Astana-2005

MINISTRY OF AGRICULTURE OF THE REPUBLIC OF KAZAKHSTAN

KAZAKH STATE AGROTECHNICAL UNIVERSITY

THEM. S. SEIFULLINA

Sorokin V.G., Nogai A.S., Ansabekova G.N.,

TUTORIAL

« Techniques for constructing and reading electrical diagrams»

for energy specialties: 2102, 2104, 2105.

Astana - 2005

Reviewed and approved “I approve”

For publication at a meeting of the educational

State Agrotechnical University named after. S.Seifullina

University named after S. Seifullina __________ _______________

Protocol No. __from______________ (Signature) (Full name)

“___” ____________ 2005

Sorokin V.G. – Associate Professor, Head Department of Electric Power and Management Kaz ATK

Nogai A.S. Professor of the Department of Electrical Supply.

Ansabekova G.N. - senior Lecturer at the Department of Electrical Supply

The training manual is compiled in accordance with the requirements curriculum and the temporary standard curriculum for the discipline “Electrical Drawings” and include all the necessary information for mastering this course.

The textbook is intended for students in specialties 2102, 2104, 2105 in Russian.

Reviewers:: Pyastolova I.A., Ph.D., Associate Professor of the Department of Operation of Electrical Equipment, Kazakh State Agrotechnical University named after. S. Seifullina

Nurakhmetov T.N.., Professor of the Department of Radioelectronics of the Eurasian National University them. L. Gumileva

Reviewed and approved at a meeting of the Electrical Supply Department.

Protocol No._ 2_ __ from “_ 30_ _ “__09_ _______2005

Reviewed and approved by the methodological commission of the Faculty of Energy.

Protocol No. _3___ from “_ 16 __ “__10_ _____2005

© Kazakh State Agrotechnical University named after. S. Seifullina

Introduction

In modern conditions, the saturation of all sectors of the national economy and everyday life (regardless of forms of ownership) with electrical products, installations, instruments, communications, computers and even electrical toys, the requirements for the rules for their clear, unified outline and reading of all types of electrical drawings have increased significantly. It must be said that modern electrical installations are so complex that it is almost impossible to manufacture, operate, or repair them “from memory” without a drawing. Such drawings are electrical diagrams.

If the drawing, called the language of technology, is an international means of transmission technical information, then the conventional graphic and letter symbols approved by the interstate standard are the international alphabet of the language of drawings.

Design (project) documents are divided into graphic (drawings and diagrams) and text (explanatory notes, calculations, technical specifications, etc.)

Of course, the development of such documentation is carried out by experienced electrical specialists.

In the process of studying in this discipline in the first year and coursework and diploma design in subsequent courses, the student acquires practical skills, accumulates reference material on elements, assemblies and blocks of electrical products, and learns to read fluently electrical circuits and automation schemes, as well as use this in practical activities.

The basics of this knowledge are necessary for all technical specialties and specializations of engineering faculties.

The purpose of this teaching aid is the opportunity to systematize the basics of knowledge in electrical disciplines, teach the rules of electrical drawing, acquire initial reference information material, and also master the basics of reading electrical circuits and automation circuits.

General information

During scientific, design development and design work, as well as during setup, installation, operation and repair of electrical installations and electrification projects, the main unified regulatory document is electrical circuits, which are regulated by international and state standards, most often included in the “ Unified system design documentation" (ESKD) GOST 2721-74, 2752-74, 2755-87. For example, GOST 2702-75, Rules for the execution of electrical circuits.

In accordance with state and international standards main types and types circuits used in electrification projects and electrical products in accordance with GOST 2701-84 are numbered with appropriate codes consisting of letters and numbers (see Table 1), which are stamped in the drawing.

Table 1. Main types and types of circuits used in electrification projects

For example, in the stamps of the drawings of a course or diploma project “The electrical circuit diagram is encrypted ABVG.ХХХХХХ 25/Э3, and the connection diagram automatic devices, of which there are several types in the complex, is encrypted as ABVG.ХХХХХХ 253 A4.2 A4, etc.

Electrical circuits are made on sheets (formats) of the following sizes: A0-841*1189; A1-594*841; A2-420*594; A3-297*420; A4-210*297-GOST 2.301-68

Electrical circuits are developed and supplied for use, usually as a complete set. For example: - standard set: structural, functional, circuit and wiring diagrams.

Taken together, electrical diagrams must contain sufficient information for the design, manufacture, installation, configuration, operation and repair of the product and at the same time must be rational, compact and easy to read. Therefore, it is necessary to understand their meaning (wording), know drawing techniques and the rules for reading them. Key terms and definitions are given in Table 2.

