RU2552541C1 - Device for verification of electricity metering by induction electricity meters - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device for verification of electricity metering by induction electricity meters consists of in-series assembly of pulse power diode and electrolytic capacitor with active loaded permitting operation at direct current connected in parallel to the capacitor, at that the assembly is placed downstream the verified electric meter. Capacitance value C of the electrolytic capacitor is calculated as per the formula C≈T/2η(1+η)R, where T is alternating current cycle in the mains provided that ratio of charge time η to discharge time of the electrolytic capacitor is many times less than one, for example of about 0.01, where R is active resistance of the load connected in parallel to the electrolytic capacitor and the pulse power diode should be rated for pulse current of I_PULSE≈2I_R/η, where I_R is rated current in the load with resistance R.

EFFECT: simplified design of the device for verification of electricity metering by induction electricity meters in comparison with the known devices intended for the same purpose at operation with active loads permitting operation at direct current.

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Description

The invention relates to the field of electrical engineering and can be used to verify the correct operation of induction-type electric meters with rotating disks when the load is asymmetric for positive and negative half-periods of the mains voltage of the complex load.

It is known that induction electric meters contain a multiplier of the instantaneous value of the load current flowing through its low-resistance current winding to the instantaneous network voltage acting in the high-resistance winding, which is realized by the action of the corresponding magnetic fields on the rotating metal disk, and at the same time the rotational moment applied to the disk is proportional to the instantaneous value of the products of these magnetic fields, that is, the product of the instantaneous current values by the voltage in the indicated coils under harmonic law of change of current and voltage with the mains frequency (50 Hz) and the power determined by counting the number of rotations of the disk, which is equivalent to the operation of integration of said instantaneous values of the products over time.

It is also known that when a purely capacitive load (lossless capacitor) is connected to the network, the meter’s disk remains stationary, although an electric current flows in the circuit, the value of which i _C (t) is determined by the value of the capacitance C of the switched capacitor according to the formula i _C (t ) = jωCU _O sinωt, where U _O - peak value of the mains voltage, ω - angular frequency of the mains voltage, j - imaginary unit, indicating that the phase of the instantaneous values of the current in the capacitor and the voltage across its plates differ by a constant time Miscellaneous be Δφ = π / 2. In this case, electric energy with a double frequency 2F = ω / π circulates through the network conductors and, therefore, through the electric meter, and the rotational moment applied to the counter disk experiences variable-value oscillations with this double frequency with the resulting rotational moment equal to zero, and the electric meter disk not spinning.

This means that the induction meter correctly takes into account electricity when an active load is turned on, at which the phases of the current and voltage do not differ in time.

Finally, it is known that the operation of an induction electric meter with a rotating disk involves working on alternating current, therefore, when using rectifier elements (power diodes), it disrupts its correct operation, although the pulsating load current (from any one half-wave of alternating current) is unsuitable in some cases for the normal operation of certain types of loads, for example, televisions, computers, microwave ovens, washing machines with induction motors. But such active loads as electric furnaces (electric stoves), lighting devices, water heaters, heating radiators, fans and vacuum cleaners with collector motors and other equipment can work equally well both on alternating, and on pulsating and direct current.

This circumstance makes it possible to create devices that violate the correct metering of electricity by induction electric meters [1-5], and one of such devices is considered in the claimed technical solution, the analogues of which the applicant has not installed. The use of such a device will allow developers of induction electric meters to verify the correctness of electricity metering when upgrading the device of such electric meters.

The aim of the invention is to simplify the device for checking the correct metering of electricity by induction electric meters in comparison with known devices of the same purpose when working on active loads that allow working on direct current.

This goal is achieved in the inventive device for checking the correct metering of electric energy by induction electric meters, consisting of a power pulse diode and an electrolytic capacitor connected in series after the verified electric meter, to which an active load is allowed to be connected in parallel, and the value of the capacitance C of the electrolytic capacitor is found by the formula С≈Т / 2η (1 + η) R, where Т is the period of the alternating current of the network, provided that the ratio η of the charge time to the discharge time of the electrolytic capacitor is many times less than unity, for example, of the order of 0.01, where R is the active resistance of the load connected in parallel to the electrolytic capacitor, and the power pulse diode must be designed for a pulse current I _IMP ≈2I _H / η, where I _H is the rated current in the load R.

