Selection of protection devices

1.3. Selecting electrical apparatus and conductors Scope of application, general requirements for 57. What is the choice of electrical apparatus using the conditions of long modes? Answer. It consists in the selection of their rated voltage by the level of insulation and the nominal current

1.4. Checking electrical apparatus and conductors under the conditions of short circuit. Application area, definition of 74. What electrical devices and conductors are considered persistent with KZ? Answer. These are considered, which under the calculated conditions of the KZ are kept

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1.1 Introduction. 3.

5.1 General. eighteen

5.3.8 Protective glasses. 25.

6. Appendix. 27.

Introduction

Checking knowledge of PTE staff.

Divided into:

1. primary;

2. Periodic;

3. Extraordinary.

Periodic The inspection is subject to:

· Personnel engaged in the exploitation of electrical installations, as well as the leading and engineering and technical composition, organizing their operation - 1 time per year;

· Guideline and engineering composition, not referring to the previous group, but in which electrical installations are conducted - 1 time in three years.

Primary The first of the periodic checks is called.

Extraordinary Checking knowledge is subject to:

· Persons who allowed PTE violations, PTEEP, MPOT, official or operational instructions;

· Persons who have a break in the work on this electrical installation of more than 6 months;

· Persons translated into a new electrical installation;

· Persons on the prescription of the management of the enterprise or on the prescription of the Inspector of Energy Pressor.

Production of shutdowns.

There should be disconnected to the current parts on which work, as well as those that can be accessed when performing work.

Available contacting uninsulated current-carrying parts can not be disconnected if they are securely fenced with insulating overlays of dry insulating materials.

The disconnection should be done in such a way that the part of the electrical installation or electrical equipment allocated to perform the part of the electrical installation or electrical equipment were separated from the current-carrying parts that are under voltage, switching devices or removing fuses, as well as disconnecting the ends of cables (wires) by which voltage can be supplied to Place of work.

Disabling can be performed:

1. Hand-controlled switching devices, the position of the contacts of which can be seen with front face Or it can be installed by examining panels on the back, opening of flaps, removal of housings. Perform these operations is necessary in compliance with security measures. If there is a complete confidence that the switching devices with closed contacts, the position of the handle or pointer corresponds to the contact position, then it is allowed not to remove the housings to check the shutdown;

2. Contactors or other switching devices with automatic drive and remote control with accessible contacts after accepting measures that eliminate the possibility of erroneous inclusion (removal of operational fuses, disconnecting the ends of the coil).

The procedure for checking the disconnected state of switching apparatuses is established by a person outstanding or a disposal.

To prevent voltage to the place of work due to the transformation, all-related power, measuring and various special transformers from both the highest and low voltage should be turned off due to the repair of electrical equipment from both the highest and low voltage.

In cases where the work is performed without the use of portable grounds, additional measures must be taken, preventing erroneous voltage supply to the place of operation: mechanical locking of the drives of the disabled devices, additional removal of the fuses convertible with switching machines, the use of insulating overlays in the switches, automata, etc. P. These technical measures should be specified when issuing a job job. If it is impossible to adopt the specified additional measures, the ends of feed or exhaust lines on the shield, assembly or directly on the place of work should be disconnected; When disconnecting the cable with the fourth (zero) residential, this core should be disconnected from the zero tire.

Navigation.

Earth imposition sites.

Groundings should be applied to current parts of all phases disconnected to produce the operation of the electrical installation site from all sides, from where the voltage can be supplied, including due to the inverse transformation.

Support is sufficient on each side of one ground. These grounding can be separated from current-handing parts or equipment on which work is performed, disconnected disconnectors, switches, automata or removed fuses.

The imposition of grounds directly to the current parts on which work is performed is required when these parts may be under induced voltage (potential) or there may be a voltage from an extraneous source of a hazardous amount. Earth embedding sites should be chosen so that the grounding is separated by a visible gap from the current-carrying parts under the voltage. When using portable groundings, their installation places should be at such a distance from the current-carrying parts remaining under the voltage so that the entry of the grounds is safe.

When working on team tires, it must be imposed at least one grounding.

In closed distribution devices Portable groundings should be superimposed on the current parts in the places installed for this. These places should be cleaned of paint and bordered with black stripes.

In all electrical installations of the attachment of portable grounds to grounding wiring, paint should be cleaned and adapted to secure the portable grounding clamp or on this wiring there should be clips (lamb).

