A circuit for preventing the generation of an erroneous output signal from a protective relay for detecting faults in a three phase alternating current electrical power distribution system, which relay uses a full wave rectified signal as an operate quantity. The circuit includes a band pass filter having an input adapted to receive the full wave rectified signal; a center frequency which is tuned to the frequency of at least one principal harmonic component of the full wave rectified signal; a gain substantially equal to -1; and an output. A two-input summing amplifier has one input which is adapted to receive the full wave rectified signal and the other input which is connected to the output of the band pass filter.

Abstract: A control system is provided in which a plurality of independent control elements are each capable of generating a random value and determining a time delay as a function of that random value. Each of the control elements accesses the magnitude of a sensed parameter and responds to that magnitude. When correction of the sensed parameter is required, each independent control element senses the need for a correction and delays by an amount of time determined randomly and independent from all other control elements. After the randomly determined time delay has elapsed for each control element, that control element again accesses the magnitude of the sensed parameter and, if correction is still required, changes the connection status of an associated switch. In a preferred embodiment of the present invention, the control element interrogates the status of its associated switch to determine if actuation would benefit the correction of the magnitude of the sensed parameter.

Abstract: A power bus fault detector for detecting faults in a predefined portion of an electrical power bus having at least one phase. Power feed lines are coupled to the predefined portion of the power bus by circuit breakers. Current transformers are used to detect the current flowing through each phase of each power feed line which is coupled to the predefined portion of the power bus. A summer generates a current differential signal for each phase that is equal to the sum of the currents detected by the current transformers. A fault detector generates a trip signal which causes the feed line circuit breakers to disconnect the feed lines from the power bus when a fault is detected in the predefined portion of the power bus. The fault detector includes a detector which detects when the current differential signal in any of the power bus's phases is substantially nonsinusoidal in shape.

Abstract: A highly accurate current-limiting circuit prevents an output current (I.sub.OUT) flowing through an output line (L.sub.OUT) from exceeding a specified value (I.sub.LIM) of an input current (I.sub.IN) flowing through an input line (L.sub.IN). The circuit contains a first channel device (10) controlled by a first reference voltage (V.sub.REF1), a current source (12) that supplies a reference current (I.sub.REF), a second channel device (14) controlled by a second reference voltage (V.sub.REF2), a current bypass device (16), and a bypass control system (18). The current gain below the specified value of the input current is close to one. By suitably choosing certain of the circuit parameters, the circuit operates in a substantially temperature-independent manner.

Abstract: An inverse-time timer for a volt/Hertz ratio relay includes a ladder of level detectors associated with a like series of counters connected in cascade with a variable voltage-to-frequency connector responsive to the v/Hz ratio signal for controlling the counters to establish the time delay for tripping.

Abstract: An arrangement is provided for checking the validity of a sensed-current signal from a current-sensing device. The sensed-current signal represents the current in a line. An associated control circuit utilizes the sensed-current signal to indicate or predict the presence of undesired overcurrent conditions. When such conditions may be present, the sensed-current signal is checked to determine if the sensed-current signal is valid; i.e., whether the sensed-current signal accurately represents the current in the line. If the sensed-current signal is invalid, no trip signal is generated to interrupt the current. If the sensed-current signal is valid, the control circuit generates a trip signal to control operation of a circuit-interrupting device. In a particular arrangement, the load on the current-sensing device is changed to determine if the sensed-current signal is valid.

Abstract: A current limiting control circuit for a d.c. motor, wherein compensation is provided for the inherent voltage drop across the armature of the d.c. motor with a first dedicated amplifier, while a second dedicated amplifier provides current limit control. In providing a separate and dedicated amplifier for the current limiting function, the limitations inherent in the current/resistance compensation circuit, such as lag in response time, are avoided.

Abstract: An electronically switched power supply that automatically adjusts its operation to produce a fixed output voltage as input voltages of different magnitudes are applied at different times and which has a circuit breaker and circuit breaker control circuitry which provides circuit breaker protection at a fixed output current as the different input voltages are applied.

Abstract: A circuit for signaling when an electrical component is consuming excessive power and for protecting the electrical component from the excessive power. The electrical component is connected to a circuit which supplies and measures the current through and measures the voltage drop across the component. The circuit produces a comparison voltage that represents the sum of the current through and voltage across the component, as normalized according to the maximum current and voltage that are expected to be used by the component. The sum of the values of the current and voltage is an approximation to the power consumed by the electrical component. The comparison voltage is compared to a threshold voltage that represents an approximate maximum power level to be sustained by the component. If the first voltage exceeds the threshold voltage, the comparator produces an overpower signal that can be used to cause the current supply to the electrical component to be interrupted.

Abstract: A bi-directional DC power controller is provided with a bi-directional DC switch connected between a pair of terminals for connection to a pair of line power conductors. A first difference amplifier is connected to receive voltages at these terminals and to produce an output voltage signal which is proportional to the difference in voltages between these terminals when the voltage at one of the terminals is greater than the voltage at the other terminal, and is constant when the voltage at the second terminal is greater than the voltage at the first terminal. A second differential amplifier also receives voltage signals from these terminals and produces an output voltage signal which is proportional to the difference in voltages between the terminals when the voltage at the second terminal is greater than the voltage at the first terminal, and which is constant when the voltage at the first terminal is greater than the voltage at the second terminal.

Abstract: A method of and apparatus for determining which if any phase of duplex supply lines wherein each phase w is assigned two conductors w1 and w2. The method and apparatus use an asymmetry value, for example a function of the relationship (output of 9) of the difference Iw1-Iw2 (output of 5) to the sum Iw1+Iw2 (output of 6) of the currents in the conductors w1 and w2. If the asymmetry level exceeds in absolute value a threshold level K(see 12 and 13), the conductor passing the current having the lowest amplitude is indicated as being sound.