Achieving the objective of the invention in the claimed technical solution is explained by the accumulation of charge on the electrolytic capacitor, at which the voltage on the capacitor varies very little in time and is almost equal to the amplitude value of the mains voltage U _MAX = (2) ^1/2 U _О , where U _О is the effective voltage value network (for example, 220 V), and at the same time, the capacitor is recharged with a pulsed current of a very large magnitude compared to the rated load current I _H in a very short period of time compared to a quarter of the alternating current equal to 5 ms at a network frequency of 50 Hz. This significantly violates the correct metering of electricity.

In addition, the occurrence of a very large pulse current during charging of the capacitor significantly reduces the voltage acting in the voltage coil of the meter due to input losses from the 0.4 kV overhead line, which also distorts the correct metering of electricity.

The device diagram is shown in Fig. 1 and includes:

1 - single-phase induction type electric meter associated with the input of the network,

2 - power pulse diode, for example avalanche,

3 - electrolytic capacitor with a capacity of C,

4 - active load with resistance R, which allows direct current operation.

When the value of the active load R is varied, when different electrical appliances with a sufficiently wide spread in power consumption are connected to the network, electrolytic capacitors of different capacitance C should be selected accordingly and equip such devices with pulse diodes selected by the pulse current, which increases the overall complexity of the equipment. Therefore, it is advisable to set the maximum maximum possible power P _{MAX of} electrical appliances for which to select the general elements of the circuit - a power pulse diode and an electrolytic capacitor.

Consider the operation of the claimed device.

It is easy to understand that at a constant time τ of the discharge circuit of the capacitor C to the load with the resistance R, where τ = RС, significantly greater than the period T of the alternating current, that is, at τ = RС >> T = 2π / ω, the electrolytic capacitor 3 will be charged to the amplitude voltage U _MAX = (2) ^1/2 U _O , and during operation, the load will vary slightly over time, for example, by ΔU for the discharge time ΔT _SIZE = T-ΔT _ZAR , where ΔT _ZAR is the capacitor charge time interval for each of the periods of alternating voltage, and ΔT _SIZE >> ΔT _ZAR , for example , we take the ratio ΔТ _ZAR / _{ΔТ SIZE} = η << 1.

Let the power pulse diode 2 is turned on so that it transmits current only in odd half-periods of alternating voltage. Then it is clear that at times t = (T / 4) + nT, where n = 0, 1, 2, ... are integers, the voltage across the electrolytic capacitor 3 reaches a maximum U _MAX equal to the amplitude of the alternating voltage (minus the voltage drop at the pn junction of a power pulse diode, of the order of 0.6 V) U _MAX = (2) ^1/2 U _O = 1.41U _O , where U _O is the effective mains voltage (220 V). This voltage is achieved by charging the capacitor for a time ΔТ _{ZAR with a} current pulse from the network. During the time _{ΔТ EXIT} = T / (1 + η) due to the resistance R flowing in the active load 4 with the resistance R, the voltage slightly decreases by the exponential law ΔU u (t) = 1.41U _O exp (-t / τ), where for of each period of the alternating voltage, the time t varies within T / 4≤t≤T. Taking into account the fact that 3T / 4 << τ, we can consider the process of voltage change during the discharge period of the capacitor to be quasilinear, which means that ΔU = 1.41U _O [1-exp (-3T / 4τ)]. In this case, the average value of the voltage acting in the load is U _CP = 1.41U _O -ΔU / 2 = 1.41U _O [1-T / 2 (1 + η) RС], provided that T / 2 (1+ η) RC = γ << 1.

