JPH0124013B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a current differential protection relay device, particularly a current differential protection relay device that can distinguish between internal and external faults regardless of saturation of a current transformer due to fault current. It is related to.

[Technical background of the invention]

As power transmission lines become larger in scale, the number of multi-terminal power transmission line systems increases, and their protection becomes more complex. For this reason, there has been a growing trend in recent years to apply a current differential protection system that applies the differential principle, which has the highest ability to identify faults inside and outside a predetermined section, to multi-terminal power transmission line protection. The principle of differential protection will be explained below with reference to FIG. That is, in this method, the absolute value of the vector sum of the currents i _A , i _{B , and i C obtained through the current transformer CT1 of each terminal A, B} , and _C | i _A + i _B + i _C
| is the operating amount, and the scalar sum of each of the currents i _A , i _B , i _C | i _A | + | i _B | + | i _C | multiplied by a constant R is the suppression amount, and the operating amount is The operation is determined based on whether the difference in the amount of suppression is greater than or equal to a certain value K, and it is determined whether there is an accident inside or outside each terminal A, B, or C. This can be expressed as an operation formula as shown below.

｜i _A ＋i _B ＋i _C ｜ −R(｜i _A ｜+｜i _B ｜+｜i _C ｜)K...(1) [Problems with background technology] Equation (1) is a simple differential current component. This is a general method that avoids malfunctions due to various errors in faults outside the section and obtains highly sensitive fault detection ability by adding the suppression amount of the two terms on the left side, rather than just detecting faults. be. For example, as shown in FIG. 2, in the event of an external fault, an excessive fault current i _F concentrates on the C terminal and flows out, making the current transformer CT1 more likely to be saturated. At that time, if the current transformer CT1 of the A and B terminals is not saturated, the inflow currents i _A and i _B of the A and B terminals are equal to the error due to the saturation of the current transformer CT that occurs at the C terminal, which is directly converted to the differential current. Depending on the degree of saturation, this may lead to malfunction. In this case, the above-mentioned malfunction can be prevented by making the second term of equation (1) relatively large, that is, by making R large. However, as shown in Figure 3, in the event of an internal accident at point F on the adjacent line 2L side of the parallel two-line transmission line,
The 2L side of the C terminal becomes the outflow terminal, and even if there is no error in the current transformer CT1, the ratio of the operating amount of the first item on the left side of equation (1) and the suppression amount of the second item are close to each other, and it can be distinguished from an external fault. There is a possibility that the ability will decrease.

In this case, if the constant R in the second item on the left side of equation (1) is made too large, a problem will occur in which the system cannot operate even though there is an internal accident. Therefore, even if an external accident causes a movement amount or an internal accident causes a suppression amount, it is necessary to identify accidents inside and outside the section with high sensitivity, and the constants R and K in equation (1) above should be appropriately selected. There is a need. Taking this situation into account, in areas where the current is relatively small, the amount of suppression is reduced to increase sensitivity.
In a region where the current is large, in order to avoid the effects of various errors such as CT saturation, a method of changing characteristics depending on the magnitude of the current is usually applied, in which the amount of suppression is relatively large and the sensitivity is low.

That is, the characteristics are as shown in the following formula.

I _d −R ₁ ×Σ｜I｜K ₀₁ ...Small current range...(2) I _d -R ₂ ×Σ|I|K ₀₂ ...Large current range...(3) However, R ₁ <R ₂ , K ₀₁ >K ₀₂ I _d = |i _A +i _B +i _C | Σ|I| = |i _A |+|i _B |+|i _C | Id, Σ|I shown by equations (2) and (3) | are the currents i A , i B , i C at terminals _A , _B , and _C , respectively, as explained in equation (1).
The vector sum |i _A +i _B +i _C | and the scalar sum of the respective currents |i _A |+|i _B |+|i _C |. Constant R ₁ ,
R ₂ is a ratio constant that limits the amount of suppression of the small current region characteristic and the large current region characteristic, respectively. Moreover, K ₀₁ and K ₀₂ are constants that determine the current sensitivity at the time of inflow at one end of the small current region characteristic and the large current region characteristic. That is, as is clear from the characteristics shown in Figure 4, the vertical axis is the operating amount and the horizontal axis is the suppressing amount, and the operating range is wide in the small current range, and narrow in the large current range. Recognize.

As shown in FIG. 2, the relationship between the operating amount and the suppression amount when the current transformer CT1 is saturated due to a concentrated excessive current flowing through the C terminal will be explained with reference to FIG. Figure 5a shows the DC saturation waveform, which is generally 1 minute from the occurrence of an accident due to the influence of the CT's residual magnetic flux, etc.
Significant waveform distortion tends to occur after 2 to 2 cycles. Therefore, compared to the sum of the currents at the non-saturated terminals A and B shown in FIG. 2B, the error increases from the first cycle to the second cycle, and an amount of operation occurs. The amount of suppression, which is the sum of the magnitude of the current at the saturated terminal C and the current at the non-saturated terminal, represented by d in the figure, increases at the same time as the accident occurs. Furthermore, the reason why there is a slight time lag between the rises of c and d in FIG. 5 with respect to the rises of the fault currents a and b is due to the reaction time of the filter, amplitude value calculation, etc. Further, FIG. 5e shows the temporal change in the magnitude of the CT saturation error.

