Abstract: A semiconductor switch is installed in a power supply line of a motor, and photocouplers, which constitute a switching control circuit for turning on and off the semiconductor switch, are series-connected between a constant-voltage source and the output ends of a comparator of a starting circuit and a comparator of a trip circuit. An overload at the time of starting the motor is detected by a current transformer, and the semiconductor switch is activated so as to readily cut off the motor driving current.

Abstract: A combination circuit breaker/motor starter includes a circuit breaker trip unit having a microprocessor and at least one removably connectable contactor or other functional module. The functional module is encoded with an identifier, such that the microprocessor can determine the type of functional module and appropriate configuration parameters, such as trip times, for the particular application of the functional module. Power is supplied continuously to the trip unit during motor overload or short circuit conditions.

Abstract: Electrical protection device for a railroad vehicle, including electrical energy consuming units 6, 7 and electrical power supply means 1 to 5, electrical energy being supplied on at least two liner electrically separated from the ground formed by the vehicle as a whole, in particular its chassis and the electrically conductive parts connected to it. The electrical protection device includes detector means 50 for detecting a short circuit alternating current flowing from one of the two power supply lines to ground, to detect any short circuit between the other power supply line and ground.

Abstract: A protection device for monitoring current in a power cable to an electrical device and for controlling a remotely located starter for the electrical device in response to a system controller. The device includes a transformer magnetically linked with the power cable to produce a voltage signal in response to the presence of a changing current within the power cable. An input circuit located in a single housing together with the transformer is electrically connected to the transformer so as to receive the voltage signal. The input circuit produces, in response to the voltage signal, either a first signal or a first circuit condition at the output terminal of the input circuit, representative of the changing current in the power cable. A switch circuit also in the same container with the transformer has a terminal for sensing either a second signal or a second circuit condition of the remotely located system controller.

Abstract: A device for operating an electric motor (10) is proposed, which evaluates overloading or blocking of the drive (11) from a characteristic of a current (40, 41) flowing through the electric motor (10). In accordance with a first embodiment, the determination of the characteristic is provided within a time interval (TI)′ the time interval (T:) occurring within the starting operation after a starting instant (To) of the electric motor (10). In accordance with another embodiment, the determination of the characteristic is provided at a prescribed sampling instant (TA) which occurs at a prescribed delay time (Tv) after a starting instant (To).

Abstract: An apparatus for controlling a current limiter of a motor for protecting the motor by limiting the amount of electric current supplied to the motor and controlling a driving force of the motor comprises of: a frequency detector for detecting the rotational frequency of the motor; a limiter controller for generating a current limiter control signal corresponding to the rotational frequency detected by the frequency detector; and a current limiter for limiting the amount of current supplied to the motor by the current limiter control signal. The current limiter of the motor is controlled by a pulse-width modulated signal in which the duty cycle changes, i.e., a PWM signal, according to the rotational speed of the motor so that a load state or deviation of an axial load of the motor is minimized to accurately control the motor.

Abstract: A motor protection circuit for an electric motor driven by a pulse width modulated amplifier. It has a capacitor and a first conduction path connected to a first terminal of the capacitor and connectable to a first conductor. It also has a second conduction path connected to the second capacitor terminal and connectable to a second conductor. There is a DC voltage difference between the first conductor and the second conductor. There is a third conduction path between the first terminal and the second terminal. The third conduction path having a resistance which is lower than the resistance of the first conduction path plus the resistance of the second conduction path. The third conduction path passes through a switch which has an input connection to be opened and closed thereby.

Abstract: An optical illumination system is comprised of: (a) a light source means having a reflective emitting surface and an intrinsic luminance (brightness), (b) a light transmitting means; (c) a light reflecting means to reflect and recycle a portion of the light emitted by the light source means back to the light source means; and (d) a light extracting means to extract a portion of the light from the light transmitting means and direct the light to the output of the illumination system. The resulting illumination system achieves an enhanced output luminance. Under certain conditions, it is possible to achieve an output luminance that is greater than the intrinsic luminance of the bare light source.

Abstract: An on-line monitor for electrical faults in the stator of an ac motor has a single di/dt current transformer or three separate di/dt current transformers coupled to the three phase conductors of the ac supply. The windings of the transformer, or transformers, are selected to generate a single sensed signal containing a linear combination of components of current in the three phase conductors weighted relatively so that algebraic differences between components from any two phase conductors is non-zero, such as preferably 2A+B-C or 3A+2B+C. The single sensed current signal is bandpass filtered to generate a pulse signal which is applied to an analyzer. The analyzer, preferably implemented by a microcontroller, generates an output based upon a combination of the amplitude and frequency of occurrence of the current pulse signal including a time attenuated accumulation of the pulses.

