RU2581186C1 - Full-wave scheme for testing electricity meters for selection of electric power - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical measurement and can be used to assess suitability of newly developed electricity from uncontrolled power selection (rollback) of power grids. Full-wave circuit for testing electricity meters for selection of electricity, comprising a bridge circuit of two parallel-connected branches, each of which used a storage capacitor pulse type, and a diagonal of bridge circuit used triac discharge circuit connected between terminals of two storage capacitors, other terminals which are connected to network, as well as a triac controller. Storage capacitors of bridge circuit are connected to chokes in corresponding charging branches of bridge circuit and discharge circuit of triac control circuit comprising storage capacitors in series with their discharge back into network. Two-link phase-shifting circuit with a step-down transformer, secondary winding of which is connected to “control electrode-cathode” junction of triac of discharge circuit. Two-link phase-shifting circuit sets phase shift of mains voltage in range of phases Δφ in range π/2 < Δφ < π relative to beginning of each period of supply voltage (at φ= 0).

EFFECT: technical result consists in simplification of device.

1 cl, 3 dwg

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 (unwinding) from power networks.

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

The closest analogue to the claimed technical solution (prototype) is a "Device for verification of induction energy metering devices", according to the 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 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 its increased complexity of the control unit transistors and triac. This disadvantage is eliminated in the inventive device.

The aim of the invention is to simplify the device.

This goal is achieved in the claimed two-half-circuit for testing electricity meters for the selection of electricity, containing a bridge circuit of two branches connected in parallel to the network, each of which uses a storage capacitor of a pulse type, and a discharge circuit triac used between the terminals of two storage circuits in the diagonal of the bridge circuit capacitors, other outputs of which are connected to the network, as well as a triac control device, characterized in that it is connected in series with storage cond The capacitors of the bridge circuit include chokes in the corresponding charging branches of the bridge circuit, and the control circuit of the discharge circuit triac, including storage capacitors in series when they are discharged back into the network, contains a two-phase phase-shifting circuit with a step-down transformer, the secondary winding of which is connected to the "control electrode-cathode" junction a triac of the discharge circuit, and the two-phase phase-shifting chain sets the phase shift of the mains voltage in the phase range Δφ in the range π / 2 <Δφ <π relative to ala each mains cycle (at φ = 0).

Achieving the objective of the invention is explained by a significant reduction in the number of equipment while maintaining a high winding power of the readings of electric meters.

The device diagram is shown in Fig. 1. In fig. 2 is a graph of the time variation of the voltage across the storage capacitors. In fig. Figure 3 shows a graph of the charging and discharge currents in each of the storage capacitors of the bridge circuit.

In fig. 1 device contains two connected subunits:

1 - bridge device, including the same storage capacitors with a capacity of C, inductors with inductance L and a high-current pulse triac S;

2 - a control unit for a triac circuit S1 of a discharge circuit of a bridge circuit 1, containing a two-phase phase-shifting circuit of identical capacitors with a capacitance C _F and a pair of resistors R ₁ and R ₂ , as well as a step-down transformer Tr, the secondary winding of which is connected to the junction electrode-cathode junction triac of the discharge circuit. The transformation coefficient k = w ₁ / w ₂ >> 1, where w ₁ and w ₂ are the number of turns of the primary and secondary windings of the transformer Tr.

Consider the operation of the claimed device.

. Величина ΔU определяется значением фазы φ₂=π/2+Δφ*, при которой начинает открываться симистор S в мостовой схеме 1. При этом напряжение $${\text{U}}_{\text{O}}{}^{\text{*}}={\text{U}}_{\text{O}}\text{sin}\left(\text{π/2}+\text{Δ}\varphi \text{*}\right)$$

