JPH0378424A - Distribution-line ground protective device - Google Patents

Abstract

PURPOSE:To specify the number of loop-circuit forming times, etc., and to take a required measure quickly by detecting the presence of relationship, in which zero-phase currents are equal in absolute value and different by 180 deg. in phase, on the basis of the voltage conversion values of zero-phase currents at every distribution line output from a multiplexer. CONSTITUTION:Outputs from corresponding zero-phase current detectors ZCT1- ZCTn are sampled by installing sample-and-hold circuits SH1-SHn in response to each zero-phase current detector ZCT1-ZCTn, zero-phase current information acquired by the sampling is held, and the held zero-phase current information is output selectively by a multiplexer MPX. The presence of relationship in which the absolute values of the zero-phase currents of each distribution line are equalized and the phase of zero-phase currents is 180 deg. is detected by a zero-phase current presence decision means CPU on the basis of the results of the outputs, and the result of the detection is stored in a readable manner. Accordingly, the malfunctions of ground directional relays 67G1-67Gn by zero- phase circulating currents can be predicted while monitoring the number of formation times and period of a loop circuit.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a distribution line that disconnects a distribution line from a busbar of a distribution substation by a ground fault direction relay operated by a zero-sequence current of the distribution line when a ground fault occurs. It relates to ground fault protection devices.

[Conventional technology]

FIG. 2 is a block connection diagram showing a conventional distribution line ground fault protection device. In the figure, 1 is a distribution transformer, 2 is a bus bar of a distribution substation connected to this distribution transformer 1, and L+
, L2. . . . is the distribution line connected to the bus 2 of the distribution substation, CB+, CBz . . . CB is each distribution line, L2. ...The circuit breaker connected between L7 and the busbar 2 of the distribution substation, ZCT, , ZCT, ... ZC
T, G are zero-phase current transformers, and these are connected to each distribution line L+, Lx,
...Ground fault direction relays 67G, 670Z of each distribution line that detects the zero-sequence current of L7 and connects its output to the secondary side
,...67G, l is manually operated. G
PT is a grounding transformer connected to the power distribution bus 2, which includes a ground fault overvoltage relay 64 that operates by detecting the zero-sequence voltage generated in the event of a ground fault, and the above-mentioned distribution line.

L2. . . . The ground fault direction relays 67G+, 6'tat, . . . 67G7 which select the ground fault direction of wrinkles are connected. Also, AND,,AND,,...
AND7 is an AND gate of n pieces, and these are the operation signal Q corresponding to the zero-sequence voltage detected by the ground fault overvoltage relay 64, and each fault direction relay 67G.

67G, , -67G, operating signals P+, Pz,”・
Perform a logical product with P7. To, Tt, . . . T, is a timer T that counts the output time (duration time) of the AND gates AND, , AND, , . . . L+,
Outputs ground fault detection signals of Lx, . . . Lfi. In addition,
This ground fault detection signal is transmitted to the above-mentioned circuit breakers CB, CBz, .
・・CB is used for safety purposes. St, St,...
・S,, is each distribution line,,Ll.

...L, between which is a loop switch connected to each of these predetermined sections, and when it is closed, it connects to the bus 2 of the distribution substation.
Together, they form a loop circuit. In addition, each distribution line...
Sectional switches (not shown) are provided for each predetermined section in L, . . . I-1.

Next, the operation will be explained. First, each distribution line, L,
, . . . If there is no abnormality in any of L7, power is normally supplied to the load connected to each section. On the other hand, each of the above distribution lines.

When a ground fault occurs at any one of Lx, . Therefore, a zero-phase secondary current flows to the ground fault direction relay 67G2 connected to the secondary side of this zero-phase current transformer ZCT2, and a zero-phase voltage is input via the grounding transformer GPT, which causes it to operate. do.