In electrical installations, the design of which is such that the entry of grounding is dangerous or impossible (for example, in some distribution cells, the Crue of individual types, etc.), additional security measures must be taken when preparing the workplace, eliminating the random voltage supply to the place of work. These measures include: locking the drive of the disconnector on the lock, the fencing of knives or the upper contacts of the specified devices with rubber caps or rigid linings from insulating material.

The list of such electrical installations should be determined and approved by the main energy level (the person responsible for the electroactivity).

Earth imposition is not required when working on equipment, if tires, wires and cables for which voltage can be fed from it from all sides, if the voltage can be supplied to it by reverse transformation or from an extraneous source, and provided that There is no voltage on this hardware. The ends of the disconnected cable at the same time must be closed in short and grounded.

General.

Protective means are called devices, devices, portable and transported devices and devices, as well as individual parts of devices, devices and devices that serve to protect staff operating on electrical installations, from electric shock, from exposure to electric arc, its combustion products, etc. .

The protective means applied in electrical installations include:

· Insulating operational rods, insulating pullers for operations with fuses, voltage pointers to determine the presence of voltage;

· Insulating stairs, insulating sites, insulating traction, grippers and tools with handles isolated;

· Rubber dielectric gloves, bots, galoishes, mats, insulating stands;

· Portable grounding;

· Temporary fences, preventive posters, insulating caps and lining;

· Safety glasses, tarpaulin mittens, filtering and insulating gas masks, safety belts, insisting ropes.

Insulating protective remedies serve to isolation of a person from current-carrying parts of electrical equipment that are under voltage, as well as for isolation of a person from the ground. Insulating protective agents are divided:

· Main protective equipment;

· For additional protective equipment.

Basic These protective agents are called, the isolation of which reliably maintains the operating voltage of electrical installations and with which the current-carrying parts are allowed to be concerned.

The test voltage for the main protective agents depends on the operating voltage of the installation and there must be at least three-time values \u200b\u200bof the linear voltage in electrical installations with an isolated neutral or with a neutral turret through a compensating machine, and at least three-time phase voltage in electrical installations with a deaf-free neutral.

Additional These protective equipment are called, which themselves cannot at this voltage to ensure safety from lesion and are only an additional measure of protection against fixed assets. They also serve to protect against tension, step stress and an additional protective agent for protection against exposure to electrical arc and products.

Additional insulating protective agents are tested by voltage independent of the voltage of the electrical installation in which they should be applied.

The main insulating protective means used in electrical installations with a voltage up to 1000 volts includes:

· Dielectric gloves;

· Instrument with isolated handles;

· Voltage pointers.

Additional insulating protective means used in electrical installations with voltage up to 1000 volts include:

· Dielectric bots;

· Dielectric rubber mats;

· Insulating stands.

Selection of certain insulating protective equipment for use during operational switching or repair work Regulated by the safety regulations during the operation of electrical installations and power lines and special instructions for performing individual works.

Portable fences, insulating overlays, insulating caps, temporary portable grounding and warning posters are designed to temporarily fencing current parts, as well as to prevent erroneous operations with switching machines.

Auxiliary protective facilities are intended for individual protection of working from light, thermal and mechanical effects. These include protective glasses, gas masks, mittens, etc.

Requirements for certain types of protective equipment and rules for use.

Dielectric gloves.

For work in electrical installations, only dielectric gloves made in compliance with the requirements of guests or technical conditions is allowed. Gloves intended for other purposes (chemical and other), apply as a protective agent when working in electrical installations is prohibited.

Dielectric gloves issued to maintain electrical installations must be several sizes. The length of the glove should be at least 350 mm. Gloves should be put on their hands on their full depths. It is not allowed to repair the edges of the gloves or drop the sleeves on top of them. When working on open air in winter time Dielectric gloves wear on top of wool. Each time the gloves must be checked for tightness by filling them with air.

Dielectric mats.

Dielectric mats are allowed as an additional protective agent in closed electrical installations of any voltage during operations with disconnectors drives, switches and trust-adjusting equipment. Dielectric mats are an insulating agent only in a dry state. Instead of rugs, insulating supports should be used in the premises of raw and with plenty of dust.

Dielectric mats should be made in accordance with the requirements of guests at least 50 × 50 cm. The top surface of the rug should be corrugated.

Control lamps.

The control lamp must be enclosed in the fittings of the insulating material with the slot for the light signal. Conductors should have a length of no more than 0.5 m and extinguish from the reinforcement into different holes in order to eliminate the possibility of closure when they pass in general input. Conductors must be securely insulated, be flexible and have hard electrodes protected in free ends, protected by insulated handles. The length of the nude end of the electrode should not exceed 1 - 2 cm.

