Device for detecting grounding of secondary ground screen of plant station and insulation state of secondary circuit of mutual inductor

Abstract

The invention relates to a plant station secondary ground screen grounding and mutual inductor secondary circuit insulation state detection device, which comprises a main control circuit, a signal generation circuit, a signal detection circuit, a power supply and a multi-stage voltage conversion circuit, the signal generation circuit is electrically connected with a ground wire of an external secondary ground grid, and the signal generation circuit directly injects a specific signal into a joint of two ends of the ground wire of the secondary ground grid in a physical connection mode; in a mutual inductance mode, alternating current signals with specific frequency are mutually inducted to a loop formed by a secondary ground screen, a ground wire, a secondary cable shielding layer and the like through a current clamp; and the signal detection circuit judges whether the secondary ground grid is reliably grounded and whether the secondary loop is in an insulation state or not by respectively detecting grounding wire current signals of the secondary ground grid and the mutual inductor loop. According to the technical scheme, reliability detection and maintenance of the grounding grid and the grounding point in the station are achieved, normal operation of primary and secondary equipment is guaranteed, and reliable operation is protected.

Description

Technical Field

[0001] The invention relates to the field of electrical measuring devices, in particular to a signal injection and detection device for detecting whether a coil in a secondary circuit of a current transformer is normally connected to the ground, and in particular to a plant secondary grounding network and transformer secondary circuit insulation state detection device. Background Art

[0002] The grounding system occupies an extremely important position in the operating equipment in the station, but the current grounding network has been in operation for a long time and lacks corresponding reasonable detection. Poor grounding often occurs due to the manufacturing process of the grounding conductor, conductor deterioration, etc., which brings safety hazards to the normal operation of secondary equipment and reliable operation of protection. In particular, whether the grounding insulation of the secondary circuit of the current transformer is intact is related to the correct operation of the protection device. There have been many incidents of incorrect protection operation caused by poor grounding of the current circuit insulation inside and outside the system, but there is currently a lack of targeted technologies and equipment to perform status detection on the grounding and current circuit insulation.

[0003] At present, common insulation defects of current loops are concentrated in poor grounding network, unreliable grounding, disconnection, soft faults, etc. They are only tested during equipment pre-test, regular inspection or protection device alarm. Due to the complexity and changeability of grounding fault conditions, and the long-term lack of monitoring of the current loop, the problem of poor grounding of the current loop cannot be discovered in time, posing a huge safety hazard.

[0004] Due to the complexity of the substation grounding network, which often constitutes multi-point grounding in a local loop and huge grounding capacitance, even if the existing grounding inspection technology shows that the electrical connection is good, there are already major grounding risks at the local grounding points. This type of problem is more prominent in practice. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0006] To this end, the purpose of the present invention is to provide a plant secondary grounding grid and transformer secondary circuit insulation status detection device, which can realize the reliability detection and maintenance of the grounding grid and grounding points within the station, and ensure the normal operation and reliable protection of primary and secondary equipment.

[0007] To achieve the above-mentioned purpose, the technical solution of the present invention provides a plant secondary grounding network and transformer secondary circuit insulation state detection device, comprising: a main control circuit, a signal generating circuit, a signal detecting circuit, a power supply and a multi-stage voltage conversion circuit, wherein the signal generating circuit is electrically connected to the grounding wire of the external secondary grounding network and the signal generating circuit is electrically connected to the grounding wire of the external secondary grounding network. In the physical connection mode, the signal generating circuit directly injects the specific signal into the two ends of the grounding wire of the secondary grounding network; in the mutual inductance mode, the AC signal of the specific frequency is mutually inducted into the loop formed by the secondary grounding network, the grounding wire, the secondary cable shielding layer, etc. through the current clamp; The signal detection circuit determines whether the secondary grounding network is reliably grounded and the insulation state of the secondary circuit by respectively detecting the grounding line current signals of the secondary grounding network and the mutual inductor circuit.

