JPH0777484B2 - Digital protection relay - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital protection relay that operates by calculating an impedance value from a voltage and a current of a power system, and particularly to improvement of its high-speed response and frequency characteristics. Is.

[Conventional technology]

Figures 4 and 5 show 46 of Electric Cooperative Research, Vol. 41, No. 4, Digital Relay (published by the Electric Cooperative Research Group in January 1986).
The conventional digital protective relay shown on page 48 has been described with respect to the mho characteristic, but the blinder characteristic can be similarly considered.

FIG. 4 is a known vector diagram expressing the blinder characteristic, in which the current of the electric power system is set as a reference on the horizontal axis, the phase is delayed by γ, and a vector (ZI) whose magnitude is Z times is obtained,
Difference vector (ZI
If the phase difference between −V) and the vector (ZI) is within 90 °, the operation area is on the left side of the straight line PQ.

FIG. 5 illustrates a conventional calculation means for realizing the blinder characteristic by a digital protective relay by sampling the electrical voltage v and the current i of the electric power system at every electrical angle of 30 ° and using the data. Is.

Next, the operation will be described. For convenience of explanation, it is assumed that instantaneous values of voltage and current are v and i, maximum values are V and I, a rated frequency is f ₀ , and a sampling period is T. Further, in order to distinguish the data for each sampling time, a time t−nT that is a predetermined number of samples n apart from the sampling time t.
(N = 0,1,2, ..., and n = 0 is the time), the voltage is v ₍₀₎ , v _(T) , v with n as a subscript.
_(2T) , ... Currents are expressed as i ₍₀₎ , i _(T) , i _(2T) , ....

The sampling period T is the rated frequency f ₀ of the power system, Is generally selected, which corresponds to an electrical angle of 30 °.

In FIG. 5, current is i = Isin (θ) and voltage is v = Vsin (θ
+ Φ), the sampling values of voltage and current are
v ₍₀₎ , v _(T) , v _(2T) , ... and i ₍₀₎ , i _(T) , i _(2T) , ..., so that (1) to (6) are replaced by v ₍₀₎ , v _(3T) , i ₍₀₎ , i
_(T) , i _(3T) , i _(4T) . I ₍₀₎ + i in the sum calculation means (7)
_(T) is obtained by the sum calculation means (8) to obtain i _(3T) + i _(4T) , and the magnification calculation means (9) and (10) respectively obtain i ₍₀₎ + i _(T) and i.
_{Multiply (3T)} + i _(4T) by Z · a.

When the difference between v ₍₀₎ and v _(3T) is calculated by the difference calculating means (11) and (12), the outputs are [Za {i ₍₀₎ + i _(T) }-v ₍₀₎ ], respectively. [Za {i _(3T) + i _(4T) }-v _(3T) ] is obtained. The product calculation means (13) and (14) calculate the product of the difference calculation means (11) and the sum calculation means (7) and the product of the difference calculation means (12) and the sum calculation means (8), respectively, so that the output is , [Z ・ a ・ {i ₍₀₎ ＋ i _(T) }-v ₍₀₎ ] ・ {i ₍₀₎ ＋ i _(T) } and [Z ・ a ・ {i _(3T) ＋ i _(4T) }, respectively −v _(3T) ] ・ {i _(3T) + i _(4T) } is obtained. Equation (1) is obtained by adding by the sum calculation means (15).

S = [Z ・ a ・ {i ₍₀₎ ＋ i _(T) }-v ₍₀₎ ] ・ {i ₍₀₎ +
i _(T) } ＋ [Z ・ a ・ {i _(3T) ＋ i _(4T) } − v _(3T) ] ・ {i _(3T) ＋ i _(4T) }
… (1) Sampling value v ₍₀₎ = Vsin (θ +
φ), v _(3T) = Vsin (θ + φ _-3T ), i ₍₀₎ = Isin (θ), i
_(T) = Isin (θ _-T ), i _(3T) = Isin (θ _-3T ), i _(4T) = Isin
Substituting (θ _-4T ) gives the equation (2).

If the decision calculation means (16) outputs this equation (2) only when it is positive, the equation (3) is obtained.

Where the value of a is And

Since the sampling period T was selected to be 30 ° at the rated frequency, substituting T = 30 ° into the equation (3) gives As is well known, this results in a blinder characteristic with a maximum sensitivity angle γ = -15 ° shown in FIG.

Based on the above results, we evaluate the conventional digital protection relay with the blind characteristic.

First, the required sampling number of voltage and current is n = 0,1,3,
Since it is 4, complete computation cannot be performed until at least 4T time has elapsed from the time n = 0, so output terminal (1
In order to obtain the judgment result in 7), time equivalent to 30 ° x 4 = 120 ° is required, and in the case of f ₀ = 50 ^HZ Seconds.

