Current limiting circuit of direct current system of quay crane
The shore-to-ship crane system maintains operation during faults by using a DC circuit with a resistive superconducting limit current device to restrict current, ensuring continuous operation and reducing energy loss.
Patent Information
- Application Number
- CN202421662654.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-15
- Publication Date
- 2025-07-15
- Estimated Expiration
- 2034-07-15
AI Technical Summary
Traditional cranes directly cut off the load when the circuit fails, resulting in the inability to complete important tasks and affecting the operating efficiency.
The current limiting circuit of the DC system of the shore bridge crane is adopted, including the power supply component and the current limiter. The current limiter automatically limits the current in the event of a fault to ensure the normal operation of the circuit.
Limit current in the event of a circuit failure, ensure the normal operation of the crane, reduce power loss, and improve the economic benefits of the circuit.
Smart Images
Figure CN223109660U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of the DC system of a crane, in particular to a current-limiting circuit for the DC system of a quay crane. Background Art
[0002] The quay bridge crane (hereinafter referred to as the crane) is a large-scale device for loading and unloading containers at a port. Its main working principle is to use a Programmable Logic Controller (PLC) for control to grab containers.
[0003] Traditional cranes use fuses and ground insulation detection methods to protect the circuit in the DC stage after rectification. When there are phenomena such as a short circuit in the power supply, this method will quickly cut off the load to protect the power supply and the load. However, when traditional protection methods such as fuses directly cut off the load, it will cause the crane that is performing tasks to be unable to operate directly, thus affecting the crane's completion of important tasks. Summary of the Utility Model
[0004] In view of this, the utility model provides a current-limiting circuit for the DC system of a quay crane, which can solve the problem that when a circuit fails, the crane cannot maintain normal operation, resulting in affecting the crane's completion of important operations.
[0005] To solve the above technical problems, the utility model adopts the following technical solutions:
[0006] The utility model provides a current-limiting circuit for the DC system of a quay crane, including a DC circuit and a load resistor connected to the DC circuit. The DC circuit is used to output direct current to the load resistor, and the load resistor is used to represent the crane or a part of the crane.
[0007] The DC circuit includes:
[0008] A power supply component, used to output direct current;
[0009] A current limiter, the current limiter is connected in series with the power supply component and the load resistor, and the current limiter has the ability to automatically limit the current in case of a line fault.
[0010] In an embodiment of the utility model, the current limiter is a resistive superconducting DC current limiter, and the strip layer of the current limiter is a metal layer.
[0011] In an embodiment of the utility model, the power supply component includes:
[0012] A power supply, used to output three-phase alternating current;
[0013] A rectifier, connected to the power supply, used to rectify the three-phase alternating current and output direct current.
[0014] In an embodiment of the present utility model, the DC circuit further includes:
[0015] A branch circuit, including a capacitor, the capacitor is connected in series with a current limiter and in parallel with a load resistor, and is used for filtering the direct current output by the power supply assembly.
[0016] In an embodiment of the present utility model, the branch circuit includes a plurality of capacitors, and the plurality of capacitors are connected in series.
[0017] In an embodiment of the present utility model, the DC circuit includes a plurality of branch circuits, and the plurality of branch circuits are connected in parallel.
[0018] In an embodiment of the present utility model, the DC circuit further includes an absorption capacitor, the absorption capacitor is connected in series with the current limiter and in parallel with the load resistor, and is used for absorbing the spike voltage in the DC circuit.
[0019] In an embodiment of the present utility model, the DC circuit further includes a resistor component, the resistor component is connected in series with the current limiter and in parallel with the load resistor, and is used for stabilizing the voltage of the DC system.
[0020] In an embodiment of the present utility model, the resistor component is a plurality of voltage-sharing resistors connected in series with each other.
[0021] In an embodiment of the present utility model, the DC circuit includes a frequency conversion component, the frequency conversion component is connected in parallel with the capacitor, the resistor component and the load resistor, and is used for performing frequency conversion processing on the DC circuit and for outputting direct current to the load resistor.
