Transformer step-down starting circuit

Abstract

The utility model relates to motor control technical field provides a transformer step-down starting circuit, include: controller, main circuit and control circuit, the main circuit includes first contactor, second contactor, third contactor, transformer, first contactor's first normally open contact, transformer and second contactor's second normally open contact series connection forms first power-on branch, connects with the motor electricity of commercial power, third contactor's third normally open contact forms second power-on branch, connects with the motor electricity of commercial power, controller and control circuit electricity is connected, the utility model provides a transformer step-down starting circuit, through first working mode utilizes transformer step-down starting to reduce motor starting impact, and in second working mode switches to full pressure high -efficient operation, while satisfying basic soft start function, this transformer step-down starting circuit no longer needs independent air duct heat dissipation, can set up in sealed cabinet body entire transformer step-down starting circuit, has reduced maintenance demand and comprehensive failure rate.

Description

Technical Field

[0001] This utility model relates to the field of motor control technology, and in particular to a transformer step-down starting circuit. Background Technology

[0002] Mobile crushing plants integrate receiving, crushing, conveying, and screening, and are widely used in rock crushing, aggregate production, and open-pit mining. Their drive systems typically employ integrated frequency converters to control motor speed. However, this system exhibits significant drawbacks in the harsh working environments characterized by high dust levels, strong vibrations, and humidity.

[0003] For example, forced air cooling in frequency converter cabinets requires independent air ducts, but the large amount of dust generated by crushing and screening can easily enter the cabinet along these ducts. Dust accumulation leads to decreased insulation and poor heat dissipation of components, causing short circuits or unstable operation. The severe vibrations of the crusher and screening machine are transmitted to the frequency converter cabinet, interfering with internal precision electronic components and control circuits, causing fluctuations in output current and affecting motor drive performance. Outdoor operations are exposed to rain and fog, causing moisture inside the frequency converter, resulting in decreased insulation and potential safety hazards such as "false tripping" or "failure to operate" in the protection circuit.

[0004] In summary, the stringent environmental requirements of integrated frequency converter systems are fundamentally at odds with the harsh operating conditions of mobile crushing plants. This results in high system failure rates, frequent maintenance, and poor reliability, severely impacting the continuous operating efficiency of the equipment. Therefore, there is an urgent need for a motor drive solution with a simpler structure, stronger environmental adaptability, and lower maintenance requirements to replace the existing frequency converter system. Utility Model Content

[0005] This utility model provides a transformer step-down starting circuit to solve the problems of high failure rate, frequent maintenance, and poor reliability of existing frequency conversion systems in harsh working environments with high dust, strong vibration, and humidity, which seriously affect the continuous operation efficiency of the equipment.

[0006] This utility model provides a transformer step-down starting circuit, including: a controller, a main circuit, and a control circuit;

[0007] The main circuit includes: a first contactor, a second contactor, a third contactor, and a transformer; the first normally open contact of the first contactor, the transformer, and the second normally open contact of the second contactor are connected in series to form a first power-on branch, which connects the mains power to the motor; the third normally open contact of the third contactor forms a second power-on branch, which connects the mains power to the motor.

[0008] The controller is electrically connected to the control loop and is adapted to control the transformer step-down starting circuit to switch between a first working mode and a second working mode.

[0009] In the first operating mode, the controller is configured to control the control loop to supply power to the first power-on branch; in the second operating mode, the controller is configured to control the control loop to supply power to the second power-on branch.

[0010] According to the present invention, a transformer step-down starting circuit includes a control circuit comprising: a first intermediate relay, a second intermediate relay, and a third intermediate relay.

[0011] The coils of the first intermediate relay and the first contactor are connected in series to form a first control branch; the coils of the second intermediate relay and the second contactor are connected in series to form a second control branch; the coils of the third intermediate relay and the third contactor are connected in series to form a third control branch.

