JP2009038929A - Dc ground-fault detection device and multiplex dc power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a ground-fault detection device of each system operates due to sneak ground fault current at a DC ground fault, and a ground-fault circuit cannot be discriminated, in a multiplex DC power supply circuit which feeds power to loads in parallel constantly. <P>SOLUTION: The DC ground-fault detection circuit having two sets of resistors connected in series between a positive electrode and a negative electrode of a DC power supply circuit, and a grounding circuit for grounding a middle point of the two sets of resistors via a third resistor, and detecting the DC ground fault by using a current flowing in the grounding circuit, comprises: backflow preventing elements 10A, 10B through which currents flow toward the middle point of the resistors from the positive electrode; and backflow preventing elements 11A, 11B through which currents flow toward the negative electrode from the middle point of the resistors. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to ground fault detection of DC control power sources such as substations and power plants, and more particularly to ground fault detection of multiplexed DC power sources.

In general, a DC control power source of a substation, a power plant or the like (hereinafter referred to as an “electric station”) is configured by connecting a plurality of batteries and setting 110V to 125V as a rated voltage. In particularly important electric stations, a DC power supply circuit is provided in a first series and a second series, and is multiplexed, for example, by duplication. (In the following description, it is shown as an example in the case of duplication, and is expressed by A series and B series.) As a method of detecting the ground fault of the DC power supply circuit, a resistance of about 10 kΩ between the positive electrode and the negative electrode is 2 A method is used in which a ground fault is detected by connecting a series connection, grounding an intermediate point thereof through a resistor of about 10 kΩ, and detecting that a ground current flows through the grounded circuit. FIG. 2 shows an example in which a DC power supply is duplicated and supplied to a load by an equivalent circuit. The DC power supply circuit 1 includes an A series and a B series, and is connected to a load 6 via a diode 2 in order to prevent contact. The DC power supply circuits 1A and 1B are respectively provided with DC ground fault detection circuits 7A and 7B. Resistors 3 and 4 are connected between the positive electrode and the negative electrode, and grounded via the resistor 5 from the intermediate point. Although a small current Il flows through the resistors 3 and 4 at all times, no current flows through the resistor 5. Here, when the ground fault 8 occurs on the positive electrode side of the DC power supply circuit 1A, the ground fault current Ifa flows through the resistor 5A through the grounding point, so that the DC ground fault can be detected. As another method for detecting a defect in a DC power supply, Patent Document 1 proposes a method for monitoring a voltage.
JP-A-5-328606

  In the double DC power supply circuit as shown in FIG. 2, when a ground fault occurs, the power circuit in which the ground fault has occurred is disconnected as quickly as possible, and operation is performed using the power circuit on the healthy side. I want to continue. Therefore, it is necessary to reliably determine the side where the ground fault has occurred with the doubled DC power supply. However, the method of FIG. 2 has a problem in that a ground fault current wraps between the DC power supply circuits 1A and 1B, and both the DC ground fault detection circuits 7A and 7B detect ground faults. FIG. 3 shows the wraparound of the ground fault current Ifb to the DC power supply circuit 1B when a ground fault occurs on the positive electrode side of the DC power supply circuit 1A. From the positive electrode of the DC power supply circuit 1A via the grounding point, it returns to the negative electrode of the DC power supply circuit 1A via the resistors 5B and 3B, the diode 2 and the load 6. FIG. 4 shows the wraparound of the ground fault current I'fb to the DC power supply 1B when a ground fault occurs on the negative electrode side of the DC power supply circuit 1A. From the positive electrode of the DC power supply circuit 1A, the diode 2, the load 6, the resistors 4B and 5B, and the grounding point are returned to the negative electrode side of the DC power supply circuit 1A from the ground fault point 9. Due to the above wraparound route, in the case of a ground fault on the DC power supply circuit 1A side, there arises a problem that not only the DC ground fault detection circuit 7A but also 7B detects the ground fault. On the other hand, in addition to having a large capacity, the DC control power supply of an electric station has a constant voltage fluctuation of about 10% of the rating, and when the charger is operated, the voltage may be close to 130% at the maximum. Therefore, the method for monitoring the voltage described in Patent Document 1 cannot accurately detect a failure of a DC power supply circuit that is a control power supply for an electric station.

