Power supply to electrical receivers second. Power supply reliability categories. Classification of electrical energy receivers and their general characteristics
All possible consumers of electricity can be divided into categories, in accordance with the need to ensure and guaranteed supply of electricity.
For example, the requirements for the reliability of power supply to residential buildings may differ significantly from similar schemes for special facilities. An example is a special “power supply” system for fire extinguishing pumping equipment, which requires the performance of its basic functions even in the absence of power.
Timely supply of electricity to various consumers requires a certain priority, as well as compliance with relevant reliability standards.
Based on these parameters, the corresponding power supply categories were developed. Their main characteristics are specified in rules for electrical installations (clause 1.2.18).
It is here that the main categories of energy consumption are highlighted, providing a certain advantage for some consumers:
- First and special group first category (especially important “non-switchable” consumers);
- Second category(the consumer can be disconnected for no more than an hour);
- Third category(the consumer may be disconnected for the period of restoration and repair work).
In the lists first category (PUE clause 1. 2. 19) there are energy consumers, the interruption of power supply to which can lead to danger to the lives of the population, serious material damage (for example, failure of expensive equipment or disruption of a complex technological process), as well as to negative social processes in the event of a failure of public services.
First of all, this category is represented by the so-called “responsible consumers”:
- emergency lighting;
- security and fire alarm systems;
- fire fighting pumps, etc.
This also includes a special group whose uninterrupted supply of electricity ensures a sharp reduction in the risk of serious fires, explosions and, accordingly, human casualties.
For the operation of such power consumers, it is necessary to provide at least two independent and, at the same time, redundant sources of electricity, providing for their automatic switching.
Typically, such power circuits involve the interconnection of two independent sources. The failure of one initiates automatic connection of the second source. The switching time between sources is usually from 0.3 s to 3 seconds (operating time). Options for backup connection of diesel generators or batteries are possible.
Typically, such sources are used as the third mandatory element of the circuit, providing the necessary reliability.
Second category (simply important, PUE clause 1. 2 .20) includes electricity consumers for whom a sudden power outage can lead to massive defects in production and/or long-term downtime, as well as disruption of the normal mode of life of large groups of the population in urban and/or rural areas.
This group also provides for two independent sources of electricity that insure each other, but a certain time is allowed for transferring the network to a backup source of supply (for example, for the duty personnel to carry out the necessary switches manually).
Complain
Section 1. General rules
Chapter 1.2. Power supply and electrical networks
Categories of electrical receivers and ensuring reliability of power supply
1.2.17. Categories of power receivers for reliability of power supply are determined during the design of the power supply system on the basis of regulatory documentation, as well as the technological part of the project.
1.2.18. With regard to ensuring the reliability of power supply, power receivers are divided into the following three categories.
Electrical receivers of the first category are electrical receivers, the interruption of power supply to which may entail a danger to human life, a threat to state security, significant material damage, disruption of a complex technological process, disruption of the functioning of particularly important elements of public utilities, communications and television facilities.
From the first category of electrical receivers, a special group of electrical receivers is distinguished, the uninterrupted operation of which is necessary for an accident-free shutdown of production in order to prevent threats to human life, explosions and fires.
Electrical receivers of the second category are electrical consumers whose power supply interruption leads to a massive undersupply of products, massive downtime of workers, machinery and industrial transport, disruption of the normal activities of a significant number of urban and rural residents.
Electrical receivers of the third category - all other electrical consumers that do not fall within the definitions of the first and second categories.
1.2.19. Electric receivers of the first category in normal modes must be provided with electricity from two independent, mutually redundant power sources, and an interruption in their power supply in the event of a power failure from one of the power sources can be allowed only for the duration of automatic power restoration.
To supply power to a special group of electrical receivers of the first category, additional power must be provided from a third independent, mutually redundant power source.
As a third independent power source for a special group of electrical receivers and as a second independent power source for the remaining electrical receivers of the first category, local power plants, power plants of power systems (in particular, generator voltage buses), uninterruptible power supply units intended for these purposes, batteries and etc.
If power supply redundancy cannot ensure the continuity of the technological process or if power supply redundancy is not economically feasible, technological redundancy must be implemented, for example, by installing mutually redundant technological units, special devices for accident-free shutdown of the technological process, operating in the event of a power supply failure.