On the other hand, at this time, the ground fault overvoltage relay 64 detects the zero-sequence voltage that occurs at the time of the accident, and outputs the operation signal Q corresponding to this zero-sequence voltage.
AND! with the operation signal Pt of the ground fault direction relay 67G2 and the AND gate AND! Enter. Therefore, the AND gate A N D z outputs a ground fault detection signal and opens the circuit breaker CB z after a predetermined period of time. Note that protection operations for ground faults occurring in other distribution lines , L, . . . Ll are performed in the same manner as described above.

By the way, there may be cases where it is necessary to carry out maintenance and inspection of each of the above-mentioned distribution lines LI+LZ+...Lfi in a limited section, for example, inspection of the distribution line L2 between the circuit breaker CB z and the loop switch S. If so, use the loop switch S
, and the circuit breaker CB.

Even after the circuit breaker CB is opened, power can continue to be supplied to various loads connected to the distribution line L2 through the circuit breaker CB1.

[Problem to be solved by the invention]

Since the conventional distribution line ground fault protection device is configured as described above, when the loop switch S1 is closed in the above-mentioned maintenance 2 inspection activities, two distribution line ground faults, , I,
2. Zero-sequence circulating current due to unbalance of the distribution line strands flows in the loop circuit connecting the bus 2 and the loop switch S of the distribution substation as shown by the arrow. In this case, since no zero-sequence voltage is normally generated, the ground fault direction relay 67 connected to the zero-sequence current transformers ZCT+ and ZCTz
Neither G+ nor 67G malfunction.

However, if a ground fault occurs at fault point F2 in another distribution line while the loop switch is closed, zero-sequence voltage will be generated in the grounding transformer GPT. and the above-mentioned zero-phase circulating current, the ground fault direction relays 61G+, 67 have the phase characteristics as shown in FIG.
If one of Gg malfunctions, AND gate A N D
+ or AND, operation signals Q and P, or P
Outputs 2. Therefore, since circuit breakers CB and CB are not connected to their own lines, one of them opens even though it is not necessary to do so, reducing the power supply capacity of the distribution line and reducing the power supply service. There was a problem.

This invention was made in view of the above-mentioned conventional situation, and provides distribution line ground fault protection in which a ground fault direction relay operated by zero-sequence current trips a breaker in the event of a ground fault to protect the distribution system. The device automatically detects at the distribution line monitoring station at the substation side that the zero-sequence current of each distribution line is based on the above-mentioned loop circuit formation, so that necessary measures can be taken quickly. The purpose is to

[Means to solve the problem]

The distribution line ground fault protection device according to the present invention includes a zero-phase current detector provided corresponding to each of a plurality of distribution lines connected to a bus bar of a distribution substation via a circuit breaker, and thereby Detecting the zero-sequence current flowing in the corresponding distribution line, receiving the output of this zero-sequence current detector, and tripping the corresponding breaker by activating the ground fault direction relay in the event of a ground fault,
In a distribution system in which a loop switch is connected between predetermined distribution lines of each of the above distribution lines, and when the loop switch is closed, it forms a loop circuit with the above bus bar, a sample hold circuit is provided corresponding to each zero-phase current detector. By doing so, the output of the corresponding zero-sequence current detector is sampled, the zero-sequence current information obtained by this sampling is held, this held zero-sequence current information is selectively outputted by a multiplexer, and based on this output result, , the zero-sequence current presence/absence determining means detects whether there is a relationship in which the absolute values of the zero-sequence currents of each distribution line are equal and the phase of the zero-sequence current is 1.80°, and the detection result can be read out. It is designed to be stored.

[For production]

The zero-sequence current presence/absence determination means in the present invention is based on the voltage conversion value of the zero-sequence current for each distribution line outputted by the multiplexer, and determines whether the absolute values of the zero-sequence currents are equal and the phase is 180°. It detects the presence or absence of the loop circuit, outputs data specifying the loop circuit position, the number of loop circuit formations, etc., or estimates the possibility of malfunction of the directional ground fault relay due to zero-sequence circulating current.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 67L is a zero-phase circulating current detection device, T r 1 , T , which is installed in a substation together with the distribution transformer 1 or in a so-called distribution line monitoring station such as a business office.
r z , . . . Tr, each zero-phase current detector (hereinafter referred to as zero-phase current transformer) ZCT, , ZCT,.