[0012] In the first operating mode, the controller is configured to control the first intermediate relay and the second intermediate relay to close, and the third intermediate relay to open, so as to control the first control branch and the second control branch to be connected.

[0013] In the second operating mode, the controller is configured to disconnect the first intermediate relay and the second intermediate relay, and close the third intermediate relay to control the third control branch to be turned on.

[0014] According to the transformer step-down starting circuit provided by this utility model, the first contactor is provided with a first normally closed contact, the second contactor is provided with a second normally closed contact, and the third contactor is provided with a third normally closed contact.

[0015] The first normally closed contact and the second normally closed contact are connected in series in the third control branch; the third normally closed contact is connected in series in the first control branch.

[0016] According to the present invention, a transformer step-down starting circuit further includes:

[0017] A timer, electrically connected to the controller, is used to count the working time in the first working mode.

[0018] According to the present invention, a transformer step-down starting circuit is provided, wherein the controller is provided with a start button and a stop button;

[0019] When the start button is pressed, the controller controls the transformer step-down start circuit to switch to the first working mode, and after the timer counts the preset time, controls the transformer step-down start circuit to switch to the second working mode.

[0020] When the stop button is pressed, the controller disconnects the motor from the mains power.

[0021] According to the transformer step-down starting circuit provided by this utility model, the main circuit further includes: a circuit breaker; the circuit breaker is connected in series with both the first power-on branch and the second power-on branch.

[0022] According to the present invention, a transformer step-down starting circuit is provided, wherein the control circuit includes: an emergency stop switch;

[0023] The emergency stop switch and the coil of the circuit breaker form a fourth control branch; so as to control the closing and opening of the circuit breaker through the emergency stop switch.

[0024] According to the transformer step-down starting circuit provided by this utility model, the control circuit further includes: a first fuse, which is connected in series with the first control branch, the second control branch, the third control branch and the fourth control branch.

[0025] According to the transformer step-down starting circuit provided by this utility model, the first contactor is provided with a fourth normally open contact, the second contactor is provided with a fifth normally open contact, and the third contactor is provided with a sixth normally open contact.

[0026] The control circuit is equipped with a first indicator light, a second indicator light, and a third indicator light;

[0027] The fourth normally open contact and the first indicator light are connected in series in the control circuit;

[0028] The fifth normally open contact and the second indicator light are connected in series in the control circuit;

[0029] The sixth normally open contact and the third indicator light are connected in series in the control circuit.

[0030] According to the transformer step-down starting circuit provided by this utility model, the control circuit further includes: a second fuse, which is connected in series with the first indicator light, the second indicator light and the third indicator light.

[0031] The transformer step-down starting circuit provided by this utility model utilizes a controller combined with a control loop to control the motor operation, eliminating the need for a frequency converter and effectively reducing frequency converter malfunctions during use. In the first operating mode, the transformer step-down starting reduces the motor starting impact, while the second operating mode switches to full-voltage high-efficiency operation. While fulfilling basic soft-start functions, this transformer step-down starting circuit eliminates the need for independent air duct cooling, allowing the entire circuit to be housed in a sealed cabinet. This provides dustproof, moisture-proof, and shockproof protection, significantly reducing maintenance requirements and the overall failure rate. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the main circuit in the transformer step-down starting circuit provided by this utility model.

[0034] Figure 2 This is a schematic diagram of the control circuit in the transformer step-down starting circuit provided by this utility model.

[0035] Figure 3 This is a circuit diagram showing the controller connection in the transformer step-down starting circuit provided by this utility model. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0037] The following is combined Figures 1-3 This invention describes the transformer step-down starting circuit provided by this utility model.

[0038] This application provides a transformer step-down starting circuit, such as... Figures 1 to 3 As shown, the transformer step-down starting circuit includes: a controller, a main circuit, and a control circuit.

