JPH0561857B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is a digital protective relay for detecting faults in a power system, and relates to an undervoltage relay with current compensation.

[Conventional technology]

Figure 8 shows, for example, Conference published by IEE.
Publication No.249 April 1985 50 pages ~
This is a circuit diagram of the conventional undervoltage relay with current compensation (hereinafter referred to as UVZ) shown on page 54.
In the figure, 1 is a voltage transformer, 2 is a current transformer,
3 and 4 are UVZ input converters for voltage and current, 5 is a phase shifter, 6 is a setting device for setting the amount of current compensation, 7,
8 is a half-wave rectifier that allows only the half-wave period of AC to pass;
9 is a setter that provides a detection level; 10 is a comparator that compares and determines the magnitude; 11 is a time limit circuit;
Configure the UVZ shown in 2.

Next, the operation will be explained with reference to FIG. 9. The voltage V and current I obtained from the power system are introduced in isolation by respective input converters 3 and 4. The current I is phase-shifted by an angle Φ by the phase shifter 5, and this angle is selected to correspond to the phase difference between voltage and current at the time of a transmission line fault, and is about 75 degrees.
When this phase-shifted current I<Φ is given to the setting device 6 that determines the current compensation amount Z, the current compensation portion ZI of ZI is passed through the half-wave rectifiers 7 and 8, respectively, to the setting value
When ko and ko are added to the comparator 10, an oval locus whose origin is on the ZI axis and whose size is surrounded by ko is obtained, as shown in Fig. 9, and the voltage V is within the range of this oval. If so, the comparator 10 outputs an output. This output is checked for a predetermined period of time by the timer circuit 11, and
Outputs the judgment result to the OUT terminal.

[Problem that the invention seeks to solve]

Since the conventional UVZ is configured as described above, it can perform only one judgment process every half cycle of AC, so the maximum missed time is half a cycle from the time an accident occurs until it is detected. The problem was that the judgment time was half a cycle and one cycle was required, resulting in a slow accident detection time. Furthermore, since the circuit configuration is an analog circuit, there is a possibility of the influence of drift, which causes problems such as the time required for adjustment and the inability to achieve high detection sensitivity. Furthermore, since it is not possible to receive digital signals from digital transformers and digital current transformers, which have recently been developed, a problem has arisen in that the range of use is limited.

This invention was made to solve the above-mentioned problems, and because numerical calculations are performed using a microprocessor, UVZ can be determined at high speed and does not require consideration of drift or aging.
The purpose is to obtain.

[Means for solving problems]

The UVZ according to this invention realizes an undervoltage relay that converts voltage and current into digital values and adds current compensation through arithmetic processing, and enables high-speed detection by reducing the number of sampling data used for arithmetic processing. In addition, it has achieved high reliability by reducing the effects of drift and aging that have been a problem with analog circuits.

[Effect]

In order to achieve this characteristic, the UVZ of this invention uses digital calculation processing to calculate the difference between the current compensation coefficients and the voltage and determine the magnitude of each, so it can operate at high speed. There is an effect that can be determined, and furthermore, by digital calculation processing, it is possible to maintain stable characteristics over a long period of time with little drift or aging.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, 13 and 14 are filters, which remove frequencies higher than 1/2 of the sampling frequency among harmonics contained in voltage and current, and 15 and 16 are sample holds, which remove the sampling frequency. 17 is a multiplexer that sequentially switches the outputs of the sample holds 15 and 16 and transmits them to the analog-to-digital converter 18; 19 is a microprocessor;
The calculation is performed using a program stored in advance in the computer, and the results are outputted to the output circuits 21 and 22.

FIG. 2 is a waveform diagram showing the operation of sample hold, in which voltage V and current I are sampled at the same time as sample signals and held until the next sample signal arrives. , it will be converted into a digital value and processed.

FIG. 3 is a vector diagram for explaining means for realizing the characteristics of an embodiment of the present invention, which is actually realized by digital calculation. In the following explanation, the same applies when a vector diagram appears.
The phase is shifted by Φ with respect to the current I, and the magnitude is set to Z.
When the multiplied vector ZI is derived and the difference from the voltage V is determined, the vector (V-ZI) is obtained. This (V-
A constant whose size (ZI) is given as a set value
When finding an area smaller than ko, as shown in the figure, ZI
A circle with radius ko centered at is obtained. That is, it shows that the tip of voltage V exists inside the circle. Therefore, if this condition is met,
By outputting the determination output from the output circuit 21 in FIG. 1, it becomes clear that the UVZ 12 has detected it. However, if the voltage V drops to the position Vo in Figure 3, the vector (Vo − ZI) becomes a constant
Since it becomes larger than ko, UVZ cannot be detected even though the voltage has decreased further, which is a problem.

