Abstract: A surgical instrument. The surgical instrument includes an elongated channel configured to support a staple cartridge, an anvil pivotably connected to the elongated channel, a knife mechanically coupled to the staple cartridge, an electric motor mechanically coupled to the knife and a control circuit electrically connected to the electric motor. The control circuit is configured to ignore an occurrence of a first predefined event based on a position of the knife, automatically stop an advancement of the knife after an occurrence of a second predefined event, and automatically restart advancement of the knife after an occurrence of a third predefined event.

Abstract: The systems and methods described are for adjusting over current protection values during changes in load current. In one aspect, a method includes, monitoring a load current amplitude value at a power input connected to an electrical load; determining a rate of change of the load current amplitude value; determining whether the rate of change of the load current amplitude value exceeds a predefined rate threshold value; in response to determining that the rate of change of the load current amplitude value exceeds the predefined rate threshold value: adjusting an over current protection value from a first over current protection value to an adjusted over current protection value for a first predefined amount of time; and at the expiration of the first predefined amount of time, at least partially reversing the adjustment to the over current protection value.

Abstract: A method for detecting and managing an electrical phase loss condition in a climate controlled transport unit (CCTU) is provided. The method includes monitoring a generator phase signal outputted from a generator of the CCTU. The method also includes calculating, via a CCTU controller, a phase shift amount based on the generator phase signal. Also, the method includes detecting an electrical phase loss condition based on the phase shift amount.

Abstract: A method of controlling at least one motor in a motorized mobility vehicle, wherein the motor is part of a drive circuit for mobilizing the mobility vehicle, the method comprising the steps of: utilizing a stored profile of a motor performance parameter to develop a compensation term for controlling the motor, wherein the stored profile is of a resistance based variable associated with the motor as a function of a further variable and dynamically updating the compensation term when the mobility vehicle is in use.

Abstract: An electrical system for starting an engine is provided. The system includes: an AC/DC rectifier powered by an AC power network to deliver a first DC voltage Vdc, a DC/AC converter module for delivering an AC voltage for starting the engine from said first DC voltage Vdc, and k n-phase inverters arranged in parallel (k>1) and each delivering power no greater than half a maximum power Pmax required for starting the engine, and the two power supply lines of each of the inverters are connected to an electronic protection device receiving the first DC voltage Vdc, and the n outputs of each of the inverters delivering the AC voltage for starting the engine via n respective series inductors.

Abstract: A drive force distribution control apparatus in which if a relay output voltage (Vah) detected by relay-output-voltage detecting means (30) is lower than a first threshold, the relay is repeatedly and successively turned on and off multiple times, and then if the relay output voltage (Vah) detected later by the relay-output-voltage detecting means (30) while an engine speed (Er) is higher than a second threshold and an ignition switch (IG) is on is still lower than the first threshold, it is determined that there is an abnormality that keeps the relay stuck open, and then control for switching the drive mode from a four-wheel-drive mode to a two-wheel-drive mode is executed.

Abstract: In an installation controlling the operation of one or more motors driving a mechanism for deploying or retracting a protective canopy over the cargo compartment of a truck or wagon, a method and device for protecting the motor windings against excessive power use by measuring the level of drawn current with a digital ammeter. If the current exceeds a threshold level of operation, a timer is started. As soon as a given absolute safe period of operation is surpassed, a breaker switch is tripped interrupting the motor power supply. A plural number of trip points can be programmed into the device.

Abstract: Systems and methods for providing overcurrent circuit protection are disclosed. A method of providing overcurrent circuit protection may include setting a threshold current value according to an operational state of a motor and sensing an amount of current being supplied to the motor. The method may further include electrically isolating the motor from a current source if the sensed current amount is greater than the threshold current value.

Abstract: A modular control assembly is provided for on-machine control of a desired machine. One embodiment has a machine mountable base and a replaceable control unit, wherein the machine mountable base has a machine protection device. In various embodiments of the machine mountable base, the machine protection device may have a short-circuit protective device and a disconnect device. In addition, various embodiments of the replaceable control unit may have a variable frequency drive, a soft start device, or an adjustable overload protection device.