...ZCT, the zero-phase current output from each fault direction relay 6
7G+, 67Gz,...67G,, input quadrature transformer R,, R,,...R,1 is the input quadrature Tr++ Trz, current/voltage connected in parallel to the secondary side of Tr3. Conversion resistor, SH,, SH,.

...SH, is a sample hold circuit, MPX is a sample hold circuit S H++ S Hz, ... SH, l
A multiplexer that selects each output one by one, A/
D is an analog/digital converter that digitally converts the output of the multiplexer MPX, ROM is a read-only memory that stores an operation determination program, and RAM is
, is a random access memory that stores various input data, Dlo is a digital output circuit, and CPU is a microprocessor as means for determining the presence or absence of a zero-sequence current. Then, it calculates the number of times the loop circuit is formed, the date and time of the loop circuit formation, and estimates the malfunction of the directional ground fault relay due to the zero-sequence ground fault current.

Note that other parts that are the same as those shown in FIG. 2 are designated by the same reference numerals, and redundant explanation thereof will be omitted.

Next, the operation will be explained. First, each distribution line L+, Lz
, . . . When all wrinkles are normal or when a ground fault occurs in a state where no loop circuit is formed, the circuit breaker CB of the distribution line involved in this fault.

Each operation when CB, . . . , CB is opened is the same as the conventional one. On the other hand, as mentioned above, the distribution line L1゜Lx,
. . . When inspecting L7 in a limited section, one of the loop switches St, S2 . . . S7 is closed to form a loop circuit as described above. For example, when the loop switch S1 is closed, the loop switch S3, the distribution lines L+, Lz, and the bus 2 of the distribution substation
A zero-sequence circulating current flows through the loop circuit created by On the other hand, zero-phase current transformer ZCT,.

Zero-sequence currents having phases different from each other by 180° flow through ZCT, and are input to input transformers Tr+, Trz and ground fault direction relays 67G, 67G2.

In addition, the zero-sequence current input to the input quadrature transformers T r , T r z is converted into voltage by the resistors R+ and Rz, and the zero-sequence current information converted to voltage is sent to each sample and hold circuit S H + S Hz. For example, they are sampled at 30° intervals and, after being held temporally, are taken out one after another by a multiplexer MPX. The zero-phase current data extracted in this way is converted into digital data by an analog/digital converter A/D, and each of these data is once stored in a random access memory RA.
Store it in M.

In addition, the microprocessor CPU generates zero-sequence current according to the program stored in the read-only memory ROM. +
Calculate each absolute value and phase of +Ioz, determine whether there is a relationship such that the absolute values are equal and the phase is 180° as described above, that is, the presence or absence of a loop circuit, and further determine the distribution line where the loop circuit is located, February or daily formation of loop circuits (
The number of occurrences), the hourly period of loop circuit formation, the magnitude of the zero-sequence current, etc. are determined, and the results are stored in the random access memory RAMt. On the other hand, as stored data,
In addition to the above, on/off status of the breaker, construction information, etc. can also be stored, and this stored data can be displayed on a display device if necessary. Furthermore, in the case where the loop circuit is present, if a ground fault occurs in another power distribution line L3, two circuit breakers on this loop circuit are It is also possible to output an operation lock signal K from the digital output circuit D10, which prevents CB, , CB, from being opened as in the conventional case.

In addition, if a failure occurs in the relevant line of the loop, on the condition that the ground fault direction relay 67G of the line other than the relevant loop line is not operating, it is possible to take measures such as not issuing the above-mentioned operation lock signal K. It can be considered as an applied development. Also, from the calculation results by the microprocessor CPU, it is found that the ground fault direction relays 61G+, 61 due to the zero-phase circulating current
It is also possible to predict a malfunction of Gz.

