The invention relates to a method, electrical circuit arrangements and insulation monitoring devices for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter. Switching-frequent interfering signals, which are caused by operating the converter, are identified and assessed in a measured displacement voltage independently of the detection of a measuring signal in order to derive a switching (off) signal if required. Complementary thereto, an interfering resistance with respect to low-frequency interfering portions generated by the converter is attained by these low-frequency interfering portions being generated from a replica of a pulse width modulation signal of the converter and being suppressed sufficiently via subtraction that a monitoring without gaps (frequency) of the insulation resistance becomes possible.

The invention relates to a method, electrical circuit arrangements and insulation monitoring devices for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter. Switching-frequent interfering signals, which are caused by operating the converter, are identified and assessed in a measured displacement voltage independently of the detection of a measuring signal in order to derive a switching (off) signal if required. Complementary thereto, an interfering resistance with respect to low-frequency interfering portions generated by the converter is attained by these low-frequency interfering portions being generated from a replica of a pulse width modulation signal of the converter and being suppressed sufficiently via subtraction that a monitoring without gaps (frequency) of the insulation resistance becomes possible.

A ground fault detection circuit can include a band-pass filter that can have a first node and a second node that can be coupled to an earth ground. The first node can be coupled to a local ground of an automatic test equipment (ATE) system for an electrical device that can be coupled via at least one wire to the ATE. The band-pass filter can be configured to pass and amplify a test current signal established at the first node in response to a coupling of one of a conductor of the at least one wire carrying the test current signal to the local ground, and a conductive element of the electrical device carrying the test current signal to the local ground. A fault alert signal can be provided to provide an indication of ground fault based on a comparison of the amplified test current signal.

Devices herein may include conductor lines connected between a power supply and load, each of the conductor lines coupled to an AC contactor and a contactor control circuit, wherein the contactor control circuit is operable to open and close one or more contactors of the AC contactor. The devices may further include a current transformer coupled to the conductor lines, the current transformer operable to output a secondary current corresponding to a primary current magnitude of an electrical current not flowing to the load, wherein the AC contactor is connected between the power supply and the load. Devices may further include a zero cross detection circuit operable to generate an interrupt at each of a plurality of zero crossings for a microprocessor, and determine whether to open the one or more contactors of the AC contactor in a predetermined optimum interval calculated with respect to the zero crossing points.

Devices herein may include conductor lines connected between a power supply and load, each of the conductor lines coupled to an AC contactor and a contactor control circuit, wherein the contactor control circuit is operable to open and close one or more contactors of the AC contactor. The devices may further include a current transformer coupled to the conductor lines, the current transformer operable to output a secondary current corresponding to a primary current magnitude of an electrical current not flowing to the load, wherein the AC contactor is connected between the power supply and the load. Devices may further include a zero cross detection circuit operable to generate an interrupt at each of a plurality of zero crossings for a microprocessor, and determine whether to open the one or more contactors of the AC contactor in a predetermined optimum interval calculated with respect to the zero crossing points.

First voltage an output unit generates a cyclic voltage that changes cyclically, and applies the cyclic voltage to the other end of a coupling capacitor via a first resistance. A second resistance and a third resistance are connected in series between a node and a second voltage output unit, the node being between the coupling capacitor and the first resistance. A voltage measurement unit measures a voltage at a voltage dividing point between the second resistance and the third resistance. In a period in which two types of fixed voltages are applied to the voltage dividing point in order, a diagnosing unit determines whether a leakage detecting device is in a normal state, based on the voltage measured by the voltage measurement unit.

First voltage an output unit generates a cyclic voltage that changes cyclically, and applies the cyclic voltage to the other end of a coupling capacitor via a first resistance. A second resistance and a third resistance are connected in series between a node and a second voltage output unit, the node being between the coupling capacitor and the first resistance. A voltage measurement unit measures a voltage at a voltage dividing point between the second resistance and the third resistance. In a period in which two types of fixed voltages are applied to the voltage dividing point in order, a diagnosing unit determines whether a leakage detecting device is in a normal state, based on the voltage measured by the voltage measurement unit.

In order to quickly and accurately diagnose the failure of a coupling capacitor of an earth leakage detection device, voltage output unit (11a, OP1) generates a periodically changing periodic voltage and applies the periodic voltage to the other end of coupling capacitor (Cc) via first resistor (R1). Second resistor (R2) and third resistor (R3) are connected in series between a connection point between coupling capacitor (Cc) and first resistor (R1), and a predetermined fixed potential. Voltage measurement unit (11b) measures a voltage at a voltage dividing point between second resistor (R2) and third resistor (R3). Diagnosis unit (11d) determines whether or not coupling capacitor (Cc) is normal based on a voltage measured when switch (MRp, MRm, MRpp) is turned on in a state where voltage output unit (11a, OP1) outputs a fixed voltage.

A common point ground fault detector monitors an outlet. The detector includes a power connection having at least hot, neutral, and ground leads for connecting to the outlet, a bench ground connector, an earth ground, to which both the ground lead and the bench ground connector are electrically connection, and through which the bench ground connector discharges electrostatic charge, and a switch electrically coupled between the earth ground and the bench ground connector. The switch enables an electrical connection between the earth ground and the bench ground connector in response to a normal operating condition of the outlet, and the switch disables the electrical connection between the earth ground and the bench ground connector in response to an abnormal operating condition of the outlet.

A system for ground fault detection includes an alternating current (AC) excitation source configured to provide an AC test signal to a circuit under test; a current transformer configured to detect a current of the AC test signal; a capacitive pickup configured to detect a voltage of the AC test signal; and a receiver which includes a display; and a processor configured to receive the voltage from the capacitive pickup; receive the current from the current transformer; and display on the display one or more components of the current.