  In order to solve the above problem, the present invention connects two sets of resistors in series between the positive electrode and the negative electrode of a DC power supply circuit, and grounds the midpoint of the two sets of resistors via a third resistor. In a DC ground fault detection circuit having a ground circuit, a reverse current blocking element having a forward direction flowing from the positive electrode toward the middle point of the resistor, and a forward direction flowing from the middle point of the resistor to the negative electrode. And a reverse flow blocking element.

  According to the present invention, when a ground fault occurs in the multiplexed DC power supply circuit, the ground fault detection circuit of the sound side DC power supply circuit can be prevented from wrapping around, and the ground fault power supply can be prevented. Discrimination and disconnection are facilitated, and it is possible to continue operation of the electric facility with a sound power source.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 shows an embodiment of the present invention. The description of the same elements as those already described with reference to FIG. In FIG. 1, 10A and 10B are elements (diodes or the like) for passing a current flowing through 3A and 3B from the positive electrode toward the middle point of the resistance connection and blocking the reverse direction. Further, 11A and 11B are elements (such as diodes) for passing a current flowing from 4A and 4B toward the negative electrode from the middle point of the resistance connection and blocking the reverse direction. In FIG. 1, the position 10 is between the positive electrode and the resistor 3, but may be an intermediate point between the resistor 3 and the resistor connection. Similarly, although the position 11 is between the resistor 4 and the negative electrode, it may be between the middle point of the resistor connection and the resistor 4.

  By this element, the ground fault sneak currents Ifb and I'fb shown in FIGS. 3 and 4 are blocked and do not flow. As a result, the ground current flows only in the DC detection circuit on the side where the ground fault occurs, and only the DC ground fault device of the circuit operates.

  Further, in the first embodiment, the example of the DC power supply circuit in which the DC power supply circuit having the above-described DC ground fault detection device is duplicated is shown. However, the DC power supply circuit in which the DC power supply circuit is tripled or multiplexed is used. Even when configured and supplied to a load, a multiplexed DC power supply circuit can be configured in which even if a ground fault occurs, the ground fault generating side circuit can be easily identified.

The figure which shows the 1st Example of this invention A diagram showing a conventional dual DC power supply circuit The figure which shows the wraparound of the ground fault current when the ground fault occurs in the positive electrode of the DC power supply circuit The figure which shows the wraparound of the ground fault current when the ground fault occurs in the negative electrode of the DC power supply circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... DC power supply circuit 2 ... Diode 3 ... Positive side connection resistance 4 ... Negative side connection resistance 5 ... Middle point ground resistance 6 ... Load 7 ... DC ground fault detection circuit 8 ... DC power supply circuit positive electrode side ground fault point 9 ... DC power supply circuit negative electrode side ground fault point 10, 11 ... Reverse current blocking element (diode etc.)

Claims (3)

  A pair of resistors connected in series between a positive electrode and a negative electrode of a DC power supply circuit, and having a ground circuit that grounds an intermediate point of the two sets of resistors through a third resistor, and a current flowing through the ground circuit In the DC ground fault detection circuit that detects a DC ground fault, a reverse current blocking element whose forward direction is a direction flowing from the positive electrode toward the intermediate point of the resistor, and a direction of flow from the intermediate point of the resistor toward the negative electrode A DC ground fault detection device comprising: a backflow prevention element in a forward direction.   2. A direct current power supply circuit comprising a double direct current power supply circuit, wherein the two direct current power supply circuits are always connected to the same load, wherein the direct current detection device according to claim 1 is provided in each direct current power supply circuit. Duplex DC power supply circuit.   2. A DC power supply circuit comprising three or more DC power supply circuits, wherein the three or more DC power supply circuits are always connected to the same load, and each DC power supply circuit includes the DC detection device according to claim 1. A multiplexed DC power supply circuit characterized.

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