RU2589940C2 - Device for testing inductive electric meters - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: invention relates to electrical measurement and can be used to assess suitability of newly developed electricity from uncontrolled power selection (theft by unwinding) from power grids. Device for testing of inductive electric meters contains storage capacitors in bridge device branches. Outputs of capacitors with one side are connected to grid conductors, and on other side to thyristor in bridge device diagonal circuit. At that, in series with storage capacitors power diodes and chokes are installed, connected to grid conductors. Thyristor control circuit includes integrating link with controlled time constant of series-connected storage capacitor and variable resistor between anode and cathode thyristor. Storage capacitor is connected to primary winding of step-down transformer via dinistor. Secondary winding of step-down transformer is connected to "control electrode-cathode” transition through in-series connected diode thyristor and limiting resistor.

EFFECT: technical result consists in significant simplification of device control.

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Description

The invention relates to the field of measuring electrical engineering and can be used to assess the suitability of newly developed electricity meters from uncontrolled selection of electricity (theft by winding) from energy networks.

Known devices for checking electricity meters [1-6].

The closest analogue to the claimed technical solution (prototype) is a "Device for checking induction meters of electricity metering" according to RF Patent No. 2521307, publ. No. 18 dated 06/27/14 [5], which contains storage capacitors charged with intermittent current at an increased interrupt frequency and smoothly discharged back to the network, as well as transistor current interruption and switching circuits for the smooth discharge of storage capacitors, characterized in that it includes two parallel-connected to the network after the verified electric meter circuits of series-connected storage capacitor and bi-directional transistor switch, forming a bridge circuit so that the storage capacitor first the first circuit is connected to the phase conductor of the network, and the capacitor of the second circuit is connected to the neutral conductor of the network, and the diagonal of this bridge circuit includes serially connected triac and inductor, and the transistors of bi-directional transistor switches of these circuits and triac connected to the corresponding outputs of the transistor control unit and triac , the synchronization of which is carried out from the network.

A disadvantage of the known device is the complexity of its transistor control unit and triac. This disadvantage is eliminated in the inventive device.

The aim of the invention is a significant simplification of the control device.

This goal is achieved in the inventive device for checking induction electric meters, which contains storage capacitors in the branches of the bridge device, the terminals of which are connected on one side to the network conductors, and on the other hand to the thyristor in the diagonal circuit of the bridge device, characterized in that they are connected in series with the storage capacitors power diodes and chokes connected to the network conductors, and the thyristor control circuit includes an integrating element with an adjustable time constant from the storage capacitor and the variable resistor between the anode and the cathode of the thyristor are connected, and the storage capacitor is connected to the primary winding of the step-down transformer through a dynistor, the secondary winding of the step-down transformer is connected to the control electrode-cathode junction of the thyristor through a diode and a limiting resistor connected in series.

The achievement of the goal of the invention is explained, firstly, by replacing the power transistors in the branches of the bridge device with passive elements - power diodes and chokes that do not require any control from the control unit, which greatly simplifies its design, and, secondly, the application a simple circuit for generating a signal that opens the thyristor at a given point in time in each of the periods of the mains voltage without using a rather cumbersome electronic circuit on microcircuits and transistors with output transformers proof operation, and without the use of a secondary power source.

In fig. 1 shows a diagram of the inventive device and its connection to the electric meter and controlling the operation of the circuit with a two-channel oscilloscope with resistor elements of communication with the latter. Figure 2 shows a graph of the instantaneous voltage value on each of the storage capacitors of the bridge device — solid lines and network voltage — dashed. Figure 3 shows a graph of the charging and discharge currents in the storage capacitors, and the temporary position of the discharge pulses can be adjusted (shown by bidirectional arrows) using an adjustable resistor of the formation circuit of the control signal for turning on the thyristor.

The device diagram (Fig. 1) includes the following elements:

C ₁ and C ₂ are storage capacitors of the same value of C (for example, 100 μF each).

L ₁ and L ₂ - chokes with the same inductances L with iron cores,

D ₁ and D ₂ - power diodes designed for the maximum charge current of storage capacitors with a reverse voltage exceeding the amplitude of the mains voltage,

Y - dinistor, opening when the voltage on it reaches the specified level,

C ₃ - additional storage capacitor circuit control the thyristor,

R ₁ and R ₂ is an adjustable resistor from a series-connected resistor of constant value R ₁ and a rheostat R ₂ ,

R ₃ is a limiting resistor that reduces the thyristor control current to a value determined by the maximum permissible values of the control current,

T - thyristor installed in the diagonal of the bridge device, D3 - diode in the circuit of the thyristor control electrode,

Tp - step-down pulse transformer.

