1. According to Article 2.0. 1 of gb50052-95 Code for Design of Power Supply and Distribution Systems, it is a first-class load under any of the following circumstances:

1) When the power supply is interrupted, personal injury or death will be caused. Like a hospital.

2) The interruption of power supply will cause huge political and economic problems. For example, major equipment is damaged, important products are scrapped, a large number of products produced by important raw materials are scrapped, and the continuous production of key enterprises in the national economy is disrupted and it takes a long time to recover.

3) The interruption of power supply will affect the normal work of important power users. For example:

Important traffic hubs, communication hubs, important hotels, large stadiums, public places where a large number of people are often concentrated for international activities and other important loads in power consumption units.

Among the first-class loads, loads that cause poisoning, explosion and fire when the load is interrupted, and loads that are not allowed to interrupt power supply in particularly important places are regarded as particularly important loads. Such as: meteorological service computer system of National Meteorological Observatory; Anti-theft signals of large museums and exhibition halls, and lighting of rare exhibits showrooms; Search the computers of important libraries (hundreds of books); Main venue, reception hall, banquet hall, etc. State Guesthouse, National Great Hall and National International Convention Center.

2. Power requirements for main loads:

1) should be powered by two power supplies. When one power supply fails, the other power supply should not be damaged at the same time.

When the capacity of the first-class load equipment is 200kw or above, two high-voltage power supplies should be used, generally from two different areas of the local system. 2) When the capacity of electrical equipment requiring dual power supply is below 100kw, and it is difficult to obtain the second power supply from the regional power grid, eps or diesel generator shall be set.

3. The particularly important load in the primary load.

In addition to two power supplies, an emergency power supply should be added. Consider the case that the first power supply system is overhauled or failed, and the second power supply fails at the same time. It is forbidden to connect other loads in the circuit that supplies power to particularly important load equipment.

Secondary and secondary loads

1. In any of the following cases, it is a secondary load: Article 2.0. 1 in Code for Design of Power Supply and Distribution Systems (gb50052-95):

1) When the power supply is interrupted, it will cause great political and economic losses. For example, major equipment is damaged, a large number of products are scrapped, the continuous production process is disrupted, and it takes a long time to recover, and key enterprises have greatly reduced production.

2) Power supply interruption will affect the normal work of important power users. For example, the important power load among power users such as transportation hub and communication hub, as well as the interruption of power supply, will lead to disorder in public places where large theaters, shopping malls and other people are concentrated.

2. Power supply requirements of secondary load

The power supply and distribution system of secondary load should be able to stop or resume power supply in time when common faults occur in power transformers or lines. You can do one of the following:

1) should be powered by two loops, and the second loop can come from the regional power grid or adjacent units; You can also bring your own diesel generator set.

2) The power supply is provided by two loops, which are respectively led out by two buses of the substation in the same area.

When the load is small or the power supply in the area is difficult, the power supply can be provided by a dedicated overhead line of 6kv or above, or by two cables, each cable should be able to bear all the secondary loads.

Third, the emergency power supply:

It is a variety of power sources and is electrically independent of the power grid. There are usually the following types:

1) diesel generator set independent of normal power supply;

2) a special feed circuit independent of the normal power supply in the power supply network;

3) battery (dry battery).

In recent years, with the development of social and urban modernization and the continuous expansion of building scale, the requirements for building power supply are getting higher and higher, especially for some important public buildings. Once the power supply is interrupted, it will cause huge political impact or economic losses. The current Code for Fire Protection Design of High-rise Civil Buildings and Code for Electrical Design of Civil Buildings have strict regulations: "The first-class load should be supplied by two power sources. When one power source fails, the other power source will not be damaged at the same time. In addition to the above two power supplies, the emergency power supply must be added to the particularly important load in the first-class load. Commonly used emergency power sources are:

(1) Generator set independent of normal power supply;

(2) Dedicated power supply lines that are effectively independent of normal power supply in the power supply network;

(3) battery.