RU2782157C1 - Method for assessing the sharing contribution of distortion sources to the supply mains voltage - Google Patents

Abstract

FIELD: electric power industry.

SUBSTANCE: invention relates to the field of electric power industry, in particular to methods for determining the effect of non-linear electricity consumers on voltage distortion at a common connection point (CCP). The amplitude of higher harmonics is measured in the mains voltage at each harmonic separately before and after the passive harmonic filter is connected, the current of the power supply system at the input of the power transformer of all consumers at each harmonic separately after the passive harmonic filter is connected. Next, the calculation of the share contribution of external sources of distortion, the first and second consumer at a harmonic of order h is carried out. Then, the calculated share contributions of the power supply system and consumers to the total distortion of the supply voltage at the harmonic of the order of h are compared and the level of higher harmonics in voltage and current is reduced for consumers with the largest contributions.

EFFECT: accurate assessment of the share contribution of each source of distortion to the mains voltage, including in the presence of external sources of distortion in the power supply system.

1 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of electric power industry, in particular to methods for determining the effect of non-linear electricity consumers on voltage distortion at a common connection point (COP). This invention can be used to regulate commercial relations between the electricity supplier and consumers in the matter of assessing the contribution of each of the consumers to the deterioration in the quality of voltage in the TOC in percentage terms.

There is a known method for determining a consumer that distorts the quality of electrical energy in a node of an energy supply organization, and its contribution to the distortion (RF patent No. 2244313, publ. 10.01.2005). This method involves the calculation of the resistance of non-distorting loads and the calculation of the distortion currents of the distorting loads of each consumer. After that, the obtained current values are correlated with the total values.

The disadvantage of this method is the fact that the authors take the algebraic sum of consumer currents as the total value of distortion currents, arguing that such an assumption will not affect the value of equity contributions. However, it is obvious that the vector sum of the currents will differ significantly from the algebraic one, since the mutual arrangement of the current vectors of each of the branches can be any.

There is a known method for determining the share of the load and the power system in changing the quality of the voltage (RF patent No. 2307364, publ. 09/27/2007), which includes the measurement and determination of the integral components of the abnormal voltages of the branches with EMF and the abnormal components of the currents of the load branches, on the basis of which the shares are calculated each power facility.

The disadvantage of this method is a significant amount of initial data concerning both the power supply system, the instantaneous values of the EMF of the system, and the consumers, the inductance L. For a correct assessment of the equity participation of each power facility, it is necessary to constantly determine the above values.

A known method of identifying the actual contribution of the subjects of electrical networks in the distortion of the quality of electrical energy at the point of common connection in the electrical network (RF patent No. 2364875, publ. 20.08.2009). According to this method, the contribution of each subject of the power system is determined based on the effective value of the voltage of the reverse wave, while the voltage of each harmonic in the HRC is decomposed into components of the direct and reverse waves using the T-transform.

The disadvantages are the need to determine in real time the wave impedance of the network at each harmonic, since its value is constantly changing and depends on the mode of operation of each of the subjects of the power system.

There is a known method for identifying a source of higher harmonics (RF patent No. 2573706, publ. 01/27/2016), in which the source of higher harmonics is determined by the dependence of the current of higher harmonics of the power supply system on the active resistance of the filter compensating device installed in parallel with one of the loads.

The disadvantage of this method is that this method only allows you to determine whether the source of distortion is the consumer or the power supply system, but does not allow you to evaluate the contribution of each of them to the total distortion in percentage terms.

There is a known method for assessing the influence of a consumer on voltage distortion at the point of common connection (RF patent No. 2627195, publ. 08/03/2017), which includes determining the parameters of autonomous voltage for each consumer separately, calculating the coefficient of its influence on voltage distortion and comparing the calculated parameters with permissible .

The disadvantage of this method is the need to calculate the parameters of the equivalent circuit, such as the conductivity of each consumer, which introduces an additional error in the final result. The authors note that the relative error in determining the parameters of the equivalent circuit when using the proposed method does not exceed 7%, which is a significant value. In addition, as a result, it is not the consumer's contribution to the total distortion that is determined, but only its influence is compared with the permissible value and a conclusion is made about the admissibility or inadmissibility of such a consumer operation mode.

