Dual-power quick switching circuit for low-voltage power supply system

Abstract

The invention relates to the technical field of low-voltage power supply and distribution systems, and discloses a dual-power-supply quick switching circuit for a low-voltage power supply system, which comprises a main power supply, a standby power supply, a circuit breaker QF1, a circuit breaker QF2, a relay KA1, a relay KA2, an alternating current contactor KM1, an alternating current contactor KM2 and a load, the main power supply is connected with the circuit breaker QF1, one path of the QF1 is connected with the KM1, and the KM1 is connected with the load; the other path is connected with the KA1 from the QF1, the KA1 is connected with the KM2, the KM2 is connected with a coil of the KM1 and then connected with the zero line N, and the 1B phase line and the 1C phase line of the main power supply are further connected with the two ends of the coil of the KA1; the standby power supply is connected with the circuit breaker QF2, one path of the QF2 is connected with the KM2, the KM2 is connected with the load, the other path of the QF2 is connected with the KA2 from the QF2, the KA2 is connected with the KM1, the KM1 is connected with a coil of the KM2 and then connected with the null line N, and the 2A phase line and the 2B phase line of the standby power supply are further connected with the two ends of the coil of the KA2. When the main power supply is abnormal, the standby power supply can be quickly switched to avoid shutdown of the lower-level equipment, the standby power supply can be automatically switched after the lower-level short circuit fault is isolated, and the power supply reliability of the low-voltage power supply and distribution system is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-voltage power supply system, and particularly relates to a dual-power quick switching circuit for low-voltage power supply system. BACKGROUND

[0002] In the operation process of the low-voltage power supply system, in order to ensure the continuous and stable power supply of the load, the dual-power automatic switching device is one of the core equipment, and its performance directly affects the power supply reliability and the normal operation of the lower electrical equipment. In the prior art, the dual-power automatic switching device usually uses a low-voltage air circuit breaker as a core control component, and the overall structure is composed of two low-voltage air circuit breakers. The working principle of the device is as follows: a detection unit is used to monitor the voltage state of two power supply sources in real time, when the detection unit identifies that one of the power supply sources loses voltage, a mechanical operating mechanism is triggered to act, first, the circuit breaker of the power supply source that loses voltage is disconnected, and then the other circuit breaker with normal power supply is connected, so as to realize the switching of the power supply circuit and try to maintain the continuous power supply of the load.

[0003] However, the existing dual-power switching device based on the low-voltage air circuit breaker has obvious defects in actual application, and it is difficult to meet the efficient and reliable power supply demand. On the one hand, the switching speed is slow, and in the process of triggering the switching when the power supply loses voltage, part of the electrical equipment in the running state will stop running due to the interruption of power supply, which not only affects the normal working efficiency of the equipment, but also may cause damage to the equipment due to sudden stop. On the other hand, when the lower electrical equipment or line of the dual-power switching device has a short-circuit fault, the circuit breaker will automatically trip due to its own protection mechanism (i.e. the internal tripping phenomenon of the circuit breaker), at this time, the device cannot realize the automatic operation of the other power supply, resulting in that the load is in a power-off state for a long time, which greatly reduces the power supply reliability of the entire power supply system, and it is difficult to adapt to the application scenarios with high power supply continuity requirements. SUMMARY

[0004] The present application provides a dual-power quick switching circuit for low-voltage power supply system, which constructs a control loop and an interlocking mechanism through a relay and an alternating current contactor, and combines with the protection of the circuit breaker, so as to quickly switch to the standby power supply to avoid the shutdown of the lower equipment when the main power supply is abnormal, and automatically put into the standby power supply after the lower short-circuit fault is isolated, thereby greatly improving the power supply reliability of the low-voltage power supply system and adapting to the scenarios with high power supply continuity requirements.

[0005] The present application provides a dual-power quick switching circuit for low-voltage power supply system, which includes a main power supply, a standby power supply, a circuit breaker QF1, a circuit breaker QF2, a relay KA1, a relay KA2, an alternating current contactor KM1, an alternating current contactor KM2, and a load.