The sampling period T is the rated frequency f ₀ of the power system
It is fixed at intervals of 30 °, but if the frequency changes to f, The value of becomes visible.

Generally, the power system is operated at the rated frequency f ₀ , but the frequency at the time of an accident often changes from f ₀ , so it is necessary to accurately determine the impedance value even in such a state. There is usually a demand to reduce the error as much as possible for a change of about ± 5%.

Considering the case where the frequency f = 52.5 ^HZ (5% increase of 50 ^HZ ), T = 31.5 °. Substituting this into Eq. (3) Considering the case of f = 47.5 ^H (5% reduction of 50 ^HZ ),
T = 28.5 °, and substituting this into equation (3) Then, when θ = 0 to 360 ° is changed, the blind characteristic as shown in FIG. 6 is obtained, and the shaded portion appears as an error depending on the value of θ.

[Problems to be Solved by the Invention]

Since the conventional digital protective relay is configured as described above, it takes a long time to obtain the determination result and the error of the determination result with respect to the fluctuation of the frequency is large.
It was a constraint condition when used as protection of the power system.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a digital protective relay that can reduce the determination time to about 1/2 and can almost ignore the determination error for frequency fluctuation.

[Means for Solving the Problems]

The digital protective appliance according to the present invention is capable of high-speed response by arithmetic processing using v ₍₀₎ , v _(T) , i ₍₀₎ , i _(T) , i _(2T) as sampling values of voltage and current. The characteristics are ensured, and the characteristic change with respect to the frequency change can be ignored.

[Work]

The digital protection relay according to the present invention has the time n =
Since the calculation is performed with the current sampling value i _{(0) to} i _{(2T) of 0} , the influence of the frequency can be ignored and the data up to the current sampling value i _{(2T) of} 2T (= 60 °) is used. Therefore, it is possible to cope with high speed.

Example of Invention

 An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, (18) and (19) are sampling values of voltage and current, and subscripts indicate values at sampling time n.
(20) and (21) are multiplying means, and the value of a is And Current sampling values of 0 and T i _{(0) (2)} and i _{(T) (3)}
Is multiplied by Z · a by magnification calculation means (20) and (21), respectively, and voltage sampling values v _{(0) (1)} and v _{(T of} 0 and T are calculated by difference calculation means (11) and (12). _{) (18)} , the outputs are {Zai ₍₀₎ −v ₍₀₎ } and {Zai _(T) −v _(T) }, respectively.

On the other hand, the difference calculation means (22) uses the current sampling value i _{(0) (2)}
And i _{(T) (3)} difference {i ₍₀₎ −i _(T) } is calculated, and the difference calculation means (2
3) is the difference between the current sampling values i _{(T) (3)} and i _{(2T) (19)} {i
_(T) −i _(2T) } is calculated.

A product calculating means (13) obtains the product of the difference calculating means (11) and (23), and a product calculating means (14) calculates the difference calculating means (12).
And (22) are obtained, and the output is {Zai ₍₀₎ −v ₍₀₎ } ・ {i _(T) −i _(2T) } {Zai _(T) −v _(T) } ・ {i ₍₀₎ −i _(T) }, and the difference is calculated by the difference calculating means (24) (8)
The formula is obtained.

S = {Zai ₍₀₎ -v ₍₀₎ } {i _(T) -i _(2T) }-{Zai _(T) -v _(T) } {i ₍₀₎ -i _(T) } ……… (8) In this equation (8), the sampling value v ₍₀₎ = Vsin (θ +
φ), v _(T) = Vsin (θ + φ _-T ), i ₍₀₎ = Isin (θ), i _(T)
= Isin (θ _-T ), i _(2T) = Isin (θ _-2T )
Expression (9) is obtained.

If this formula (9) is output by the judgment calculation means (16) only when it is positive, then since Isin _(T) > 0, formula (10) is obtained.

Since the sampling period T was selected to be 30 ° at the rated frequency, substituting T = 30 ° into the equation (10), As is well known, this results in the blinder characteristic shown in FIG. 4 with the maximum sensitivity angle γ = -15 °.

Based on the above results, the digital protection relay having the blinder characteristic of the present invention will be evaluated.

First, the required number of samplings for voltage and current is n = 0,1,2,
Therefore, after 2T time has elapsed from the time n = 0, a complete calculation can be performed, and therefore a judgment result can be obtained at the output terminal (17) in a time equivalent to 30 ° × 2 = 60 °, f ₀ = 50
^In the case of ^HZ , Seconds.

