JPH0124012B2 - - 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 at the terminals A, _B , and _C at each end, |i _A +i _B +i _C | and the scalar sum of each of the currents i _A , i _B , i _C , |i _A |+|i _B
The suppression amount is the amount obtained by multiplying |+|i _C | by the constant R,
The operation is determined based on whether or not the difference between the amount of operation and the amount of suppression is greater than a certain value K, and it is determined whether an accident has occurred 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 in background technology] Equation (1) is a simple differential current component. This is a general method that does not detect only the size, but also adds the suppression amount of the second term on the left side to avoid malfunctions due to various errors caused by external accidents and to obtain highly sensitive failure detection ability. It is a method. 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 it easy for the current transformer CT1 to become saturated. And at that time, the inflow current at terminals A and B
For i _A and i _B , if the current transformer CT1 at the A and B terminals is not saturated, the error caused by the saturation of the current transformer CT at the C terminal will directly become the differential current, and it will depend 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. However, as shown in Figure 3, 2L of parallel two-circuit transmission line
In the event of an internal fault at point F on the side, the 2L side of the C terminal becomes an outflow terminal, and even if there is no error in the current transformer CT1, the ratio between the operating amount of the first item on the left side of equation (1) and the suppression amount of the second item There is a possibility that the ability to distinguish from external accidents will deteriorate as the accident approaches. In this case, if the suppression amount of the second item in equation (1) is excessively increased, 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
need to be selected appropriately.

Considering this situation, in regions where the current is relatively small, the amount of suppression is made small to achieve high sensitivity, and in regions where the current is large, the amount of suppression is made relatively small to avoid the effects of various errors such as CT saturation. A method in which the characteristics are changed depending on the magnitude of the current, which is a method in which the characteristics are changed depending on the magnitude of the current, is usually applied. 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 ……Small 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 | I _d shown by equations (2) and (3), Σ|I| are currents i A , i B , i C at terminals _A , _B , and _C , respectively, as explained in equation (1).
The vector sum of |i _A +i _B +i _C | and each of the above-mentioned currents i _A ,
The scalar sum of i _B and i _C is |i _A |+|i _B |+|i _C |. The constants R ₁ and R ₂ are ratio constants that limit the magnitude of the small current region characteristic and the large current region characteristic, respectively. or,
K ₀₁ and K ₀₂ are constants that determine the small current range characteristics and the current sensitivity when one end of the large current range flows in.

As shown in the characteristics in Figure 4, the vertical axis is the amount of operation,
The horizontal axis is the amount of suppression, and it can be seen that the operating range is wide in the small current range, and narrow in the large current range. 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. FIG. 5a shows a DC saturation waveform, and generally large waveform distortions tend to occur after the first or second cycle from the occurrence of an accident due to the influence of the residual magnetic flux of the CT. 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. However, at that time, the amount of suppression shown by the sum of the magnitude of the current at the saturated terminal C shown in FIG. 5c and the current at the non-saturated terminal shown at d in FIG. Furthermore, Fig. 5c,
The reason why there is a slight time delay in the rise of d with respect to the rise of 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.

(i) Since it takes one to two cycles from the occurrence of an accident until the effect of waveform distortion due to CT saturation appears, the amount of suppression becomes larger than the amount of operation, and during the transient period until the current becomes large, the small value of equation (2) is It never enters the operating range of the current range characteristics. In addition, even if it enters the operating region of the small current region characteristic when saturation continues, it becomes a non-operating region with the large current region characteristic, and malfunction can be prevented.

(ii) If the accident is removed while the effect of CT saturation, which decays with a certain time constant, remains,
The error due to the residual magnetic flux of the CT at the saturation terminal remains as the operating amount, and compared to the fact that the suppression amount decreases at the same time as the fault is removed, the operating amount falls more slowly, and this time coordination leads to malfunction.

The time relationship between the amount of movement and the amount of suppression shown in (i) and (ii) above is shown in FIG.

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 a case where the magnitude of the suppression amount rises earlier than the magnitude of the operation amount. The diagram shows the change between BC when waveform distortion becomes relatively noticeable and the amount of operation increases. While CT saturation continues, the area is mainly in the area shown by the hatched area in FIG. The degree of saturation also attenuates under a certain time constant, but if the fault is removed before the influence completely disappears, the CT of the saturation terminal The error due to the influence of the residual magnetic flux remains transiently, and the decrease in the amount of operation becomes slow, making it impossible to achieve temporal coordination between the amount of operation and the amount of suppression. In other words, the trajectory is from C' to D and back to A in FIG. Point D is a region where both the large current region and the small current region are operating, and is determined to be a malfunction.