Abstract: An illumination device comprises a waveguide having a peripheral edge. A series of point light sources are mounted in spaced relationship adjacent a peripheral portion of the waveguide. A series of diffusive reflective surfaces, preferably formed by posts, are disposed adjacent the peripheral portion of the waveguide, between pairs of the point light sources. The diffusive reflective surfaces are oriented relative to the series of point light sources and the waveguide so as to introduce light into regions of the waveguide between pairs of the point light sources, whereby the peripheral portion of the waveguide is substantially uniformly illuminated.

Abstract: Emergency shut-down circuit is provided for a multiplexed circuit. The emergency shut-down circuit includes a plurality of contacts arrayed in parallel to each other and which are synchronously opened and closed. A plurality of electromagnetic contactors are operated according to a open or closed state of each of the plurality of emergency shut-down switches and are connected in series to a main circuit power circuit for a motor.

Abstract: A simple, off-chip circuit and method for endowing high efficiency IGBTs with short-circuit capability, that is essentially transparent to the user. The invention involves adding an external common emitter resistor to reduce the effective gain of an IGBT under short circuit. Under normal operating conditions, the voltage across the resistor is small, such that the modifying effect on the normal operating gate-emitter voltage is almost negligible.

Abstract: An internal self-test and status reporting system for an electrical device with a plurality of components, a power supply and a microcontroller or microprocessor. The self-test system powers on and off each component one at a time and measures an amount of current drawn by the component with an internal current sensor. The self-test system compares the measured amount of current drawn by the component with an expected, predetermined current value or range. The self-test system then reports whether the measured amount of current drawn by the component matches the expected, predetermined current value or is within the expected, predetermined current range. The self-test system reports the results of the self-test by generating a pattern of signals on a general purpose input/output (GPIO) line, displaying a message on a display of the device, or generating a sound with a speaker of the device.

Abstract: In a motor drive apparatus, a motor drive circuit includes an H bridge circuit composed of four field effect transistors or FETs, and resistors each having electrical resistance sufficiently higher than that of each of the FETs which would be presented when the FET has an ON-state trouble. These resistors are connected in parallel to the respective FETs. To perform a ON-state trouble detecting test on the individual FETs, an OFF signal is fed to all the FETs. If all the EFTS are free of the ON-state trouble, electric potential, representing a result of higher potential of a battery being divided by the resistors, appears at two input terminals of an electric motor connected to the motor drive circuit. If two of the FETs, having their drains connected to a higher-potential electrode of the battery, have the ON-state trouble, the higher potential of the battery appears at the two terminals of the electric motor.

Abstract: A system for controlling electric motors in binary and hybrid applications, particularly motors which are used to control windows which can be moved downwards from one extreme position to another extreme position by a single touch of the switch, and between other positions by depressing the switch so long as movement is desired. In this system, a control element is placed in series with the electric motor. The control element has an interrupt component and a sense component which are coupled in series, and the series combination is coupled in parallel with a control component. When the electric motor reaches one of its extreme positions, the sense component senses an increase in the current drawn by the motor. The sense component then signals the control component to cause the interrupt component to interrupt the current and stop the motor.

Abstract: The present invention provides a speed control device for a ceiling fan which comprises a MOSFET, a signal generator and an overload protector. The MOSFET is connected to the ceiling fan and power source via a bridge rectifier for controlling power supplied to said ceiling fan. The signal generator provides a control signal to the MOSFET, wherein the control signal is a cyclic signal whose voltage level is progressively increased and then decreased when it reaches a predetermined level whereby the MOSFET is cyclically and progressively turned on and turned off. The overload protector is connected between the drain and gate of said MOSFET for detecting an abnormally large current flow through said MOSFET to cut off said MOSFET thereby preventing the ceiling fan from possible damage.

Abstract: A fan venturi blockage detector for a DC electric fan and an associated method are disclosed employing a current detector for measuring the input current to the DC electric fan, and a processor connected to the current detector. The processor stores the measured input current value for the minimum input current to the fan under normal operating conditions, and sets a minimum current threshold at a value less than the normal operating condition measured current. The processor compares subsequent measured input current values with the minimum current threshold value, and provides an error signal upon the subsequent measured input current having a value equal to or less than the minimum current threshold value.

