A transformer cooling system control circuit
Patent Information
- Application Number
- CN202522037371.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-22
- Publication Date
- 2026-11-03
- Estimated Expiration
- 2035-09-22
AI Technical Summary
Oil-immersed transformers are difficult to dissipate heat effectively under high temperature and high load conditions, resulting in excessive temperature rise, which affects the electrical performance and service life of the transformer and poses safety hazards.
A transformer cooling system control circuit was designed, including a temperature signal acquisition circuit, a cooling fan control circuit, a circulating oil pump control circuit, and an indicator circuit. By acquiring transformer temperature information in real time, the start and stop states of the cooling fan and the circulating oil pump are precisely controlled to achieve dynamic adjustment of the cooling strategy and improve heat dissipation efficiency.
Effectively controlling transformer temperature within a reasonable range ensures safe, stable, and efficient operation of the transformer, extends its service life, and improves the ability of maintenance personnel to intuitively monitor equipment status.
Smart Images
Figure CN224934315U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of oil-immersed transformer cooling control technology, and in particular to a transformer cooling system control circuit. Background Technology
[0002] In power systems, transformers, as critical electrical equipment, undertake important tasks such as voltage transformation, power transmission, and distribution. The stability of their operation directly affects the safe and reliable operation of the entire power system. Temperature is one of the key factors affecting transformer performance and lifespan. If a transformer operates in a high-temperature environment for a long time, it will accelerate the aging of insulation materials, reduce the insulation performance of the transformer, and thus shorten its service life. It may even cause serious safety accidents, posing a great threat to the stable operation of the power system.
[0003] Currently, oil-immersed transformers are one of the most widely used types of transformers in power systems. Some oil-immersed transformers use natural cooling, relying on the natural convection and radiation of the transformer's own oil tank and heat sink to dissipate the heat generated during operation. This cooling method is simple in structure and low in cost, and can meet the heat dissipation requirements of transformers under normal operating conditions to a certain extent. However, in some high-temperature environments, when the transformer is operating under high load, natural cooling is insufficient to effectively and promptly dissipate heat, leading to a high temperature rise in the transformer. Excessive temperature not only affects the electrical performance of the transformer, such as increasing winding resistance and reducing transformer efficiency, but also accelerates the aging of insulation materials, seriously affecting the service life and operational safety of the transformer.
[0004] Therefore, there is an urgent need for a transformer cooling system control circuit to solve the problem of excessive temperature rise in oil-immersed transformers under high temperature and high load conditions, thereby controlling the transformer temperature within a reasonable range and ensuring that the transformer can operate well and stably. Summary of the Invention
[0005] The purpose of this application is to provide a transformer cooling system control circuit that can accurately and intelligently regulate the start-up, shutdown, and operating status of the cooling fan and circulating oil pump based on the real-time temperature of the oil-immersed transformer under different operating conditions. A temperature signal acquisition circuit acquires the transformer temperature information in real time and accurately transmits it to the cooling fan control circuit and the circulating oil pump control circuit, enabling them to operate in an orderly manner according to preset temperature thresholds. Simultaneously, an indicator circuit visually displays the operating status of the fan and circulating oil pump, facilitating maintenance personnel to promptly grasp the equipment's operating status, effectively improving the transformer's heat dissipation efficiency, stabilizing the transformer temperature within a reasonable range, ensuring the safe, stable, and efficient operation of the transformer, and extending its service life.
[0006] To achieve the above objectives, this application provides the following solution:
[0007] This application provides a control circuit for a transformer cooling system, including:
[0008] Temperature signal acquisition circuit, cooling fan control circuit, circulating oil pump control circuit, and indicator circuit;
[0009] The output of the temperature signal acquisition circuit is connected to the input of the cooling fan control circuit and the circulating oil pump control circuit, respectively, for transmitting the temperature signal of the oil-immersed transformer.
[0010] The output terminal of the cooling fan control circuit is connected to the cooling fan and is used to control the fan connected to the transformer;
[0011] The output terminal of the circulating oil pump control circuit is connected to the circulating oil pump and is used to control the oil pump connected to the transformer.