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 operation amount and the suppression amount shown in equations (2) and (3) above may not 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-mentioned problems, and it is possible to prevent malfunctions caused by CT errors caused by concentrated fault current flowing, even though the accident is outside the section. The purpose is to provide a current differential protection relay device.

[Summary of the invention]

The present invention focuses on the amount of suppression that rapidly attenuates in the wake of accident elimination, and uses the maximum value from among the sampling values sampled from each terminal at each time as the amount of suppression, and also uses the falling amount of the operation amount. By delaying the fall of the suppression amount, it is attempted to achieve time coordination with the motion amount.

[Embodiments of the invention]

Examples will be described below with reference to the drawings.

FIG. 7 is a configuration diagram of an embodiment of the 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. Here, the current taken into the current differential relay 3 is converted into a predetermined amount of electricity by the input converter 31,
The amount of electricity obtained by removing the amount of electricity of unnecessary frequency components through the filter 32 is held in the sampling/hold circuit (S/H) 33 until the next sampling. Then, the held electric quantity is introduced into an analog-to-digital converter circuit (A/D converter circuit) 35 via a multiplexer circuit (MPX) 34, and the digital quantity i _An , which is the electric quantity obtained from this, is transferred to the transmission device 4. are sent to the B and C terminals respectively. At the same time, receive electrical quantities i _Bn and i _Cn sampled at the same time from terminals B and C,
It is 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/O) 39 based on the determination result.

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

I _dn −R ₁ ×I _RMAXn K ₀₁ …(4) I _dn −R ₂ ×I _RMAXn K ₀₂ …(5) I _RMAXn = MAX(I _Rn , I _Rn-1 , I _Rn-2 , … I _Rn-o )
……(6) I _{( )n} =｜i _{( )n} ｜+｜i _{( )n-1} ｜+｜i _{( )n-2} ｜+……
＋｜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 are characteristic equations in each operating current range expressed using the amount of suppression as the maximum value among the sampled values, and Equation (4) is Equation (5) shows the characteristics in the small current region and the characteristics in the large current region, respectively. Equation (6) means detecting the maximum amount of suppression from among each sampling value, and Equation (7) is a calculation equation for calculating the amplitude value using each sampling value. Note that d, A, B, and C are respectively inserted in parentheses in the formula. 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 time series (m) and (m-
The difference in 1) is one sampling, meaning that (m) is the latest sampling time.

FIG. 8 is a flowchart for explaining the operation. First, in Step 801, data of each required 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 ) are read out, and in Step 802, a differential current component (i _dn , i _dn-1 , ... i _dn-5 ) is created.
The differential current i _dn is created from each terminal current i _An , i _Bn , i _Cn using equation (8). In Step803, Step801,
Data string obtained in 802 (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 ), we create quantities I _An , I _Bn , I _Cn , and I _dn that are proportional to the magnitude of the alternating current electricity amount shown by equation (7).
In Step 804, I _An , I _Bn , I _Cn obtained in Step 803
The suppression amount I _Rn is calculated from equation (9). Furthermore, I _Rn
Since it is necessary for n samplings after time m, it is stored in a predetermined data memory (RAM) 36. In Step ₈₀₅ , _a predetermined _{data memory (} RAM ) 36 and detects the maximum value I _RMAXn among I _Rn and (I _Rn-1 , I _Rn-2 . . . I _Rn-o ). Step806 is Step805
and (I _RMAXn , I _dn ) obtained in 803 and the constant R ₁ ,
It is detected from K ₀₁ whether equation (4) holds. If this is established, in Step 807,
(I _RMAXn , I _dn ) and constants obtained in Steps 805 and 803
It is detected from R ₂ and K ₀₂ whether equation (5) holds. 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. Further, if the equation (5) does not hold in Step 807, it is determined that the operation is not performed and the process proceeds to the next step. By carrying out 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 during accident removal when the effect of the CT saturation described above still remains. That is, by making the fall of the suppression amount more gradual than the fall of the operation amount when eliminating an accident, malfunctions can be prevented.