The following can be seen from Figure 5e. In other words, it takes one to two cycles from the occurrence of an accident until the effect of waveform distortion due to CT saturation appears, so the amount of suppression increases before the amount of operation, but after that, the differential current (error current) increases. Become. Therefore, malfunctions occur due to the relationship between the value of the ratio constant of the small current area characteristic and the degree of saturation.

FIG. 6 shows the temporal relationship between the amount of operation and the amount of suppression described above. Point A in FIG. 6 is under constant load, and the period from the occurrence of an accident until the influence of waveform distortion due to CT saturation appears is represented by the change between AB. That is,
This shows that the magnitude of the suppression amount is faster than the rise in the magnitude of the motion amount. After that, the waveform distortion appears relatively clearly, the amount of operation becomes large, and the amount of suppression becomes small. That is, it is expressed between BC. From point C, the degree of saturation decreases, the amount of operation decreases, and the amount of suppression rises to enter region D. That is, due to the movement from B→C→D, there is a possibility that the C point zone enters the malfunction area. So C
If the ratio constant is increased to increase the suppression amount in order to avoid the point zone, the detection sensitivity in the event of an internal accident accompanied by a normal spill will be reduced.

As mentioned above, the current differential protection device that responds according to the operation formulas shown in equations (2) and (3) is applied to multi-terminal protection, and moreover, the current is concentrated in one terminal.
When CT saturation occurs, time coordination between the operating amount and the suppression amount shown by equations (2) and (3) above cannot be achieved, which may lead to malfunction in the event of an accident outside the section.

[Purpose of the invention]

The present invention has been made with the aim of solving the above problems, and even though the accident occurs outside the section, malfunctions may occur due to the CT error caused by the concentrated flow of fault current. The purpose of the present invention is to provide a current differential protection relay device that is free of current.

[Summary of the invention]

The present invention focuses on the difference current as the amount of operation caused by waveform distortion, uses the minimum difference current based on the sampling value sampled from each terminal at each time as the amount of operation, and moreover, On the other hand, by delaying the rise of the difference current, time coordination with the amount of suppression is attempted.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. 7th
The figure is a configuration diagram of an embodiment of a current differential protection relay device according to the present invention. In FIG. 7, A, B, and C are electrical stations, and in this embodiment, a three-terminal system is shown. Note that since each terminal has the same configuration, only electric station A will be explained. 2 is a power transmission line provided between each terminal, and current at each end is introduced into a current differential relay 3 via a current transformer 1. The current taken into the current differential relay 3 is input to the input converter 3.
1, it is converted into a predetermined amount of electricity, and the filter 32
The amount of electricity obtained by removing the amount of electricity of unnecessary frequency components through the sampling and holding circuit (S/H circuit) 33 is held until the next sampling time. Then, the held electric quantity is transferred to an analog/digital conversion circuit (A/D conversion circuit) 3 via a multiplexer circuit (MPX) 34.
5, and the digital quantity i _An , which is the electrical quantity obtained therefrom, is sent to the B and C terminals via the transmission device 4, respectively. At the same time, the electrical quantities i _Bn and i _Cn sampled at the same time from the B and C terminals are received and stored in the data storage memory (RAM) 36 together with the self-end electrical quantity i _An . Then, using the stored data as described above, a central operation is performed by a program instruction in a program memory (ROM) 38 that stores predetermined processing contents according to an algorithm based on equations (4) to (9) described later. Processing unit (CPU) 3
7 performs arithmetic processing, and outputs the result via an input/output interface circuit (I/) 39 based on the determination result.

In the device having the above configuration, as shown below (4)
Equation (9) is calculated.