[0006] The output end of the main power source is connected to the input end of the circuit breaker QF1, the output end of the circuit breaker QF1 is divided into two paths, one path is connected to the main contact input end of the AC contactor KM1, the main contact output end of the AC contactor KM1 is connected to the input end of the load, providing a main power supply path for the load, the other path is connected to the normally open contact one end of the relay KA1, the normally open contact other end of the relay KA1 is connected to the first auxiliary normally closed contact one end of the AC contactor KM2, the first auxiliary normally closed contact other end of the AC contactor KM2 is connected to the second auxiliary normally closed contact one end of the AC contactor KM2, the second auxiliary normally closed contact other end of the AC contactor KM2 is connected to the coil one end of the AC contactor KM1, the coil other end of the AC contactor KM1 is connected to the zero line N, and the 1B and 1C phase lines of the main power source are also connected to the coil two ends of the relay KA1, forming a monitoring circuit of the relay KA1.

[0007] The output end of the standby power source is connected to the input end of the circuit breaker QF2, the output end of the circuit breaker QF2 is divided into two paths, one path is connected to the main contact input end of the AC contactor KM2, the main contact output end of the AC contactor KM2 is connected to the input end of the load, providing a standby power supply path for the load, the other path is connected to the normally open contact one end of the relay KA2, the normally open contact other end of the relay KA2 is connected to the first auxiliary normally closed contact one end of the AC contactor KM1, the first auxiliary normally closed contact other end of the AC contactor KM1 is connected to the second auxiliary normally closed contact one end of the AC contactor KM1, the second auxiliary normally closed contact other end of the AC contactor KM1 is connected to the coil one end of the AC contactor KM2, the coil other end of the AC contactor KM2 is connected to the zero line N, and the 2A and 2B phase lines of the standby power source are also connected to the coil two ends of the relay KA2, forming a monitoring circuit of the relay KA2.

[0008] Further, the main power source and the standby power source are both three-phase AC power sources, the phase lines of the main power source are marked as 1A, 1B and 1C, the phase lines of the standby power source are marked as 2A, 2B and 2C, the main power source and the standby power source are taken from two different power supply systems, the main power source has priority in power supply, and the standby power source takes over in case of failure to ensure continuous power supply for the load, and the phase is checked after power supply to ensure consistency of phase sequence.

[0009] Further, in the circuit of the main power source, the auxiliary normally closed contacts of the two AC contactors KM2 are taken from the auxiliary contacts at the left and right ends of the contactors.

[0010] Further, the current value of the circuit breaker QF1 and the circuit breaker QF2 is less than or equal to 3A.

[0011] Further, in the main power supply circuit, the working voltage of the relay KA1 and the working voltage of the AC contactor KM1 meet the detection of three-phase power supply point at the same time.

[0012] Further, in the standby power supply circuit, the working voltage of the relay KA2 and the working voltage of the AC contactor KM2 meet the detection of three-phase power supply point at the same time.

[0013] Further, in the main power supply normal power supply stage, the main power supply is normal, the circuit breaker QF1 is closed, the main power supply supplies power to the relay KA1 coil, the normally open contact of the relay KA1 is closed, the main power supply control circuit is turned on, and the current flows through the closed normally open contact of the relay KA1 and the auxiliary normally closed contact of the AC contactor KM2 to the coil of the AC contactor KM1, and the coil of the AC contactor KM1 is energized to act; the main contact of the AC contactor KM1 is closed, and the main power supply supplies power to the load through the circuit breaker QF1 and the AC contactor KM1; at the same time, the auxiliary normally closed contact of the AC contactor KM1 is opened to cut off the standby power supply KM2 control circuit to avoid misoperation of the standby power supply.

[0014] Further, in the main power supply abnormal switching stage, the main power supply is abnormal, the relay KA1 loses power, its normally open contact is opened, and the coil of the AC contactor KM1 is de-energized; the main contact of the AC contactor KM1 is opened, and the main power supply stops supplying power; at the same time, the auxiliary normally closed contact of the AC contactor KM1 is closed to prepare for the conduction of the standby power supply circuit; the standby power supply is normal and the circuit breaker QF2 is closed, the standby power supply supplies power to the relay KA2 coil, the relay KA2 acts, its normally open contact is closed, the control circuit of the standby power supply is turned on, and the current flows through the closed normally open contact of the relay KA2 and the auxiliary normally closed contact of the AC contactor KM1 to the coil of the AC contactor KM2, and the coil of the AC contactor KM2 is energized to act; the main contact of the AC contactor KM2 is closed, and the standby power supply supplies power to the load through the circuit breaker QF2 and the AC contactor KM2; at the same time, the auxiliary normally closed contact of the AC contactor KM2 is opened to prevent the AC contactor KM1 from misacting when the main power supply is restored.

