A dual power supply switching circuit and a dual power supply circuit

Abstract

This utility model relates to a dual power supply switching circuit and a dual power supply circuit, belonging to the field of high-voltage switch control technology. The switching circuit includes: a coil of a first contactor and a normally closed contact of a second contactor connected in series to the main power supply line between the main power supply and the electrical load; a normally open contact of the first contactor connected in series on the main power supply line; a coil of the second contactor and a normally open contact of a time relay connected in series to the backup power supply line between the backup power supply and the electrical load; a normally open contact of the second contactor connected in series on the backup power supply line; a coil of an undervoltage relay connected to the main power supply line; and a normally closed contact of the undervoltage relay and a coil of the time relay connected in series to the backup power supply line. This utility model, by using an undervoltage relay and a time relay, reduces frequent switching between main and backup power supplies, and has a simple circuit structure, low cost, and is easy to maintain.

Description

Technical Field

[0001] This utility model relates to a dual power supply switching circuit and a dual power supply circuit, belonging to the field of high voltage switch control technology. Background Technology

[0002] During substation operation, critical circuits typically employ a dual-power supply system consisting of a main power supply and a backup power supply. If the main power supply voltage drops below the required value and fails to recover to its rated voltage within a certain timeframe, the system automatically switches to the backup power supply to meet the safe operation requirements of different substations.

[0003] Figure 1 It is an existing dual power supply switching device that is connected to both the main power supply and the backup power supply. When the voltage of the main power supply drops below the required voltage value and fails to recover to the rated voltage within a certain period of time, it automatically switches to the backup power supply for power supply.

[0004] Firstly, dual-power switching devices are bulky, requiring specially designed mounting plates for installation and occupying significant control cabinet space, which contradicts the current market trend towards equipment miniaturization. Secondly, the internal workings of dual-power switching devices are complex and cannot be fully represented in the control schematics provided by switchgear manufacturers. Thirdly, dual-power switching devices utilize integrated circuits; in the event of a fault or device damage, power plant maintenance personnel cannot locate the fault or repair the internal circuits, requiring repairs or replacement by the manufacturer's technicians, resulting in long maintenance cycles and high costs. Fourthly, when subsequent power loads increase, existing dual-power switching devices may become insufficient, necessitating a complete replacement if the product cannot be upgraded.

[0005] Chinese utility model application CN221842365U discloses a dual-power supply circuit and its switching circuit. This dual-power supply circuit and its switching circuit belong to the field of high-voltage switch control technology. It includes a first switching switch for the main power supply circuit and a second switching switch for the backup power supply circuit. The first switching switch is a first contactor, with its normally open contact connected in series in the main power supply circuit. The coil of the first contactor and the normally closed contact of the second contactor are connected in series in the line between the main power supply circuit and the normally open contact of the first contactor. The second switching switch is a second contactor, with its normally open contact connected in series in the backup power supply circuit. The coil of the second contactor and the normally closed contact of the first contactor are connected in series in the line between the backup power supply circuit and the normally open contact of the second contactor. This achieves automatic switching of the power supply and interlocking between the main and backup power supplies.

[0006] Although the dual power supply circuit and its switching circuit provided by this solution are simple in structure and low in cost, this solution lacks requirements for switching time. As soon as the voltage of the main power supply circuit is abnormal, it immediately switches to the backup power supply circuit, which will cause frequent switching between the main and backup power supplies. Utility Model Content

[0007] The purpose of this invention is to provide a dual power supply switching circuit and a dual power supply circuit. By connecting the coil of the first relay and the normally closed contact of the second relay in series to the two ends of the main power supply, interlocking between the main and backup power supplies is achieved. By adding an undervoltage relay and a time relay, the switching conditions between the main and backup power supplies are made stricter. Switching will only occur if both the voltage and time conditions are met, which reduces the occurrence of misjudgments and also reduces the switching frequency between the main and backup power supplies.

