JP2665759B2 - Digital protection relay - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital protection relay for calculating resistance and inductance (or reactance) from voltage and current.

[Conventional technology]

FIG. 4 is a principle diagram of the Maw element of the conventional digital protection relay shown in, for example, Mitsubishi Electric Technical Report (Vol. 54, No. 11, 1980) issued by Mitsubishi Electric Corporation in November 1980. is there. As shown in the figure, the vector of the difference between the vector obtained by multiplying the current vector by the impedance and the voltage vector (
−) Is determined, and it is determined whether the phase difference between the difference vector (−) and the voltage vector is within 90 °.
If the phase is within 90 °, it is determined that the voltage vector has entered the circumference shown in the operation range.

If this is expressed by an equation, as a phase difference γ between the current and the voltage and an impedance angle θ of the impedance, That is, the impedance || / || is || cos (θ
^{If it} is smaller than −−γ), it is determined to be within the circle.

Next, a method for realizing this with the algorithm of the digital protection relay device will be described.

The AC voltage V (t) and the AC current i (t) are simultaneously sampled at a sampling interval T, and T is a time corresponding to 30 ° in electrical angle.

When the AC current i (t) is advanced by θ, i (t) · ^ejθ (cosθ) · i (t) − (sinθ) · i (t−3T). Assuming that the two vectors are a reference vector Vpol (t) and an operation vector Vop (t), Vpol (t) = V (t) Vop (t) = || i (t) e ^{j θ−} V (t) = || ｛(cos θ) · i (t) − (sin θ) · i (t−3T)} − V (t) The condition that the two vectors Vpol (t) and Vop (t) are within 90 ° can be obtained by an equation.

Vpol (t−3T) · Vop (t−3T) + Vpol (t) · Vop (t)> 0 In all of the above expressions, expressions, and expressions, the condition is that the frequency of the AC voltage and the AC current is constant. It is established.

[Problems to be solved by the invention]

However, in recent power systems, the increase in cable systems,
When a system fault occurs due to an increase in static capacitors for power factor improvement, etc., high-frequency current and voltage of free oscillation resonating with the reactance of the transmission line occur, and the order of these harmonics becomes close to the fundamental wave, and The content has become very large.

Therefore, in the above equation focusing only on the fundamental wave, a case has emerged in which the error is very large and cannot be put to practical use.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a digital protection relay capable of accurately determining a high-order harmonic content even if the content thereof is large.

[Means for solving the problem]

The digital protection relay according to the present invention obtains a resistance component and an inductance component (or a reactance component) by using a sampling value of a voltage and a current and solving a binary simultaneous equation using an AC theory. Specifically, in a digital protection relay obtained by sampling the voltage and current of the power system at a fixed cycle and performing digital conversion, and then calculating and processing the resistance R and the inductance L based on the digitally converted values, The sampling cycle is represented by T, the sampling time t, and the time t separated from the sampling time t by a predetermined number of samples l.
The above voltage and current at each
(T) and V (t-lT), i (t) and i (t-lT), the time t and t ± mT before and after the time t-lT, respectively.
And the current at each of the times t−lT ± mT (where m is a positive integer) is i (t ± mT) and i (t−lT
± mT), where Km is the constant corresponding to the positive integer m, To determine whether at least one of these values is within a predetermined value, and to sample the voltage and current of the power system at regular intervals. After digital conversion, the digital protection relay is obtained by arithmetically processing the resistance R and the reactance ωL based on the digitally converted numerical values. In the digital protection relay, the sampling cycle is T, the sampling time t and the sampling time t The voltage and the current at each of the times t-1T separated by a predetermined number of samples 1 from v are represented by v (t) and v (t-1T), respectively.
, I (t) and i (t−lT), the above t and the above time t−
The current at each of the times t ± mT and t−lT ± mT (where m is a positive integer) before and after each IT is represented by i (t ± mT) and i (t−lT ± mT), respectively. Where Km is the constant corresponding to the integer m and ω is the angular frequency, Thus, the values of the resistance R and the reactance ωL of the power system are obtained, and it is determined whether at least one of these values is within a predetermined value.

