RU2242072C1 - Method for computer-aided active monitoring of current and voltage fluctuations - Google Patents

Abstract

FIELD: measurement technology; measuring and monitoring basic quality characteristics of electrical energy.

SUBSTANCE: voltage fluctuations are measured and presented in the form of analog curves of electrical energy basic characteristics. RMS value of current and voltage are determined for half-cycle of variations of these quantities at frequency of fundamental harmonic component and used to acquire information about quantitative estimate of peak-to-peak values of current and voltage fluctuations, as well as to determine amplitude-frequency response of human visual analyzer of current and voltage flicker dose. Relevant correcting devices generate control signal in case electrical energy quality characteristics exceed specified values.

EFFECT: provision for automating processes of current and voltage fluctuation measurements and active control.

1 cl, 3 dwg

Description

The invention relates to electrical engineering and can be used as part of integrated active control of all indicators of the quality of electrical energy.

In the practice of using electric energy, oscillations are usually estimated only by voltage. Such an assessment can be considered objective, if we assume that electric power systems consist only of linear elements, when the shape of the current practically does not differ from the shape of the voltage. But this cannot be said about modern electric power systems, which include more and more non-linear elements. Therefore, in modern electric power systems, along with the assessment of voltage fluctuations for an objective control of voltage quality, current fluctuations should be evaluated.

Oscillations of voltage and current are considered short-term (up to one minute) deviations of these values from nominal values. Moreover, these deviations must be steady. Therefore, the duration of the assessment of the levels of voltage and current fluctuations should be at least ten minutes. Only under these conditions can we count on an objective judgment on the state of the levels of voltage and current fluctuations.

According to the requirements of the current interstate standard GOST 13109-97 “Quality standards for electric energy in public power supply systems” [1], voltage fluctuations are evaluated by two indicators of the quality of electric energy: the magnitude of the change and the dose of flicker. Similar indicators should be evaluated and current fluctuations.

The closest technical solution to the proposed method of automated active control of voltage and current fluctuations can be called a flicker meter [2]. A similar technical solution was implemented in the ERIS-KE.02 device developed by Energokontrol LLC. However, this device is intended only for passive monitoring of indicators of the quality of electric energy, that is, only for recording the quantitative characteristics of these indicators and, in the best case, for recording compliance or non-compliance with their normative values.

The objective of the invention is the formation of an algorithm for automated active control of voltage and current fluctuations, that is, the creation of an algorithm for generating a control signal for devices designed to adjust the levels of voltage and current fluctuations. Such devices may be, for example, smoothing devices.

The technical result is achieved by the fact that the initial data for the algorithm for active control of voltage and current fluctuations are analog curves of these characteristics of electrical energy, converted in an analog-to-digital converter into a set of discrete values, from which it is necessary to obtain the effective values of voltage and current for half the period of change of these values at the frequency of the main harmonic component, necessary to obtain information about the quantitative assessment of the magnitude of the changes in voltage and current, and Also, if you use an amplitude-frequency characteristic of human visual analyzer - flicker voltage and current. In case of violation of the normative values of these indicators of the quality of electric energy, a control signal is generated by the corresponding corrective devices. Automation of active control of voltage and current fluctuations is provided by using computer technology.

To determine the level of voltage fluctuations, the recommendations of the interstate standard in force in Russia are quite acceptable here [1].

The range of fluctuations in the interstate standard is recommended to be determined by the formula

where U _i and U _{i + 1} are the effective values of two adjacent extremes of the voltage curve; U _nom - the current nominal value of the analyzed voltage.

The voltages U _i and U _{i + 1} used in formula (1) are represented by their effective values determined on each half-period of the fundamental frequency. The procedure for determining these values can be implemented when performing calculations according to the formula

where T ₀ - the period of change of the main harmonic component of the voltage; u is the instantaneous value of the analyzed voltage.