Abstract: A vehicle cooling system including a motor control apparatus that controls operation of a system motor when a cooling fan driven by the motor locks due to foreign matter interference or freezing. When motor input current is detected to be overcurrent, the controller limits the current flow. When current flowing to the electric motor is detected to be overcurrent and ambient air temperature is at or above a predetermined temperature, the controller stops energization of the motor. Thus, when the cooling fan freezes and locks, energization of the motor is maintained until ambient air temperature reaches or exceeds the predetermined temperature. Therefore, when the frozen-locked state is eliminated due to a subsequent temperature rise, an ordinary operating state can again be obtained without the controller subsequently detecting surge current, generated as a result of the motor being re-started from a fully stopped state, as overcurrent and therefore incorrectly stopping motor energization.

Abstract: A library apparatus having a motor driving control circuit including a processor, a motor driver circuit, a relay, a motor abnormal condition detection circuit, a current control circuit, an excess current detection circuit, and an abnormal current monitor circuit. The motor abnormal condition detection circuit is connected to the motor driver circuit, and detects an abnormal condition of at least one of the motor and the motor driver circuit. Upon detecting an abnormal condition, the motor abnormal condition detection circuit outputs a motor abnormal condition detection signal which prompts the current control circuit to regulate the current flowing through the motor driver circuit. If the current control circuit is unsuccessful, the excess current detection circuit outputs an excess current detection signal which triggers the relay to close the power source circuit of the motor driver circuit.

Abstract: An electric vehicle control device controls an induction motor with a VVVF inverter. A first calculation means calculates a rotor-resistance correction value of the induction motor based on a torque current instruction value for vector control of the induction motor and an actual torque current value. A second calculation means calculates a corrected rotor-resistance value based on the rotor-resistance correction value and a reference rotor-resistance value. A third calculation means calculates an estimated rotor temperature of the induction motor based on the corrected rotor-resistance value, the reference rotor-resistance value, and a temperature coefficient determined by a material of a rotor. The thermal condition of the induction motor is thus monitored in real time without installing a temperature sensor on the induction motor.

Abstract: An apparatus including only first and second sensors for determining three phase motor currents and providing complete over-current protection to a three phase motor having three input lines. The first and second sensors measure first and second combined currents wherein the first combined current is the current through the first and second lines and the second combined current is at least the current through the second line and at least one of the first or second combined currents include the third current. The first and second combined currents are used to provide the over-current protection and are used to determine all of the first, second and third line currents.

Abstract: Method and device for monitoring a load, which can be driven by means of an output stage as a function of the control signals of a control unit, the output stage carrying out fault monitoring and emitting an appropriate fault signal, wherein faults are detected only when at least one further condition is satisfied in addition to the fault signal.

Abstract: A wiper control system including a current sensing device is used in conjunction with a park position switch to limit the current drawn by windshield wiper motor whenever the system experiences restrictions in a park mode. The arrangement of components is effective for preventing damage to the motor and motor control system caused by excessive current draw whenever the motor stalls, arcs, or experiences excessive loads. However, the current sensing portion of the circuit is essentially disabled when the motor is in its normal operating mode thus preserving the fail safe operation of the wipers.

Abstract: An express down vehicle window lift motor drive system in which an overcurrent detection circuit (10) interprets the flow of electrical power to the lift motor when the motor current exceeds a threshold which is set dynamically as a function of motor in-rush or peak current. Motor current is measured as a small voltage drop across a current shunt. When the current level rises above the dynamically set threshold energization of the motor is halted.

Abstract: The invention relates to a method of current limitation in a direct current motor, with the following steps: in successive cycles, the motor is turned on at a predetermined place in the cycle and, after lapse of a predetermined time interval, the motor current is tested in a first test and, if found to be too high, the current is shut off; after lapse of another interval measured from the first test, the motor current is tested again during the same cycle and, if found to be too high, is shut off if it was not shut off previously; after lapse of a third interval, measured from the second test, the motor current is turned on, insofar as it was shut off at either of the two tests, and the cycle is repeated.

Abstract: A machine includes first and second electrically actuated components and a shutdown circuit electrically interconnected therewith. The shutdown circuit has a current sense relay element which is electrically connected to the first electrically actuated machine component. The current sense relay element includes a coil capable of generating a magnetic field in response to direct current flowing therethrough and a reed switch adjacent the coil which is movable between open and closed positions in response to the presence of the magnetic field. The reed switch is normally closed when the direct current flowing to the first electrically actuated machine component is at or above a predetermined level. The reed switch opens when the direct current flowing to the first electrically actuated machine component falls below the predetermined level.