If feasibility studies are available, it is recommended that the power supply to power receivers of the first category with a particularly complex continuous technological process require a long time to restore normal operation from two independent mutually redundant power sources, which are subject to additional requirements determined by the features of the technological process.
1.2.20. Electrical receivers of the second category in normal modes must be provided with electricity from two independent, mutually redundant power sources.
I. Not bad
Ph.D., technical director of the business group "Center-SB",
Lead technical engineer support from Poliset-SB LLC
As you know, this year there was a complete update of the regulatory framework defining the requirements for fire alarm and fire extinguishing systems: Federal Law No. 123-FZ “Technical Regulations on Fire Safety Requirements” came into force, GOST R 53325-2009 “Fire fighting equipment” came into force . Fire automatic equipment. General technical requirements. Test methods". In the Code of Practice SP 5.13130.2009 “Fire protection systems. Fire alarm and fire extinguishing installations are automatic. Design Norms and Rules” there is a section “Power supply of fire alarm systems and fire extinguishing installations” and a separate Code of Practice SP 6.13130.2009 “Fire protection systems. Electrical equipment. Fire safety requirements." In addition, the PUE (seventh edition, 2002) is in force - Rules for the construction of electrical installations, which are referenced in SP 5.13130.2009. Let's consider what requirements these documents impose on power supplies, and try to determine their physical meaning and the possibilities of practical implementation.
CATEGORIES OF ELECTRICAL RECEIVERS BY POWER SUPPLY RELIABILITY
In the PUE, Chapter 1.2, all electrical receivers (devices, units and other consumers of electricity) to ensure the reliability of power supply are divided into categories I, II and III, in addition, a special group of electrical receivers is allocated in category I. Category I includes electrical receivers, “an interruption in the power supply of which may entail a danger to human life, a threat to state security, significant material damage, disruption of a complex technological process, disruption of the functioning of particularly important elements of public utilities, communications and television facilities.” A special group of category I includes electrical receivers, “the uninterrupted operation of which is necessary for an accident-free shutdown of production in order to prevent a threat to human life, explosions and fires.” Category II is “electrical receivers whose power supply interruption leads to a massive undersupply of products, massive downtime of workers, machinery and industrial transport, disruption of the normal activities of a significant number of urban and rural residents,” and all other electrical receivers are included in category III.
For each category of power receivers, the PUE defines requirements for the reliability of power supply. Electric receivers of category I “must be provided with electricity from two independent, mutually redundant power sources...”, and for electrical receivers of a special group of category I, “additional power must be provided from a third independent, mutually redundant power source,” which ensures even higher reliability of power supply. Electric receivers of category II also “must be provided with electricity from two independent mutually redundant power sources,” however, if for category I automatic power restoration must be ensured, then for category II interruptions in power supply are allowed for the time necessary to turn on the backup power by the actions of duty personnel or field operations brigades. And for category III, power supply “can be provided from a single power source, provided that power supply interruptions necessary to repair or replace a damaged element of the power supply system do not exceed 1 day.”
Thus, if for electrical receivers of categories II and III in the PUE, significant interruptions in the power supply are allowed, determined by the inclusion of backup power in manual mode and the time of troubleshooting, then for electrical receivers of category I it is stated that “an interruption in their power supply in the event of a failure of power supply from one of the power sources may be allowed only for the duration of automatic power restoration.”
POWER SUPPLY FOR FIRE PROTECTION SYSTEMS
In general, the PUE prescribes determining the category of power receivers in the process of designing a power supply system. Codes of rules SP 5.13130.2009 in clause 15.1 and SP 6.13130.2009 in clause 4.2 indicate that “in terms of the degree of ensuring reliability of power supply, electrical receivers of automatic fire extinguishing installations and fire alarm systems should be classified as category I according to the Rules for the Construction of Electrical Installations, with the exception of compressor electric motors , drainage and foam concentrate pumps belonging to the III category of power supply, as well as the cases specified in 15.3, 15.4 (4.3, 4.4).” Indeed, as a result of a power outage to fire alarm and fire extinguishing systems, a real danger to human life is created and significant material damage is possible.