Portable grounding.

Portable groundings in the absence of stationary grounding knives are the most reliable means of protection when working on disabled areas of equipment or line in case of erroneous voltage supply to a disconnected area or appeared on it induced voltage.

Portable groundings consist of the following parts:

· Earth wires and to shorten the current parts of all three phases of installation. It is allowed to use a separate portable grounding for each phase;

· Clips for connecting grounding wires to the grounding bus and short-circuit wires to the current-generating parts.

Portable groundings must satisfy the following conditions:

· Wires for shorting and grounding should be made of flexible uninsulated copper livers and have a cross section that meets the requirements of thermal stability with short circuits, but not less than 25 mm 2 in electrical installations with a voltage above 1000 volts and at least 16 mm 2 in electrical installations up to 1000 volts ; In networks with a grounded neutral cross section of wires should meet the requirements of thermal stability with a single-phase short circuit;

· Clamps for attaching short-circuit wires to tires should be such a design so that when the short circuit current passes, the portable grounding could not be reduced from the place of electrodynamic effort. Clamps should have a device that allows them to impose, fixing and removing from tires with a rod to impose a ground. Flexible copper wire must join directly to the clamp without a transition tip;

· The tip on the ground wire must be made in the form of a clamp or match the clamp design (lamb) serving to attach to grounding wiring or design;

· All attachments of portable grounding elements must be made firmly and securely by pressing, welding or rolling with subsequent soldering. Applying single soldering is prohibited.

Portable grounds before each installation must be viewed. When detecting the destruction of contact compounds, violations mechanical strength Conductors, melting, cliff live, etc. Portable grounding should be seized from application.

When grounding, you first attach the grounding wire to the "Earth", then check the absence of voltage on grounded current-handing parts, after which the wiring clips with the rod are imposed on the current-carrying parts and secure there with the same barbell or hands in dielectric gloves. Removing the ground is made in reverse order. All overlay operations and removal of portable grounds must be performed using dielectric gloves.

Warning posters.

Warning posters should be used to prevent the danger of approximation to parts under voltage, to prohibit the operating with switching devices that the voltage may be sent to work to work, to indicate the working personally prepared for the work of the seat and for reminder of the measures taken .

Posters are divided into four groups:

1. warning;

3. Allowers;

4. Remind.

By the nature of the application, posters can be permanent portable.

Portable warning posters are made of insulating or poorly conductive electric current (cardboard, plywood, plastic materials).

Permanent posters should be made of tin or plastic materials.

Protective glasses.

Protective glasses are used at:

1. Works without removal of voltage near and on current-carrying parts that are under voltage, including when changing fuses;

2. Cutting cables and autopsy couplings on cable lines in operation;

3. soldering, welding (on wires, tires, cables, etc.), cooking and warming up the mastic and pouring it cable couplings, inputs, etc.;

4. Dockey and grinding rings and collectors;

5. Working with electrolyte and maintenance rechargeable batteries;

6. Sharpening the tool and other works related to the danger of eye damage.

It is allowed to apply only glasses made in accordance with the requirements of guests.

Application.

Literature: "Methods for selecting conductors and protection equipment when connecting electrical receivers", TOE.

Question number 70.Calculate which current consumes a 100 watt lamp at a network voltage 36 and 220 volts. What power is available on each lamp if two lamps 220 V 100 watts are activated in series in a 220 volt network? Draw a scheme.

Question number 71.Calculate the current consumed by a three-phase electric motor if the data is indicated on its name: U \u003d 380 V, P \u003d 3 kW, Cos J \u003d 0.85, H \u003d 0.95. What is H?

Question number 72.When the segment is turned on, the PNSV-1'1.2 wire is 28 meters long and 3 ohm resistance to the linear voltage of TP current in the wire is 15 amps. What should be the length of the segments of the wire so that you can connect them to the star (three) and the current in the wire remained the same (15 amps)?

Question number 73.At the voltage u \u003d 80 volts in the segment of the PNSV-1'1.2 wire, a length of 28 meters and the resistance of 3.7 Ohm current is 15 amps. What should be the length of the wire so that the current in it remains the same at a voltage of 36 volts?

Question number 74.Three lamps are connected to the star, the total point is connected to zero. The current in the phases is 3 amperes. How will the current change in the phases, if one of the lamps permits? How will the current change in the zero wire?

Question number 75.What is the value of the insulation resistance of the extension 220 volts should fall, so that a single-phase UzO is 30 mA is guaranteed to turn off the line?