Abstract: A system for controlling circulating currents in a motor. A power supply link having upper and lower rails supplied by a power supply provides power to the motor windings. The power supply link also has power switches responsive to a motor control signal for selectively connecting the rails to the windings in alternating on and off intervals. The system includes a first resistive shunt in the upper rail of the power supply link between the power supply and the power switches and a second resistive shunt in the lower rail of the power supply link between the power supply and the power switches. The power supply link routes current circulating in the power supply link and windings through either the first or second resistive shunt for continuously sensing current in the rails. The system also includes a current regulation circuit which generates an overcurrent signal as a function of the current sensed in either the first or second resistive shunt exceeding a maximum current level.

Abstract: A protection device for monitoring current in a power cable to an electrical device and for controlling a remotely located starter for the electrical device in response to a system controller. The device includes a transformer magnetically linked with the power cable to produce a voltage signal in response to the presence of a changing current within the power cable. An input circuit located in a single housing together with the transformer is electrically connected to the transformer so as to receive the voltage signal. The input circuit produces, in response to the voltage signal, either a first signal or a first circuit condition at the output terminal of the input circuit, representative of the changing current in the power cable. A switch circuit also in the same container with the transformer has a terminal for sensing either a second signal or a second circuit condition of the remotely located system controller.

Abstract: A grounded terminal of a motor driver for controlling an actuator motor is connected to a ground terminal of a control unit through a grounded wire, and therefore connected to a grounded point. Since a ground wire of the stabilized power supply circuit is connected to the ground wire of the control unit, the stabilized power-supply circuit also has its ground connected with the grounded point disposed outside the control unit. A cut-wire avoidance diode is connected between the ground wire of the stabilized power supply circuit and a power transistor unit in a manner such that its cathode is connected to the power transistor unit, which enables the stabilized power-supply circuit to remain grounded even when the control unit is disconnected from the grounded point.

Abstract: An electric appliance control system is provided for use with an electric power unit such as an electric lawn mower. The electric appliance control system includes a battery, a selectively operable switch, a relay having first and second contacts, a control means, a charger circuit and an operator presence switch. The relay is operable by the switch to connect the electric power unit to the battery. The first and second contacts of the relay pass amperage therethrough between the battery and the electric power unit. The first contact is normally open and the second contact is normally closed. The control means includes a negative temperature coefficient thermistor in series with the first contact and multiple thermistors arranged in parallel and utilized in series with the second contact. The negative temperature coefficient thermistor variably increases the amperage passing through the first contact of the relay upon the selective operation of the switch to connect the electric power unit to the battery.

Abstract: A time-compensated overcurrent detection circuit shuts off a D.C. motor during large overcurrent conditions caused by actual constraints on the motor. The circuit prevents premature motor shut off by establishing a minimum activation time for shutting off the D.C. motor. An overcurrent time compensator establishes a minimum time period for activating a motor reset signal after sensing an overcurrent condition. The circuitry uses a relatively small capacitor that provides quick response to overcurrent conditions.

Abstract: An elevator drive fault detector for detecting operational faults in an elevator drive having an inverter and only one circuit breaker includes a current sensor, a monitoring device, a control device and an operational control system. The current sensor provides a current sensor signal. The monitoring device determines if an operational fault exists in response to the current sensor signal and provides an operational signal. The monitoring device disables the operational signal if the monitoring device determines that an operational fault exists or if the elevator drive fault detector performs a system check operation. The operational control system provides both the run command and an operational check signal and is responsive to the operational signal such that if the operational signal is disabled then the operational control system opens the one circuit breaker and disables the run command such that the control device disables a PWM signal.

Abstract: A fire extinguishing system in which a calculated quantity of a liquid chemical foamant is introduced into the main water stream being directed at a fire equipped with a protective circuit for limiting the amount of average current flowing within a motor driving a fluid pump used to inject the chemical foamant, in addition to an electronic fuse circuit for automatically shutting off the power being supplied to the low-level electronics.