Table 2. Terms and definitions

Types of electrical circuits

Structural diagrams

Structural scheme defines the main functional parts of the product, their purpose and relationships (for example, see Fig. 1.1).

The functional parts in the diagram are depicted as rectangles.

Graphic construction The diagram should give the most visual representation of the sequence of interaction of functional parts in the product, for which purpose the name of the functions is indicated in each part and explanatory (indicative) inscriptions and parameters are made.

Z.U.

UE

PE

V.E.

OU.

R.O.

THEM.

Functional diagrams

The functional diagram explains certain processes of control functioning, both electrical and technological, occurring in the system and device as a whole, and in individual parts and elements.

These diagrams will be discussed in more detail as functional and technological automation diagrams in Part 2 of the book.

Schematic diagrams

Schematic (complete) diagram - a diagram that defines the complete composition of elements, nodes and connections between them, as well as the elements with which input and output circuits begin and end (connectors, clamps, terminals, etc.) and gives a detailed idea of ​​the principles of operation products (installations).

The basic requirements of the standards for the rules for implementing circuit diagrams are enshrined in GOST 2.710-81, GOST 2.755-87, GOST 2.721-74, GOST 34.201-89, GOST 21.403-80.

Schemes are drawn for devices, apparatus and systems that are in a disconnected (de-energized) state.

The reference graphic material of electrical circuits, as a rule, does not correspond to the scale and general appearance of the element, and therefore the standards introduce requirements for drawing elements in the form of conventional graphic images and applying conventional alphanumeric designations, which naturally introduces certain difficulties in the study.

In order to read diagrams meaningfully, you need to understand what is depicted on it. To do this, you should: know the terminology and understand the system for constructing graphic and alphanumeric symbols of circuit elements; know in what cases one or another designation is used.

Conventional graphic symbols are formed from the simplest geometric shapes: squares, rectangles, circles, as well as from solid and dashed lines and dots. Their combination according to the system provided by the standard makes it possible to easily depict everything that is required: apparatus, instruments, electrical machines, mechanical and electrical communication lines, types of winding connections, type of current, nature and methods of regulation, etc.

To construct conventional graphic symbols means to provide a special sign for each element, but then tens of thousands of complex symbols would be required. Since new elements and devices appear every day, new connection methods and it would be impossible to provide designations in advance for all cases. The symbols would be difficult both to depict and to read.

To simplify the display and reading, standards and rules allow fairly clear fragments to be drawn in diagrams without detail (blocks, harnesses, connectors, logic gates etc.), or use additional generally accepted images.

The following reference material is offered for study and use in the educational process: conventional letter symbols and conventional graphic images.

Conventionally, alphabetic and digital designations in electrical circuits are assigned to all elements, devices and functional groups in the form of one-letter and two-letter codes with numbers GOST 2.710-81 (it is recommended to use two-letter codes).

Alphanumeric designations are intended for recording information about elements and devices in code, either printed on drawings, or used as information in text documents.

In electrical circuits, the positional designation of an element consists of three parts that have an independent semantic meaning and are written without separating marks and spaces (letters of the Latin alphabet), see table. 3

In the first part, one letter (one-letter code) or several letters (two-letter code) indicate the type of elements, for example, R-resistor, PA-ammeter.

In the second part, indicate the number of the element among similar ones (R1, R1, C1, C2, HL1, HL2, etc.). It is allowed to add to the device number through a dot the conditional number of the depicted part of the device (for example, KV1.5 is the fifth contact of the KV1 relay). However, usually when making schematic electrical diagrams, including the separated method of execution, various elements of the same type, for example, contacts of one device (relay, etc.), are not assigned special positional designations; they have the same designation as the device to which they belong. So, all KV relay contacts will have the position designation KV1. The first and second parts of the designation are mandatory.

The third part indicates the functional purpose of the elements (R1F-resistor R1, used as a protective one).

Two-letter codes to indicate the functional purpose of the elements are given in Table 3.

