JP2011141203A - Ground fault detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ground fault detection device capable of detecting a ground fault current in a DC source circuit with high sensitivity. <P>SOLUTION: In the ground fault detection device 1, a control circuit 11 measures an inter-ground voltage V<SB>P</SB>at a P side of a DC source E and an inter-ground voltage V<SB>N</SB>at an N side thereof and calculates an unbalance ratio α which a ratio of the inter-ground voltage V<SB>P</SB>at the P side to the inter-ground voltage V<SB>N</SB>at the N side. The control circuit determines whether or not the calculated unbalance ratio α exceeds a predetermined threshold T. When it is determined that the unbalance ratio α exceeds the predetermined threshold T, the control circuit determines that the ground fault current flows in the DC current circuit 10 so as to detect the ground fault. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ground fault detection device that detects a ground fault in a DC power supply circuit.

  2. Description of the Related Art Conventionally, electric devices and control devices in power plants, substations, and the like have a DC power supply circuit, and power is supplied to the electric devices and the control device by the DC power supply circuit. In a DC power supply circuit, an insulation failure may occur during a period of high humidity such as a rainy season, and a ground fault may occur.

  In order to prevent such a ground fault accident, a technique for protecting a DC power supply circuit with a circuit for detecting a change in voltage by a DC ground fault detection relay (64D), a sensor for detecting a change in current, or the like has been proposed ( For example, see Patent Documents 1 to 3).

JP-A-7-55869 Japanese Patent Laid-Open No. 4-151574 JP 58-165622 A

  However, the techniques described in Patent Documents 1 to 3 such as a circuit for detecting a change in voltage by a DC ground fault detection relay (64D) and a sensor for detecting a change in current detect the ground fault current in the DC power supply circuit. Since the detection level is low, there are many cases where the ground fault current cannot be detected when a ground fault occurs due to a high resistance, such as a cable insulation failure. Therefore, a ground fault current flows into the DC power supply circuit, and a ground fault accident occurs, for example, a fuse associated with the DC circuit of the control device is disconnected. When such a ground fault occurs, it takes time to recover from a failure of the electrical device or its control device.

  Accordingly, an object of the present invention is to provide a ground fault detection device capable of detecting a ground fault current in a DC power supply circuit with high sensitivity.

  The ground fault detection device of the present invention is a ground fault detection device for detecting a ground fault in a DC power supply circuit, and measures positive side voltage measuring means for measuring a voltage between the positive sides of the DC power source constituting the DC power supply circuit. And negative voltage measuring means for measuring the negative side ground voltage of the DC power source, and an unbalance for calculating an unbalance rate that is a ratio of the positive side ground voltage and the negative side ground voltage. The unbalance rate is determined by the rate calculation means, the unbalance rate determination means for determining whether the unbalance rate calculated by the unbalance rate calculation means exceeds a predetermined threshold, and the unbalance rate determination means. And a ground fault determining means for detecting the ground fault by determining that the ground fault current is flowing in the DC power supply circuit when it is determined that the predetermined threshold value is exceeded. .

  According to the present invention, the unbalance rate that is the ratio of the positive side ground voltage and the negative side ground voltage is calculated, and it is determined whether or not the calculated unbalance rate exceeds a predetermined threshold. When it is determined that the unbalance rate exceeds a predetermined threshold, a ground fault is detected by determining that a ground fault current is flowing in the DC power supply circuit.

  Here, as a result of obtaining the relationship between the unbalance rate and the ground fault resistance at the time of the occurrence of the ground fault, the unbalance rate is clear between the normal time and the time of the ground fault occurrence even when the value of the ground fault resistance is high. It turned out that it becomes a different value.

  Therefore, since the ground fault detection device of the present invention determines whether or not the ground fault current flows using the unbalance rate, even if the value of the ground fault resistance when the ground fault occurs is high, It can be determined that a fault current is flowing, and a ground fault can be detected with high sensitivity.

  Further, the unbalance rate calculation means includes a first unbalance rate that is a ratio of the positive side ground voltage to the negative side ground voltage, and the negative side ground relative to the positive side ground voltage. A second unbalance rate that is a ratio of the voltage between the two is calculated, and the unbalance rate determination means determines whether or not the first unbalance rate and the second unbalance rate exceed a predetermined threshold value. The ground fault determination means determines that the ground fault current flows on the positive electrode side of the DC power supply when it is determined that the first unbalance rate exceeds the predetermined threshold. When it is determined that the second unbalance rate exceeds the predetermined threshold, it is preferable to determine that the ground fault current is flowing on the negative electrode side of the DC power supply.

  According to this invention, when it is determined that the first unbalance rate exceeds the predetermined threshold value, the ground fault determination means determines that the ground fault current flows on the positive electrode side of the DC power supply, When it is determined that the unbalance rate of 2 exceeds a predetermined threshold, it is determined that a ground fault current is flowing on the negative electrode side of the DC power supply.