In addition, the communication elements of the device with a two-channel oscilloscope are: R ₄ - low resistance resistor (of the order of 0.05 Ohm) of the circuit for measuring the charge current and discharge of storage capacitors C ₁ and C ₂ passing through the current winding of the meter, R ₅ and R ₆ are resistors a voltage divider applied to the voltage coil of the meter, that is, to the network conductors - phase and zero.

In fig. 2, the dashed line (mains voltage) coincides with the solid line of the voltage across the storage capacitors during their charge in the interval of the first quarter of each period of the mains voltage (from zero to T / 4).

In fig. 3, the charge current flows in the first quarter of the network period and has a quasi-sinusoidal shape with a double network frequency (a half period of the charge current corresponds to a quarter of the network voltage period), and the discharge current is an exponentially decaying short pulse whose amplitude is K times the amplitude of the charging current and the charging area and discharge pulses are equal at low internal losses in the bridge device, which corresponds to the law of conservation of charge. This is reflected in the integral equality shown in Fig. 3.

Consider the operation of the claimed device.

In the first quarter of the positive half-cycle, the storage capacitors C ₁ and C ₂ are charged through power diodes and chokes connected in series with them, which for the charging current, which lasts for a sufficiently long period of time (5 ms), represent low resistances, and by the end of the quarter of the period the voltage on storage capacitors reaches an amplitude voltage value of the order of U _O = 300 B.

Thyristor T is closed. The installation of power diodes in the branches of the bridge device maintains this charge voltage of the storage capacitors during the second quarter of the positive half-cycle. At the moment the thyristor is turned on in the diagonal of the bridge device, the storage capacitors are switched on in series, and the voltage on the network conductors rises to a value of the order of 600V, and the series-connected storage capacitors are quickly discharged back into the network with a small internal resistance of the network (about 0.3 ... 0.5 Ohm) depending on the remoteness of the subscriber from the electrical substation and input resistance from the power line (for example, from the overhead line VL-0.4 kV).

It is advantageous to choose the turn-on moment of the thyristor when the sine wave of the alternating voltage of the network passes the zero level, that is, when the positive half-cycle at the time T / 2 ends.

The installation of power diodes D ₁ and D ₂ shown in Fig. ₁ eliminates the possibility of overcharging storage capacitors, that is, the device operates in a half-wave mode. Therefore, the chokes L ₁ and L ₂ operate on a pulsating current (one direction) and must have appropriate gaps in their magnetic circuits, designed for the corresponding charge currents, which eliminates the effect of magnetic saturation of the magnetic circuits of the chokes.

Inductors L ₁ and L ₂ perform a protective function for the significant penetration of the discharge current of the storage capacitors themselves upon opening the thyristor. In the prototype device, such transient function was performed by power transistors, which, when the thyristor (triac) was opened, should have been reliably closed by signals from the control unit. Otherwise, these power transistors would be punctured by a huge discharge current of the order of 300 V / 0.1 Ohm = 3000 A (with an open transistor resistance of 0.1 Ohm). In the considered circuit, this danger does not exist, since there are no power transistors. And, given the wide range of short discharge pulses (of the order of ΔF = 1 / Δt _SIZE = 2.3τ, where τ = r _C C / 2 is the time constant of the discharge process, r _C is the internal resistance of the network (0.3 ... 0.5 Ω ). Thus, with the capacitance of the storage capacitors C = 100 μF and r _C = 0.3 Ohm, we have the duration of the discharge pulse Δt _PIT = 2.3 * 0.3 * 10 ^-4 / 2 = 0.345 * 10 ^-4 s = 34, 5 μs. Therefore, the width of the spectrum of the discharge pulse is of the order of 30 kHz, and the inductance of the inductor L is of the order of X _L = 2π ΔF L. Thus, when using the inductor D 170-0.04 - 2.2 with an inductance of 40 mH, we have X _L = 6.28 * 30000 * 0.04 = 7536 Ohm >>> r _C. almost the entire discharge current from the storage capacitors during the discharge is fed back to the network.For a charging current, such a choke is an inductive resistance of only 12.5 Ohms (for a network with a frequency of 50 Hz), and the charge does not drag out any noticeably in time In this case, the charge time constant at C = 100 μF in each branch of the bridge device is only 1.3 ms, which is 3.85 times less than the total charge time. In addition, you can choose other chokes with a lower value of inductance, for example, chokes of type D 177 - 0.0025 - 12.5 with an inductance of only 2.5 mH (their inductive resistance at a frequency of 50 Hz will be only 0.8 Ohms, and at a frequency of 30 kHz, it is 470 Ohm >> r _C ).

