JP2682930B2 - Digital relay device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital relay device for operating a protection relay of a power system based on the amount of change in the current of the power system.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing a conventional digital relay device, for example, "Protective Relay Engineering" published by the Institute of Electrical Engineers of Japan, July 20, 1981, page 102. 1 is a busbar, 2 is a power transmission line, 3 is a circuit breaker that connects the busbars 1 and 2 to each other, 4 is one cycle of the frequency in the power system as a sampling cycle, and a quarter cycle of the frequency is set for each sampling cycle Is a current detecting means (see FIG. 10) for detecting the current of the power system with a time difference corresponding to the current converter (C
T) 5, an input conversion circuit 6, a filter circuit 7, a sample hold circuit 8 and an analog-digital converter 10.

Reference numeral 11 is a memory for storing the current detected by the current detection means 4, 12 is a subtraction circuit for subtracting the current i ₂ at time t-360 ° from current i _{0 at} time t, and 13 is time t-90 °. From current i _{1 at} time t
Subtraction circuit for subtracting current i ₃ at −450 °, 14
Is a squaring circuit for squaring the subtraction result of the subtraction circuit 12, 15 is a squaring circuit for squaring the subtraction result of the subtraction circuit 13, and 16 is 2
An addition circuit for adding the calculation results of the multiplication circuits 14 and 15, 17
Is an output circuit that outputs a relay operation command when the addition result of the addition circuit 16 is larger than a predetermined value K.

FIG. 10 is a waveform diagram of a current in a power system. I ₀ · i ₁ is a current detected in the latest sampling cycle (current i ₁ is ahead of current i ₀ by a quarter cycle). (Leading by 90 ° in phase), I ₀ is the maximum value of current in the latest sampling period, i ₂ · i
₃ is the current detected in the previous sampling cycle (current i ₃
Is ahead of the current i ₂ by a quarter cycle (phase 90
Advance), I ₁ is the maximum value of current in the previous sampling period.

Next, the operation will be described. First, the current detection unit 4 detects the current of the power system for each sampling cycle, and the currents i ₀ , i ₁ , i ₂ , i detected in the memory 11 are detected.
Remember ₃ . Here, since the current i ₀ and the current i ₂ have the same phase, they can be expressed as follows. _{i 0 = I 0 sinωt i 2} = I 1 sin (ωt-360 °) = I 1 sinωt addition, since the current i ₁ and the current i ₃ is also the same phase, can be expressed as follows. i ₁ = I ₀ sin (ωt−90 °) = − I ₀ cosωt i ₃ = I ₁ sin (ωt−450 °) = − I ₁ cosωt

In the following configuration, the square value ΔI ² of the difference (variable flow rate) between the current I ₀ and the current I ₁ is obtained by using the thus detected currents i ₀ , i ₁ , i ₂ and i _3. First, the subtraction circuits 12 and 13 calculate the difference between the current i ₀ and the current i ₂ and the difference between the current i ₁ and the current i ₃ as described below. i ₀ −i ₂ = (I ₀ −I ₁ ) sin ωt i ₁ −i ₃ = − (I ₀ −I ₁ ) cos ωt

Next, the squaring circuits 14 and 15 square the subtraction results of the subtracting circuits 12 and 13, as shown below. ^{_{(I 0 -i 2) 2 =}} (I 0 -I 1) 2 sin 2 ωt (i 1 -i 3) 2 = (I 0 -I 1) 2 cos 2 ωt

Further, in the adder circuit 16, the squaring circuit 14.1
By adding the calculation result of 5, the square value Δ of the variable flow rate
I ² can be obtained. ^{_{That, (i 0 -i 2) 2}} + (i 1 -i 3) 2 = (I 0 -I 1) 2 sin 2 ωt + (I 0 -I 1) 2 cos 2 ωt = (I 0 -I 1) ² (sin ² ωt + cos ² ωt) = (I ₀ −I ₁ ) ² = ΔI ²

Then, the output circuit 17 at the final stage compares the square value ΔI ² of the variable flow rate thus obtained with the predetermined value K, and when the square value ΔI ² of the variable flow rate is larger, the electric power is increased. It judges that an accident has occurred in the system and outputs a relay operation command.

[0010]

Since the conventional digital relay device is constructed as described above, the frequency in the power system is the reference frequency due to the influence of an accident or the like (the normal frequency when the accident or the like does not occur). If it deviates from the frequency), the phases of the currents detected in each sampling cycle will not be the same phase (i ₀ and i ₂ and i ₁ and i _3).
Therefore, there is a problem that an error occurs in the calculation of the amount of change in the current, and as a result, the reliability of protection of the power system is reduced.

The present invention has been made to solve the above problems, and provides a digital relay device capable of accurately calculating the amount of change in current even when the frequency of the power system deviates from the reference frequency. The purpose is to

[0012]

In a digital relay device according to the present invention, either one of the current vectors in the latest sampling cycle or the previous sampling cycle is moved symmetrically about the current vector in the previous sampling cycle. In addition to obtaining the current vector after, the difference between the current vector that has not been axisymmetrically moved and the current vector after axisymmetrical movement among the current vectors in the latest or last two sampling cycles is calculated. When it is large, the relay operation command is output.