Question number 76.Determine which power is released in an active symmetric three-phase load with a linear voltage of 42 volts and a linear current of ampere.

The document is provided by the site http://note-s.narod.ru

Rules for the technical operation of consumer electrical installations.

Electrical safety regulations.

Inter-sectoral rules for labor protection.

PTB - safety regulations.

Clampographer As applied to voltage indexes, a resistor is called a limiting (limiting) maximum current through the device.

Dielectric - not conductive (poorly conductive) electric current.

1. Basic requirements for organizing safe operation of electrical installations. 3.

1.1 Introduction. 3.

1.2 Personnel requirements serving electrical installation. 3.

2. Qualification groups for electrical safety. four

2.1 Check knowledge of PTE staff. five

3. Electrical safety in current electrical installations up to 1000 volts. Manufacturing jobs. 6.

3.1 Technical measures to ensure the safety of stress removal. 7.

3.1.1 Production of shutdowns. eight

3.1.2 Highlighting the warning posters, the fence of the place of work. nine

3.1.3 Checking the absence of voltage. nine

3.1.4 Seating grounds. 10

3.2 Organizational activities ensuring the safety of work. 12

3.2.1 Outfit, disposal, current operation. 12

3.3 Events that ensure the safety of work without removal of voltage near and on current-carrying parts under voltage. 13

4. Production of individual types of work. fourteen

4.1 Measurement of insulation resistance by portable megommeters. fourteen

4.2 PTE in the production of works by power tools and portable luminaires. fifteen

4.2.1 Choosing a power tool protection class depending on the working conditions. fifteen

4.2.2 Connecting and rules for performing work with power tools. fifteen

4.2.3 Responsibilities of the employee issuing an outfit (order) to perform the work of the power tools. sixteen

5. Rules for the use of protective agents used in electrical installations. eighteen

5.1 General. eighteen

5.2 General rules Use protective means. nineteen

5.3 Requirements for certain types of protective facilities and rules for use. twenty

5.3.1 Dielectric gloves. twenty

5.3.2 Dielectric bots and galoishes. twenty

5.3.3 Dielectric mats. 21.

5.3.4 Instrument with isolated handles. 21.

5.3.5 Voltage pointers up to 500 volts operating on the principle of active current flow. 22.

5.3.6 Portable grounding. 24.

5.3.7 Warning posters. 25.

5.3.8 Protective glasses. 25.

5.3.9 Safety belts, Monterix claws, insisting ropes and stairs. 26.

6. Appendix. 27.

6.1 Classification of premises (works) by the degree of danger of electric shock. 27.

6.2 Classification of electrical products. 28.

6.3 List of exam questions on the 3rd electrical safety group. 29.

6.3.1 Topic: "Knowledge of the device serviced equipment and rules of its operation - Uzo". 29.

6.3.2 Topic: "Knowledge of rules for using protective means." 29.

6.3.3 Topic: "Knowledge of PTE, PTEEP and MPOTS in terms of organizational and technical measures that ensure the safety of work." thirty

6.3.4 Topic: " Separate species works - power tools, megommeters. " thirty

6.3.5 Topic: "Elementary knowledge of electrical engineering". 31.

1. Basic requirements for organizing safe operation of electrical installations.

Introduction

The present toolkit Designed for the preparation of electrical personnel workers on a 3-group electrical safety (with tolerance to 1000 volts) based on active PTEEP, PTE and MPOT.

Requirements for personnel serving electrical installation.

The personnel serving the electrical installation, in the part, for him relating, should know:

· Rules for the technical operation of consumer electrical installations (PTEEP);

· Rules of electrical installation devices (PUE);

· Manuals on the device and operation of the electrical installations fixed behind it;

· Property and operational instructions in relation to the position and work being held;

· Rules for the release of a person from the effect of electric current;

· Rules for first aid victim from electric current.

Qualification groups for electrical safety.

Mon2-600-630A-y3-KEAZ Ine \u003d 597A shutdown current 630

In the event of operational (technological) overloads and emergency modes, which are a consequence of the disorders of the scheme, the electrical circuits of the emergency circuit flow current, superior to the nominal values \u200b\u200bfor which electrical equipment is calculated.

As a result of the impact of emergency currents and overheating of current wires is broken electrical insulation, burn and melted contact surfaces of connecting tires and electrical apparatus. Electrodynamic strikes cause damage to tires, insulators and reactor windings.