[0008] In the above technical solution, preferably, the signal generating circuit includes: At least an input end consisting of a transformer T1 and a resistor R95 connected in series to the transformer T1, a current clamp mutual inductance interface JP11 and a physical connection interface JP10 connected in parallel to the input end, a capacitor C105 connected in parallel to the transformer T1, inductors L7 and L8 are connected to both ends of the transformer T1, respectively, the inductors L7 and L8 are connected to chips U45 and U46 respectively, the chip U45 is connected to capacitors C106 and C108 connected in parallel, the chip U46 is connected to capacitors C107 and C109 connected in parallel, and the chips U45 and U46 are grounded in series.

[0009] In the above technical solution, preferably, the signal detection circuit includes: An LC resonant frequency selection unit consisting of at least a current clamp frequency selection interface and a capacitor C38, a signal amplification unit consisting of at least an operational amplifier U40 and resistors R6, R7, R8, capacitors C17, C91 and a diode ZD2 connected to the operational amplifier U40, a signal acquisition unit and a signal output unit respectively connected to the signal amplification unit, the signal acquisition unit comprising a single-chip microcomputer U6 and capacitors C18 and C20 connected to the single-chip microcomputer U6, the current clamp frequency selection interface and the capacitor C38 are connected in series, and the signal output unit comprises connected capacitors C15, C16, C21 and resistors R9 and R10.

[0010] In the above technical scheme, preferably, the main control circuit includes a control chip U2 and capacitors C78, ​​C79, C92-C95, X2, C110, C58, resistors R25, R58, R90, R91, inductor L9, switch SW4, program download and debugging interface H1, and diode LED5 connected to the control chip U2; the capacitors C78, ​​C79, and X2 are connected in series and then grounded; the capacitors C58, C110 and resistor R25 and inductor L9 are connected in series and then grounded; the capacitors C92-C94 are connected in parallel and then grounded; the resistor R90 and capacitor C95 are connected in series and then grounded; the switch SW4 is connected in parallel with the capacitor C95; and the program download and debugging interface H1 is grounded.

[0011] In the above technical solution, preferably, the multi-stage voltage conversion circuit includes a primary voltage conversion unit that converts the power supply voltage 7.4V of the power supply into 5V, and the primary voltage conversion unit includes a conversion chip U44 and capacitors C41-C43, C64-C66, resistors R36-R38 and inductor L5 connected to the conversion chip U44.

[0012] In the above technical scheme, preferably, the multi-stage voltage conversion circuit also includes a secondary voltage conversion unit that converts the 5V supply voltage into 3.3V, and the secondary voltage conversion unit includes a conversion chip U44 and capacitors C15, C16, C4, C5, C8, C9, diode LED1, and resistor R5 connected to the conversion chip U44.

[0013] Compared with the prior art, the advantages of the plant secondary grounding grid and transformer secondary circuit insulation state detection device provided by the present invention are: realizing reliability detection and maintenance of the grounding grid and grounding points within the station, ensuring the normal operation of primary and secondary equipment and reliable protection operation; realizing insulation state detection of the current secondary circuit, avoiding false protection operation, and eliminating major safety hazards; adding necessary secondary equipment maintenance means, effectively extending the service life of the equipment, reducing the working hours of grassroots staff, and improving work efficiency; and being able to test and discover multi-point grounding conditions of the current circuit during construction, ensuring safe and stable operation of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 A circuit structure diagram of a primary voltage conversion circuit according to an embodiment of the present invention is shown; Figure 2 A circuit structure diagram of a secondary voltage conversion circuit according to an embodiment of the present invention is shown; Figure 3 A circuit structure diagram of a main control circuit involved in an embodiment of the present invention is shown; Figure 4 A circuit structure diagram of a signal generating circuit according to an embodiment of the present invention is shown; Figure 5 A circuit structure diagram of a signal detection circuit according to an embodiment of the present invention is shown; Figure 6 A circuit principle block diagram of a detection device involved in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0015] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0016] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0017] like Figures 1 to 6 As shown, according to an embodiment of the present invention, a plant substation secondary earth grid grounding and transformer secondary circuit insulation state detection device includes: a main control circuit, a signal generating circuit, a signal detecting circuit, a power supply and a multi-stage voltage conversion circuit, wherein the signal generating circuit is electrically connected to the grounding wire of the external secondary earth grid and the signal generating circuit is electrically connected to the grounding wire of the external secondary earth grid. In a physical connection mode, the signal generating circuit directly injects a specific signal into the connection points at both ends of the grounding wire of the secondary earth grid; in a mutual inductance mode, an AC signal of a specific frequency is mutually sensed into a loop formed by the secondary earth grid, the grounding wire, the secondary cable shielding layer, etc. through a current clamp; The signal detection circuit determines whether the secondary grounding network is reliably grounded and the insulation state of the secondary circuit by respectively detecting the grounding line current signals of the secondary grounding network and the mutual inductor circuit.

