RU2645434C1 - Device for measuring differential current - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment and can be used for measuring leakage currents in the wiring and electrical equipment. Technical result is achieved due to fact that in the device for measuring the differential current containing a sensitive element in the form of a toroidal transformer with two primary and one secondary windings, AC power source, amplifier, an indicating unit and a power supply, an AC voltage to DC voltage converter, a photodiode and a light source, while the input of the sensing element being connected to an alternating current source, output of the sensing element through the AC-to-DC converter is connected to the first arm of the photodiode, second arm of which is connected to the output by a source of light flux, input of the light flux is connected to the power unit, third arm of the photodiode through the amplifier is connected to the input of the indicating unit.

EFFECT: technical result of the claimed technical solution is simplification of the procedure for converting the signal of the secondary winding of the differential transformer.

1 cl, 1 dwg

Description

The invention relates to the field of measuring equipment and can be used to measure leakage currents from objects connected to electric voltage sources, for example, to measure leakage currents in apartment networks, as well as to measure leakage currents of individual household appliances.

Known protective shutdown device (see V.K. Monakov, V.S. Rozanov, A.V. Trubitsyn. Life safety. M: MSTU MIREA, 2014, p. 30-33). This device contains a differential current transformer, a trigger, an actuator and a unit for testing. A differential transformer with two primary windings is connected to an electrical receiver (load) and an AC source. The secondary winding of the transformer is connected to the starting element, which in turn is connected to the actuator.

In the absence of differential current - leakage current, equal in magnitude currents flowing through the primary on-turn transformer windings flow, determining the nature of the load. Equal currents in counter-connected windings induce vector-counter-directed magnetic fluxes in the magnetic core of the transformer. The resulting magnetic flux is zero, the current in the secondary of the differential transformer is also zero.

When a leakage current appears, the equality of currents in the windings is violated and a differential current occurs, due to which there is an imbalance of magnetic fluxes and, as a result, the emergence of an emf in the secondary winding of the transformer, proportional to the leakage current. The signal from the output of the secondary winding through the starting element acts on the actuator, which ensures the opening of the electrical circuit.

The disadvantage of this known device is the low accuracy when converting emf secondary winding of the transformer.

The closest technical solution to the proposed one is the one adopted by the author for the prototype (RU 41374 U1, 04/20/2004), containing a measuring unit, including a differential current transformer and an element for connecting to the measured circuit, and a low-pass filter, signal amplifier, power supply, microcontroller, display unit, interface, temperature measurement unit and external device.

The principle of operation of this device is based on measuring the differential current of the zero sequence of phases that occurs when an uncompensated leakage current appears in the network through the conductivity of the phase insulation to earth. In the absence of insulation damage, the geometric sum of magnetic fluxes induced in the core by linear currents is zero, therefore, in the secondary winding of the emf not inducible. If the insulation is damaged, zero sequence currents appear, causing an uncompensated magnetic flux in the core of the differential transformer, which induces an emf. in the secondary winding, the value of which is proportional to the value of the leakage current.

The device operates as follows. The measurement unit is connected to the dissection of the phase and neutral wires. Using the low-pass filter, the necessary signal is extracted, this signal is amplified in the signal amplifier with a high input resistance, the amplified signal is fed to the analog input of the microcontroller, and using the built-in ADC of the microcontroller, the received signal is converted to a digital value. Using the calibration curve embedded in the microcontroller, the input signal is converted into a leakage current, the ambient temperature is measured at the same time, and an adjustment is made to the leakage current. The obtained value is displayed on the digital indicator of the display unit, at the same time these values can be transmitted to an external device via the interface.

The disadvantage of this known device is the complexity of the conversion process emf secondary winding of a toroidal transformer proportional to the leakage current.

The technical result of the claimed technical solution is to simplify the process of converting the signal of the secondary winding of a differential transformer.

The technical result is achieved by the fact that in the device for measuring the differential current, containing a sensing element in the form of a toroidal transformer with two primary and one secondary windings, an alternating current source, an amplifier, an indication unit and a power supply unit, an ac-to-dc voltage converter, a photodiode and a light flux source, the input of the sensor being connected to an alternating current source, the output of the sensor via an AC converter DC voltage is connected to the first arm of the photodiode, the second arm of which is connected to the output by the light source, the input of the light flux is connected to the power supply, the third arm of the photodiode is connected through the amplifier to the input of the display unit.

The essence of the claimed invention, characterized by a combination of the above features, is that the converted emf the secondary winding of the toroidal transformer acts on the photodiode illuminated by the light flux and the value of the differential current is measured by the magnitude of the photodiode of the photodiode.

The presence in the inventive device of a combination of the listed existing features allows us to solve the problem of measuring the differential current based on measuring the photocurrent of photodiodes with the desired technical result, i.e. simplification of the process of converting the signal of the secondary winding of the toroidal transformer (sensitive element).

The drawing shows a functional diagram of the proposed device.

This device contains an AC source 1 connected to the input of the sensing element 2, an AC / DC converter 3, a photodiode 4, a light source 5, a power supply 6, an amplifier 7, connected by an output to an input of an indication unit 8.

The device operates as follows. The absence of differential current in the network leads to the fact that a zero signal is observed at the output of the sensing element. The signal that appears at the output of the sensing element 2, which is different from zero, and corresponding to the leakage current, is fed to the input of the AC voltage to DC voltage converter 3. After rectification of this signal in this converter, its DC voltage is supplied to photodiode 4. Moreover, according to the proposed technical In this case, the solution uses the photodiode mode (the blocking voltage is applied to the photodiode) of the photodiode. When the photodiode is illuminated with the light flux of the light flux source 5, a photocurrent flows through the photodiode. Previously, from the output of the power supply unit 6, voltage is supplied to the light source to generate light radiation. As a rule, the magnitude of this photocurrent arising in this case depends on the voltage applied to the photodiode and the light flux intensity. In the case under consideration, the light flux intensity is assumed to be a constant value. Then the photocurrent of this photodiode (at a constant value of the light flux) will be a function of the voltage applied to the diode. In other words, by the magnitude of the photocurrent arising in this case, one can judge the leakage current in the network. Next, the photocurrent is amplified by amplifier 7 and transferred to indication unit 8. Information is displayed here that allows measuring the value of the differential current.

Thus, according to the proposed technical solution based on measuring the photocurrent of the photodiode illuminated by a constant amount of luminous flux and controlled by the voltage of the AC to DC voltage converter, it is possible to simplify the procedure for converting the signal of the secondary winding of a differential transformer.

The proposed device can be successfully used as a technical means of warning about the occurrence of leakage current in the wiring and electrical equipment.

Claims (1)

A device for measuring the differential current, containing a sensitive element in the form of a toroidal transformer with two primary and one secondary windings, an alternating current source, an amplifier, an indication unit and a power supply unit, characterized in that an alternating voltage to DC voltage converter, a photodiode and a source are introduced therein luminous flux, and the input of the sensing element is connected to an alternating current source, the output of the sensing element through an AC / DC converter Goes voltage is connected to the photodiode first arm, a second arm which is connected to the output of the source light flux of the light flux source input is connected to the power supply, the third port of the photodiode through an amplifier connected to the input of the indication unit.

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