[0012] The input terminals of the indicator circuit are connected to the status signal terminals of the cooling fan control circuit and the circulating oil pump control circuit, respectively, and the operating status of the cooling fan and the circulating oil pump is displayed through indicator lights.
[0013] According to the specific embodiments provided in this application, this application has the following technical effects:
[0014] This application provides a transformer cooling system control circuit. By setting up a temperature signal acquisition circuit and connecting its output to the inputs of a cooling fan control circuit and a circulating oil pump control circuit to transmit the temperature signal of the oil-immersed transformer, it solves the problem of not being able to obtain the accurate real-time temperature of the transformer, thus making it difficult to accurately control the cooling equipment. This provides the basic data support for dynamically adjusting the cooling strategy based on the actual temperature of the transformer. By constructing a cooling fan control circuit, whose output is connected to the cooling fan to control the fan connected to the transformer, and setting up a circulating oil pump control circuit, whose output is connected to the circulating oil pump to control the oil pump connected to the transformer, it solves the problem of not being able to reasonably allocate cooling resources under different temperature conditions of the transformer. This enables the orderly start-up of fans or oil pumps for targeted cooling based on temperature, improving heat dissipation efficiency. By designing an indicator circuit, whose input is connected to the status signal terminals of the cooling fan control circuit and the circulating oil pump control circuit, the operating status of the cooling fan and circulating oil pump is displayed through indicator lights. This solves the problem of maintenance personnel not being able to grasp the working status of the cooling equipment in a timely manner, and achieves intuitive and convenient equipment status monitoring. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This is a schematic diagram of the cooling control circuit connection for an oil-immersed transformer provided in one embodiment of this application. Detailed Implementation
[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0018] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0019] In one exemplary embodiment, a transformer cooling system control circuit is provided, comprising:
[0020] Temperature signal acquisition circuit, cooling fan control circuit, circulating oil pump control circuit, and indicator circuit.
[0021] The output of the temperature signal acquisition circuit is connected to the input of the cooling fan control circuit and the circulating oil pump control circuit, respectively, and is used to transmit the temperature signal of the oil-immersed transformer.
[0022] The output of the cooling fan control circuit is connected to the fan and is used to control the fan connected to the transformer.
[0023] The output of the circulating oil pump control circuit is connected to the circulating oil pump and is used to control the oil pump connected to the transformer.
[0024] The input terminals of the indicator circuit are connected to the status signal terminals of the cooling fan control circuit and the circulating oil pump control circuit, respectively, and the operating status of the cooling fan and the circulating oil pump is displayed through indicator lights.
[0025] By implementing the above-mentioned transformer cooling system control circuit, this application can accurately and intelligently regulate the cooling fan and circulating oil pump according to the actual temperature of the oil-immersed transformer, effectively improve the heat dissipation efficiency of the transformer, stabilize the transformer temperature within a reasonable range, ensure the safe, stable and efficient operation of the transformer, and extend its service life.
[0026] In another exemplary embodiment of this application, the temperature signal acquisition circuit includes a first temperature controller and a second temperature controller connected in parallel.
[0027] The temperature sensing elements of the first temperature controller and the second temperature controller are both installed inside the oil tank of the oil-immersed transformer.
[0028] The normally open contact of the first temperature controller constitutes the start-up condition input terminal of the cooling fan control circuit, and the normally open contact of the second temperature controller constitutes the start-up condition input terminal of the circulating oil pump control circuit.
[0029] In another exemplary embodiment of this application, the cooling fan control circuit includes: a mode selection switch, a fan start button, a first intermediate relay, a second intermediate relay, a third intermediate relay, a first fan contactor, and a second fan contactor.
[0030] The automatic contact of the mode selection switch is connected in series with the normally open contact of the first temperature controller. One end is connected to the phase line, and the other end is connected to the neutral line through the coil of the first fan contactor, forming an automatic start branch.
[0031] The first normally open contact of the first intermediate relay is connected in parallel across the two normally open contacts of the first temperature controller to form a self-holding mechanism.
[0032] The manual contact of the mode selection switch is connected in series with the fan start button and then in parallel across the two ends of the automatic start branch.
[0033] After the coils of the first and second fan contactors are connected in parallel, one end is connected to the phase line, and the other end is connected to the neutral line via the second normally open contact of the first intermediate relay.
