Soft start system based on excitation current reduction

Abstract

The utility model discloses a soft start system based on excitation current reduction, which is characterized in that a time relay mainly controls the switching of a live wire between a power resistor and an alternating current contactor, the power resistor magnetizes a transformer at the moment of electrification, and the alternating current contactor is connected into a circuit by the time relay after the magnetization is completed; and after the power resistor is short-circuited, the circuit is cut out, so that the purpose of suppressing the excitation inrush current is finally achieved, the excitation effect caused by voltage abrupt change at the power-on moment of the isolation transformer can be avoided, and the excitation abrupt change of the isolation transformer during power-on is effectively reduced.

Description

Technical Field

[0001] This utility model relates to the field of electromechanical equipment, and in particular to a soft-start system based on reducing excitation current. Background Technology

[0002] Currently, large transformers and large motors on the market experience magnetic saturation the moment they are energized. This generates an excitation effect that can damage equipment and the power grid. The occurrence of inrush current is influenced by the excitation voltage. That is, any change in system voltage affects the excitation voltage, resulting in inrush current. Under different conditions, inrush currents of varying degrees will occur, including initial inrush, recovery inrush, and sympathetic inrush, as described below. The instantaneous peak value and duration depend on the combined effects of the above factors and may reach 8 to 30 times the transformer's rated current.

[0003] There are currently three solutions on the market:

[0004] The first type is the series reactor. However, the equipment is large and its installation is limited. Its application range is small, and it is generally used in high-power, high-voltage equipment such as large motors and substations. Moreover, reactors are divided into inductive reactors and capacitive reactors, and their introduction can bring new excitation interference or reduce the overall useful power of the equipment.

[0005] The second type is the transformer differential protector. However, these can cost thousands or even tens of thousands of yuan, are bulky, complex to use, and require a high level of expertise from the user.

[0006] The third type is the transformer soft starter. It is bulky and only suitable for high-power equipment in the kilowatt range. Its protection capability for transformer equipment with a power of less than kilowatt is questionable.

[0007] In summary, a soft-start system based on reducing excitation current is needed to address the shortcomings of existing technologies. Utility Model Content

[0008] To address the shortcomings of existing technologies, this invention provides a soft-start system based on reducing excitation current, aiming to solve the aforementioned problems.

[0009] To achieve the above objectives, this utility model provides the following technical solution: a soft-start system based on reducing excitation current, comprising a time relay, an AC contactor, a power resistor, and an isolation transformer.

[0010] A time relay is used to control the switching of the live wire between a power resistor and an AC contactor;

[0011] An AC contactor is used to cut off a power resistor from the circuit.

[0012] A power resistor is used to form a circuit with the primary winding of an isolation transformer and to magnetize the primary winding.

[0013] An isolation transformer is used to electrically isolate the input and output terminals of a power source.

[0014] Optionally, the time relay is provided with one control circuit and two load circuits. The load circuit is used to connect the load, and the control circuit is used to control the time relay. The time relay is also provided with a time knob, which is used to adjust the control time.

[0015] Optionally, the AC contactor is provided with two control circuits and three load circuits. The control circuits are used to control the contacts in the AC contactor, and the load circuits are used to connect the load.

[0016] Optionally, the AC contactor is provided with connection pins A1, A2, 1 / L1, 2 / T1, 3 / L1, 4 / T1, 5 / L1, and 6 / T1.

[0017] Contact pins A1 and A2 are used for control input contacts;

[0018] Contact pins 1 / L1 and 2 / T1 are used for the input / output contacts of the first load.

[0019] Contact pins 3 / L1 and 4 / T1 are used for the input / output contacts of the second load.

[0020] Contact pins 5 / L1 and 6 / T1 are used for the input / output contacts of the third load.

[0021] Optionally, the power resistor is an RX24 gold aluminum case resistor used for pre-magnetizing the transformer.

[0022] Optionally, the working process of the soft start system is as follows: connect the soft start system to the input power supply, set the time relay to delay the power-on time, and after the power-on time is over, control the AC contactor to engage.

[0023] The beneficial effects of this utility model are:

[0024] 1. In this utility model, the time relay mainly controls the switching of the live wire between the power resistor and the AC contactor. At the moment of power-on, the power resistor magnetizes the transformer. After magnetization is completed, the time relay connects the AC contactor to the circuit and disconnects the power resistor from the circuit after short-circuiting. This ultimately achieves the purpose of suppressing the inrush current and avoids the excitation effect caused by the voltage change at the moment of power-on of the isolation transformer, effectively reducing the excitation change of the isolation transformer at the moment of power-on.

[0025] 2. In this utility model, the cause of the excitation inrush current is simplified as follows: when the power is applied, the primary winding of the isolation transformer is magnetically saturated, and the induced electromotive force no longer increases with the increase of current. If the current increases further, the incremental part is the short-circuit current, which is no longer constrained by the induced electromotive force. The power resistor during pre-magnetization will limit the current of the entire circuit, so that the increased current is limited within the threshold of the induced electromotive force.

[0026] 3. In this utility model, the power resistor and the primary winding of the isolation transformer form a circuit to magnetize the primary winding of the isolation transformer. After the time relay counts for five seconds, it controls the AC contactor to close, directly connecting the live wire to the primary winding of the isolation transformer. Within the five seconds of the time relay, the resistor has completed magnetizing the primary winding of the isolation transformer. The live wire connected by the AC contactor and the resistor form a parallel state. The voltage across the resistor is the same, so the resistor does not work. After the live wire is connected to the primary winding of the isolation transformer, only a small current will be generated because the voltage difference is small. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a system structure of the present invention.