[0008] To achieve the above objectives, the solution of this utility model includes:

[0009] This utility model discloses a dual power supply switching circuit, comprising: a first contactor and a second contactor for switching contact states when the coil is energized; an undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and resetting contact states when the supply voltage is less than a preset voltage; and a time relay for switching contact states when the coil is energized for a duration greater than a preset time.

[0010] The coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line between the main power supply and the electrical load; the normally open contact of the first contactor is connected in series on the main power supply line.

[0011] The coil of the second contactor and the normally open contact of the time relay are connected in series to connect to the backup power supply line between the backup power supply and the electrical load; the normally open contact of the second contactor is connected in series on the backup power supply line.

[0012] The coil of the undervoltage relay is connected to the main power supply line; the normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line.

[0013] Furthermore, it also includes: a main power supply circuit breaker connected in series on the main power supply line.

[0014] Furthermore, it also includes: a backup power supply circuit breaker connected in series on the backup power supply line.

[0015] This utility model discloses a dual power supply circuit, including a main power supply, a backup power supply, a main power supply line for connecting the main power supply to the electrical load, and a backup power supply line for connecting the backup power supply to the electrical load. It also includes: a first contactor and a second contactor for switching contact states when the coil is energized; an undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and resetting the contact states when the supply voltage is less than the preset voltage; and a time relay for switching contact states when the coil is energized for a duration greater than a preset time.

[0016] The coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line; the normally open contact of the first contactor is connected in series to the main power supply line.

[0017] The coil of the second contactor and the normally open contact of the time relay are connected in series and then connected to the backup power supply line; the normally open contact of the second contactor is connected in series on the backup power supply line.

[0018] The coil of the undervoltage relay is connected to the main power supply line; the normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line.

[0019] Furthermore, it also includes: a main power supply circuit breaker connected in series on the main power supply line.

[0020] Furthermore, it also includes: a backup power supply circuit breaker connected in series on the backup power supply line.

[0021] Furthermore, both the main power supply and the backup power supply are AC / DC power supplies capable of providing DC or AC power.

[0022] The beneficial effects of this utility model are as follows: As a pioneering invention, this utility model provides a dual power supply switching circuit and a dual power supply circuit, including a first contactor and a second contactor for switching contact states when the coil is energized; an undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and resetting contact states when the supply voltage is less than the preset voltage; a time relay for switching contact states when the coil is energized for a duration greater than a preset time; the coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line between the main power supply and the electrical load; the normally open contact of the first contactor is connected in series to the main power supply line; the coil of the second contactor and the normally open contact of the time relay are connected in series to the backup power supply line between the backup power supply and the electrical load; the normally open contact of the second contactor is connected in series to the backup power supply line; the coil of the undervoltage relay is connected to the main power supply line; the normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line. This utility model provides a dual power supply switching circuit and a dual power supply circuit. Firstly, by connecting the coil of the first relay and the normally closed contact of the second relay in series to the two ends of the main power supply, interlocking between the main and backup power supplies is achieved. Secondly, the addition of an undervoltage relay and a time relay makes the switching conditions between the main and backup power supplies more stringent; both voltage and time conditions must be met before switching occurs, reducing the occurrence of misjudgments and lowering the switching frequency between the main and backup power supplies. Thirdly, the circuit structure is simple and low-cost. Fourthly, in the event of a fault, power plant maintenance personnel can quickly locate the fault and only need to replace the faulty component, without replacing all components in the entire circuit, thus facilitating maintenance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an existing dual power supply switching device;

[0024] Figure 2 This is a schematic diagram of a dual power supply circuit provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] The concept of this utility model is to use undervoltage relays and time relays to change the switching conditions of the main and backup power supplies in a dual power supply circuit.

[0027] Specifically: a first contactor and a second contactor for switching contact states when the coil is energized; an undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and returning the contact states when the supply voltage is less than the preset voltage; a time relay for switching contact states when the coil is energized for a duration greater than a preset time; the coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line between the main power supply and the electrical load; the normally open contact of the first contactor is connected in series to the main power supply line; the coil of the second contactor and the normally open contact of the time relay are connected in series to the backup power supply line between the backup power supply and the electrical load; the normally open contact of the second contactor is connected in series to the backup power supply line; the coil of the undervoltage relay is connected to the main power supply line; the normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line.

