What is Standby Power?

Buildings with a higher level of power supply should be able to provide sufficient power under normal conditions and sufficient backup power when the power supply in normal use fails. Emergency power must also be available to ensure disaster relief and personnel evacuation. Any building needs to consume a large amount of power to be able to use and operate normally. The main source of power consumed by buildings is the national or regional power grid. When the power grid cannot guarantee power supply or has special conditions, it will also use its own small power plant as the main power source Supplementary power; in many cases, diesel generator sets and battery energy storage equipment will also be set up as backup and emergency power sources.

According to the current design code,

In general civil buildings, the power load can be divided into first, second and third load according to importance; according to the use function, it can be divided into: 1) electricity for maintaining normal work and life; 2) guaranteeing comfort Electricity; 3) Three kinds of electricity to ensure the safety of buildings and people. Although some loads have the same load level, because of different functions, the power supply considerations are different.

The 1st category of electricity includes: residential, office and commercial general work and living lighting electricity, domestic water pumps, heating power in northern winter, ordinary elevator power for non-fire fighting, etc., once the power cannot be supplied, it will affect residents Life, shopping mall operations, and normal office work are inconvenient.

The second type of electricity includes: residential and office air-conditioning, entertainment activities, ventilation in ordinary places, etc., if it cannot supply electricity, it will make people uncomfortable to a certain extent.

The third type of electricity includes: smoke exhaust fans, stair pressurized fans, fire elevators, fire pumps and personnel evacuation lighting used in various places during fires. If the power supply cannot be guaranteed, it will cause great safety risks. And even directly cause accidents, threatening the safety of buildings and people.

Of the above three types of loads, the third type of load is related to the safety of the building and personnel, and electricity must be guaranteed; when the power supply of the power grid cannot meet the needs, an emergency power supply must be provided.

1) The power supply such as domestic water pumps to maintain normal life in the load, heating power in northern winter, and ordinary elevator power for non-fire protection are as important as fire power, and power should be guaranteed; when the power supply of the grid cannot meet the needs , Need to set a backup power.

The general working and lighting power of the first type of load and the second type of load can selectively supply standby power.

In many cases, the power supply of the power grid cannot meet the requirements of building power consumption. At this time, the internal power supply needs to be set up as a backup and emergency power supply. The first consideration was the use of diesel generators.

The role and scope of use of a diesel engine determines the capacity of the diesel generator set. In most cases, the generator set doubles as an emergency power source and a backup power source, and its capacity needs to be considered to meet different needs. The capacity of a generator that doubles as an emergency power source and a backup power source should be greater than the capacity required to maintain normal domestic electricity loads. Its emergency output capacity should be greater than the capacity required for emergency loads such as firefighting. Special care should be taken when selecting a generator. : 1) The rated output capacity of a diesel generator set is not the same as the emergency output capacity, the former is about 10% larger than the latter; 2) The total capacity of the load carried by the generator should be less than its nominal value. Needed wealth.

In modern buildings, because of the importance of certain buildings, a lot of computers are used in many buildings, and many places have high requirements for the continuity of power supply. For example: airports, railways, banks, hospitals, important office buildings, important conference centers and other important places and general building fire and security systems, computer rooms, and so on. Such occasions not only require the provision of sufficient backup power, but also have higher requirements for the conversion time of electrical energy. For such places, in addition to providing the necessary backup power, a UPS uninterruptible power supply system that is stored by the battery should be set according to the equipment's requirements for electrical energy conversion time. The conversion time of the uninterruptible power system must meet the minimum allowable power outage time of the equipment Requirements, places with extremely high time requirements can be powered by floating charging.

The advantages of diesel generators are very obvious. As long as the diesel can ensure the supply, it can supply reliable electrical energy for a long time. This advantage is particularly important in the fields of field operations, disaster relief, and other areas where power supply cannot be guaranteed. In many cases, the reliability of diesel generator power is much higher than that of grid power.

However, the disadvantages of diesel generators are as obvious as the advantages: 1) The generator requires sufficient oxygen to operate, and the smoke generated by fuel oil seriously pollutes the air. To set up a generator in a building, it is necessary to consider the intake air, exhaust air, smoke exhaust channels and smoke removal. Equipment, in areas with strong environmental protection awareness, it is also required that the smoke exhaust outlet must be at the highest wind direction of the building group, which brings some trouble to the building design; 2) The noise and vibration generated by the generator during operation pollute the environment, and the rooms around the generator room are used Limited; 3) Long start-up time of the generator set cannot meet the power conversion time requirements of some equipment.

then

Battery as power source

In actual engineering, power supply schemes are different, and each power supply scheme has different power distribution schemes to choose from:

Solution 1: Power supply scheme for Class I and II loads that are powered by two high-voltage power sources and not provided with emergency power sources such as generator sets: Transformers should be arranged in groups, and the number of transformers in each group should not be excessive. They should be powered by different high-voltage lines. The two lines of each important load respectively lead to transformers powered by different high-voltage lines.

Option 2: Power supply scheme for one or two loads that are powered by one high-voltage power source and set emergency power sources such as generator sets: two lines for each important load, one from the transformer and one from the generator.

Option 3: Power supply scheme for the first and second loads that are powered by two high-voltage power sources and set emergency power sources such as generator sets: It can be the same as the second option. Two lines of each important load are routed from the transformer and one route. Since the generator.

Option 4: For the power supply scheme of the first and second-stage loads that are powered by two high-voltage power sources and set emergency power sources such as generator sets, this solution can also be adopted: transformers are arranged in groups, and each group has a transformer (tentatively called Backup transformer) The low-voltage side and the diesel generator are connected by a self-throwing and self-resetting dual power transfer switch. After the switch, a separate bus section is formed. The emergency or backup power for all important loads of this transformer group is derived from the bus section Note that the power supply capacity of the standby transformer should not be less than the power supply capacity of the generator. I often use the fourth option in the design. I once set six transformers in a project as a group.

Solution four has obvious advantages over solution three: first, each transformer with an important load in solution three cannot be powered for any reason, and the generator must be started. Solution four is only started if the backup transformer cannot supply power. The starting conditions for diesel generators are simplified, and the number of generator starts is reduced. Second, if the transformer with important loads and the standby transformer can be powered by different high-voltage power supplies, the important loads will have two power grids and generator power triple. Guaranteed, the reliability of power supply is the best; Third, when the dual load monitoring system with important loads is used, only two power sources can be effectively monitored under normal conditions. The third option of this condition is impossible.

For the power supply scheme with only one high-voltage power supply and no emergency power supply such as a generator set, the two power supplies of the second-level important load should be led from different transformers as much as possible.

In actual projects, diesel generators are generally selected as backup (emergency) power sources, UPS is used as a guaranteed power source for computer loads, and a certain number of emergency lamps powered by EPS or batteries are provided.

EPS has brought new options to designers. Some designers use EPS as a backup power source. Although this has great benefits, its own limitations limit its use.

For Class I or II buildings with two power sources, the power level is relatively high. EPS is actually used as a backup power source or an emergency fire power source. The power supply time required for fire protection equipment in general projects is not too long, and the longest (rooms that need to be illuminated during a fire) does not exceed 3 hours. In this case, using EPS is naturally a good choice; but if it is only one power supply For second-class buildings, standby (emergency) is used in most cases as a backup power source for non-firefighting loads such as elevators, domestic water pumps, sewage pumps, etc. The failure time of the main power source is difficult to determine, the use time of the backup power source is unpredictable, and EPS is used as a backup (Emergency) The power supply is not sufficient. Even if you increase the number of batteries, you can still only supply power for a limited time and still cannot meet the need for backup power.