JPH0322822A - Digital bus protective relay - Google Patents

Abstract

PURPOSE:To detect only one-line ground fault reliably by blocking output from a current differential element employing zero-phase current based on the output from at least one of means for detecting the magnitude of zero-phase current in respective feeders. CONSTITUTION:A neutral point is grounded through a resistor 11 for limiting ground current. Outputs from CTs 4-1-4-3 on feeders 3-1-3-3 connected with a bus 2 are sampled and held 6 in a digital bus protective relay 1 through auxiliary current transformers 5-1-5-3, then they are multiplexed 7 and A/D converted 8 and fed to a CPU 9. The CPU 9 executes logic operation through a current differential element 87S employing phase current, a current differential element 87G employing zero-phase current, and a ground overcurrent judging element 51G for judging the magnitude of zero-phase current in each feeder. Operation of current operating element employing zero-phase current is blocked based on the detection results of the magnitude of zero-phase current in each feeder. By such arrangement, protective operation is carried out reliably only for one-line ground fault.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is a digital bus protection relay, and in particular, uses a current differential principle using zero-sequence current to prevent ground faults in resistance-grounded busbars. Concerning digital bus protection relays for detection. (Prior Art) FIG. 6 shows an example of the construction of a digital bus protection relay according to the prior art. Further, FIG. 7 shows an example of a protection sequence.

In FIG. 6, the digital bus protection relay 1 includes each feeder 3-1 . 3-2. 3-
Current transformer 4-1 provided in 3. 4-2. 4-3
A secondary current (1'!l) is introduced, but in this case, each feeder current is matched by auxiliary current transformers 5-1, 5-2, and 5-3. 6 at a constant sampling frequency, sequentially selected by a multiplexer, and sent to the ^/D converter 8 where it is converted into a digital quantity.
A protection calculation is performed based on the digital data of the system current output from the /D converter 8, and protection operations such as system accident detection and protection output transmission are performed. The setting section 10 inputs accident detection sensitivity, operation time setting, etc. to the CPU 9. Furthermore, the neutral point grounding resistor 11 connected to the transformer neutral point limits the ground fault current in this system from exceeding a predetermined value. Although the zero-sequence current is not shown here, it is obtained by connecting the residual circuit of each phase current, and this is introduced from the auxiliary current transformer for the zero-sequence current, which is also not shown, and the each phase current shown in Figure 6. Similarly, it is introduced into the CPU 9.

As shown in Fig. 6, CPtl 9 also performs calculations of the 87S element for detecting short-circuit accidents, the 87G element for detecting ground faults, and the overcurrent detection element 51, and the protection sequence processing shown in Fig. 7. . The other processes are not related to the present invention, so their explanation will be omitted.

In FIG. 7, 87S element 12. The 87G element 13 is a differential element that detects faults inside the bus bar based on the current differential principle described below, and the 51G element 15 is an overcurrent detection element that responds to electrical faults in each phase of each feeder.

In the top configuration example of the digital busbar protection relay shown in FIG. 6, the phase currents 1,
From 12.13, calculate the vector sum ■,1, then I ``”i +i,, +i3, and under normal conditions, d1, and in the event of an external fault on the bus, the current flowing into the bus and the current flowing out are equal, and l I , 1 l =O<K. Here, K is the operating level of 878 element 12, and 87S element 1
2 is inactive. However, in the event of an internal accident on the busbar,
The current flowing into the bus bar is large, I■,>K, and 87
The three elements 12 are activated and can determine whether an accident occurs inside or outside the bus. The 87G element 13 has a zero-sequence current of 1 in the above process.
~1 to find IIOd01 03 and the operating level k. This is used to determine the motion by comparing the The 51 element 15 is provided for each feeder in order to prevent the 87G element 13 from malfunctioning due to a zero-phase error current caused by a large current, as shown below. In general, resistance grounding systems can cause inductive disturbances to communication lines and damage to the human body! Considering the 5 harmonics, the transformer neutral point earthing resistance 1 shown in Figure 6
1 is chosen to limit the ground fault current to a few hundred amps. The 87G element 13 is very sensitive to detect and operate on this current.

If a short circuit accident with a large current of several tens of {k^} occurs, even if no direct zero-sequence current is generated due to the accident, for example, due to an error current of several percent, the 87G element 1
3 malfunctions are possible. Therefore, for the 87G element 13, two-wire accidents involving large currents are generally considered to be outside its protection responsibilities.