[0022] The above technical solution of the present utility model has at least the following beneficial effects:
[0023] The current limiting circuit of the DC system of the quay crane of the present utility model can increase the impedance when a fault occurs in the DC circuit by setting a current limiter on the DC circuit, so as to limit the current in the DC circuit within a normal range. Compared with the traditional crane circuit where the crane cannot maintain normal operation when a fault occurs, the current limiter in the present utility model can limit the current in the circuit when a circuit fault occurs, ensuring that the crane can maintain operation, which is beneficial to protecting the DC system of the crane. At the same time, the impedance of the current limiter is small when the crane circuit is working normally, which can reduce the power loss in the circuit, thereby improving the economic benefits of the crane circuit. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 is a schematic structural diagram of the current limiting circuit of the DC system of the quay crane according to an embodiment of the present utility model Figure 1 ;
[0025] Figure 2 is a resistance change diagram of the current limiter according to an embodiment of the present utility model;
[0026] Figure 3 Temperature change diagram of the current limiter according to an embodiment of the present utility model;
[0027] Figure 4 Current change diagram of the current limiting circuit according to an embodiment of the present utility model;
[0028] Figure 5 Voltage change diagram on the DC side of the current limiting circuit and both sides of the current limiter according to an embodiment of the present utility model;
[0029] Figure 6 Structural schematic of the current limiting circuit of the DC system of the quay crane according to an embodiment of the present utility model Figure 2 。
[0030] Reference numerals:
[0031] 100, current limiting circuit; 10, DC circuit; 11, power supply component; 111, rectifier; 12, current limiter; 20, branch circuit; 21, capacitive component; 22, resistive component; 23, frequency conversion component; 24, switch; 25, first resistor; 26, first inductor; 30, load resistor. Detailed implementation manners
[0032] To make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions of the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are some but not all of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present utility model fall within the scope of protection of the present utility model.
[0033] To facilitate the understanding of the technical solutions of the present utility model, the technical problems to be solved by the present utility model will be described first below.
[0034] The circuit system of the crane adopts an AC-DC-AC voltage conversion method, and converts the industrial frequency alternating current into adjustable voltage and adjustable frequency alternating current through filtering, rectification and inversion. The crane usually adopts methods such as fuses and ground insulation detection for protection in the DC stage after rectification. In terms of current limiting, the circuit system mostly uses high-impedance transformers and current limiting reactors to limit the fault current. During normal use, the voltage drops of devices such as high-impedance transformers and current limiting reactors may account for 4-10% of the line voltage drop, thus affecting the power factor of the power supply. At the same time, when a fault occurs in the line, methods such as fuses directly cut off the operation of the resistor of the crane, which may cause the crane to be unable to operate directly and may have a great impact on the key operations being carried out by the crane.
[0035] Based on the above technical problems, the present utility model provides a current-limiting circuit for the DC system of a quay crane, which can reduce power loss during normal circuit operation and automatically limit the current in case of a circuit fault, thereby maintaining the normal operation of the crane until maintenance personnel eliminate the short-circuit fault.
[0036] The following specifically describes a current-limiting circuit for the DC system of a quay crane according to an embodiment of the present utility model in conjunction with the accompanying drawings.
[0037] Refer to Figure 1 , Figure 1 which shows the structural schematic of the current-limiting circuit 100 of the DC system of a quay crane according to an embodiment of the present utility model. Figure 1 The current-limiting circuit 100 includes a DC circuit 10 and a load resistor 30 connected to the DC circuit 10. The DC circuit 10 is used to output direct current to the load resistor 30, and the load resistor 30 is used to represent the crane or a part of the crane. The load resistor 30 can be a resistor on the crane.
[0038] Among them, as Figure 1 shown, the DC circuit 10 includes a power supply component 11 and a current limiter 12. The power supply component 11 is used to output direct current. The current limiter 12 is connected in series with the power supply component 11 and the load resistor 30, and the current limiter 12 has the ability to automatically limit the current in case of a circuit fault. That is to say, when a short-circuit fault occurs in the circuit, the current limiter can keep the circuit in a conducting state.