FIG. 9 shows the time relationship between the amount of suppression and the amount of operation using n as a parameter. Note that n here is the number of past samplings based on the current time. In Figure 9, the horizontal axis is time, and the vertical axis is the amount of movement I _dn.
and the magnitude of the suppression amount (R ₁ I _RMAXn +K ₀₁ ). If we pay attention to the amount of motion in the figure, we can see that the influence of the CT error is reduced by a certain time constant, and the amount of motion is reduced. When the fault is removed at time t ₀ , only the influence of the CT residual magnetic flux at the saturated terminal remains, and at the non-saturated terminal, as soon as the fault is removed, only the load current remains, so the operating amount remains for a certain period of time from t ₀ . . After that, it attenuates to almost zero level.

Next, focusing on the amount of suppression, I _RMAX = I _Rn for n = 0
In this case, the amount of suppression is only during T ₀ (R ₁ I _RMAXn + K ₀₁ )
may be smaller than the operating amount I _dn . but,
When n=3 or more, the operation amount does not exceed the suppression amount and malfunction does not occur. In the case of n=2, there is a malfunction period only for T ₂ , but it is much smaller than T ₀ . As described above, it has become clear that by slowing down the fall of the suppression amount, it is possible to prevent malfunctions due to the uneven time coordination at the time of the fall of the operation amount and the suppression amount described above. In addition, as a method to make the fall of the suppression amount gradual, (6)
This can be realized not only by the method of the formula but also by the formula below.

I _RMAXn = MAX (I _Rn , ξI _RMAXn-1 ) (10) Here, I _Rn is the same as the above-mentioned value calculated from equations (7) and (9). However, I _RMAXn is a constant ξ smaller than 1 between I _Rn at time m and I _RMAXn-1 at (m-1) time.
The value multiplied by ξI _RMAXn-1 shall be the larger value.

FIG. 10 is a flowchart for explaining the operation. In Figure 10, in Step 101,
Necessary terminal data (i _An , i _An-1 , ...i _An-5 ), (i _Bn , i _Bn-1 ...) from the data memory (RAM) 36
i _Bn-5 ), i _Cn , i _Cn-1 , ...i _Cn-5 ),
In Step 102, the differential current (i _dn , i _dn-1 , ...
i _dn-5 ). The differential current (i _dn ) is the current at each terminal.
It is created using equation (8) from i _An and i _Bn i _Cn . Step103
Similarly to Step 803 in Figure 8, quantities I _An , I Bn , I _Bn , which are proportional to the magnitude of AC electricity are calculated based on equation (7).
Create I _Cn and I _dn . In Step 104, I _Rn is created based on equation (9) from the magnitudes of the terminal currents I _An , I _Bn , and I _Cn obtained in Step 803. In Step 105
The magnitude of I _Rn obtained in Step 104 is compared with the value obtained by multiplying the calculation result I _RMAXn-1 at the previous sampling point stored in a predetermined data memory (RAM) 36 by a constant ξ, and the larger one is detected. . At the same time, the value (I _RMAXn ) is stored in the data memory (RAM) 36 that had previously stored the above-mentioned I _RMAXn-1 .
In Step 106, I _RMAXn obtained in Step 105 and Step 103
It is detected from the I _dn obtained in and the constants (R ₁ , K ₀₁ ) whether equation (4) holds. If it holds true here, it is detected in Step 107 whether equation (5) holds or not from (I _RMAXn , I _dn ) obtained in Step 105 and Step 103 and constants (R ₂ , K ₀₂ ). If this is true, it is determined that there is an operation and the process proceeds to the next step. Step106 or
If 107 is not satisfied, it is 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 insufficient coordination of the fall times of the operation amount and the suppression amount, as in the case of equation (6).

FIG. 11 shows the time relationship between the amount of suppression and the amount of operation using ξ as a parameter. As can be seen from FIG. 11, if ξ approaches 1, the fall of the suppression amount can be further delayed.

Here, the qualitative meaning of equation (10) is that when the fall of the suppression amount I _Rn is abrupt, it becomes smooth due to the effect of ξI _RMAX-1 , and conversely, when the fall of I _Rn is smooth, This means that I _Rn is dominant.

As described above, by the method shown by equations (6) and (10) proposed by the present invention, it is possible to prevent malfunctions due to insufficient coordination of the fall time of the operation amount and suppression amount when removing an out-of-section accident. .

Note that the present invention is not limited to the above embodiments, but can also be applied to the following methods. In other words, as a current differential relay, small current range,
In addition to the large current area characteristics (4) and (5), which have the two characteristics, the present invention can also be applied to the suppression when the advantages of both characteristics are combined into one characteristic. Furthermore, if the malfunction phenomenon during fault elimination, which is the subject of the present invention, is a problem in the small current range, I _RMAXn in equation (6) or (10) can be applied only to the small current range characteristic in equation (4) above. I _Rn may be applied as the amount of suppression of the large current characteristics.