In the conventional example shown in FIG.
The system is designed to prevent operation in the event of a two-line accident. When a large current flows into the bus bar, 878 elements are used to detect and protect the bus.

(Problem to be Solved by the Invention) Here, the operation value setting of the overcurrent detection element is erroneously activated when a one-line ground fault occurs inside the bus bar, and even though the 87G element should be activated, this operation does not occur. It is necessary to decide so as not to prevent this.

Figure 8 shows the relationship between the zero-sequence current and various currents, and the line B16 shows the relationship between the load current and the zero-sequence current. A straight line 17 shows the relationship between the ground fault phase current and the zero-sequence current at the time of a one-wire ground fault. Here, 18 indicates the maximum load current ILOADmax, and 19 indicates the maximum fault current I in the event of a single-wire ground fault.]LGnax. Further, 20 indicates the operating value level of the zero-sequence difference current element 87G element. Is the overcurrent detection element 51 properly adjusted? value 2
1 is ■,. ADlaX ■If it is greater than the sum of LGllax,■ it was necessary. With such a setting, when the load current decreases, for example, to zero, the straight line 17 representing the zero-sequence current relationship at the time of a one-line ground fault becomes a broken line 822.

23 is a case where a two-wire short-circuit accident occurs due to the maximum load current state, indicating that the 87G element malfunctions at the point where it intersects with straight line 20. However, since the set value of the 51 elements is greater than or equal to 21, the operation output of the 87G element is blocked by the operation of the 51 elements. Here, 24 is the case where the load current is zero,
8 because it intersects with straight line 20 below the setting value of 51 elements 21.
There was a high possibility that this would result in unnecessary operation of the 7G element. In addition, because a similar current flows in the event of a different-phase ground fault, there is a possibility of an unnecessary response.

The present invention was made in order to solve the above problems, and an object of the present invention is to provide a digital busbar protection relay that can reliably prevent the operation of the 87G element in the event of a short circuit of two or more wires or a ground fault. It is said that

[Archives of the invention] (Means for solving the problem) The present invention includes a current differential element using a zero-sequence current, a means for detecting the magnitude of the zero-sequence current of each feeder, and at least one of the means. and means for blocking the output of the differential element by the output.

(Function) With the above means, in the event of an accident involving two or more wires involving large currents, unnecessary response of the current differential element due to zero-sequence current can be prevented, and only single-line ground faults on the busbar can be reliably detected and protected. can.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a top view of one embodiment of a digital busbar protection relay according to the present invention. In FIG. 1, the same parts as in FIG. 6 have the same functions, are given the same reference numerals, and description thereof will be omitted.

In Fig. 1, the configuration is the same as in Fig. 6, but
The essential information processed by CPU 9 is different. In FIG. 1, the CPU 9 includes a current differential element 873 using each phase current, a current differential element 87G using zero-sequence current, and a ground fault overcurrent detection element 51G that determines the magnitude of zero-sequence current for each feeder.
The process is being carried out. FIG. 2 shows a protection sequence diagram of a digital type busbar protection relay having the above-mentioned horizontal direction. In FIG. 2, each phase current differential element 87S element 12. The zero-sequence current differential element 87G element 13 has the same function as each element with the same reference numeral shown in FIG. 6, and the explanation thereof will be omitted.

The 51G element 14 shown in FIG. This prevents unnecessary reactions. Here, in setting the operation value of the 51G element 14, since the operation determination amount is a zero-sequence current, there is no need to consider the constant load current, and ground fault overcurrent can be detected with high sensitivity.

FIG. 8 shows a setting value of 25 for the 51G element, which can achieve a significant improvement in detection sensitivity compared to the conventional setting value of 21. Figure 3 shows an example of a flowchart explaining the operation of the protection sequence diagram shown in Figure 2. FIG. 3 shows the zero-sequence current l of each feeder 1 to n from the system. 1 to 'On are introduced into the relay.

In FIG. 3, in step 831, zero-sequence currents 1.1 to 'On of each feeder are introduced, and in step 832, a vector sum of the zero-sequence currents of each feeder necessary for determining the operation of the 87G element is calculated. Here, since a comparison with the operating level is required, the absolute value +1o,l is obtained.