Table 3. Position designation of circuit elements (letter codes)

Examples of element types	Code
Measuring instruments:	P
Ammeter	PA
Active energy meter	P.I.
Reactive energy meter	PK
Ohmmeter	PR
Recording device:	PS
Voltmeter	PV
Wattmeter	PW
Switches and disconnectors in power circuits:	Q
Automatic switch	QF
Short circuit	QK
Disconnector (limit switch)	QS
Transformers, autotransformers:	T
Current transformer	T.A.
Electromagnetic stabilizer	T.S.
Voltage transformer	TV
Capacitors	C
Generators, power supplies:	G
Battery	G.B.
Engines	M
Inductors, chokes, reactors	L
Arresters, Fuses, protection devices:	F
Discrete instantaneous current protection element	F.A.
Discrete inertial current protection element	FP
fuse	F.U.
Discrete voltage protection element, arrester	F.V.
Various elements:	E
A heating element	E.K.
Lighting lamp	EL
Relays, contactors, starters:	K
Current relay	K.A.
Indicator relay	KH
Electrothermal relay	KK
Contactor, magnetic starter	K.M.
Time relay	KT
Voltage relay	KV
Device (amplifier, unit, devices)	A.A.
Converters of non-electric quantities into electricity	B.A.
Display device	M.A.
Integrated circuits: analog, digital	DA,DD
Transistors	VT
Diodes	VD
Thyristor	VS
Switch-switch	S.A.
Push-button switch	S.B.

If necessary, sections of electrical circuits are marked on the diagram to identify sections of circuits, and may reflect their functional purpose in the diagram. Sections of the circuit separated by breaking or closing contacts of devices, relay windings, resistors and other elements have different markings. Sections of the circuit separated by detachable or permanent contact connections must have the same markings. To identify differences in sections of circuits, it is allowed to add numbers or other designations to the markings, for example, 75-4 (section 4 belongs to the control circuit of engines 75).

The markings are affixed sequentially from the input of the load power source, and the branching sections of the circuit are placed from top to bottom and from left to right. Power circuits alternating current marked with letters indicating phases and sequential numbers (A, B, C, A1, B1, C1, etc.).

Input output power circuits direct current marked with polarity: plus “+”, minus “-”. Sections of circuits with positive polarity are marked with even numbers, and sections of negative polarity with odd numbers. Control circuits (starting and stopping electric motors, alarms, protection, blocking, measurement) are marked with sequential Arabic numerals.

The sequence of numbers can be set within the functional circuit. Marking can be done with numbers taking into account the functional characteristics of the circuits, which makes the circuit easier to read, for example:

Measuring, control, regulation circuits……………….from 1 to 399

Signaling circuits……………………………………………………….from 400 to 799

Power circuits……………………………………………………………...from 800 to 999

The marking (number) is placed near the ends or in the middle of the chain section (if the chain is vertical, to the left of the image of the chain section, if horizontal, above the image of the section).

For additional information on the principle of operation of components and individual devices, the circuit diagram is supplemented with tables, notes, and cyclograms. Table 4 can serve as an illustration of such information.

Table 4. Cyclogram.

Contact

Time in minutes

Contact assignment

K1

CEP motor control

K2

Stirrer control

K3

Fan control

K4

Valve 1 control

K5

Valve control 2

K6

Valve control 3

Conventionally graphic images elements are made in lines with a thickness of 0.2 to 1 mm. (depending on sheet format and functional significance). So, for example, for general power circuits you can use lines 1 mm thick, for power circuits of individual consumers - up to 0.6 mm thick, for control circuits - 0.2-0.4 mm thick. Conventionally, graphic images of the main elements are shown in Table 5.