To limit the amplitude of emergency currents and the duration of their flow, special devices and electrical equipment protection systems are used. Protection devices must turn off the emergency chain earlier than the individual elements may fail.

With large overloads or short circuit, the defense device must immediately turn off the entire electrical installation or part of it with maximum speed to ensure further performance or if the accident is a consequence of failure of one of the elements of the chain, prevent failure of other electrical equipment.

In the case of small overloads that are not dangerous to equipment for a certain time, the protection system can affect the warning signaling for the information of the service personnel or on the automatic control system to reduce the current.

Since the main factor leading to the failure of electrical equipment is the thermal action effect, on the principle of construction, protective devices are divided into current and thermal.

Current protective devices control values \u200b\u200bor ratios of values \u200b\u200bflowing through the equipment of currents.

Thermal protective devices measure the temperature of electrical equipment directly.

Semiconductor devices have a low overload capacity compared to other power equipment, and increased requirements for the protection devices and other converters are made to the device for protecting semiconductor rectifiers. Protective devices in installations with semiconductor rectifiers are selected based on the permissible overload characteristics of power diodes or thyristors, taking into account the fact that it will be defended by other equipment in the circuit of the accident, since it has a greater overload capacity.

The use of certain means of protection is determined by the parameters of the power circuit of the converter and the overload capacity of semiconductor devices.

Regardless of the installation parameters and the type of protective devices and systems used, the following general protection requirements allocate.

1. Speed \u200b\u200b- ensuring the minimum possible response time of protection that does not exceed the permissible.

2. Selectivity. Emergency shutdown should be carried out only in the chain where the cause of the accident occurred. And other sections of the power chain should remain in operation.

3. Electrodynamic resistance. The maximum current limited by protective devices should not exceed the value of electrodynamic resistance for this electrical installation.

4. Overvoltage levels. Disabling emergency current should not cause overvoltages dangerous for semiconductor devices.

5. Reliability. Protection devices should not fail when disabling emergency currents.

6. Noise immunity. When interference appears on the network of your own needs and in the control circuits, the defense device should not be partitioned false.

7. Sensitivity. Protection should be triggered with all damage and currents dangerous for semiconductor devices, regardless of the place and nature of the accident.

Select fuses.

Fuses are selected under the following conditions:

1) on nominal voltage network:

URD. \u003e \u003d UD.,

where is the UAV. - nominal fuse voltage;

UD - nominal network voltage;

2) by long-term estimated current line;

Ine. Will. \u003e \u003d Idlt. ;

where I is. Will. - the rated current of the melting insert;

IDLIT - long calculated circuit current.

In addition, when using the rapid fuses, the fuses should not be burned from the short-term current impetus, for example, from the launchers of electric motors. Therefore, when choosing fuses of such electrical receivers, the following condition is also necessary:

Ine. Will. \u003e \u003d ID / 3.1,

where the IP is the starting current of the engine.

Often there is a need to protect the main line, which feeds a group of electric motors, and some of them or they can all be allowed simultaneously. In this case, the fuses are selected according to the following ratio:

Ine. Will. \u003e \u003d IKR / 3.1 (at easy starting conditions)

Ine. Will. \u003e \u003d Ikr / (1.5 - 2) (with severe starting conditions),

where IKR \u003d i'put + i'Dlit is the maximum short-term current line;

I'put - starting current of the electric motor or group at the same time included engines, when starting which a short-term current line reaches the greatest value;

I'Dlit is a long-term settlement current of the line until the start of the electric motor (or the electric motors group) is determined without taking into account the operating current of the used electric motor (or group of engines).

For three-phase electrical receivers of alternating current;

wherein is the nominal power of the electrical receiving (or group of electrical receivers), kW; U - rated voltage (for alternating current electrical applicants - linear voltage of the network), kV;

- Power factor; - efficiency efficiency.

Select circuit breakers.

The choice of circuit breakers is made according to the rated voltage and current in compliance. the following conditions:

UD.A. \u003e \u003d UD.; Ine. \u003e \u003d IDLIT;

where u is. - nominal voltage of the circuit breaker;

UD - nominal network voltage; Where is Ine.A. - nominal circuit of the circuit breaker; IDLIT - long calculated circuit current.

In addition, it is necessary to be correctly selected: the rated current of the release of the IOIN.; The current of the installation of the electromagnetic element of the combined release of the IUT.EL.MAGN; The rated current of the setpoint of the thermal release or the thermal element of the combined release - IU.U.Text.

The rated currents of the electromagnetic, thermal or combined release must be at least the rated motor current:

Ine. \u003e \u003d Ine.DV.

