Method for computer-aided on-line measurement of current and voltage unbalance level

FIELD: electrical and power engineering.

SUBSTANCE: proposed method intended for measuring current and voltage unbalance level and organizing on-line impact on them in three-phase power systems characterized in low quality of their power characteristics includes measurement of unbalance level with respect to reverse and zero sequence of both line and phase voltages and currents at frequency of each harmonic component. Frequency at which unbalance in analyzed characteristics occurs is found. Results obtained are used to generate control signal by correcting devices.

EFFECT: facilitated procedure.

1 cl, 5 dwg

 

The invention relates to electrical engineering and can be used to control and organization of active influence on the level of voltage unbalance and current in electrical power systems three-phase execution, characterized by low quality of electricity.

The symmetry of the stress means the equality of the phase (line) voltage between them. The angle of the phase shift between them in three-phase versions of the corresponding power system must be equal to 120°.

Symmetry currents in this way means the equality of these currents between themselves and the phase angle between them in three-phase versions of the corresponding power system 120°.

The symmetry of voltages and currents affect the function of electrical devices, circuits automatic and information support, electric motors, transformers, power lines and other electrical equipment.

Current Russian interstate standard GOST 13109-97 “Rules of electric power quality in electrical systems General purpose” [1] prescribed to assess only the asymmetry of the line voltage. For assessment of voltage unbalance standard introduces asymmetry coefficient stresses what about the reverse sequence and asymmetry coefficient voltage zero-sequence.

Indeed, knowing the magnitude of the line voltage, it is possible to judge phase. Any change of the phase voltage will affect the magnitude of the line. Assessment of the level of voltage unbalance only linear voltage may be sufficient for the passive control of the aforesaid problems. For the active control of the level of voltage unbalance, when it is necessary to definitely establish the most probable from the point of view of the optimal solution subject to appropriate corrective devices. It is obvious that change is only one phase voltage will inevitably cause a change of two linear. Therefore, for the formation of active influence on the level of voltage unbalance necessary information about the phase voltages.

In addition, the effectiveness of active influence on the level of voltage unbalance cannot be effective without taking into account the level of unbalance currents. Moreover, without information about the level of unbalance currents impossible accurate and objective assessment of electric power quality in modern power systems, saturated nonlinear elements.

In modern power systems, the asymmetry of voltages and currents, as a rule, is accompanied by a nonsinusoidal of these quantities. This fact must also be taken into account when the authority is implementing an active control of the level of asymmetry of voltages and currents.

As corrective devices here stands for the results of any technical solutions aimed at reducing the level of asymmetry of voltages and currents. Most of these solutions are aimed at reducing the differences of the values of phase voltages between line voltage between the currents between them [2]. It is in this aspect and consider the problem of formation of an active control of the level of asymmetry of voltages and currents.

The objective of the invention is to provide a method of automated control of voltages and currents.

The technical result is achieved by the fact that you control the level of asymmetry is not only linear, but also phase voltages and currents at the frequency of each harmonic component by simple comparison of the corresponding values with the use of computers. As a result of such control, if necessary, formed the control signal for the corresponding corrective devices.

The process of forming the control signal correcting device is preceded by a passive monitoring of the level of asymmetry of the relevant characteristics of electrical energy.

Figure 1 and 2 shows the variations of the structural schema of the algorithm of the passive control of the level of asymmetry of these characteristics. Figure 3 shows with nocturna diagram of the algorithm for active control of the level of asymmetry of the line voltage, 4 shows a structural diagram of the algorithm for active control of the phase voltages, and figure 5 - current.

The source data for the active control of the level of unbalance voltages and currents are the temporal characteristics of each line and phase voltage and current. In order to perform the necessary analysis, these characteristics must be present in the form of a set of discrete values. For this it is best to use an analog-to-digital Converter multi-channel execution.

From this it follows that for monitoring the level of asymmetry in the node power system three-phase execution requires a 9-channel analog-to-digital Converter. In this case, if the transmission line near the analyzed site power system performed without splitting the wires. Otherwise, the number required for performing the tasks channel analog-to-digital Converter doubles, triples, whateverelse and so on depending on the number of splits.

When analyzing the level of the unbalance current and the voltage at node six-phase power system performance requires a minimum of 27-channel analog-to-digital Converter.

But often in practice, the supply of industrial and ins the objects are three-phase power system performance. Therefore, further consideration should be taken exactly three-phase power system.

The analysis of this kind especially in modern power systems, different low quality of electricity, should be preceded by an analysis of the level of nonsinusoidal line and phase voltages and currents. It should be guided by the recommendations of the patent for invention №2122186 “Method for quantitative assessment of subharmonic and fractional harmonic components periodically changing values” [3].