Next, when calculating the calculation accuracy when the frequency changes,
When f = 52.5 ^HZ (5% increase of 50 ^HZ ), substituting T = 31.5 ° into equation (10) When f = 47.5 ^HZ (5% reduction of 50 ^HZ ), substituting T = 28.5 ° into equation (10) gives As shown in Fig. 2, the error is about ± 0.3%,
The characteristics are almost the same as those at the rated frequency.

FIG. 3 is a hardware configuration diagram of the digital protective relay (38) of the present invention. In the figure, (25) is a voltage transformer,
(26) is a current transformer, (27) and (28) are input converters, which convert the voltage and current of the power system into values that can be easily processed, and (29) and (30) are filters, which are well known. Of the harmonics contained in the voltage and current, the sampling frequency
It removes more than 1/2 frequency components. (31) (3
2) is a sample hold, which holds the sampling value until the next sampling time. Reference numeral (33) is a multiplexer which sequentially switches the outputs of the sample and hold (31) and (32) and transmits them to the analog / digital converter (34). Reference numeral (35) is a microprocessor, which executes an operation using a program stored in advance in a memory (36) and outputs the result to an output circuit (37). (38) is a digital protective relay.

In the above embodiment, the voltage and the current are expressed as v and i, respectively, but when used in a power system, as is well known, calculation is performed as a line input and a phase input for a short-circuit accident and a ground fault, respectively. It is clear to do.

Also, when a zero-phase current is used for zero-phase compensation, the same calculation can be performed. Further, in the above-mentioned embodiment, the case of γ≈15 ° is illustrated, but also in the case of γ≈0 °, another constant k is given to the basic equation, and the arithmetic expression {Z · i _(t) −v _{( t)} } {i _(tT) -k * i _(t-2T) }-{Z * i _(tT) -v _(tT) } {i _(t) -k * i _(tT) }> 0, and a constant If k is set to a predetermined value and calculation is performed, the same effect as that of the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the present invention, the current sampling values i _{(0) to} i _(2T) at the time are used to use the sampling values within the two sampling times. There is an effect that high speed determination is possible, and even if there is a frequency change, an error can be almost ignored and a high accuracy is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a means for calculating a blinder characteristic according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of a blinder characteristic obtained by the calculating means of the present invention, and FIG. 3 is a calculating means of the present invention. FIG. 4 is a block diagram showing a hardware configuration of a digital protective relay for realizing the above, FIG. 4 is a vector diagram for obtaining a conventional blinder characteristic, FIG. 5 is a block diagram showing a means for calculating a conventional blinder characteristic, and FIG. FIG. 6 is a frequency characteristic diagram of a blinder characteristic obtained by the calculating means of FIG. In the figure, (1) to (6), (18) and (19) are sampling values of voltage and current, (9), (10), (20),
(21) is a magnification calculation means, (11), (12), (22), (2
3) and (24) are difference calculation means, (13) and (14) are product calculation means, (15) is sum calculation means, (16) is judgment calculation means, and (1)
7) is an output terminal, (25) is a voltage transformer, (26) is a current transformer, (27) and (28) are input converters, (39) and (30) are filters, (31) and (32). ) Is sample hold, (33)
Is a multiplexer, (34) is an analog-to-digital converter, (35) is a microprocessor, (36) is a memory,
(37) is the output circuit, (38) is the digital protective relay. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A digital protection relay for detecting a power system fault by sampling the voltage and current of the power system at a constant cycle T, converting them to digital values, and then performing arithmetic processing based on the numerical values to detect the accident of the power system. Sampling value v of each of the voltage and current at time t−nT (n = 0, 1, 2, ...) That is 1/12 of the period at the rated frequency and is a predetermined number of samples n away from the sampling time t.
_(t-nT) and i _(t-nT) are obtained, and the following equation is obtained: {Z · i _(t) −v _(t) } · {i _(tT) −i _(t-2T) } − {Z · i _(tT) −v _(tT) } · {i _(t) −i _(tT) }> 0. 2. A digital protection relay for detecting a power system fault by sampling the voltage and current of the power system at a constant cycle T, converting them to digital values, and then performing arithmetic processing based on the numerical values to detect the accident of the power system. Sampling value v of each of the voltage and current at time t−nT (n = 0, 1, 2, ...) That is 1/12 of the period at the rated frequency and is a predetermined number of samples n away from the sampling time t.
_(t-nT) and i _(t-nT) are obtained, and given constants Z and a are given. The following equation {Z · a · i _(t) −v _(t) } · {i _(tT) −i _(t-2T) } − {Z · i _(tT) −v _(tT) } · {i _{( t)} -i _(tT) }> 0 A digital protective relay provided with a calculation means for executing a calculation.