[Action]

In the digital protection relay according to the present invention, the circuit equation at the two sampling times is changed to a binary simultaneous equation requiring a differential value of the current, and the difference current at the time before and after the sampling time is corrected by an optimal number. And then add a plurality of them. As a result, even if harmonics are included, the resistance and inductance (or reactance) can be accurately calculated.
Can be requested.

(Example of the invention)

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, (1) is a power system, (2) is a voltage transformer, and (3) is a current transformer, which respectively introduces the voltage and current of the power system. (4) and (5) are input converters for obtaining easily processable voltage values, (6) and (7) are sampling and holding circuits for holding instantaneous values of the voltage values at regular intervals, (8) is a multiplexer which sequentially switches inputs and passes a voltage value to an analog-to-digital converter shown in (9) at the next stage, and (10) is an arithmetic unit which converts a digitized numerical value into (11) ) Is processed by a predetermined calculation method in the memory shown in FIG.

Here, assuming an impedance in which a resistance component R and an inductance L are connected in series, and a current i flows as shown in FIG. 2, a voltage v is obtained at both ends.

When sampling at a constant period T, i (t−2T), i
(T−T), i (t),... V (t−2T), V (t−
T) and V (t) are obtained.

If it is assumed that the flowing alternating current includes the nth harmonic in the fundamental wave, it can be expressed as in the following equation.

Where I: the effective value of the fundamental wave ω: angular velocity t: time α: the initial phase of the fundamental wave k: the harmonic content n: the order of the harmonic β: the initial phase of the harmonic The currents in this equation are R and L , The voltage at both ends can be expressed as a circuit equation at time t.

Similarly, the time (t−
T) Therefore, from the formulas and formulas, V (t), V (t−T), i
(T), i (t−T), △ i (t), △ i (t−T)
If these values are obtained, the resistance R and the inductance L can be obtained.

Equations and equations can be obtained by solving the equations as a simultaneous equation and solving with a determinant.

An expression can be expressed by an expression when expressed by reactance.

Here, V (t), V (t−T), i (t), i (t−T)
Is obtained as a sampling value.
How to determine i (t) and △ i (t−T) will be described.

Now, as a method of obtaining △ i (t) at time t,
Four current values i (t−2T, t−2T, t−T, t + T, t + 2T)
An example using T), i (t−T), i (t + T), i (t + 2T) will be described.

An equation is assumed with numerical constants K ₁ and K ₂ .

Meaning of expression, the difference between the current value of one sample before and after the time t, and calculates the sum of those multiplied by a numeric constant K ₁ and those obtained by multiplying the numeric constant K ₂ to the difference between the current value of 2 samples before and after Things.

Similarly, D (t−T) at time (t−T) becomes an equation.

On the other hand, differentiating the expression results in the expression.

Here, the formulas and formulas are all given if the condition of 2 ｛K ₁ sin (ωТ) + K ₂ sin (2ωТ)｝ = ω 2 ｛K ₁ sin (nωТ) + K ₂ sin (2nωТ)｝ = nω holds. The same can be said. In addition,
There are many methods for deriving the constant Km. Here, the basic concept will be described. The differential approximation expression (expression) and the actual differential expression () become equal when the condition of the expression and the expression is satisfied. That is, assuming that the numerical constants K1 and K2 in the expression are values satisfying the expression and the expression, the differential approximation expression (expression) accurately derives a differential value for two types of frequencies ω and nω. . The numerical constants K1 and K2 may be obtained by solving the equations using simultaneous equations.

In the above example, the number of terms in the approximation formula is two (K1 and K2 terms)
And the value of P in the expression in the claims is P = 2
Becomes The differential approximation formula of the present application, ΣKm · ｛i (t + mT) −i
The number P of terms in (t−mT)｝ is completely arbitrary, and an accurate differential value is derived at any frequency (ω) at that time (the selection of the value of Km is also arbitrary).
When these K ₁ and K ₂ are obtained by a determinant method, the following equations are obtained.

For example, the fundamental wave is 50Hz and the sampling frequency is 600Hz
Then, when the second harmonic (n = 2) is included, the values of K ₁ and K ₂ can be replaced by ω = 2 to replace the expression by the expression.
π × 50, Assuming that n = 2, K ₁ = 429.15 K ₂ = −66.39, and D (t) = 429.15 {i (t + T) −i (t−T)} − 66.39 {i (t + 2T) −i (t−2T)} Is calculated, the value of di (t) / dt is obtained.