[0028] An implementation method for a dual power supply switching circuit:

[0029] The dual power supply switching circuit provided in this embodiment of the invention is applied to dual power supply circuits. Figure 2 This is a schematic diagram of a dual-power supply circuit provided in an embodiment of this utility model, as shown below. Figure 2 As shown, the dual power supply circuit includes a main power supply, a backup power supply, a main power supply line for connecting the main power supply to the electrical load, a backup power supply line for connecting the backup power supply to the electrical load, and a dual power supply switching circuit.

[0030] The dual power supply switching circuit includes: a first contactor-KC1 and a second contactor-KC2 for switching the contact state when the coil is energized; an undervoltage relay-KX for switching the contact state when the supply voltage is greater than a preset voltage and resetting the contact state when the supply voltage is less than a preset voltage; and a time relay-KT for switching the contact state when the coil is energized for a duration greater than a preset time.

[0031] Specifically, the coils (A1, A2) of the first contactor-KC1 and the normally closed contacts (31, 32) of the second contactor-KC2 are connected in series to the main power supply line; the normally open contacts of the first contactor-KC1 are connected in series to the main power supply line; the coil of the second contactor-KC2 and the normally open contacts (15, 16) of the time relay KT are connected in series to the backup power supply line; the normally open contacts of the second contactor-KC2 are connected in series to the backup power supply line; the coil of the undervoltage relay-KX is connected to the main power supply line; the normally closed contacts (1, 3) of the undervoltage relay-KX and the coils (A1, A2) of the time relay KT are connected in series to the backup power supply line.

[0032] The preset voltage and preset time are determined based on the application scenario (or different operating conditions) of the dual power supply circuit and can be adjusted. For example, the primary fire emergency power supply requires switching to be completed within 30 seconds, the secondary fire emergency power supply requires power supply to be completed within 60 seconds, the emergency lighting power supply requires switching to be completed within 5 seconds, and some financial venues require power supply to be completed within 1.5 seconds.

[0033] The energization duration of the coil of the time relay KT is also called the fault duration.

[0034] If the load on the main power supply and backup power supply increases in the future, only the corresponding contactors need to be replaced with larger ones; other components do not need to be replaced, making it easy to upgrade.

[0035] In order to reduce the occurrence of safety accidents and ensure the personal safety of maintenance personnel during maintenance, as an optional implementation method, it also includes: a main power supply circuit breaker-FJ1 connected in series on the power supply line and a backup power supply circuit breaker-FJ2 connected in series on the backup power supply line.

[0036] The main power supply and backup power supply are AC / DC power supplies capable of providing direct current (DC) or alternating current (AC). Both the main and backup power supplies can be single-phase or three-phase. If both are single-phase, each power supply line includes two lines: a positive line and a negative line. If both are three-phase, each power supply line includes three live wires and one neutral wire.

[0037] The following examples illustrate this, using single-phase and three-phase power supplies as both the main power supply and the backup power supply.

[0038] When both the main power supply and the backup power supply are single-phase: the normally open contacts of the first contactor-KC1 and the normally open contacts of the second contactor-KC2 can each include only one set; the coil of the undervoltage relay-KX also includes only one; the normally open contacts of the main power supply circuit breaker-FJ1 and the normally open contacts of the backup power supply circuit breaker-FJ2 include two sets.