Table 5. Conventionally graphic images of electrical circuits

Name	Conditional image
Designation for general use
Separate wire
Crossing of wires, communication lines A) without connection B) with electrical connection	A) B)
Cable, harness
Screened line
Electrical signal direction
Mechanical link
Current-collecting mobile device for EPS A) general designation B) controlled noitograph	A) B)
Acceptable image of circuits of three-phase symmetrical systems (single-line image)
A) grounding B) housing	A) B)
Contact A) dismountable B) permanent connection C) plug connector	A) B) C)
Electric cars
Electric machine A) general designation B) with the designation of the rotor and stator (single-line image)	A) B)
Asynchronous machine with wound rotor
Two-phase asynchronous machine
DC machine
DC machine with mixed excitation
Inductors, chokes, transformers
Winding inductors, choke, transformer
Inductor with ferromagnetic core
Reactor
Single-phase transformer with ferromagnetic core A) main image B) acceptable image	A) B)
Three-phase transformer A) general designation B) three-winding	A) or in)
Autotransformer A) three-phase B) single-phase
Measuring current transformer
Voltage transformer A) single-phase B) three-phase	A) B)
Core (magnetic core) A) ferromagnetic B) diamagnetic	A) B)
Switching and contact devices
High voltage power switch
High voltage disconnector
Short circuit
Coil of relay, contactor and magnetic starter A) general designation B) thermal relay	A) IN)
Switching device contact A) making contact B) opening contact	A) B)
Plug socket A) open wiring B) closed wiring	A) B)
Contact with mechanical connection (limit switch, pressure switch)
Thermal relay contact
Three-pole switch A) without automatic return B) with automatic return	A) B)
Normally closed contact with retarder (time relay contact) A) when triggered B) when returned	A) B)
Contact A) switching B) with middle position	A) B)
Power circuit contact
Push-button switches A) normally open contact B) normally open contact	A) IN)
Contact of electrothermal relay (with spaced method)
Switch single-pole, three-position (bar)
Switches with complex switching
Resistors, capacitors
Resistor is constant
Variable resistor a) parametric c) potentiometer c) rheostat d) subscript e) thermistor	A) B) C) D) E)
Electric heater
Constant capacitor A) general image B) polar C) electrolytic	A) B) C)
Arrester
fuse
Devices
Device A) integrating (electric energy meter) B) recording	A) B)
Electrical measuring device (for example, ammeter)
Signaling equipment
Incandescent lamp A) lighting and signal lamp B) lamp	A) B)
Gas-filled indicators A) low pressure lamp B) gas-discharge sign indicator
Secondary power sources and their elements
Type of current and purpose A) constant B) single-phase alternating C) three-phase alternating industrial frequency D) alternating high frequency	A) B) C) D)
Galvanic or battery cell	or
power unit
Bridge diode connection diagrams A) single-phase B) three-phase	A) IN)
Zener diodes a) single-sided b) double-sided	A) B)
Elements of electronic circuits
A) diode B) thyristor C) LED D) optocoupler	A) B) C) D)
Transistors type A) p-p-p b) p-p-p	A) B)
Unijunction transistor
Unipolar field effect transistors A) p-channel B) p-channel	A) B)
MIS – transistor
Elements of integrated electronic technology
Basic element
Logical circuits A) repeater B) inverter (NOT) C) addition (OR) D) multiplication (AND)	A) B) C) D)
Bipolar cell (trigger)
Decoder
Digital counter
Operational amplifier

Almost any basic electrical circuit is built on the basis of elementary circuits and standard components. This greatly simplifies the development, construction and reading of circuits of any complexity.

It is recommended to depict individual circuits of basic electrical circuits with horizontal (vertical) lines (rows) in a sequence from top to bottom (from left to right), determined by the order of connections and operation of the elements installed in them. This method of executing circuits is called line-by-line. To make it easier to find elements on the diagram, the lines are numbered: 1,2,3,4, etc. (see Fig. 2)

Switching devices (contacts, relays, push-button switches, etc.) on diagrams, as a rule, should be depicted in a position corresponding to the absence of current in all circuit circuits and external forced forces. If the diagram adopts other provisions for such devices, this should be specified in the note. Contacts of signaling and control devices are depicted with a rational value of their parameters.

Fig 1.2 Example of designation of line chains.

If the diagram is complex, to make it easier to read, explanatory notes should be given on the right side of the lines, for example: “Engine is on,” etc.

Devices on the diagrams can be depicted in a combined or separated manner (Fig. 3). With the combined method, the components of the devices (for example, the coil and contacts of relay K1) are depicted close to each other. With the spaced method, the components are placed in different places of the diagram so that the individual parts of the circuit are depicted more clearly. It is allowed to show some devices in the diagram in a spaced manner, and others (more structurally complex) - in a combined manner. It is also allowed (if the entire circuit is made in a spaced manner) on the free field of the sheet to give graphic designations of individual devices made in a combined way (Figure 1.3).

Figure 1.3. Schematic diagram of electric motor control:

a) – a combined method of depicting elements; b) – spaced-out method of depicting elements: A1 – contactor; A2 – push-button station; A3 – thermal protection relay; KM – magnetic starter: KK1, KK2 – thermal protection relay contacts (A3).

Thus, we became acquainted with the technique of drawing electrical installation diagrams (see Table 2). A complex of electrical installations for transport transmission, distribution (power supply) of electricity is called electrical networks. They have a complex of overhead and cable lines, substations, distribution devices, conductors, etc. Electrical networks up to 1000V and over 1000V.

Substations provide transformation and distribution of electricity. For this purpose, a technological facility is located on the territory of the substation electrical equipment connected according to the main electrical circuit diagram. An example of which is shown in Fig. 4.

Fig.4. Diagram of a 110 kV substation with separators and short circuiters.

Techniques for reading electrical diagrams

Reading schematic diagram they begin by determining the purpose of the device, the composition of its circuit (power part, control unit, protection, etc.) and familiarizing themselves with the list of elements, for which they find each of them on the diagram, read all the notes and explanations.