Steg S33 obtains the absolute value of the zero-sequence current for each feeder necessary for determining the operation of the 51G element. Step 83
In steps 4 to S39, if even one of the zero-sequence currents of the 1 to n feeders is equal to or higher than the comparison level, the flag G is set to 0, and in other cases, the flag G is set to 1 to block the output of the 87G element. , setting the permissible flag. That is, in step S34, an initial value 1 is given to counter j, and in step S35, the absolute value 11o,l of the zero-sequence current of feeder N8 corresponding to the value of j is compared with the detection level.
Here, steps 836 to 83& are repeated sequentially up to n using counter j when the conditions are not met. Set flag G=1. However, if the condition is satisfied in step S335, there is no need to repeat the process until j becomes ri, and the process proceeds to step S39, where the flag G=O is set.

Next, in step S40, the operation of the 87G element is determined, in step 341, the operation flag F is set to F=1 when the condition is met, and in step 342, when the flag of the 51G element is permissible, the operation output is sent in step S43. ．． In step 334, the 87G element is used when the condition in step 840 is not satisfied, and in step 345, the 87G element is restored, including when the condition in step 842 is not satisfied. According to the above embodiment, the magnitude of the zero-sequence current of each feeder is detected for each feeder, and the operation of the current differential element due to the zero-sequence current is blocked based on the detection result.
It is possible to provide a digital protection relay having a differential element using zero-sequence current, which operates reliably only in the event of a one-line ground fault.

In addition, in the above embodiment, the case where only the 51G element of the earth fault overcurrent element is used as the element that prevents the operation of the current differential element is explained, but the present invention is not limited to this, and for example, the conventional There is no problem when used in combination with the overcurrent element 51G element. FIG. 4 shows a treetop view in this case.

Furthermore, a protection sequence diagram is shown in FIG. Here, the 51G element prevents the unnecessary response of the 87G element due to the zero-sequence current such as the short circuit fault current phase in the event of a different phase ground fault, and the 51G element prevents the unnecessary response of the 87G element due to the zero-sequence error current caused by the large current in the event of a short circuit fault of two or more wires. Each can be expected to be effective in preventing reaction.

Furthermore, as another example, the ground number that occurs during a ground fault accident
＠ In a configuration where a ground fault overvoltage detection element that responds to voltage is part of the operating conditions of the 87G element, the ground fault overcurrent element 51G
It goes without saying that similar effects can be obtained by adding other elements.

[Effects of the Invention] As explained above, according to the present invention, when any of the zero-sequence currents of each feeder is equal to or higher than a predetermined value, the operational output of the differential element due to the zero-sequence current is blocked. It is possible to provide a digital bus protection relay that can prevent unnecessary response of the ground fault differential element due to a large current in the event of a fault in two or more wires, and improve the reliability of reliably detecting a bus lit ground fault fault.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the digital bus protection relay according to the present invention, FIG. 2 is a protection sequence diagram of the embodiment of the digital bus protection relay according to the invention, and FIG. 3 shows the operation of FIG. 2. Flow chart to explain, FIG. 4 is a diagram of another embodiment, FIG. 5 is a protection sequence diagram of another embodiment, FIG. 6 is a configuration diagram of a conventional digital f-ray protection relay, and FIG. 7 is a diagram of a conventional digital f-line protection relay. FIG. 8, a protection sequence diagram of a conventional digital busbar protection relay, is a diagram for explaining the characteristics of the prior art and the present invention. 1...Digital type bus bar protection relay 2...Bus bar 3...Feeder 4...
・Current transformer 5...Auxiliary current transformer 6...Sample and hold circuit 7...Multiplexer 8...A/D converter 9・
...CPU 10...Setting section 11...
・Neutral point grounding resistance 12...873 element 13...
87G element 14...51G element 15...
51 elements

Claims (1)

[Claims] In digital bus protection relays that protect against ground faults on resistive grounding system buses using differential elements that use the vector sum of the zero-sequence currents of all feeders connected to the bus, means for detecting the magnitude of each zero-sequence current, overcurrent detection means for detecting that the magnitude of each zero-sequence current exceeds a predetermined value and deriving an operating output, and at least one operating output of each of the above-mentioned means. A digital bus protection relay comprising: means for blocking the output of the differential element.