A dual power supply refers to a power supply system that is supplied by two independent power lines to the same load. These two power lines usually come from substations in different directions or from different busbars in the same substation with two or more incoming lines. One of the power sources is referred to as the primary power source, while the other serves as the standby power source. When the primary power source is operating normally, it provides power to all electronic devices and loads in the system.

However, if the primary power source fails due to voltage abnormalities or current interruptions, the control unit will detect this immediately and send a signal, after which the system will automatically switch to the standby power source to ensure continuous operation of the load. In other words, a distribution room is equipped with two independent power sources (from two different supply systems) to ensure uninterrupted power supply, referred to as a dual power supply. During normal operation, one power source supplies power while the other acts as a backup. When the primary power source fails, the standby power source is activated, providing power immediately after the outage. Such a facility is referred to as a dual power supply facility or dual power distribution to the substation. The schematic diagram is as follows:

Dual power supplies are widely used in applications requiring high-reliability power supply systems, such as communication base stations, data centers, and medical equipment. The advantages include significantly improving the reliability and stability of equipment, avoiding serious consequences such as data loss and equipment damage due to brief power outages.

To prevent dual power supply users from accidentally connecting the two power sources together (closing the circuit), causing backfeed and energizing the de-energized circuit, posing an electrical hazard to maintenance personnel working on the circuit, a manual bidirectional (dual-throw) switch should be used. This switch can only connect to one side of the power source. When one power source is activated, the other is disconnected. For dual power supply users with automatic switching devices, the two power sources on the low-voltage busbar can be controlled by two sets of devices, as shown in the diagram.

Here's a detailed analysis of the control principle of this contactor-type dual power supply: Imagine being on-site, following my thought process and operations: First, close 1QF and 2QF, then close 1S. The AC contactor closes the auxiliary contact of 2KM, connecting the 1KM main contact, and the primary power source is activated. At the same time, the auxiliary contact of 1KM opens, cutting off the 2KM circuit to prevent the secondary power source from activating. When the primary power source fails or faults occur, the 1KM main contact opens, disconnecting the primary power source from the busbar. Simultaneously, its auxiliary contact closes when closing 2S (if automatic switching to the secondary power source is required, 2S can be closed after 1KM is activated). The 2KM coil of the contactor is energized, and the 2KM main contact closes, activating the secondary power source.

The auxiliary contact of 2KM opens, ensuring the primary power source is not activated when the secondary power source is in operation. If the 1KM main contact welds or jams, it won't disconnect. At this time, its auxiliary contact in series in the contactor coil circuit remains open, preventing 2KM from closing.

What is the difference between dual power supply and dual power transfer switch?

Dual power supply mainly refers to a device or system with two power inputs. The primary purpose of this design is to ensure continuous and stable power supply. In everyday use, one power source is usually active while the other serves as a backup. When the active power source fails or is interrupted, the standby power source automatically takes over to ensure the normal operation of electrical equipment or systems.

This design is commonly found in servers, computers, and other critical equipment or systems. On the other hand, a dual power transfer switch is a device used in dual power systems to achieve automatic power switching. When the primary power source fails or there is a power outage, the dual power transfer switch can automatically detect and switch to the standby power source, ensuring uninterrupted operation of equipment or systems. This switch is often used in elevators, fire alarms, surveillance systems, etc., to maintain continuous power supply during emergencies. The physical representation is as shown in the diagram.