Learning to read electrical circuit diagrams

I already talked about how to read circuit diagrams in the first part. Now I would like to reveal this topic more completely, so that even a beginner in electronics does not have questions. So, let's go. Let's start with the electrical connections.

It is no secret that in a circuit any radio component, for example a microcircuit, can be connected by a huge number of conductors to other elements of the circuit. In order to free up space on the circuit diagram and remove “repetitive connecting lines”, they are combined into a kind of “virtual” harness - they designate a group communication line. On the diagrams group line denoted as follows.

Here's an example.

As you can see, such a group line is thicker than other conductors in the circuit.

To avoid confusion about which conductors go where, they are numbered.

In the figure I marked the connecting wire under the number 8 . It connects pin 30 of the DD2 chip and 8 XP5 connector pin. In addition, pay attention to where the 4th wire goes. For the XP5 connector, it is connected not to pin 2 of the connector, but to pin 1, which is why it is indicated on the right side of the connecting conductor. The 5th conductor is connected to the 2nd pin of the XP5 connector, which comes from the 33rd pin of the DD2 chip. I note that the connecting conductors under different numbers are not electrically connected to each other, and in real life printed circuit board can be spread across different parts fees.

The electronic content of many devices consists of blocks. And, therefore, detachable connections are used to connect them. This is how detachable connections are indicated on the diagrams.

XP1 - this is a fork (aka "Dad"), XS1 - this is a socket (aka “Mom”). All together this is “Papa-Mama” or connector X1 (X2 ).

Electronic devices may also contain mechanically coupled elements. Let me explain what we are talking about.

For example, there are variable resistors that have a built-in switch. I talked about one of these in the article about variable resistors. This is how they are indicated on the circuit diagram. Where SA1 - a switch, and R1 - variable resistor. The dotted line indicates the mechanical connection of these elements.

Previously, such variable resistors were very often used in portable radios. When we turned the volume control knob (our variable resistor), the contacts of the built-in switch first closed. Thus, we turned on the receiver and immediately adjusted the volume with the same knob. I note that the variable resistor and switch do not have electrical contact. They are only connected mechanically.

The same situation is with electromagnetic relays. The relay coil itself and its contacts do not have an electrical connection, but they are mechanically connected. We apply current to the relay winding - the contacts close or open.

Since the control part (relay winding) and the executive part (relay contacts) can be separated on the circuit diagram, their connection is indicated by dotted line. Sometimes the dotted line don't draw at all, and the contacts simply indicate their belonging to the relay ( K1.1) and contact group number (K1. 1 ) and (K1. 2 ).

Another fairly clear example is the volume control of a stereo amplifier. To adjust the volume, two variable resistors are required. But adjusting the volume in each channel separately is impractical. Therefore, dual variable resistors are used, where two variable resistors have one control shaft. Here is an example from a real circuit.

In the figure, I highlighted two parallel lines in red - they indicate the mechanical connection of these resistors, namely that they have one common control shaft. You may have already noticed that these resistors have a special position designation R4. 1 and R4. 2 . Where R4 - this is the resistor and its serial number in the circuit, and 1 And 2 indicate sections of this dual resistor.

Also, the mechanical connection of two or more variable resistors can be indicated by a dotted line rather than two solid ones.

I note that electrically these variable resistors have no contact between themselves. Their terminals can only be connected in a circuit.

It is no secret that many radio equipment components are sensitive to the effects of external or “neighboring” electromagnetic fields. This is especially true in transceiver equipment. To protect such units from unwanted electromagnetic influences, they are placed in a screen and shielded. As a rule, the screen is connected to the common wire of the circuit. This is shown in the diagrams like this.

The contour is screened here 1T1 , and the screen itself is depicted by a dash-dotted line, which is connected to a common wire. The shielding material can be aluminum, metal casing, foil, copper plate, etc.

This is how shielded communication lines are designated. The figure in the lower right corner shows a group of three shielded conductors.

Coaxial cable is also designated in a similar way. Here's a look at its designation.

In reality, a shielded wire (coaxial) is an insulated conductor that is externally covered or wrapped with a shield of conductive material. This may be copper braiding or foil covering. The screen, as a rule, is connected to a common wire and thereby removes electromagnetic interference and interference.

Repeating elements.

There are frequent cases when electronic device Absolutely identical elements are used and it is inappropriate to clutter the circuit diagram with them. Here, take a look at this example.

Here we see that the circuit contains resistors R8 - R15 of the same rating and power. Only 8 pieces. Each of them connects the corresponding pin of the microcircuit and a four-digit seven-segment indicator. In order not to indicate these repeating resistors on the diagram, they were simply replaced with bold dots.

