Consumer power categories

According to PUE, all consumers of electric energy are conditionally divided into three categories (groups), depending on their importance. In this case, we are talking about how reliable the consumer's energy supply should be, taking into account all possible factors. Here are the characteristics of each of the consumer power categories and the corresponding requirements for the reliability of their power supply.

First category

The first category of power supply includes the most important consumers, the interruption of the power supply to which can lead to accidents, major accidents, causing major material damage due to the failure of entire sets of equipment, interconnected systems. These users include:

• mining, chemical and other hazardous industries;

• important health facilities (intensive care units, large dispensaries, maternity wards, etc.) and other state institutions;

• boilers, pumping stations of the first category, interruption of the power supply, which leads to the failure of the city's life support systems;

• traction substations of urban electrified transport;

• communication installations, dispatch centers of city systems, server rooms;

• elevators, fire detection devices, fire protection devices, burglar alarms in large buildings with a large number of people in them.

Consumers in this category must be powered by two independent power sources — two power lines fed by separate power transformers. The most dangerous users can have a third independent power supply for greater reliability. Interruption of power to users of the first category is allowed only for the time of automatic switching on of the backup power source.

Depending on the user's power, an electrical wire, battery or diesel generator can act as a backup power source.

PUE defines an independent power supply as a source in which the voltage after an emergency mode is stored within the specified limits when it disappears on a different power source. Independent feeders include two sections or bus systems of one or two power plants or substations, subject to the following two conditions:

• each of the sections or bus systems is in turn powered by an independent power source,

• sections (systems) of tires are not connected to each other or have a connection that is automatically broken when the normal robots of one of the sections (systems) of tires.

Second category

The second category of supply includes consumers when the power is turned off, the operation of important city systems stops, there is a huge product defect in production, there is a risk of failure of large interconnected systems and production cycles.

In addition to enterprises, the second category of power supply includes:

• children's institutions;

• medical facilities and pharmacies;

• city ​​institutions, educational institutions, large shopping centers, sports facilities where there may be a large crowd of people;

• all boiler and pumping stations, except those belonging to the first category.

The second power category provides users with power from two independent sources. In this case, a power outage is allowed during which time the electrical service personnel will arrive at the facility and perform the necessary operational switching.

Third category

The third category of electricity supply to consumers includes all other consumers that are not included in the first two categories. Usually these are small settlements, urban institutions, systems, the interruption of the power supply does not lead to consequences. Also, this category includes residential buildings, private sector, rural and garage cooperatives.

Consumers of the third category are powered by one power source. Interruption of power supply to consumers of this category, as a rule, is no more than one day — for the duration of emergency restoration works.

When dividing users into categories, many factors are taken into account, possible risks are assessed and the most reliable and optimal options are selected.

Maximum permissible number of hours of disconnection per year and terms for restoring the power supply

Electricity issues, including power supply reliability, are defined in the customer's contract with the electricity company.The contract establishes a permissible number of outage hours per year and periods for power restoration (this is actually the permissible duration of a power outage according to PUE).

For I and II categories of reliability, the permissible number of hours of disconnection per year and the terms for restoring the power supply are determined by the parties depending on the specific parameters of the power supply scheme, availability of backup power supplies and functions technological process of the user, but there cannot be more than the predicted corresponding values ​​III reliability category, for which the permissible number of hours of shutdown per year is 72 hours (but not more than 24 hours in a row, including the period of power restoration).

What gives the division of users into categories

Dividing consumers into categories, first of all, allows you to correctly design a certain section of the electrical network, connect it to the unified power system. The main goal is to build the most efficient network, which, on the one hand, should fully meet the power needs of all users, meet the requirements for power reliability, and on the other hand, be simplified as much as possible with in order to optimize the means of maintenance and repair of networks.

During the operation of electrical networks, the division of consumers into power supply categories allows maintaining the stability of the interconnected power system in the event of a power shortage due to a shutdown of the power plant unit or a serious accident in the main networks.In this case, automatic devices work, which disconnect users of the third category from the network, and in case of a large shortage of energy - from the second category.

These measures make it possible to keep the most important users of the first category in operation and to avoid man-made disasters on a regional scale, loss of human life, accidents in individual facilities and material damage.

In home power supply systems, the most commonly used principle of hot standby mode: the power of transformers TP, GPP (and the throughput of the entire supply circuit to them) is selected more than required by maintaining a normal mode, to ensure power supply electric receivers I and II category in emergency mode, when as a result of which one power supply circuit fails (or scheduled shutdown).

The cold reserve, as a rule, is not used (although it is more profitable from the point of view of overall performance), the current one, as provided for automatically turning on network elements under load without preliminary tests.