[0039] In the embodiment of the present utility model, as Figure 1 shown, the DC circuit 10 includes a power supply component 11 and a current limiter 12 connected in series with each other. The power supply component 11 is connected to the AC system of the crane and is used to convert alternating current into the direct current required by the DC circuit 10 to maintain the operation of the DC circuit 10. The DC circuit 10 and the load resistor 30 are connected in parallel to form the circuit system of the crane, which is used to maintain the normal operation of the crane. When a short circuit occurs in the circuit, the current limiter 12 can increase its own impedance, thereby limiting the current in the DC circuit 10.
[0040] Compared with the prior art in which the crane circuit cannot maintain normal operation when a fault occurs, the current-limiting circuit 100 in the embodiment of the present utility model can increase the impedance in case of a circuit fault, thereby limiting the current in the DC circuit 10 within the normal range, ensuring the normal operation of the crane and being beneficial to protecting the DC system of the crane. At the same time, the impedance of the current limiter 12 is relatively small during the normal operation of the crane circuit, which can reduce the power loss in the circuit, thereby improving the economic efficiency of the crane circuit.
[0041] In an embodiment of the present utility model, the current limiter 12 can be a resistive superconducting DC current limiter 12, and the strip layer of the current limiter 12 is a metal layer. In some other embodiments of the present utility model, the current limiter 12 can also be an inductor, an adjustable resistor, etc. The present utility model does not uniquely define the type of the current limiter 12.
[0042] The parameters of the resistive superconducting DC current limiter 12 are shown in Table 1 below.
[0043] Table 1 Parameters of the resistive superconducting DC current limiter 12
[0044] Parameter Value Width of current limiter / cm 1.2 Thickness of superconducting layer / cm 0.0001 Thickness of copper layer / cm 0.004 Thickness of silver layer / cm 0.0003 Thickness of Hastelloy layer / cm 0.005 Length of current limiter / m 16.2 Limiting inductance / μH 4.1
[0045] As shown in Table 1, the strip layer selected for the resistive superconducting DC current limiter 12 can be copper, silver, YBCO, and Hastelloy. Hastelloy is used as the substrate of the strip, the silver layer is used as the buffer layer, YBCO is used as the high-temperature superconducting layer, and the copper layer is used as the stabilizing layer.
[0046] Combined with Table 1 and referring to Figure 2 , Figure 2 shows the resistance change diagram of the current limiter 12 in an embodiment of the present utility model. As shown in Table 1 and Figure 2 shown, a short-circuit fault in the DC circuit 10 will cause a sudden surge in the current in the line. Since the current passing through the resistive superconducting DC current limiter 12 exceeds its critical current (i.e., 508 A), this will cause the resistive superconducting DC current limiter 12 to lose its superconductivity. When the resistive superconducting DC current limiter 12 loses its superconductivity, the short-circuit current mainly flows through the stabilizing layer. The magnitude of the current-limiting resistance of the resistive superconducting DC current limiter 12 depends on the strip length and the number of selected parallel branches, and is the total resistance of the stabilizing layer to the environment. Since the fluctuation speed of the short-circuit current is very fast when a short-circuit fault occurs in the high-voltage DC circuit 10, the superconducting state will transition to the non-superconducting state within 0.1 millisecond after the fault occurs. Approximately 0.1 millisecond later, the change rate slows down compared with the previous change rate. After the limiting current reaches the highest point, the current will slowly decrease until it approaches the steady-state operating current before the fault occurs, and there will be no sudden change in the current during this process.
[0047] Referring to Figure 3 , Figure 3 shows the temperature change diagram of the current limiter 12 in an embodiment of the present utility model. As Figure 3As shown, the initial operating ambient temperature of the resistive superconducting DC current limiter 12 is set to 77K (in a liquid nitrogen environment), and the critical temperature is 93K. Due to the extremely fast current change rate during a short-circuit fault, the process of the resistive superconducting DC current limiter 12 transitioning from the superconducting state to the fully non-superconducting state is extremely short, and the temperature propagation in the superconducting tape is relatively slow. Therefore, the entire superconducting current limiting unit can be simplified to a unit that only exchanges heat with liquid nitrogen. When a short-circuit fault occurs in the system, the resistive superconducting DC current limiter 12 loses its superconductivity and generates resistance, thereby accumulating heat and increasing the temperature of the superconducting element. Approximately 0.2 milliseconds after the short circuit occurs, the temperature of the superconducting element reaches the critical temperature of 93K and above. At this time, the superconducting current limiting element is close to the state of completely losing superconductivity. In addition, the temperature range of the material of the resistive superconducting DC current limiter 12 is 77 to 300K, which is beneficial to ensuring the stability of the current limiting circuit 100.
