Method for detecting earth faults and frequency converter system with earth fault detection
AssigneeHitachi Energy Ltd
InventorsDan Wu, Beat Buchmann, Christian Schlegel
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Abstract
A method of detecting earth faults, at a frequency converter connected between a first grid operating at a first frequency and a second grid operating at a different, second frequency, comprises determining a common mode voltage at the side of the converter connected to the second grid, determining levels of components of the first frequency and the second frequency in the common mode voltage, and determining if the levels are above pre-set threshold levels, indicating that an earth fault is present at the side of the converter connected to the grid operating at the respective frequency.
Claims13
A method of detecting earth faults at a frequency converter connected between a first grid and a second grid, wherein the first grid operates at a first frequency and the second grid operates at a different, second frequency, the method comprising:
- determining a common mode voltage at a side of the converter connected to one of the grids,
- determining levels of components of the first frequency and the second frequency in the common mode voltage, wherein determining the level of the component of the first frequency comprises applying a first filtering procedure on the common mode voltage and wherein determining the level of the component of the second frequency comprises applying a second filtering procedure on the common mode voltage,
- determining if the levels are above pre-set threshold levels, indicating that an earth fault is present at the side of the converter connected to the grid operating at the respective frequency, and
- initiating a protection action at the side of the converter where the earth fault is indicated to be present or at both sides of the converter.
A frequency converter system with selective earth fault detection, comprising
- a frequency converter connected between a first grid configured to operate at a first frequency and a second grid configured to operate at a second frequency,
- a voltage sensor for determining a common mode voltage, the voltage sensor being connected between the frequency converter and one of the grids, and
- a processing device for determining levels of components of the first frequency and the second frequency in the common mode voltage and for determining if the levels are above pre-set threshold levels, wherein determining the level of the component of the first frequency comprises applying a first filtering procedure on the common mode voltage and wherein determining the level of the component of the second frequency comprises applying a second filtering procedure on the common mode voltage.
Dependencies are inferred from the claim text.