Similarly, the equation is represented by D (t−T) = 429.15 {i (t) −i (t−2T)} − 66.39 {i (t + T) −i (t−3T)}. If you calculate Is obtained.

Therefore, the formula and the formula are The resistance and the inductance can be calculated with high accuracy regardless of the second harmonic content k.

In the above example, K ₁ and K ₂ are selected so that the error becomes zero when the second harmonic is superimposed. However, when other harmonics are superimposed, n of the equation is set to that value, and By solving the simultaneous equations, K ₁ and K ₂ can be selected to optimal values.

FIG. 3 is a processing flowchart showing a method in which the computing unit (10) and the memory (11) in FIG. Using the sampling value of the current value (13), perform each difference operation (14)
The K ₁ and K ₂ are performed in multiply (15). Each sum operation (1
6) is performed, multiplication (17) is performed, and each difference operation (18) is performed. Finally, by performing the division (19), a desired R is obtained. The equation may be similarly developed for L. Further, a method of extending the harmonic order will be described on the assumption that the contained harmonic orders are differently superimposed depending on the case.

Now, as a method of obtaining △ i (t) at time t,
From the six current values at times t−3T, t−2T, t−T, t + T, t + 2T, t + 3T, numerical constants are set as K ₁ , K ₂ , and K _3. Here, the equations are as follows: 2 ｛K ₁ sin (ωT) + K ₂ sin (2ωT) + K ₃ sin (3ωT)｝ = ω 2 ｛K ₁ sin (nωT) + K ₂ sin (2nωT) + K ₃ sin (3nωT If the condition of｝ = nω is satisfied, it can be said that they are completely equal.
Since there are _three K ₁ , K ₂ , and K ₃ , the equation is expressed as the n _1st harmonic and
Assuming that n holds with the _second harmonic, 2 ｛K ₁ sin (n ₁ ωT) + K ₂ sin (2n ₁ ωT) + K ₃ sin (3n ₁ ωT)｝ = n ₁ ω 2 ｛K ₁ sin (n ₂ ωT) + K ₂ sin (2n ₂ ωT) + K ₃ sin (3n ₂ ωT)｝ = n ₂ ω, and K ₁ , K ₂ , and K ₃ can be obtained from the equations.

If the above method is extended, it is possible to obtain the differential value of the current by removing the influence of harmonics that may be included. Further, it can be determined from the equation that n is not an integer and may be a subharmonic.

In the above-described embodiment, the simultaneous equations at the sampling times adjacent to each other at the time t and the time t−T are described as being solved by the equations as described above. A distant binary system may be used.

In the above embodiment, the resistance R and the inductance L (or the reactance ωL) are described as being calculated. However, R and L (or ωL) are stored in the memory, and the calculation results are calculated. It is possible to determine the magnitude, and it is also possible to determine the phase difference between the voltage and the current from R and L (or ωL).

In the above-described embodiment, the voltage and the current are described as being introduced one by one. However, the voltage and the current obtained by the relation between the phase and the line in the power system or the relation including the zero phase may be used. The same effects as those of the above embodiment can be obtained.