That is, the following equations are obtained: I _dn −R ₁ ×I _RMAXn K ₀₁ ……(11) I _dn −R ₂ ×I _Rn K ₀₂ ……(12). However, formula (6) or formula (10) is applied to I _RMAXn . 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} ｜ ...(13) However, d, A, B, and C are entered in ( ).

Furthermore, the operating formula of the current differential relay is not limited to formulas (4) to (9), and may be the square value of the amplitude value of the alternating current amount as shown in the following formula.

I ² _dn −R ₁ ′×I ² _RMAXn K ₀₁ ′ I ² _dn −R ₂ ′×I ² _RMAXn K ₀₂ ′ I ² _RMAX = MAX(I ² _Rn , I ² _Rn-1 ……I ² _Rn-o ) I ² _{( )n} = i _{( )n} + i _{( )n-3} I ² _RMAXn = I ² _An + I ² _Bn + I ² _Cn ...(14) However, d, A, B, and C are entered in ().

R ₁ ′, R ₂ B′, K ₀₁ ′, and K ₀₂ ′ are constants. 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, as the quantities corresponding to the above formulas (8) and (9), i _dn = i _(1)n + i _(2)n +...+i _(N)n I _Rn = I _(1)n + I _{( 2)n} +...+I _(N)n ...(15) is calculated, and formulas (4), (5), and (6) are applied to this. Note that N in parentheses is the number of terminals. In this example, the protection zone was explained as a power transmission line, but
It goes without saying that the present invention is not limited to this, and can also be applied to the protection of busbars, transformers, etc., for example.

〔Effect of the invention〕

As explained above, according to the present invention, by using the maximum value from among the sampling values sampled from each terminal as the suppression amount and delaying the fall of the suppression amount from the fall of the operation amount,
Since the amount of suppression and the amount of operation are configured to be time-coordinated, it is possible to provide a current differential protection relay device that can prevent malfunctions when removing an out-of-section fault.

[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 CT DC saturation waveform and the current amplitude value of each terminal, and Figure 6 is the amount of operation and suppression during fault removal when the CT is saturated and when the influence of saturation remains. Diagram conceptually showing the relationship with quantity,
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 for explaining the time coordination between the operating amount and the suppression amount. FIG. 10 is a flowchart explaining the case of time coordination using other detected quantities;
The figure is a diagram illustrating time coordination between the amount of operation and the amount of suppression. DESCRIPTION OF SYMBOLS 1...Current transformer, 2...Power transmission line, 3...Current differential relay, 4...Transmission device, 31...Input converter, 32...
Filter, 33...Sampling hold circuit, 3
4... Multiplexer, 35... Analog/digital conversion circuit, 36... Data memory, 37... Central processing unit, 38... Program memory, 39... Input/output interface circuit.

Claims (1)

[Scope of Claims] 1. In a current differential protection relay device that samples the current value of each terminal of a power system at the same time and at a constant period, and performs a protection calculation using these sampled detection data, A means for reading each required terminal data from a data memory in which data is stored, a means for creating an operation amount based on each read data, and a means for creating an operation amount based on each terminal data string in the data memory. means for creating an amplitude value proportional to the amount, means for creating and storing a suppression amount based on each of the amplitude values, and detecting a maximum value from among the stored suppression amounts for the past n samplings. A current differential protection relay device comprising: a means for determining operation using a maximum value of the operation amount and the suppression amount; and a determination means having a small current region characteristic and a large current region characteristic for determining an operation using the maximum value of the operation amount and the suppression amount. 2. In a current differential protection relay device that samples the current value of each terminal of the power system at the same time and at a fixed period, and performs protection calculations using these sampled detection data, data in which detection data is stored. A means for reading out each required terminal data from the memory, a means for creating an operating quantity based on each read data, and an amplitude value proportional to each electrical quantity using each terminal data string in the data memory. means for creating and storing a suppression amount based on each of the amplitude values, and a suppression amount obtained by multiplying the already stored suppression amount used a certain time ago by a positive constant. and a means for selecting a larger one from the amount of suppression created at the current time, and a determination means having a small current region characteristic and a large current region characteristic that determines the operation using the amount of operation and the selected amount of suppression. A current differential protection relay device characterized by comprising: