JPH04325827A - Faint ground fault distribution line recognizing system - Google Patents

Abstract

PURPOSE:To realize recognition of faintly grounded distribution line without interrupting an FCB and to realize uninterruptible recognition of faintly grounded distribution line which has not been realized yet. CONSTITUTION:A ground voltage detecting section detects a ground voltage Vo and a zero-phase current detecting section detects zero-phase currents I01-I0n of respective distribution lines. When a ground voltage monitoring section 18 detects increase of the ground voltage Vo, a recognition operating section 22 is actuated. A faintly grounded distribution line is then specified based on the zero-phase currents I01-I0n of respective distribution lines and the directions of the zero-phase currents I01-I0n are determined from the phases of the zero- phase currents I01-I0n at a current direction detecting section 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high voltage distribution line protection technology in distribution substations, and more particularly to a device for recognizing a slight ground fault distribution line in which a slight ground fault has occurred.

0002

2. Description of the Related Art FIG. 2 shows a detection device for protecting against ground faults in power distribution lines.

[0003] In this device, a ground potential transformer (GPT) 2 and a ground fault overvoltage relay are connected to a plurality of distribution lines 1-1 to 1-n (usually 5 to 8 distribution lines) connected to one bank. (OVG)3 is installed. Each distribution line 1-1
~1-n, protective circuit breakers 4-1~4-n are installed, and furthermore, zero-phase current transformers (ZCT) 5-1~5-n and earth fault direction relay (DG) 6-1 ~6-n are installed.

FIG. 3 shows the ground fault current that flows during a ground fault accident. Here, it is assumed that a ground fault has occurred in the distribution line 1-1 among the distribution lines 1-1 to 1-n.

Since the distribution lines 1-1 to 1-n each have a ground capacitance C1 to Cn, if a ground fault occurs in the distribution line 1-1, the healthy distribution lines 1-2 to 1-n There is a zero-sequence current (earth fault current) I0 in the direction from the load side to the power supply side.
2 to I0n flow, and all of these currents I02 to I0n flow into the distribution line 1-1.

[0006] Therefore, ZCT5-1 of distribution line 1-1
The zero-sequence current I01 detected in the direction from the power supply side to the load side has a value shown in the following equation (1).

I01=I02+I03+...+I0n
...(1) Here, assuming that the ground capacitances C1 to Cn of each distribution line are all equal, the zero-sequence current I0 of the faulty distribution line is equal to the zero-sequence current I0 flowing to other healthy distribution lines. (n-1) times, and has the largest value among all distribution lines.

[0008] When a ground fault occurs, DG and O
VG is activated and protective measures are taken. In other words, DG6-1 operates under the condition that the zero-sequence current I01 is larger than a predetermined value (the operating sensitivity of DG6-1) and the direction of the current is from the power supply side to the load side. The ground fault distribution line is identified as 1-1. Furthermore, O.V.
FCB4-1 is cut off on the condition that G3 performs a backup operation.

However, if the resistance at the ground fault point is relatively large, a micro-ground fault condition occurs in which only a small zero-sequence current flows. At this time, if the I0 value does not reach the operating sensitivity of the DG, the OVG
Even if DG 3 operates, DG 6-1 does not operate, so the slight ground fault distribution line cannot be identified.

Therefore, in the case of this slight ground fault, conventionally, while monitoring the operation of OVG3, FCB1-1 to FCB1-1-
The slight ground fault distribution line was identified by sequentially cutting off the FCBs until the OVG3 stopped operating (until the slight ground fault condition was resolved).

[0011]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, when identifying a slightly grounded distribution line,
Since the method of sequentially shutting off the CBs 1-1 to 1-n was used, there was a problem in that power outages occurred even on healthy distribution lines. In particular, if the slightly grounded distribution line was the last to be disconnected, all FCBs 1-1 to 1-n of one bank would be disconnected, resulting in a wide-scale power outage similar to the bank total power outage accident. Ru.

[0012] In recent years, due to the social environment where the use of OA, FA, HA, etc. is progressing, high reliability of power supply is required, but the above-mentioned problems are a factor that impedes the reliability of power supply.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a slight ground fault distribution line recognition device that can identify a slight ground fault distribution line without causing a power outage to a healthy power distribution line.

[0014]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides recognition of slightly grounded distribution lines for a plurality of distribution lines connected to the same bank at a distribution substation. The apparatus for carrying out this test is constructed by the following means.

(1) A ground fault voltage detection section that detects the ground fault voltage applied to the ground fault overvoltage relay of the bank.

(2) A zero-sequence current detection section that detects the zero-sequence current of each distribution line.

(3) A current direction detection section that determines the phase of each zero-sequence current with reference to the ground fault voltage and detects the direction of each zero-sequence current.

(4) A ground fault voltage monitoring unit that monitors the ground fault voltage and notifies a start command when the ground fault voltage exceeds a reference value.