[0048] Reference Figure 4 , Figure 4 The current change diagram of the current limiting circuit 100 according to an embodiment of the present invention. As Figure 4 shown, in the circuit without a current limiter, when a short circuit occurs, the current in the current stabilizes at about 360A (such as Figure 4 the broken line 1). When a short-circuit fault occurs (0.1 second), when using the resistive superconducting DC current limiter 12 and not using the resistive superconducting DC current limiter 12, the highest peak values of the DC side short-circuit current are approximately 1KA (such as Figure 4 the curve 2) and 3.6KA respectively. The current limiting ratio is 28%, and the fault current is limited from 3.6KA to 1KA, which is beneficial to protecting the DC circuit 10 of the crane.
[0049] Reference Figure 5 , Figure 5 shows the voltage change diagram of the DC side of the current limiting circuit 100 and both sides of the current limiter 12 according to an embodiment of the present invention. As Figure 5 shown, the voltage of the power supply component 11 has been stable at about 0.72KV (such as Figure 5 the straight line 3). Since the resistive superconducting DC current limiter 12 is in the superconducting state before the short-circuit fault and the external resistance is zero, the voltage across the resistive superconducting DC current limiter 12 is also zero at this time. After the system has a short-circuit fault at 0.1s, the resistive superconducting DC current limiter 12 begins to lose its superconductivity, the current increases rapidly, and at the same time, a superconducting resistance is generated. At about 0.1s, the limiting current reaches the peak value, resulting in the voltage across the resistive superconducting DC current limiter 12 reaching the peak value (such as Figure 5Due to the decrease in the limiting current and the voltage division of other components on the line, the voltage across the resistive superconducting DC limiter 12 drops below the voltage of the power supply component 11. As the limiting current tends to the current in the normal state and the superconducting resistance gradually increases, the voltage across the superconducting resistance in the entire DC circuit 10 gradually increases, so that the voltage across the resistive superconducting DC limiter 12 slowly tends to the voltage of the power supply component 11, which helps to ensure the stability of the DC circuit 10.
[0050] In an embodiment of the present invention, referring to Figure 6 , Figure 6 shows a schematic structure of the current limiting circuit 100 of the DC system of the quay crane according to an embodiment of the present invention. Figure 2 As Figure 1 and Figure 6 shown, the power supply component 11 includes a power supply (not shown) and a rectifier 111. The power supply is used to output three-phase alternating current. The rectifier 111 is connected to the power supply and is used to rectify the three-phase alternating current and output direct current.
[0051] In an embodiment of the present invention, as Figure 1 and Figure 6 shown, the DC circuit 10 further includes a branch circuit 20. The branch circuit 20 can be integrally connected in series with the DC circuit 10 and is used for further processing such as filtering and frequency conversion of the circuit. The branch circuit 20 includes a capacitor 21. The capacitor 21 is connected in series with the current limiter 12 and is connected in parallel with the load resistor 30, and is used for filtering the direct current output by the power supply component 11.
[0052] Among them, as Figure 1 shown, the branch circuit 20 is connected in parallel with the load resistor 30. A switch 24, a first resistor 25 and a first inductor 26 can be provided on the branch circuit 20. The switch 24 is used to close when a short circuit fault occurs in the line. The first resistor 25 is the total resistance in the branch circuit 20. The first inductor 26 can filter the branch circuit 20.
[0053] Taking the DC side voltage of 0.72 kV and the load resistor 30 of 2 Ω as an example for illustration. The parameters of the DC system are shown in Table 2 below.
