RU94348U1 - ELECTRIC ENERGY METER WITH OUTDOOR CURRENT SENSORS - Google Patents

Abstract

 An electric energy meter with external current sensors, containing current sensors, communication wires, three measuring current transformers, the primary windings of which are connected in series with the phase wires in series with the load, three voltage sensors connected at the input to the corresponding phase wires and the neutral wire, and at the output connected to the corresponding voltage inputs of the measuring unit, the digital inputs and outputs of which are connected to the digital inputs and outputs of the controller, other digital inputs and outputs and outputs of the cat They are connected to digital inputs and outputs and inputs of the auxiliary unit block, which is also connected to phase wires and a neutral wire, and also has digital inputs and outputs for communication with the external environment, characterized in that the current sensors are located at the output of the corresponding current measuring transformers forming together with them a single structural module, and communication wires connect the outputs of the current sensors with the corresponding current inputs of the measuring unit.

Description

The proposed utility model relates to electrical engineering and can be used to build electric energy meters (EE).

The known meter is an EE single-phase NP5 series (www.el-matrix.ru Technical description and operation manual ADD. 410061.101, Matrix LLC, Fig. 2.1 a) which uses a current sensor (current transformer) integrated in the meter housing, included in dissection of the phase wire in series with the load.

However, the inclusion of a current sensor in the meter housing limits the value of the maximum meter current at the level of (50-100) A. This is explained by the limited size of the current contacts for structural reasons, which sets the permissible power dissipation in the contacts and, therefore, the maximum meter current.

In addition, a counter is known that allows working with high currents in the load (Three-phase electric energy meters NP5 series. Www.el-matrix.ru Technical description and operation manual ADDM. 410001.102, Matrix LLC, fig. 2.1.c, fig.4.3 .e, d) containing current transformers (current sensors) in the current circuit, one for each phase A, B, C, the secondary winding of which is connected to the current inputs of the measuring unit (current), and the primary windings are connected through connecting wires to the secondary windings of the respective measuring transforms tori current, the primary windings of which are incorporated crosscuts phase conductors in series with the load. In addition, three (by the number of phases A, B, C) outputs of voltage sensors (resistive voltage dividers) are connected to the voltage inputs (voltage) of the meter’s measuring unit, and the outputs of voltage dividers (DNs) are connected to the corresponding phase wires and the neutral wire. On the other hand, the digital inputs and outputs of the measuring unit are connected to the corresponding inputs and outputs of the controller, digital inputs and outputs, the outputs of which are connected to the auxiliary unit of the meter.

However, such a construction of the counter current circuit, namely: measuring current transformer (ITT) - connecting wires - current sensor (current transformer), which is traditional for current transformer counters, leads to an increase in load resistance in the secondary circuit of ITT due to connecting wires, because the distance from the ITT to the meter can be several tens of meters. As follows from (V.O. Arutyunov. Electrical Measuring Instruments and Measurements. SEI ML 1958. 632 pages, formulas: 15-7 and the last on page 323) the angular error of the ITT is greater, the greater the load resistance in secondary circuit. In addition, with increasing distance from the ITT to the counter, the cross-sectional area of the connecting wires increases. For example, when the distance from the ITT to the meter is 50 m, the diameter of the copper wire must be at least 3.3 mm, to ensure a rated power in the secondary circuit of ITT 5 VA, with a rated current of 5 A, consumed only on connecting wires with a rated current of 5 A .

The objective of the proposed utility model is to reduce the measurement error of electrical energy.

The task is achieved in that in the counter, containing: three current sensors, three pairs of communication wires, three measuring current transformers, the primary windings of which are included in the cut-out of the corresponding phase wires, three voltage sensors, the first inputs of which are connected to the corresponding phase wires, the second - connected to the neutral wire, and the outputs are connected to the corresponding voltage inputs of the measuring unit, the digital inputs and outputs of which are connected to the inputs and outputs of the controller, other digital inputs and outputs and you an ode, which is connected to the digital inputs / outputs and inputs of the block of auxiliary nodes of the meter, which in addition is connected to phase wires and a neutral wire, and also has digital inputs and outputs for communication with the external environment, characterized in that the current sensors are located directly on the output of the corresponding current transformers, forming a single structural module with them, and communication wires connect the outputs of the current sensor with the corresponding current inputs of the measuring unit.

The drawing shows a functional diagram of the proposed electricity meter with remote current sensors. It contains:

measuring current transformers (1, 2, 3);

current sensors (4, 5, 6);

communication wires (L) (7, 8, 9);

measuring unit (IB) 10;

voltage sensors (11, 12, 13);

controller (K) 14;

block of auxiliary units (BWI) 15.

