RU2742902C1 - Method for determining compensating device connection points - Google Patents

Abstract

FIELD: electrical and power engineering.

SUBSTANCE: invention relates to a method for reducing the total losses of active power in electrical networks by reducing the level of reactive power and higher harmonics. According to the method, measurements of active power, power factor, total harmonic distortion, the length of the power transmission line are carried out using an electrical energy quality analyzer, then the connection points of compensating devices are selected taking into account the topology of the distribution network, which are determined based on the contribution of the load to the total losses of active power according to the formula

,

based on the results of the calculation, a ranking histogram is constructed in descending order of the value of Z_i, on which the accumulated Pareto percentage curve is imposed, the permissible level of contribution to the total active power losses is set, then the loads that have a greater contribution to the total active power losses are determined, after which compensating devices are connected directly at these loads.

EFFECT: increase in quality of electricity and decrease in total losses of active power due to the point connection of compensating devices in distribution network of the enterprise.

1 cl, 4 dwg, 4 tbl

Description

The invention relates to electrical engineering and power engineering, and in particular to a method for reducing the total losses of active power in electrical networks by reducing the level of reactive power and higher harmonics. The method can be used in power supply systems of industrial enterprises with nonlinear and linear active-inductive load to reduce the total losses of active power in medium voltage distribution networks.

A known method of placing compensating devices in distribution networks of enterprises

used in power supply systems of industrial enterprises with equipment generating higher harmonics of current, as well as in active filters.

The disadvantage of this method is that when choosing compensating devices, only the reactive power of the load is taken into account, while, in the case of a nonlinear load, current and voltage harmonics are not taken into account, which can lead to failure of the compensating device, and the method does not allow determining the connection points of the compensating devices.

There is a known method of joint compensation of reactive power, suppression of higher harmonic currents and balancing of railway traction load currents (patent RU 2665697 C1 published 09/04/2018), which consists in joint compensation of reactive power, suppression of higher harmonic currents and balancing of traction load currents.

The disadvantage of this method is the complexity of its application with distributed networks of medium voltage, since the calculation of the required values requires a lot of measurements of instantaneous values, which requires accurate measuring instruments simultaneously with a powerful microcontroller.

A known method of placing capacitor devices in rural distribution networks of 0.4 kV (patent RU 2563250 C1 published on 20.09.2015), which consists in determining the values of the lengths of the main line, two-phase and three-phase branches from the main; measurement in nodes corresponding to the obtained values, voltage and power factor.

The disadvantage of this method is the process of measuring the reactive power factor due to the fact that this factor does not have a clear definition and methodology for its measurement. Also, the method does not take into account the influence of already connected capacitor banks, which may affect the choice of connection points for new capacitor banks.

A known method for selecting and placing compensating devices in the electrical network of an enterprise

which consists in the fact that the capacitor banks must be distributed between the substations of the projected network in such a way that the power losses in the network are minimal.

The disadvantage of this method is the fact that in order to determine the connection points of compensating devices in a complex electrical distribution network, it is necessary to use special methods for optimizing modes and calculating on a computer using special programs, which leads to a complication of the analysis and, consequently, to additional time costs.

There is a known method for the rational arrangement of reactive power compensation devices, taking into account the generalized characteristics of the mode ( https://helpiks.org/8-1853.html , date of access: 05.11.2019), which consists in identifying "hard" nodes and assessing the amount of reactive power compensation using generalized characteristics of the regime.

The disadvantage of this method is that it requires a lot of calculations using special programs. Also, in the presence of higher harmonic distortions in the network, the use of the method seems to be impossible, since the presence of harmonic distortions in the distribution network is not taken into account by this method. The use of this method in conditions of non-sinusoidal current or voltage curve may lead to failure of the compensating devices.

There is a known method for compensating for higher harmonics and improving the quality of consumed electricity (patent RU No. 2674166, publ. 05.12.2018), taken as a prototype, which consists in achieving the minimum indicators of current distortion and prompt response to changes in the harmonic composition of the current.

The disadvantage of this method is the use of an active filter, which is rather complex in design and use of a device associated with a large number of calculations, which requires additional computing power, which in turn increases the response time constant to changes in the harmonic composition of the current or voltage, and also leads to additional energy consumption.

The technical result is to improve the quality of electricity and reduce the total losses of active power due to the point connection of compensating devices in the distribution network of the enterprise.

