SU375560A1 - DEVICE FOR MEASUREMENT OF ELECTRICAL ENERGY - Google Patents

Description

The invention relates to devices for measuring electrical energy of alternating current with a frequency output, comprising current and voltage input current transducers, linear voltage-to-frequency linear transducers with identical characteristics, and pulse counters.

The known devices of this type are complex and of little reliability and, moreover, do not provide high accuracy due to the errors of multiple transformations of the input quantities.

The purpose of the invention is to improve the measurement accuracy and simplify the device. For this purpose, in the proposed device, to perform a nonlinear operation of squaring the sum and difference of transformed voltages, two linear transducers are used, to the input of one of which, together with the reference voltage, is fed through the input converters, the sum of two transformed voltages, and - the difference of these voltages together with the reference voltage.

FIG. 1 shows a circuit diagram of a push-pull linear voltage converter of the device described; in fig. 2 is a block diagram of the described device; in fig. 3 is one of the possible options for the implementation of converters of input values of current and wiring.

In a two-stroke voltage converter, the dependence of the frequency of self-oscillations on the magnitude of the input voltage is close to linear and can be approximately expressed by the formula:

  1 rt,

where S is the cross section of the transformer core; BS is induction saturation of the core material;

W is the number of turns in the collector windings, which are assumed to be equal.

Duration

of both half periods of voltage is inversely proportional to the input voltage: T25 GW

one

(2)

i / BX

If the input of the converter, in addition to the voltage t / o, additionally includes voltages and and t / a, as shown in FIG. 1, for both parts of the converter, the input voltage will be different in magnitude. Indeed, for the left (according to the diagram) part of the converter, the input voltage will be: f / BX. 0-f (f /: +.), A for right: in. 0 - (t / 1 -.). in this case, the duration of the half-periods of the generated voltage will also be different. In accordance with formula (2) in the case when the transistor TI is open, and curved, the duration of the semi-period will be rabbi: in gz) f / o + (U, + and) and when locked TI and open Ha: 2SWBs f / o- ( "If -2) The duration of the full period will be equal to the sum of Q + Q2 and is expressed by the formula: G. (5) ul (Ui + U,) Accordingly, the expression for the frequency of the output voltage of the converter will be: f / O (i / l + f / 2) r 4SWBs 0 If in the diagram in FIG. 1 in both branches to change the polarity of one of the input voltages, for example, Uz to the opposite, then a formula similar to expression (6) can be obtained for this case; f ,, 0 (Ui-U, y 4SWBs 0 And different from it in that the second term in the numerator is the square of the difference of the voltages Uj and U. Subtracting (6) from (7), we get the expression: Af fff -IZ / OA / / - /, (8) from which it follows that the frequency difference is proportional to the product of the voltages Ui and f / 2, provided that the voltage UQ is kept strictly constant. The above relations are valid under the condition that the voltages U and Uz unchanged in magnitude or their rate of change is such that for a time equal to the duration of the period T, the magnitudes of the stresses will be neglected It is also small. The ratio between the voltages f / o, Ui and Uz must be such that the resulting voltage is in any case the same polarity as L / o and is in the linear region of the converter characteristic. in time, Ui-Vz is proportional to the number of periods of the difference frequency D / for a certain period of time. In order to convert variable voltages by the considered method, it is necessary to select the parameters of the transformer and the value of the reference voltage Uo tayuim with the expectation that: the duration period to the converted voltages of several tens of times greater than the duration of the output .perioda -nair voltage converter. Theoretical analysis shows that conversion errors will be less than 0.1%, provided that the natural frequency of the converter is approximately forty times higher than the frequency of convertible tensions. The voltage and the current of the circuit, in which the power consumption is measured, are converted with the help of ancillary devices VU and VUZ (see Fig. 2) into voltages of a certain value Ui and f / 2, respectively, proportional to the INPUT values, which are then fed to the inputs voltage converters to frequency Pr1 and Pr. Auxiliary devices must satisfy two basic requirements: first, to ensure high accuracy of the converter, and, secondly, to have dual outputs that are not galvanically interconnected, so that two output voltages can be removed, Proportional to the same input value. In the case of reversible current and voltage, instrument transformers can be used as auxiliary devices. Flpi and Pr converters are powered by a common oinopHoro UQ voltage source and must have identical characteristics. The dependence of the frequency on the control voltage must be linear or well approximated in some part of the forward, offset or not shifted relative to the origin. Converters must allow separate control of the half-period duration of the output voltage. The above-described push-pull converter with a saturable transformer, a transistor multivibrator with separate control, a recharge current and capacitances along the basic circuits, and other types of devices satisfy these requirements. In the block diagram of FIG. Figure 2 conventionally shows that the voltages Ui and U2 are included in the control branches of the Pr1 converter, which are interconnected according to each other, and the Pr2 converter is interconnected. Under these conditions, the output frequency converters Pr and I / 92 In the general form will be defined by the expressions + a (t / i +.); f, f, + a. (U, and,) de / o and a are constant values depending on the parameters of the transducers.

Taking into account the requirements for the identity of the characteristics of the constant / o and o, both converters must be equal in magnitude.

With the help of pulse counters MF and MF (see Fig. 2), the number of frequency impulses /, and is determined. / g for a certain time interval,.

The difference between the indications of the counters MF, and MF2 taking into account formulas (9) and (10) will be equal to:

AA A (f2- /,) ,,. (11)

In the case when the voltages t / i and Uz are sinusoidal values, formula (II) will have the form

N, U, .f ,, (12)

where Ui and / 2 are the effective stress values / 1 and Uz. Ф - angle of phase shift between Ui

and t / 2.

It follows from formula (12) that the difference in meter readings is proportional to the energy consumed in the circuit.

FIG. Figure 3 shows an auxiliary converter circuit for connecting main converters to a measured circuit.

It consists of two current transformers TTt and TTz, the secondary circuits of which are closed to active resistances, and a voltage transformer TN with output windings.

Subject invention

A device for measuring AC electrical power with frequency output, containing current and voltage input converters, linear voltage-to-frequency linear transducers with identical characteristics and pulse counters, characterized in that, in order to improve the accuracy of measurement and simplification of the device, In this case, two linear transducers are used to perform the nonlinear operation of squaring the sum and difference of reformable stresses, the input of one of which, together with the reference voltage The voltage is applied through the specified converters of input values of the sum of two transformable voltages, and the input of the other is the difference of these voltages, together with the reference voltage.

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