Measuring current transformers (1, 2, 3) are included by the primary winding in the dissection of the phase wires A, B and C, respectively, in series with the load. Current sensors 4, 5, 6 are located in the same structural module together with ITT (1, 2, 3), respectively, and the secondary windings of ITT (1, 2, 3) are connected directly to the inputs of the DT (4, 5, 6), respectively, and the outputs of the DT (4, 5, 6) are connected through the corresponding communication wires A (7, 8, 9) to the corresponding current inputs of the measuring unit 10. The inputs of the voltage sensors (11, 12, 13) are connected at one end to phases A, B, respectively C, the other - to the zero wire. The outputs of the DN (11, 12, 13) are connected to the corresponding voltage inputs of the measuring input 10. The digital inputs and outputs of IB 10 are connected to the inputs and outputs of the controller 14, the digital outputs and inputs of which are connected to the inputs and outputs and inputs of the auxiliary unit BVU 15, which has additional digital inputs and outputs, and is also connected to buses A, B, C and zero.

The individual meter nodes are made as follows: ITT (1, 2, 3) - standard, manufactured by industry, DT (4, 5, 6) - these are either current transformers or shunts, communication wires L (7, 8, 9) are twisted pair, two or three - core cable, etc., measuring unit 10 - these are two analog-to-digital converters, controlled from the controller 14, through digital inputs and outputs. The controller 14 includes a microprocessor, a digital memory for storing code processing programs coming from IB 10, as well as the constants necessary for the counter to function correctly, a clock and other elements necessary for operation. The block of auxiliary nodes of the counter 15 contains a power supply, a display, modems and other nodes necessary for the operation of the counter.

The proposed counter works as follows. Using ITT (1, 2, 3) and DT (4, 5, 6), large-scale conversion of large phase currents in the load into small currents (units mA) is carried out, which are fed to the current through communication wires L (7, 8, 9) IB 10 inputs. IB 10 voltage inputs are supplied with voltage from the outputs of the NAM (11, 12, 13), which are proportional to the phase voltages of the electric network, because DN inputs (11, 12, 13) are connected to phase wires and a neutral wire. In DN (11, 12, 13) the input voltage is reduced to the required level. In IB 10, the instantaneous values of currents and voltages are converted into codes, which are transmitted through digital inputs and outputs to controller 14, where the received codes are processed in order to obtain the values of electric energy, parameters of currents and voltages, etc.

The results of the calculated parameters from K 14 through digital outputs-inputs and outputs are supplied to the auxiliary unit block of the BVU 15, where they are displayed and transmitted through modem devices outside the counter.

The combination of ITT (1, 2, 3) and DT (4, 5. 6) in one structural device, followed by connection, using communication wires L (7, 8, 9), of the outputs of the DT (4, 5, 6) with the current inputs of the information security 10 allows to practically reduce the load resistance in the secondary circuit of the ITT, which, according to V.O. Arutyunova, mentioned in the book, gives minimal errors. Consider an example. Typically, current sensors made on current transformers have a number of turns of the secondary winding w2) of several thousand. We take w2 equal to 1000. Then the minimum current at the DT output will be 5 mA. The nominal input voltage for the ADC, standing in the current channel IB 10 usually does not exceed 0.5 V. Then the resistance of the resistor that converts the current into voltage will be 100 Ohms. We assume that the resistance of the secondary winding of the DT and the communication wires have the same resistance. Thus, the total resistance of the secondary circuit DT is 200 Ohms. The primary winding of the DT has one turn of copper wire (3-5) mm in diameter and a length of (5-10) cm. We calculate the total load resistance in the secondary circuit of the ITT, reduced to the primary winding, i.e. 200 Ohm: 1000 × 1000 = 200 μOhm. To this resistance, you need to add the resistance of one turn of the primary winding of the DT, which is 34 μOhm (calculated for a copper wire 4 mm in diameter and 8 cm in length). Thus, the load resistance in the secondary circuit of the ITT is 234 μOhm, which is equivalent to a short circuit of the secondary winding. If we compare the obtained resistance with the load resistance of 0.2 Ohms, which was previously obtained in the above example for ITT, included in the traditional way (as in the prototype), then the gain in resistance is approximately 85 times. In addition, the communication wires in the proposed meter must pass current within 10 mA, which is easily implemented using conventional communication cables.

Claims (1)

An electric energy meter with external current sensors, containing current sensors, communication wires, three measuring current transformers, the primary windings of which are connected in series with the phase wires in series with the load, three voltage sensors connected at the input to the corresponding phase wires and the neutral wire, and at the output connected to the corresponding voltage inputs of the measuring unit, the digital inputs and outputs of which are connected to the digital inputs and outputs of the controller, other digital inputs and outputs and outputs of the cat They are connected to digital inputs and outputs and inputs of the auxiliary unit block, which is also connected to phase wires and a neutral wire, and also has digital inputs and outputs for communication with the external environment, characterized in that the current sensors are located at the output of the corresponding current measuring transformers forming together with them a single structural module, and communication wires connect the outputs of the current sensors with the corresponding current inputs of the measuring unit.