Arc protection device integrated into digital instrument transformer

Abstract

FIELD: electrical engineering.SUBSTANCE: invention can be used in digital measuring transformers to provide arc fault protection functions in cells of complete switchgear units of 6-35 kV electrical substations. An optical sensor is integrated into a digital measuring transformer comprising a Rogowski coil placed on a current conductor in the transformer housing, and an electronic-digital unit in which a multi-channel analogue-to-digital converter, a programmable microcontroller and a configurable relay with a discrete output are located. The sensor consists of a light guide connected to the front panel of the digital electronic unit and a photodetector located on the board of said unit. The photodetector is connected to a multi-channel analogue-to-digital converter via a current-to-voltage converter, forming an optical channel. The Rogowski coil is connected to a multi-channel analogue-to-digital converter via a circuit comprising an integrator and a low-pass filter, forming a current measurement channel used to implement overcurrent protection. The multichannel analogue-to-digital converter is connected to a programmable microcontroller via a digital interface. Based on the results of processing the analogue-to-digital conversion of the current signals of the optical channel and the current measurement channel, the microcontroller generates signals about the start and operation of the arc protection. The specified signals can be transmitted as telesignaling via the “МЭК” 61850-8-1 GOOSE protocol or used to transmit control signals to the built-in discrete output of the configurable relay.EFFECT: providing the ability to detect an electric arc inside the cells of complete switchgear without installing additional external sensors and separate arc protection devices, without significantly complicating its design, and also eliminating false alarms at low connection currents due to the use of a maximum current protection signal implemented in the transformer itself.5 cl, 1 dwg

Description

[0001] The invention relates to the field of electrical engineering and can be used in digital measuring transformers to provide arc fault protection functions in cells of complete switchgear units of 6-35 kV electrical substations.

[0002] Currently, digital current and voltage measuring transformers are available, containing both analog and digital components. The analog component is used to obtain low-voltage current and voltage signals, while the digital component digitizes and processes the signals, transmitting the resulting values ​​via a digital interface. The presence of a digital component, in addition to measuring current and voltage, allows the transformer to implement additional functions. One such function may be to protect the switchgear during short circuits within it, accompanied by an open electric arc. Arc protection is used to detect electric arcs and prevent further damage to electrical equipment. Upon detection of an electric arc, the arc protection device generates a signal that can be transmitted directly to trip the high-voltage circuit breaker or to other relay protection and automation devices.

[0003] Among the existing technical solutions, digital combined current and voltage transformers are known (patent RU 220445 U1, SPK H01F 38 / 36, G01R 15 / 00, G01R 19 / 25, published 09 / 14 / 2023), having a sealed cast housing made of polymeric electrical insulating material, containing a Rogowski coil placed on a rectilinear cylindrical conductor, and a capacitive voltage divider formed by a high-voltage cylindrical capacitor, the first plate of which is a conductor, and the second plate is a metal strip (sensor), placed inside the Rogowski coil, electrically connected by a signal wire passing in a supporting metal tube, with a low-voltage capacitor placed in an electronic unit installed in a grounded metal base of the transformer with a removable cover, operating under the control of a programmable controller, and performing the functions analog-to-digital signal conversion,coming from a capacitive divider and a Rogowski coil, digital signal processing, obtaining synchronization signals, transmitting data via digital interfaces with the implementation of an algorithm for increasing the accuracy of measurements in the range of low current values.

[0004] These transformers do not have built-in arc fault protection.

[0005] Existing methods of arc fault protection involve installing external optical sensors and separate arc protection devices. These sensors can be of various types: photodetectors (photodiodes, phototransistors, etc.) and fiber optic sensors.

[0006] The disadvantages of these methods are: the need to install additional arc protection devices, the labor-intensive installation of fiber-optic sensors, the difficulty of replacing them if they fail, the need to provide communication channels between the main relay protection device and the arc protection device in order to eliminate false alarms at low connection currents, and increased material costs.

[0007] The closest technical solution to the invention is an arc protection device (patent RU 201607 U1, IPC H02H 7 / 00 (2006.01, published 12 / 23 / 2020)), containing a light detection and testing unit, which has a built-in microcontroller with an analog-to-digital converter, a digital high-pass filter; the light detection and testing unit, the control unit, the discrete output unit and the discrete input unit are electrically connected to each other via a digital serial CAN bus; each relay of the discrete output unit is configured to operate as a result of a logical function described using the Boolean algebra function AND, OR, as well as an inversion function, while the variable functions are the trigger signals of fiber optic sensors and discrete inputs, which are fed to the discrete output unit via the CAN bus.

[0008] The disadvantage of this device is the labor-intensive installation due to the use of external fiber-optic sensors, the need to receive maximum current protection signals from an external relay protection device, as well as increased material costs.

