RU2071073C1 - Device for measuring asymmetry of voltages - Google Patents

Abstract

FIELD: electric measuring technology. SUBSTANCE: device is related to equipment measuring parameters of quality of electric energy in power supply systems and may be used to determine share contribution of Users into asymmetry of voltages of power system. Device includes input unit 1, shunt 2, two filters 5 and 6 of symmetric components of reverse sequence, two selective amplifiers 7 and 8, two detectors 9 and 10, phasemeter 11, three analog-to-digital converters 12, 13 and 14, three counters 15, 16 and 17 with proper couplings. EFFECT: increased functional reliability. 3 dwg

Description

 The invention relates to electrical engineering, in particular to devices for measuring the asymmetry of voltage of three-phase systems.

 A device is known for measuring the amplitude-phase asymmetry of a three-phase system of variable voltages, comprising a three-phase modulating voltage generator, modulators, phase shift units, an output filter, a sign sensor for increments of the input signal of a filter, logic cells, a decoder, a binary counter, and a shift pulse generator (1). The disadvantages of the device include the impossibility of determining their share of consumers in the deterioration of voltage unbalance.

 Closest to the technical nature of the claimed device is selected as a prototype device for measuring asymmetry parameters. This is a commercially available device "Type asymmetry meter 43204" (2), containing an input device, a shunt, a unit for converting the components of the negative sequence of the first harmonic, consisting of a series-connected filter of symmetrical components of the negative sequence, a selective amplifier and detector, a signal display unit, consisting of analog -digital converter and reading device, phase meter, control unit and amplifier recorder. The input device is connected to a three-phase network, the shunt is connected in series to the network, their outputs are connected to the switch, the output switch is connected to the first harmonic reverse sequence conversion unit, which consists of a filter of symmetrical components of the negative sequence, a selective amplifier, a detector, its block is connected to the filter of symmetric components correction, which in turn is connected to the control unit, which serves to control the operation of the correction unit, one input of the control unit p It is connected to the phasometer; by the second input, the phasometer is connected to the output of the selective amplifier. The output of the inverse sequence conversion unit of the first harmonic and the phasemeter output are connected to various inputs of the signal display unit.

где U₂, U_ном соответственно напряжение обратной последовательности и номинальное напряжение.This device is designed to determine the quality indicators of electricity, and in particular the coefficient of the reverse sequence of voltages (K _2U ), which is equal to the ratio:

where U ₂ , U _nom, respectively, the voltage of the negative sequence and the rated voltage.

где D долевое участие потребителей в ухудшении несимметрии напряжений;
K $\genfrac{}{}{0ex}{}{\text{откл}}{\text{2U}}$ , K $\genfrac{}{}{0ex}{}{\text{вкл}}{\text{2U}}$ коэффициент обратной последовательности напряжений соответственно при отключенном и при включенном потребителе.Knowing the coefficient K ₂ U, it is possible to determine the share of consumers in the deterioration of the voltage unbalance according to the formula (1)

where D is the share of consumers in the deterioration of the voltage unbalance;
K $\genfrac{}{}{0ex}{}{\text{off}}{\text{2U}}$ , K $\genfrac{}{}{0ex}{}{\text{on}}{\text{2U}}$ the coefficient of the reverse sequence of voltages, respectively, when the consumer is turned off and on.

 However, with such a device it is impossible to measure the share during continuous operation of consumers, which, in turn, affects the accuracy of the measurement. This is due to the fact that any power supply system is a dynamic system, and since there is a certain period of time between the switched off and on state of the consumer, changes in the system that are not related to this consumer can occur, which leads to a random error that cannot be estimated.

 The purpose of the invention is the determination of the parameters of the quality of electricity during continuous operation of consumers, which allows to determine the share of the consumer in the deterioration of voltage unbalance.

 This goal is achieved by the fact that the device for measuring the asymmetry parameters contains a second filter of symmetrical components of the negative sequence in series and a second selective amplifier, a second detector, a second analog-to-digital converter and a second readout unit, a third analog-to-digital converter and a third readout connected in series block, with the first, second, third inputs of the shunt connected to the corresponding inputs of the second filter are symmetrical x components of the reverse sequence, the output of the second selective amplifier is connected to the input of the second detector and the second input of the phase meter, the input of which is connected to the input of the third analog-to-digital converter.

 Thus, the claimed device meets the criterion of "novelty."

 A comparison of the proposed solution with other technical solutions shows that the phase meter, analog-to-digital Converter, reading device are widely known.

 However, when introduced in this connection with other circuit elements into the inventive device for measuring asymmetry parameters, the device acquires new capabilities, i.e. with it, it is possible to determine the share of the consumer working continuously in the deterioration of the voltage unbalance. Therefore, the set of essential features for the achieved positive effect makes it possible to conclude that the proposed technical solution meets the criterion of "significant differences".