. При С=100 мкФ имеем W_ЗАР=4,5 Дж, что определяет среднюю мгновенную мощность заряда за четверть периода Т / 4 как P_CP=4 W_3AP/Т=18/ / 0,02=900 Вт. Следовательно, средний ток заряда составляет величину I _{СР ЗАР}= 900 / 220=4,09 А, а максимальное значение зарядного тока в фазном проводнике сети (при фазе φ*=π/8) равно 1 махзар=4*1,41*4,09=23,1 А.The charge energy W _{ZAR of} each of the two storage capacitors of the bridge device is calculated as $$W_{3\mathrm{BUT}R}=\mathrm{<figure-callout\; id="2"\; label="C\; U\; O"\; filenames="00000006.png"\; state="\{\{state\}\}">C\; </figure-callout>}{U}_O^{}{}_2^{}/2$$

. At C = 100 μF, we have W _ZAR = 4.5 J, which determines the average instantaneous charge power for a quarter of the T / 4 period as P _CP = 4 W _3AP / T = 18 / / 0.02 = 900 W. Therefore, the average charge current is I _{SR ZAR} = _900/220 = 4.09 A, and the maximum value of the charging current in the phase conductor of the network (with phase φ * = π / 8) is 1 makhzar = 4 * 1.41 * 4 , 09 = 23.1 A.

The total charge energy is equal to twice the charge energy of each of the two storage capacitors, that is, it is equal to 9 J. In this example, the power P _ZAR , which the meter will count when charging, is equal to P _ZAR = 9 J · 50 Hz = 450 Tue

Based on the law of conservation of charge, neglecting, as a first approximation, the very small losses in the bridge device, we can write the obvious relation

where 3 τ is the duration of the discharge pulse near its zero level, K >> 1 is the excess of the amplitude of the discharge pulse I TIME MAX max over the amplitude of the charge, taken as a unit level. Thus _{I ENABLE ·} I _MAX ≈2 U _O / r _C.

If the discharge of the storage capacitors is carried out at times t = T / 2 in each period of the alternating voltage of the network (when the sinusoid of the network passes through zero), then an exponentially decreasing voltage occurs on the network conductors and in the counter voltage coil, the initial value of which is equal to the doubled amplitude of the network voltage 2 U _O = 600 V. In this case, the discharge current pulse also decreases exponentially from the relative value of K to zero in about 3 x time. Therefore, we can write an expression for the relative intensity of the unwinding of the counter readings in the discharge of storage capacitors in the form

since the induction (and any other) meter takes into account electricity as a result of integration over time from the instantaneous values of the product of the effective current passing through the meter by the instantaneous voltage applied to it, taking into account the signs of these quantities. With the coincidence of signs, accounting takes place in the forward direction, and with different signs, in the opposite, reverse direction.

The expression for G shows how many times the reverse energy reading of the meter is greater than the direct (correct) metering. From this it follows that the counter rewinding will be calculated according to the formula in units of the rewinding power

Calculations of the program MathCad result from the expression (1) to the value k = 223.3 and from the expression (2) to the value G = 1,575, therefore, for a considered example (C = 100 uF, T = 0.02 s and r _C = 0 , 3 Ohms), the winding power according to (3) is ΔР = 0.575 * 450 = 258.6 W.

If the consumer has a payload included in the network exceeding the winding power ΔР, then the disk of its counter will rotate much more slowly than in the case without using the switched-on winding device. But still, the disk will rotate in the forward (right) direction, which will practically exclude the possibility for controllers to determine the fact of the theft of electricity from visual observations of the meters, if you do not use special devices, in particular, current clamps, which determine the current in the phase conductor, if the meter located outside the user's premises, for example, on the landing of an apartment building or on a support outside the individual house. This means that the use of the inventive unwinding device can cause very significant damage to the country's energy system, which determines the urgent need for the development and installation of new types of meters for users that are not sensitive to such kind of readings. This version of the electric meter was proposed by the author in [7]. For example, it is possible to recommend the development of electric meters working according to a half-wave circuit, allowing current to flow in only one direction.