[0015] Further, during the main power recovery reset phase, when the main power returns to normal, the relay KA1 operates again, and its normally open contacts close. However, the AC contactor KM2 remains in the operating state, that is, its auxiliary normally closed contacts are open, and the control circuit of the AC contactor KM1 is temporarily not connected, so the AC contactor KM1 does not operate. If the backup power supply is abnormal or manually switched, the relay KA2 loses power, that is, its normally open contacts open, the coil of the AC contactor KM2 is de-energized, and its main contacts open, so the backup power supply stops supplying power. The auxiliary normally closed contacts of the AC contactor KM2 resume closing, the control circuit of the main power KM1 is conducted, the coil of the AC contactor KM1 is energized and operates, and its main contacts close, and the main power supply resumes power supply to the load and restores the main power priority mode.

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention constructs a control circuit and an interlock mechanism through relays and AC contactors. With the help of the real-time monitoring of the three-phase states of the main and backup power supplies by the relays, combined with the fast response characteristics of the contactor coils and auxiliary contacts, when the main power supply is abnormal, the abnormal power supply circuit can be quickly cut off and the backup power supply circuit can be conducted, effectively avoiding the problem that the lower-level electrical equipment stops running due to slow switching speed, thus ensuring the continuous operation of the equipment and reducing the downtime damage. At the same time, through the coordinated protection logic of the circuit breaker and the contactor, when a short-circuit fault occurs in the lower-level electrical equipment or line, the fault can be isolated by relying on the circuit breaker, and the backup power supply state can be continuously monitored by the relay. After the fault isolation, the automatic input of the backup power supply circuit can be triggered in a timely manner, successfully solving the defect in the prior art that the backup power supply cannot be automatically switched after a fault trip, and ultimately greatly improving the power supply reliability of the low-voltage power supply and distribution system and better adapting to the application scenarios with high requirements for power supply continuity. Brief Description of the Drawings

[0018] Figure 1 It is the circuit structure diagram of the dual-power fast-switching circuit for the low-voltage power supply system of the present invention. <​​​​​​​​​​​​​The output terminals of the main power supply (three-phase AC power supply, phase line identifiers 1A, 1B, 1C) are respectively connected to the input terminals of the circuit breaker QF1. The output terminals of the circuit breaker QF1 are divided into two paths. One path is connected to the input terminals of the main contacts of the AC contactor KM1. The output terminals of the main contacts of the AC contactor KM1 are connected to the input terminals of the load, providing a main power supply path for the load. The other path draws a phase line from the output terminals of the circuit breaker QF1 and connects it to line 101. The other end of line 101 is connected to one end of the normally open contact of the current (voltage) relay KA1. The other end of the normally open contact of the relay KA1 is connected to line 103. Line 103 is connected to one end of the first auxiliary normally closed contact of the AC contactor KM2. The other end of the first auxiliary normally closed contact of the AC contactor KM2 is connected to line 105. Line 105 is connected to one end of the second auxiliary normally closed contact of the AC contactor KM2. The other end of the second auxiliary normally closed contact of the AC contactor KM2 is connected to line 107. Line 107 is connected to one end of the coil of the AC contactor KM1. The other end of the coil of the AC contactor KM1 is connected to the neutral line N. At the same time, the phase lines 1B and 1C of the main power supply are also connected to both ends of the coil of the relay KA1, forming a monitoring circuit for KA1.

[0023] The output terminals of the standby power supply (three-phase AC power supply, phase line identifiers 2A, 2B, 2C) are respectively connected to the input terminals of the circuit breaker QF2. The output terminals of the circuit breaker QF2 are divided into two paths. One path is connected to the input terminals of the main contacts of the AC contactor KM2. The output terminals of the main contacts of the AC contactor KM2 are connected to the input terminals of the load, providing a standby power supply path for the load. The other path draws a phase line from the output terminals of the circuit breaker QF2 and connects it to line 201 (corresponding to line 101 on the main power supply side). The other end of line 201 is connected to one end of the normally open contact of the current (voltage) relay KA2. The other end of the normally open contact of the relay KA2 is connected to line 203 (corresponding to line 103 on the main power supply side). Line 203 is connected to one end of the first auxiliary normally closed contact of the AC contactor KM1. The other end of the first auxiliary normally closed contact of the AC contactor KM1 is connected to line 205 (corresponding to line 105 on the main power supply side). Line 205 is connected to one end of the second auxiliary normally closed contact of the AC contactor KM1. The other end of the second auxiliary normally closed contact of the AC contactor KM1 is connected to line 207 (corresponding to line 107 on the main power supply side). Line 207 is connected to one end of the coil of the AC contactor KM2. The other end of the coil of the AC contactor KM2 is connected to the neutral line N. At the same time, the phase lines 2A and 2B of the standby power supply are also connected to both ends of the coil of the relay KA2, forming a monitoring circuit for KA2.