〔The invention's effect〕

As described above, according to the present invention, after the voltage and current of the power system are sampled at a fixed cycle and digitally converted,
In the digital protection relay obtained by calculating the resistance R and the inductance L based on the digitally converted numerical values, the sampling cycle is separated by T, the sampling time t, and a predetermined number of samples 1 from the sampling time t. The voltages and currents at the respective times t-1T are represented by V (t), V (t-1T) and i, respectively.
(T) and i (t−lT), the time t and the time t−lT
The currents at t ± mT and t−lT ± mT (where m is a positive integer) before and after i are respectively i (t ± mT) and i (t−lT ± mT), When the constant corresponding to the integer m is Km, The value of the subsequent component R and the value of the inductance L of the power system are determined and whether or not at least one of these values is within a predetermined value is determined. In the digital protection relay obtained by performing arithmetic processing on the resistance R and the reactance ωL based on the digitally converted numerical values after sampling and digital conversion, the sampling cycle is T,
The sampling time t and the sampling time t
The voltage and the current at the respective times t-1T separated by a predetermined number of samples 1 from V are represented by V (t) and V (t), respectively.
−lT), i (t) and i (t−lT), and the time of t ± mT and t−lT ± mT (where m is a positive integer) before and after the time t and the time t−lT, respectively. Where i (t ± mT) and i (t−lT ± mT) are the above currents, Km is a constant corresponding to the positive integer m, and ω is an angular frequency. Thus, the values of the resistance R and the reactance ωL of the power system are determined, and it is determined whether at least one of these values is within a predetermined value. Therefore, even if harmonics are included, the resistance and the resistance can be accurately determined. The inductance (or reactance) can be determined.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital protection relay according to an embodiment of the present invention, FIG. 2 is a diagram showing a sampling relationship between a voltage and a current, FIG. 3 is a processing flowchart for obtaining a resistance component, and FIG. The figure is a principle diagram of a conventional moh element. (1) is a power system, (2) is a voltage transformer, (3) is a current transformer, (4) and (5) are input converters, (6) and (7).
Is a sampling and holding circuit, (8) is a multiplexer, (9) is an analog / digital converter, (10) is an arithmetic unit, and (11) is a memory. In the drawings, the same reference numerals indicate the same or corresponding parts.

Continuation of the front page (72) Inventor Kazuyoshi Yoshida 1-3-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Inside Tokyo Electric Power Company (72) Inventor Nozomi Suzuki 1-1-2 Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Electric Corporation Control Factory (72) Inventor Gensaburo Kotani 1-2-1, Wadazakicho, Hyogo-ku, Kobe City, Hyogo Prefecture Mitsubishi Electric Corporation Control Factory (72) Inventor Wataru Kayamori Hyogo-ku, Kobe City, Hyogo Prefecture 1-1-2 Tazaki-cho, Mitsubishi Electric Corporation Control Company (72) Inventor Shigeo Fujii 6-1-1, Hamayama-dori, Hyogo-ku, Kobe-shi, Hyogo Pref. Mitsubishi Electric Engineering Co., Ltd. Kobe Office (56) References JP JP-A-63-56123 (JP, A) JP-A-60-39312 (JP, A) JP-A-51-53236 (JP, A) JP-A-62-100125 (JP, A)

Claims (2)

(57) [Claims] 1. A voltage and a current of a power system are sampled at a fixed period and are converted into a digital signal. Then, based on the digitally converted numerical value, a resistance R and an inductance L are determined.
In the digital protection relay obtained by calculating the above, the sampling cycle is T, the sampling time t, and the voltage and current at the time t-1T at a predetermined number of samples 1 away from the sampling time t, respectively. v (t) and v (t-1T) and i (t) and i
(T-1T), the current at each of the time t ± mT and t-1T ± mT (where m is a positive integer) before and after the time t and the time t-1T, respectively, is represented by i (t ± m
T) and i (t−1T ± mT), corresponding to the above positive integer m, Km is a constant arbitrarily selected so that an accurate differential value is derived at any frequency, and P is an arbitrary positive integer. And the following equation A value of the resistance R and the inductance L of the power system, and determining whether at least one of the values is within a predetermined value. 2. A method according to claim 1, wherein the voltage and current of the power system are sampled at a constant period and converted into digital data, and the resistance R and the reactance ωL are calculated based on the digitally converted numerical values.
In the digital protection relay obtained by calculating the above, the sampling cycle is T, the sampling time t, and the voltage and current at the time t-1T at a predetermined number of samples 1 away from the sampling time t, respectively. v (t) and v (t-1T) and i (t) and i
(T-1T), the current at each of the time t ± mT and t-1T ± mT (where m is a positive integer) before and after the time t and the time t-1T, respectively, is represented by i (t ± m
T) and i (t−1T ± mT), corresponding to the above positive integer m, Km is a constant arbitrarily selected so that an accurate differential value is derived at any frequency, and P is an arbitrary positive integer. And the following equation A digital protection relay characterized in that a value of a resistance R and a value of a reactance ωL of a power system are obtained, and whether or not at least one of these values is within a predetermined value is determined.