There is a known method for determining the actual contribution of distortion sources to the values of power quality indicators at the point of general connection (RF patent No. 2236016, published on September 10, 2004), in which the actual contribution of each subject-source of distortion is considered directly proportional to the projection of the current of the subject-source of distortion on the total current all subjects-sources of distortions.

The disadvantage of this method is that all subjects are divided into sources and consumers of distortions, while in real power systems, most consumers are a set of various linear and non-linear loads. Such loads, according to this method, result exclusively in the source entity or the consumer entity. In this case, the contribution of the subjects-consumers of distortions is missed, while they also contain sources of higher harmonics. In addition, the subject's belonging to the sources or consumers of distortions is determined by the phase angles of the shift between the distortion voltage and the corresponding current of higher harmonics. In other words, according to the sign of the distortion power at each of the harmonics. However, the distortion voltage in the electrical network node is the result of the joint work of all sources of distortion connected to the PTS. With a significant phase difference between the consumer distortion currents, one or more distorting consumers will have positive distortion powers and be perceived as non-distorting.

There is a known method for determining the contribution of distortion sources to the supply voltage of consumers based on the connection of a resonant passive filter of higher harmonics, (Shklyarskiy, Y.; Skamyin, A.; Vladimirov, I.; Gazizov, F. Distortion Load Identification Based on the Application of Compensating Devices. Energies 2020, 13, 1430) taken as a prototype. The share contribution of distortion sources is determined by calculating the harmonic currents of the non-linear load of the consumer by subtracting the measured current of the input connection from the filter current at the frequency of the highest harmonic (when the harmonic current of the input connection flows to the consumer), or by summing the measured current of the input connection and the filter current at the frequency of the highest harmonic (when the harmonic current of the input connection to the consumer flows). The ratio of harmonic currents of non-linear loads of consumers is equal to the ratio of voltages at the frequencies of higher harmonics created by the currents of non-linear loads of consumers.

The disadvantage of this method is that it is necessary to connect passive filters of higher harmonics for each consumer and to carry out simultaneous measurements on input connections and filters. In addition, on the basis of this method, it is possible to determine the share contribution of consumers relative to each other, and not their share contribution to the total voltage distortion at the point of common connection. Also, the disadvantage is the inability to assess the contribution of one consumer relative to the contribution of the entire power system, since the connection of a passive harmonic filter at a single consumer allows you to determine only the amplitude of the harmonic current of its non-linear load.

The technical result is an accurate assessment of the contribution of each source of distortion to the mains voltage, including in the presence of external sources of distortion in the power supply system.

The technical result is achieved by the fact that

measure the amplitude of higher harmonics in the mains voltage at each harmonic separately before and after connecting the passive harmonic filter, the current of the power supply system at the input of the power transformer of all consumers at each harmonic separately after connecting the passive harmonic filter, then calculate the contribution of external sources of distortion, of the first and second consumer on the harmonic of the order h according to the expressions:

DV _SESh \u003d 100 ∙ U _VHh / U _0h

DV _1h = 100 ∙ I _1Пh / | I _0h + I _Фh |

DV _2h = 100 ∙ I _2Ph / | I _0h + I _Фh |, where

DV _SESh - share contribution of the power supply system to the total distortion of the supply voltage at the harmonic of the order of h,

DV _1h - share contribution of the first consumer to the total distortion of the supply voltage at the harmonic of order h,

DV _2h - fractional contribution of the second consumer to the total distortion of the supply voltage at the harmonic of order h,

U _0h - harmonic amplitude of the order h of the mains supply voltage before connecting the passive harmonic filter,

U _VHh - harmonic amplitude of the order h of the mains supply voltage on the higher voltage side of the input power transformer of the consumer after connecting the passive harmonic filter,

I _0h - complex current of the power supply system at a harmonic frequency of order h,

I _Фh - complex current of the passive harmonic filter at harmonic frequency of order h,

I _1Ph - current amplitude of the input connection of the first consumer at a harmonic frequency of the order h,

I _2Ph - the amplitude of the current of the input connection of the second consumer at a harmonic frequency of the order of h,

then, the calculated share contributions of the power supply system and consumers to the total distortion of the supply voltage at the harmonic of the order of h are compared and the level of higher harmonics in voltage and current is reduced for consumers with the largest contributions.