[0039] Specifically, the first switching control branch, formed by connecting the coils (A1, A2) of the first contactor-KC1 and the normally closed contacts (31, 32) of the second contactor-KC2 in series, is connected at one end to the positive power supply line in the main power supply line and at the other end to the negative power supply line in the main power supply line; the first set of normally open contacts (1, 2) of the first contactor-KC1 is connected in series to the positive power supply line in the main power supply line; the second switching control branch, formed by connecting the coil of the second contactor-KC2 and the normally open contacts (15, 16) of the time relay KT in series, is connected at one end to the positive power supply line in the backup power supply line and at the other end to the negative power supply line in the backup power supply line; the first set of normally open contacts (1, 2) of the second contactor-KC2 is connected in series to the positive power supply line in the backup power supply line; the undervoltage relay-KX The coil 2 is connected to the positive power supply line in the main power supply line; the normally closed contacts (1, 3) of the undervoltage relay-KX and the coils (A1, A2) of the time relay KT are connected in series, with one end connected to the positive power supply line in the backup power supply line and the other end connected to the negative power supply line in the backup power supply line; the first set of normally open contacts (1, 2) of the main power supply circuit breaker-FJ1 is connected in series to the positive power supply line in the main power supply line, and the fourth set of normally open contacts (7, 8) of the main power supply circuit breaker-FJ1 is connected in series to the negative power supply line in the main power supply line; the first set of normally open contacts (1, 2) of the backup power supply circuit breaker-FJ2 is connected in series to the positive power supply line in the backup power supply line, and the fourth set of normally open contacts (7, 8) of the backup power supply circuit breaker-FJ2 is connected in series to the negative power supply line in the backup power supply line.

[0040] When both the main power supply and the backup power supply are single-phase, the working principle of the dual power supply switching circuit is as follows: During system operation, both the main power supply circuit breaker-FJ1 and the backup power supply circuit breaker-FJ2 are in use. The first set of normally open contacts (1,2) and the fourth set of normally open contacts (7,8) of the main power supply circuit breaker-FJ1, and the first set of normally open contacts (1,2) and the fourth set of normally open contacts (7,8) of the backup power supply circuit breaker-FJ2 are closed. At this time, the coil of the first contactor-KC1 is energized, and the coil of the undervoltage relay-KX is energized. The first set of normally open contacts (1,2) of the first contactor-KC1 closes. Since the supply voltage is greater than the preset voltage of the undervoltage relay-KX, the normally closed contact (1,3) of the undervoltage relay-KX opens. Since the normally closed contacts (1, 3) of the undervoltage relay-KX are open, the coil of the time relay KT is not energized. The normally open contacts (15, 18) of the time relay KT remain open, so the coil of the second contactor-KC2 is not energized. Therefore, the normally closed contacts (31, 32) of the second contactor-KC2 remain closed, and the first set of normally open contacts (1, 2) of the second contactor-KC2 remains open. At this time, the power supply circuit of the backup power supply is disconnected, and the power supply of the electrical load is provided by the main power supply.

[0041] When the main power supply fails, the supply voltage begins to decrease until it falls below the preset voltage. At this point, the contacts of the undervoltage relay-KX return to their initial state. The normally closed contacts (1, 3) of the undervoltage relay-KX then return to their normally closed state from the open state. The coil of the time relay KT is then energized. After the coil of the time relay KT is energized, timing begins. When the energization time of the time relay KT exceeds the preset time, the normally open contacts (15, 18) of the time relay KT close (i.e., the (15, 16) contacts of the time relay KT switch to the (15, 18) contacts, causing the normally open contacts (15, 18) to close). The coil of the second relay-KC2 is then energized. After the coil of the second relay-KC2 is energized, the normally closed contacts (31, 32) of the second relay-KC2 switch from the normally closed state to the normally open state, and the first set of normally open contacts (1, 2) of the second relay-KC2 switch from the normally open state to the normally closed state. Since the normally closed contacts (31, 32) of the second contactor-KC2 have been switched to the normally open state, the coil of the first contactor-KC1 is de-energized, and the first set of normally open contacts (1, 2) of the first contactor-KC1 are switched from the normally closed state to the normally open state. Therefore, the power supply circuit of the main power supply is disconnected, and the power supply of the electrical load is provided by the backup power supply.