Abstract: An inverter system having a semiconductor device, and a railway vehicle using this inverter, provide a more accurate determination of whether an abnormal heat generation from the inverter is associated with an error of the inverter system or is due to other causes, by use of a plurality of temperature detecting elements at a plurality of sites associated with the semiconductor device. An error detection section applies inputs from the temperature detecting elements, captures a trend of the differential value based on the plurality of temperature inputs using period sampling wherein an error associated with the semiconductor device, and not from some other condition such as outside environment temperature, is determined based on differences from, or a change in, the initial trend.

Abstract: The invention relates to a method for variation of a rated current which is specific of a motor by providing a rated current basic value signal (2) depending on a rated current basic value of the motor Irated, and by detecting an actual temperature Tact, providing a corresponding temperature signal (4), determining an actual rated current Iact depending on the rated current basic value signal (2) and the temperature signal (4), and providing a corresponding rated current signal (6). Additionally, the inventive method allows to determine the actual rated current depending on the speed of the motor. The invention also relates to a device for varying the rated current of a motor depending on a temperature and optionally depending on a speed of the motor. The inventive device can be used in a measuring system for determining the utilization rate and for monitoring the temperature of a motor.

Abstract: A control portion instructs supply of an offset voltage while a disk remains stopped at the time of start. While the disk remains stopped at the time of start, a differential operational amplifier detects a voltage difference between a first voltage supply line and a second voltage supply line. When the absolute value of the voltage difference output by the differential operational amplifier is equal to or lower than a prescribed threshold value, a failure determination portion determines that a spindle motor has shorted out.

Abstract: A method of controlling in-rush current to a DC motor is disclosed. The method may include operating the DC motor in a first mode including applying back-EMF across a relay coil to maintain the relay in an open configuration when the back-EMF is below a predetermined voltage. The method may also include operating the DC motor in a second mode including applying the back-EMF across the relay coil to maintain the relay in a closed configuration when the back-EMF is equal to or above the predetermined voltage.

Abstract: A motor-drive circuit comprising: a current-passage-control circuit to perform ON/OFF control of a drive transistor connected to a motor coil to pass current through the motor coil; an overcurrent-state-detection circuit to detect whether current passing through the drive transistor is in an overcurrent state where the current exceeds a predetermined threshold value; a charging and discharging circuit to start charging a capacitor in response to detecting the overcurrent state by the overcurrent-state-detection circuit and subsequently discharge the capacitor in response to not detecting the overcurrent state; and an overcurrent-protection-control circuit to stop the ON/OFF control to turn off the drive transistor, for an elapsed charging period for a charging voltage of the capacitor at a predetermined voltage to exceed a threshold voltage, and determine whether to perform such an overcurrent-protection-control as to turn off the drive transistor by detection of the overcurrent state, after the charging peri

Abstract: A motor lock detection circuit for detecting lock of a motor, comprising: a binarizing circuit to binarize a signal, obtained from the motor, having a frequency corresponding to rotation speed of the motor, to generate a binary signal; an edge detecting circuit to generate an edge detection signal when detecting an edge of the binary signal; a first counter to count based on a first counter clock, be reset according to the edge detection signal generated by the edge detecting circuit, and generate a count signal when counting for a first count period longer than an interval between edges of the binary signal; and a second counter to count based on a second counter clock, be reset according to the count signal, and generate a motor lock detection signal indicative of detection of lock of the motor when counting for a second count period longer than the first count period.

Abstract: One embodiment of the present invention discloses a method for the automatic adjustment of a protective device having an excess-current release, particularly a low-voltage circuit breaker, which includes an asynchronous motor as a load, said motor requiring protection from overload, and also protects the energy distribution system from a short circuit, wherein at least one release time Tp is to be set as a parameter on the excess-current release, the time ensuring that thermal overload of the asynchronous motor does not occur.

Abstract: A motorcycle has a transmission including a transmission mechanism and an electronic control unit (ECU). The transmission mechanism includes a crankshaft as an input shaft, a driven shaft as an output shaft and an electric motor. The electric motor changes continuously the transmission ratio between the crankshaft and the driven shaft. The ECU estimates the heat value of the motor from a rate of change in the transmission ratio. When the estimate heat value reaches or exceeds a specified value the electric motor is restricted or stopped.