[0018] In the above technical solution, preferably, the signal generating circuit includes: At least an input end consisting of a transformer T1 and a resistor R95 connected in series to the transformer T1, a current clamp mutual inductance interface JP11 and a physical connection interface JP10 connected in parallel to the input end, a capacitor C105 connected in parallel to the transformer T1, inductors L7 and L8 are connected to both ends of the transformer T1, respectively, the inductors L7 and L8 are connected to chips U45 and U46 respectively, the chip U45 is connected to capacitors C106 and C108 connected in parallel, the chip U46 is connected to capacitors C107 and C109 connected in parallel, and the chips U45 and U46 are grounded in series.

[0019] In this embodiment, the detection principle of the device is that after a signal is input to the ground wire, the signal can be detected at the other end of the ground wire. If the ground wire is abnormally grounded, the ground wire and the secondary cable shielding layer, other ground wires, and the secondary ground grid do not form a loop, and the signal cannot be detected. Based on this principle, it can be judged whether the connection of the ground wire is intact. Figure 4The circuit shown is a signal generating circuit, through which a sine wave can be generated. The data of this signal will not affect the original circuit. After this circuit generates a sine wave, it passes through a specific transformer, which acts as an isolation to isolate the signal generating circuit from the circuit under test. In this design, there are two signal input methods, which can be used through the two interfaces JP10 and JP11 respectively. One is to inject the signal through the mutual inductance of the current clamp, the interface is JP11, and the other is to directly inject the measured line through direct connection, the interface is JP10.

[0020] In the above embodiment, preferably, the signal detection circuit includes: An LC resonant frequency selection unit consisting of at least a current clamp frequency selection interface and a capacitor C38, a signal amplification unit consisting of at least an operational amplifier U40 and resistors R6, R7, R8, capacitors C17, C91 and a diode ZD2 connected to the operational amplifier U40, a signal acquisition unit and a signal output unit respectively connected to the signal amplification unit, the signal acquisition unit comprising a single-chip microcomputer U6 and capacitors C18 and C20 connected to the single-chip microcomputer U6, the current clamp frequency selection interface and the capacitor C38 are connected in series, and the signal output unit comprises connected capacitors C15, C16, C21 and resistors R9 and R10.

[0021] In this embodiment, after the signal is generated and applied to the tested line, the signal is collected by using a current clamp at another section of the tested line. If the current clamp collects the current signal, it can be known that the line connection is good. If the current signal cannot be collected, it can be known that there is a problem with the line connection. Figure 5 As shown, the function of this circuit is mainly to process the signal collected by the current clamp. JP6 is connected to the current clamp. The secondary coil of the current clamp and C38 form a series LC resonant frequency selection network to select the injected frequency signal, which greatly improves the signal-to-noise ratio and anti-interference ability of the system. Then the signal is appropriately amplified by the amplifier circuit composed of U40 to meet the amplitude requirements of the single-chip microcomputer for the collected signal. Finally, it is output from ADC_I to the single-chip microcomputer ADC for sampling. In this circuit, the amplification factor of the amplifier circuit can also be controlled by an active digital potentiometer to adapt to different input signal strengths.