[0009] The technical objective of the present invention is to provide the ability to detect an electric arc inside the cells of complete switchgear units without installing additional external sensors and separate arc protection devices by creating an arc protection device integrated into a digital measuring transformer, wherein the stated objective is solved by placing a light guide and a photodetector, forming an optical sensor of an electric arc, in the electronic-digital unit of the transformer without significantly complicating its design, as well as eliminating false alarms at low connection currents due to the use of a maximum current protection signal implemented in the transformer itself.

[0010] The technical result is achieved by integrating an optical sensor into a digital measuring transformer comprising a Rogowski coil located on a current path within the transformer housing and an electronic-digital unit housing a multi-channel analog-to-digital converter, a programmable microcontroller, and a configurable relay with a discrete output. The sensor consists of a light guide connected to the front panel of the electronic-digital unit and a photodetector located on the circuit board of said unit. The photodetector is connected to the multi-channel analog-to-digital converter via a current-to-voltage converter, forming an optical channel. The Rogowski coil is connected to the multi-channel analog-to-digital converter via a circuit containing an integrator and a low-pass filter, forming a current measurement channel used to implement overcurrent protection.A multichannel analog-to-digital converter is connected to a programmable microcontroller via a digital interface. The microcontroller, based on the results of analog-to-digital conversion of the optical and current measurement channel current signals, generates signals for arc protection system activation and actuation. These signals can be transmitted as remote signaling via the IEC 61850-8-1 GOOSE protocol or used to transmit control signals to the built-in discrete output of a configurable relay.

[0011] The technical essence of the invention is explained by a drawing, which shows in the form of a diagram the design of an arc protection device integrated into a digital measuring transformer.

[0012] Structurally, the device consists of a Rogowski coil RC, an electronic-digital unit 1, an integrator 3, a low-pass filter 4, a light guide 2, a photodetector 5, a current-to-voltage converter 6, a multi-channel analog-to-digital converter 7, a programmable microcontroller 8, a configurable relay 9, and a power supply 10.

[0013] The presented design involves integrating an arc protection device into a digital measuring transformer by modifying the circuit of the electronic digital unit of transformer 1.

[0014] The modification of the circuit of the electronic-digital unit of the transformer 1 is performed as follows. In the electronic-digital unit 1, in addition to the existing current measurement channel, implemented on the basis of the Rogowski coil RC, placed on the current lead in the high-voltage part of the transformer, integrator 3 and low-pass filter 4, located in the electronic-digital unit 1, an optical channel is added, consisting of a light guide 2, brought out with the receiving end part to the front panel of the electronic-digital unit 1, a photodetector 5, optically coupled with the output end part of the light guide 2 and a current-to-voltage converter 6, located in the electronic-digital unit 1.

[0015] The arc protection device contains two independent channels: an optical channel (based on a light guide 2 and a photodetector 5) and a current measurement channel (based on a Rogowski RC coil).

[0016] The optical channel is designed to detect the light emitted by an electric arc. The channel's operation is based on the conversion of the optical signal into an electrical signal and its processing. The device's optical channel contains a light guide 2, which is a flexible or rigid conductor made of polymer optical fiber or quartz glass. Its receiving end is secured in an opening on the front panel of the digital unit 1 and protected by a transparent, dirt-resistant window. The output end of the light guide 2 is optically coupled to a photodetector 5 mounted on a printed circuit board. Photodetector 5 is based on a semiconductor photoelectric converter, such as a photodiode or phototransistor.When using a photodiode, the resulting output signal is fed to current-to-voltage converter 6, which is a transimpedance amplifier with an operational amplifier with negative feedback. This amplifier converts the current to voltage and amplifies the signal amplitude. When using a phototransistor, current is converted to voltage by connecting a load resistor in series with the phototransistor in a DC circuit. The resulting output signals are used to calculate the optical signal parameters required for the arc fault protection algorithm.

[0017] The current measurement channel is used to implement overcurrent protection and monitor the presence of short-circuit current during an electric arc. The Rogowski RC coil, due to the absence of magnetic saturation, provides a linear characteristic over a wide current range. The voltage signal read from the Rogowski RC coil is proportional to the derivative of the primary circuit current. To obtain a signal proportional to the current, it is fed to the input of integrator 3, implemented using a low-noise operational amplifier. The signal at the output of integrator 3 contains high-frequency interference, which is suppressed by low-pass filter 4. The resulting output signals are used to calculate the current parameters required for the arc fault protection algorithm.

[0018] Joint processing of signals from these channels ensures reliable detection of electric arc.