[0039] The main circuit includes a first contactor KM1, a second contactor KM2, a third contactor KM3, and a transformer TAT. The first normally open contact of the first contactor KM1, the transformer TAT, and the second normally open contact of the second contactor KM2 are connected in series to form a first power-on branch, which connects the mains power to the motor. The third normally open contact of the third contactor KM3 forms a second power-on branch, which connects the mains power to the motor. The controller is electrically connected to the control circuit and is suitable for controlling the transformer step-down starting circuit to switch between the first operating mode and the second operating mode.

[0040] In this embodiment, the main circuit is used to complete the power transmission between the mains power and the three-phase AC motor, and the control circuit is used to complete the switching of each contactor in the main circuit under the scheduling of the controller.

[0041] In this embodiment, the transformer TAT is a three-phase autotransformer. Its primary winding is connected to the mains power supply via the first contactor KM1, and its secondary winding is connected to the motor terminals via the second contactor KM2. The turns ratio of the transformer TAT determines the voltage drop during motor startup, which in turn determines the magnitude of the starting current and starting torque.

[0042] The first power-on branch is formed by connecting the first normally open contact of the first contactor KM1, the transformer TAT, and the second normally open contact of the second contactor KM2 in series. When the first contactor KM1 and the second contactor KM2 are closed simultaneously, the mains power is stepped down by the transformer TAT and supplied to the motor, and the motor enters the first operating mode (i.e., the "reduced voltage start" stage). At this time, the motor terminal voltage is lower than the rated voltage, thereby limiting the starting current to about 2 to 3 times the rated current, significantly reducing the impact on the power grid and the impact on the motor windings and mechanical structure.

[0043] The second power-on branch is formed solely by the third normally open contact of the third contactor KM3. When the third contactor KM3 is closed, the mains power is directly connected to the motor through the third normally open contact, and the motor enters the second operating mode (i.e., the "full-voltage operation" stage). At this time, the motor terminal voltage is the rated voltage, and the motor can continuously output rated power under rated operating conditions.

[0044] The controller can be a microcontroller, DSP, PLC, or a dedicated motor starter control chip, and its internal control logic is "reduced voltage start-delay switching-full voltage operation". The controller adaptively optimizes the start-up curve by collecting feedback signals such as motor current, voltage, speed, and temperature.

[0045] In the first operating mode, the controller is configured to control the control loop, controlling the first power-on branch to conduct, thereby supplying power to the first power-on branch. The mains power is stepped down by transformer TAT and then supplied to the motor, which starts under stepped-down conditions. In the second operating mode, the controller is configured to control the control loop, controlling the second power-on branch to conduct, thereby supplying power to the second power-on branch. In this mode, the motor operates under full voltage regulation.

[0046] The transformer step-down starting circuit provided by this utility model utilizes a controller combined with a control loop to control the motor operation, eliminating the need for a frequency converter and effectively reducing frequency converter malfunctions during use. In the first operating mode, the transformer step-down starting reduces the motor starting impact, while the second operating mode switches to full-voltage high-efficiency operation. While fulfilling basic soft-start functions, this transformer step-down starting circuit eliminates the need for independent air duct cooling, allowing the entire circuit to be housed in a sealed cabinet. This provides dustproof, moisture-proof, and shockproof protection, significantly reducing maintenance requirements and the overall failure rate.

[0047] In some embodiments, such as Figures 1 to 3 As shown, the control circuit includes: a first intermediate relay KA1, a second intermediate relay KA2, and a third intermediate relay KA3; the coils of the first intermediate relay KA1 and the first contactor KM1 are connected in series to form a first control branch; the coils of the second intermediate relay KA2 and the second contactor KM2 are connected in series to form a second control branch; and the coils of the third intermediate relay KA3 and the third contactor KM3 are connected in series to form a third control branch.

