RU2520163C2 - Method for detecting unauthorised paralleling of feeders of distributing substations on user's side, and device for its implementation - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method is based on determination of a correlation (statistical interrelationship) degree, amplitude difference and difference of phases of consumed currents at analysis time interval. As per analysis results of consumed currents a decision is taken on belonging of signals from consumed current sensors as per analysed connections to a class corresponding to unauthorised paralleling of feeders, or to a class corresponding to absence of fact of paralleling. A device for implementation of this method includes consumed current sensors, analogue-to-digital converters, amplitude and phase detectors, a correlation device, a discrepancy calculation unit, threshold devices, a threshold shaping unit, a decision device and an indication device.

EFFECT: possibility of detecting the fact of unauthorised paralleling of feeders of distributing substations on the user's side.

2 cl, 1 dwg

Description

The present invention relates to measuring equipment, namely to systems for monitoring the modes of energy consumption in order to determine the possible parallelization of feeders on the consumer side.

A device for protecting electrical networks [1] is known, which uses a wireless data transmission channel based on the use of the WAP protocol to control breakers installed in monitored lines. The device provides the ability to detect short circuits of cable lines. The disadvantage is the inability to detect the fact of power supply of one electrical installation from two feeders.

Known selective device for determining single-phase short circuits in cable lines [2], related to measuring equipment, which monitors the state of the cable network of large electrical substations, containing a series-connected zero-sequence current transformer and matching cascade, multiplexer, analog-to-digital converter (ADC), amplitude and phase meters, control unit, logic processing unit, indicator unit, OR circuit, section number determination unit. To implement the invention, methods of digital processing of signals received from zero-sequence current transformers are used. This device allows you to determine the connection of the feeder to the ground. The disadvantage is the inability to detect the fact of power supply of one electrical installation from two feeders.

As the prototype of the device, the closest selective set of features for the determination of single-phase faults in cable lines [2] was selected.

The technical task of the invention is to detect the fact of unauthorized parallelization of feeders of distribution substations on the consumer side. The method implemented in the proposed device is based on determining the degree of correlation (statistical interconnectedness), the amplitude difference and the phase difference of the consumption currents on the analysis time interval. Based on the results of the analysis of consumption currents, a decision is made on whether the signals from the sensors of the consumption currents belong to the analyzed connections to the class corresponding to unauthorized parallelization of feeders, or to the class corresponding to the absence of the fact of parallelization.

The mutual correlation function [3, 4] of samples of discrete samples of two signals from current consumption sensors has the following form:

$$R_{\mathrm{1,2}}=\frac{{\displaystyle \sum _{j=0}^{N-\mathrm{one}}(I{\mathrm{one}}_j=\stackrel{}{{\hat{m}}_{{}_{I\mathrm{one}}}){(I{2}_j-\hat{m})}_{{}_{I2}}}}}{0.5\left[{\displaystyle \sum _{j=0}^{N-\mathrm{one}}(I{\mathrm{one}}_j=\stackrel{}{{\hat{m}}_{{}_{I\mathrm{one}}}{)}^2{(I{2}_j-\hat{m})}^2{}_{{}_{I2}}}}\right]},\text{(one)}$$

where R _{l, 2} is the mutual correlation function;

N is the number of analyzed samples of consumption currents;

I1 _j and I2 _j -je samples of signals I1 and I2 from current sensors connected to the first and second feeders, respectively;

и $${\hat{m}}_{{}_{I2}}$$

- оценки математического ожидания по выборкам сигналов I1 и I2 соответственно. $${\hat{m}}_{{}_{I\mathrm{one}}}$$

and $${\hat{m}}_{{}_{I2}}$$

- estimates of mathematical expectation from samples of signals I1 and I2, respectively.

If the signals of the current sensors are statistically independent, then the cross-correlation function R _{1,2 is} approximately equal to zero. In the presence of a correlated component in the analyzed samples, characteristic of the case of parallelization, the mutual correlation function R _{l, 2} tends to unity.

The decisive rule in this case is:

1. if R _{l, 2} > M / _por.k , then a decision on parallelization is issued;

2. if R _1,2 <M _then . _k , then a decision is issued on the absence of parallelization. $$$$

In accordance with the first law of Kirchhoff [5, 6], when parallelizing the load on the consumer side, equality

$$I_n(t)=I_{\mathrm{one}}(t)+I_2(t),\text{(2)}$$

where I _n (t) is the instantaneous value of the effective current supplied to the load;

I ₁ (t) and I ₂ (t) are the instantaneous values of the current consumption from the first and second feeders, respectively.