Let us dwell on the question of generating a control signal for opening the thyristor T of the bridge device at time t = T / 2 in each period of the mains voltage. As a thyristor, you should choose a high-current avalanche thyristor, for example, type TL-150 with a pulse current of up to 2500A and an average current of 150A. To start it, a voltage on its control electrode of order + 5V relative to the thyristor cathode with a holding current ≥0.2A is required. When connecting a circuit from an additional storage capacitor C ₃ and resistors R ₁ and R ₂ parallel to the anode and cathode of the thyristor T (Fig. 1), between which an increasing voltage of up to 600 V is applied during the first quarter of the T / 4 time period and this voltage is maintained in subsequent a quarter of the period, as can be seen in Fig. 2, an additional capacitor C ₃ is charged with a time constant (R ₁ + R ₂ ) C ₃ . The additional capacitor charged in this case is connected to the thyristor control electrode-cathode junction through the dynistor Y connected in series and the step-down transformer primary winding Tr, the secondary winding of which is connected to the thyristor T control electrode-cathode junction through the limiting resistor R ₃ and diode D ₃ . If, for example, a KN102Z type dynistor with a direct breakdown voltage of 120 V is selected as the element Y, then at the moment of the breakdown of the dynistor at phases of the ac mains voltage φ = π in each of the periods of the ac mains voltage, a pulse voltage from the secondary winding will be applied to the control transition of the thyristor T step-down transformer Tr with a transformation ratio of 2.25: 1 (for the corresponding inclusion of the transformer TOT62) during the discharge of the additional storage capacitor C ₃ and the initial current of the control electrode b ud will be of the order of 0.5 A with a limiting resistor R ₃ Ohms. In this case, the additional capacitor C ₃ will be discharged, however, the current of the control electrode will decrease exponentially from 0.5A to a holding current of 0.2A during the time during which the thyristor opens and remains open during the entire discharge time of the storage capacitors C ₁ and C ₂ and closes automatically as the storage capacitors discharge, when the voltage of the anode-cathode on the thyristor is reset.

Let us consider how the capacity of the additional storage capacitor C _{3 of the} integrating circuit is selected. Assuming that the peak current of the thyristor T control electrode when it is turned on is 0.5 A at an initial voltage of 120V / 2.25 = 53.3 V, we find the peak power of the thyristor on-pulse of 53.3 V · 0.5 A = 26.7 W, which decreases during the turn-on time of the thyristor Δt _ON . From here we find the energy to which the capacitor C ₃ should be charged. This energy is equal to ₃ · 120 C ² / C 2 = 7200 J _3. On the other hand, this energy is determined by multiplying the average power trigger pulse 53.3 · (0.5 + 0.2) / 2 = 18.65 watts per time switching on Δt _ON , which is determined from the expression Δt _ON = 2.3 R _CRF C ₃ , where R _CRF = 2.25 ² (R ₃ + r ₂ + 5V / 0.5 A) + r ₁ - reduced to the primary winding of the step-down transformer Tr is the resistance of the discharge circuit (with a transformation coefficient of 2.25: 1), r ₁ and r ₂ are the active resistances of the primary and secondary windings of the transformer Tr, equal to 36 and 5.5 Ohms. Comparing the energy of the additional storage capacitor C ₃ according to the rule 7200 C ₃ = 18.65 W · 2.3 R _CRC C ₃ = 43 R _CRC C ₃ , we find the resistance value R _CRC , which for the example under consideration is equal to R _CRC = 7200/43 = 167.4 ohms. Then R ₃ = [(167.4-36) / 2.25 ² ] -10-5.5 = 10.5 Ohms. The duration of the switching pulse will be equal to Δt _ON = 2.3 · 167.4 · C ₃ = 385 C ₃ . The opening time of the thyristor TL-150 is 10 μs. Let the duration of the triggering pulse be taken equal to 20 μs, then the value of the capacitance C ₃ = 2 · 10 ^-5 / 385 = 0.052 μF. Thus, the value of this capacitance can be selected as 0.05 μF per operating voltage of 160V (type OSK73P-3). If we take the average charge voltage of this capacitor to 520 V for a time T / 2 = 10 ms, during which the voltage across the capacitor C ₃ reaches 120 V (breakdown values of the KN102Zh dynistor), then we can find the resistance (R ₁ + R ₂ ), taking into account the constant the charge time of the integrating circuit (R ₁ + R ₂ ) C ₃ . Let the charging time of the storage capacitor C ₃ be equal to ΔT _ON = 10 ms, C ₃ = 0.05 μF, U _{CHARGED AVERAGE} = 520B, U _SAMPLES = 120B, then we have the expression: U _SAMPLES / U _{CHARGED AVERAGE} = 1-exp [ -ΔT _ON / (R ₁ + R ₂ ) C ₃ ]. Substituting the known quantities into this expression, we obtain 1,300 = exp [ΔT _ON / (R ₁ + R ₂ ) C ₃ ] or, which is the same, ln 1,3 = ΔT _ON / (R ₁ + R ₂ ) C ₃ = 0.262 . Then R ₁ + R ₂ = 52.4 kΩ. Choose R ₁ = 47 kOhm (2 W) and R ₂ = 10 kOhm (rheostat). Also choose R ₃ = 9.1 Ohm (2 W). Diode D ₃ - 2D202A.