The method is illustrated by the following drawing:

fig. 1 is an equivalent circuit for determining equity contributions at the harmonic frequency.

1 - complex resistance of the power supply system (SES);

2 - input power transformer of the consumer;

3 - SES voltage meter;

4 - SES current meter;

5 - current meter of the first consumer;

6 - passive harmonic filter current meter;

7 - current meter of the second consumer;

8 - non-linear load of the first consumer;

9 - linear load of the first consumer;

10 - passive harmonic filter;

11 - non-linear load of the second consumer;

12 - linear load of the second consumer;

13 - non-linear load of the third consumer.

The method is carried out as follows. A voltage meter SES 3 is installed in the electrical network, which determines the amplitude of higher harmonics in the mains voltage at each harmonic h separately before connecting the passive harmonic filter 10.

In case of exceeding the values of higher harmonics in the supply network voltage of the order of h, established by the norms and standards, the following actions are performed. A passive harmonic filter is connected, tuned to a harmonic of the order h, which exceeds the normalized values. Using the voltage meter SES 3, the amplitude of the higher voltage harmonics is determined, which characterizes the fractional contribution of the non-linear load of the third consumer 13.

The current meter SES 4 is installed, which determines the amplitude of the currents of the higher harmonics of the SES flowing through the complex resistance of the SES 1, the current meter of the first consumer 5 is installed, which determines the amplitude of the currents of the higher harmonics of the first consumer, the current meter of the second consumer 7 is installed, which determines the amplitude of the currents of the higher harmonics of the second consumer, a current meter of the passive harmonic filter 6 is installed, which determines the amplitude of the current of higher harmonics flowing through the passive harmonic filter 10 on each harmonic h separately.

Next, the share contribution of SES on the considered harmonic of order h is calculated by the expression:

where U _0h is the amplitude of the harmonics of the order h of the supply voltage of the network, determined by the voltage meter SES 3 before connecting the passive harmonic filter;

U _VHh - the amplitude of the voltage of the higher harmonic of the order of h on the side of the higher voltage of the input power transformer of the consumer, determined by the SES 3 voltage meter after connecting the passive harmonic filter.

Next, the share contribution of the first and second consumers on the considered harmonic is calculated according to the expressions:

where I _0h is the complex current of the SES at a harmonic frequency of the order of h, determined by the current meter SES 4;

I _Фh - complex current of the passive harmonic filter at a harmonic frequency of order h, determined by the current meter of the passive harmonic filter 6;

I _1Ph - current amplitude of the input connection of the first consumer at a harmonic frequency of the order of h, determined by the current meter of the first consumer 5;

I _2Ph - the amplitude of the current of the input connection of the second consumer at a harmonic frequency of the order of h, determined by the current meter of the second consumer 7.

The validity of using this approach is confirmed by the following. From the diagram in Fig. 1 it follows that the share contribution of the voltage of the first and second consumers to the total distortion of the supply voltage can be determined as follows:

where U _P1h is the amplitude of the harmonic of order h at the point of connection of the first consumer to the network;

U _P2h - harmonic amplitude of order h at the point of connection of the second consumer to the network;

I _1h - the amplitude of the current of the non-linear load of the first consumer at a harmonic frequency of the order of h;

I _1h - complex current of the non-linear load of the first consumer at a harmonic frequency of order h;

I _2h - complex current of the non-linear load of the second consumer at a harmonic frequency of order h.