Abstract: Apparatus for monitoring the functioning of motor driven equipment, including current sensing apparatus connectable to the power input of the motor and producing a current signal; signal correction apparatus receiving as input the current signal and operative to demodulate the current signal, filter the current signal to retain low frequencies thereof, and convert the current signal from analog to digital form and producing a corrected signal; a memory; a controller in operative connection with the memory, receiving the corrected signal, and having a calibration state and an operation state, and operative, when in the calibration state, to compute the calibration norm of the corrected signal based partly on data contained in the memory and to store the calibration norm in the memory and operative, when in the operation state, to compute the operation norm of the corrected signal based partly on data contained in the memory and to compare the operation norm with the stored calibration norm and to produce a fun

Abstract: An arrangement (1) for limiting the short-circuit current in a three-phase electric power line connected with one or more motors/generators (2) in which in each power line phase (3) leading to the generator/motor (2) at least one pair of series switches (4) are disposed, which are formed by semiconductor switch elements connected in anti-parallel, and in the section between the series switches (4) and the generator/motor (2) elements such as short-circuiting switches (6) are disposed which in case of a short-circuit cause the current of the generator (2) to be shunted away such that the operation of the series switches (4) is assured and the current cannot get into the power line. With the very simple structure of the system, very fast switching times are achieved.

Abstract: A current sensing module for use with a variable speed AC motor control drive system for use with devices such as treadmills and including a module to sense the current of pulse width modulated signals provided to an AC motor wherein the current sensing module includes a fast sense circuit to sense excessive current conditions in the pulse width modulated signals and a slow sense circuit to sense average current values in excess of desired values over a predetermined period of time to protect the AC motor from damage caused by the increased frictional resistance to the rotation of the walk belt on the treadmill deck as the walk belt and treadmill deck wear out.

Abstract: During a learning stage a motor current signal is monitored, and estimated motor torque is used to transform the current signal into a time-frequency spectra including a plurality of segments representative of good operating modes. A representative parameter and a respective boundary of each segment is estimated. The current signal is monitored during a test stage to obtain test data, and the test data is compared with the representative parameter and the respective boundary of each respective segment to detect the presence of a fault in a motor. Frequencies at which broken bar faults are likely to occur in a motor can be estimated using the estimated motor torque, and a weighting function can highlight such frequencies during estimation of the parameter. The current signal can be further subdivided into the segments by monitoring sidebands of the frequency components of current spectrum strips of each segment.

Abstract: A switched reluctance machine capable of improved operation under fault conditions. The machine includes a controller which responds to a fault in a phase winding by cutting off current to the phase windings of all stator poles that are aligned with a rotor pole at the time the stator pole having the phase winding with the fault therein aligned with a rotor pole. Consequently, there is no magnetic flux in the stator or rotor at such time. Therefore, no current is induced in the faulted phase winding. This avoids generation of a counter torque, as well as avoiding potential catastrophic failure of the SR machine.

Abstract: A phase current reconstruction circuit (10) senses and reconstructs a phase current in a phase bridges (12A). An amplifier (32) in a phase current reconstruction element (22) amplifies a voltage signal across a sensing resistor (18). The amplified voltage signal is transmitted to a sample and hold circuit (34), which reconstructs the phase current in the phase bridge (12A). An over-current comparator (36) compares the amplified voltage signal with a predetermined reference voltage to detect an over-current in the phase bridge(12A). If the over-current in the phase bridge (12A) is detected, an over-current latch (38) interrupts the pulse width modulation signal from a microcontroller (26) to a power switch (16A) in the phase bridge (12A), thereby switching off and protecting the power switch (16A) from damage that may be caused by the over-current.

Abstract: A motor starter includes separable contacts; an operating mechanism for operating the separable contacts; an overload relay controller including a memory for storing the settings for a plurality of selectable operating features, and a microprocessor for retrieving the settings from the memory and employing the settings at least for controlling the operating mechanism; and a programmer module temporarily engaging the overload relay controller for changing the settings in the memory.

Abstract: A protective circuit controls the operation of a floor cleaning machine provided with a brush motor and a vacuum motor. The protective circuit disables the vacuum motor when an operator starts the brush motor and then restarts the vacuum motor provided it was previously running. The floor cleaning machine is also provided with provisions for adjusting the action of the brush and thus changing the load current of the brush motor. The load current of the brush motor is continuously compared to a first level overload current and an indicator alerts the operator to a first level overload condition allowing a predetermined time for the load current to be reduced by adjusting the brush. If the load current is not reduced, then the brush motor is de-energized. If a second level overload condition of the brush motor occurs at any time, the brush motor is de-energized immediately.