.At the beginning of the positive half-wave of the alternating voltage of the network through the inductors L, the charge of the storage capacitors C occurs in each of the two branches of the bridge circuit 1 during the first quarter of the period, and more precisely in the range of voltage phase variation 0≤φ≤π / 2 + Δφ *. In this case, the small value Δφ * determines a certain decrease in the voltage across the storage capacitors by the value ΔU << U _O relative to the amplitude voltage of the network U _O = (2) ^1/2 U _C , where U _C is the effective voltage of the network, which is normal to 220 V ( for a single-phase network), so that the final voltage to which the storage capacitors are charged $${\text{U}}_{\text{O}}{}^{\text{*}}={\text{U}}_{\text{O}}-\text{ΔU}$$

. The value ΔU is determined by the value of the phase φ ₂ = π / 2 + Δφ *, at which the triac S begins to open in the bridge circuit 1. In this case, the voltage $${\text{U}}_{\text{O}}{}^{\text{*}}={\text{U}}_{\text{O}}\text{sin}\left(\text{π / 2}+\text{Δ}\varphi \text{*}\right)$$

.

. В этот же момент времени со стороны сети действует встречно напряжение $${\text{U}}_{\text{O}}{}^{\text{*}}$$

к указанному двойному напряжению последовательно включенных симистором S накопительных конденсаторов C, что приводит к протеканию разрядного тока обратно в сеть с амплитудой $${\text{I}}_{\text{MAX}\text{РАЗР}}=\left({\text{2U}}_{\text{O}}{}^{\text{*}}-{\text{U}}_{\text{O}}{}^{\text{*}}\right){\text{/r}}_{\text{C}}={\text{U}}_{\text{O}}\text{cos}\text{Δ}\varphi {\text{*/r}}_{\text{C}}$$

, где r_C - активное сопротивление проводников сети до подключения заявляемого устройства, включающее сумму сопротивлений проводников до электросчетчика, сопротивление токовой обмотки последнего, ввод к электросчетчику от ВЛ-0,4 кВ и сопротивление самой воздушной (кабельной) линии ВЛ-0,4 кВ. Величина сопротивления гс для различных абонентов варьирует обычно в диапазоне 0,3≤r_C≤0,5 Ом. Поэтому разрядный ток I_{max разр} имеет большую амплитуду порядка одного килоампера, что определяет выбор соответствующего симистора S. Например, при Δφ*=0,1π имеем cos Δφ*=0,951, и тогда при r_C=0,3 Ом получим I_{max разр}=295,9 / 0,3=986 A. При таком максимуме разрядного тока можно выбрать, например, в качестве разрядника симистор ТС 152-160-10.When the triac S is turned on at phase φ _{2, the} voltage at two identical storage capacitors C doubles and becomes equal $$\text{2}{\text{U}}_{\text{O}}{}^{\text{*}}$$

. At the same moment in time, the voltage is opposite $${\text{U}}_{\text{O}}{}^{\text{*}}$$

to the specified double voltage of the storage capacitors C sequentially connected by the triac S, which leads to the discharge current flowing back into the network with an amplitude $${\text{I}}_{\text{MAX}\text{SIZE}}=\left({\text{2U}}_{\text{O}}{}^{\text{*}}-{\text{U}}_{\text{O}}{}^{\text{*}}\right){\text{/ r}}_{\text{C}}={\text{U}}_{\text{O}}\text{cos}\text{Δ}\varphi {\text{* / r}}_{\text{C}}$$

where r _C is the active resistance of the network conductors before connecting the inventive device, including the sum of the resistances of the conductors to the electric meter, the resistance of the current winding of the latter, input to the electric meter from VL-0.4 kV and the resistance of the overhead (cable) line VL-0.4 kV . The value of the resistance gc for different subscribers usually varies in the range of 0.3≤r _C ≤0.5 Ohms. Therefore, the discharge current I _{max bit} has a large amplitude of the order of one kiloampere, which determines the choice of the corresponding triac S. For example, for Δφ * = 0.1π we have cos Δφ * = 0.951, and then at r _C = 0.3 Ω we get I _{max bit} = 295.9 / 0.3 = 986 A. With this maximum discharge current, you can choose, for example, a triac ТС 152-160-10 as a spark gap.