[0013]

Since the current vector calculating means in the present invention moves either one of the current vectors in the latest sampling cycle or the sampling cycle before the previous one in line symmetry around the current vector in the previous sampling cycle, no line symmetry movement is performed. The current vector on the one side and the current vector after the line-symmetrical movement have the same phase.

[0014]

[Embodiment 1] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a digital relay device according to an embodiment of the present invention. In the figure, the same reference numerals as those of the conventional one indicate the same or corresponding portions, and the explanation thereof will be omitted.

Reference numeral 21 is a reference frequency in the power system (see FIG. 2).
(See Fig. 2)
The current detection means for detecting the current of the power system with a time interval corresponding to 1/4 cycle of the reference frequency for each sampling cycle as a sampling cycle, and 22 for current detection The two currents in each sampling period detected by the means 21 are vector-combined (i ₀ and i ₁ , i ₂ and i ₃ , i ₄ and i _5).
Current vector X ₀ · X ₁ · X ₂ and the current vector X ₀ · X _{2 in} the latest or last sampling cycle is centered on the current vector X ₂ in the previous sampling cycle. A current vector calculation circuit (current vector calculation means) for obtaining the current vector Y after the line symmetry movement by moving the line vector symmetrically with respect to the current vector X, and the current vector calculation circuit 23 among the current vectors X ₀ and X _{2 in} the latest or last sampling cycle. The current vector X _{0 on the} side where the line-symmetrical movement was not performed by 22
(Or X ₂ ) and the current vector Y after the line-symmetrical movement are obtained, and the relay operation command output means outputs a relay operation command when the difference is larger than a predetermined value K.

Further, in FIG. 2, i ₀ · i ₁ are currents detected in the latest sampling cycle (current i ₁ and current i _1
0 is the current detected with a time difference corresponding to 1/4 cycle of the reference frequency), i ₂ · i ₃ is the current detected in the previous sampling cycle (current i ₂ and current i ₃ are 4 minutes of the reference frequency) Current detected with a time difference corresponding to one cycle of i) and i ₄ · i ₅ are currents detected in the sampling cycle two times before (current i ₄ and current i ₅ are a quarter of the reference frequency).
It is a current detected with a time difference corresponding to the cycle).

Next, the operation will be described. First, as a premise of the description, when the frequency in the power system and the reference frequency match, i ₀ · i ₂ · i ₄ and i ₁ · i ₃ · i ₅
2 have the same phase, but as shown in FIG. 2, if the frequency and the reference frequency in the power system deviate due to an accident or the like, i ₀ · i ₂ · i ₄ and i ₁ · i ₃
・ It is noted here that i ₅ is no longer in the same phase.

Similar to the conventional one, the currents i ₀ , i ₁ ... i ₅ detected by the current detecting means 21 are stored in the memory 11, and the current vector calculation circuit 22 causes the current i _{0 as} shown below. , I ₁ ... i ₅ are vector-combined to obtain the current vectors X ₀ , X ₁ , and X ₂ . X ₀ = i ₀ + ji ₁ (1) X ₁ = i ₂ + ji ₃ (2) X ₂ = i ₄ + ji ₅ (3) (1), ( The expressions (2) and (3) are expressed in polar coordinates as follows (see FIG. 4). X ₀ = (i ₀ , i ₁ ) (4) X ₁ = (i ₂ , i ₃ ) (5) X ₂ = (i ₄ , i ₅ ) ...・ (6)

Further, as shown in FIG. 5, the current vector X
₀ and the current angle theta ₀ of vector X _1, the current vector X ₁
Since the angle θ ₁ formed by the current vector X ₂ and the current vector X ₂ is equal, the current vector Y 2 (see FIG. 6) obtained by moving the current vector X ₂ about the current vector X ₁ as a center and the current vector X ₀ have the same phase. .

Here, the process of obtaining the current vector Y by the current vector calculation circuit 22 will be specifically described as follows. That is, in order to line symmetry move current vector X ₂ around the current vector X _1, as shown in FIG. 6, the straight line P connecting the current vector X ₂ and the current vector Y is perpendicular to the current vector X _1. Therefore, the following arithmetic expression is established.

[0021]

(Equation 1)

Further, the current vector X ₂ and the current vector Y
Since the magnitudes of are the same, the following formula is established. i ₄ ² + i ₅ ² = α ² + β ² (8)

By solving equations (7) and (8), α and β can be obtained as follows.

[0024]

(Equation 2)

Next, in the subtraction circuits 12 and 13, using the current vector Y (α, β) obtained as described above, (i
_0- α) and (i ₁ -β) are calculated, and then square circuits 14 and 15 calculate (i ₀ -α) ² and (i ₁ -β) ² to add circuit 16 Then, as shown below, the calculation results of the squaring circuits 14 and 15 are added. (I ₀ −α) ² + (i ₁ −β) ² (12) Here, focusing on the equation (12), the square value of the difference between the current vector X ₀ and the current vector Y is expressed. This can be regarded as the square value of the variable flow rate ΔI of the current. ΔI ² = (i ₀ −α) ² + (i ₁ −β) ² (13)

As described above, the current vector X ₀
Since the current vector Y is the same phase as, (13) in square value △ I ² of variable flow of current is sought expressions, it can be seen that the frequency of the power system accurately obtained even deviate from the reference frequency.