[0034] The normally open auxiliary contact of the first fan contactor is connected in parallel with the coil of the first fan contactor to form a self-locking mechanism for the first fan.
[0035] The normally open auxiliary contact of the second fan contactor is connected in parallel with the coil of the second fan contactor to form a self-locking mechanism for the second fan.
[0036] One end of the coil of the second intermediate relay is connected to the phase line, and the other end is connected to the neutral line after passing through the normally open auxiliary contact of the first fan contactor and the normally open auxiliary contact of the second fan contactor in parallel to the common point. This is used to output a synchronization signal to the circulating oil pump control circuit.
[0037] The coil of the third intermediate relay is controlled by the normally open contact of the second intermediate relay, and the normally open contact of the third intermediate relay is connected in series with the normally open contact of the second temperature controller.
[0038] In another exemplary embodiment of this application, the circulating oil pump control circuit includes: an oil pump start button, a fourth intermediate relay, a star contactor, a delta contactor, an oil pump contactor, a time relay, and a star-delta switch.
[0039] The normally open contact of the third intermediate relay is connected in series with the normally open contact of the second temperature controller. One end is connected to the phase line, and the other end is connected to the neutral line through the oil pump contactor coil, thus forming the oil pump starting condition circuit.
[0040] The oil pump start button is connected in parallel with the oil pump start condition circuit to form a manual start branch.
[0041] The normally open auxiliary contact of the oil pump contactor is connected in series with the star contactor coil and then bridging the phase line and the neutral line.
[0042] The normally open auxiliary contact of the star contactor is connected in series with the coil of the time relay and then bridging the phase line and the neutral line.
[0043] The delayed closing contact of the time relay is connected in series with the coil of the fourth intermediate relay and then bridging the phase line and the neutral line.
[0044] The normally open contact of the fourth intermediate relay is connected in series with the coil of the delta contactor and then bridging the phase line and the neutral line.
[0045] The normally closed auxiliary contact of the star contactor is connected in series in the coil circuit of the delta contactor, and the normally closed auxiliary contact of the delta contactor is connected in series in the coil circuit of the star contactor, forming an electrical interlock.
[0046] The automatic contacts of the star-delta changeover switch are connected to the time relay coil circuit.
[0047] In another exemplary embodiment of this application, the indicating circuit includes: a first indicator light, a second indicator light, and a third indicator light.
[0048] The first indicator light and the normally open contact of the third intermediate relay are connected in series and then bridged between the phase line and the neutral line to indicate the operating status of the cooling fan.
[0049] The second indicator light is connected in series with the normally open auxiliary contact of the star contactor and then bridging the phase line and the neutral line to indicate the star start status of the oil pump.
[0050] The third indicator light is connected in series with the normally open auxiliary contact of the delta contactor and then bridging the phase line and the neutral line to indicate the operating status of the oil pump delta.
[0051] In another exemplary embodiment of this application, the mode selection switch is a three-position locking type changeover switch, including an automatic position, a manual position, and a stop position.
[0052] The automatic position only activates the automatic contact; the manual position only activates the manual contact; the stop position disconnects all contacts. The automatic and manual contacts are mechanically interlocked to prevent simultaneous closure; the handle is in neutral when in the middle position to prevent accidental operation.
[0053] In another exemplary embodiment of this application, the manual contact of the star-delta changeover switch is connected to the coil circuit of the fourth intermediate relay, and the automatic contact of the star-delta changeover switch forms a mechanical interlock with the manual contact.
[0054] In another exemplary embodiment of this application, the temperature signal acquisition circuit further includes a first fan thermal relay and a second fan thermal relay.
[0055] In the cooling fan control circuit, the second normally open contact of the first intermediate relay, the normally closed contact of the first fan thermal relay, and the normally closed contact of the second fan thermal relay are connected in series and then connected to the neutral line to form unified overload protection for the contactor coils of the two cooling fans.
[0056] In another exemplary embodiment of this application, the circulating oil pump control circuit further includes an oil pump thermal relay.
[0057] The normally closed contact of the oil pump thermal relay is connected in series in the oil pump contactor coil circuit to form overload protection.