  As a result, the ground fault detection device of the present invention uses the first unbalance rate and the second unbalance rate to cause a ground fault on the positive electrode side or the negative electrode side of the DC power source, or It can be determined whether a ground fault has occurred in the power supply circuit.

  ADVANTAGE OF THE INVENTION According to this invention, the ground fault detection apparatus which can detect the ground fault in a DC power supply circuit with high sensitivity can be provided.

It is a circuit diagram which shows the structure of the ground fault detection apparatus 1 which is one Embodiment of this invention. It is a figure which shows the process at the time of determining whether the ground fault has generate | occur | produced in the control circuit. Is a graph showing the relationship between the unbalance index α and ground fault resistance r _g.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a ground fault detection apparatus 1 according to an embodiment of the present invention. Circuit diagram of FIG. 1, the positive electrode side of the DC power source E that constitutes a DC power supply circuit 10, a ground fault is generated, and shows a state when the ground fault current I _g flows.

As shown in FIG. 1, the ground fault detection device 1 of the present embodiment detects a ground fault current of the DC power supply circuit 10. DC power supply circuit 10 includes a DC power source E, a resistor _{R 1,} a resistor _{R 2,} a resistor _{R D,} and a ground fault resistor _{r g.} The ground fault detection apparatus 1 includes a control circuit 11 (positive side voltage measurement means, negative side voltage measurement means, unbalance rate calculation means, unbalance rate determination means, ground fault determination means).

The resistor R ₁ and the resistor R ₂ are connected in series with the DC power source E. One end of the resistor R ₁ is connected to the P side (positive electrode side) of the DC power source E, and the other end is connected to the resistor R ₂ . Resistor R ₂ has one end connected to the N side of the DC power source E (negative side), is connected to the other end and a resistor R _1.

Resistor R _D has one end connected between the resistors R ₁ and R _2, the other end connected to ground.
The control circuit 11, P-side of the resistor _{R 1,} and connected to the N side of the resistor _{R 2,} the ground voltage _{V P} to be described later, and measurable configured ground voltage _{V N.}

At the time of ground fault occurs, the DC power supply circuit 10, are deemed to grounding resistor r _g is generated. Fault resistance r _g has one end connected to the positive electrode side of the resistor R _1, the other end is connected to ground (GND).
During ground fault occurs, the ground-side ground fault resistor r _g, and the ground side of the resistor R _D is electrically connected, the ground fault current I _g is through the ground from the ground-fault resistance r _g, the resistance R _D And flow. At this time, the current I ₀ flows in the DC power source E, and the current I flows in the resistor R ₁ .

In the ground fault detection device 1 of the present embodiment, the control circuit 11 detects the ground fault current by executing the following process when the ground fault occurs as described above.
First, when a ground fault occurs, the control circuit 11 measures the P-side ground voltage V _{P of} the DC power source E that constitutes the DC power source circuit 10 and the N-side ground voltage V _N of the DC power source E.

Here, the ground voltage V _N at the ground voltage V _P and the negative electrode side of the positive electrode side may be using equation (1) and (2) below, is measured. Note that the resistance values of the resistors R ₁ and R ₂ are R.

Then, the control circuit 11 calculates the unbalance rate α based on the measured P-side ground voltage V _P and N-side ground voltage V _N. Specifically, the control circuit 11 uses an unbalance rate α, which is a ratio of the measured P-side ground voltage _VP and the N-side ground voltage V _N , using the following equation (3). To calculate.

In the normal state (equilibrium state) of the DC power supply circuit 10, since the ground fault resistance r _g = ∞, α≈1 in Expression (3).
Then, the control circuit 11 determines whether or not the calculated unbalance rate α exceeds a predetermined threshold T.

Specifically, the control circuit 11 sets the unbalance rate α ₁ (first) as a ratio of the measured P-side ground voltage _VP and the N-side ground voltage V _N as the unbalance rate α. ) And α ₂ (second unbalance rate) are used. The unbalance rates α ₁ and α ₂ are calculated using the following equations (4) and (5). As shown in the equations (3) and (4), the unbalance rate α and the unbalance rate α ₁ are the same value.

FIG. 2 is a diagram illustrating processing in the control circuit 11 when determining whether or not a ground fault has occurred.
As shown in FIG. 2, the control circuit 11 determines whether or not the calculated unbalance rates α ₁ and α ₂ exceed a predetermined threshold T (T = 1.5). The control circuit 11, when the unbalance rate alpha ₁ exceeds a predetermined threshold T, it is determined that the ground fault current flows to the P side, detects that the ground fault is occurring on the P side. The reason for T = 1.5 will be described later.

On the other hand, the control circuit 11 detects that the unbalance index alpha ₂ is when exceeding the predetermined threshold T, it is determined that the ground fault current on the N side is flowing, ground fault has occurred in the N side To do.
In addition, the control circuit 11 determines that the ground fault current does not flow when the unbalance rates α ₁ and α ₂ do not exceed the predetermined threshold T.

  When the control circuit 11 detects that a ground fault has occurred on the P side or N side of the DC power supply circuit 10, for example, an alarm device causes a ground fault on the P side or N side of the DC power supply circuit 10. An alarm is displayed to indicate that it has occurred.