(5) The operation is started by a start command, and the zero-sequence current of each distribution line is compared and determined. A recognition calculation unit that recognizes a slightly grounded distribution line on the condition that it is oriented sideways. Here, it is possible to determine whether the zero-sequence current is larger than the threshold value by determining the magnitude of the difference or ratio between the two.

[0020]

[Operation] When a slight ground fault occurs in a certain distribution line, a slight ground fault current flows through all the distribution lines in the same bank. This slight ground fault current flows from a healthy power distribution line to a slight ground fault distribution line. Therefore, in a distribution line with a slight ground fault, the current value is the largest compared to a healthy distribution line, and in a healthy distribution line, the current in a slight ground fault flows from the load side to the power supply side, whereas In distribution lines, the flow is in the opposite direction.

In view of this phenomenon, in the present invention, a slightly grounded distribution line is recognized based on the ground fault voltage detected by the ground fault voltage detection section and the zero-sequence current detection section and the zero-sequence current of each distribution line. .

That is, the ground fault voltage is monitored by the ground fault voltage monitoring unit to detect a rise in the ground fault voltage, and the detection of the ground fault voltage rise is used as a trigger to start recognizing a slightly ground fault distribution line. Then, the recognition calculation unit evaluates the magnitude of each zero-sequence current by comparing the zero-sequence current in each distribution line with a reference value, and the current direction detection unit evaluates the zero-sequence current obtained from the phase of the zero-sequence current. Identify the slightly grounded distribution line by considering the direction of the ground.

[0023]

[Embodiment] An embodiment of the present invention will be described below based on FIG.

FIG. 1 shows the configuration of a slight ground fault recognition device according to an embodiment of the present invention.

[0025] This device is installed in a power distribution substation,
V0 detected by GPT2 (see Figure 2) and ZCT5-1
-5-n (see FIG. 2) detects I01 to I0n to recognize a slight ground fault distribution line.

The analog input switching unit 7 receives V0, I01 to I0n input via the auxiliary PT 8 and the auxiliary CT 9.
is input to the A/D converter 10. The A/D converter 10 converts V0, I01 to I0n into digital values. V0 grasping section 11 and I0 grasping section 1
2 is for grasping (holding) V0 and I0, respectively.

The I0 phase determining section 13 determines the phase of I0 with respect to V0 based on the sampling value of V0 and the sampling value of I0.

[0028] The smoothing calculation units 14 and 15 each have V0
, I0, a smoothing operation is performed in units of a fixed number of samples. By performing this smoothing calculation, the V0 measurement value and I0 measurement value from which the influence of sudden abnormal values has been removed can be obtained. The I0 value display section 16 displays the smoothed I0 value.

The V0 value setting section 17 holds a set V0 value for starting slight ground fault recognition. This setting V0 value is
This is the upper limit threshold of the V0 value, and can be set to any value corresponding to the micro-ground fault state that is the detection target.

The V0 value monitoring section 18 monitors the V0 value from the smoothing calculation section 14 based on the set V0 value, and determines that V0 is excessive when this V0 value exceeds the set V0 value. The alarm section 19 outputs an alarm upon receiving this V0 excessive determination, and is provided as necessary. Here, a configuration is shown in which an alarm is output based on the V0 excessive determination by the V0 value monitoring unit 18, but means is separately provided for monitoring the smoothed V0 value based on the set V0 value for alarm, It is also possible to adopt a configuration in which an alarm is output based on the monitoring results. In this case, it is also possible to set multiple levels of alarm levels and perform an alarm output operation according to the level of the smoothed V0 value.

The starting unit 20 receives the V0 from the V0 monitoring unit 18.
Upon receiving an excessive determination or a slight ground fault recognition execution command from the manual command section 21, a starting command is notified to the slight ground fault distribution line recognition calculation section 22. The manual command section 21 is for manually inputting a slight ground fault recognition execution command.

The slight ground fault distribution line recognition calculation section 22 starts its operation upon receiving a startup command, and recognizes a slight ground fault distribution line based on a predetermined determination logic. The slightly ground fault distribution line output unit 23 is composed of relays and other output elements, and outputs the recognition result of the slightly ground fault distribution line recognition calculation unit 22 to a display device or FCB control device (not shown) in the substation. It is.

The I0 reference value setting section 24 sets the I0 (I01 to I0n) reference value for recognizing a slight ground fault distribution line. This I0 reference value is based on the measurement results of the residual I0 (I01 to I0n) values of each distribution line during normal times.
It is set in advance for each value of 01 to I0n, and can be changed arbitrarily to correspond to changes in the power distribution system state.

The FCB state grasping section 25 receives the current FCB ON/OFF state signal from the outside and transfers it to the slight ground fault distribution line recognition calculation section 22 . This FCB state grasping section 25 can be omitted depending on the determination logic.

After the one-time slight ground fault distribution line recognition operation is completed, the reset command unit 26 instructs the slight ground fault distribution line recognition calculation unit 22
This initializes the .