[0058] In another exemplary embodiment of this application, the cooling fan control circuit, the circulating oil pump control circuit, and the indicator circuit are all installed in the same control box.
[0059] The temperature sensing elements of the first and second temperature controllers are installed in the oil tank of the oil-immersed transformer. The normally open contacts of the first and second temperature controllers are respectively led to the terminal blocks inside the control box through shielded wires.
[0060] The normally open contact of the first temperature controller is pluggable to the automatic start branch of the cooling fan control circuit; the normally open contact of the second temperature controller is pluggable to the start condition circuit of the circulating oil pump control circuit.
[0061] The following uses a specific example of the control process of an oil-immersed transformer cooling control circuit to illustrate this application.
[0062] like Figure 1 The diagram shows a schematic of the cooling control circuit for an oil-immersed transformer. This circuit is used in the cooling system of an oil-immersed transformer. The states shown for each component in the circuit are their initial states.
[0063] 1. Section 101 in the diagram is the cooling fan control section.
[0064] 1. When the transformer inlet valve switch SQ1 and outlet valve switch SQ2 are opened, the corresponding contacts SQ1-11 / 12 and SQ2-11 / 12 will close.
[0065] 2. When the pressure in the oil pipeline reaches the specified value, the pressure relay KP-13 / 14 will switch from open to closed.
[0066] 3. When the above conditions are met, the coil of the first intermediate relay KA1 is energized, and the first normally open contact KA1-13 / 14 of the first intermediate relay is closed.
[0067] 4. When the rotation mode selection switch SA1 is switched to manual control, the manual contact SA1-11 / 14 of the mode selection switch is closed. At this time, pressing the fan start button SB2 energizes the first fan contactor KM1 and the second fan contactor KM2, and the corresponding two fans in the main circuit start running. The first normally open auxiliary contact KM1-13 / 14 of the first fan contactor changes from open to closed, forming a self-locking state.
[0068] 5. When the coil of the first fan contactor KM1 is energized, the second normally open auxiliary contact KM1-23 / 24 of the first fan contactor and the first normally open auxiliary contact KM2-13 / 14 of the second fan contactor are all closed, and at this time the coil of the third intermediate relay KA3 is energized.
[0069] II. Section 102 in the figure is the circulating oil pump control section.
[0070] When the coil of the third intermediate relay KA3 is energized, the first normally open contact KA3-13 / 14 of the third intermediate relay changes from open to closed. When the oil pump start button SB3 is pressed, the coil of the oil pump contactor KM3 is energized, the first normally open contact KA3-13 / 14 of the third intermediate relay closes, and the coil of the star contactor KMY is energized. At this time, the oil pump is in the Y-connected start state.
[0071] If the star-delta changeover switch SA2 is in the automatic position at this time, the coil of the time relay KT is energized. After a 5-second delay, the time-delay closing contact KT-17 / 18 of the time relay changes from open to closed, the coil of the fourth intermediate relay KA4 is energized, and the first normally open contact KA4-13 / 14 and the second normally open contact KA4-23 / 24 of the fourth intermediate relay close.
[0072] At this time, the KMD coil of the delta contactor is energized, and the first normally open contact KMD-13 / 14 of the delta contactor closes to form a self-locking mechanism, keeping the KMD coil continuously energized. The first normally closed contact KMD-11 / 12 and the second normally closed contact KMD-21 / 22 of the delta contactor change from closed to open. At this time, the KMY coil of the star contactor is de-energized, and the KT coil of the time relay is also de-energized. The circuit operates in a delta connection configuration.
[0073] If the star-delta changeover switch SA2 is in manual control mode, since SA2 is a three-position changeover switch (meaning it has one neutral position), when rotated to this neutral position, neither the automatic contact SA2-11 / 12 nor the manual contact SA2-11 / 14 of the star-delta changeover switch are connected. At this time, pressing the oil pump start button SB3 energizes the coil of the oil pump contactor KM3, closing the normally open auxiliary contact KM3-13 / 14 of the oil pump contactor, and energizing the coil of the star contactor KMY. At this point, the oil pump is in Y-connection start mode.