Thus are formed the source data for the implementation of the proposed algorithm here the analysis of the level of asymmetry of voltages and currents.

The ultimate goal of this algorithm is the formation of the control signal corresponding corrective means. To identify the necessity of forming such control is necessary to assess the current to the active intervention level of unbalance voltages and currents, that is to perform passive monitoring of appropriate indicators of quality of electrical energy.

According to the recommendations of the current international standard [1], as well as several publications on relevant topics, the level of asymmetry of voltages and currents appreciate you normally would, using the concept of voltages and currents direct, inverse and zero pic is of egovernance. This quantitative evaluation of the regulatory requirements for nonsinusoidal voltage interstate standard is defined as the ratio of the unbalance voltage in a reverse sequence k2Uand the asymmetry coefficient of the voltage zero-sequence k0U. The level of unbalance currents this standard, unfortunately, is not evaluated.

Quantitative values of voltages and currents direct, inverse and zero sequence is often defined using applied in the method of symmetrical components method of decomposition of the main characteristics of electric power to these components. Moreover, when non-sinusoidal modes of consumption of electrical energy, this decomposition has the sense to run for the frequency of each harmonic component of voltage and current.

Decomposition of nonsymmetric systems of linear voltage symmetrical components direct, inverse and zero sequence on the frequency ν-the harmonic component, denoted here by the symbol UνC1C2lshould be calculated by the formulas:

where α=ej120°statement of rotation;- image is agenia on the complex plane current values of the line voltages at the frequency ν -the harmonic component.

Unbalanced three-phase system phase voltages should be decomposed in a similar way:

whereimages on the complex plane RMS values of phase voltages at the frequency ν-the harmonic component.

Unbalanced three-phase system of currents at a frequency of ν-the harmonic component can be represented as follows:

whereimages on the complex plane the effective values of currents at a frequency of ν-the harmonic component.

RMS line voltage direct sequence is defined as the geometric sum of current values of all line voltage of this sequence at all registered in the spectrum of the corresponding voltage harmonic components:

Likewise determined by the current values of the line voltages inverse and zero sequence:

Likewise determined and deystvuyuyuschee phase voltages and currents direct, inverse and zero sequence:

Then we proceed to the determination of the coefficients of the unbalance voltage reverse and zero sequences. And in this case should determine these coefficients for the linear and the phase voltage is:

Here it is necessary to determine the coefficients of asymmetry of the currents reverse and zero sequences:

Now we should define the permissible values of these coefficients and to proceed with the verification of the conformity of the analyzed indicators of the quality of electric energy to its normative values:

where σ2Uand σ0U- the valid values of the coefficients of asymmetry Lina is different voltages inverse and zero sequence; σ2Uand σ0U- valid values of the coefficients of asymmetry phase voltage reverse and zero-sequence; σ2Iand σ0I- valid values of the coefficients of asymmetry reverse currents and zero sequence.

The generalized block diagram described here, the passive control of the level of unbalance voltages and currents are presented in figure 1. Judging from this figure, the source information here comes from the analog-to-digital Converter (ADC) block GARD, where it turns out the spectral composition of the analyzed characteristics. Further, when the systematic use of equalities(1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16), (17), (18) and inequalities(19), (20), (21), (22), (23), (24) it turns out the necessity of active influence on the level of asymmetry of voltages and currents.

If in a controlled power supply system is a relatively low level of nonsinusoidal voltages and currents, the passive control of the level of asymmetry can be done only on the characteristics of electric energy at the frequency of the main harmonic component as Pets the current standard [1]. GOST 13109-97 level of voltage unbalance is proposed to determine more generally through a single coefficients unbalance voltage reverse and zero consequently the values.

Thus, the effective value of the direct voltage sequence here would be as follows:

where U1ABU1BCand U1CA- valid values are linear (interphase) stresses the fundamental frequency.

RMS voltage negative sequence fundamental frequency is proposed to determine:

RMS voltage zero sequence fundamental frequency is recommended to determine:

where U1Aand U1B- effective values of phase voltages at the frequency of the main harmonic component.

The coefficients of voltage asymmetry inverse and zero sequence in this case will be determined from the formula

It is the quantitative values of these coefficients are GOST 13109-97 for General purpose power supply. The actual level of voltage asymmetry in this case is checked like this:

where σ2Uand σ0U- valid interstate standard values of the coefficients of the inverse and zero sequence./p>

The generalized block diagram of such a passive level control of voltage asymmetry presented in figure 2. Here you can see that the original information comes from the analog-to-digital Converter (ADC) block GARD, where it turns out the spectral composition of the analyzed characteristics. Further, when the systematic use of equalities(25), (26), (27), (28), (29) and inequalities (30) and (31) reveals the need for active influence on the level of asymmetry of voltages and currents.