When connecting a passive harmonic filter to consumer buses, measuring the amplitudes of the currents of the input connection of the first and second consumers I _1Ph and I _2Ph using current meters 5 and 7 allows you to determine the amplitudes of the currents of the non-linear load of consumers I _1h and I _2h . The complex addition of currents I _0h and I _Фh almost completely coincides with the total current of the nonlinear loads of two consumers I _1h and I _2h , which allows us to determine the amplitude of their total vector:

It should be noted that the complex addition of the current vectors I _0h and I _Phh leads to the exclusion of the influence of the non-linear load of the third consumer 13 on the determination of the percentage contributions of the first and second consumer to the total supply voltage distortion created by these consumers.

In the course of the analytical determination of the equity contributions of the first and second consumers, the following coefficients (6-9) were used:

- комплексная величина, показывающая во сколько раз комплексное сопротивление линейной нагрузки первого потребителя 9 больше комплексного сопротивления СЭС на гармонике h;where

- a complex value showing how many times the complex resistance of the linear load of the first consumer 9 is greater than the complex resistance of the solar power plant at the harmonic h;

- комплексная величина, показывающая во сколько раз комплексное сопротивление линейной нагрузки второго потребителя 12 больше комплексного сопротивления СЭС на гармонике h;

- a complex value showing how many times the complex resistance of the linear load of the second consumer 12 is greater than the complex resistance of the SES at the harmonic h;

- комплексная величина, показывающая во сколько раз комплексное сопротивление пассивного фильтра гармоник больше комплексного сопротивления СЭС на гармонике h;

- a complex value showing how many times the complex resistance of the passive harmonic filter is greater than the complex resistance of the SES at the harmonic h;

Then the expressions for the equity contributions of the first and second consumers take the following form:

Since the coefficients A and B tend to zero due to the low value of the resistance of the passive harmonic filter, then the fractional contributions of consumers, calculated based on the currents of the non-linear loads of two consumers I _1h and I _2h , correspond to the fractional contributions of consumers, calculated based on the currents of the input connections of the first consumer I _1Пh , second consumer I _2Пh , SES current I _0h and passive harmonic filter current I _Фh .

As a result, the share contributions to the total distortion of the supply voltage of external sources of distortion relative to the input power transformer of consumers and the share contributions of all consumers powered by the transformer at the harmonic h are determined, which is necessary when choosing the parameters and the place of connection of devices for reducing the level of higher harmonics, which are connected primarily at consumers with the largest equity contributions.

The method is illustrated by the following example. The calculation of the non-sinusoidal mode for the SES presented in Fig. 1. The circuit parameters are presented in Table 1.

Table 1 - Initial data for calculating the equivalent circuit Power system resistance Z0 _(h=1) = 0.01 Ohm Input power transformer resistance Z _TR(h=1) = 0.02 Ohm Active resistance of the first consumer R1 _(h=1) = 0.58 Ohm Inductive reactance of the first consumer X _L1(h=1) = 0.72 Ohm Capacitance of the first consumer X _C1(h=1) = 1.2 Ohm Active resistance of the second consumer R2 _(h=1) = 1.16 Ohm Inductive reactance of the second consumer X _L2(h=1) = 1.44 Ohm Non-linear load current of the first consumer (h=5) I ₁ = 60 BUT Non-linear load current of the second consumer (h=5) I ₂ = twenty BUT Non-linear load current of the third consumer (h=5) I ₃ = fifty BUT Passive filter active resistance R _Ф(h=1) = 0.02 Ohm Inductive reactance of the passive filter X _LF(h=1) = 0.24 Ohm Passive filter capacitance X _CF(h=1) = 6.0 Ohm

The calculation is presented at a harmonic frequency of the order h=5. In accordance with the described method, the voltage amplitude of the fifth harmonic of the mains is determined before the filter is connected:

U _0h \u003d 24.7 (V)

This value exceeds the limits established by GOST. Next, a passive harmonic filter is connected, tuned to resonance at the frequency of the fifth harmonic. The amplitude of the fifth voltage harmonic is determined, which characterizes the fractional contribution of the non-linear load of the third consumer.