Further, in clause 15.2 it is stated that “power supply to electrical receivers should be carried out in accordance with the PUE, taking into account the requirements of 15.3, 15.4.” The PUE clause 1.2.10 gives the definition of an independent power source - this is “a power source on which the voltage is maintained in a post-emergency mode within regulated limits when it disappears from another or other power sources.” According to clause 1.2.19 of the PUE, local power plants, power plants of power systems (in particular, generator voltage busbars), uninterruptible power supply units intended for these purposes, batteries, etc. can be used as an independent power source for “electrical receivers of category I”. » Codes of rules SP 5.13130.2009, SP 6.13130.2009 also allow powering automatic fire extinguishing installations and fire alarm systems “from one source - from different transformers of a two-transformer substation or from two nearby single-transformer substations connected to different supply lines laid along different routes, with an automatic transfer device, usually on the low voltage side.” At facilities of the III category of power supply reliability, if there is one power source, “it is allowed to use electric storage batteries or uninterruptible power units as a backup power source, which must provide power to the specified power receivers in standby mode for 24 hours...”, then the requirements diverge: “plus 1 hour” according to SP 5.13130.2009, but “plus 3 hours” according to SP 6.13130.2009, “operation of the fire automatic system in emergency mode.” However, in both joint ventures “it is allowed to limit the operating time of the backup source in alarm mode to 1.3 times the time the fire automatic system performs tasks.” Thus, in order to meet the requirements of the PUE for providing power supply of the I reliability category at the III reliability category facilities, it is necessary to use at least two power sources: the main network and backup battery, with monitoring of the performance of each source, including in terms of sufficient battery capacity, and with automatic activation of a backup source in the event of a power failure from the network source, both when the network is disconnected and when it malfunctions.
Previously valid NPB 86-2000 “DC power supplies for fire protection equipment. General technical requirements. Test Methods" determined the requirements only for DC power supplies, and issues of power backup were practically not considered. Although it was noted that the source must have indicators of connection to electrical networks, that it may contain a battery, etc. There was no requirement to specify the backup time when operating on battery power. Obviously, it was implied that redundancy issues should be addressed during the system design process. The average time between failures of a DC source, according to NPB 86-2000, must be at least 40,000 hours, which is a little more than 4.5 years, and the service life of the battery also usually does not exceed 4-5 years. Thus, during a service life of about 10 years, you can count on several failures of the mains power supply, battery, or both.
For example, consider the operation of an uninterruptible power supply certified according to NPB 86-2000. We can assume that it is powered from two independent power supply sources: a ~220 V network and a battery, which is allowed at facilities of category III power supply reliability. But if the source itself fails, its replacement with subsequent repairs is required. Thus, the reliability of power supply is reduced, at least, to category II in the presence of spare parts and on-duty personnel authorized to carry out repair work, or when an operational team arrives at any time of the day and on any day of the week. In most cases, power supply restoration will not occur even within 24 hours (and taking into account weekends, within several days), i.e. In reality, the reliability of power supply does not even correspond to category III. In addition, according to NPB 86-2000, the power source with the battery must generate a fault signal for some reason at the minimum value of the battery voltage specified in the TD for the battery, i.e. when the backup period has already ended and when the system power is turned off, a fault signal is automatically generated at the monitoring station.
SOURCES OF THE I CATEGORY OF POWER SUPPLY RELIABILITY
The new GOST R 53325-2009 introduces the concept of “source of category I reliability of power supply to fire protection equipment”, the definition of which is devoted to the entire 5th section. It is natural to assume that these sources of category I power supply reliability should ensure the reliability of power supply of category I and they can be used to power power receivers of category I, including fire protection equipment. The requirements state that these sources must be powered “from a minimum of two independent power supply sources (main and backup (standby))” and that they “must provide uninterrupted power supply to fire protection equipment in the event of a malfunction of the main or backup (backup) power supply sources.” However, GOST R 53325-2009 does not say anything about its own reliability; it only states that it “must be designed for round-the-clock continuous operation”, “must be a repairable and serviceable product” and that its average service life “must be at least 10 years". There is no required minimum mean time between failures of a power supply reliability category I source.
However, despite the use of the phrase “I category of power supply reliability” in the name of the sources, the fire protection means themselves remain category I electrical receivers and must be provided with power without interruption, and not just the power source. The inclusion of a power supply of category I power supply reliability between independent power supplies and fire protection equipment should not reduce the category of their power supply.