[0048] In this embodiment, during operation, the controller first outputs a control signal to activate the first intermediate relay KA1 and the second intermediate relay KA2, connecting the first and second control branches. This energizes the coils of the first contactor KM1 and the second contactor KM2, causing their main contacts to close. The mains power is stepped down by the transformer TAT and supplied to the motor, which starts under the stepped-down condition. The controller's internal timer begins timing and simultaneously monitors the motor current. When the current drops below 1.2 times the rated current for more than 0.5 seconds, or when the timer reaches a preset time (e.g., adjustable from 5 to 15 seconds), the controller determines that the motor has completed its acceleration.

[0049] The controller first disconnects the first intermediate relay KA1 and the second intermediate relay KA2, de-energizing the coils of the first contactor KM1 and the second contactor KM2 and opening their main contacts. After a power-off gap of 50~100 ms, a signal is output to activate the third intermediate relay KA3, connecting the third control branch and energizing the coil of the third contactor KM3, closing its main contacts. This power-off gap ensures reliable disconnection of the transformer TAT from the mains power while allowing the motor to maintain a high speed under inertia, avoiding secondary inrush current.

[0050] In some embodiments, such as Figures 1 to 3 As shown, the first contactor KM1 has a first normally closed contact, the second contactor KM2 has a second normally closed contact, and the third contactor KM3 has a third normally closed contact; the first and second normally closed contacts are connected in series in the third control branch. The third normally closed contact is connected in series in the first control branch.

[0051] After connecting the first normally closed contact and the second normally closed contact in series, the third control branch is then connected in series. The coil of the third contactor KM3 can only be energized when both the first contactor KM1 and the second contactor KM2 are in the released state (i.e., both the first and second normally closed contacts are closed). As long as either the first contactor KM1 or the second contactor KM2 is energized, its corresponding normally closed contact will open, and the coil of the third contactor will be forcibly de-energized, thereby blocking the direct mains power supply path and preventing it from running parallel to the transformer path.

[0052] Similarly, after the third contactor is connected in series in the first control branch, the coil of the second contactor KM2 can only be energized when the third contactor KM3 is in the released state; once the third contactor KM3 is energized, the third normally closed contact opens, and the coil of the first contactor KM1 is immediately de-energized, ensuring that the transformer circuit cannot be simultaneously connected with the mains power supply circuit.

[0053] In some embodiments, the transformer step-down starting circuit further includes a timer. The timer is electrically connected to the controller or is located within the controller, and is used to count the working time in the first working mode. The timer can be an independent module electrically connected to the controller's I / O port, or it can be directly built into the timing unit of the controller MCU / PLC and implemented by a software counter.

[0054] Specifically, the controller is equipped with a start button and a stop button; when the start button is pressed, the controller controls the transformer step-down start circuit to switch to the first working mode, and after the timer counts the preset time, it controls the transformer step-down start circuit to switch to the second working mode; when the stop button is pressed, the controller controls the motor to disconnect from the mains power.

[0055] For example, when the operator presses the start button, the controller receives a "start request" signal. The controller first outputs a control signal to activate the first intermediate relay KA1 and the second intermediate relay KA2, connecting the first and second control branches. This energizes the coils of the first contactor KM1 and the second contactor KM2, closing their main contacts. The mains power is stepped down by the transformer TAT and supplied to the motor, which starts under reduced voltage conditions. The controller's internal timer begins timing and simultaneously monitors the motor current. When the current drops below 1.2 times the rated current for more than 0.5 seconds, or when the timer reaches a preset time (e.g., adjustable from 5 to 15 seconds), the controller determines that the motor has completed its acceleration. The controller first disconnects the first intermediate relay KA1 and the second intermediate relay KA2, causing the coils of the first contactor KM1 and the second contactor KM2 to be de-energized and their main contacts to open. After a period of de-energization (50~100ms), the controller outputs a signal to activate the third intermediate relay KA3, which in turn activates the third control branch, energizes the coil of the third contactor KM3, and closes its main contacts.

[0056] When the stop button is pressed, the first intermediate relay KA1, the second intermediate relay KA2, and the third intermediate relay KA3 are all released, and the coils of the first contactor KM1, the second contactor KM2, and the third contactor KM3 are all de-energized. The motor is disconnected from the mains power.