One more example. Crossover (filter) circuit for speaker. Pay attention to how instead of three identical capacitors C1 - C3, only one capacitor is indicated on the diagram, and the number of these capacitors is marked next to it. As can be seen from the diagram, these capacitors must be connected in parallel to obtain a total capacitance of 3 μF.

Likewise with capacitors C6 - C15 (10 µF) and C16 - C18 (11.7 µF). They must be connected in parallel and installed in place of the indicated capacitors.

It should be noted that the rules for designating radio components and elements on diagrams in foreign documentation are somewhat different. But, to a person who has received at least basic knowledge on this topic it will be much easier to understand them.

In our age of total electronics and electrification, various equipment that uses current in their work has become not only a part of large enterprises and energy networks, but also home appliances. In this regard, the question of how to read electrical circuits interests many people. Understanding the basic principles of circuit construction, the electrical processes that occur in them, and standard graphic symbols, you can easily read almost any drawing of this kind.

Before reading electrical diagrams, you need to thoroughly understand their structure and construction principles. And then even the most complex and intricate scheme will no longer seem like just a meaningless set of “Kabbalistic symbols” and ornate patterns. And the question of how to read electrical circuits will become resolved.

All graphic symbols are characterized by a sufficient simple form styles. If possible, they contain the most characteristic features and characteristics of each component, which greatly facilitates their memorization. The symbols do not reflect the dimensions of the element, but only its type and some specifications. Having understood these intricacies, you will take the first step towards answering the question of how to learn to read electrical circuits.

You also need to know that all symbols necessarily contain certain alphanumeric abbreviations that display some parameters of these circuit elements. A separate theme is the various lines that symbolize electrical wiring. The following types of lines are mainly used:

• the thick solid one represents wires, cables, buses, windings, resistors, capacitors, etc.;
• a solid double thick line indicates cores and connections to the body;
• dashed thick - displays a grid of various electronic devices;
• thin line - depicts mechanical connection and shielding lines on electrical circuits.

Knowing the meaning of the symbols above can play a key role in answering the question of how to read electrical diagrams. However, no less important are the subtleties of conventional alphanumeric abbreviations, which, according to the rules, are written in the form of a certain sequence of letters, numbers and symbols on one line without spaces. A position designator often consists of three parts: the type of element, its number, and the function it performs.

Letter codes for element types are groups that are assigned specific meanings. They can be one- or two-letter. All their values ​​are indicated in detail in the technical documentation and special reference literature, where all the parameters of the elements that are represented by this symbol in the diagrams are given in great detail. By the way, if you are interested in how to read car electrical diagrams, then you can be sure that for them this principle remains unchanged, since almost all documents of this kind are drawn up according to a single standard.

True, not everything is so simple. There are many special schemes that are sometimes difficult to understand even for professionals. Here, just knowing the symbols is not enough. It is necessary to have a good understanding of all the intricacies of the work of this device. It is not difficult to understand and remember symbols and alphanumeric abbreviations, but they can only give an idea of ​​the structure of the device, but not of its operating principle. For this we already need at least a minimal theoretical basis.

Electrical circuit diagrams

The main purpose of schematic electrical diagrams is to reflect with sufficient completeness and clarity the mutual connection of individual devices, automation equipment and auxiliary equipment that are part of the functional units of automation systems, taking into account the sequence of their operation and the principle of operation. serve to study the principle of operation of the automation system; they are also necessary in.

Circuit diagrams are the basis for the development of other project documents: wiring diagrams and tables of switchboards and consoles, external wiring diagrams, connection diagrams, etc.

When developing automation systems technological processes usually they carry out schematic electrical diagrams of independent elements, installations or sections of the automated system, for example, a valve control diagram, an automatic and remote control pump, tank level signaling circuit, etc.

Schematic electrical diagrams are drawn up on the basis of automation diagrams, based on specified algorithms for the functioning of individual control, alarm, automatic regulation and control units and general technical requirements requirements for the automated object.

Schematic electrical diagrams depict devices, devices, and communication lines between individual elements, blocks and modules of these devices in a conventional form.

In general, circuit diagrams contain:

1) conventional images of the operating principle of one or another functional unit of the automation system;

2) explanatory notes;

3) parts of individual elements (devices, electrical devices) of a given circuit, used in other circuits, as well as elements of devices from other circuits;

4) diagrams of switching contacts of multi-position devices;

5) a list of devices and equipment used in this scheme;

6) a list of drawings related to this scheme, general explanations and notes. To read circuit diagrams, you need to know the algorithm for the functioning of the circuit, understand the principle of operation of devices, devices on the basis of which the circuit diagram is built.