I _dMINn −R ₁ ×I _Rn ≧K ₀₁ …(4) I _dMINn −R ₂ ×I _Rn ≧K ₀₂ …(5) I _dMINn = MIN(I _dn , I _dn-1 , I _dn-2 … I _dn-o ) …(6) I _{( )n} =｜i _{( )n} ｜+｜i _{( )n-1} ｜+…+｜i _{( )n-5} ｜+
K ₁ ｜｜i _{( )n} ｜−｜i _{( )n-3} ｜｜＋｜｜i _{( )n-1} ｜ −｜i _{( )n-4} ｜｜＋｜｜i _{( )n-2} ｜ −｜i _{( )n-5} |
|}……(7) i _dn =i _An +i _Bn +i _Cn ……(8) I _Rn =I _An +I _Bn +I _Cn ……(9) Equations (4) and (5) above calculate the minimum difference current. These are the characteristic equations for each operating current range used, and equation (4) is the small current range characteristic,
Equation (5) shows the large current range characteristics. Equation (6) means detecting the minimum difference current from among each sampling value, and Equation (7) is a calculation equation for calculating the amplitude value using each sampling value. Also, in the ceremony ( )
, d, A, B, and C are entered respectively. Equations (8) and (9) are equations for calculating the difference current as the operating amount and the sum current as the suppression amount from the sampling current values at each end. Furthermore, in the above equation, m represents a sampling time series, and it is assumed that the amount of alternating current is sampled every 30 degrees. Therefore, the difference between the time series (m) and (m-1) is one sampling, which means that (m) is the latest sampling time.

FIG. 8 is a flowchart for explaining the operation. First, in Step 801, required data of each terminal (i _An , i _An-1 , ..., i _An-5 ), (i _Bn , i _Bn-1 , ...,
i _Bn-5 ), (i _Cn , i _Cn-1 ,..., i _Cn-5 ),
In Step 802, the differential current (i _dn , i _dn-1 ,...
i _dn-5 ). The differential current i _dn is each terminal current i _An ,
It is created from i _Bn and i _Cn using equation (8). In Step 803, the data strings (i _An , i _Bn , i _Cn , i _dn ), (i _An-1 , i _Bn-1 , i _Cn-1 ,
i _dn-1 )... (i _An-5 , i _Bn-5 , i _Cn-5 , i _dn-5 ) to (7)
A quantity proportional to the amount of alternating current electricity shown by the formula
Create I _An , I _Bn , I _Cn , and I _dn . In Step804
The suppression amount I _Rn is determined from I _An , I _Bn , and I _Cn determined in Step 803 using equation (9). Furthermore, I _Rn is stored in a predetermined data memory (RAM) 36 because it is required for n samplings after time m. Step805
In step 804, each of the above-mentioned data is retrieved from a predetermined data memory (RAM) 36 that stores the I _dn obtained in Step 804 and the values (I _{dn -1} , ...I _dn-o ) during the past n samplings of I dn. and I _dn and (I _dn-1 , I _dn-2
. . . Detect the minimum value I _dMINn among I _dn-o ).
In Step 806, it is detected from (I _dMINn , I _Rn ) obtained in Step 805 and Step 804 and the constants R ₁ and K ₀₁ whether equation (4) holds. If this holds true, it is detected in Step 807 whether or not equation (5) holds from (I _dMINn , I _Rn ) obtained in Steps 805 and 804 and the constants R ₂ and K ₀₂ . If this is established, it is determined that there is an operation and the process proceeds to the next step. If the equation (4) does not hold in step 806, it is determined that there is no operation and the process proceeds to the next step. Furthermore
If the equation (5) does not hold in step 807, it is also determined that there is no operation and the process proceeds to the next step. By performing the above processing, it is possible to prevent malfunctions due to lack of time coordination between the amount of suppression and the amount of operation in a state where the influence of CT saturation described above has become noticeable. That is, when the influence of CT saturation appears, malfunction can be prevented by making the rise of the operation amount more gradual than the fall of the suppression amount.

FIG. 9 shows the time relationship between the amount of suppression and the amount of operation using n as a parameter. Note that n shown here means the number of past samplings going back from the present time. In FIG. 9, the horizontal axis shows time, and the vertical axis shows the magnitude of the operation amount I _dMINn and the suppression amount (R ₂ ×I _Rn +K ₀₂ ). If we pay attention to the amount of suppression in the same figure, we can see that the influence of the CT error increases with a certain time constant, and the amount of suppression decreases. Next, looking at the amount of movement, if I _dMINn = I _dn for n = 0, then T ₀
The amount of operation I _dMINn may become larger than the amount of suppression (R ₂ ×I _Rn +K ₀₂ ) only during this period. However, when n=3 or more, the amount of operation does not exceed the amount of suppression, and malfunction does not occur. Further, in the case of n=2, there is a malfunction period only during T ₂ , but it is much smaller than T ₀ . In other words, it has become clear that malfunctions due to inconsistent temporal coordination between the amount of movement and the amount of suppression can be prevented.
Note that the present invention is not limited to the above embodiments, but can also be applied to the following methods.

Small current range and large current range characteristics as a current differential relay
In addition to the two characteristics of formulas (4) and (5), the present invention can also be applied to operations with one characteristic that takes into account the advantages of both characteristics. Furthermore, if the malfunction phenomenon during CT saturation, which is the object of the present invention, is a problem in a large current range, the following formula may be applied.

