DC. detection circuit and DC. earthing current detection circuit

Abstract

A direct current detection circuit has a zero-phase current transformer with source lines inserted therethrough for detecting current differences among them and generates a comparison voltage value based on a divided voltage value obtained between the zero-phase current transformer and a voltage divider resistor according to a change in the self-impedance of the zero-phase current transformer. An offset current is passed through the zero-phase current transformer to make it possible to detect on the basis of the comparison voltage value a direct current value in a range which is otherwise difficult to detect accurately on the basis of the comparison voltage value because of influence of hysteresis characteristic of the zero-phase current transformer. A control circuit detects a present direct current value based on the comparison voltage value and the value of the offset current.

Description

technical field [0001] The present invention relates to a direct current detection circuit for detecting a direct current using a zero-phase current transformer (hereinafter abbreviated as ZCT) using a magnetic material such as permalloy, such as detecting whether a direct current grounding current is generated, for example, for connection protection of a connection system device The DC ground current detection circuit. Background technique [0002] In the past, as a DC ground current detection circuit used as such a DC current detection circuit, a technique is known as follows: For example, a connection system device for converting DC power from a DC power supply into AC power, using a converter to detect the current from the DC power supply. The current difference between the current flowing out of the positive side and the current flowing out of the negative side is used to determine whether a DC ground current is generated according to the level of the current difference...

AI Technical Summary

Problems solved by technology

[0016] However, according to the DC ground current detection circuit 107 using such a ZCT 10, under the influence of the hysteresis characteristic of the ZCT 10, in the small current range, for example, as shown in FIG. In the current range (hatched part), for example, in the case of detecting a DC current value of 15 mA, the comparison voltage value V5 becomes two points, and it becomes difficult to detect an accurate DC current value based on the comparison voltage value V5. As a result, Cannot accurately detect whether a DC ground current is generated

[0017] Moreover, not only the DC ground current detection circuit 107, but also the general DC current detection circuit is also affected by the hysteresis characteristic of the ZCT 10, and cannot accurately detect the current DC current value based on the comparison voltage value.

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