Abstract: A disc apparatus which can accurately judge whether or not a spindle motor is at fault due to a short circuit is provided. A disc apparatus (1) includes a spindle motor (3) which rotates a disc (2), a differential operational amplifier (5) which detects a difference between voltages of a positive terminal and a negative terminal of the spindle motor (3) as a detecting voltage level, a failure judgment unit (10) which judges whether or not the spindle motor (3) is at fault based on the detecting voltage level, and a disc determination means (12) which determines a type of the disc (2). The failure judgment unit (10) judges that the spindle motor (3) is at fault when the detecting voltage level becomes lower than a predetermined threshold level five times continuously during a start-up that the spindle motor (3) starts driving when the disc (2) is in stopped state while the disc determination means (12) determines the type of the disc (2).

Abstract: In response to a system-off instruction, the drive system control technique of the invention controls individual motors of an electric cooling water pump and an electric cooling fan to stop (step S100), waits for elapse of a preset reference time period since start of the control of stopping the motors (step S110), and turns off a relay to disconnect a supply of electric power from a battery to a CPU of a control unit (step S120). Inactivation of the relay after elapse of the preset reference time period since start of the control of stopping the motor disconnects the supply of electric power to the control unit in the state of sufficiently low back emf generated by the motors. This arrangement effectively prevents malfunction of the control unit due to the back emf generated by the motors.

Abstract: To provide a motor control apparatus, including a rotational number detecting means for detecting the rotational number of a motor; a current detecting means for detecting a motor current; a voltage detecting means for detecting an impressed voltage to be supplied to a motor; a temperature estimating means for obtaining a motor temperature from the rotational number of a motor, the motor current, and the impressed voltage; and a protection signal generating means for generating an operational signal in order to protect the motor when the obtained motor temperature exceeds a predetermined value.

Abstract: A control device for soft starting and protecting overload of a motor in a power tool is disclosed. The control device comprises a power switch, a varistor, several diodes, several resistors, several capacitors, a relay, a transistor, a triac, and a microcontroller. The microcontroller is embedded with program such that, after the power switch is turned on, the microcontroller generates a smooth soft start voltage to drive the power tool. With the characteristics of power-control device, the voltage sent to motor is increased from low to full range. When the speed of motor is increased from low to the maximum, the microcontroller turns off the power-control device and turns on a relay.

Abstract: A starting system for a single-phase induction motor, comprising: a stator having a running coil (11) and a starting coil (12); a power source (F) which supplies current to said running coil (11) and said starting coil (12); a running switch (S1) and a starting switch (S2), respectively connecting the running coil (11) and the starting coil (12) to the power source (F) when in a closed condition; and a control unit (30) which is programmed to operate the running switch (S1) so as to cause a delay in the supply of the current supplied to the running coil (11) in relation to the supplied of the to the starting coil (12), during the motor start for a determined time interval which is previously defined and considered from the zero-crossing moment of the current supplied to the stator.

Abstract: A system and method is disclosed for intelligent power management of actuators such as those used in papermaking. Multiple power supply units are connected to a common power bus. The power bus is connected at predetermined locations to a communications bus. The communications bus is connected in series with all of the actuators. The actuators are arranged in predetermined groups. A computing device determines if electrical power can be supplied to some or all of the actuators that are requesting simultaneous movement and if there is insufficient power for all such actuators the computing device issues permission for actuators to move based on a preselected criteria.

Abstract: A control device for soft starting and protecting overload of a motor in a power tool is disclosed. The control device comprises a power switch, a varistor, several diodes, several resistors, several capacitors, a relay, a transistor, a triac, and a microcontroller. The microcontroller is embedded with program such that, after the power switch is turned on, the microcontroller generates a smooth soft start voltage to drive the power tool. With the characteristics of power-control device, the voltage sent to motor is increased from low to full range. When the speed of motor is increased from low to the maximum, the microcontroller turns off the power-control device and turns on a relay.

Abstract: Resistance of the coil of a DC motor is calculated by using the motor current and the motor voltage, and the coil temperature is estimated by using the resistance-temperature characteristics of the coil.

Abstract: A motor start relay (100) comprises a positive temperature PTC thermistor, a PTC case 400 of heat resistant resin for receiving the PTC thermistor horizontally, first and second contact/terminals (500, 560) each having contacts electrically engaged with a respective electrode surface of the PTC thermistor in the PTC case (400), a housing (200) receiving the PTC case (400) and a cover (300) attached on the housing (200). FIG. 9 shows the failsafe mechanism of the present invention. In case of a crack occurring in the PTC thermistor, thermistor portion PTC1 is rotated by spring contact (510) with a force F1, and thermistor portion PTC2 is pushed by spring contact (570) at the reverse direction and is dropped through an opening of the PTC case (400).