[0019] Analog signals from the optical and current measurement channel outputs are fed to the inputs of multichannel analog-to-digital converter 7, which is selected based on the required bit depth, sampling frequency, and noise minimization. The resulting digital signals, in the form of digital streams of discrete numerical values, are fed to programmable microcontroller 8 to execute the overcurrent protection and light flash detection algorithms.

[0020] Programmable microcontroller 8 reads digitized signals from multichannel analog-to-digital converter 7 and executes the following calculation algorithms to implement the arc fault protection function. For the optical channel, a light flash is detected using two algorithms: calculating the amplitude and rate of rise of the signal. The obtained values ​​are compared with threshold values. If the set values ​​of the optical signal amplitude and / or the rate of rise of the signal are exceeded, a conclusion is made about the possible occurrence of an electric arc. For the current measurement channel, the measured current value is compared with the overcurrent protection (OCP) setting. The final decision about the occurrence of an electric arc is made when two conditions are met: the optical channel detects a light flash and the overcurrent protection setting is exceeded via the current measurement channel.When both conditions are met simultaneously, a signal is generated that is used as a telesignal for further transmission via the digital interfaces of the transformer using the IEC 61850-8-1 GOOSE protocol, or the generation of control signals (CS) to the built-in discrete output of the adjustable relay 9 is activated. To power the electronic digital unit 1, a built-in power supply 10 is used, converting the input direct voltage into a direct voltage of a lower value.

[0021] A key feature and advantage of this invention is the ability to add a built-in arc fault protection function to an existing transformer's digital electronics unit without significantly complicating the transformer's design. This is achieved by modifying only the low-voltage circuitry located within the transformer's digital electronics unit. The current measurement channel existing within the transformer's digital electronics unit is used to implement overcurrent protection.

[0022] The present invention operates as follows.

[0023] When an electric arc occurs in a switchgear cubicle, a light flash occurs, accompanied by a significant increase in current in the digital instrument transformer's busbar. The light flash is detected in the optical channel, which consists of a photodetector and a light guide connected to the front panel of the digital electronics unit. The increase in current in the busbar is detected in the current measurement channel, which is based on a Rogowski coil. Signals from the optical channel and current measurement channel outputs are fed to the inputs of a multichannel analog-to-digital converter, digitized, and transmitted to a programmable microcontroller, where they are processed by software. When conditions indicating the occurrence of an electric arc in the cubicle are met, the programmable microcontroller generates an output signal to trip.

[0024] Thus, the proposed invention makes it possible to promptly detect the occurrence of an open electric arc inside a cubicle of a complete switchgear without the use of external fiber-optic sensors due to the placement of a photodetector inside the electronic-digital unit with a light guide brought out to its front panel, without significantly complicating the design of the digital measuring transformer and increasing its dimensions; eliminates the possibility of false alarms at low connection currents due to the implementation of maximum current protection directly in the transformer; eliminates the need to organize external communication channels for receiving maximum current protection signals from an external relay protection device, which makes it possible to abandon the installation of separate arc protection devices and, as a result, reduces the material costs of the equipment and its maintenance.

Claims

1. An arc protection device integrated into a digital measuring transformer, comprising a Rogowski coil mounted on a conductor in the transformer housing, and an electronic-digital unit including an integrator, a low-pass filter, a multi-channel analog-to-digital converter, a programmable microcontroller and a configurable relay with a discrete output, characterized in that an optical sensor is integrated into the electronic-digital unit, containing a light guide brought out to the front panel of the electronic-digital unit, and a photodetector placed on the board of the said unit and connected through a current-to-voltage converter to the multi-channel analog-to-digital converter, forming an optical channel, wherein the Rogowski coil is connected through a series-connected integrator and low-pass filter to the multi-channel analog-to-digital converter to form a current measurement channel,wherein the multi-channel analog-to-digital converter is connected via a digital interface to a programmable microcontroller, which, based on the results of processing the analog-to-digital conversion of the current signals of the optical channel and the current measurement channel, generates signals about the start and operation of the arc protection as a telesignaling for transmission via the IEC 61850-8-1 GOOSE protocol or transmits control signals to the built-in discrete output of the configurable relay.

2. The device according to paragraph 1, characterized in that the photodetector is made on the basis of a semiconductor photoelectric converter.

3. The device according to paragraph 2, characterized in that when the photodetector is made in the form of a photodiode, the current-to-voltage converter is made in the form of a transimpedance amplifier on an operational amplifier with negative feedback.

4. The device according to paragraph 2, characterized in that when the photodetector is made in the form of a phototransistor, the current-to-voltage converter is made in the form of a load resistor connected in series with the phototransistor in a DC voltage circuit.

5. The device according to paragraph 1, characterized in that the light guide is made of polymer optical fiber, quartz glass.

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