The installation of the electromagnetic release (cut-off) or the electromagnetic element of the combined release taking into account the inaccuracy of the response and deviations of the actual

starting current from celibory data is selected from the condition

Iust.el.Magn. \u003e \u003d 1.25 IP. \u003d 1.25 3.1 7 \u003d 27 and Ip \u003d 7 i

where i will - Engine starting current.

Rated current installation of a thermal release or a thermal element of a combined release:

IT.Ust.tepl. \u003e \u003d Ine.DV.

Also select the installation of circuit breakers and to protect the circuits of other electrical acceptors of the power supply system, such as chains of control - measuring instruments et al. (if there is a need for this, since in most cases to protect devices and other similar electrical receivers low power For considerations of sensitivity it turns out to be necessary to apply fuses). It should be borne in mind that if the circuit breaker with an electromagnetic release is installed in the circuits of electrical receivers, when the starting current drops do not arise, then there is no need to adjust from the latter and the installation current of the electromagnetic release in this case should be selected as minimally possible.

Selection of thermal relays of magnetic starters.

Thermal relays are selected by the rated current of the engine (or long-term calculated current):

IT.T.R\u003e \u003d IU.DV. ;

When choosing a heat relay, it is necessary to strive to ensure that the installation current is in the center of the regulatory range.

Results of calculation and selection of protection devices.

Analysis of failures and non-standard modes of electrical machinery allows you to allocate the following types of accidents, often occurring in practice:

Short circuit (KZ) on the clips of the machine or in the stator winding;

The inhibited rotor when starting the engine (MOG mode mode, especially often occurs when it is directly started);

Open phase of the stator winding (often occurs when the windings are protected by fuses);

Technological overloads arising when load sketch during the engine operation;

Cooling disorder caused by system malfunction forced ventilation engine;

Reducing the insulation resistance that occurs as a result of aging isolation due to cyclic temperature overloads.

Emergency regimes in chains asynchronous engine There may be either a short-term increase in current in 12 ... 17 times compared with nominal or long-term current flow, in 5 ... 7 times higher than its nominal value.

To protect the electrical circuits from the CZ mode, circuit breakers, current relays and fuses are widely used. When overcurrent, the current requires other protective equipment. Thus, when one of the phases of an asynchronous engine is most effective, minimal current and temperature protection are the most effective; less efficient but efficient - heavy protection (thermal relays). With the inverted rotor, the maximum current relays and temperature protection are very effective, less efficient - thermal protection. When overloading, the best results gives temperature protection. Thermal relays are also effective. With engine cooling violation, only temperature protection can prevent an accident.

Reducing the insulation resistance of the engine stator winding can trigger both overload in the chain and KZ.

Protection with such an accident is carried out by special devices for monitoring the insulation of the engine winding.

The main emergency mode in the lighting installations is KZ. Overload protection is required only for lighting plants operated indoors and explosion and fire-hazardous medium. The most common protection device of the lighting settings is the circuit breaker. When inclusion of incandescent bulbs, a short-term flow of current appears, at 10 ... 20 times higher than the rated current. Approximately 0.06 with current decreases to nominal. The value of the current throw is determined by the power of the lamps. When choosing a type of incandescent lamp protection, it is necessary to take into account the features of their starting characteristics.

Due to the wide distribution of power semiconductor equipment, it requires the use of efficient devices. One of the main deficiencies of power semiconductor devices is their low current overload capacity, which imposes harsh conditions on the protection equipment (by speed, selectivity and trigger reliability). Currently, high-speed circuit breakers, semiconductor switches, vacuum switches, pulsed arc switches, high-speed fuses, etc. are used to protect power semiconductor devices (both external and internal), high-speed fuses, etc. The conditions for their operation.

Special place is occupied by the protection of electrical chains. Currently, networks are widely used from 0.4 to 750 square meters. The main, most dangerous and frequent types of damage in the networks are CZ between the phases and the closure of the phase to the Earth.

The main mass of consumers is powered by the distribution networks with a voltage of 0.4; 6 and 10 kV (recently found wide application 0.66 kV voltage network). To power stationary power consumers and lighting installations general purpose The three-phase four-wire networks of 380/220 V with a deaf-free neutral are used. Power consumers are connected to linear stresses of the network, and lighting - to phase. Powerful power consumers, such as electric motors with a capacity of 160 kW and above, have voltages 0.66; 6 and 10 square meters.