Abstract: A control apparatus for protected switching of a load encompasses at least two switch units in series with a load, to permit delivery of energy to a load when each switch unit is switched on and to block it when at least one of the switch units is shut off; an electronic control system for triggering each switch unit via a first switching path and second switching paths, and for monitoring its state; a delay element on the first switching path, such that each switch unit can be shut off both by way of a shutoff signal conveyed via the first switching path and by way of a shutoff signal conveyed via the second switching path; and in a state in which one of the switch units is shut off and the other is switched on, the electronic control system ascertains a malfunction of the first switching path if, after output of a shutoff signal on the first switching path, the other switch unit does not shut off within a predefined time window.

Abstract: An abnormality detection apparatus, which reduces erroneous detection of an open abnormality of a relay, includes a microcomputer that activates the relay and determines whether the output voltage of the relay is less than a threshold value. When the output voltage is less than the threshold value, the microcomputer repeats the activation of the relay and the determination. The detection unit detects the occurrence of an open abnormality when the repetition number exceeds two.

Abstract: A starting circuit for a single-phase induction motor includes a motor starting positive characteristic thermistor and a triac arranged in a series connection, and a triac control positive characteristic thermistor connected in parallel with the motor starting positive characteristic thermistor, and including one terminal thereof connected to a gate of the triac. The triac control positive characteristic thermistor has a volume in the range of about 4.5 mm3 to about 30 mm3. The relationship of (?2×V×sin 45°)/R?I is maintained with the triac control positive characteristic thermistor within an operating temperature range, where V represents a root-mean-square value of a power source voltage, R represents a resistance of the triac control positive characteristic thermistor, and I represents a gate turn-on current of the triac. The gate turn-on current I at an operating temperature of about 25° C. is about 20 mA or less.

Abstract: A protective device includes a signal input intended for connection to a sensor, a signal output intended for connection to an evaluation unit, and an isolation element for galvanically separating the signal input from the signal output. The provision of the protective device prevents a transmission of overvoltages from the sensor to the evaluating unit.

Abstract: The present invention includes apparatus and methods to suppress transients that would otherwise have an effect on a power supply. The present invention accomplishes this by providing a power supply transient suppressor between the power supply and an inductive load, such as a spindle motor of a disc drive. The power supply transient suppressor is turned off at certain desired times so that transients caused by the inductive load do not affect the power supply. One apparatus to accomplish this suppression is to use an isolation transistor and a blocking diode. The blocking diode can be a discrete device or can be inherent in the isolation transistor. The isolation transistor is turned on and off so that undesired transients are not passed to the power supply. For example, during spin up of the spindle motor, the isolation transistor can be turned on and off to block the transients from passing to the power supply.

Abstract: An electronic control device has a power switch for driving and supplying an electrical drive for a fitting which is to be controlled. The invention provides for the power switch to be driven by an electronic computer assembly arranged inside the housing of the control device and which can be supplied with parameterization data for driving the electrical drive for the fitting.

Abstract: In a device for controlling the power supply of the electric motor of a starter of a motor vehicle, and of an automobile in particular, a power switch is connected in series with the electric motor to control the motor power. The switch consists of an electronic power unit capable of being controlled.

Abstract: A combination current sensor and relay has an improved housing. In one aspect, the housing includes light emitting diodes on an upper surface that indicate open circuit and short circuit conditions. In another aspect, the housing includes a securement structure for a circuit board that includes the transformer and switches for device operation, together with aligned openings therein for routing wires to external devices. In another aspect, a multiple position switch is included on the upper surface that indicates multiple modes of operation of the device. In another aspect, the housing may be assembled in multiple parts by affixing a first portion to a support, a circuit board to the first portion, and a second portion to the first portion. In another aspect, the housing is suitable for engagement to alternatively a junction box and a duplex box. In another aspect, the configuration of the upper surface provides usability advantages.

