Method and system for monitoring impedance in a conductor
AssigneeHella GmbH & Co. KGaA
InventorAlan Wayne Brown
Life of this patent
Estimating the term…
Abstract
A method for monitoring the line impedance of a protective earth (“PE”) conductor is provided. The method injects a small stimulus current at a frequency much higher than the grid frequency. The stimulus current circulates in the loops between a grid-connected device and a grid source, creating small voltage drops in the grid conductors, resulting in a common mode voltage which can be measured. The method then includes measuring the common mode voltage and the residual current at a point of common coupling (“PCC”). The method then includes monitoring the resistive and reactive parts of the line impedance. For example, the method can monitor the line impedance and report a broken PE conductor or a high PE resistance, beyond a given threshold where safety becomes a concern.
Claims19
A method comprising:
- providing a protective earth circuit between a grid voltage and a grid-connected device, the protective earth circuit including a protective earth conductor;
- applying a stimulus current to the protective earth conductor, the stimulus current including a stimulus frequency, the stimulus frequency being greater than a grid frequency;
- measuring a common mode voltage and a residual current at a point of common coupling between the grid voltage and the grid-connected device;
- determining an impedance at the point of common coupling based on the measured common mode voltage and the measured residual current, the impedance including a reactive component and a resistive component;
- and
- generating an alert in response to the measured impedance at the point of common coupling exceeding a predetermined threshold.
A system comprising:
- a plurality of current carrying wires electrically coupled to a grid voltage and a grid-connected device, each of the grid voltage and the grid-connected device including a protective earth terminal;
- a protective earth conductor electrically coupled to the protective earth terminal of the grid voltage and the protective earth terminal of the grid-connected device;
- and
- a protective earth monitoring circuit for monitoring an impedance of the protective earth conductor, the protective earth monitoring circuit comprising:
- a stimulus injector that is configured to apply a stimulus current to the protective earth conductor, the stimulus current including a stimulus frequency, the stimulus frequency being greater than a frequency of the grid voltage,
- a measurement circuit for measuring a common mode voltage and a residual current in the plurality of current carrying wires;
- and
- a processor coupled to the output of the measurement circuit, the processor being configured to calculate the impedance of the protective earth conductor based on the measured common mode voltage and the measured residual current.
Dependencies are inferred from the claim text.