Schematic diagrams of monitoring and control systems according to their intended purpose can be divided into control circuits, process control and signaling, automatic regulation and power supply. Schematic diagrams by type can be electrical, pneumatic, hydraulic and combined. Currently, electrical and pneumatic circuits are most widely used.

The electrical circuit diagram is the first working document, on the basis of which:

1) carry out drawings for the manufacture of products ( common types and wiring diagrams and tables of switchboards, consoles, cabinets, etc.) and their connections with devices, actuators and among themselves;

2) check the correctness of the connections made;

3) set settings for protection devices, means of monitoring and regulating the process;

4) set up travel and limit switches;

5) analyze the circuit both during the design process and during commissioning and operation in case of deviation from the specified operating mode of the installation, premature failure of any element, etc.

Thus, depending on the work being done, reading a circuit diagram has different purposes.

In addition, if reading wiring diagrams comes down to determining what, where and how to install, route and connect, then reading a circuit diagram is much more difficult. In many cases, it requires deep knowledge, mastery of reading techniques and the ability to analyze the information received. And finally, an error made in a schematic diagram will inevitably be repeated in all subsequent documents. As a result, you will again have to return to reading the circuit diagram in order to identify what error was made in it or what in a particular case does not correspond to the correct circuit diagram (for example, a multi-contact software relay is connected correctly, but the duration or sequence of contact switching set during setup does not correspond to the task) .

The listed tasks are quite complex, and consideration of many of them is beyond the scope of this article. Nevertheless, it is useful to explain what their essence is and list the main technical solutions.

1. Reading a schematic diagram always begins with a general familiarization with it and the list of elements, finding each of them on the diagram, reading all the notes and explanations.

2. They determine the power supply system for electric motors, windings of magnetic starters, relays, electromagnets, complete instruments, regulators, etc. To do this, find all power sources on the diagram, identify for each of them the type of current, rated voltage, phasing in alternating current circuits and polarity in direct current circuits, and compare the obtained data with the nominal data of the equipment used.

Using the diagram, general switching devices are identified, as well as protection devices: circuit breakers, fuses, maximum current and minimum voltage relays, etc. The settings of the devices are determined from the inscriptions on the diagram, tables or notes and, finally, the protection zone of each of them is assessed.

Familiarization with the power supply system may be necessary to: identify the causes of power failure; determining the order in which power should be supplied to the circuit (this is not always indifferent); checking the correct phasing and polarity (incorrect phasing can, for example, in redundancy circuits, lead to a short circuit, change in the direction of rotation of electric motors, breakdown of capacitors, disruption of circuit separation using diodes, failure of polarized relays, etc.); assessing the consequences of blowing each fuse.

3. They study all possible circuits of each electrical receiver: electric motor, magnetic starter windings, relays, devices, etc. But there are many electrical receivers in the circuit and it is far from indifferent from which one to start reading the circuit - this is determined by the task at hand. If you need to determine its operating conditions from the diagram (or check whether they correspond to the specified ones), then start with the main electrical receiver, for example, with a valve motor. Subsequent electrical receivers will reveal themselves.

For example, to start an electric motor you need to turn on. Therefore, the next electrical receiver should be the winding of the magnetic starter. If its circuit includes the contact of an intermediate relay, it is necessary to consider the circuit of its winding, etc. But there may be another problem: some element of the circuit has failed, for example, a certain signal lamp does not light up. Then it will be the first power receiver.

It is very important to emphasize that if you do not adhere to a certain focus when reading the scheme, you can waste a lot of time without solving anything.

So, when studying the selected electrical receiver, you need to trace all its possible circuits from pole to pole (from phase to phase, from phase to zero, depending on the power system). In this case, it is necessary, firstly, to identify all contacts, diodes, resistors, etc., included in the circuit.

We especially emphasize that you cannot consider several circuits at once. You must first study, for example, the circuit for turning on the winding of the “Forward” magnetic starter with local control, establishing in what position the elements included in this circuit should be (the mode switch is in the “Local control” position, the “Backward” magnetic starter is disabled), which needs to be done to turn on the winding of the magnetic starter (press the “Forward” push-button switch), etc. Then you should mentally turn off the magnetic starter. Having examined the local control circuit, mentally move the mode switch to the “ Automatic control” and study the next chain.

Familiarization with each circuit of the electrical circuit has the purpose of:

A) determine the action conditions that the circuit satisfies;

b) identify errors; for example, a circuit may have contacts connected in series that should never be closed at the same time;

V) define possible reasons refusal. A faulty circuit, for example, includes contacts of three devices. By examining each of them, it is easy to identify the faulty one. Such tasks arise during setup and troubleshooting during operation;

G) identify elements in which timing relationships may be violated, either as a result of incorrect adjustment or due to an incorrect assessment by the designer of actual operating conditions.