Abstract: A short circuit protection circuit which has a first short circuit protection circuit in parallel with a second short circuit protection circuit is disclosed. The first short circuit protection circuit includes a sense resistor and a comparator for detecting the short circuit, and a transistor and current source for turning off the low side driver when the short circuit is detected. The second short circuit protection circuit includes a current mirror, zener diode, transistor, and current source connected in series. The second short circuit protection circuit is in parallel with the first short circuit protection circuit. The second short circuit protection circuit accelerates the turn-off of the low-side driver with out affecting the stability of the circuit.

Abstract: The driving apparatus for a power antenna, e.g. an extensible-retractable automotive radio antenna, is provided with stability function which controls the operation of the motor driving the power antenna until the power antenna is varied into a state for performing normal operation, and provides hysteresis to prevent a state of the controlling signal from being varied too often by a voltage drop generated in rotation of the motor.

Abstract: This invention aims to realize a superior control system for electric automobile, wherein the current can be accurately controlled according to the state of the automobile and yet high driving performance and charging performance can be achieved. When in the drive mode of the automobile, the system detects the current for drive using the current detector, controls the current of the inverter, and drives the induction motor. When in the charge mode, the system detects the current for charge using the current detector, controls the inverter, and charges the battery with the current from an external power supply. The intensity of the current differs by several times when driving and when charging, but the current detection range of the current detector for drive is wider than the current detection range of the current detector for charge. Therefore, the system detects higher current very accurately when driving and detects lower current very accurately when charging.

Abstract: A method and device for detecting an out-of-balance condition of a load which is driven by a motor is disclosed. A present instantaneous value of a current of a motor which is driving a load is detected and an average value of the detected instantaneous value over time is established. The present instantaneous value is compared to the established average value, and the number of times which the instantaneous value differs from the average value by at least a prescribed amount is counted. If this number exceeds a certain number, it is determined that the load which the motor is driving is out of balance.

Abstract: A method for fault correction in a power converter circuit arrangement. The power converter circuit arrangement has a plurality of switch modules which consist, for their part, of a parallel circuit of semiconductor chips. The semiconductor chips are interconnected via connecting wires, preferably bonding wires. If, because of a defect, a chip forms a short circuit, the connecting wires of chip are severed by specific current pulses. The advantage resides in that a short circuit of an individual chip does not put the entire circuit arrangement out of operation.

Abstract: A method of operating a switched reluctance machine is disclosed, which provides electrical current overload protection. The stator winding motor drive employs a high-side semiconductor switch, along with a corresponding high-side gate driver (which incorporates a bootstrap-type drive circuit). A low-side semiconductor switch, and a corresponding gate driver is also used to thereby define a two-switch per phase topology. The high-side MOSFET switch gate driver must have rising, and falling edges from an associated controller in order for the bootstrap drive power supply portion to function. A drive controller is configured so that it will generate these rising, and falling edges only when the motor is moving, as indicated by a speed signal. Therefore, if the motor stops moving, due to an unexpected load, such as a seized pump connected to an output shaft thereof, the speed signal will so indicate the stall, wherein the controller will not generate a signal having rising and falling edges.

Abstract: A winch system including an electric motor is protected against an overload condition by use of a current sense device and a current limiting device. The current limiting device employs multiple current thresholds to account for normal current usage by the motor during an initial current inrush period and during subsequent normal operation. The current limiting device also references battery voltage to establish current thresholds as a function thereof and thereby establish shutdown conditions corresponding to consistent motor load conditions. Overall, the current limiting device is responsive to multiple winch device states of operation and more fully protects the winch system against damage due to an overload condition.

Abstract: A device and apparatus for monitoring faults in a three phase induction machine are disclosed herein. The device and method utilize values of the currents in the three phases and the voltages of the three phases to estimate a current portion which is not substantially affected by the load torque effects of the machine. This current portion is related to the unacceptable magnetic fields present in the machine. These fields are typically caused by electrical or mechanical problems in the machine, and when the current portion exceeds a predetermined limit, operation of the machine can be discontinued.

Abstract: An automatic fault monitoring system prevents the detection of fault conditions during operating modes or conditions that can produce false fault conditions. A motor control system that utilizes an H-bridge circuit having active devices, preferably field effect transistors, in each arm of the bridge. The motor is connected in the leg of the bridge. Currents and voltages are sensed in each arm as different operating conditions represented by input control signals, which may be computer generated, drive the bridge and place the transistors in different states (on or off). Such operating conditions include rotation of the motor in opposite directions and reversal of direction. Fault detection logic is responsive to currents and voltages in the arms and leg of the bridge and provides outputs indicative of over-current fault conditions in the arm and open circuit fault conditions in the leg.