[0022] In the above embodiment, preferably, the main control circuit includes a control chip U2 and capacitors C78, ​​C79, C92-C95, X2, C110, C58, resistors R25, R58, R90, R91, inductor L9, switch SW4, program download and debugging interface H1, and diode LED5 connected to the control chip U2; the capacitors C78, ​​C79, and X2 are connected in series and then grounded; the capacitors C58, C110 and resistor R25 and inductor L9 are connected in series and then grounded; the capacitors C92-C94 are connected in parallel and then grounded; the resistor R90 and capacitor C95 are connected in series and then grounded; the switch SW4 is connected in parallel with the capacitor C95; and the program download and debugging interface H1 is grounded.

[0023] In this embodiment, this design uses STM32F103C8T6 as the main controller. Figure 3 As shown, the basic circuit for the operation of the SMT32 microcontroller requires an external high-speed crystal oscillator circuit, a power-on reset circuit, a startup mode selection circuit, a power decoupling circuit, and a program download circuit.

[0024] This part integrates multiple key interfaces to realize complex signal processing and control functions. Among them, the ADC_I interface is used to receive external analog signals, but it does not receive external analog signals directly, but is connected to the output of an operational amplifier circuit. This operational amplifier pre-processes the input analog signal, such as amplification and filtering, to ensure that the signal achieves the best signal-to-noise ratio and dynamic range before converting it to a digital signal. Subsequently, the signal processed by the operational amplifier is read by the ADC_I interface and converted into a digital signal for internal processing by the MCU.

[0025] In addition, the MCU is also equipped with SPI communication interfaces (SPI_CK, SPI_CS, SPI_DI), which are not only used for high-speed and reliable serial communication with external devices, but also specifically used to control the gain of the operational amplifier connected before ADC_I. By sending instructions through the SPI interface, the MCU can adjust the gain of the operational amplifier in real time, thereby achieving precise control of the input signal amplitude to meet the measurement requirements in different application scenarios.

[0026] In terms of signal output, the MCU generates pulse width modulation (SPWM) signals through its SPWM output ports (such as SPWM1_A and SPWM2_A), and these signals are sent to the H-bridge program download and debugging interface. In the H-bridge, the SPWM signal is processed by the switch control of the power electronic device and the filter circuit, and finally converted into a smooth sine wave signal output, realizing the DC to AC inverter function. This sine wave is used to input into the circuit under test.

[0027] In the above embodiment, preferably, the multi-stage voltage conversion circuit includes a primary voltage conversion unit that converts the power supply voltage 7.4V of the power supply into 5V, and the primary voltage conversion unit includes a conversion chip U44 and capacitors C41-C43, C64-C66, resistors R36-R38 and inductor L5 connected to the conversion chip U44.

[0028] In this embodiment, the circuit for converting 7.4V to 5V is designed using a BUCK step-down and voltage-stabilized switching power supply circuit. Figure 1 As shown, the power conversion control chip used is TPS563201DDCR.

[0029] Furthermore, the multi-stage voltage conversion circuit also includes a secondary voltage conversion unit that converts a 5V supply voltage into 3.3V, and the secondary voltage conversion unit includes a conversion chip U22 and capacitors C15, C16, C4, C5, C8, C9, a diode LED1, and a resistor R5 connected to the conversion chip U22.

[0030] In this embodiment, the device is powered by a 7.4V lithium battery, and 5V and 3.3V voltage sources are obtained through multiple step-down circuits respectively, and each power supply is designed in a step-by-step conversion manner, which greatly reduces the heat generated by the power conversion circuit, ensures the conversion efficiency, and also improves the safety and reliability of the system operation.