I _dn −R ₁ ×I _Rn ≧K ₀₁ …(10) I _dMINn −R ₂ ×I _Rn ≧K ₀₂ …(11) In other words, only for the operating amount of equation (11) that indicates large current characteristics
Using I _dMINn , the small current characteristic is expressed by equation (10). Furthermore, it goes without saying that the following equation may be used instead of equation (7) for the amplitude value.

I _{( )n} = ₅ 〓 ⁱ⁼⁰ ｜i _{( )ni} ｜ …(12) Furthermore, the operating formula of a current differential relay is not limited to formulas (4) to (9), but can be expressed as It is also possible to use the square value of the amplitude value of the quantity.

I ² _dMINn −R′ ₁ ×I ² _RM ≧K′ ₀₁ I ² _dMINn −R′ ₂ ×I ² _RM ≧K′ ₀₂ I ² _dMINn = MIN(I ² _dn , I ² _dn-1 , …I ² _{dn -o} ) I ² _{( )n} = i ² _{( )n} + i ² _{( )n-3} I ² _Rn = I ² _An + I ² _Bn + I ² _Cn ……(13) However, R′ ₁ , R′ ₂ , K ' ₀₁ and K' ₀₂ are constants.Also, in the above embodiment, the power system has been described as having a three-terminal configuration, but it can also be applied to a two-terminal configuration, a four-terminal configuration, or more. In this case, the above (8) and (9)
As a quantity corresponding to the formula, i _dn = i(1) _n +i(2) _n +...+i _(N)n I _Rn = I(1) _n +I(2) _n +...+I _(N)n ... It is sufficient to calculate each of (14) and apply the above-mentioned equations (4), (5), and (6) thereto. Note that N in equation (14) is the number of terminals. Although the protection section is described as a power transmission line in this embodiment, it is not limited to this, and can also be applied to protection of busbars, transformers, etc., for example. Further, in the above explanation, the sum of the current amplitude values at each end is used as the suppression amount I _Rn , but various methods such as the following formula can be considered.

I _Rn = MAX (I(1) _n , I(2) _n ……I _(N)n )……(15) In other words, equation (15) is the maximum terminal current amplitude of each terminal current amplitude value I _{( )n} The value is taken as the suppression amount I _Rn .

〔Effect of the invention〕

As explained above, according to the present invention, the minimum difference current between each terminal is used as the amount of operation, and the rise of the amount of operation is delayed relative to the fall of the amount of suppression, thereby achieving time coordination between the amount of suppression and the amount of operation. Therefore, it is possible to provide a current differential protection relay device that does not malfunction even if the CT is saturated due to current flowing concentrated in one terminal in the event of an external fault in the section.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the general principle of the current differential protection system, Figure 2 is a diagram explaining how current flows concentrated in one terminal when an external failure occurs, and Figure 3 is a diagram explaining how current flows when an internal failure occurs. Figure 4 is a diagram for explaining the case where a terminal leaks out, and Figure 4 is a diagram for giving a general explanation of the small current area characteristics and large current area characteristics of a current differential relay.
Figure 5 is a diagram explaining the temporal relationship between the DC saturation waveform of the CT, the current amplitude value of each terminal, and the amplitude value of the differential current, and Figure 6 is a diagram explaining the relationship between the operation amount and the suppression amount when the CT is saturated. A conceptual diagram, FIG. 7 is a configuration diagram of an embodiment of the current differential relay device according to the present invention, FIG. 8 is a flowchart for explaining the operation, and FIG. 9 is a diagram showing the time between the operating amount and the suppression amount. It is a diagram explaining cooperation. DESCRIPTION OF SYMBOLS 1... Current transformer, 2... Power transmission line, 3... Current differential relay, 31... Input converter, 32... Filter, 33
...Sampling hold circuit, 34...Multiplexer, 35...Analog/digital conversion circuit, 36
...Data memory, 37...Central processing unit, 38
...Program memory, 39...I/O interface circuit. 4...Transmission device.

Claims (1)

[Scope of Claims] 1. A sampling circuit that detects sampling data by sampling the current value of each terminal of the power system at the same time and with a constant cycle, and an analog/digital conversion circuit that converts the sampling data into digital data. In a current differential protective relay device comprising an arithmetic circuit that performs a predetermined arithmetic operation using the digital data, and a memory circuit that stores the digital data and the arithmetic results, The first step is to calculate the operating amount proportional to the vector sum of the currents.
means, a second means for calculating a suppression amount derived from the sampling value of each terminal current and proportional to the scalar sum of the currents, and a third means for storing the calculation result from the first means; a fourth means for detecting the minimum value from the calculation results stored by the first means and the calculation results stored by the third means; A current differential protection relay device comprising: fifth means for determining operation using the output as a suppression amount. 2. Claim 1, characterized in that the amount of operation and the amount of suppression are each set to the square of the amplitude value of the amount of alternating current.
Current differential protection relay device as described in .