[0028] Figure 2 This is a schematic diagram of a system wiring according to the present invention.

[0029] Figure 3 This is a schematic diagram of the system principle of this utility model. Detailed Implementation

[0030] To more clearly illustrate the technical solutions in the embodiments of the 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 only some embodiments of the utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] like Figure 1 , 2 As shown in Figure 3, a soft-start system based on reducing excitation current includes a time relay, an AC contactor, a power resistor, and an isolation transformer.

[0032] A time relay is used to control the switching of the live wire between a power resistor and an AC contactor;

[0033] An AC contactor is used to cut off a power resistor from the circuit.

[0034] A power resistor is used to form a circuit with the primary winding of an isolation transformer and to magnetize the primary winding.

[0035] An isolation transformer is used to electrically isolate the input and output terminals of a power source.

[0036] The time relay is equipped with one control circuit and two load circuits. The load circuit is used to connect the load, and the control circuit is used to control the time relay. The time relay is also equipped with a time knob, which is used to adjust the control time.

[0037] The AC contactor is equipped with two control circuits and three load circuits. The control circuits are used to control the contacts in the AC contactor, and the load circuits are used to connect the load.

[0038] The AC contactor is equipped with connection pins A1, A2, 1 / L1, 2 / T1, 3 / L1, 4 / T1, 5 / L1, and 6 / T1.

[0039] Contact pins A1 and A2 are used for control input contacts and have no polarity restriction.

[0040] Contact pins 1 / L1 and 2 / T1 are used for the input / output contacts of the first load and have no directional restriction.

[0041] Contact pins 3 / L1 and 4 / T1 are used for the input / output contacts of the second load and have no directional restriction.

[0042] Contact pins 5 / L1 and 6 / T1 are used for the input / output contacts of the third load and have no directional restriction.

[0043] The power resistors are RX24 gold aluminum-cased resistors, used for pre-magnetizing the transformer.

[0044] The working process of the soft starter system is as follows: connect the soft starter system to the input power supply, set the time relay to delay the power-on time, and after the power-on time is over, control the AC contactor to close.

[0045] The cause of the inrush current in this invention can be simplified as follows: upon power-up, the primary winding of the isolation transformer becomes magnetically saturated. The induced electromotive force (EMF) then no longer increases with increasing current; any further increase in current results in a short-circuit current, no longer constrained by the induced EMF. The power resistor during pre-magnetization limits the current in the entire circuit, keeping the increased current within the threshold of the induced EMF.

[0046] Connect the power soft starter circuit to the system, set the time relay to delay the power-on time, and then power on.

[0047] Delayed power-on circuit autonomous operation and annotation: The power resistor and the primary winding of the isolation transformer form a circuit to magnetize the primary winding of the isolation transformer. After a five-second timer, the AC contactor is activated, directly connecting the live wire to the primary winding of the isolation transformer. Within the five seconds of the timer, the resistor has completed magnetizing the primary winding of the isolation transformer. The live wire connected by the AC contactor and the resistor form a parallel connection, and the voltage across the resistor is the same, so the resistor does not operate. Because the voltage difference is small after the live wire is connected to the primary winding of the isolation transformer, only a small current is generated.

[0048] A soft-start method that pre-magnetizes the transformer is applied, which avoids the excitation effect caused by the voltage surge at the moment of power-on, as well as the excitation voltage and current caused by the sudden voltage input. This effectively reduces the excitation surge of the isolation transformer at power-on.

[0049] Based on the results: Before the introduction of the soft starter circuit, the 1000Va isolation transformer used had a current greater than 5A at the moment of power-on, frequently blowing the 5A fuse pre-installed in the system. After the introduction of the soft starter circuit, the fuse in the pre-installed system was changed to a 1A rated value. After passing 200 on-off tests, the fuse was in good condition. The current during power-on changed from blowing the 5A fuse to not blowing the 1A fuse, indicating that the soft starter circuit can effectively suppress the excitation effect.

[0050] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A soft start system based on reducing the field current, characterized by, time relay, AC contactor, power resistor and isolation transformer, time relay, for controlling the switching of the live wire between the power resistor and the AC contactor; AC contactor, for cutting the power resistor out of the circuit; power resistor, for forming a loop with the primary winding of the isolation transformer and magnetizing the primary winding; isolation transformer, for electrically isolating the input and output of the power supply.

2. The soft start system based on reducing the field current according to claim 1, characterized in that, A control circuit and two load circuits are arranged in the time relay, the load circuits are used for connecting loads, and the control circuit is used for controlling the time relay.

3. The soft start system based on reducing the field current according to claim 1, characterized in that, Two control circuits and three load circuits are arranged in the AC contactor, the control circuits are used for controlling the contacts in the AC contactor, and the load circuits are used for connecting loads.

4. The soft start system based on reducing the field current according to claim 3, characterized in that, A1, A2, 1 / L1, 2 / T1, 3 / L1, 4 / T1, 5 / L1 and 6 / T1 connecting pins are arranged on the AC contactor, A1 and A2 connecting pins, for controlling input contacts; 1 / L1 and 2 / T1 connecting pins, for input and output contacts of the first load circuit; 3 / L1 and 4 / T1 connecting pins, for input and output contacts of the second load circuit; 5 / L1 and 6 / T1 connecting pins, for input and output contacts of the third load circuit.

5. The soft start system based on reducing the field current according to claim 1, characterized in that, The power resistor adopts RX24 golden aluminum shell resistor, for pre-magnetizing the transformer.

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