[0042] When the main power supply voltage gradually recovers to exceed the preset voltage, the coil 2 of the undervoltage relay-KX is energized, and the normally closed contact (1, 3) of the undervoltage relay-KX switches from the closed state to the open state. At this time, the coil of the time relay KT is de-energized, and the normally closed contact (15, 18) of the time relay KT is opened (that is, the (15, 18) contact of the time relay KT switches to the (15, 16) contact, so that the normally open contact (15, 18) is opened). At this time, the coil of the second relay-KC2 is de-energized, and the normally closed contact (31, 32) of the second relay-KC2 returns from the normally open state to the normally closed state. The first set of normally open contacts (1, 2) of the second relay-KC2 is opened, and the power supply circuit of the backup power supply is cut off. After the normally closed contacts (31, 32) of the second contactor-KC2 are closed, the coil of the first relay-KC1 is re-energized, and the first set of normally open contacts (1, 2) of the first relay-KC1 is switched from the normally open state to the normally closed state. At this time, the power supply circuit of the main power supply is reconnected, and the power supply of the electrical load is provided by the main power supply.

[0043] When both the main power supply and the backup power supply are three-phase: the normally open contacts of the first contactor-KC1 and the normally open contacts of the second contactor-KC2 can each include three sets; the coil of the undervoltage relay-KX includes three; the normally open contacts of the main power supply circuit breaker-FJ1 and the normally open contacts of the backup power supply circuit breaker-FJ2 include three sets.

[0044] Specifically, the first switching control branch, formed by the coils (A1, A2) of the first contactor-KC1 and the normally closed contacts (31, 32) of the second contactor-KC2 connected in series, is connected at one end to any one phase of the main power supply line and at the other end to the neutral wire of the main power supply line; the first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4), and the third set of normally open contacts (5, 6) of the first contactor-KC1 are connected in series to the three phases of the main power supply line; the second switching control branch, formed by the coils (A1, A2) of the second contactor-KC2 and the normally open contacts (15, 16) of the time relay KT connected in series, is connected at one end to any one phase of the backup power supply line and at the other end to the neutral wire of the backup power supply line; the first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4), and the third set of normally open contacts (5, 6) of the second contactor-KC2 are connected in series to the three phases of the backup power supply line; undervoltage relay- Coils 2, 8, and 9 of KX are connected to the three live wires in the main power supply line, respectively. The normally closed contacts (1, 3) of the undervoltage relay-KX and the coils (A1, A2) of the time relay KT are connected in series, with one end connected to any live wire in the backup power supply line and the other end connected to the neutral wire in the backup power supply line. The first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4), and the third set of normally open contacts (5, 6) of the main power supply circuit breaker-FJ1 are connected in series. On the three-phase live wires of the main power supply line, the fourth set of normally open contacts (7, 8) of the main power supply circuit breaker-FJ1 is connected in series with the neutral wire of the main power supply line; the first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4) and the third set of normally open contacts (5, 6) of the backup power supply circuit breaker-FJ2 are connected in series with the three-phase live wires of the backup power supply line, and the fourth set of normally open contacts (7, 8) of the backup power supply circuit breaker-FJ2 is connected in series with the neutral wire of the backup power supply line.

[0045] When both the main power supply and the backup power supply are three-phase, the working principle of the dual power supply switching circuit is as follows: When the system is running, both the main power supply circuit breaker-FJ1 and the backup power supply circuit breaker-FJ2 are put into use. Then, the first set of normally open contacts (1,2), the second set of normally open contacts (3,4), the third set of normally open contacts (5,6) and the fourth set of normally open contacts (7,8) of the main power supply circuit breaker-FJ1 are closed. The first set of normally open contacts (1,2), the second set of normally open contacts (3,4), the third set of normally open contacts (5,6) and the fourth set of normally open contacts (7,8) of the backup power supply circuit breaker-FJ2 are closed, and the power supply circuit of the main power supply is connected. At this time, the coil of the first contactor-KC1 is energized, and the coils 2, 8 and 9 of the undervoltage relay-KX are also energized. Then, the first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4), the third set of normally open contacts (5, 6) and the fourth set of normally open contacts (7, 8) of the first contactor-KC1 are all closed. Since the supply voltage is greater than the preset voltage of the undervoltage relay-KX at this time, the normally closed contacts (1, 3) of the undervoltage relay-KX are opened.