. Проводник этих дросселей должен быть рассчитан на среднее значение зарядного тока, которое находится из выражения I_{ср зар}= C U_O/ 4 Т. Для данного примера I_{ср зар}=0,375 A с амплитудой зарядного тока около 1,06 A в каждой из ветвей мостовой схемы. Этот процесс заряда указан на рис. 3. На рис. 2 показан процесс увеличения напряжения на каждом из двух накопительных конденсаторов. В диапазоне фаз 0≤φ≤π/2 напряжение на конденсаторах почти достигает уровня U_O, а затем в диапазоне фаз π/2≤φ≤π/2+Δφ* оно незначительно снижается до величины $$U_O{}^{*}$$

(на малую величину ΔU, как показано на рис. 2).The charge current of the storage capacitors occurs through the inductors L, the active resistance of which should be no more than R _dr ≤T / 20 C. At T = 0.02 s for R _dr we get the value of R _dr ≤0.001 / C. So, at C = 100 μF = 10 ^-4 F this inductor resistance should be no more than 10 Ohms, so that the storage capacitors have time to fully charge to a value $${\text{U}}_{\text{O}}{}^{\text{*}}$$

. The conductor of these chokes should be designed for the average value of the charging current, which is found from the expression I _{cf zar} = CU _O / 4 T. For this example, I _{cf zar} = 0.375 A with a charging current amplitude of about 1.06 A in each of the branches of the bridge circuit . This charge process is shown in Fig. 3. In fig. 2 shows the process of increasing voltage on each of the two storage capacitors. In the phase range 0≤φ≤π / 2, the voltage across the capacitors almost reaches the level of U _O , and then in the phase range π / 2≤φ≤π / 2 + Δφ * it slightly decreases to $$U_O{}^{*}$$

(by a small value of ΔU, as shown in Fig. 2).

.It is interesting to note that the inductance of the chokes L should be chosen according to the condition of a series voltage resonance, for which the equality T / 2 = 2π (L C) ^1/2 or L = (T / 4π) ² / C = 2.5 mH (at C = 100 μF). The wave impedance of such a series circuit at a series resonance frequency of 100 Hz is ρ = (L / C) ^1/2 = (0.0025 / 0.0001) ^1/2 = 5 Ohms. If the active resistance of the inductor is more than 5 Ohms, then the quality factor of such a circuit is Q = ρ / R _dr <1, and therefore the voltage in the storage capacitors does not exceed the value $${\text{U}}_{\text{O}}{}^{\text{*}}$$

.

Under the action of the negative half-wave of each period of the alternating voltage of the network, all processes similar to the above are repeated, and the storage capacitors of the bridge circuit are recharged, as can be seen in Fig. 2 and 3. This eliminates the use of polar electrolytic capacitors in the circuit. Suitable may be pulsed capacitors of the type K75-17-1000 V-50 μF or K75-40-750 V-100 μF - ОЖО.464.230 TU.

If we neglect the energy losses inside the circuit along its discharge circuit, we can write the expression:

where K >> 1 is a dimensionless factor equal to the ratio of the amplitude of the discharge pulse to the amplitude of the charging one (for φ = π / 8), taking into account the equality of the areas under the curves of the charging and discharge currents, that is, K is the relative amplitude of the discharge pulse with respect to the amplitude of the charging taken as unit.

по сравнению с напряжением $${\text{U}}_{\text{O}}{}^{\text{*}}$$

, действующим в момент времени, соответствующий фазе φ₂, и принимаемого за единичный уровень, можно записать отношение энергий разряда к энергии заряда в показаниях индукционного счетчика в следующей форме:Given the important fact that the voltage amplitude in the series-connected storage capacitors at the beginning of the discharge is $$\text{2}{\text{U}}_{\text{O}}{}^{\text{*}}$$

compared to voltage $${\text{U}}_{\text{O}}{}^{\text{*}}$$

operating at the time moment corresponding to the phase φ ₂ and taken as the unit level, we can write the ratio of the discharge energies to the charge energy in the readings of the induction counter in the following form:

(при Δφ*=0,1π) находим мощность «отмотки» показаний электросчетчика ΔP=(L-1)Р_ЗАР=479,6 Вт. Амплитуда разрядного импульса I_{разр max}, как указывалось, равна $${\text{I}}_{\text{РАЗР}\text{MAX}}={\text{U}}_{\text{O}}{}^{\text{*}}{\text{/r}}_{\text{C}}=\text{295}\text{,9/0}\text{,3}=\text{986}\text{A}$$

.From the expression (1) for the initial data for T = 0.02 s and τ = r _C C / 2 = 5 · 10 ^{-5 s,} we obtain K = 11.166. Substituting K into expression (2) we find L = 1,575. At charge power $${\text{P}}_{\text{ZAR}}=\text{2}\text{C}{\text{U}}_{\text{O}}{}^{\text{*}{}^{\text{2}}}\text{/ T}=\text{834}\text{Tue}$$

(at Δφ * = 0.1π) we find the power of the "unwinding" of the meter readings ΔP = (L-1) P _ZAR = 479.6 watts. The amplitude of the discharge pulse I _{bit max} , as indicated, is equal to $${\text{I}}_{\text{SIZE}\text{MAX}}={\text{U}}_{\text{O}}{}^{\text{*}}{\text{/ r}}_{\text{C}}=\text{295}\text{9/0}\text{, 3}=\text{986}\text{A}$$

.

The real reachable value of the “unwinding” power turns out to be slightly less than the calculated value, since there are unavoidable losses in the discharge circuit scheme taking into account the internal resistance of the capacitors and the thyristor, as well as the supply conductors from the circuit to the electric meter, which are usually spaced from each other. In addition, a very short duration of the discharge pulse (about 34 μs), whose spectrum width (about 30 kHz) is significantly higher than the mains frequency by more than two orders of magnitude, can affect the reduction of the “unwinding” power. Therefore, the real power ΔP is determined empirically for each of these schemes, taking into account the differences in the internal resistance of the network at the location of the device in question, as well as the parameters of the elements used in the device. By the way, the internal resistance r _{C of the} network is easily determined by the formula:

where U _XX is the mains voltage at idle (no load). U _H - voltage in the load connected to the network load R _H (preferably a sufficiently powerful load). For example, at an open circuit voltage U _XX = 220 V and when a powerful load R _H = 24 Ohm is connected, the measured voltage value on it decreases to U _H = 217.3 V (the power dissipated in the load is 2 kW). Then the internal resistance of the network is determined according to (3) in the value of r _C = 24 [(220 / 217.3) -1] = 0.298 Ohm.

For the considered example, when using storage capacitors with a capacity of 100 μF, the winding power in an induction electric meter, for example, type СО-2М, which is still widespread in the country, is about 550 W. To increase it, it is necessary to increase the capacitance C of the storage capacitors, which accordingly increases the time constant of the discharge circuit m and, accordingly, extends the duration of the discharge pulse equal to Δt _{SIZE MAX} ≈3τ and is measured almost at a level close to zero. The question arises, to what limit values can the capacitance C of storage capacitors be increased?

, поэтому наибольшая мощность заряда равна $${\text{P}}_{\text{ЗAР}}=\text{2}\text{C}{\text{U}}_{\text{O}}{}^{\text{*}{}^{\text{2}}}\text{/T}=2\cdot \mathrm{0,0111}\cdot {220}^2/\mathrm{0,02}==53724\text{Вт}$$

, и тогда наибольшая возможная величина мощности отмотки ΔP_MAX=53724·0,666=35780 Вт. При этом величина фазы открытия симистора S должна быть φ₂=3π/8.The maximum value of capacitance C for this circuit should be less than T / 4 = 5 ms. So at r _C = 0.3 Ohm, the maximum capacitance value is C _MAX = T / 6 r _C = 0.0111 F = 11100 μF. In this case, the value $${\text{U}}_{\text{O}}{}^{\text{*}}=\text{220}\text{B}$$