The device allows you to determine the asymmetry parameters, such as: the voltage of the negative sequence (U ₂ ) and the current of the negative sequence (I ₂ ), and also, thanks to the newly introduced blocks and connections, and the phase angle between them / Φ ₂ /.

где D долевое участие;
U₂, I₂ напряжение и ток обратной последовательности, В, А;
U_ном номинальное напряжение, В;
S_кз мощность короткого замыкания, В, А;
Φ₂ угол между

Эта формула вытекает из формулы (1).The measurement additionally uses the angle values to calculate the share of consumers in the deterioration of the asymmetry in the expression:

where D is equity;
U ₂ , I ₂ voltage and current of the negative sequence, V, A;
U _nom rated voltage, V;
S _KZ short-circuit power, V, A;
Φ ₂ angle between

This formula follows from formula (1).

где U₂ действительное значение напряжений обратной последовательности основной частоты 3-х фазной системы напряжений, В;
U_ном номинальное напряжение сети, В.According to GOST 13109-87

where U _{2 is the} actual voltage value of the negative sequence of the fundamental frequency of the 3-phase voltage system, V;
U _nom rated voltage of a network, V.

где U $\genfrac{}{}{0ex}{}{\text{откл}}{\text{2}}$ , U $\genfrac{}{}{0ex}{}{\text{вкл}}{\text{2}}$ действующее значение напряжений обратной последовательности основной частоты, соответственно при отключенном и при включенном потребителе, В.Substituting (3) in (1) and making mathematical transformations, we obtain:

where u $\genfrac{}{}{0ex}{}{\text{off}}{\text{2}}$ , U $\genfrac{}{}{0ex}{}{\text{on}}{\text{2}}$ the effective value of the voltages of the reverse sequence of the fundamental frequency, respectively, with the consumer turned off and on, V.

Для того, чтобы формулу (5) привести к формуле (4), необходимо левую и правую часть уравнения разделить на

, получится:

Если взять модуль от левой части, то выражение

будет соответствовать отношению

в формуле (4), т.е.Next, a classical power supply scheme for consumers is presented, shown in FIG. 2. According to this scheme, you can make the equation:

In order to bring formula (5) to formula (4), it is necessary to divide the left and right sides of the equation by

, it turns out:

If we take the module from the left side, then the expression

will correspond to the ratio

in the formula (4), i.e.

Это объясняется тем, что при отключении потребителя напряжение на ГРБТ будет равно электродвижущей силе (ЭДС). Однако для того, чтобы уровнять левую и правую часть уравнения (6) необходимо взять модуль и от правой части в этом случае выражение (6) примет вид:

В уравнении (8)

можно представить реактивным сопротивлением (Х), так как в системах электроснабжения активное сопротивление (Z) много меньше Х, а следовательно, им можно пренебречь
Z_2c jx_2с, (9)
однако

следовательно,

Для преобразования тока и напряжения обратной последовательности /

/ из векторной формы в алгебраическую строится векторная диаграмма на один из возможных случаев, которая представлена на фиг. 3.

This is due to the fact that when the consumer is turned off, the voltage on the HLBT will be equal to the electromotive force (EMF). However, in order to level the left and right sides of equation (6), it is necessary to take the module and from the right side in this case expression (6) will take the form:

In equation (8)

can be represented by reactance (X), since in power supply systems the active resistance (Z) is much less than X, and therefore, it can be neglected
Z _2c jx _2s , (9)
but

hence,

To convert current and negative sequence voltage /

/ from a vector form to an algebraic one, a vector diagram is constructed for one of the possible cases, which is presented in FIG. 3.

Подставляя (11), (12), (13) в (8), получим:

Согласно фиг. 3 можно сделать вывод, что сумма углов Φ, v_I2 и (-Φ_U2) всегда будет равна углу между векторами

, это вытекает из соображений, что изменяясь, углы Φ, Φ_I2 и (-Φ_U2) изменяют на такую же величину, только противоположного знака, и угол Φ₂.According to FIG. 3:

Substituting (11), (12), (13) in (8), we obtain:

According to FIG. 3 we can conclude that the sum of the angles Φ, v _I2 and (-Φ _U2 ) will always be equal to the angle between the vectors

, this follows from the considerations that when changing, the angles Φ, Φ _I2 and (-Φ _U2 ) change by the same amount, only of the opposite sign, and the angle Φ ₂ .