[0046] Because the normally closed contacts (1, 3) of the undervoltage relay-KX are open, the coil of the time relay KT is not energized. The normally open contacts (15, 18) of the time relay KT remain open, so the coil of the second contactor-KC2 is not energized. Therefore, the normally closed contacts (31, 32) of the second contactor-KC2 remain closed. The first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4), the third set of normally open contacts (5, 6), and the fourth set of normally open contacts (7, 8) of the second contactor-KC2 all remain open. At this time, the power supply circuit of the backup power supply is disconnected. Therefore, the power supply for the electrical load is provided by the main power supply.

[0047] When any phase of the main power supply fails, the supply voltage of that circuit begins to decrease until it is lower than the preset voltage. At this point, the contacts of the undervoltage relay-KX return to their initial state. The normally closed contacts (1, 3) of the undervoltage relay-KX return to their normally closed state from the open state. The coil of the time relay KT is then energized. After the coil of the time relay KT is energized, timing begins. When the energization time of the coil of the time relay KT exceeds the preset time, the normally open contacts (15, 18) of the time relay KT close (i.e., the (15, 16) contacts of the time relay KT switch to the (15, 18) contacts, causing the normally open contacts (15, 18) to close). The coil of the second relay-KC2 is then energized.

[0048] After the coil of the second relay-KC2 is energized, the normally closed contacts (31, 32) of the second relay-KC2 switch from the normally closed state to the normally open state. The first group of normally open contacts (1, 2), the second group of normally open contacts (3, 4), the third group of normally open contacts (5, 6), and the fourth group of normally open contacts (7, 8) of the second relay-KC2 all switch from the normally open state to the normally closed state, and the power supply circuit of the backup power supply is connected. Since the normally closed contacts (31, 32) of the second contactor-KC2 have switched to the normally open state, the coil of the first contactor-KC1 is de-energized. The first group of normally open contacts (1, 2), the second group of normally open contacts (3, 4), the third group of normally open contacts (5, 6), and the fourth group of normally open contacts (7, 8) of the first contactor-KC1 all switch from the normally closed state to the normally open state, and the power supply circuit of the main power supply is disconnected. At this time, the power supply for the electrical load is provided by the backup power supply.

[0049] When the main power supply voltage gradually recovers to exceed the preset voltage, the coil 2 of the undervoltage relay-KX is energized, and the normally closed contact (1, 3) of the undervoltage relay-KX switches from the closed state to the open state. At this time, the coil of the time relay KT is de-energized, and the normally closed contact (15, 18) of the time relay KT is opened (that is, the (15, 18) contact of the time relay KT switches to the (15, 16) contact, so that the normally open contact (15, 18) is opened). At this time, the coil of the second relay-KC2 is de-energized, and the normally closed contact (31, 32) of the second relay-KC2 returns from the normally open state to the normally closed state. The first group of normally open contacts (1, 2), the second group of normally open contacts (3, 4), the third group of normally open contacts (5, 6) and the fourth group of normally open contacts (7, 8) of the second relay-KC2 are all opened. At this time, the power supply circuit of the backup power supply is cut off. After the normally closed contacts (31, 32) of the second contactor-KC2 are closed, the coil of the first relay-KC1 is re-energized. The first set of normally open contacts (1, 2), the second set of normally open contacts (3, 4), the third set of normally open contacts (5, 6), and the fourth set of normally open contacts (7, 8) of the first relay-KC1 are all switched from the normally open state to the normally closed state. At this time, the power supply circuit of the main power supply is reconnected, and the power supply of the electrical load is provided by the main power supply.