Note that with an increase in the capacitance of the storage capacitor C _{3, in} order to increase the energy of the unlocking pulse of more powerful thyristors, it is necessary to correspondingly reduce the value of the resistors R ₁ and R ₂ . So, with C ₃ = 0.5 μF, R ₁ = 5.6 kOhm, R ₂ = 3.3 kOhm (rheostat) should be selected to maintain a constant time constant (R ₁ + R ₂ ) C ₃ .

By adjusting the resistance value R _{2, the} discharge pulse can be shifted in time (indicated by bidirectional arrows in Fig. 3) so that its beginning falls on the phase φ = π of the alternating voltage of the network in each of its periods.

With an increase in the capacitance of the storage capacitors, the unwinding power increases, however, there is a limit to the increase in the capacitance C, limited by the internal resistance of the network. The maximum permissible value of capacitance C decreases with increasing this resistance. As calculations show, at r _C = 0.3 Ohm, the maximum unwinding power can be about ΔР _MAX = 10 kW with a capacitance C _MAX = 4300 μF. K75-40-750 V pulse capacitors of 100 μF each (a total of 86 pieces) should be used. EPCOS electrolytic capacitors of large capacity can also be used in the range 220 ... 330,000 uF, with a voltage of up to 500 V, having significantly smaller dimensions and weight. Large-capacity electrochemical capacitors (500 μF) with an operating voltage of up to 500 V and discharge currents of up to 5000 A can be used.

The inventive device can be used in the development of new electric meters operating on a half-wave circuit, allowing the flow of current in only one direction [7].

Literature

1. Smaller OF, Device for checking the operation of single-phase induction electric meters, Patent No. 2474825, Publ. in the bull. No 4 on 02/10/2013.

2. Smaller OF, Bridge device for checking electric meters of active energy of induction type, Patent No. 2522706, publ. in No. 20 of 07/20/2014.

3. Smaller OF, Device for monitoring electric meters, Patent No. 2521782, publ. No. 19 dated 07/10/2014.

4. Smaller OF, Device for researching the operation of induction electric meters, Patent No. 2523109, publ. in No. 20 of 07/20/2014.

5. Smaller OF, Device for checking induction electricity meters, Patent No. 2521307, publ. No. 18 dated 06/27/14 (prototype).

6. Smaller OF, Device for checking induction electric meters, Patent No. 2532861, publ. No. 31 of 11/10/2014.

7. Smaller OF, Electricity metering device, Patent No. 2521767, publ. No. 19 dated 07/10/2014.

Patent Search Data

RU 2338217 C1, 10.11.2008 RU 2181894 C1, 04/27/2002 RU 2190859 C2, 10/10/2002 RU 2178892 C2, 01/27/2002 SU 1781628 A1, 12/15/1992 SU 1780022 A1, 12/07/1992 SU 1422199 A1, 09/07/1988 US 7692421 B2, 04/06/2010 US 6362745 B1, 03/26/2002 EP 1065508 A2, 01/03/2001.

Claims (1)

A device for checking induction electric meters, which contains storage capacitors in the branches of the bridge device, the terminals of which are connected on one side to the network conductors and, on the other hand, to the thyristor in the diagonal circuit of the bridge device, characterized in that power diodes and chokes are connected in series with the storage capacitors, connected to the conductors of the network, and the thyristor control circuit includes an integrating link with an adjustable time constant from sequentially connected storage a capacitor and a variable resistor between the anode and the cathode of the thyristor, and the storage capacitor is connected to the primary winding of the step-down transformer through a dynistor, the secondary winding of the step-down transformer is connected to the transition "control electrode - cathode" of the thyristor through a diode and a limiting resistor connected in series.

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