[0031] In the circuit system, the 3.3V power supply is used to support the operation of the chip or the module with a load of only tens of mA, and the voltage difference of the converted 3.3V power supply is not very large, so the LDO circuit design is usually adopted. The linear output capability of the LDO circuit is also very suitable for the main control chip that is sensitive to the power ripple, such as Figure 2 As shown, the system's 3.3V power supply uses a linear voltage regulator power management chip RT9013-3.3.

[0032] In the structural diagrams of various circuits or units of the present invention, the same reference numerals represent connection relationships, such as the 3V3 terminal in the signal detection circuit is connected to the 3V3 terminal in the main control circuit, and the +7.4V in the signal generating circuit is connected to the +7.4V terminal in the multi-stage voltage conversion circuit. Other circuit diagrams are the same as the above examples and will not be repeated here.

[0033] The present invention aims to solve the problem of detecting the connection status of the coil to the ground in the secondary circuit of the transformer, and ensure the safety and reliability of the power system. Traditional detection methods may have problems such as inaccurate detection, complicated operation or affecting the normal operation of the system. The present invention proposes a method for detecting the connection status of the secondary circuit of the transformer based on signal injection and detection technology. The method injects a sinusoidal wave signal of a specific frequency into one end of the grounding wire, and detects the presence or absence of the signal at the other end, so as to determine whether the grounding wire and the secondary cable shielding layer, other grounding wires and the secondary ground network form a valid loop. The signal generating circuit adopts a high-precision design to ensure that the generated sinusoidal wave signal is pure and free of interference, and is isolated from the circuit under test by an isolation transformer to ensure the safety of the test process and the measurement accuracy. In addition, the present invention provides two signal input methods: current clamp mutual inductance injection and direct connection injection, to meet the detection needs in different scenarios.

[0034] The following effects can be achieved: High accuracy: Through precise signal injection and detection technology, the connection status of the grounding wire can be accurately judged, effectively avoiding misjudgment and missed judgment.

[0035] Good safety: The signal generating circuit and the circuit under test are isolated by an isolation transformer, ensuring that there will be no impact on the power system during the test, thus ensuring the safety of the test.

[0036] Strong flexibility: It provides two signal input methods: current clamp mutual inductance injection and direct connection injection, which can meet the needs of different detection scenarios and improve the flexibility and convenience of detection.

[0037] Improve power system stability: By timely detecting and repairing ground wire connection problems, electrical faults caused by poor grounding can be reduced, and the overall stability and reliability of the power system can be improved.

[0038] Reduce maintenance costs: Reduce power outage time and repair costs caused by electrical failures, and reduce the maintenance costs of the power system.

[0039] Improve work efficiency: The detection process is fast and simple, which improves the work efficiency of maintenance personnel and shortens troubleshooting and repair time.

[0040] Reduce power outage losses: Timely detect and repair ground wire connection problems to reduce economic losses caused by power outages, including production interruptions, equipment damage, etc.

[0041] Save maintenance costs: Through accurate detection and positioning, unnecessary maintenance and replacement work is reduced, saving maintenance costs and resource consumption.

[0042] Figure 6The overall structure of the device is mainly divided into four parts, the power supply part, the main control part, the signal output part and the signal acquisition part. The power supply part mainly inputs 7.4V, and the voltage is reduced to 5V and 3.3V after two consecutive voltage reductions. The main function of the main control part is to generate signals, collect signals and make judgments. The most important parts are the signal output part and the signal acquisition part. These two parts realize the main functions of the present invention. The signal output part includes a signal generation circuit. After the signal is generated, it is isolated by a transformer, and then directly injected through JP10 and JP11 or injected by mutual inductance. The signal acquisition part mainly includes an amplifier circuit and a resonant frequency selection circuit, which are collected through JP6.

[0043] In the present invention, the term "plurality" refers to two or more than two, unless otherwise clearly defined. The terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0044] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by terms such as “upper”, “lower”, “left”, “right”, “front” and “back” are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific orientation, and therefore, cannot be understood as a limitation on the present invention.