Figure 3 is a graph showing the relationship between the unbalance index α and ground fault resistance r _g. 3, the vertical axis represents the unbalance index alpha, the horizontal axis shows the ground fault resistance r _g. The unbalance rate α was calculated assuming that R ₁ = R ₂ = ₂₀ kΩ and R _D = 10 kΩ.

As shown in FIG. 3, the results of the obtained relation between the unbalanced ratio alpha and fault resistance r _g, when the ground fault resistance r _{g =} 80k ohms, the unbalanced ratio alpha = 1.5. In other words, since the unbalance rate α has a change of about 150% with respect to the equilibrium state (α≈1), the value is clearly different between the normal state (equilibrium state) and the occurrence of ground fault (unbalanced state). Become. Thereby, the control circuit 11 can detect whether or not the ground fault current flows by setting the predetermined threshold T to T = 1.5.

  Thus, the ground fault detection apparatus 1 of the present embodiment can detect a ground fault even if the ground fault resistance is about 80 kΩ.

As described above, according to the ground fault detection apparatus 1 of the present embodiment, the control circuit 11 measures the P-side ground voltage _VP and the N-side ground voltage V _N of the DC power source E, and P The unbalance rate α, which is the ratio of the side-to-ground voltage _VP and the N-side ground voltage V _N , is calculated. Then, the control circuit 11 determines whether or not the calculated unbalance rate α exceeds a predetermined threshold T, and when it is determined that the unbalance rate α exceeds the predetermined threshold T, the DC power supply circuit 10, the ground fault is detected by determining that the ground fault current is flowing.

  Here, as described above, as a result of obtaining the relationship between the unbalance rate and the ground fault resistance at the time of occurrence of the ground fault, the unbalance rate is the same as that at normal time even when the value of the ground fault resistance is high. It was found that the values were clearly different at the time of occurrence.

Therefore, the ground fault detector 1 of the present embodiment, in order to determine whether the ground fault current is flowing with unbalanced ratio alpha, when the value of the ground-fault resistance r _g when a ground fault occurs is high Even if it exists, it can be determined that the ground fault current is flowing, and the ground fault can be detected with high sensitivity.

Further, according to the ground fault detection device 1 of the present embodiment, the control circuit 11 determines that the ground fault current is on the P side of the DC power source E when it is determined that the unbalance rate α ₁ exceeds the predetermined threshold T. determines that is flowing, if the unbalance rate alpha ₂ is determined to exceed the predetermined threshold T, it is determined that the ground fault current is flowing in the N side of the DC power source E, an unbalanced ratio alpha When it is determined that ₁ and the unbalance rate α ₂ do not exceed the predetermined threshold T, it is determined that no ground fault current is flowing in the DC power supply circuit 10.

Thus, the control circuit 11 uses the unbalance rate α ₁ and the unbalance rate α ₂ to cause a ground fault on the P side or the N side of the DC power supply circuit 10 or in the DC power supply circuit 10. Whether or not a ground fault has occurred can be determined.

  As mentioned above, although one Embodiment of this invention was described, this invention is not restrict | limited to embodiment mentioned above, It can change suitably. The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 1 Ground fault detection apparatus 10 DC power supply circuit 11 Control circuit (positive side voltage measurement means, negative side voltage measurement means, unbalance rate calculation means, unbalance rate determination means, ground fault determination means)

Claims (2)

A ground fault detection device for detecting a ground fault in a DC power supply circuit,
A positive side voltage measuring means for measuring a voltage between the positive side of the DC power source constituting the DC power source circuit and a ground;
Negative voltage measuring means for measuring the voltage between the negative electrode side ground of the DC power supply,
An unbalance rate calculating means for calculating an unbalance rate that is a ratio of the voltage between the ground on the positive electrode side and the voltage between the ground on the negative electrode side;
Unbalance rate determination means for determining whether or not the unbalance rate calculated by the unbalance rate calculation means exceeds a predetermined threshold;
When the unbalance rate is determined by the unbalance rate determination means to exceed the predetermined threshold, the ground fault is detected by determining that a ground fault current is flowing in the DC power supply circuit. A ground fault detection device comprising a fault determination means. The unbalance rate calculating means includes:
A first unbalance factor that is a ratio of the positive-side ground voltage to the negative-side ground voltage, and a second unbalance ratio that is a ratio of the negative-side ground voltage to the positive-side ground voltage. Calculate the equilibrium rate,
The unbalance rate determination means includes
Determining whether the first unbalance rate and the second unbalance rate exceed a predetermined threshold;
The ground fault determination means includes
If it is determined that the first unbalance rate exceeds the predetermined threshold, it is determined that the ground fault current is flowing on the positive electrode side of the DC power supply,
2. The method according to claim 1, wherein when it is determined that the second unbalance rate exceeds the predetermined threshold, it is determined that the ground fault current flows on a negative electrode side of the DC power supply. Ground fault detection device.

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