Let γ = 0.01. Then the capacitance value of the electrolytic capacitor is found by the formula: C = T / 2γ (1 + η) R. At T = 20 ms, γ = η = 0.01, we get C = 0.99 / R≈1 / R (here the capacity is expressed in Farads, the load in Ohms). The average voltage value is U _CP = 1.41U _O (1-γ) = 1.396U _O and ΔU = 2U _O (1.41-1.396) = 0.028U _O = 6.16 V. Thus, we can assume that the active the load operates on a purely direct current and at an average voltage U _CP = 307.12 V (without taking into account the small voltage drop at the pn junction of the power pulse diode).

, The capacitor charge begins in each period of the alternating voltage at the time when the voltage across the capacitor reaches the minimum value of 1.41U _O -ΔU = 304.04 V, and during the time ΔТ _ZAR = ηТ / (1 + η) increases to the maximum value of U _MAX == 1.41U _O = 310.2 V. The energy of the recharge W _3AP electrolytic capacitor is calculated by the formula $$W_{3\mathrm{BUT}R}=C\left\{2U_O^2-{\left[1.41U_O-\Delta U)\right]}^2\right\}/2=C\left[1.41U_O\Delta U-\Delta U^2/2\right]\approx 1.41C{U}_O\Delta U$$

,

since ΔU << 2.82 U _O by the initial condition.

, где I_H=U_СР/R - среднее значение тока в нагрузке, умноженной на интервал времени ΔТ_РАЗР=Т/(1+η), то есть имеем $$W_{РАЗР}=U_{СР}^{2}T/\left(1+\eta \right)R=2U_O^2{\left(1-\gamma \right)}^{2}T/\left(1+\eta \right)R$$

. При условии γ=η=0,01, Т=0,02 сек и U_O=220 В имеем W_РАЗР=1878,7/R Джоулей. Следовательно, из равенства W_ЗАР=W_РАЗР получаем соотношение 1,41СU_OΔU=1878,7/R. При сделанных допущениях находим связь между элементами С и R в виде: С=1878,7/1,41RU_OΔU=0,983/R≈1 c/R Ом [Ф].According to the law of conservation and conversion of energy, the energy of the charge W _ZAR for the time interval ΔТ _ZAR = ηТ / (1 + η) is equal to the discharge energy W _Razr capacitor 3 for the time period _{ΔТ ZAR} = T / (1 + η) and is equal to the average power in the load $$R_{\mathrm{FROM}R}=I_H^{2}R$$

, where I _H = U _СР / R is the average value of the current in the load multiplied by the time interval _{ΔТ SIZE} = T / (1 + η), that is, we have $$W_{R\mathrm{BUT}3R}=U_{\mathrm{FROM}R}^{2}T/\left(\mathrm{one}+\eta \right)R=2U_O^2{\left(\mathrm{one}-\gamma \right)}^{2}T/\left(\mathrm{one}+\eta \right)R$$

. Under the condition γ = η = 0.01, T = 0.02 sec and U _O = 220 V, we have W _PIT = 1878.7 / R Joules. Therefore, from the equality W _ZAR = W _PIT, we obtain the ratio 1.41СU _O ΔU = 1878.7 / R. Under the assumptions made, we find the relationship between the elements C and R in the form: C = 1878.7 / 1.41RU _O ΔU = 0.983 / R≈1 c / R Ohm [Ф].

The average value of the charge current of the electrolytic capacitor is so many times greater than the average value of the discharge current (load current I _H ), how many times the charge time is less than the discharge time, that is, I _{CP ZAR} = I _H / η. The shape of the charge current pulse is bell-shaped - at the beginning and end of the charge, the current is zero, therefore, the maximum of the charge current pulse is twice the average value of the charging current, that is, I _IMP ≈2I _H / η.

