JPH0772742B2 - DC control circuit Ground fault detection sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC control circuit ground fault detection sensor which prevents malfunction due to an AC component induced in a DC control circuit.

[0002]

2. Description of the Related Art In a power generation and substation, a plurality of direct current control circuits using a direct current voltage of 100 V as an operating power source are formed in order to control the operation of generators, transformers, and electrical equipment such as various devices. The contacts and operating coils that make up the DC control circuit are scattered at respective positions within the power generation and substation, and these contacts and operating coils are connected and connected by a control cable. In the DC control circuit, when the contacts, operating coils, connection points, etc., which are the constituent elements, are deteriorated or malfunction, insulation deterioration may occur and a ground fault may occur. This ground fault is generally a minor one (micro-ground fault) in the initial stage, but if left unattended, it will cause a short-circuit of the DC power supply or burnout of the device due to the spread of the fault, so early in the early stage. It is necessary to search for and remove the faulty part. That is, from a plurality of DC control circuits,
It is necessary to identify the ground fault line, quickly search for the fault point, and eliminate it. As one means for achieving this object, there is a DC control circuit ground fault discriminating device.

As shown in FIG. 2, the DC control circuit ground fault discriminating apparatus 1 is connected between the midpoint of two resistors connected to a DC power source and the ground, and is installed on the DC board 2. The failure detection relay 64D and the ground fault detection sensor Sg installed in the NFB board 3 are respectively guided to the contacts of the failure detection relay 64D and guided to the failure detection relay 64D and the ground fault. It detects and displays the ground fault occurrence line from the operation of the detection sensor Sg, and is installed on the ground fault detection device installation board 5. In FIG. 2, 6 is a battery / charging device panel.

As shown in FIG. 3, the ground fault detection sensor Sg is controlled by connecting exciting coils of _two current transformers CT ₁ and CT ₂ of the same rating in antiparallel and exciting them by an AC exciting power source AC. Connect the cables P and N to two current transformers CT ₁ and CT ₂
As two inputs to the current transformers CT ₁ and CT ₂ ,
The output coils of the _two current transformers CT ₁ and CT ₂ are connected in series to detect the ground fault of the DC control circuit based on the presence / absence of a difference in output current. The difference between the output currents is converted into a voltage through the resistor and the operational amplifier OA.

When there is no ground fault, the current I supplied from the control cable P returns to the control cable N through the load L, as shown in FIG. 3 (a). In the two current transformers CT ₁ and CT ₂ penetrating, the control cables P and N
Since the currents are the same and in opposite directions, there is no magnetomotive force due to the current I, and magnetomotive forces Φ ₁ and Φ ₂ due to the AC excitation power supply AC.
Exists, the output W _{1 of} the _two current transformers CT ₁ and CT ₂ ,
W ₂ is generated by magnetomotive forces Φ ₁ and Φ ₂ . Figure 3
As shown in (b), in the H-Φ curve, the AC magnetic field Ha generated by the AC excitation power supply AC changes around Ho, and the magnetomotive forces Φ ₁ and Φ _{2 of the two} current transformers CT ₁ and CT ₂ are changed. Are equal. Therefore, the output W of the current transformers CT ₁ and CT _{2
Since 1} and W ₂ are equal, no output is generated in the operational amplifier OA.

When there is a ground fault, as shown in FIG. 4 (a), the current I supplied from the control cable P is a ground fault current Ig flowing from the ground fault point (flows to the failure detection relay 64D circuit). .), Only I-Ig returns to the control cable N. Therefore, a difference occurs in the control cables P and N by the amount of the ground fault current Ig, and in the current transformers CT ₁ and CT ₂ , the magnetic field due to this difference current and the magnetic field due to the AC excitation power source AC are superimposed. That is, as shown in FIG. 4B, H-Φ
In the curve, the AC magnetic field Ha generated by the AC excitation power source AC centered on Ho shifts, and the DC magnetic field H caused by the difference current shifts.
An alternating magnetic field Ha centered on d is obtained. The magnetic flux Φ is set to be saturated in the alternating magnetic field + Ha. Therefore, when there is a ground fault, the current transformers CT ₁ and CT ₂
Outputs W ₁ and W ₂ are different from each other, and an output is generated in the operational amplifier OA. In this way, the ground fault is detected by the presence or absence of the output of the operational amplifier OA.

In FIGS. 3 and 4, the exciting coils of the _two current transformers CT ₁ and CT ₂ are connected in antiparallel and the output coils are connected in series, but the exciting coils are connected in series. Similar effects can be obtained by connecting the output coils in antiparallel.

[0008]

In this prior art, the ground fault is detected by the current imbalance of the control cables P and N at the time of the ground fault, but the current imbalance of the control cables P and N is generated. -It also occurs when induction components are superimposed on the DC control circuit due to the influence of various AC power sources in the substation. That is, the AC induction component flows to the ground through the ground capacitance C. In this case, the ground fault current I
The same action as that in which g flows is performed, and the ground fault detection sensor Sg malfunctions even though no ground fault has occurred. As long as there is no actual ground fault, even if the ground fault detection sensor Sg malfunctions, the failure detection relay 64D does not operate, so there is no problem. However, when the ground fault detection sensor Sg is malfunctioning, a ground fault occurs in another DC control circuit, the ground fault detection sensor Sg of the DC control circuit operates normally, and the failure detection relay 64D operates, The fault generating circuit cannot be discriminated.

