The application includes a method to control a leakage current protection device in a photovoltaic apparatus, said photovoltaic apparatus being adapted to be electrically connected to an electric power distribution grid having one or more phase voltages at an AC section of the photovoltaic apparatus. The method includes executing a first control procedure to control the leakage current protection device, the first control procedure providing for a comparison of current check values indicative of leakage currents in the photovoltaic apparatus with one or more predefined current threshold values for the leakage currents. The method includes executing a monitoring procedure to check the phase voltages and identify possible relevant positive transients of the phase voltages. If the monitoring procedure identifies relevant positive transients of the phase voltages, one or more new current threshold values for the leakage currents are provided, the execution of the first control procedure is terminated and a second control procedure to control the leakage current protection device is executed, the second control procedure providing for a comparison of the current check values with the new current threshold values for the leakage currents, the second control procedure being executed for a predefined time interval only. After the predefined period of time has passed, the execution of the second monitoring procedure is terminated and the first control procedure is again executed.

A ground fault overvoltage relay device is configured to: determine whether or not a first condition is satisfied, the first condition being that at least two of line voltages between respective two phases are less than or equal to a first threshold value; determine whether or not a second condition is satisfied, the second condition being that a ratio between a minimum value of the line voltages between the respective two phases and a minimum value of the respective phase voltages is less than or equal to a second threshold value; determine whether or not a third condition is satisfied, the third condition being that the zero-phase voltage is greater than a third threshold value; and lock a ground fault detection output when the first condition is satisfied, or when the second condition is satisfied and the third condition is not satisfied.

A ground fault overvoltage relay device is configured to: determine whether or not a first condition is satisfied, the first condition being that at least two of line voltages between respective two phases are less than or equal to a first threshold value; determine whether or not a second condition is satisfied, the second condition being that a ratio between a minimum value of the line voltages between the respective two phases and a minimum value of the respective phase voltages is less than or equal to a second threshold value; determine whether or not a third condition is satisfied, the third condition being that the zero-phase voltage is greater than a third threshold value; and lock a ground fault detection output when the first condition is satisfied, or when the second condition is satisfied and the third condition is not satisfied.

A method for locating a ground fault in an IT network which has a converter with a rectifier connected to a power transmission network, a DC link and an inverter connected to an electrical machine includes measuring a common-mode voltage property of the converter or of the power transmission network and comparing the common-mode voltage property with an output voltage property of an output voltage of the inverter. When the IT network experiences a ground fault, the comparison of the common-mode voltage property with the output voltage property is used to determine whether a machine area of the IT network connected downstream of the converter, which includes the electrical machine and a connecting line between the electrical machine and the converter, causes the ground fault.

A method for locating a ground fault in an IT network which has a converter with a rectifier connected to a power transmission network, a DC link and an inverter connected to an electrical machine includes measuring a common-mode voltage property of the converter or of the power transmission network and comparing the common-mode voltage property with an output voltage property of an output voltage of the inverter. When the IT network experiences a ground fault, the comparison of the common-mode voltage property with the output voltage property is used to determine whether a machine area of the IT network connected downstream of the converter, which includes the electrical machine and a connecting line between the electrical machine and the converter, causes the ground fault.

The application includes a method to control a leakage current protection device in a photovoltaic apparatus, said photovoltaic apparatus being adapted to be electrically connected to an electric power distribution grid having one or more phase voltages at an AC section of the photovoltaic apparatus. The method includes executing a first control procedure to control the leakage current protection device, the first control procedure providing for a comparison of current check values indicative of leakage currents in the photovoltaic apparatus with one or more predefined current threshold values for the leakage currents. The method includes executing a monitoring procedure to check the phase voltages and identify possible relevant positive transients of the phase voltages. If the monitoring procedure identifies relevant positive transients of the phase voltages, one or more new current threshold values for the leakage currents are provided, the execution of the first control procedure is terminated and a second control procedure to control the leakage current protection device is executed, the second control procedure providing for a comparison of the current check values with the new current threshold values for the leakage currents, the second control procedure being executed for a predefined time interval only. After the predefined period of time has passed, the execution of the second monitoring procedure is terminated and the first control procedure is again executed.

The application includes a method to control a leakage current protection device in a photovoltaic apparatus, said photovoltaic apparatus being adapted to be electrically connected to an electric power distribution grid having one or more phase voltages at an AC section of the photovoltaic apparatus. The method includes executing a first control procedure to control the leakage current protection device, the first control procedure providing for a comparison of current check values indicative of leakage currents in the photovoltaic apparatus with one or more predefined current threshold values for the leakage currents. The method includes executing a monitoring procedure to check the phase voltages and identify possible relevant positive transients of the phase voltages. If the monitoring procedure identifies relevant positive transients of the phase voltages, one or more new current threshold values for the leakage currents are provided, the execution of the first control procedure is terminated and a second control procedure to control the leakage current protection device is executed, the second control procedure providing for a comparison of the current check values with the new current threshold values for the leakage currents, the second control procedure being executed for a predefined time interval only. After the predefined period of time has passed, the execution of the second monitoring procedure is terminated and the first control procedure is again executed.

A method for identifying element failure in capacitor banks is provided. Capacitor bank phase current is measured and a zero-sequence or negative-sequence current is calculated or measured. A three-phase voltage is measured from a three-phase bus voltage transformer and a zero-sequence voltage or negative-sequence voltage is calculated. A compensated unbalance current is calculated and compared to a predetermined acceptable range. A failure is identified where the compensated unbalance current is outside the predetermined acceptable range.

A method for identifying element failure in capacitor banks is provided. Capacitor bank phase current is measured and a zero-sequence or negative-sequence current is calculated or measured. A three-phase voltage is measured from a three-phase bus voltage transformer and a zero-sequence voltage or negative-sequence voltage is calculated. A compensated unbalance current is calculated and compared to a predetermined acceptable range. A failure is identified where the compensated unbalance current is outside the predetermined acceptable range.

Fault classification and zone identification in a power transmission system are described. Voltage or current measurements are obtained at a terminal of the transmission line in each of the three phases measured during a fault. Modal transformations are performed on voltage or current measurements to obtain traveling wave signals with reference to each of the three phases. Based on the magnitude of the traveling wave signals the fault is classified.