An electric-wire protection device that protects an electric wire by cutting off power to the wire when its temperature is elevated above a predetermined value is presented. The device includes switching means to control the conduction of power to the wire, current measuring means to measure a current in the wire, environment temperature detecting means to detect a temperature of the environment surrounding the wire, electric-wire temperature calculating means to calculate the temperature of the wire using the value of the current in the wire and the environment temperature, limiting means to stop the conduction of power to the wire when the temperature is greater than or equal to a predetermined value, peripheral component current measuring means to measure the current flowing to a component at the periphery of the environment temperature detecting means, thermal influence acquisition means to obtains an amount of temperature increase caused by the component at the environment temperature detecting means, and environment temperature correcting means to correct the environment temperature based on the amount of temperature increase.

An emulating device for emulating a bimetallic strip, the emulating device comprising a current sensor capable of measuring a line current (I.sub.P) flowing through the emulating device, the emulating device being capable of providing a value representative of a cumulative thermal state over time t, which value is referred to as cumulative thermal state, by recursively adding a value representative of an initial thermal state, which value is referred to as initial thermal state, and a value representative of a present thermal state, which value is referred to as present thermal state, which is determined on the basis of the line current (I.sub.P).

An emulating device for emulating a bimetallic strip, the emulating device comprising a current sensor capable of measuring a line current (I.sub.P) flowing through the emulating device, the emulating device being capable of providing a value representative of a cumulative thermal state over time t, which value is referred to as cumulative thermal state, by recursively adding a value representative of an initial thermal state, which value is referred to as initial thermal state, and a value representative of a present thermal state, which value is referred to as present thermal state, which is determined on the basis of the line current (I.sub.P).

A switch device includes a switching element that connects/disconnects a current path from a power supply terminal to a ground terminal via a load, and an overcurrent protection circuit that limits output current flowing in the switching element to be an overcurrent limit value or less. When an output short circuit of the load is detected, the overcurrent protection circuit decreases the overcurrent limit value to be lower as a power supply voltage is higher. In addition, the switch device preferably includes a switching element that connects/disconnects a current path from a power supply terminal to a ground terminal via a load, an intermittent control unit that intermittently drives the switching element when an abnormality is detected, and an output voltage monitoring portion that disables the intermittent control unit until an output voltage applied to the load reaches its target value.

A switch device includes a switching element that connects/disconnects a current path from a power supply terminal to a ground terminal via a load, and an overcurrent protection circuit that limits output current flowing in the switching element to be an overcurrent limit value or less. When an output short circuit of the load is detected, the overcurrent protection circuit decreases the overcurrent limit value to be lower as a power supply voltage is higher. In addition, the switch device preferably includes a switching element that connects/disconnects a current path from a power supply terminal to a ground terminal via a load, an intermittent control unit that intermittently drives the switching element when an abnormality is detected, and an output voltage monitoring portion that disables the intermittent control unit until an output voltage applied to the load reaches its target value.

In a power distribution device, a current detection circuit detects a current value of a current flowing through a wire. When a switch is on, a microcomputer determines whether or not a predetermined condition is satisfied, based on the current value detected by the current detection circuit. If it is determined by the microcomputer that the predetermined condition is satisfied, a drive circuit turns off the switch.

An overcurrent protection device is for protecting a load arranged in a DC grid. The load is coupled to a supply busbar, which is connectable to a supply potential of the DC grid, in the DC grid via the overcurrent protection device. The overcurrent protection device is designed to ascertain a current trigger value based upon a detected value of a current flowing through the overcurrent protection device and a trigger characteristic which is assigned to the load and is based on the current; compare the current trigger value with a threshold, and either trigger the overcurrent protection device or not, based upon the result of the comparison. The current is taken into consideration together with a first or a second factor in the trigger characteristic based upon the current direction.

According to an embodiment, a current monitoring circuit includes a signal shaping unit configured to receive a current sense signal and provide a modified current signal; a filter configured to receive the modified current signal and to provide a respective filtered signal; a comparator configured to receive the filtered signal and a threshold value and to indicate when the filtered signal exceeds the threshold value. The signal shaping unit is configured to calculate a level of the modified current signal from a corresponding level of the current sense signal in accordance with non-linear function.

In a method for monitoring a winding temperature of a winding of an electric machine powered by a converter, a heating power applied to the winding of the electric machine is determined and evaluated using a thermal model. A relative increase in a resistance of the winding, when the winding heats up, is determined from the heating power in comparison with a standard reference value for 20° C. winding temperature. The winding temperature is calculated from the relative increase in the resistance, and a warning signal and/or a switch-off signal is generated when a critical winding temperature value is exceeded.

In a method for monitoring a winding temperature of a winding of an electric machine powered by a converter, a heating power applied to the winding of the electric machine is determined and evaluated using a thermal model. A relative increase in a resistance of the winding, when the winding heats up, is determined from the heating power in comparison with a standard reference value for 20° C. winding temperature. The winding temperature is calculated from the relative increase in the resistance, and a warning signal and/or a switch-off signal is generated when a critical winding temperature value is exceeded.