The present invention has been made for the purpose of solving the problems of the prior art.

[0010]

Means for solving the above problems will be described below with reference to FIG. 1 corresponding to the embodiment. According to the present invention, the exciting coils of the _two current transformers CT ₁ and CT ₂ are excited by an AC excitation power source AC, and the control cables P and N are passed through the _two current transformers CT ₁ and CT ₂ to form two coils. In the DC control circuit ground fault detection sensor for detecting the ground fault of the DC control circuit by the difference between the output currents of the current transformers CT ₁ and CT ₂ , the control cables P and N are connected to the current transformer CT ₃ for induction detection.
AC current induced in the control cables P and N is detected at the output side of the current transformer CT ₃ for inductive detection and converted into a reverse polarity, which is converted into two current transformers C.
Two current transformers CT ₁ and CT ₂ are provided via a feedback cable F that passes through T ₁ and CT ₂ and a current transformer CT ₃ for inductive detection.
And the current transformer CT ₃ for inductive detection.

[0011]

In the structure thus constructed, the magnetic field due to the alternating current component induced in the control cable P or N is canceled by the magnetic field due to the reverse polarity alternating current component returned to the feedback cable F.

[0012]

1 is a diagram showing an embodiment of the present invention. In FIG. 1, CT ₃ is a current transformer for inductive detection and F is a return cable.

The exciting coil of the current transformer CT ₃ for inductive detection is opened, and the output coil is connected to the resistor R ₃ and the operational amplifier OA ₃ . Output current is resistor R ₃ and operational amplifier OA
₃ , through the resistor R and the like, it has the same value as the AC component induced in one of the control cables P, N that is the input of the current transformer CT ₃ for induction detection, and is converted to the opposite polarity.

The feedback cable F has one end connected to the output side of the operational amplifier OA ₃ via a resistor R, and the other end having two current transformers CT ₁ and CT ₂ and a current transformer CT ₃ for induction detection. It penetrates and is grounded. What is also passed through the feedback cable F induction detecting current transformer CT ₃ is to cancel the output of the induction detecting current transformer CT ₃ by the negative feedback of induced AC component.

When an AC component is induced in one of the control cables P and N, the induction detecting current transformer CT ₃ detects the induced component by causing a current to flow to the output side thereof, and the current is detected via the operational amplifier OA _3. The induced component is reversed in polarity. The induced component having the opposite polarity is connected to the two current transformers CT ₁ via the feedback cable F.
Returned to CT ₂ . Therefore, two current transformers CT ₁ ,
In CT ₂ , the magnetic field due to the induced alternating current component is canceled by the returned magnetic field due to the reverse polarity alternating current component.
Therefore, no output is generated in the operational amplifier OA due to the AC component induced in the DC control circuit. That is, no malfunction occurs due to the induced alternating current component.

[0016]

As described above, the present invention is
The exciting coils of the two current transformers are excited by an AC excitation power source, and the control cable is passed through the two current transformers,
In the DC control circuit ground fault detection sensor for detecting the ground fault of the DC control circuit by the difference in the output current of the individual current transformers, the control cable is passed through the current transformer for inductive detection and is guided to the control cable. An alternating current component is detected at the output side of the current transformer for inductive detection and converted into a reverse polarity, which is passed through the two current transformers and a feedback cable penetrating the current transformer for inductive detection. And is fed back to the two current transformers and the current transformer for inductive detection. Therefore, the magnetic field due to the alternating current component induced in the control cable is canceled by the magnetic field due to the reverse polarity alternating current component returned to the feedback cable. Therefore, according to the present invention, it is possible to obtain an effect of avoiding a malfunction due to the induced alternating current component.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a DC control circuit ground fault determination device.

FIG. 3 is a diagram showing a ground fault detection sensor in normal times,
(A) is a figure which shows a state, (b) is a magnetic field-magnetic flux curve.

4A and 4B are diagrams showing a ground fault detection sensor at the time of a ground fault accident or AC induction, wherein FIG. 4A is a diagram showing a state and FIG. 4B is a magnetic field-flux curve.

[Explanation of symbols]

CT ₃ Current transformer for inductive detection F Return cable

Claims (1)

[Claims] 1. A DC control circuit in which exciting coils of two current transformers are excited by an AC exciting power source, a control cable is passed through the two current transformers, and a difference in output current of the two current transformers is used. In the DC control circuit ground fault detection sensor for detecting the ground fault of, the control cable is passed through the induction detecting current transformer, and the AC component induced in the control cable is output from the induction detecting current transformer. At the same time and converted to the opposite polarity, and the two current transformers and the one for the induction detection through a feedback cable that passes through the two current transformers and the one for the induction detection. DC control circuit ground fault detection sensor characterized by being fed back to a current transformer