FIG. 4 is an explanatory diagram of a device that realizes the characteristics of an embodiment of the present invention. In this figure, as an example, Z of vector ZI derived from current I is expressed as Z=O,
Z ₁ and Z ₂ are three vectors O, Z ₁ I, and Z ₂ I, and the difference from the voltage V is also (V-O) =
As three values, V, (V-Z ₁ I), and (V-Z ₂ I), the magnitude of each difference is determined by comparing with a constant ko.
In the same way as explained in Fig. 3, in Fig. 4, a circle 23 centered at the origin (ZI=O), a circle 24 centered at Z ₁ I, and a circle 25 centered at Z ₂ I are obtained. However, since only the vector (V-Z ₁ I) is smaller than the constant ko, it will be output. The voltage V is
Regardless of whether it is inside circles 23, 24, or 25,
In order to obtain output from UVZ, it can be achieved by calculating the logical sum of these outputs. Therefore, the detection area for UVZ is within the logical sum of the three circles shown in FIG.

By developing this idea and increasing the number of vectors ZI, the characteristics of the portion parallel to ZI can be made closer to a straight line.

FIG. 5 is a flowchart illustrating an example of an arithmetic processing method for realizing the UVZ of the present invention.
In the following description, the sampling frequency is 12 times the frequency of the voltage and current, that is, an electrical angle of 30° with respect to the frequency of the voltage and current, and the symbol is indicated as T. The data at the current sample point is marked (+) with a suffix, and the previous data is marked (t).
-T), (t-2T), ... Therefore, if the phase difference is θ, the voltage and current are v(t-nT)=Vsin {(ωt+θ)-30°×n}=Vsin
{ωt+θ)−nT}……i(t−nT)=Isin(ωt−30゜×n)=Isin(ωt−nT
)
... However, n=0, 1, 2, 3...

If the phase shift angle of current I is Φ = 75°, then i (t + 75°) = Isin (ωt + 75°) = I (0.2588sinω
t+0.9659cosωt)... On the other hand, i(t-T)Isin(ωt-30゜) =√3/2i(t)-1/2-Icosωt ∴ Icosωt=√3i(t)-2i(t-T) ... Therefore, by substituting the formula, the formula is i(t+75°)=0.2588i(t)+0.9659×{√3i(t)−2
i(t-T)}=1.9319×{i(t)-i(t-T)}...
becomes.

In Figure 5, {{i(t)-i(t-T)}29 is calculated from the data of i(t)27 and i(t-T)28, and then
The formula is realized by multiplying by K30=1.9319. With K=2.0 than with K=1.9319, microprocessor processing can be executed with shift instructions, so
K=2.0 may also be used, which means that Z
It can be corrected by converting by multiplying by . next,
Multiply by the constants Z=O31, Z=Z ₁ 32, Z=Z ₂ 33,
O, KZ ₁ {i(t)-i(t-T)}, KZ ₂ {i(t)-i(t
−T)} and subtract each from v(t)26 to obtain the respective difference D ₀₀ = v(t) 34 ... D ₀₁ = [v(t)−KZ ₁ {i(t)− i(t-T)}] 35)
…… D ₀₂ = [v(t)−KZ ₂ {i(t)−i(t−T)}]36
... get...

Similarly, the same calculation process is performed one sample before, and {i(t-T)-i(t-2T)}39 is calculated from i(t-T)28 and i(t-2T)38. seek, K{i
(t-T)-i(t-2T)}40, Φ=75° is realized, O41, KZ ₁ {i(t-T)-i(t-2T)}42,
Calculate KZ ₂ {i(t-T)-i(t-2T)}43 and subtract each from the voltage v(t-T)37 to get the difference DT ₀ =v(t-T)44... ... DT ₁ = [v(t-T)-KZ ₁ {i(t-T)-i
(t-2T)}]45... DT ₂ = [v(t-T)-KZ ₂ {i(t-T)-i
(t−2T)}]46 ... is obtained.

Here, to find the amplitude value of the sine wave from two pieces of data 30 degrees apart on the sine wave, v ² (t) + v ² (t - T) - 3v (t) v (t - T) = V ² sin ² (ω
t+θ)+V ² sin ² {(ωt+θ)−T} −√3V ² sin(ωt+θ) sin {(ωt+θ)−T}=1
/4V ₂ , so V ² = 4 {v ² (t)+v ² (t-T)-3v(t)v(t-T)}
Since there is a relationship between , , and , the amplitude value can be obtained by using the same formula as M ₀₀ , M ₀₁ , and M ₀₂ , then M ² ₀₀ = 4 {D ² ₀₀ + D T ² ₀ −3D ₀₀ DT ₀ }=4{v2(t) +v(t- ² T)−√3v(t)v(t−T)}47 …… M ² ₀₁ = 4{D ² ₀₁ +D ² T ₁ −√3D ₀₁ DT ₁ −√3D ₀₁ D T}=4 [[v(t)−KZ ₁ {i(t)−i(t−T)}] ² +
[v(t-T) -KZ ₁ }i(t-T)-i(t-2T)}] ² -3[v(t
)−KZ ₁ {i(t) −i(t−T)}] [v(t−T)−KZ ₁ {i(t−
T)−i(t−2T)}]]48… M ² ₀₂ 4{D ² ₀₂ +D ² T ² −3D ₀₂ DT ² −3D ₀₂ D T}=4 [[v(t)−KZ ₂ { i(t)−i(t−T)}] ₂ +
[v(t-T) -KZ ₂ {i(t-T)-i(t-2T)}] ² -3[v(t
)−KZ ₂ {i(t) −i(t−T)}] [v(t−T)−KZ ₂ {i(t−
T)-i(t-2T)}]]49... is obtained.