The results of the passive control of the level of asymmetry of the main characteristics of electrical energy, in particular, the facts of exceeding pre-established normative values of the relevant indicators of the quality of electric energy are entitled to proceed to the active control of the level of asymmetry of these characteristics.

Because the asymmetry of voltages and currents is shown in the form of violation of equality between phase or line voltages and currents, it makes sense to assess the level of asymmetry of the corresponding values by simple comparison. It is necessary for the formation of the control signal corresponding corrective devices.

First of all you now need to decide which pair or any pair of line or phase voltages, and can be, currents are responsible for the violation of normative values level the asymmetry of the analyzed characteristics of electrical energy.

For this purpose it is necessary to determine the quantitative level of tolerance for violations of this inequality, the excess of which is highly undesirable. This value can best be defined in percentage as allowable relative error:

where amaxand Amin- maximum and minimum values of the pair of current values of the linear or phase values of voltage or current.

Call this value by level of asymmetry of one or another voltage or current.

The permissible level of asymmetry of the line voltage will be denoted by the symbol σU, phase - σUcurrent - σ1.

Effective values of voltages and currents determined from the geometric summation obtained in the analog-to-digital Converter discrete values. For example, the current values of the line voltages will be as follows:

where UABPUHRVand URAAdiscrete values of the line voltage at the p-vol quantization; N is the number of quantizations in the one-period changes of the analyzed values.

Effective values of phase voltages will be defined like this:

where UApUBPand UCpdiscrete values of phase voltages when R is the quantization.

Effective values of the phase currents are defined as:

where IAp, IBpand ICpdiscrete values of the currents in p-volume quantization.

The level of asymmetry of the line voltage provided

determined and established its compliance with the valid values:

If you violate this inequality we can conclude about the mismatch between the level of asymmetry of its regulatory requirements and to begin to develop appropriate measures.

Provided

conclusion on the compliance of the level of asymmetry of its regulatory requirements can be done after verification of the fulfillment of the inequality

Provided

mandatory validation inequality

And

need to check the inequality

The following pair of linear voltage assumes the following options.

If

there must be inequality

If

it should be

Similarly checks the level of asymmetry of the phase voltages of its normative value.

If

it should be

And if

If

it should be

And if

If

there must be inequality

And if

The level of unbalance current is checked in a similar manner.

If

the compliance level of the unbalance current of its normative values will be defined like this:

If

the compliance level of the unbalance current of its normative values is defined a little differently:

And beyond.

If

it should be

If

it should be

If

it should be

If

it should be

Obviously, the violation of the inequalities(54), (56), (58), (60), (62) and (64) are already inherently involve the violation of the inequalities(44), (46), (48), (50) and (52). Check the degree of compliance with those and other inequalities are necessary for the selection of the appropriate method of active influence on the level of voltage unbalance.

However, the fact of violation of the inequalities(44), (46), (48), (50), (52), (54), (56), (58), (60), (62), (64), (66), (68), (70), (72), (74) or (76) does not mean that you must immediately proceed to the formation of the control signal for the corresponding corrective device. It is not excluded that one of the reasons for the increased level of unbalance of voltage and current is the presence in the spectra of the analyzed characteristics of the harmonic components having frequencies other than the primary, with unequal amplitudes and different shifts of harmonic components relative to the starting point of the analysis referred to the nature of the stick. This may occur even if the level of non-sinusoidality of the respective voltage and current satisfy their regulatory requirements. Then to reduce the asymmetry of the analyzed characteristics of the electrical energy may be sufficient formation of the control signal for the correction device, which may reduce the share of the presence of voltage or current of the appropriate frequency.

To determine the presence of this fact, it is necessary to determine the value of the normative values of the levels of asymmetry line and phase voltages and currents at frequencies of all possible harmonic components and to assess the actual levels of asymmetry of these values with those normative values.

Guideline values for the permissible levels of line and phase voltages and currents at frequencies of harmonic components should not exceed guideline values. In the extreme case, the normative value line and phase voltages and currents at frequencies v's harmonic components, defined in percentage as allowable relative error,

can be taken equal to a pre-existing values of the analyzed characteristics. However, there are see the SL to identify newly normative values, a new symbolism: the maximum permissible level of a linear voltage to frequency ν -the harmonic component will be denoted by the symbol σνU, phase voltage - σνUcurrent - σνI.