[0057] Based on the above embodiments, in some embodiments, such as Figure 1As shown, the main circuit also includes circuit breaker QF1. Circuit breaker QF1 is connected in series with both the first and second energized branches. By placing circuit breaker QF1 at the common front end of both the first and second energized branches, unified start-up and shutdown of the entire transformer step-down starting circuit and the motor are achieved. Regardless of whether the current operation is step-down starting (first working mode) or full-voltage operation (second working mode), in the event of a fault, the tripping of circuit breaker QF1 can immediately disconnect the mains power, ensuring system safety.

[0058] In this embodiment, the control circuit includes: an emergency stop switch SBJ1; the emergency stop switch SBJ1 and the coil of the circuit breaker QF1 form a fourth control branch; to control the closing and opening of the circuit breaker through the emergency stop switch. By directly connecting the emergency stop switch SBJ1 and the trip coil of the circuit breaker QF1 in series to form the fourth control branch, this embodiment adds a pure hardware, highest-priority emergency stop link in addition to the original "controller-intermediate relay-contactor" logic, ensuring that in the most extreme fault or personal danger scenarios, the system can cut off all power supply within milliseconds.

[0059] like Figure 2 As shown, the control circuit also includes a first fuse FU2, which is connected in series with the first control branch, the second control branch, the third control branch and the fourth control branch.

[0060] The first fuse FU2 has its input terminal connected to the control power supply. Its output terminal is simultaneously connected to four parallel control branches: the first control branch (KA1→KM1 coil), the second control branch (KA2→KM2 coil), the third control branch (KA3→KM3 coil), and the fourth control branch (SBJ1→QF1 shunt / undervoltage coil XT). When an overload or short circuit occurs in the control circuit, the first fuse FU2 blows, all four branches lose power simultaneously, all contactor coils and circuit breaker trip coils are disconnected, and the main circuit is immediately isolated from the mains power, achieving centralized short-circuit and overload protection for the control power supply.

[0061] In some embodiments, such as Figure 1-3 As shown, the first contactor KM1 has a fourth normally open contact, the second contactor KM2 has a fifth normally open contact, and the third contactor KM3 has a sixth normally open contact; the control circuit has a first indicator light P1, a second indicator light P2, and a third indicator light P3; the fourth normally open contact and the first indicator light P1 are connected in series in the control circuit; the fifth normally open contact and the second indicator light P2 are connected in series in the control circuit; and the sixth normally open contact and the third indicator light P3 are connected in series in the control circuit.

[0062] In this embodiment, the fourth normally open contact of the first contactor KM1 is connected in series with the first indicator light P1 and then bridging the control power supply; the fifth normally open contact of the second contactor KM2 is connected in series with the second indicator light P2 and then bridging the control power supply; and the sixth normally open contact of the third contactor KM3 is connected in series with the third indicator light P3 and then bridging the control power supply.

[0063] During the reduced-voltage start-up phase, KM1 and KM2 close, and KM3 opens. The KM1 coil is energized, and the first indicator light P1 illuminates; simultaneously, the KM2 coil is energized, and the second indicator light P2 illuminates. When the KM3 coil is de-energized, the third indicator light P3 goes out. During full-voltage operation (KM1 and KM2 open, KM3 closed), the first indicator light P1 and the second indicator light P2 go out, and the third indicator light P3 illuminates. In a shutdown or fault state, all normally open contacts reset, and the first indicator light P1, the second indicator light P2, and the third indicator light P3 indicate "Main circuit completely de-energized."

[0064] In addition, such as Figure 2 As shown, the control circuit also includes a second fuse FU3, which is connected in series with the first indicator light P1, the second indicator light P2 and the third indicator light P3.