[0054] Table 2 Parameters of the DC system
[0055] Parameter Value <![CDATA[DC side voltage U DC / kV]]> 0.72 Load resistance load / Ω 2 Fault occurrence time t / s 0.1 <![CDATA[First resistor R sc / Ω]]> 0.02
[0056] As shown in Table 2, Figures 1 to 5As shown, when the circuit is operating normally, switch 24 is open, the branch circuit 20 where it is located is not conducting, the external resistance of the current limiter 12 is zero, and the power supply component 11 only supplies power to the load resistor 30. When a short - circuit problem occurs in the circuit, switch 24 closes. The first resistor 25 is 0.02Ω, and the impedance of the branch circuit 20 is much smaller than the value of the load resistor 30, which is 2Ω. The current passing through the branch circuit 20 will rise rapidly. At the moment of 0.1s when the fault occurs, the current rises to 3.5A (as shown by the broken line in Figure 4 ).
[0057] At this time, after the current limiter 12 reaches the critical current, it will automatically increase its impedance. The impedance of the current limiter 12 increases from 0 to about 0.4Ω (as shown by the curve in Figure 2 ), and the temperature of the current limiter 12 rises from 0 to about 240K (as shown by the curve in Figure 3 ). The increase in the resistance of the current limiter 12 causes the current in the current - limiting circuit 100 to decrease from 1KA to about 0.2KA (as shown by curve 2 in Figure 4 ), thus playing a role in current limiting. Due to the increase in impedance, a voltage is generated across the current limiter 12, and the voltage rises from 0 to about 0.7kV (as shown by curve 4 in Figure 5 ). That is to say, the voltage across the current limiter 12 will approach the voltage of 0.7kV across the load resistor 30 (as shown by the straight line 3 in Figure 5 ), thereby protecting the DC system of the crane.
[0058] In an embodiment of the present utility model, as shown in Figure 6 , the branch circuit 20 may include a plurality of capacitors 21. The plurality of capacitors 21 are connected in series, which is beneficial for filtering signals in the circuit.
[0059] In an embodiment of the present utility model, as shown in Figure 6 , the DC circuit 10 includes a plurality of branch circuits 20. The plurality of branch circuits 20 are connected in parallel, which can reduce the voltage loss of the DC circuit 10 and facilitate extending the service life of the circuit.
[0060] In an embodiment of the present utility model, as shown in Figure 6 , the DC circuit 10 may further include an absorption capacitor. The absorption capacitor is connected in series with the current limiter 12 and in parallel with the load resistor 30, and is used to absorb the spike voltage in the DC circuit 10. That is to say, the absorption capacitor can be arranged on one of the plurality of branch circuits 20, which is beneficial for maintaining the safety of the DC circuit 10.
[0061] In an embodiment of the present utility model, as shown in Figure 6As shown, the DC circuit 10 further includes a resistor component 22. The resistor component 22 is connected in series with the current limiter 12 and in parallel with the load resistor 30, and is used for stabilizing the voltage of the DC system. That is to say, the resistor component 22 can be arranged on one of the multiple branch circuits 20, which can effectively protect the sensitive components in the circuit from overvoltage or overcurrent damage, and then maintain the stability of the DC circuit 10.
[0062] In an embodiment of the present invention, as Figure 6 shown, the resistor component 22 is a plurality of equalizing resistors connected in series with each other, which is convenient for improving the stability of the DC system.
[0063] In an embodiment of the present invention, as Figure 6 shown, the DC circuit 10 includes a frequency conversion component 23. The frequency conversion component 23 is connected in parallel with the capacitor 21, the resistor component 22 and the load resistor 30, and is used for performing frequency conversion processing on the DC circuit 10 and for outputting direct current to the load resistor 30. That is to say, the frequency conversion component 23 can be arranged on one of the multiple branch circuits 20. The frequency conversion component 23 can be an insulated gate bipolar transistor, which is convenient for performing frequency conversion processing on the DC circuit 10.
[0064] Next, the working principle will be described in conjunction with the structure of the current limiting circuit 100 of the DC system of the quay crane according to the embodiment of the present invention.