[0074] At this time, manually switch the star-delta changeover switch SA2 from the "neutral" position to the "manual" position. The manual contact SA2-11 / 14 of the star-delta changeover switch is closed, the coil of the fourth intermediate relay KA4 is energized, and the first normally open contact KA4-13 / 14 and the second normally open contact KA4-23 / 24 of the fourth intermediate relay are closed.
[0075] At this time, the KMD coil of the delta contactor is energized, and the first normally open auxiliary contact KMD-13 / 14 of the delta contactor closes to form a self-locking mechanism. The KMD contactor remains energized, while the first normally closed auxiliary contact KMD-11 / 12 and the second normally closed auxiliary contact KMD-21 / 22 of the delta contactor change from closed to open. At this time, the KMY coil of the star contactor is de-energized. The circuit operates in a delta connection configuration.
[0076] 3. In section 101 of the diagram: Turn the mode selection switch SA1 to the automatic position, and the automatic contact SA1-11 / 12 of the mode selection switch will be closed. At this time, the two sets of temperature controllers, the first temperature controller WK1 and the second temperature controller WK2, will detect the oil temperature.
[0077] 1. The starting temperature of the first temperature controller WK1 is set to 60 degrees Celsius. When the oil temperature inside the transformer reaches 60 degrees Celsius, it activates, closing the normally open contact WK1-11 / 14 of the first temperature controller. This energizes the coil of the first fan contactor KM1, and the second normally open auxiliary contact KM1-23 / 24 of the first fan contactor changes from open to closed, continuously energizing the coils of both the first and second fan contactors KM1 and KM2. This corresponds to the starting of both fans. Then, the second normally open auxiliary contact KM1-23 / 24 of the first fan contactor and the first normally open auxiliary contact KM2-13 / 14 of the second fan contactor close, energizing the coil of the third intermediate relay KA3, and closing the first normally open contact KA3-13 / 14 of the third intermediate relay.
[0078] 2. When the oil temperature continues to rise and reaches 70 degrees Celsius, the second temperature controller WK2 starts, and the normally open contact WK2-13 / 14 of the second temperature controller changes from open to closed. The coil of the fifth intermediate relay KA5 is energized, and the first normally open contact KA5-13 / 14 of the fifth intermediate relay closes. The coil of the oil pump contactor KM3 is energized, and the normally open auxiliary contact KM3-13 / 14 of the oil pump contactor closes. The coil of the star contactor KMY is energized. At this time, the oil pump is in the Y-connected start state.
[0079] At this time, the effect of the star-delta changeover switch SA2 in manual or automatic mode is the same as described above.
[0080] IV. Section 103 in the diagram: This section is the indicator section.
[0081] 1. When the coil of the third intermediate relay KA3 is energized, the second normally open contact KA3-23 / 24 of the third intermediate relay closes, and the first indicator light H1 lights up, indicating that the two fans are starting to run.
[0082] 2. When the KMY coil of the star contactor is energized, the first normally open auxiliary contact KAY-13 / 14 of the star contactor KMY closes, and the second indicator light H2 illuminates, indicating that the oil pump is in the Y-connection start state at this time.
[0083] 3. When the KMD coil of the delta contactor is energized, the second normally open auxiliary contact KAD-23 / 24 of the KMD delta contactor closes, and the third indicator light H3 illuminates, indicating that the oil pump is in Δ connection operation at this time.
[0084] V. In part 101 of the diagram: the first normally closed auxiliary contact FR1-17 / 18 of the first fan thermal relay FR1 and the first normally closed auxiliary contact FR2-17 / 18 of the second fan thermal relay FR1 are connected in series with the coil of the first fan contactor KM1. When either of the two fan thermal relays in the main circuit operates, the corresponding normally closed contact opens, the coil of the first fan contactor KM1 is de-energized, and the fan stops running, thus providing thermal overload protection.
[0085] VI. In section 102 of the diagram: When the thermal relay of the oil pump main circuit activates, the first normally closed auxiliary contact FR3-17 / 18 of the oil pump thermal relay FR3 changes from closed to open. At this time, the coil of the oil pump contactor KM3 is de-energized, and the oil pump stops running, thus providing thermal overload protection.