Based on the hypothesis of the identity of step-down transformers of a distribution substation (in particular, the equality of their internal resistances) and the resistance of feeders, the expression

$$I_{\mathrm{one}}(t)=I_2(t).\text{(3)}$$

$$$$

Thus, in case of unauthorized parallelization of feeders on the consumer side, the equality of the instantaneous values of the current consumption currents from each pair of analyzed feeders should be satisfied for a long time interval. Under normal operating conditions, equality (3) will be observed only at certain points in time. Therefore, the algorithm can be built on the value of the 1-norm of residual signals from a pair of analyzed sensors

$${\hat{m}}_{{}_{\mathrm{one}}}=\frac{\mathrm{one}}{N}{\displaystyle \sum _{j=0}^{N-\mathrm{one}}|\; |\; |I{\mathrm{one}}_j-I{2}_j|\; |\; |},\text{(four)}$$

- 1-норма невязки сигналов с пары анализируемых датчиков. Решающее правило при этом имеет вид:Where $${\hat{m}}_{{}_{\mathrm{one}}}$$

- 1-norm of residual signals from a pair of analyzed sensors. The decisive rule in this case is:

<М_пор.а, то выдается решение о запараллеливании;1. if $${\hat{m}}_{{}_I}$$

<M _por.a , then a decision on parallelization is issued;

>М_пор.а, то выдается решение об отсутствии запараллеливания. Согласно положениям теории символического метода анализа гармонических колебаний в цепях с сосредоточенными параметрами [5, 6] при комплексном характере нагрузки2. if $${\hat{m}}_{{}_I}$$

> M _por.a , then a decision is issued on the absence of parallelization. According to the provisions of the theory of the symbolic method of analysis of harmonic oscillations in circuits with lumped parameters [5, 6] with a complex nature of the load

$$Z=R+iX,\text{(5)}$$

where Z is the complex load resistance;

R is the resistive resistance;

X is the reactance caused by the capacitive or inductive nature of the load;

i is the imaginary unit;

the phases of the current and voltage at the load differ by $${\varphi }_U-{\varphi }_I={\varphi }_Z=arctg(X/R),-\pi /2\le {\varphi }_Z\le \pi /2.\text{(6)}$$

where f _U is the phase of the voltage;

φ _I is the phase of the current;

φ _Z - the difference between the phases of the current and voltage.

It follows from (6) that when parallelizing the load, the phases of the currents of consumption of the pairs of analyzed feeders will be identical, since the load will be common for them, and during normal operation in most cases the phases will not be equal, because their complex loads described by expression (5), will be different. Therefore, using one of the consumption currents as a reference oscillation, it is possible to average the voltage from the output of a phase detector with a cosine discriminating characteristic over a certain period of time and, if it exceeds the threshold M _pores . _f , issue a decision on parallelization.

The values of the above thresholds are determined in accordance with the selected quality criterion. For example, in the case of using the Neumann-Pearson criterion, the threshold is selected based on a given level of false alarms and the probability of correct detection.

To solve the above technical problem, a device containing, for each pair of feeders allocated to the consumer, consumption current sensors, the inputs of which are connected to the feeders of the distribution substation, ADC, amplitude detectors, phase detector, while the inputs of the amplitude and phase detectors are connected to the outputs of the ADC, a device, an indication device, the input of which is connected to the output of the deciding device, a correlator, a residual calculation unit, three threshold devices and a threshold generation unit are introduced. In this case, the ADC inputs are connected to the outputs of the consumption current sensors, the inputs of the correlator and the residual calculation unit are connected to the outputs of the amplitude detectors of the analyzed pair, the inputs of the first, second, and third threshold devices are connected respectively to the outputs of the correlator, residual calculation unit, and phase detector. The outputs of the threshold forming unit are connected to the inputs of the threshold devices, and the inputs of the deciding device are connected to the outputs of the three threshold devices.