[0024] Primary circuit: Main power supply (1A, 1B, 1C, power supply system A) → QF1 → KM1 main contact → load; Backup power supply (2A, 2B, 2C, power supply system B) → QF2 → KM2 main contact → load; Phase verification is required before commissioning to ensure that the phase sequence of 1A-2A, 1B-2B, and 1C-2C is consistent to avoid power supply conflicts.

[0025] Secondary control loop (voltage detection and switching logic):

[0026] Main power supply side: KA1 coil is connected in parallel to the three phases of the main power supply (or power is drawn through a voltage transformer, 1B, 1C and implicit 1A phase voltage detection) to monitor the three phase voltage in real time; KM1 coil circuit: N→KM1 coil→KM2 normally closed auxiliary contact→KA1 normally open auxiliary contact→QF1 rear phase line (must meet the requirement of conducting when the three phase voltage is normal).

[0027] Backup power supply side: KA2 coil is connected in parallel with three phases of backup power supply (2A, 2B and implied 2C phase voltage detection); KM2 coil circuit: N→KM2 coil→KM1 normally closed auxiliary contact→KA2 normally open auxiliary contact→QF2 rear phase line (conducting when the three phase voltage is normal).

[0028] KM1 and KM2 auxiliary normally closed contacts are "electrical interlock" (connected in series with the other coil circuit), and KA1 and KA2 normally open contacts are "voltage condition lock" (closed when the three-phase power supply voltage is normal).

[0029] In one embodiment, the materials required for the AC contact dual power switching device are installed in a fixed base plate, according to... Figure 1 Each component is configured individually. The main circuit AC contactor uses an ABB series fast contactor, whose theoretical closing time is approximately 20ms.

[0030] Both the main power supply and the backup power supply are three-phase AC power sources. The phase lines of the main power supply are labeled 1A, 1B, and 1C, and the phase lines of the backup power supply are labeled 2A, 2B, and 2C. The main power supply and backup power supply are drawn from two different power supply systems. The main power supply has priority, and in the event of a fault, the backup power supply takes over to ensure continuous power supply to the load. Phase sequence checks are performed after power is supplied to ensure consistency, and the three-phase voltage is monitored in real time to provide a basis for switching between the main and backup power supplies. The primary circuits of the main and backup power supplies use power points from two different power supply systems to improve power supply reliability. After the main and backup power supplies supply power, phase sequence checks are performed promptly to ensure consistency between the two incoming power points.

[0031] In one embodiment, in the main power supply circuit, the auxiliary normally closed contacts of the two AC contactors KM2 are taken from the auxiliary contacts at the left and right ends of the contactors, which further ensures the reliability of the contactor operation.

[0032] In one embodiment, when selecting components, the current values ​​of circuit breakers QF1 and QF2 are less than or equal to 3A. Circuit breakers QF1 and QF2 control the on / off switching of the primary circuits of the main and backup power supplies, and also provide short-circuit and overload protection. In the event of a fault, they automatically disconnect and isolate the faulty power supply.

[0033] In one embodiment, in the main power supply circuit, the operating voltage of the relay KA1 and the operating voltage of the AC contactor KM1 simultaneously satisfy the detection of the three-phase power supply point (e.g., if the relay KA1 is AC380V, the contactor KM1 should be AC220V). In the backup power supply circuit, the operating voltage of the relay KA2 and the operating voltage of the AC contactor KM2 simultaneously satisfy the detection of the three-phase power supply point.