In the equality (77) characters Asνmaxand Aνminmean maximum and minimum values of a pair of linear or phase values of voltage or current at the frequency of the v-th harmonic component.

The level of asymmetry of the linear voltage to frequency ν-the harmonic component of the subject

to determine the compliance check its valid values:

Provided

conclusion on the compliance of the level of voltage unbalance on the frequency ν-the harmonic component can be done after checking the inequality

Provided

need to check the inequality

And when another condition

you should verify the inequality

If

it should be

If

you should run the following condition:

EN is a logical inequality must be met for phase voltage ν -the harmonic component.

If

it should be

If, on the contrary,

in order to maintain an acceptable level of asymmetry of the phase voltages at the frequency ν-the harmonic component must meet the inequality

When

it is necessary to conform to the inequality

And when

you need to have

If

it should be

And if

to maintain an acceptable level of phase unbalance voltage to frequency ν-the harmonic component need to be

The compliance level of the unbalance current at the frequency of the v-th harmonic component of its valid value is checked in a similar manner.

So, if

this will be followed if the inequality

If

then with the e level of unbalance current on frequency ν -the harmonic component will be checked a little differently:

If

you need to have

If

it should be

If

it should be

If

that should keep the inequality

When the violation of the inequalities(79), (81), (83), (85), (87), (89), (91), (93), (95), (97), (99), (101), (103), (105), (107), (109), (111) or (113), you can proceed to the formation of the control corresponding corrective signal devices.

Figure 3 shows the structural diagram of the algorithm of analysis of the level of asymmetry of the line voltage, figure 4 shows the structural diagram of the algorithm of analysis of the asymmetry of the phase voltages, and figure 5 - level of unbalance of the currents at node three-phase power system. The inputs to these algorithms are the results of the passive pre-control level of asymmetry of the analyzed characteristics of electric power (1 or 2). Here check the compliance level of unbalance of voltages and currents with their regulatory requirements of the region accompanied the acidity of violations of these requirements in block F. In block f>0 is read all the facts of such violations and, if any, begins the process of forming the control signal for the corresponding corrective devices.

It should be noted that, as a corrective device in this case can be used not only balancing devices, but also devices designed to reduce the level of nonsinusoidal voltage and current.

So can be implemented automated active control of the level of asymmetry of voltages and currents. This implementation is quite possible with the use of computers (the processor and analog-to-digital Converter).

Sources of information

1. Norms of quality of electric energy in power supply systems General purpose: GOST 13109-97. - Minsk: the interstate Council for standardization, Metrology and certification, 1998. - S.

2. Zielonko IV Indicators of power quality and control in industrial plants. - 2nd ed., revised and enlarged extra - M.: Energoatomizdat, 1986. - 168s.

3. The method of quantitative evaluation of subharmonic and higher fractional harmonic periodically changing values / Gaebelein, Englobal, Swiderian, Eaaea, Avinadav, Caimari, Mailfrom. - The patent of Russia №2122186, MKI 6 G 01 J 3/28. - Fraternal industrial tool is here No. 96112228/25; Appl. 14.06.96; publ. 20.11.98.

The method of automated control of the level of asymmetry of voltages and currents of the unification processes quantitative estimation of the spectral line and phase voltages and currents, passive control of the level of asymmetry line or phase voltages and currents and the generation of control signals corresponding corrective devices, the source data for which are information about analog curves line and phase voltages and currents of the analyzed power system in discrete time, performed with the use of computers, wherein the passive control levels in the asymmetry of line and phase voltages and currents for the assessment of conformity of the coefficients of asymmetry line and phase voltages and currents on reverse order and coefficients of asymmetry line and phase voltages and currents at the zero sequence their pre-established normative values, and the definition of line and phase voltages and currents direct, zero and reverse sequence takes into account the spectral composition of the analyzed characteristics of electric energy, as well as alternative solutions in electroenergetic is a mini systems, low nonsinusoidal voltages and currents, passive control is performed based on the analysis of line voltage at the frequency of the main harmonic component, in violation of established normative values for the quantitative assessment of levels of asymmetry is generated a control signal corresponding corrective devices, for which the result of comparison of the RMS values of the analyzed variables, it turns out a line or phase voltages or currents are responsible for violating the level of asymmetry of the analyzed characteristics of electric energy, then the result of the comparison liable for infringement of the level of asymmetry line or phase voltages or currents of each harmonic component, it turns out, at what frequency is the symmetry breaking of the analyzed characteristics, and further based on the obtained information formed a control signal corresponding corrective devices.



 

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