Figure 1 shows a structural diagram of a device for detecting unauthorized parallelization of distribution substation feeders on the consumer side, containing for each pair of feeders allocated to the consumer (not shown in figure 1), the first and second consumption current sensors 1 and 2, the inputs of which are connected to distribution feeders substations, the first and second ADCs 3 and 4, the inputs of which are connected to the outputs of the sensors of current consumption 1 and 2, respectively. The device is equipped for each pair of feeders allocated to the consumer, the first and second amplitude detectors 5 and 6, the inputs of which are connected to the outputs of the ADC 3 and 4, respectively, a phase detector 7, the inputs of which are connected to the outputs of the ADC 3 and 4, the correlator 8, the inputs of which are connected to the outputs of the amplitude detectors 5 and 6, the residual calculation unit 9, the inputs of which are connected to the outputs of the amplitude detectors 5 and 6, and three threshold devices 11, 12 and 13. The inputs of the first, second and third threshold devices are connected respectively to the output correlator 8, residual calculation unit 9, phase detector 7. The device also comprises a threshold generation unit 10, the outputs of which are connected to the inputs of threshold devices 11, 12 and 13, a resolver 14, whose inputs are connected to the outputs of three threshold devices 11, 12 and 13 , and an indication device 15, the input of which is connected to the output of the deciding device 14.

The operation of the device can be described as follows. The signals from the consumption current sensors 1 and 2 are converted to digital form using the ADC 3 and 4. By means of the amplitude detectors 5 and 6, the envelope of the signals of the current sensors is extracted. Correlator 8 determines the correlation coefficient. The obtained value is compared with the threshold in the threshold device 11. If the threshold is exceeded, a decision is made whether or not the feeders are parallelized on the consumer side in accordance with the sign of correlation of the readings of the currents of the consumption sensors. To determine the fact of parallelization by the proximity of the amplitudes of the currents of the consumption sensors, the residual calculation unit 9 determines the average value of the module of the difference in the amplitudes of the samples of the consumption currents, the obtained value is compared with the threshold in the threshold device 12. If the threshold is not exceeded, a decision is made on the presence of parallelization by the amplitude attribute. Similarly, to determine the fact of parallelization by the proximity of the phases of the currents of the consumption sensors by the phase detector 7, the average value of the phase difference module of the samples of the consumption currents is determined, the obtained value is compared with the threshold in the threshold device 13. When the threshold is exceeded, a decision is made on the presence of parallelization by phase. The thresholds supplied to the threshold devices 11, 12 and 13 are formed in the threshold generation unit 10 in accordance with a quality criterion selected by the user. The final decision on the presence or absence of parallelization is made in the solver 14 according to the totality of the results provided by the Signs described above, in accordance with the so-called “3 out of 3”, “2 out of 3” or “1 out of 3” rule. When a fact of parallelization is detected by the indicating device 15, an information signal is generated.

Bibliography

1. Montjean, Dominique. Protection for power grid having an infrared data transmission link using the WAP protocol // Patent WO No. 0213349,2002.

2. Koshelev V.I., Dubov D.A., Konovalov E.B. Selective device for determining single-phase faults in cable lines // Patent RU No. 2316010, 2008.

3. Bendat J., Piersol A. Measurement and analysis of random processes. -M .: Mir, 1974. -464 p.

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Claims (2)

1. A method for detecting unauthorized parallelization of feeders of distribution substations on the consumer side, in which the correlation coefficient of the consumption currents is determined, the average value of the module of the difference in the amplitude of the samples of the consumption currents is determined, the average value of the module of the phase difference of the samples of the consumption currents is determined, the obtained values are compared with thresholds, based on the results comparisons with thresholds make a decision on the presence or absence of the fact of parallelization of feeders at distribution substations x on the consumer side. 2. A device for detecting unauthorized parallelization of distribution substation feeders on the consumer side, containing for each pair of feeders allocated to the consumer two consumption current sensors, the inputs of which are connected to the distribution substation feeders, two ADCs, two amplitude detectors, a phase detector, and the inputs of amplitude and phase detectors connected to the outputs of the ADC, a solver, an indication device, the input of which is connected to the output of a solver, characterized in that a relator, a residual calculation unit, three threshold devices, a threshold generation unit, while the ADC inputs are connected to the outputs of the consumption current sensors, the inputs of the correlator and the residual calculation unit are connected to the outputs of the amplitude detectors of the pair being analyzed, the inputs of the first, second, and third threshold devices are connected respectively to the outputs of the correlator, the residual computation unit, the phase detector, the outputs of the threshold generation unit are connected to the inputs of the threshold devices, the inputs of the solving device are connected to the outputs of the x threshold devices.