[0034] Relays KA1 and KA2 monitor the three-phase voltage of the main and backup power supplies. When the voltage of a phase of the main power supply is lower than the release voltage of the KM coil, relay KA1 is de-energized. Similarly, relay KA2 detects the three-phase voltage of the backup power supply, providing voltage status signals for the switching logic. AC contactors KM1 and KM2 control the primary circuit of the main and backup power supplies and the load through their main contacts. The coil voltage is controlled by the power supply and the logic of the KA relays. When a power supply is abnormal (phase voltage too low), the corresponding KM coil is de-energized, the main contacts open, and the faulty circuit is disconnected while the backup circuit is activated.

[0035] The working process of the dual power supply fast switching circuit of this invention is as follows:

[0036] (1) Normal power supply stage

[0037] When the main power supply (1A, 1B, 1C, three-phase AC power) is normal, circuit breaker QF1 is closed first. The main power supply is split into two paths through circuit breaker QF1: one path connects to the coil of relay KA1 (connected to phase lines 1B and 1C) through the output terminal of circuit breaker QF1. Relay KA1 operates upon detecting normal three-phase voltage (or current), and its normally open contact closes, connecting lines 101 and 103; the other path waits to supply power to the main contacts of AC contactor KM1 through the output terminal of circuit breaker QF1. At this time, although circuit breaker QF2 can be closed on the backup power supply side, the 2A and 2B phase lines of the backup power supply only cause relay KA2 to operate (normally open contact closes), without triggering subsequent circuits.

[0038] In the main power control circuit, current flows from the phase line of the circuit breaker QF1 output terminal into line 101, then through the normally open contact of the closed relay KA1 into line 103, and then sequentially through the two auxiliary normally closed contacts of AC contactor KM2 (corresponding to lines 103-105 and 105-107 respectively), finally flowing into one end of the coil of AC contactor KM1 through line 107. The other end of the coil of AC contactor KM1 is connected to the neutral line N, forming a complete circuit. After the coil of AC contactor KM1 is energized, it operates, its main contacts close, and the main power supply is stably delivered to the load through circuit breaker QF1 and the main contacts of AC contactor KM1, realizing priority power supply of the main power supply; at the same time, the two auxiliary normally closed contacts of AC contactor KM1 (corresponding to lines 203-205 and 205-207 on the backup power supply side) open, cutting off the control circuit of KM2 on the backup power supply side, and preventing the backup power supply from being accidentally switched on.

[0039] (2) Main power supply abnormal switching phase

[0040] When the main power supply malfunctions (e.g., a phase voltage is lower than the release value of the AC contactor KM1 coil, phase loss, or power failure), phases 1B and 1C on the main power supply side cannot provide normal operating conditions for relay KA1. Relay KA1 de-energizes and releases, its normally open contacts open, and the circuit between lines 101 and 103 is broken. The AC contactor KM1 coil loses current and is de-energized, its main contacts open, and the main power supply stops supplying power to the load. Simultaneously, the two auxiliary normally closed contacts of AC contactor KM1 (lines 203-205 and 205-207 on the backup power supply side) reopen, preparing for the backup power supply control circuit to conduct.

[0041] If the backup power supply (2A, 2B, 2C, three-phase AC power) is normal and circuit breaker QF2 is closed, the 2A and 2B phase lines of the backup power supply will keep relay KA2 in an active state, with its normally open contact closed, connecting lines 201 and 203. In the backup power supply control circuit, current flows from the phase line leading from the output terminal of circuit breaker QF2 into line 201, passes through the closed normally open contact of relay KA2 into line 203, and then sequentially passes through the two auxiliary normally closed contacts (lines 203-205 and 205-207) of AC contactor KM1, before flowing into one end of the coil of AC contactor KM2 via line 207. The other end of the coil of AC contactor KM2 is connected to the neutral line N, forming a circuit. When the coil of AC contactor KM2 is energized, the main contacts close, and the backup power supply quickly switches to the load through circuit breaker QF2 and the main contacts of AC contactor KM2 to ensure continuous power supply to the load. At the same time, the two auxiliary normally closed contacts of AC contactor KM2 (line 103-105 and line 105-107 on the main power supply side) open to prevent AC contactor KM1 from malfunctioning when the main power supply is restored.

