Dual-circuit power supply refers to two lines of equal voltage coming from two substations or two compartments of a single substation. When one line fails and loses power, the other line can be immediately switched on and put into use.
Dual power supply and dual circuit power supply are generally considered to be the same thing and are used interchangeably. However, I believe there are some differences. Dual power supply, of course, draws power from two sources (of different natures), and there are naturally two power supply lines; if "one for use and one for backup" refers to the power sources, then it is dual power supply.
If "one for use and one for backup" refers to the power supply line, then it cannot be called dual power supply. However, whether it should be called dual-circuit power supply is also a matter I personally feel is somewhat inappropriate, and I'm not sure what the correct term should be. The standard does not interpret dual-circuit power supply in this way. Dual power supply is more reliable than dual-circuit, but for a single building, the two may seem to have no difference, but in fact, there is a significant difference.
I. Dual power supply
Dual power supply means that the power is drawn from two different power sources, and there are two power supply lines. If "one for use and one for backup" refers to the power source, then it is a dual power supply.
Generally, a dual power supply may be approved if one of the following conditions is met:
(1) Important Party, government, and military organs, and key national defense and scientific research projects will suffer serious consequences due to power outages. (2) Important news and broadcasting centers, transportation and communication hubs, public utilities, and medical and health units will suffer serious consequences due to power outages. (3) Military industrial units and factories will suffer personal injury and equipment accidents, large-scale loss of raw materials, large-scale scrapping of products, production stoppages, and long-term inability to resume operations due to power outages. (4) Important public places. (5) Those with special requirements for the continuity of power supply based on the characteristics of production.
II. Dual-circuit power supply
Dual-circuit power supply refers to two lines of equal voltage coming from two substations or two sections of a single substation. When one line fails and loses power, the other line can be immediately switched on and put into operation. This is commonly used in schools and businesses for its convenience and speed. For example, the Wuhan Light Rail has two independent power stations and uses a dual-circuit power supply system, ensuring normal operation even in the event of a power outage.
If "one for use and one for backup" refers to the feeder lines, then it cannot be called dual power supply. Dual power supply is more reliable than dual circuit, but for a single building, the two may seem indistinguishable, as there are often only two incoming lines. Dual power supply can occur when the two incoming lines are connected to different regional substations; conversely, dual circuit can occur when the two incoming lines are connected to different busbars of the same regional substation. Therefore, the "circuit" in "dual circuit" refers to the circuit originating from the regional substation. Dual power supply means the power sources are different and independent; if one power source fails, the second will not fail simultaneously, thus meeting the power supply needs of primary and secondary loads. Dual circuit, on the other hand, generally refers to the end-point, where a backup circuit is activated after one line fails to supply power to the equipment. The two circuits may be from the same power source or different power sources.
III. The difference between dual power supply and dual circuit power supply
Let's start by understanding the definitions of dual power supply and dual circuit:
(1) Dual power supply: A device controlled by a microprocessor for switching between grid power and grid power or between grid power and generator power in a power grid system, which can provide continuous power supply. The two power sources come from different substations (or one power source and one generator).
(2) Dual circuit: A circuit with two power supply sources for a load. The two power sources come from the same substation and different bus sections (sometimes due to load switching, the two bus sections may be connected in parallel).
First, according to GB50052-2009, the current standard term for dual power supply is "dual power source": a load is powered by two circuits that are independent of each other for safe power supply. Second, the power source for a dual power source should be a substation within the power industry, not a substation within the project itself (the project as a whole is considered as a load). Third, the transformers for the power source must be drawn from different busbar sections. Some substations in certain areas have two transformers, but both are connected from a single busbar section, using a single busbar or single busbar segmented wiring method, which cannot be considered a dual power source. Therefore, a dual power source should be a power supply composed of power sources drawn from different busbar sections within the power industry substation. This requirement does not apply to dual circuits. Two circuits or ring networks connected from a single transformer, or two power sources connected from two transformers on the same busbar section, can all be considered dual circuits. Dual circuit power sources can only ensure the power supply needs of secondary and lower-level loads. Dual power supply involves drawing two power sources from two independent substations, or from two transformers in a single substation, each drawing a power source from its own busbar. This ensures the independence of each power source, and if one power source fails, the other can still guarantee reliable power to the building. Dual power supply can be either dual-source or single-source dual-circuit. In single-source dual-circuit supply, a failure in the power source or busbar will interrupt the power supply to the entire building.
In summary, and based on domestic experience with electricity loads, dual-circuit power supplies are primarily used for secondary loads with high power requirements, such as hospitals and banks. These systems are often designed with two power supply circuits, ensuring continuity and reliability of power supply should one power source fail. Therefore, a dual-circuit power supply uses only one power source, while a dual-power supply uses two independent power sources. Power is switched to the other power source when a fault occurs or when demand arises. Dual-power supplies are mainly used for primary loads with even higher requirements.