Furthermore, the random access memory RAMZ has a zero-sequence current 1. By storing information such as the size of the accident, the distribution line where the accident occurred, and the date and time, this information can be read out as needed. Furthermore, the zero-phase circulating current detection device 6
7X, random access memory RAM+, RAM
In addition to the contents of z, the practicality can be further improved by storing information such as breaker on/off, sectional switch on/off, and construction information so that all these contents can be monitored.

〔Effect of the invention〕

As described above, according to the present invention, a zero-sequence current detector is provided corresponding to each of a plurality of distribution lines connected to a busbar of a distribution substation via a circuit breaker, and thereby the corresponding distribution By detecting the zero-sequence current flowing through the electric wires and receiving the output of this zero-sequence current detector, the ground fault direction relay is activated in the event of a ground fault, thereby tripping the corresponding circuit breaker, and disconnecting the specified circuit breaker from each of the above distribution lines. In a power distribution system in which a loop switch is connected between distribution lines and forms a loop circuit together with the above bus when closed, a sample hold circuit is provided corresponding to each zero-sequence current detector to detect the corresponding zero-sequence current. The output of the detector is sampled, the zero-sequence current information obtained by this sampling is held, the held zero-sequence current information is selectively outputted by a multiplexer, and based on this output result, the zero-sequence current presence determination means The loop circuit detects whether there is a relationship in which the absolute values of the zero-sequence currents of each distribution line are equal and the phase of the zero-sequence currents is 180°, and stores the detection results in a readable manner. By monitoring the number and timing of occurrences, it is possible to set the timing for maintenance management of power distribution lines, and to predict malfunctions of ground fault direction relays due to zero-sequence circulating current.

It is also possible to display the monitoring results and to prevent accidental opening of circuit breakers in normal power distribution lines forming a loop circuit.

[Brief explanation of drawings]

Fig. 1 is a block connection diagram showing a distribution line ground fault protection device according to an embodiment of the present invention, Fig. 2 is a block connection diagram showing a conventional distribution line ground fault protection device, and Fig. 3 is a block connection diagram showing a distribution line ground fault protection device according to an embodiment of the present invention. FIG. 3 is a graph diagram showing phase characteristics. 2 is the busbar of the distribution substation, CB,,CB,...CB
, breaker, L, ,L2. ...Shii is the power distribution line, 67
c,,67C;z,...67G7 is a ground fault direction relay,
ZCT+, ZCTz, . . . ZCT is a zero-phase current detector, S, , S2. ...S7 is a loop switch, R1,
R2,...R, l resistor, SH,, SH2゜...
SH, , is a sample hold circuit, MPX is a multiplexer, and CPU is a zero-sequence current determination means (microprocessor). In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A zero-sequence current detector is provided corresponding to each of a plurality of distribution lines connected to a busbar of a distribution substation via a circuit breaker, and detects zero-sequence current flowing in the corresponding distribution line; a ground fault direction relay to which the output of the current detector is supplied and operates in the event of a ground fault to trip the corresponding breaker;
In a power distribution system equipped with a plurality of loop breakers connected between predetermined distribution lines of each of the above distribution lines and forming a loop circuit together with the busbar of the above distribution substation when closed, each of the above zero-phase current detection A sample and hold circuit is provided corresponding to each sample and hold circuit to sample the output of the corresponding zero-sequence current detector and hold the zero-sequence current information obtained by this sampling, and a sample-and-hold circuit that samples the output of the corresponding zero-sequence current detector and holds the zero-sequence current information obtained by this sampling; Based on a multiplexer that selectively outputs information and the output of the multiplexer, detects whether or not there is a relationship such that the absolute values of the zero-sequence currents of the distribution lines are equal and the phase of the zero-sequence currents is 180°, and 1. A distribution line ground fault protection device comprising: zero-sequence current presence/absence determining means for readably storing detection results.