The invention relates to a method for ascertaining an earth fault and the earth-fault direction in a three-phase network which is operated in a compensated manner or in an insulated manner. Value pairs of a zero voltage and a zero current are measured, the active or reactive energy is calculated, and a voltage flag and a current flag are combined by a Boolean link, wherein the presence of a earth fault is ascertained depending on the result, and a decision is made as to whether the earth-fault direction is signalled as “forward” or “reverse” at least on the basis of the sign of the active or reactive energy.

A power supply apparatus with limited power source capability includes a power path, a current sensing resistor, a control unit, and a switch. The power path is coupled between a transformer and an output port of the power supply apparatus. The current sensing resistor is disposed on the power path. The control unit is coupled to the current sensing resistor. The switch is disposed on the power path. When the control unit determines that a sense voltage of the current sensing resistor is less than a first threshold value and a signal voltage of the control unit is greater than a second threshold value, the control unit turns off the switch.

The invention relates to a method for ascertaining an earth fault and the earth-fault direction in a three-phase network which is operated in a compensated manner or in an insulated manner. Value pairs of a zero voltage and a zero current are measured, the active or reactive energy is calculated, and a voltage flag and a current flag are combined by a Boolean link, wherein the presence of a earth fault is ascertained depending on the result, and a decision is made as to whether the earth-fault direction is signalled as forward or reverse at least on the basis of the sign of the active or reactive energy.

Methods and systems for detecting a falling power line in a power transmission or distribution system are described. Electrical measurements at various points in the power distribution system are used to detect changes in a power line indicating that the conductor has broken or become disconnected. Upon detection, control mechanisms are used to deenergize the conductor while the conductor is falling and/or before it contacts the ground.

The present invention provides a smart overvoltage protection circuit (100) comprising an AC power line (110), at least one switch (120) connected to the AC power line (110) and an overvoltage detection module (130) connected to the at least one switch (120) and the AC power 0 line (110). Further, the overvoltage detection module (130) comprises a voltage divider (210), a sensing circuitry (220) and a control module (230) such that the voltage divider (210) is configured to divide voltage of the AC power line (110) to obtain divided voltage, the sensing circuitry (220) is configured to generate a first output signal and a second output signal 5 and the control module (230) is configured to receive the first output signal and the second output signal and turn the at least one switch (120) from a closed position to an open position in response to receiving the first output signal.

Provided is a control system that can appropriately determine whether or not supply of power to a load is abnormal, and can specify a detailed reason of the abnormality. A control circuit supplies power to a load and shuts off the supply of power in accordance with a power supply/shutoff instruction to supply or shut off power from a battery to the load. The power supply/shutoff instruction is output from a microcomputer to the control circuit. A control unit determines whether or not the supply of power from the battery to the load is abnormal, based on (i) whether the power supply/shutoff instruction output from the output unit is to supply power or shut off the supply of power, (ii) the value of a current flowing from the battery to the load, and (iii) the value of a voltage applied to the load, and specifies a reason of the abnormality.