The technical result is achieved by measuring the active power, the power factor, the total harmonic distortion, the length of the transmission line of the power transmission line using the power quality analyzer, then the selection of the connection points of the compensating devices is carried out taking into account the topology of the distribution network, which are determined based on the contribution of the load to total active power losses according to the formula

– длина линии от источника питания до

–й нагрузки, км,Where:

- the length of the line from the power source to

-Th load, km,

– суммарная длина линий рассматриваемой сети, км,

- total length of lines of the considered network, km,

– активная мощность

–й нагрузки, кВт,

- active power

-Th load, kW,

– суммарная активная мощность нагрузки, кВт,

- total active load power, kW,

– коэффициент мощности

–й нагрузки, о.е.,

- Power factor

–Th load, p.u,

– средневзвешенный коэффициент мощности нагрузок предприятия, о.е.,

– коэффициент искажения по току

–й нагрузки, о.е.,

Is the weighted average power factor of the enterprise's loads, p.u.,

- current distortion factor

–Th load, p.u,

– средневзвешенный коэффициент искажения по току, о.е.,

- weighted average current distortion coefficient, p.u.,

, на которую накладывают кривую накопленного процента Парето, задают допустимый уровень вклада в суммарные потери активной мощности, затем определяют нагрузки, имеющие больший вклад в суммарные потери активной мощности, после этого подключают компенсирующие устройства непосредственно у этих нагрузок.then, based on the calculation results, a ranking histogram is constructed in descending order of magnitude

, on which the accumulated Pareto percentage curve is imposed, the permissible level of contribution to the total active power losses is set, then the loads that have a greater contribution to the total active power losses are determined, after which compensating devices are connected directly at these loads.

The method is illustrated by the following figures:

fig. 1 - algorithm for implementing the method of connecting compensating devices

fig. 2 - distribution network of the medium voltage electrical complex

fig. 3 - simulated single-phase medium voltage network equivalent circuit

fig. 4 - histograms of total active power losses for various consumers

The method is carried out as follows. The algorithm for implementing the method for connecting compensating devices is shown in Fig. 1. At the first stage, it is necessary to obtain data by instrumental measurements of active power (kW), power factor (p.u. - relative units), total harmonic distortion factor (p.u. - relative units), the length of the power transmission line using the analyzer the quality of electrical energy stationary or portable, or an operating data collection system (provided that these parameters can be measured).

для каждой нагрузки по следующей формуле:Next, using the data obtained, calculate the total losses of active power

for each load according to the following formula:

– длина линии от источника питания до

-й нагрузки, км;Where:

- the length of the line from the power source to

th load, km;

– суммарная длина линий рассматриваемой сети, км;

- total length of lines of the considered network, km;

– активная мощность

-й нагрузки, кВт;

- active power

th load, kW;

– суммарная активная мощность нагрузки, кВт;

- total active power of the load, kW;

– коэффициент мощности

-й нагрузки, о.е.;

- Power factor

th load, o.e.;

– средневзвешенный коэффициент мощности нагрузок предприятия, о.е.;

Is the weighted average power factor of the enterprise's loads, p.u .;

– коэффициент искажения по току

–й нагрузки, о.е.;

- current distortion factor

–Th load, o.u .;

– средневзвешенный коэффициент искажения по току, о.е.

Is the weighted average current distortion coefficient, p.u.

Current distortion cannot be measured by the vast majority of instrumentation, but is related to current THD by the following expression:

– суммарный коэффициент гармонических искажений, о.е.Where:

- total harmonic distortion, p.u.

, на которую накладывается кривая накопленного процента Парето и задается допустимый уровень вклада в суммарные потери активной мощности в процентах, как правило 80 %, слева от точки пересечения допустимого уровня вклада в суммарные потери активной мощности и кривой Парето нагрузки имеют больший вклад в суммарные потери активной мощности, что, в свою очередь, обуславливает необходимость подключать компенсирующие устройства непосредственно у этих нагрузок (фиг. 4).After that, the calculation result is presented in the form of a histogram, ranked in descending order of magnitude

, on which the curve of the accumulated Pareto percentage is superimposed and the admissible level of contribution to the total losses of active power in percent is set, as a rule, 80%, to the left of the intersection of the admissible level of the contribution to the total losses of active power and the Pareto curve, the loads have a greater contribution to the total losses of active power , which, in turn, necessitates connecting compensating devices directly at these loads (Fig. 4).

называется оптимальным по Парето, если не существует

такого, что

для всех

и

хотя бы для одного

. задавшись уровнем накопленного процента. Компенсирующее устройство подключается непосредственно у нагрузки с наибольшим вкладом в суммарные потери активной мощности. The Pareto method is used in various fields of knowledge, the interpretation of the method from economics is widely known - 20% of efforts give 80% of the result. Mathematically, the Pareto method is defined as: solution vector

is called Pareto optimal if it does not exist

such that

for all

and

for at least one

... having set the level of accumulated interest. The compensating device is connected directly to the load with the greatest contribution to the total active power losses.

The method is illustrated by the following examples. There is a medium voltage network (Fig. 2) containing both linear and non-linear loads. Compensating devices are connected to medium voltage busbars. The implementation of the method is carried out on the basis of simulation modeling, for which a simulation scheme has been created (Fig. 3). The adequacy of the simulation results is due to the use of specialized software Matlab.

For this scheme, the application of the method is as follows. Table 1 shows the initial data required to calculate the total active power losses.