According to GOST R 53325-2009, in the power supply reliability category I source, the requirement for automatic generation of a fault signal at a minimum value of battery voltage is retained, but the requirement is added to “ensure the possibility of transmitting information to external circuits about the absence of output voltage and input voltage of power supply at any input,” which will allow you to take timely actions when switching to backup power, and not when the entire system is de-energized. In addition, optical indicators must be provided for “the presence (within normal limits) of main and backup or reserve power supplies (separately for each power supply input) and the presence of output voltage.”
The technical documentation, along with the rated value of the output voltage and its permissible deviation and other characteristics, must indicate the current consumed by the source from the main and backup or standby power sources at maximum current in the output power circuit and in the absence of load, evaluate the efficiency of the source and power dissipation at various operating modes.
However, even if all the requirements of GOST R 53325-2009 are met in a power supply of category I power supply reliability, a significant reduction in the battery capacity during operation is possible and it is possible to disconnect power from the battery if the network source malfunctions, which eliminates redundancy until the power source is replaced. If a malfunction occurs in a network power supply of power supply reliability category I, the system must be supplied with power from the battery, as well as when one of the power supply sources is disconnected, so that the power supply reliability does not decrease. On the other hand, if the charging system, the battery capacity and the degree of its reduction during operation, as well as the performance of a second independent source, are not controlled, there is a high probability that the required backup time will not be available when the main power supply is turned off.
Returning to the requirements of the PUE regarding the reliability of power supply of Category I automatic fire extinguishing installations and fire alarm systems, “an interruption in the power supply of which may entail a danger to human life, a threat to state security, significant material damage...”, they “must be provided with electricity from two independent mutually redundant power sources,” rather than from one power source of uncertain reliability with a battery of unknown capacity. Thus, a paradoxical situation arises when a source of “I” category of reliability of power supply for fire protection equipment according to GOST R 53325-2009 does not provide reliability of power supply of “I” category according to PUE. In this case, you can use known methods to increase the reliability of devices, for example, to increase the reliability of the power supply, you can use two power supplies in hot standby mode. Of course, fire protection systems must also have the technical ability to connect several independent power sources to achieve category I power supply reliability. That is, to have appropriate inputs, which is already being done in practice. For example, the security and fire alarm control devices “Signal-20P” and “Signal-20P SMD” each have two 12/24 V power inputs, which allow you to connect two independent power sources (Fig. 1), one of which is modest marked as "optional". This ensures redundancy of the sources themselves, and it is possible to disconnect and replace a faulty power source, replace batteries, etc. without disrupting the system. Of course, to implement all functions, the system must have “Fault” signal outputs from each source, not shown in the diagram.
The power inputs are isolated by diodes (Fig. 2), and the power supply with the higher output voltage is always under load. This ensures backup of the sources in any operating mode; if the mains power is turned off, the backup time will be determined by the total capacity of the batteries of both power sources, i.e. Battery backup is also provided. Of course, it is possible to use other methods to improve power supply reliability.
Undoubtedly, the positive side of the new regulatory documents issued in accordance with the Technical Regulations on Fire Safety Requirements is that the vital importance of fire protection systems and the high reliability of their power supply are once again emphasized. The class of power sources for fire protection equipment has expanded significantly, the requirements for them have increased, etc. However, we should not forget that the requirement to classify electrical receivers of automatic fire extinguishing installations and fire alarm systems as Category I of the degree of ensuring the reliability of power supply according to the Rules for the Construction of Electrical Installations was also contained in all respects the well-known NPB 88-2001 and NPB 88-2001*, and power supplies have been successfully certified according to NPB 86-2000.
Rice. 1. Connection diagram of two power supplies to the control panel “Signal-20P”, “Signal-20P SMD”
Rice. 2. Isolation of two inputs of power supplies using diodes
Uninterrupted power supply– this is the absence of undersupply of energy and power to the consumer. Compliance with this requirement guarantees that the consumer receives the required amount of electrical energy and power. The system must have enough station capacity, the networks must transmit the necessary energy, and there must be an appropriate supply of fuel. Continuity will whistle from the entire range of capabilities of system objects. During the development of the system and during its operation, such system parameters are determined that ensure uninterrupted power supply.
Reliability- This is a guarantee of uninterrupted operation.