[0045] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A plant secondary grounding grid and transformer secondary circuit insulation state detection device, characterized in that: include: A main control circuit, a signal generating circuit, a signal detecting circuit, a power supply and a multi-stage voltage conversion circuit, wherein the signal generating circuit is electrically connected to a grounding wire of the external secondary grounding network and the signal generating circuit is electrically connected to a grounding wire of the external secondary grounding network. When using physical connection, the signal generating circuit directly injects a specific signal into the connection points of the grounding wire of the secondary ground grid; When using mutual inductance, an AC signal of a specific frequency is mutually inducted into a loop formed by a secondary earth grid, a grounding wire, a secondary cable shielding layer, etc. through a current clamp; the signal detection circuit determines whether the secondary earth grid is reliably grounded and the insulation status of the secondary loop by respectively detecting the grounding wire current signals of the secondary earth grid and the mutual inductor loop.

2. The plant secondary grid grounding and transformer secondary circuit insulation state detection device according to claim 1 is characterized in that: The signal generating circuit comprises: At least an input end consisting of a transformer T1 and a resistor R95 connected in series to the transformer T1, a current clamp mutual inductance interface JP11 and a physical connection interface JP10 connected in parallel to the input end, a capacitor C105 connected in parallel to the transformer T1, inductors L7 and L8 are connected to both ends of the transformer T1, respectively, the inductors L7 and L8 are connected to chips U45 and U46 respectively, the chip U45 is connected to capacitors C106 and C108 connected in parallel, the chip U46 is connected to capacitors C107 and C109 connected in parallel, and the chips U45 and U46 are grounded in series.

3. The plant secondary grid grounding and transformer secondary circuit insulation state detection device according to claim 2 is characterized in that: The signal detection circuit comprises: An LC resonant frequency selection unit consisting of at least a current clamp frequency selection interface and a capacitor C38, a signal amplification unit consisting of at least an operational amplifier U40 and resistors R6, R7, R8, capacitors C17, C91 and a diode ZD2 connected to the operational amplifier U40, a signal acquisition unit and a signal output unit respectively connected to the signal amplification unit, the signal acquisition unit comprising a single-chip microcomputer U6 and capacitors C18 and C20 connected to the single-chip microcomputer U6, the current clamp frequency selection interface and the capacitor C38 are connected in series, and the signal output unit comprises connected capacitors C15, C16, C21 and resistors R9 and R10.

4. The plant secondary grid grounding and transformer secondary circuit insulation state detection device according to claim 3 is characterized in that: The main control circuit includes a control chip U2 and capacitors C78, ​​C79, C92-C95, X2, C110, C58, resistors R25, R58, R90, R91, inductor L9, switch SW4, program download and debugging interface H1, and diode LED5 connected to the control chip U2. The capacitors C78, ​​C79, and X2 are connected in series and then grounded. The capacitors C58, C110 and resistor R25 and inductor L9 are connected in series and then grounded. The capacitors C92-C94 are connected in parallel and then grounded. The resistor R90 and capacitor C95 are connected in series and then grounded. The switch SW4 is connected in parallel with the capacitor C95, and the program download and debugging interface H1 is grounded.

5. The plant secondary grid grounding and transformer secondary circuit insulation state detection device according to claim 4 is characterized in that: The multi-stage voltage conversion circuit includes a primary voltage conversion unit that converts the power supply voltage 7.4V of the power supply into 5V. The primary voltage conversion unit includes a conversion chip U44 and capacitors C41-C43, C64-C66, resistors R36-R38 and inductor L5 connected to the conversion chip U44.

6. The plant secondary grid grounding and transformer secondary circuit insulation state detection device according to claim 5 is characterized in that: The multi-stage voltage conversion circuit also includes a secondary voltage conversion unit that converts a 5V supply voltage into 3.3V. The secondary voltage conversion unit includes a conversion chip U44 and capacitors C15, C16, C4, C5, C8, C9, a diode LED1, and a resistor R5 connected to the conversion chip U44.

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