и при этом емкость электролитического конденсатора должна быть порядка С≈1/18,86=0,053, Ф=53000 мкФ на рабочее напряжение, не ниже 400-450 В. Отметим, что импульсное протекание столь большого тока через электросчетчик нарушает его правильную работу еще и потому, что при этом токе возникает падение напряжения на подводящих проводниках ввода от ВЛ-0,4 кВ (в максимуме импульсного тока). Кроме того, при импульсной работе токовой обмотки счетчика с одной полярностью тока существенно нарушается процесс перемножения тока на напряжение с участием токов Фуко, возбуждаемых в металлическом диске индукционного электросчетчика, и учет электроэнергии существенно уменьшается.Consider an example in which the claimed circuit is designed to power a number of active loads, included separately or together, designed for the greatest possible power consumption. Let such a power P _MAX = 5 kW at a voltage of U _CP = 307.12 V. The total current of such a load is I _H = 5000 / 307.12 = 16.28 A. In this case, the power pulse diode must be selected for the possibility of a pulse current of duration of the order of 0.2 ms with a magnitude of the order of 3.3 kA with a dissipation power of at least 20 watts. Load resistance $$R=U_{\mathrm{FROM}R}^2/P_{M\mathrm{BUT}X}=18.86\text{A.}\mathrm{ABOUT}m$$

and the capacitance of the electrolytic capacitor should be of the order of C≈1 / 18.86 = 0.053, F = 53000 μF per operating voltage, not lower than 400-450 V. Note that the pulsed flow of such a large current through the electric meter violates its correct operation also because at this current a voltage drop occurs at the input lead-in conductors from the 0.4 kV overhead line (at the maximum of the pulse current). In addition, during pulsed operation of the current winding of the meter with one current polarity, the process of multiplying the current by voltage with the participation of Foucault currents excited in the metal disk of the induction electric meter is significantly disrupted, and the metering of electricity is significantly reduced.

It should be specially noted that the average value of the voltage in the load is significantly higher than the effective one for which the consumption devices are designed, and this can be dangerous when the load is directly connected to the electrolytic capacitor due to overvoltage. Therefore, you should either connect an additional quenching resistor r = R-220 / I _{H in} series with the payload, or use a pulse-width modulator (PWM) between the electrolytic capacitor and the payload, at the output of which a smoothing capacitor of relatively small capacity should be installed. In this case, the PWM circuit is controlled by the autoregulation system by comparing a part of the voltage arising from this additional capacitor with a certain standard with the development of a difference control signal according to the static or astatic duty cycle pattern of high-frequency pulses charging the specified additional capacitor with a frequency of the order of 5 ... 10 kHz. In this case, the capacitance of such a capacitor is chosen 100 ... 200 times less than the capacitance of the electrolytic capacitor (for the considered example, it can be chosen equal to 220 ... 470 μF for a voltage of 400 ... 450 V). This capacity should allow operation in the frequency mode. Using a PWM control scheme can significantly increase the efficiency of the energy consumption system.

The inventive device, it is advisable to use at enterprises developing electricity metering devices, including induction type, to exclude the possibility of theft of electricity when users use this kind of schemes.

Literature

1. Smaller O.F. A device for checking the operation of single-phase induction electric meters, Patent No. 2474825, publ. in No. 4 of 02/10/2013.

2. Smaller O.F. A device for testing the sensitivity of three-phase digital electricity meters, Patent No. 2474833, publ. in No. 4 of 02/10/2013.

3. Smaller O.F. The sensitivity control scheme of three-phase electronic electricity meters, Patent No. 2474834, publ. in No. 4 of 02/10/2013.

4. Smaller O.F. A device for checking the sensitivity of induction meters of electric energy to frequency modulation of the operating current, Patent No. 2474826, publ. in No. 4 of 02/10/2013.

5. Smaller O.F. A device for checking induction electric meters, Patent No. 2498323, publ. No. 31 of 11/10/2013.

Claims (1)

A device for checking the correctness of electricity metering by induction electric meters, consisting of a power pulse diode and an electrolytic capacitor connected in series after the verified electric meter, to which an active load is allowed to be connected in direct current, and the capacitance C of the electrolytic capacitor is found by the formula C≈T / 2η (1 + η) R, where T is the period of the alternating current of the network, provided that the ratio η of the charge time to the discharge time of the electrolytic conde Satoru much smaller than unity, e.g., about 0.01, wherein R - load resistance connected in parallel to the electrolytic capacitor and the power switching diode must be designed for the pulse current I _imp ≈2I _H / η, where I _H - nominal current in the load with resistance R.