Abstract: A ground fault relay, especially useful to detect motor leakage currents due to insulation failure. The invention operates in two (2) modes. The first mode is a “look-ahead” mode where possible motor circuit insulation failure is detected prior to the electrical motor being turned on, and the second mode is “real time” mode which detects leakage currents after the motor is turned on and during running of the motor. Processing circuitry is disclosed which enables a user to set predetermined values of leakage current to be detected and to trip the relay after comparison of the leakage current and the predetermined value, if the former is larger than the latter. This invention is able to accurately detect extremely small values of ground leakage current without experiencing nuisance tripping due to extraneous noise.

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 phase monitor for a short-circuited asynchronous three-phase motor comprises a first and a second sensing unit, both of which are connected to a supply voltage line to the motor in order to sense the voltage conditions on the line, and a control switch which is controlled by the two sensing units and connected in a control circuit for a supply voltage switch for the motor, connected in the supply voltage line. When the supply voltage line is connected to a supply voltage source, the first sensing unit causes an immediate switching-on operation of the control circuit if the voltage conditions on the supply voltage line sensed by the first sensing unit at that moment are acceptable.

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: Static isolator for the DC supply circuit of a load (MO) in the event of a surge, consisting of a dipole intended to be inserted into the power circuit of the load and comprising means for detecting a surge (R1, R2, T3, CI), means for filtering and storing the supply voltage (C, R1), means for cutting off the supply to the load (T3, R2, R8, R9, T4, T1, R7, R4), means for detecting the disappearance of the supply voltage (C, R1, R3, R6, T6) and means for erasing the storage means (R2, R6, T3, T6).

Abstract: Apparatus for protecting and starting a three-phase motor uses the three-phase field rotation torque produced by three voltage coils, connected to a three-phase power supply, spaced 120 degrees apart from each other, acting on an aluminum disk having a limited range of rotation. When a start button is pushed connecting the voltage coils in wye configuration, the tendency of the disk to turn is converted to an electrical signal for starting the motor. The apparatus prevents the motor from starting if phase energization is abnormal or phase rotation is not in a predetermined direction. The present apparatus also provides continuous monitoring of the motor with three-phase rotation torque produced by three current coils, which are connected in series with the motor and, in one embodiment, may be wound around the same cores as the voltage coils.

Abstract: An overload protecting device which includes a comparator 11 to which an output voltage V10 in proportion to the current flowing through a motor 5 and a start detecting reference voltage E11 are inputted, and a comparator 13 to which the output voltage V10 and an overload detecting reference voltage E13 are inputted, a starting timer 14 for clocking a first period of time T1 lapsing since the output of a signal from the comparator 11, an overload timer 14 for clocking a second period of time T2, which is shorter than the first period of time T1, lapsing since the output of a signal from the comparator 13, a transient finish detecting circuit 300 for outputting a signal V33 representing a finish of transient of the motor 5 finish based on signal outputted from the comparators 11 and 13, and an overload trip relay 18 for cutting off a motor current to the motor 5 through the logical operation of the signal V33 representing motor transient finish or an output signal V12 from the starting timer 12, with an output

Abstract: A portable electric working machine of the present invention includes a motor case portion housing an electric motor, a working portion driven by the electric motor, a handle connected to the motor case portion or the working portion and a power source switch disposed within a grip portion of the handle. Electric power is supplied to the electric motor through the power source switch. A spark-preventing capacitor accommodated within the motor case portion is interposed between a pair of terminals of the electric motor. The portable electric working machine of the present invention does not require a large-sized grip portion of a handle, and can prevent a locking of contacts of a power source switch due to contact transition by preventing sparking between the contacts so that a small-sized microswitch can be used.

Abstract: A turn-on control circuit having a comparator supplied with a turn-on voltage increasing gradually during the turn-on phase of a device for protection. When the control voltage reaches a predetermined value, the comparator supplies a diagnostic enabling signal to a diagnostic stage, which, in the event an undesired condition is detected at an output of the device, supplies a clamp enabling signal to the control terminal of a clamping transistor located between the input of the circuit and ground, and which, when enabled, prevents the turn-on voltage from increasing further, and so prevents the device from being turned on.