[0086] The advantages of using star-delta (Y-Δ) reduced-pressure starting when starting an oil pump:
[0087] It can significantly reduce the starting current. When starting directly, the starting current of the motor can be 5-7 times or even higher than the rated current.
[0088] In a star connection, the voltage applied to each phase winding is the line voltage. (Approximately 58%), therefore the starting current (line current) is about 1 / 3 of the direct starting current (line current). This greatly reduces the impact on the power grid and avoids a sudden drop in power supply voltage due to excessive starting current, thus protecting the normal operation of other electrical equipment on the same power source.
[0089] The reduced starting current means that there is no need to configure excessively large transformer capacity and cable cross-section for the short startup process.
[0090] In summary, to enhance heat dissipation, this application adds two fans and one oil pump. When the temperature rises to the set temperature, the fans are first activated to cool the heat sink. If the temperature continues to rise, the oil pump is activated to accelerate the internal oil circulation and cooling of the transformer. Through the combined operation of the fans and oil pump, the transformer temperature is controlled within a reasonable range, ensuring optimal transformer operation.
[0091] Therefore, based on the control circuit provided in this application, when the transformer temperature rises, selecting the automatic mode automatically starts two fans to deliver airflow through the gaps in the transformer heat sink, thereby reducing the transformer oil temperature. When the ambient temperature is high or the transformer's load is large, causing the temperature to rise continuously, the oil pump is started to circulate the oil. The oil circulation and fan airflow work together to cool the transformer. Simultaneously, this circuit uses fewer control components, achieving a very flexible control method. It can be fully automatic, requiring no human intervention, or manually adjusted according to actual conditions.
[0092] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.
[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0094] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A control circuit for a cooling system of an oil-immersed transformer, characterized in that, The control circuit of the oil-immersed transformer cooling system includes: a temperature signal acquisition circuit, a cooling fan control circuit, a circulating oil pump control circuit, and an indicator circuit; The output of the temperature signal acquisition circuit is connected to the input of the cooling fan control circuit and the circulating oil pump control circuit, respectively, for transmitting the temperature signal of the oil-immersed transformer. The output terminal of the cooling fan control circuit is connected to the cooling fan and is used to control the fan connected to the transformer; The output terminal of the circulating oil pump control circuit is connected to the circulating oil pump and is used to control the oil pump connected to the transformer. The input terminals of the indicator circuit are connected to the status signal terminals of the cooling fan control circuit and the circulating oil pump control circuit, respectively, and the operating status of the cooling fan and the circulating oil pump is displayed through indicator lights.
2. The transformer cooling system control circuit according to claim 1, characterized in that, The temperature signal acquisition circuit includes a first temperature controller and a second temperature controller connected in parallel. The temperature sensing elements of the first temperature controller and the second temperature controller are both installed inside the oil tank of the oil-immersed transformer. The normally open contact of the first temperature controller constitutes the start-up condition input terminal of the cooling fan control circuit, and the normally open contact of the second temperature controller constitutes the start-up condition input terminal of the circulating oil pump control circuit.
3. The control circuit for the oil-immersed transformer cooling system according to claim 2, characterized in that, The cooling fan control circuit includes: a mode selection switch, a fan start button, a first intermediate relay, a second intermediate relay, a third intermediate relay, a first fan contactor, and a second fan contactor; The automatic contact of the mode selection switch is connected in series with the normally open contact of the first temperature controller. One end is connected to the phase line, and the other end is connected to the neutral line through the coil of the first fan contactor, forming an automatic start branch. The first normally open contact of the first intermediate relay is connected in parallel across the two normally open contacts of the first temperature controller to form a self-holding mechanism; The manual contact of the mode selection switch is connected in series with the fan start button and then connected in parallel across the two ends of the automatic start branch. After the coils of the first and second fan contactors are connected in parallel, one end is connected to the phase line, and the other end is connected to the neutral line through the second normally open contact of the first intermediate relay. The normally open auxiliary contact of the first fan contactor is connected in parallel with the coil of the first fan contactor to form a self-locking mechanism for the first fan. The normally open auxiliary contact of the second fan contactor is connected in parallel with the coil of the second fan contactor to form a self-locking mechanism for the second fan. One end of the coil of the second intermediate relay is connected to the phase line, and the other end is connected to the neutral line after passing through the normally open auxiliary contact of the first fan contactor and the normally open auxiliary contact of the second fan contactor in parallel to the common point. This is used to output a synchronization signal to the circulating oil pump control circuit. The coil of the third intermediate relay is controlled by the normally open contact of the second intermediate relay, and the normally open contact of the third intermediate relay is connected in series with the normally open contact of the second temperature controller.