From the point of view of ensuring reliable and uninterrupted power supply, electricity receivers are divided into three categories (PUE 1.2.17-1.2.20):
Electrical receivers 1 category– these are electronic devices, the interruption of power supply of which may entail a danger to human life, a threat to the security of the state, significant material damage, disruption of a complex technological process, disruption of the functioning of particularly important elements of public utilities, communications and television facilities.
These are electricity consumers such as large metallurgical plants, chemical enterprises with a continuous production cycle, livestock farms, hospitals, water supply, and sewerage. The issue of reliability of power supply to consumers is related to the number of independent power sources, power supply scheme and category of consumers. Receivers of the 1st category must have at least two independent power supplies with an ATS of no more than 1 s. (two-transformer substation; power system and factory thermal power plant), power supply via single-circuit lines.
Two or more power sources are called independent if a violation of the regime or damage to one of them does not result in the failure of the other.
Among the electrical receivers of the 1st category, it stands out special group electrical receivers, the uninterrupted operation of which is necessary for an accident-free shutdown of production in order to prevent a threat to human life, explosions and fires.
These are, for example, circulation pumps in nuclear reactors, control systems at petrochemical plants. For a special group, a third independent power source (diesel generator, battery) must be provided. If it is not possible to achieve absolute failure-free operation with reserves, technological redundancy and accident-free production shutdown devices are used.
Electrical receivers 2 categories– electrical receivers, an interruption in the power supply of which leads to a massive shortage of products, massive downtime of workers, machinery and industrial transport, disruption of the normal life of a significant number of urban and rural residents.
In category 2 electrical equipment, the power supply can be interrupted from 3 hours to a day and must be provided through two independent inputs, but the reserve can be turned on manually. These are, for example, mechanical engineering factories, houses with electric stoves. Receivers of the 2nd category can have one or two independent power sources (this is decided depending on the importance that a given industrial enterprise has in the country’s economy and local conditions). Power supply to electrical receivers of this category is allowed via one overhead line, or one cable line with two or more cables, or through one transformer, if it is possible to carry out emergency repairs in it or replace a damaged transformer from a centralized reserve in no more than 1 day.
Electrical receivers 3 categories– these are electronic signatures that do not fall under the definition of categories 1 and 2. For example, receivers of auxiliary workshops that do not determine the technological process of the main production.
Electric power supply of category 3 electrical equipment can be provided from a single power source if the repair or replacement of damaged equipment does not exceed 1 day. But if, according to local conditions, it is possible to provide power without significant costs from a second source, then power backup is also used for this category of receivers.
Reliability of power supply is ensured by the creation of an appropriate circuit (circuit reliability), the use of appropriate units, switching devices, transformers (hardware reliability). It is achieved through the design of equipment and its proper operation. Reliability is also related to modes (mode reliability), which requires the selection of informed decisions on the use of equipment, stations and systems, ensuring system stability, etc.
Reliability and continuity come with costs. The higher these requirements, the more money needs to be invested in appropriate technology.
The most significant reduction in reliability occurs as a result of system failures, which can be very severe. However, the probability of such accidents is low, and it is not economically justifiable to provide an extremely high level of reliability in these rare cases. It is better to allow a power outage. It is important that the consumer knows what level of reliability is guaranteed. If a consumer demands an individually high level of reliability, then they have to pay for it.
There are two fundamental approaches to assessing the reliability of power supply systems. The first is based on regulatory documents (PUE, GOST), in which all electrical receivers are divided into three categories. The implementation of this approach in the formation of SES does not formally present any difficulties. However, as a rule, consumers belonging to different categories are connected to network nodes. At the same time, if you focus on the least responsible consumers (choose the simplest and cheapest scheme), then the most responsible consumers will not be provided with the required level of reliability. If you rely on them when choosing a scheme, this can lead to unjustified complication and increase in cost of the SES scheme. It should also be taken into account that the requirements of the PUE were formulated in relation to a centralized economy, based on global economic interests. Of course, in market economic conditions, these requirements must be preserved in relation to at least cases of power supply interruption that lead to danger to human life, explosions, fires and, possibly, other adverse consequences.