The main emergency modes in such networks are: single-phase KZ (up to 60% of accidents), three-phase KZ (up to 10%), two-phase KZ to Earth (up to 20%), two-phase KZ (up to 10%).

Protection electrical networks Voltage up to 1000 V is carried out, as a rule, devices are sewn, and the voltage network over 1000 V has relay protection.

The most common network protection devices are circuit breakers and fuses. If you need to have protection with high speed, sensitivity or selectivity, then apply relay protection, made on the basis of relays and circuit breakers.

Electrical networks voltage up to 1000 in indoors should also have overload protection, made, as a rule, on the basis of circuit breakers with thermal or combined releases.

The main task facing the choice of consumer protection and electrical networks is the coordination of the characteristics of protection devices with utmost load characteristics (depending on the permissible current from the duration of its flow) of various consumers and networks (wires and cables). For each specific type of consumers, the most complete negotiation can be achieved when using a specific type of protection devices. In the event of a complete matching, the voltamper and temporal characteristics of the protection device on the chart pass higher and as close as possible to the load characteristic of the consumer.

1. Requirements presented when choosing protection equipment.

When choosing the protection devices for onboard electrical networks, the following requirements are presented:

1. Protection devices must reliably work and disconnect the electrical circuits with short and unacceptable overloads and should not give false positives in normal modes.

2. When triggered, protection devices must act on shutdown, while the action must be irreversible (it should not be automatic re-enabled after eliminating overload or KZ). Reinforcement should be done manually.

3. Protection devices must provide selective (selective) disconnection of the circuit area with KZ. At the same time, intact sections of the power supply system should not be disconnected. In the event of a KZ in the network of the power supply system, protection devices must only make those shutdowns that are necessary to eliminate KZ.

4. The sensitivity of the protection devices should be sufficient to work when the smallest force Current of the KZ in the protection zone and with dangerous overloads.

5. Protection devices in AC power supply systems should react to all types of KZ: single-phase, two-phase and three-phase.

6. AC lines that feed directly consumers for which non-non-phase modes are not allowed should be protected by three-phase machines.

7. Protection devices should have sufficient speed in order to ensure the smallest time break of consumers, preventing the emergence of a fire or damage to the elements of the power supply system and disrupt the stability of its work.

8. To protect the AC and DC networks, protection devices allowed for use in newly developed and modifiable products should be used.

Note. Basically, the vehicle protection vehicles with free discharge should be applied. The automata without free discharge is allowed to be applied in cases where there is no free-length protection automata with the required characteristics.

9. Protection devices must be selected:

- on the rated voltage of the chain;

- largest and character of current load.

10. The selected protection devices must provide wire protection.

11. The selected protection devices must be checked:

- on resistance to CW currents (on electrodynamic, thermal stability and switching capacity);

- on the selectivity of the triggering with KZ;

- on sensitivity to current CW.

Note. The devices intended to protect the emergency power supply system in power supply from emergency sources, no resistance to CW currents are not checked. This check is performed when the system is powered from the main sources. .

2. Methods for selecting protection equipment.

Protection devices in primary distribution networks must be selected taking into account the long-term maximum current strength, the number of channels of the split line, taking into account the unevenness of the current distribution in the wires of the split lines.

The nominal force of the current of the protection of one channel of the split line of the primary distribution network is determined by the formula

where I N.A. - nominal strength of the current of the dismissal line protection, and;

I L. - current strength line, and;

a.- coefficient of non-uniformity spending, for onboard networks is taken equal to 1.075;

n. - number of split line channels;

k. - Number of backup channels.

Consider the methodology for selecting protection devices for the secondary distribution network, which is known to provide power to electricity consumers directly from tires and the CIA.

Electricity consumer feeders protection devices must be chosen based on the condition of ensuring the normal operation of consumers at a current in a circuit equal to or less than its nominal value, as well as with non-hazardous overloads (for example, when starting the engine) in different conditions ambient (Temperature, vacuum).

Note. Consumer protection in technically reasonable cases should be provided for by the developer of these consumers.

To protect chains, protection devices must be selected with a rated voltage equal to or more of the rated voltage of the protected chain.

Apparatuses for protecting consumer feeders need to be chosen based on the nature of the work of consumers.

By the nature of the work of electricity consumers are divided into two main groups:

- consumers who do not have currents of a large continuous starting force and overload current (lighting devices, heating devices, transformers, aggregate control circuits, contactors, relays, etc.);

- electricity consumers, including electric motors (various electromechanisms, fuel and oil pumps, electric transducers, fans, etc.).