, therefore, the maximum charge power is $${\text{P}}_{\text{ZAR}}=\text{2}\text{C}{\text{U}}_{\text{O}}{}^{\text{*}{}^{\text{2}}}\text{/ T}=2\cdot 0.0111\cdot {220}^2/0.02==53724\text{Tue}$$

, and then the largest possible value of the winding power ΔP _MAX = 53724 · 0.666 = 35780 watts. In this case, the magnitude of the opening phase of the triac S should be φ ₂ = 3π / 8.

The selection of a sufficiently large value of the capacitance of the storage capacitors determines the considerable cost of the entire device, however, with a total capacity of two storage capacitors of 22000 μF, it is possible to obtain a winding power of the order of 35 kW. This means that at a cost of 1 kWh for 5 r each, the “savings” from theft of electricity by unscrupulous users will amount to about 128,000 rubles per month of continuous operation of such a device. This can cause very significant damage to energy supplying organizations, which directs the developers of new electricity meters to develop electricity metering devices that are insensitive to the unwinding of their readings by such a claimed device. By rewinding, it is necessary to understand non-literal reverse in the meter readings, which is impossible, for example, in digital metering devices or in induction-type devices with a backstop of the rotating disk. If the power consumption by the user payload is less than the unwinding power, then such metering devices will not take into account the power consumed by the load. If the power consumed by the load is greater than the unwinding power, then the meter will record only the power equal to the difference of these capacities, that is, in any case, damage will be caused to power supply organizations.

A few words should be said about the parameters of the elements of the control unit 2. Let φ ₂ = π / 4 + Δφ * = 1.05 π / 4, as for the initially considered example with C = 100 μF. Then it is easy to calculate that when choosing capacitors С _Ф = 1 μF, the value of the resistor R ₁ = 1.3 kOhm (with a power of 8 W), and the value of the resistor R ₂ when using a step-down transformer Tr with a transformation coefficient k = 10 should be equal to R ₂ = 13 Ohms (with a power of 3 W), on which an alternating voltage occurs with an effective voltage value of 5.5 V, sufficient to start the triac S.

Note that, as the discharge of the storage capacitors is completed, the triac S automatically closes until it is next turned on in each of the half-periods of the mains voltage. When a positive voltage acts on the triac anode, its inclusion is also carried out by a positive voltage at a given level. If a negative voltage acts on the triac anode, then the control voltage on the triac control electrode is negative, which is automatically performed using a transformer Tr when it is turned on accordingly, indicated by dots (Fig. 1) on its windings.

The proposal should be recommended to the developers of electric meters to test their insensitivity to the "unwinding" of the readings of the consumed electricity. An example of such a counter was proposed in [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.

7692421 B2, Apr 6, 2010 US 6362745 Patent Search Data

RU 2338217 C1, 11/10/2008. 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 B1, 03/26/2002 EP 1065508 A2, 03/03/2001.

Claims (1)

A two-half-wave circuit for testing electricity meters for power take-off, containing a bridge circuit of two branches connected in parallel to the network, each of which uses a pulse-type storage capacitor, and a discharge circuit triac used between the terminals of two storage capacitors, the other terminals of which are used in the diagonal of the bridge circuit connected to the network, as well as a triac control device, characterized in that the dros is connected in series with the storage capacitors of the bridge circuit ate in the corresponding charging branches of the bridge circuit, and the control circuit of the discharge circuit triac, including storage capacitors in series when they are discharged back into the network, contains a two-phase phase-shifting circuit with a step-down transformer, the secondary winding of which is connected to the "control electrode-cathode" junction of the discharge circuit simistor, moreover, the two-phase phase-shifting chain sets the phase shift of the mains voltage in the phase range Δφ in the range π / 2 <Δφ <π relative to the beginning of each period of the mains voltage (for φ = 0).

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