Several decades ago, the "Rules for the Installation of Electrical Installations" (PUE) were formulated for the first time. From that moment on, they were often changed and supplemented, but the purpose of this document remained the same - to ensure the safety of people using various electrical installations. In particular, it spelled out which power scheme is used by a consumer or a group, and this determines the categories of power supply reliability. There are 3 groups in total.
Content
- First category
- Second category
- Third category
First category
Oftentimes, people often wonder why some electricity consumers never experience problems with their power supply. The answer to this question is given by the PUE, namely, the categories of power consumers prescribed in them for the reliability of power supply. According to the rules, for consumers of this group, power outages are unacceptable, as they will cause serious troubles:
- The appearance of a large number of defective products.
- The risks to human life are becoming extremely high.
- Disruption of the performance of expensive equipment and its failure.
- The most complex technical processes are interrupted.
- There are problems with the work of utilities.
The 1st category of power supply mainly includes industrial facilitieswhere business interruption could cause serious problems, such as stopping mine fans.
It is quite obvious that in this case, not only will the process of mining stop, but the life of the workers of the facility will also be in jeopardy.
This group mainly includes enterprises of the chemical and metallurgical industries. In other industries, the number of consumers in this group is significantly less. For example, at metallurgical enterprises with an incomplete production cycle (blast furnace shops, etc.) ) about 80% of electrical equipment is classified in the first category. In turn, at enterprises of the same industry with a full production cycle, the percentage of such electrical installations ranges from 25 to 40 percent.
When working on a project for a power supply system, it is important to study the features of the technical process of the consumer's production. It is extremely important here to consider and analyze various situations, without overestimating the capacity of the object. In addition, a backup power supply system should be provided. An example of electrical installations of this type can be the following:
- Lifting machines installed in mines for emergency evacuation of people in case of an emergency.
- Blast furnace cooling pumps.
- Sewer systems.
Second category
If there are interruptions in the power supply of representatives of this group, then electric transport may stop, massive downtime of expensive equipment, etc. 
For consumers of the 2nd category of power supply reliability, it is also necessary to provide backup power systems, but unlike the first group, power outages are possible for manual input of the emergency power supply system. In situations where the automatic reserve entry system does not require serious financial investments during its creation, it can also be used for objects of the second group.
This group is the most numerous in the entire industry. It may contain loads that are close in requirements to both the first and third groups. When creating power supply systems for consumers of this group, it is necessary to walk as carefully as possible and not to use emergency power constantly.
All these requirements are clearly spelled out in the PUE and under certain circumstances, it is allowed not to create a backup power system for category 2 of power supply. Most often, when determining the level of reliability of power supply, calculations are used that determine the minimum costs that can be obtained during production stops.
Third category
This group includes all consumers who do not fit the definition of the first two. Among them are residential buildings, as well as auxiliary production and workshops, in which there is no serial production. In accordance with the rules, the third category of reliability of power supply to consumers allows an interruption in the supply of electricity for the period necessary for repair work. In this case, the duration of the downtime should not exceed 24 hours.
During the design of power supply for consumers of this category, options should be provided laying the power grid and creating backup transformers for the possibility of quick restoration work.
Based on the requirements specified in the rules, when designing power supply systems at all facilities, it is necessary to take into account a large number of factors. Also, the PUE provides for a change in the group, but only if the technological process changes significantly.