The second approach involves an economic (quantitative) assessment of the undersupply of electricity - economic damage due to the undersupply of electricity. It is recommended to be used primarily in cases where the compared variants of SES schemes differ significantly in the reliability of power supply, as well as for assessing measures aimed at increasing reliability. The disadvantage of this approach is the ambiguity (inaccuracy) of the numerical values of specific losses from the undersupply of electricity to consumers.
In market conditions, the economic interests of individual organizations come to the fore: the electricity supply (electricity supplier) and the electricity consumer. In relation to the electricity supply organization, economic damage will manifest itself due to loss of profit due to undersupply of electricity due to interruptions in power supply, penalties from consumers for undersupply of electricity, additional costs for emergency repairs of damaged network elements, etc. Also in industrialized countries with market economies, it is considered acceptable assessment of economic damage caused to society by power outages.
Typically, a power system selects an appropriate level of reliability based on customer requirements. They are determined during a design accident, for which reliability standards are established, for example, for the stability of power systems. It is believed that electrical power elements and the system should provide a reliability level of 0.9 - 0.99 during operation. For consumers of a special group of category 1, the reliability level is 0.999. But it is well known that even at this calculated level, accidents are possible (Chernobyl nuclear power plant). Technology can never be absolutely reliable. When determining the reliability level, the safety of equipment, especially expensive equipment, is guaranteed.
Of course, there are cases when super-severe accidents occur in the energy system and then all reliability guarantees are violated. But protecting consumers completely from such accidents is not economically feasible. Although after such severe accidents, certain measures to improve reliability should be taken.
To ensure reliability, there are reserves: when transmitting energy along power lines, when choosing transformer power, switching devices, and station capacities. EPS always has an emergency power reserve. Maintaining a reserve requires certain costs both during the creation of the system and during its operation. Obviously, costs depend on the category of consumers in terms of reliability and, accordingly, should be taken into account in the electricity tariff.
For the normal operation of an industrial enterprise, in addition to power supply reliability, it is important to maintain voltage and frequency stability.
Several decades ago, the “Rules for the Construction of Electrical Installations” (RUE) were first formulated. 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 states which power supply scheme is used by the consumer or group, and this determines the categories of power supply reliability. There are 3 groups in total.
First category
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 receivers prescribed in them for the reliability of power supply. In accordance with the rules, power outages are unacceptable for consumers in this group, as they will cause serious trouble:
- The appearance of a large number of defective products.
- The risks to human life are becoming extremely high.
- Malfunction of expensive equipment and its failure.
- The most complex technical processes are interrupted.
- Problems arise with the work of public utilities.
Category 1 of power supply mainly includes industrial facilities, the cessation of activity at which can cause serious problems, for example, stopping the mine fans.
It is quite obvious that in this case, not only will the mining process stop, but also the lives of the facility’s workers will be at risk.
This group mainly includes enterprises in the chemical and metallurgical industries. In other industries, the number of consumers in the group under consideration is significantly smaller. 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.
While working on a power supply system project, it is important to study the features of the consumer's manufacturing process. Here it is extremely important 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 may be the following:
- Lifting machines installed in mines for emergency evacuation of people in the event of an emergency.
- Blast furnace cooling pumps.
- Sewage systems.
Second category
If there are interruptions in the power supply to representatives of this group, then electric transport may stop, massive downtime of expensive equipment, etc. 
For consumers of category 2 power supply reliability, it is also necessary to provide backup power systems, but unlike the first group, interruptions in the power supply are possible for manual entry of the emergency power supply system. In situations where an automatic reserve entry system does not require serious financial investments during its creation, it can also be used for objects of the second group.
In the entire industry, this group is the most numerous. It may contain loads that are close in requirements to both the first and third groups. When creating power supply systems for consumers in this group, you must be as careful as possible and not constantly use emergency power.
All these requirements are clearly stated in the PUE and, under certain circumstances, backup power systems for category 2 power supply may not be created. Most often, when determining the level of reliability of energy supply, calculations are used that determine the minimum costs that can be obtained during production shutdowns.
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 mass production. In accordance with the rules, the third category of reliability of power supply to consumers allows for an interruption in the supply of electricity for the period necessary to carry out repair work. In this case, the duration of downtime should not exceed 24 hours.
When designing power supplies for consumers in this category, options for laying out the power network and creating backup transformers should be provided to allow for 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. The PUE also provides for a group change, but only if the technological process changes significantly.