[0065] When a fault occurs in the DC system circuit, the switch 24 closes, and the current in the current limiting circuit 100 increases instantaneously. The current limiter 12 loses superconductivity, the resistance of the current limiter 12 starts to increase from zero, the temperature of the current limiter 12 rises, the current in the current limiting circuit 100 starts to decrease to the normal range, and the voltage across the current limiter 12 starts to increase from zero to be close to the voltage across the load resistor 30. That is to say, the voltage across the current limiter 12 is close to the voltage of the power supply component 11, realizing current limiting for the DC system. When the DC system is working normally, the switch 24 is disconnected, and the resistance of the current limiter 12 is zero, reducing the power loss in the DC system.
[0066] In summary, the current limiting circuit 100 of the DC system of the quay crane of the present invention can increase the impedance when a fault occurs in the DC circuit 10 by arranging the current limiter 12 on the DC circuit 10, so as to limit the current in the DC circuit 10 within the normal range, ensure that the crane can continue to work, and is beneficial to protecting the DC system of the crane. At the same time, the impedance of the current limiter 12 is small when the crane circuit is working normally, which can reduce the power loss in the circuit, thereby improving the economic benefits of the crane circuit.
[0067] Unless otherwise defined, the technical terms or scientific terms used in this utility model shall have the ordinary meanings as understood by those of ordinary skill in the field to which this utility model pertains. The "first", "second" and similar terms used in this utility model do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "a" or "an" do not denote a quantity limitation, but mean that there is at least one. The terms "connected" or "coupled" and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right" etc. are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationships also change accordingly.
[0068] The above are the preferred embodiments of this utility model. It should be noted that for those of ordinary skill in the art, without departing from the principle of this utility model, several improvements and modifications can be made, and these improvements and modifications should also be regarded as within the protection scope of this utility model.
Claims
1. A current limiting circuit for a DC system of a quay crane, characterized in that It includes a DC circuit and a load resistor connected to the DC circuit. The DC circuit is used to output direct current to the load resistor, and the load resistor is used to represent the crane or a part of the crane. The DC circuit includes: A power supply component for outputting direct current; A current limiter. The current limiter is connected in series with the power supply component and the load resistor, and has the ability to automatically limit the current in case of a line fault.
2. The current limiting circuit of the DC system of the quay crane according to claim 1, characterized in that, The current limiter is a resistive superconducting DC current limiter, and the tape layer of the current limiter is a metal layer.
3. The current-limiting circuit of the DC system of the quay crane according to claim 1, characterized in that, The power supply component includes: A power supply for outputting three-phase alternating current; A rectifier connected to the power supply, for rectifying the three-phase alternating current and outputting direct current.
4. The current limiting circuit of the DC system of the quay crane according to claim 1, characterized in that The DC circuit further includes: A branch circuit including a capacitor. The capacitor is connected in series with the current limiter and in parallel with the load resistor, and is used for filtering the direct current output by the power supply component.
5. The current limiting circuit of the DC system of the quay crane according to claim 4, characterized in that, The branch circuit includes a plurality of the capacitors, and the plurality of capacitors are connected in series.
6. The current limiting circuit of the DC system of the quay crane according to claim 4, characterized in that, The DC circuit includes a plurality of the branch circuits, and the plurality of branch circuits are connected in parallel.
7. The current limiting circuit of the DC system of the quay crane according to claim 4, characterized in that, The DC circuit further includes an absorption capacitor. The absorption capacitor is connected in series with the current limiter and in parallel with the load resistor, and is used for absorbing the spike voltage in the DC circuit.
8. The current limiting circuit of the DC system of the quay crane according to claim 7, characterized in that, The DC circuit further includes a resistor component. The resistor component is connected in series with the current limiter and in parallel with the load resistor, and is used for stabilizing the voltage of the DC system.
9. The current limiting circuit of the DC system of the quay crane according to claim 8, characterized in that, The resistor component is a plurality of equalizing resistors connected in series with each other.
10. The current limiting circuit of the DC system of the quay crane according to claim 8, characterized in that, The DC circuit includes a frequency conversion component. The frequency conversion component is connected in parallel with the capacitor, the resistor component and the load resistor, and is used for frequency conversion processing of the DC circuit and for outputting direct current to the load resistor.