For consumer feeders who do not have a large current starting force, the nominal strength of the current protection devices should be equal to the rated strength of the consumer current or have a greater value to it:

I N.A.³ I N.Pot, (2)

where I N.Pot - Nominal consumer current, A.

For consumer feeders, including engines with prolonged and short-term operation, protection devices must be selected in accordance with the terms:

where t Start. MAX - the time at which the rms of the consumer's rms value has the maximum value, C;

- the response time of the protection apparatus by time-current (also called the ampere-second) characteristic for environmental conditions in which the protection device is located at a current equal I cf.kv. MAX, C;

I cf.kv. max - maximum rms value of the launcher current, A.

t Start. Max I. I cf.kv. Max is determined by the curve of changes in the range of the consumer current in time. The root-mean-square starting force for any time of time is determined from the waveform of the power current of the current stream (Fig. 1)

according to the formula

where n T. - the amount of equal intervals in the portion T curve of the change strength during start;

I 1, ..., I NT - average values \u200b\u200bof current strength in the intervals in the section of the curve, A.

Note. With approximate calculations, the value I cf.kv. Max for alternating current engines with start time< 1 сек может быть принято равным 0,9 I start. (I start. - the value of the starting force of the motor current specified in technical conditions on them), t Start. Max can be taken equal to 0.5 s.

All of the above is illustrated. 2a and 2b.

For consumers of the second group, it is recommended to use thermal protection machines. This is explained by the protection of such consumers the fuses have significant disadvantages. Show it. In fig. 3 shows the ampere-second characteristics of the protection and fuse machine with the same rated current selected by condition (3). From the figure it is clear that the condition (3) is satisfied for the protection machine, because t A1 (AZ)\u003e T Start. Max, and for the fuse - no, because t a1 (pr)< t пуск. Max.

If you still need to select a fuse, then to perform condition (2), it is necessary to increase the rated current of the fuse. Then condition (2) will be recorded as I N.Pr1\u003e I N.Pot. And the ampere-second characteristic of such a fuse (PR1) will be shifted to the right (Fig. 4) with respect to the initially selected fuse PR and now condition (3) is performed, i.e.

t A1 (PR1)\u003e T Start. Max. But such a solution has a significant drawback. Let there be a current overload I dried., ie . I N.PR1\u003e I HERE. \u003e I n.pot.

This will lead to the fact that I N.PR1\u003e Ipr1 fuse will not work. But because I dried. \u003e I n.pot., Due to overload, the consumer fails. Thus in the range of currents I N.Pr1.< I > I N.Pot. The consumer is not protected. Therefore, fuses are recommended to be installed in chains where there is no overload.

If for any reason you have to put fuses, they must be selected so that the maximum meaning of the ranges of the current streams of currents does not exceed half the strength of the operation of the fuses defined by the protective characteristic during the time equal to t Start. MAX, i.e.

in accordance with Fig. 2b.

To protect consumer feeders with a re-short-term or pulsed load, the nominal strength of the current protection devices should be selected from the condition:

where I cf.kv.u. - the standard consumer current for the cycle of re-short-term or pulsed load, and;

The response time of the protection apparatus by time and current characteristic for environmental conditions in which the protection device is located, with ( I cf.kv.u.) Max;

(t U.) max - the time at which the rms momentum of the pulse or re-short-term load has the maximum value, C;

(I cf.kv.u.) Max - maximum value of the average mean value of the current pulse or re-short-term load, A.

(t U.) Max and ( I cf.kv.u.) Max are determined by the curve of changes in the range of current load current over time. For any time ( I cf.kv.u.) T. Determined from the oscillogram of the current force of the pulse or re-short-term load by the formula:

where I cf.kv. 1 ,…,I cf.kv.k. - the mean meanwearing values \u200b\u200bof the pulse current strength, and;

t. 1 ,…,t K. - pulse duration, C;

t C. - time cycle of the action of impulse or re-short-term

load.

I cf.kv. 1 ,…,I cf.kv.k. Defined by a formula, similar to (4), with n in this case will indicate the amount of equal intervals on the pulse current section.

Fuses should be selected so that the maximum values \u200b\u200bof the mean meanwearing current of the pulse or re-short-term load current did not exceed half the strength of the operation of the fuses defined by the protective characteristic during the time equal to (T U) Max (Fig. 5).

To protect feeders that feed the consumer group, the nominal strength of the current protection devices should be selected taking into account the rated current of consumer current and the simultaneity of their work in accordance with the condition:

where I N.Pot. - Nominal strength of current at the same time working consumers.