тогда

Приводится выражение под знаком модуля в тригонометрическую форму

Находится модуль

Производим преобразование подкоренного выражения

Подставляя (15) в (20), получим:

Подставляя это выражение в (14) и учитывая формулу (7), получим исходную формулу (2):

Таким образом, измерив данным прибором параметры несимметрии U₂ и I₂ и угол между ними Φ₂, можно определить долевое участие потребителя в ухудшении несимметрии напряжений. Параметры U_ном, S $\genfrac{}{}{0ex}{}{\text{(1)}}{\text{кз}}$ , S $\genfrac{}{}{0ex}{}{\text{(3)}}{\text{кз}}$ обычно известны, либо определяются известным методом.To facilitate further transformations, we denote

then

An expression under the sign of the module is given in the trigonometric form

Module is located

We transform the root expression

Substituting (15) in (20), we obtain:

Substituting this expression in (14) and taking into account formula (7), we obtain the original formula (2):

Thus, by measuring with this device the asymmetry parameters U ₂ and I ₂ and the angle between them Φ ₂ , it is possible to determine the share of the consumer in the deterioration of voltage asymmetry. Parameters U _nom , S $\genfrac{}{}{0ex}{}{\text{(one)}}{\text{KZ}}$ , S $\genfrac{}{}{0ex}{}{\text{(3)}}{\text{KZ}}$ usually known, or determined by a known method.

In FIG. 1 shows a block diagram of a device;
in FIG. 2 shows a classic power supply circuit for consumers.

The following notation is used in the diagram:
SLBP division of the balance sheet;
E _2c , E _2p EMF of the reverse sequence, respectively, of the system and the consumer, V.

U ₂ , I ₂ voltage and current of the negative sequence, V, A.

In FIG. Figure 3 shows one of the possible cases of the mutual arrangement of vectors and the following notation is accepted:
U ₁ , U ₂ voltage forward and reverse sequences, V,
I ₁ , I ₂ currents of the forward and reverse sequences, A;
and also the angles between them are indicated.

 A device for measuring voltage asymmetry parameters comprises an input unit 1, a shunt 2, two first harmonic reverse sequence conversion blocks 3.4, two filters 5 and 6 of symmetrical components, two selective amplifiers 7 and 8, two detectors 9 and 10, a phase meter 11, three analog-to-digital converters 12,13 and 14 and three reading blocks 15,16 and 17.

 The device operates as follows.

 The parameters of the three-phase voltage of the network through the input unit 1, and the parameters of the three-phase current through the shunt 2 are brought to the same level and fed to the conversion units of the components of the negative sequence of the first harmonic 3 and 4, respectively, at the outputs of these blocks in proportion to the components of the negative sequence of the first harmonic, a constant voltage signal is generated, whose level is proportional to the level of this component. The conversion blocks 3.4 work in a similar way: from the outputs of blocks 1 (or 2), the signal goes to a filter 5 (or 6) of symmetrical components, where the reverse sequence component is extracted, from the output of this block, the signal goes to a selective amplifier 7 (or 8), where the first harmonic is extracted, the detector 9 (or 10) converts the alternating voltage signal into a constant voltage signal, while the alternating voltage signals from the outputs of blocks 7 and 8, which are part of blocks 3 and 4, enter the phase mp 11 which by comparing the time difference between the passages through zero level signals from both units, generates at its output a DC voltage signal proportional to this difference. The DC voltage signals from blocks 3,4,11 are fed to the corresponding analog-to-digital converters 12,13 and 14, which convert the DC voltage signal into codes that are supplied to the reading blocks 15,16 and 17.

Thus, connecting the device to the network on the HFB, we obtain at the outputs of blocks 15-17, respectively, the values of the voltage of the negative sequence (U ₂ ), the current of the negative sequence (I ₂ ) and the value of the phase shift between them (Φ ₂ ), and knowing the data asymmetry parameters, you can calculate the equity using the above formula.

Claims (1)

 A device for measuring voltage asymmetry comprising a series-connected input unit, a first filter of symmetrical components of the negative sequence and a first selective amplifier, series-connected a first detector, a first analog-to-digital converter and a first reading unit, as well as a shunt and a phase meter, and the output of the first selective amplifier is connected with the input of the first detector and the first input of the phase meter, characterized in that, in order to determine the parameters of the quality of electricity with continuous intermittent operation of the consumer, a second filter of symmetrical components of the negative sequence and a second selective amplifier, series-connected a second detector, a second analog-to-digital converter and a second readout unit, series-connected a third analog-to-digital converter and a third readout unit, the first the second, third outputs of the shunt are connected to the corresponding inputs of the second filter of symmetrical components of the negative sequence, the output torogo selective amplifier is connected to the input of the second detector and a second input of the phase meter, the output of which is connected to the input of the third analog-to-digital converter.

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