When implementing the control of the amplitude of voltage fluctuations in this case, when a preliminary decomposition of the analog values of voltage and current into discrete ones is provided already at the initial stage of analysis, the mathematical formulation for determining the effective voltage value (2) can be presented in a different form:

where N ₀ is the number of quantizations (discrete values) for the period of change of the main harmonic component of the analyzed voltage; u _p is the magnitude of the voltage during p-th quantization; Δt is the value of one quantization, determined by the formula

Formula (3) taking into account equality (4) appears in the form

The determination of the effective values of the analyzed voltage for each half of the period of variation of the main harmonic component of this voltage should be performed within ten minutes. Then it is necessary to fix the facts of short-term (less than one minute) voltage deviations from its nominal value. If the duration of the voltage deviation exceeds one minute, then we should talk about another indicator of the quality of electric energy, namely, voltage deviation.

Further, using the formula (1), one can determine the magnitude of the magnitude of the recorded voltage fluctuations.

It is advisable to check the compliance of the calculated ranges of voltage fluctuations based on the inequality

where kδ _U is the standard value of the range of voltage fluctuations.

Similar calculations should be performed to evaluate the magnitude of the current oscillations.

The procedure for estimating the magnitude of the current fluctuation should begin with determining the effective values of the analyzed current for each half of the period of variation of the main harmonic component according to the formula

where i _p is the current value at the rth quantization.

Then you should determine the magnitude of the recorded current fluctuations:

where I _i and I _{i + 1} are the effective values of two adjacent current extremes; I _{i + 1} - the current rated value of the analyzed current.

Next, you need to check the compliance of the magnitude of the current fluctuations calculated by formula (8) with their normative values:

where kδ _I is the standard value of the range of current oscillations.

Violation of inequalities (6) or (9) is the reason for the formation of a control signal for appropriate corrective devices or a signal for performing other technical or organizational measures.

Somewhat more complicated is the assessment of the flicker dose.

Judging by the definition given in the current interstate standard [1], it turns out that flicker is the subjective perception by a person of fluctuations in the luminous flux of artificial lighting sources caused by voltage fluctuations in the electrical network that supplies these sources.

From the same source of information, it follows that the dose of a flicker is a measure of a person's susceptibility to the effects of a flicker over a specified period of time.

It is also said here that the flicker perception time is the minimum time for a subjective perception of a flicker by a person caused by voltage fluctuations of a certain shape.

Here, apparently, it is appropriate to make an amendment regarding the fact that the fluctuations in the light flux are caused by fluctuations in electrical energy, which is characterized not only by voltage but also by current.

The flicker dose should be measured with a flicker meter. The implementation of this device with automated active control of voltage and current fluctuations is extremely difficult. Here you should go along the path of searching for an analytical determination of the dose of flicker. The situation is complicated by the subjective nature of this indicator of the quality of electric energy.

In this case, it makes sense to use the amplitude-frequency characteristic of the human visual analyzer. However, this characteristic, as a rule, is purely individual in nature. Here, apparently, it is appropriate to use the averaged amplitude-frequency characteristic given in [2]. A similar characteristic is duplicated in figure 1.

In this case, one of the most acceptable formulations for determining the dose of a flicker by voltage can be represented as follows:

where q (f) is the ordinate of the amplitude-frequency characteristic of the human visual analyzer at an oscillation frequency ƒ; T _u - flicker dose measurement period ψ _tSU .

The minimum measurement period for determining the short-term dose of flicker according to formula (10) according to the current interstate standard is determined by a time interval of 10 (ten) minutes. Judging by the above, the amplitude of the oscillations is also measured for the same time interval.

We can talk about the dose of flicker only if several voltage fluctuations are recorded during this measurement period. Only in this case can we judge the frequency of these oscillations and determine it by the formula

where n is the number of voltage fluctuations during the measurement period, equal to at least 10 (ten) minutes and estimated in seconds.

It is precisely at this frequency that the ordinate necessary for formula (10) follows from the amplitude-frequency characteristic shown in Fig. 1.

The range of voltage fluctuations according to the recommendations of the current interstate standard is determined for each half of the period of change of the main harmonic component of this voltage. If the frequency of the main harmonic component of the voltage is 50 (fifty) hertz, then half of its period will be 10 (ten) milliseconds; the time interval equal to 10 (ten) minutes includes 60,000 (sixty thousand) such half-periods.