[0065] Under normal conditions, the second fuse FU3 is in the conducting state, and the three indicator lights illuminate and extinguish normally as the corresponding contactors engage / disengage. When an overload or short circuit fault occurs in the indicator light circuit, the second fuse FU3 blows, instantly cutting off all power to the first indicator light P1, the second indicator light P2, and the third indicator light P3, preventing the fault from spreading upstream; at the same time, it alerts maintenance personnel to "indicator light power failure," facilitating rapid location of the fault.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A transformer step-down starting circuit, characterized in that, include: Controller, main circuit, and control circuit; The main circuit includes: a first contactor, a second contactor, a third contactor, and a transformer; The first normally open contact of the first contactor, the transformer, and the second normally open contact of the second contactor are connected in series to form a first power-on branch, which connects the mains power to the motor; the third normally open contact of the third contactor forms a second power-on branch, which connects the mains power to the motor. The controller is electrically connected to the control loop and is adapted to control the transformer step-down starting circuit to switch between a first working mode and a second working mode. In the first operating mode, the controller is configured to control the control loop to supply power to the first power-on branch; in the second operating mode, the controller is configured to control the control loop to supply power to the second power-on branch.

2. The transformer step-down starting circuit according to claim 1, characterized in that, The control circuit includes: a first intermediate relay, a second intermediate relay, and a third intermediate relay; The coils of the first intermediate relay and the first contactor are connected in series to form a first control branch; the coils of the second intermediate relay and the second contactor are connected in series to form a second control branch; the coils of the third intermediate relay and the third contactor are connected in series to form a third control branch. In the first operating mode, the controller is configured to control the first intermediate relay and the second intermediate relay to close, and the third intermediate relay to open, so as to control the first control branch and the second control branch to be connected. In the second operating mode, the controller is configured to disconnect the first intermediate relay and the second intermediate relay, and close the third intermediate relay to control the third control branch to be turned on.

3. The transformer step-down starting circuit according to claim 2, characterized in that, The first contactor has a first normally closed contact, the second contactor has a second normally closed contact, and the third contactor has a third normally closed contact. The first normally closed contact and the second normally closed contact are connected in series in the third control branch; the third normally closed contact is connected in series in the first control branch.

4. The transformer step-down starting circuit according to claim 1, characterized in that, The transformer step-down starting circuit also includes: A timer, electrically connected to the controller, is used to count the working time in the first working mode.

5. The transformer step-down starting circuit according to claim 4, characterized in that, The controller is equipped with a start button and a stop button; When the start button is pressed, the controller controls the transformer step-down start circuit to switch to the first working mode, and after the timer counts the preset time, controls the transformer step-down start circuit to switch to the second working mode. When the stop button is pressed, the controller disconnects the motor from the mains power.

6. The transformer step-down starting circuit according to claim 2, characterized in that, The main circuit also includes a circuit breaker; the circuit breaker is connected in series with both the first power-on branch and the second power-on branch.

7. The transformer step-down starting circuit according to claim 6, characterized in that, The control circuit includes: an emergency stop switch; The emergency stop switch and the coil of the circuit breaker form a fourth control branch; so as to control the closing and opening of the circuit breaker through the emergency stop switch.

8. The transformer step-down starting circuit according to claim 7, characterized in that, The control circuit further includes a first fuse, which is connected in series with the first control branch, the second control branch, the third control branch, and the fourth control branch.

9. The transformer step-down starting circuit according to claim 1, characterized in that, The first contactor has a fourth normally open contact, the second contactor has a fifth normally open contact, and the third contactor has a sixth normally open contact; The control circuit is equipped with a first indicator light, a second indicator light, and a third indicator light; The fourth normally open contact and the first indicator light are connected in series in the control circuit; The fifth normally open contact and the second indicator light are connected in series in the control circuit; The sixth normally open contact and the third indicator light are connected in series in the control circuit.

10. The transformer step-down starting circuit according to claim 9, characterized in that, The control circuit also includes a second fuse, which is connected in series with the first indicator light, the second indicator light, and the third indicator light.

Images