Table 1 - Initial data

P / p No. Load name Active power, kW Power factor, p.u. Power transmission line length, km Total harmonic distortion, p.u. one Shop number 1 1,000.00 0.71 ten 0 2 Shop number 2 2,000.00 0.89 five 0.07 3 Shop No. 3 2,100.00 0.73 25 0.2 four Shop No. 4 1,000.00 0.32 ten 0 five Shop No. 5 2,000.00 0.69 15 0 6 Shop number 6 2,000.00 0.89 17 0

The initial data were active power (kW), power factor (p.u.), total harmonic distortion factor (p.u.), length of the power transmission line (km), which were obtained from a metallurgical enterprise. The circuit (Fig. 2) is radial, the visual simplicity of the circuit is due to the fact that the average voltage level is considered, i.e. 6 (10) kV. Obviously, it is impractical to consider this circuit at all voltage levels, since often compensating devices are connected precisely to the average voltage level.

The simulation circuit is a single-phase equivalent circuit. High-frequency harmonic distortions are modeled by current sources. Simulation data are presented in Table 2.

Table 2 - Result of simulation

P / p No. Load name Line current, A Loss of active power, kW one Shop number 1 130.6 17.1 2 Shop number 2 211.1 22.3 3 Shop No. 3 276.1 190.6 four Shop No. 4 272.7 74.4 five Shop No. 5 246.8 91.4 6 Shop number 6 198.1 66.7 7 Total losses - 462.4

.To determine the connection points, according to the proposed method, the data from Table 1 are entered into the program that implements the algorithm for determining the connection points of the compensating devices, the result is a histogram (Fig. 4). The algorithm is based on calculating the contribution of the load to the total losses of active power

...

The histogram shows that the greatest contribution to the total losses of active power is made by loads numbered 3, 5, 4, 6. However, according to the proposed method, compensating devices must be connected at a load that creates 80% losses (Pareto method). Thus, having compensated for the distortions created by loads 3, 5, 4, the total losses of active power will decrease to the optimal level (according to the criterion of the ratio of costs for compensating devices to the effect of their use) (Table 3).

Table 3 - Result of distortion compensation according to the proposed method

P / p No. Load name Line current, A Loss of active power, kW one Shop number 1 132.8 17.6 2 Shop number 2 214.9 23.1 3 Shop No. 3 193 93.1 four Shop No. 4 96.9 9.4 five Shop No. 5 189.4 53.8 6 Shop number 6 201.4 69.0 7 Total losses - 266

Comparison with other possible ways of connecting compensating devices is presented in table 4.

Table 4 - Comparison of the results of using compensating devices in different ways

P / p No. Load name Losses of active power without compensation, kW Loss of active power when compensated by the proposed method, kW Losses of active power when compensating for all distortions, kW Active power losses with centralized compensation, kW one Shop number 1 17.1 17.6 9.5492 18.1172 2 Shop number 2 22.3 23.1 19.0906 23.6096 3 Shop No. 3 190.6 93.1 94.6729 138,651 four Shop No. 4 74.4 9.4 9.5492 79.0734 five Shop No. 5 91.4 53.8 54.6642 97,1554 6 Shop number 6 66.7 69.0 61.37 70,886 7 Total losses 462.4 266.0 248,896 427,492 8 Reduction of active power losses,% 0 42.5 46.2 7.5

From the analysis of the data in Table 4, it can be seen that the greatest effect in the form of a decrease in active power losses is achieved when compensating devices are connected directly at each load. However, the effect of the proposed method is not much lower - 42.5% versus 46.2%, the difference is less than 4% with a difference in costs of more than 50%, because it is necessary to connect only three compensating devices instead of 6. The centralized compensation method showed the worst result, only 7.5% from which it follows that with this method the enterprise does not get rid of distortions within its distribution network, as a result of this, this method is economically inexpedient to use.

As a result of applying the method, the level of power quality increases, the total losses of active power are reduced due to the point connection of compensating devices in the distribution network of the enterprise.

Claims (10)

A method for determining the connection points of compensating devices, which consists in the operation algorithm of the device for compensating for higher harmonics, characterized in that they measure the active power, power factor, total harmonic distortion, the length of the transmission line of the power transmission line using an electrical energy quality analyzer, then select the connection points of compensating devices taking into account the topology of the distribution network, which are determined based on the contribution of the load to the total losses active power according to the formula:

where: l _i is the length of the line from the power source to the i-th load, km, l _∑ - total length of lines of the considered network, km, P _i - active power of the i-th load, kW, P _∑ - total active power of the load, kW, K _Mi - power factor

i-th load, p.u, K _M∑ is the weighted average power factor of the enterprise loads, p.u., k _i is the distortion factor for the current of the i-th load, p.u., k _∑ - weighted average current distortion coefficient, p.u., then, based on the results of the calculation, a ranking histogram is constructed in descending order of the value of Z _i , on which the accumulated Pareto percentage curve is imposed, the permissible level of contribution to the total active power losses is set, then the loads that have a greater contribution to the total active power losses are determined, after which compensating devices are connected directly have these loads.

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