U _VN \u003d 1.59 (V)

Therefore, the equity contribution of SES is defined as:

DV_SES = 100 ∙ 1.59 / 24.7 = 6.4%

Next, the amplitudes of the currents of the fifth harmonic of the input connection of the first and second consumers are determined:

I _1Ph = 57.96 (A); I _2Ph \u003d 18.35 (A)

Next, the complex current of the SES and the complex current of the passive harmonic filter at the frequency of the fifth harmonic are determined:

I _Фh = 81.97e ^j172.7 (A); I _0h \u003d 27.46e ^-j141.7 (A)

Next, the amplitude of the total current of the SES and the current of the passive harmonic filter at the frequency of the fifth harmonic is determined:

| I _0h + I _Фh | = 76.19 (A)

The next step is to determine the contribution of the first and second consumers to the distortion of the supply voltage:

DV _1h \u003d 100 ∙ 57.96 / 76.19 \u003d 76%; DV _2h \u003d 100 ∙ 18.35 / 76.19 \u003d 24%

The determination of the equity contributions of the first and second consumers is carried out regardless of external sources of distortion. However, their contribution must be determined in the total distortion of the supply voltage, the values of which must be determined with the exception of the contribution of an external source of distortion.

Thus, the share contribution of SES is 6.4% in the total distortion of the supply voltage, the share contribution of the first and second consumer in the remaining part of the supply voltage distortion is 76% and 24%, respectively.

Let us calculate the coefficients A and B, which characterize the deviation of the values of the consumers' equity contributions when they are calculated from the harmonic currents of the consumers' non-linear loads:

A = 0.015; B=0.034

Such values indicate a slight error in determining the share contributions according to the described method, which can be calculated when determining the share contributions of consumers based on the currents of their non-linear loads:

DV _1h = 100 ∙ 60 / 80 = 75%; DV _2h = 100 ∙ 20 / 80 = 25%

Based on the developed method, it is possible to determine the location of sources of distortion, and therefore to determine consumers with the largest share contributions to the total distortion of the order h supplying the harmonic. As a result, it is possible to make an informed decision on the appropriateness of using means to reduce supply voltage distortion, as well as to select their parameters.

Claims (14)

A method for assessing the share contribution of consumers to the total distortion of the supply voltage, including measuring the currents of the input connections of consumers and the currents of the passive harmonic filter on each harmonic separately, characterized in that the amplitude of higher harmonics is measured in the supply voltage at each harmonic separately before and after connecting the passive harmonic filter, the current of the power supply system at the input of the power transformer of all consumers at each harmonic separately after connecting the passive harmonic filter, then the fractional contribution of external sources of distortion, the first and second consumer at the harmonic of order h is calculated using the expressions: DV _SESh \u003d 100 ∙ U _VHh / U _0h DV _1h =100∙I _1Пh /| I _0h + I _Фh | DV _2h =100∙I _2Ph /| I _0h + I _Фh |, where DV _SESh - share contribution of the power supply system to the total distortion of the supply voltage at the harmonic of the order of h, DV _1h is the share contribution of the first consumer to the total distortion of the supply voltage at the harmonic of order h, DV _2h is the share contribution of the second consumer to the total distortion of the supply voltage at the harmonic of order h, U _0h is the harmonic amplitude of the order h of the mains supply voltage before connecting the passive harmonic filter, U _ВНh is the amplitude of the harmonic of the order h of the mains supply voltage on the higher voltage side of the input power transformer of the consumer after connecting the passive harmonic filter, I _0h - complex current of the power supply system at a harmonic frequency of order h, I _Phh - complex current of the passive harmonic filter at a harmonic frequency of order h, I _1Пh - current amplitude of the input connection of the first consumer at a harmonic frequency of order h, I _2Ph - the amplitude of the current of the input connection of the second consumer at a harmonic frequency of the order of h, then, the calculated share contributions of the power supply system and consumers to the total distortion of the supply voltage at the harmonic of the order of h are compared and the level of higher harmonics in voltage and current is reduced for consumers with the largest contributions.

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