[0042] (3) Main power restoration and reset stage

[0043] After the main power supply fault is cleared and normal operation is restored, phase lines 1B and 1C on the main power supply side resume normal operation of relay KA1. Relay KA1 operates again, its normally open contact closes, and lines 101 and 103 become conductive. However, the backup power supply is still providing normal power at this time, and AC contactor KM2 is in the operating state. Its two auxiliary normally closed contacts (lines 103-105 and 105-107 on the main power supply side) remain open, and the control circuit of AC contactor KM1 on the main power supply side remains open. AC contactor KM1 does not operate temporarily.

[0044] If main power supply needs to be restored (e.g., due to manual switching or backup power supply malfunction), when the backup power supply malfunctions, phases 2A and 2B cannot provide normal conditions for relay KA2. Relay KA2 de-energizes and releases, its normally open contact opens, the connection between lines 201 and 203 is broken, the coil of AC contactor KM2 is de-energized, its main contacts open, and the backup power supply stops supplying power to the load. Simultaneously, the two auxiliary normally closed contacts of AC contactor KM2 (lines 103-105 and 105-107 on the main power side) reopen. The control circuit of AC contactor KM1 on the main power side is re-connected through the closed normally open contact of relay KA1 and the auxiliary normally closed contact of AC contactor KM2. The coil of AC contactor KM1 is energized and operates, the main contacts close, and the main power supply resumes supplying power to the load. The circuit returns to the initial state where the main power supply has priority.

[0045] This invention can simultaneously detect the voltage values ​​of three phases in a power supply line. When the voltage value of one phase is lower than the coil voltage release value of the AC contactor, it will automatically disconnect the abnormal power supply circuit contactor and quickly and automatically connect the contactor of the other power supply circuit, greatly improving the reliability of power supply. It uses the undervoltage release auxiliary contact of the AC contactor to drive the start command of the AC contactor of the other power supply circuit for automatic closing and power supply. It is applicable to power supply (distribution) circuits with AC contactors below 630A. It is a one-time investment, easy to install, simple, reliable and easy to operate system, with wide applicability and can be integrated into configuration. It can also be widely used in electrical power distribution circuits.

[0046] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0047] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A dual-power fast switching circuit for a low-voltage power supply system, characterized in that, Includes main power supply, backup power supply, circuit breaker QF1, circuit breaker QF2, relay KA1, relay KA2, AC contactor KM1, AC contactor KM2, and load; The output terminals of the main power supply are respectively connected to the input terminals of the circuit breaker QF1. The output terminals of the circuit breaker QF1 are divided into two paths. One path is connected to the main contact input terminal of the AC contactor KM1. The main contact output terminal of the AC contactor KM1 is connected to the input terminal of the load, providing a main power supply path for the load. Another phase line is led out from the output terminal of the circuit breaker QF1 and connected to one end of the normally open contact of the relay KA1. The other end of the normally open contact of the relay KA1 is connected to one end of the first auxiliary normally closed contact of the AC contactor KM2. The other end of the first auxiliary normally closed contact of the AC contactor KM2 is connected to one end of the second auxiliary normally closed contact of the AC contactor KM2. The other end of the second auxiliary normally closed contact of the AC contactor KM2 is connected to one end of the coil of the AC contactor KM1. The other end of the coil of the AC contactor KM1 is connected to the neutral line N. At the same time, the 1B and 1C phase lines of the main power supply are also connected to the two ends of the coil of the relay KA1, forming the monitoring circuit of the relay KA1. The output terminals of the backup power supply are respectively connected to the input terminals of the circuit breaker QF2. The output terminals of the circuit breaker QF2 are divided into two paths. One path is connected to the main contact input terminal of the AC contactor KM2. The main contact output terminal of the AC contactor KM2 is connected to the input terminal of the load, providing a backup power supply path for the load. Another phase line is led out from the output terminal of the circuit breaker QF2 and connected to one end of the normally open contact of the relay KA2. The other end of the normally open contact of the relay KA2 is connected to one end of the first auxiliary normally closed contact of the AC contactor KM1. The other end of the first auxiliary normally closed contact of the AC contactor KM1 is connected to one end of the second auxiliary normally closed contact of the AC contactor KM1. The other end of the second auxiliary normally closed contact of the AC contactor KM1 is connected to one end of the coil of the AC contactor KM2. The other end of the coil of the AC contactor KM2 is connected to the neutral line N. At the same time, the 2A and 2B phase lines of the backup power supply are also connected to the two ends of the coil of the relay KA2, forming the monitoring circuit of the relay KA2.