Then, the output circuit 17 at the final stage compares the square value ΔI ² of the variable flow rate thus obtained with the predetermined value K, and when the square value ΔI ² of the variable flow rate is larger, the electric power is increased. It judges that an accident has occurred in the system and outputs a relay operation command. Here, although compared to the square value △ I ² a predetermined value K of the variable flow, variable flow △ I (which was 1 square of half of K) predetermined value H be compared with the results are the same Is.

Embodiment 2 FIG. In the first embodiment, the current vector calculation circuit 22 applies the linear equation (linear function) to obtain the current vector Y. However, as shown in FIG. 7, a triangular function is used. The current vector Y may be obtained. In FIG. 8, 22a is an arithmetic circuit that calculates sin θ, 22b is an arithmetic circuit that calculates cos θ, and 22c is an arithmetic circuit that calculates α and β.

Next, the operation will be described. Except for the current vector calculation circuit 22, the description is omitted because it is the same as in the first embodiment. The angle between the current vector X ₂ and the current vector X _{1 and} the angle between the current vector X ₁ and the current vector Y are θ, the angle between the current vector Y and the X axis is ρ, and the current vector X _{2 is changed} to the current vector X ₁ . When the length of the dropped perpendicular is P, the following arithmetic expression holds.

[0030]

(Equation 3)

Further, the following equation is obtained from the equations (14) and (15). α = i ₄ + 2Pcos (90 ° −θ−ρ) = i ₄ + 2P (sin θcosρ + cos θsinρ) (17) β = i ₅ −2Psin (90 ° −θ−ρ) = i ₅ + 2P (cos θcosρ−sin θsin ρ) .. (18) Further, since | X ₂ | = | Y |, the following formula is established.

[0032]

(Equation 4)

Equations (19) and (20) are converted into equations (17) and (1
Substituting into equation (8) gives:

[0034]

(Equation 5)

Since sin θ and cos θ are outer products and inner products of the angle θ formed by the current vector X ₂ and the current vector X ₁ , they are as follows.

[0036]

(Equation 6)

(21), (22), (23), (24)
By solving the equation, α and β can be obtained (the result is the same as the equations (11) and (12)).

Embodiment 3 FIG. In the first and second embodiments,
Has been described as to be compared with the current vector X ₀ the current vector X ₂ moves axisymmetric, it may be compared with the current vector X ₂ the current vector X ₀ moves axisymmetric.

Embodiment 4 FIG. In addition, in the first and second embodiments,
Although the one in which the current is detected at the sampling cycle of one time the reference frequency has been described, the current may be detected at the sampling cycle twice the reference frequency as shown in FIG.

[0040]

As described above, according to the present invention, either one of the current vectors in the latest sampling cycle or the previous sampling cycle is moved symmetrically about the current vector in the previous sampling cycle, and the current after the line symmetrical movement is moved. When calculating the vector, calculate the difference between the current vector that was not axisymmetrically moved and the current vector after the axisymmetrical movement, of the current vectors in the latest or previous sampling period, and if this difference is greater than the specified value, relay Since it is configured to output the operation command, the relay operation command is always output based on the comparison of current vectors of the same phase, so even if the frequency of the power system deviates from the reference frequency, the current The amount of change can be calculated, and as a result, the reliability of protection of the power system is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital relay device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing frequencies and reference frequencies of a power system.

FIG. 3 is a waveform diagram showing a frequency of a power system.

FIG. 4 is a vector diagram showing a current vector.

FIG. 5 is a vector diagram showing a current vector.

FIG. 6 is an explanatory diagram for explaining line-symmetrical movement.

FIG. 7 is an explanatory diagram for explaining line-symmetrical movement.

FIG. 8 is a block diagram showing a digital relay device according to another embodiment of the present invention.

FIG. 9 is a block diagram showing a conventional digital relay device.

FIG. 10 is a waveform diagram showing a frequency of a power system.

[Explanation of symbols]

 21 current detection means 22 current vector operation circuit (current vector operation means) 23 relay operation command output means

Claims (1)

(57) [Claims] 1. A power system that has a time interval corresponding to a cycle that is an integral multiple of a reference frequency in a power system as a sampling cycle, with a time difference that corresponds to a quarter cycle of the reference frequency for each sampling cycle. Current detecting means for detecting the current of the current and the two currents in each sampling period detected by the current detecting means are vector-synthesized to obtain the current vector, and either one of the current vector in the latest or the previous sampling period is determined. A current vector calculating means for axisymmetrically moving the current vector in the previous sampling cycle to obtain the current vector after the axisymmetric movement, and a current vector calculating means for the current vector in the latest or last sampling cycle are line-symmetrical by the current vector calculating means. Current vector of the one that was not moved And a relay operation command output means for determining a difference between the current vectors after the line-symmetrical movement and outputting a relay operation command when the difference is larger than a predetermined value.