4. The control circuit for the oil-immersed transformer cooling system according to claim 3, characterized in that, The circulating oil pump control circuit includes: an oil pump start button, a fourth intermediate relay, a star contactor, a delta contactor, an oil pump contactor, a time relay, and a star-delta changeover switch; The normally open contact of the third intermediate relay is connected in series with the normally open contact of the second temperature controller. One end is connected to the phase line, and the other end is connected to the neutral line through the oil pump contactor coil, thus forming the oil pump starting condition circuit. The oil pump start button is connected in parallel with the oil pump start condition circuit to form a manual start branch; The normally open auxiliary contact of the oil pump contactor is connected in series with the star contactor coil and then bridging the phase line and the neutral line. The normally open auxiliary contact of the star contactor is connected in series with the coil of the time relay and then bridging the phase line and the neutral line. The delayed closing contact of the time relay is connected in series with the coil of the fourth intermediate relay and then bridging the phase line and the neutral line. The normally open contact of the fourth intermediate relay is connected in series with the coil of the delta contactor and then bridging the phase line and the neutral line. The normally closed auxiliary contact of the star contactor is connected in series in the coil circuit of the delta contactor, and the normally closed auxiliary contact of the delta contactor is connected in series in the coil circuit of the star contactor to form an electrical interlock. The automatic contacts of the star-delta changeover switch are connected to the time relay coil circuit.
5. The control circuit for the oil-immersed transformer cooling system according to claim 4, characterized in that, The indicator circuit includes: a first indicator light, a second indicator light, and a third indicator light; The first indicator light and the normally open contact of the third intermediate relay are connected in series and then bridged between the phase line and the neutral line to indicate the operating status of the fan; The second indicator light is connected in series with the normally open auxiliary contact of the star contactor and then bridging the phase line and the neutral line to indicate the star start status of the oil pump. The third indicator light is connected in series with the normally open auxiliary contact of the delta contactor and then bridging the phase line and the neutral line to indicate the operating status of the oil pump delta.
6. The transformer cooling system control circuit according to claim 3, characterized in that, The mode selection switch is a three-position locking type changeover switch, including automatic position, manual position and stop position; Automatic position only connects the automatic contacts; manual position only connects the manual contacts; stop position disconnects all contacts.
7. The transformer cooling system control circuit according to claim 4, characterized in that, The manual contact of the star-delta changeover switch is connected to the coil circuit of the fourth intermediate relay, and the automatic contact of the star-delta changeover switch is mechanically interlocked with the manual contact.
8. The transformer cooling system control circuit according to claim 3, characterized in that, The temperature signal acquisition circuit also includes a first fan thermal relay and a second fan thermal relay. In the cooling fan control circuit, the second normally open contact of the first intermediate relay, the normally closed contact of the first fan thermal relay, and the normally closed contact of the second fan thermal relay are connected in series and then connected to the neutral line to form unified overload protection for the contactor coils of the two cooling fans.
9. The transformer cooling system control circuit according to claim 4, characterized in that, The circulating oil pump control circuit also includes an oil pump thermal relay; The normally closed contact of the oil pump thermal relay is connected in series in the oil pump contactor coil circuit to form overload protection.
10. The transformer cooling system control circuit according to claim 2, characterized in that, The cooling fan control circuit, circulating oil pump control circuit, and indicator circuit are all installed in the same control box; The temperature sensing elements of the first and second temperature controllers are installed in the oil tank of the oil-immersed transformer. The normally open contacts of the first and second temperature controllers are respectively led to the terminal blocks inside the control box through shielded wires. The normally open contact of the first temperature controller is pluggable to the automatic start branch of the cooling fan control circuit; the normally open contact of the second temperature controller is pluggable to the start condition circuit of the circulating oil pump control circuit.