2. The dual-power fast switching circuit for low-voltage power supply systems according to claim 1, characterized in that, Both the main power supply and the backup power supply are three-phase AC power supplies. The phase lines of the main power supply are labeled 1A, 1B, and 1C, and the phase lines of the backup power supply are labeled 2A, 2B, and 2C. The main power supply and the backup power supply are drawn from two different power supply systems. The main power supply has priority in supplying power. In the event of a failure, the backup power supply takes over to ensure continuous power supply to the load. After power is supplied, the phase sequence is checked to ensure consistency.

3. The dual-power fast switching circuit for low-voltage power supply systems according to claim 1, characterized in that, In the main power supply circuit, the auxiliary normally closed contacts of the two AC contactors KM2 are taken from the auxiliary contacts at the left and right ends of the contactor.

4. The dual-power fast switching circuit for low-voltage power supply systems according to claim 1, characterized in that, The current values ​​of circuit breakers QF1 and QF2 are less than or equal to 3A.

5. The dual-power fast switching circuit for low-voltage power supply systems according to claim 1, characterized in that, In the main power supply circuit, the operating voltage of the relay KA1 and the operating voltage of the AC contactor KM1 simultaneously satisfy the detection of the three-phase power supply point.

6. The dual-power fast switching circuit for low-voltage power supply systems according to claim 1, characterized in that, In the backup power supply circuit, the operating voltage of the relay KA2 and the operating voltage of the AC contactor KM2 simultaneously satisfy the detection of the three-phase power supply point.

7. The dual-power fast switching circuit for low-voltage power supply systems according to claim 1, characterized in that, During the normal power supply phase, when the main power supply is normal, the circuit breaker QF1 is closed, and the main power supply supplies power to the coil of the relay KA1. The normally open contact of the relay KA1 closes, the main power supply control circuit is activated, and current flows into the coil of the AC contactor KM1 through the closed normally open contact of the relay KA1 and the auxiliary normally closed contact of the AC contactor KM2, energizing the coil of the AC contactor KM1. The main contacts of the AC contactor KM1 close, and the main power supply supplies power to the load through the circuit breaker QF1 and the AC contactor KM1. At the same time, the auxiliary normally closed contact of the AC contactor KM1 opens, cutting off the control circuit of the backup power supply KM2 to prevent accidental activation of the backup power supply.

8. The dual-power fast switching circuit for a low-voltage power supply system according to claim 7, characterized in that, During the main power supply failure switching phase, if the main power supply fails, relay KA1 loses power, its normally open contact opens, and the coil of AC contactor KM1 is de-energized; the main contacts of AC contactor KM1 open, and the main power supply stops supplying power; simultaneously, the auxiliary normally closed contact of AC contactor KM1 closes again, preparing for the backup power supply circuit to conduct; if the backup power supply is normal and circuit breaker QF2 is closed, the backup power supply supplies power to the coil of relay KA2, relay KA2 operates, its normally open contact closes, the control circuit of the backup power supply is conducted, and current flows into the coil of AC contactor KM2 through the closed normally open contact of relay KA2 and the auxiliary normally closed contact of AC contactor KM1, energizing the coil of AC contactor KM2; the main contacts of AC contactor KM2 close, and the backup power supply supplies power to the load through circuit breaker QF2 and AC contactor KM2; simultaneously, the auxiliary normally closed contact of AC contactor KM2 opens to prevent the AC contactor KM1 from malfunctioning when the main power supply is restored.

9. The dual-power fast switching circuit for a low-voltage power supply system according to claim 8, characterized in that, During the main power restoration and reset phase, when the main power supply returns to normal, the relay KA1 restarts, its normally open contact closes, but the AC contactor KM2 remains operational, i.e., its auxiliary normally closed contact opens, the control circuit of the AC contactor KM1 is temporarily disconnected, and the AC contactor KM1 does not operate. If the backup power supply is abnormal, or if manually switched, the relay KA2 loses power, i.e., its normally open contact opens, the coil of the AC contactor KM2 is de-energized, its main contacts open, and the backup power supply stops supplying power. The auxiliary normally closed contact of the AC contactor KM2 closes again, the control circuit of the main power supply KM1 is activated, the coil of the AC contactor KM1 is energized and operates, its main contacts close, the main power supply resumes supplying power to the load, and the main power priority mode is restored.

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