Motor overload protection device is equipped with a thermal monitor that can determine expected rotor temperature rise from rotor resistance estimates. The thermal monitor determines expected rotor temperature rise by using a correlation between rotor temperature rise computed from rotor resistance estimates, and motor thermal state estimates. The correlation can be derived by fitting a line to a plurality of points, with each point defined by an ordered pair composed of a rotor temperature rise estimate and a corresponding motor thermal state estimate, and determining a slope of the line. This rotor temperature slope can then be used by the thermal monitor to determine a rotor temperature rise given a rotor resistance estimate and a corresponding motor thermal state estimate. If the rotor temperature rise exceeds an expected rotor temperature rise by more than a predefined threshold, the thermal monitor issues an alarm and/or takes corrective actions in some embodiments.

An induction motor overheat monitoring method and device detects overheating of an induction motor from a detection value of a current sensor. A resistance calculation relationship data indicating a relationship between a resistance and a feature amount at the time of starting of the induction motor and a determination reference value for determining overheating are stored in advance. At each starting, a current of the induction motor is detected, a signal regarding a phase angle difference is calculated, and a feature amount of the motor is calculated from the signal regarding the phase angle difference. Further, a resistance of the induction motor is calculated by using the feature amount of the motor and the resistance calculation reference data stored in advance. Then, a temperature of the induction motor is calculated from the resistance of the induction motor, and it is determined if the motor is overheated.

A power supply control apparatus includes: a semiconductor switching element switched with PWM control; a PWM signal output unit outputting a PWM signal; a current circuit outputting a current related to a current flowing through the semiconductor switching element; a filter circuit converting the current that is output from the current circuit to a voltage; an overcurrent protection circuit turning off the semiconductor switching element based on a voltage value of the voltage filtered by the filter circuit; a voltage detection unit detecting the voltage value of the voltage at a timing near an end of a pulse of a PWM signal; a temperature estimation unit estimating, a temperature of an electric wire through which a current flows that also flows through the semiconductor switching element; and an electric wire protection unit turning off the semiconductor switching element based on the temperature estimated by the temperature estimation unit.

An overcurrent protection device is to be provided between a power supply and a load circuit including an electric load and an electric wire electrically connected with each other, and includes a switching element, a current detector, a characteristic estimation portion, and a controller. The switching element switches flowing and interrupting of a load current that flows from the power supply to the electric load. The current detector detects the load current. The characteristic estimation portion estimates a thermal characteristic of the electric wire based on the load current detected by the current detector. The controller outputs an overcurrent protection signal for interrupting the load current so as to protect the load circuit from an overcurrent to the switching element based on the thermal characteristic estimated by the characteristic estimation portion and the load current detected by the current detector.

A circuit breaker includes: at least one switching path of a first terminal of the circuit breaker to a second terminal of the circuit breaker; at least one semiconductor switch arranged in the switching path; a semiconductor version switch for predefinably interrupting the switching path upon actuation by a release of the circuit breaker; a characteristic variable unit connected to the release; and a current measuring arrangement for ascertaining a current profile through the at least one semiconductor switch, the current measuring arrangement being connected with the characteristic variable unit. The characteristic variable unit correlates a characteristic variable with a junction temperature of the at least one semiconductor switch that is ascertained from the current profile through the at least one semiconductor switch.

A power supply system includes: a battery; a master device supplied with power from the battery; and a slave device supplied with power from the master device via a first power supply line. The slave device supplies power to a load via a second power supply line. The master device estimates a temperature of the second power supply line. When the estimated temperature of the second power supply line is higher than a second cutoff threshold, power supply via the second power supply line is cut off.

An embodiment electronic circuit includes an electronic switch comprising a load path, and a control circuit configured to drive the electronic switch. The control circuit is configured to operate in one of a first operation mode and a second operation mode based at least on a level of a load current of the electronic switch. In the first operation mode the control circuit is configured to generate a first protection signal based on a current-time-characteristic of the load current and drive the electronic switch based on the first protection signal. The control circuit is configured to generate a status signal such that the status signal has a wakeup pulse when the operation mode changes from the second operation mode to the first operation mode and, after the wakeup pulse, a signal level representing a level of the load current.

The overload relay units within a motor control group have the timing function for their motor thermal memories under the control of a central controller in communication with the overload relays. Thus expensive timing components and control of timestamps can be removed from individual overload relays. Further reduction of individual overload relay components can be accomplished by removing the nonvolatile memory function from the individual overload relays and allowing the central controller to perform the nonvolatile memory functions for the overload relays. The motor thermal model function for the overload relays can remain in the overload relays or might be moved to the central controller if communication bandwidth permits.

An electric-wire protection device includes a voltage adjustment unit that adjusts the voltage to a load, and a controller that includes a temperature calculation unit that calculates temperature information on an electric wire from a value of current, and makes the voltage adjustment unit into a shut-off state based on the temperature information. The temperature information is calculated from an amount of temperature changes based on the current value and a predetermined initial value. The controller shifts into a sleep state when a sleep condition is satisfied that includes a condition that the temperature information is lower than the initial value. The initial value when the controller returns from the sleep state is based on a convergence value of temperature in conducting energization on the electric wire at a maximum value of steady-state current.

A circuit interrupter for protecting a protected circuit includes separable contacts, an operating mechanism structured to trip open the separable contacts, a current sensor structured to sense a current flowing through the protected circuit, a temperature sensor structured to sense a temperature of the protected circuit proximate the current sensor, and a processor configured to select a trip time based on the sensed current, to adjust the selected trip time based on the sensed temperature, and to cause the operating mechanism to trip open the separable contacts when the adjusted selected trip time is reached.