Next, the operation of this device will be explained.

The V0 value monitoring section 18 constantly monitors the V0 value. When a slight ground fault occurs in the distribution line, the V0 value increases. The V0 value monitoring section 18 detects this increase in the V0 value and notifies the starting section 20 of this, and upon receiving this, the starting section 20
starts the calculation operation of the slight ground fault distribution line recognition calculation unit 22. In addition, even if the V0 monitoring unit 18 does not operate, if the operator determines that it is necessary to perform slight ground fault distribution line recognition, the manual command unit 21 can input a startup command.
It is also possible to activate the slight ground fault distribution line recognition calculation unit 22.

The slightly ground fault distribution line recognition calculation unit 22 receives the I0 phase θ from the I0 phase determination unit 13, the smoothed I0 value from the smoothing calculation unit 15, the I0 reference value from the I0 reference value setting unit 24, and the FCB. Based on the FCB ON/OFF status signal from the status grasping unit 25, a slight ground fault distribution line is recognized using a predetermined determination logic, and the slight ground fault distribution line is identified.

This recognition result is notified to the operator on a display device in the substation, or is output to the FCB control device to shut off the FCB of the slightly grounded distribution line. When the recognition operation is completed, the slight ground fault distribution line recognition calculation unit 22 is initialized by a reset command.

[0040] Next, the determination logic in recognizing a slight ground fault distribution line will be explained.

In this device, based on the following discrimination logic,
We will identify whether or not a ground fault has occurred on each distribution line.

(1) There is a start command.

[0043] Occurrence of a slight ground fault is detected by an increase in the V0 value and a startup command is notified, and upon receiving this startup command, a recognition operation is performed when a slight ground fault occurs.

(2) The current I0 is directed from the power supply side to the load side.

[0045] The direction of current I0 is I with reference to the V0 value.
It can be determined by the phase θ of 0 value. The direction of the slight earth fault current is
As mentioned above, in a healthy distribution line, the direction is from the load side to the power supply side, and in a slightly grounded distribution line, the direction is from the power supply side to the load side. It is possible to recognize whether

(3) Compare the I0 reference value and the I0 value (smoothed I0 value) for each distribution line, and the comparison result satisfies a predetermined condition.

[0047] Since the I0 value is large in a slightly grounded distribution line, each I0 value should be compared with the I0 reference value, and the line with the largest deviation (difference or ratio) between the two should be recognized as a slightly grounded distribution line. Can be done. Specifically, any of the following can be adopted as the above-mentioned predetermined conditions.

(a) The difference ΔI0 between the I0 reference value and the I0 value is equal to or greater than a certain value and is the largest compared to ΔI0 for other distribution lines.

(b) The ratio r between the I0 reference value and the I0 value is equal to or greater than a certain value, and is maximum compared to r for other distribution lines.

(c) Both conditions (a) and (b) above are satisfied.

(4) FCB is inserted.

This can be determined from the FCB on/off state signal. Note that this condition can also be omitted.

(5) The I0 value is the largest compared to the I0 values of other distribution lines. This condition can also be omitted.

[0054]

[Effects of the Invention] As explained above, according to the present invention, the ground fault voltage of the bank and the zero-sequence current of each distribution line are detected, the recognition operation is performed using these values, and the magnitude of the zero-sequence current is detected. Since the distribution line with a slight ground fault can be identified based on the direction of the fault, it is possible to recognize the distribution line with a slight ground fault without interrupting the FCB, and it is possible to detect a slight ground fault due to uninterrupted power, which was previously impossible. It becomes possible to recognize power distribution lines.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a slight ground fault recognition device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the configuration of a protection detection device against a ground fault in a power distribution line.

FIG. 3 is an explanatory diagram showing how a ground fault current flows during a ground fault accident.

[Explanation of symbols]

2...GPT 5-1~5-n...ZCT 13...I0 phase discrimination section 17...V0 value setting section 18...V0 value monitoring section 20...Starting part 22...Slight ground fault distribution line recognition calculation unit 24...I0 reference value setting section

Claims (1)

[Claims] Claim 1: A device for recognizing a slightly grounded distribution line in multiple distribution lines connected to the same bank at a distribution substation, which detects the ground fault voltage applied to the ground fault overvoltage relay of the bank. A ground fault voltage detection part detects the zero-sequence current of each distribution line, a zero-sequence current detection part detects the zero-sequence current of each distribution line, and the phase of each zero-sequence current is determined based on the ground fault voltage, and the direction of each zero-sequence current is determined. a current direction detection unit that monitors the ground fault voltage and notifies a start command when the ground fault voltage exceeds a reference value; This system compares and determines the zero-sequence current of the ground, and recognizes a slightly grounded distribution line on the condition that the zero-sequence current is larger than the reference value and the direction of the zero-sequence current is from the power supply side to the load side. What is claimed is: 1. A slight ground fault distribution line recognition device, comprising: a recognition calculation unit that performs