[0050] This utility model provides a dual power supply switching circuit, including a first contactor and a second contactor for switching contact states when the coil is energized; an undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and resetting contact states when the supply voltage is less than the preset voltage; and a time relay for switching contact states when the coil is energized for a duration greater than a preset time. The coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line between the main power supply and the electrical load. The normally open contact of the first contactor is connected in series to the main power supply line. The coil of the second contactor and the normally open contact of the time relay are connected in series to the backup power supply line between the backup power supply and the electrical load. The normally open contact of the second contactor is connected in series to the backup power supply line. The coil of the undervoltage relay is connected to the main power supply line. The normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line. This utility model provides a dual-power switching circuit. Firstly, by connecting the coil of the first relay and the normally closed contact of the second relay in series to the two ends of the main power supply, interlocking between the main and backup power supplies is achieved. Secondly, the addition of an undervoltage relay and a time relay makes the switching conditions between the main and backup power supplies more stringent; both voltage and time conditions must be met before switching occurs, reducing misjudgments and lowering the switching frequency. Thirdly, the circuit structure is simple and low-cost. Fourthly, in the event of a fault, power plant maintenance personnel can quickly locate the fault and only need to replace the faulty component, without replacing all components in the entire circuit, thus facilitating maintenance.

[0051] An implementation method for a dual power supply circuit:

[0052] For the implementation of the dual power supply circuit, please refer to the relevant description in the aforementioned "A Dual Power Supply Switching Circuit", which will not be repeated here.

[0053] The dual power supply circuit provided in this embodiment of the utility model can achieve the same beneficial effects as the aforementioned dual power switching circuit, and will not be described again here.

Claims

1. A dual power supply switching circuit, characterized in that, include: First and second contactors used to switch contact states when the coil is energized; An undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and for restoring contact states when the supply voltage is less than the preset voltage; a time relay for switching contact states when the coil is energized for a period longer than a preset time; The coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line between the main power supply and the electrical load; the normally open contact of the first contactor is connected in series on the main power supply line. The coil of the second contactor and the normally open contact of the time relay are connected in series to connect to the backup power supply line between the backup power supply and the electrical load. The normally open contact of the second contactor is connected in series on the backup power supply line; The coil of the undervoltage relay is connected to the main power supply line; the normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line.

2. The dual power supply switching circuit according to claim 1, characterized in that, Also includes: The main power supply circuit breaker is connected in series on the main power supply line.

3. The dual power supply switching circuit according to claim 1, characterized in that, Also includes: A backup power supply circuit breaker is connected in series on the backup power supply line.

4. A dual-power supply circuit, comprising a main power supply, a backup power supply, a main power supply line for connecting the main power supply to the electrical load, and a backup power supply line for connecting the backup power supply to the electrical load, characterized in that, It also includes: a first contactor and a second contactor for switching contact states when the coil is energized; an undervoltage relay for switching contact states when the supply voltage is greater than a preset voltage and for resetting contact states when the supply voltage is less than the preset voltage; and a time relay for switching contact states when the coil is energized for a duration greater than a preset time. The coil of the first contactor and the normally closed contact of the second contactor are connected in series to the main power supply line; the normally open contact of the first contactor is connected in series to the main power supply line. The coil of the second contactor and the normally open contact of the time relay are connected in series and then connected to the backup power supply line; the normally open contact of the second contactor is connected in series on the backup power supply line. The coil of the undervoltage relay is connected to the main power supply line; the normally closed contact of the undervoltage relay and the coil of the time relay are connected in series to the backup power supply line.

5. The dual power supply circuit according to claim 4, characterized in that, Also includes: The main power supply circuit breaker is connected in series on the main power supply line.

6. The dual power supply circuit according to claim 4, characterized in that, Also includes: A backup power supply circuit breaker is connected in series on the backup power supply line.

7. The dual power supply circuit according to any one of claims 4-6, characterized in that, Both the main power supply and the backup power supply are AC / DC power supplies capable of providing DC or AC power.

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