The integer constant that determines the detection range is given by k ² ₀ 50, and by comparison calculation M ² ₀₀ ≦k ² ₀ 51, M ² ₀₁ ≦k ² ₀ 52,
M ² ₀₂ ≦k ² ₀ 53 is calculated, and if the condition is satisfied, it is passed through the logical sum 54, and if one of them is determined,
Output is obtained at OUT.

FIG. 6 is an explanatory diagram for calculating the UVZ detection time according to the present invention. A is the voltage V, B is the current I with a phase delayed by 75° from V, C is the current compensation amount with Φ = 75°, D is the voltage V with current compensation, and E is the amplitude value calculation result. F is the sampling time, and it is assumed that the accident occurred at point F immediately after time (t-3T). The amount of current compensation (c) after the accident occurs is the current i(t-
2T), i(t-T), and i(t), so it becomes an accurate value at time t. Therefore, since the amplitude value calculation in E also becomes an accurate value after the accident at time t, the maximum detection time for which M ² ₀₁ ≦k ² ₀ becomes {(t-2T) after the accident occurs. -(t-3T)}+{t-(t-2T)}
+
{(t+T)-t}=4T, that is, the time equivalent to 30°×4=120°, which is 1/3 cycle of the power system. Specifically, in a 50Hz power system, (1/50) ×
(1/3)Sec=6.67mSec.

In addition, in the above embodiment, an example is shown in which voltage and current data are used every 30 degrees, but in addition to this, there are also examples of using data every 60 degrees or 90 degrees, such as phase shift calculation and amplitude value calculation. By changing as shown in FIG. 7, the UVZ characteristics shown in FIG. 4 can be realized. (M ₀₂ is not shown because it is sufficient to change Z ₁ of M ₀₁ to Z ₂ ).

〔Effect of the invention〕

As described above, according to the present invention, a digital arithmetic processing method is used and a plurality of current compensation coefficients are used to obtain the difference between the voltage and the voltage, and the magnitude thereof is determined. It has the effect of being able to be detected and maintaining stable characteristics over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram showing a UVZ according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of sample and hold operation, Fig. 3 is a vector diagram illustrating means for realizing the characteristics of this invention, and Fig. 4 is an explanatory diagram showing the characteristics of this invention, FIG. 5 is a flowchart diagram explaining the arithmetic processing method, FIG. 6 is an explanatory diagram for calculating the detection time, and FIG. FIG. 8 is a circuit configuration diagram of a conventional UVZ, and FIG. 9 is a diagram showing characteristics of a conventional UVZ. In the figure, 1 is a voltage transformer, 2 is a current transformer, 3 and 4 are input converters, 5 is a phase shifter, 6 is a setting device, 7 and 8 are half-wave rectifiers, 9 is a setter, and 10 is a comparison 11 is a time limit circuit, 12 is UVZ, 13,
14 is a filter, 15 and 16 are sample and hold, 17 is a multiplexer, 18 is an analog-to-digital converter, 19 is a microprocessor, 20 is a memory, 21 and 22 are output circuits, 23, 24,
25 is a circle indicating characteristics, 26, 27, 28, 37,
38 is input data, 29, 34, 35, 36, 3
9, 44, 45, 46 are difference calculations, 30, 31,
32, 33, 40, 41, 42, 43 are multiplication operations, 47, 48, 49 are amplitude value operations, 50 are setting values, 51, 52, 53 are comparison operations, and 54 are logical sums. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a digital protective relay that detects faults in the power system by sampling the voltage and current of the power system at regular intervals, converting them into digital data, and performing calculations based on the values, the current is converted to a predetermined phase by a phase shift calculation. means for converting the phase shift calculation result into a plurality of sizes by performing a plurality of magnification calculations with different magnification factors; means for obtaining a difference; means for obtaining the magnitude of each of the plurality of difference calculation results by calculating an amplitude value; and a comparison calculation between the plurality of amplitude value calculation results and a predetermined setting value to obtain respective determination results. A digital protection relay comprising: a means for outputting a signal; and a signal indicating that one of the plurality of judgment outputs has been output.