In view of the above, formula (10) can be represented in a more acceptable form for this case:

where k is the number of voltage fluctuation ranges δU recorded during the measurement cycle.

Next, after determining the numerical value of the short-term dose of flicker, one should check its compliance with its normative value by inequality

where kΨ _SU is the normative (permissible) value of the short-term dose of the flicker by voltage.

Violation of this inequality is an occasion for the formation of a control signal for relevant technical and organizational measures.

Under condition (13), it makes sense to check the stability of this indicator of the quality of electric energy and determine the long-term dose of flicker. To do this, continue the procedure of the measurements described above.

To determine the long-term dose of flicker, the entire complex of measurements of a short-term (ten-minute) dose of flicker should be repeated another 11 (eleven) times, that is, the measurement cycle is extended to two hours. Quantitatively, a long dose of flicker voltage is determined by the formula

where Ψ _tSUi is the short-term voltage flicker dose in the i-th time interval.

A long-term dose of voltage flicker is usually normalized. Checking the compliance of this indicator of the quality of electric energy is carried out by the inequality

where kΨ _LU is the maximum allowable value of the long-term flicker dose in voltage.

This determines the dose of the flicker by voltage, as well as its duration.

Fluctuations in current also affect the human visual analyzer. In modern electric power systems, as mentioned above, current fluctuations may not repeat voltage fluctuations. Therefore, it makes sense to evaluate the current flicker dose.

The current dose of the flicker should be evaluated in the same manner as described. In this case, formulas (10), (12) and (13) are somewhat modified.

So, the initial formulation for determining the current flicker dose has the form

For this case, the short-term current flicker dose makes sense to determine as follows:

where k is the number of current oscillation ranges δI recorded per measurement cycle.

Before the described procedure, the standard value of the short-term current flicker dose kΨ _SI should be established.

Checking the compliance of the actual short-term current dose of the flicker with its standard value is performed by the inequality

A long current flicker dose is formed from twelve consecutive measurements of short-term flicker doses:

where Ψ _tSIi is the short-term current flicker dose on the i-th time interval.

For a long dose of flicker, regulatory values should also be set, compliance verification of which should be performed according to the inequality

where kψ _LI is the maximum permissible value of a continuous current flicker dose.

Figure 2 presents a structural diagram for assessing the level of voltage fluctuations, and figure 3 is a structural diagram for assessing the level of current fluctuations. The following notation is used in these schemes: i and j are the current half-periods of the analyzed characteristic; k is the number of current one-minute time intervals; t and n are the current numbers of recorded fluctuations of the analyzed characteristics for a ten-minute interval, in this case, voltage; L is the number of the ten minute measurement time interval.

This seems to be an algorithm for actively controlling the level of voltage and current fluctuations, which is implemented with the modern development of computer technology. It should be borne in mind that the amplitude-frequency characteristic of the human visual analyzer must be set in advance, at least in the form as shown in Fig. 1, and stored in the memory of the corresponding processor.

Sources of information

1. Standards for the quality of electric energy in general-purpose power supply systems: GOST 13109-97. - Minsk: Interstate Council for Standardization, Metrology and Certification, 1998. - 31 p.

2. Zhezhelenko I.V. Electricity quality indicators and their control in industrial enterprises. - 2nd ed., Revised. and add. - M .: Energoatomizdat, 1986. - 168 p.

Claims (1)

A method of automated active control of voltage and current fluctuations, performed by means of computer technology, which consists in comparing the actual ranges of fluctuations and doses of voltage and current flicker with standard values of these values, characterized in that the procedure for determining the actual ranges of fluctuations and doses of voltage and current flicker is preceded by conversion of analog values of voltage and current to discrete, identification of geometric mean values of voltage and current for each half of their period from changes, and then the fact of voltage and current fluctuations is revealed, the amplitude of their oscillations is determined and, using the amplitude-frequency characteristics of the human visual analyzer, short-term and then long-term doses of voltage and current flicker are determined, and when the actual values of the amplitude of the fluctuations and doses of voltage and current flicker are exceeded of their standard values, a control signal of corrective devices is formed.

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