Abstract: A system which drives a compressor of a refrigeration system at one or more speeds. The system includes a motor having a stationary assembly and a rotatable assembly. The stationary assembly includes windings adapted to be commutated in at least one preselected sequence. The rotatable assembly is in magnetic coupling relation to the stationary assembly and in driving relation to the compressor. The motor drives the compressor at a desired speed corresponding to a speed select signal representative of one of the speeds. The system further includes an application specific integrated circuit (ASIC) connected to the motor. The ASIC receives the speed select signal and is responsive to it for generating a commutation reference signal. The commutation reference signal in combination with the commutation signal generates a peak current demand signal and thereby cause the motor to operate at the desired speed.

Abstract: In a relay device, a first PTC thermistor has one end connected to a first external connecting terminal, and the other end connected to one end of a second PTC thermistor, the other end of which is connected to a second external connecting terminal, and the thermo-switch is thermally coupled to the first and second PTC thermistors, and connected in parallel with the second PTC thermistor. The thermo-switch is held closed when not heated, and is opened by heat generated by the first or second PTC thermistor. Therefore, the relay device is low in initial resistance, and small in power consumption during heat balance.

Abstract: A circuit for protecting the ac generator and/or load of a diesel-engine generator set is provided. Included is a circuit for measuring indications of the current in each phase of the ac generator, and a switching circuit for protecting the ac generator if the current in any phase is greater than a predetermined current for a predetermined length of time (overcurrent), or if the current in any phase is less than a predetermined function of the currents in each of the phases for the predetermined length of time (imbalance). The circuit which protects the ac generator preferably short circuits the field winding of the ac generator and thereby turns off the ac generator, and/or closes a fuel valve to effectively turn off the engine should the current imbalance or overcurrent be sensed. In conjunction with the protection circuit, a switch interlock and/or circuit breaker arrangement for shock protection is provided.

Abstract: In an apparatus for safety monitoring of protective arrangements with normal or enhanced safeguard for machinery performing multiple-axis rotations with shutoff contactors in the power supply section of the machine and an external monitoring circuit for safety hoods, contact, and manual permission for limited rotation, it is proposed that a power supply unit and a control unit, each in separate subhousings, be arranged in a basic device, with a plug contact connection being provided between the two that is separable and serves for interposed series connection of further supplementary monitoring units, with each monitoring unit monitoring certain shaft circuits of the target system and delivering its output signals in parallel on continuous tie lines guided via the respective plug contact means to the power supply unit, which activates shutoff contactors located in the power section of the target system via output relays.

Abstract: A three-phase power monitor operates a contactor between a supply of three phase electrical power and a three phase load. A phase integrity detector has three inputs connected respectively to the three phases of the electrical power. If a loss, reversal, or dissymmetry is detected, a photoemitting device is actuated. Actuation can also result from low or high line frequency. A power supply circuit is input with the three phases of power and has an output providing a dc level corresponding to the voltage level of the three-phase electrical power. A hold circuit has a first time constant associated with it and attains a hold level when current is applied to its input, but reverts to a release level after this current ceases. An interrogator circuit is coupled to the power supply and to the input of the hold circuit and provides a periodic recharge current to the hold circuit at a period that is shorter than the period of the hold circuit.

Abstract: In order to drive the stepper motor of a floppy disk drive with practically constant current in the face of fluctuations in supply voltage fed from a host system, a power control pulse generator circuit is provided which produces a series of power control pulses having a duty ratio dependent upon fluctuating supply voltage. The power control pulses are used for interrupting the excitation of the stepper motor windings during track seek operation. The power control pulses are generated by first repeatedly counting clock pulses from the host system to a predetermined number to provide periodically varying digital data, then translating the digital data into a triangular wave having an amplitude dependent upon the supply voltage, and then comparing the triangular wave with a reference voltage.

Abstract: A circuit for protecting the ac generator and/or load of a diesel-engine generator set is provided. Included is a circuit for measuring indications of the current in each phase of the ac generator, and a switching circuit for protecting the ac generator if the current in any phase is greater than a predetermined current for a predetermined length of time, or if the current in any phase is less than a predetermined function of the currents in each of the phases for the predetermined length of time. For diesel-engine generator sets which generate three phase 460 V at up to thirty amperes continuously, the preferred predetermined overcurrent for any phase of the ac generator is thirty-five amperes, and the predetermined length of time (to permit inrush currents) is five seconds. Preferably the current in any phase should be less than fifty percent of the average of the current in the three phases.