Typical shortcomings are too short pulses (the controlled mechanism does not have time to complete the started cycle), too long pulses (the controlled mechanism, having completed the cycle, begins to repeat it), violation of the required switching order (for example, valves and the pump are turned on in the wrong order , or sufficient intervals are not maintained between operations);

d) identify devices that may have incorrect settings; a typical example is an incorrect setting of the current relay in the valve control circuit;

e) identify devices whose switching capacity is insufficient for the switched circuits, or the rated voltage is lower than required, or the operating currents of the circuits are greater than the rated currents of the device, etc.. P.

Typical examples: the contacts of an electric contact thermometer are directly inserted into the magnetic starter circuit, which is completely unacceptable; in the 220 V voltage circuit a diode is used reverse voltage 250 V, which is not enough, since it may be under a voltage of 310 V (K2-220 V); the rated current of the diode is 0.3 A, but it is connected to a circuit through which a current of 0.4 A passes, which will cause unacceptable overheating; the signal switch lamp 24 V, 0.1 A is connected to a voltage of 220 V through an additional resistor of the PE-10 type with a resistance of 220 Ohms. The lamp will glow normally, but the resistor will burn out, since the power released in it is approximately twice the rated one;

and) identify devices susceptible to switching overvoltages and evaluate protective measures against them(for example, damping circuits);

h) identify devices whose operation may be unacceptably influenced by adjacent circuits, and evaluate means of protection against influences;

And) identify possible false circuits both in normal modes and during transient processes, for example, recharging of capacitors, the entry into a sensitive electrical receiver of energy released when the inductance is turned off, etc.

False circuits are sometimes formed not only when there is an unexpected connection, but also when a contact is not closed or one fuse is blown, while the rest remain intact. For example, the intermediate relay of a process control sensor is connected through one power circuit, and its opening contact is connected through another. If the fuse blows, the intermediate relay will release, which will be perceived by the circuit as a violation of the mode. In this case, it is impossible to separate the power circuits or you need to design the circuit differently, etc.

False circuits can be formed if the supply voltage supply order is not observed, which indicates poor design quality. In correctly designed circuits, the sequence of supply of supply voltages, as well as their restoration after disturbances, should not lead to any operational switching;

To) evaluate the consequences of insulation failure one by one at each point of the circuit. For example, if the buttons are connected to the neutral working conductor, and the starter winding is connected to the phase winding (it is necessary to turn it on the other way around), then when the “Stop” push-button switch is connected to the grounding conductor, the starter cannot be turned off. If the wire after the “Start” push-button switch is shorted to ground, the starter will turn on automatically;

k) evaluate the purpose of each contact, diode, resistor, capacitor, for which we proceed from the assumption that the element or contact in question is missing, and evaluate what consequences this will lead to.

4. Set the behavior of the circuit during a partial power outage, as well as when it is restored. This most important issue, unfortunately, is often underestimated, so one of the main tasks of reading a circuit is to check whether the device can come from any intermediate state to a working state and whether unexpected operational switching will occur. That is why the standard requires that circuits be depicted under the assumption that the power is turned off and the devices and their parts (for example, relay armatures) are not subject to forced influences. From this starting point we need to analyze the schemes. Interaction time diagrams, which reflect the dynamics of the circuit’s operation, and not just some steady state, are of great help in analyzing circuits.

An electrical diagram is a detailed drawing showing all the electronic parts and components that are connected by conductors. Knowledge of the operating principle of electrical circuits is the key to a well-assembled electrical appliance. That is, the assembler must know how electronic elements are indicated on the diagram, what icons, alphabetic or numeric symbols correspond to them. In the material we will understand the key symbols and basics of how to learn to read electrical circuit diagrams.

Any electrical circuit includes a number of parts consisting of smaller elements. Let us take as an example an electric iron, which contains inside a heating element, a temperature sensor, light bulbs, fuses, and also has a wire with a plug. Other household appliances have an advanced configuration with circuit breakers, electric motors, transformers, and between them there are connectors for the full interaction of the components of the device and fulfill the purpose of each of them.

Therefore, the problem often arises of how to learn to decipher electrical diagrams that contain graphic symbols. The principles of reading circuit diagrams are important for those involved in electrical installation, repair of household appliances, connection electrical devices. Knowledge of the principles of reading electrical circuits is necessary to understand the interaction of elements and the functioning of devices.

Types of electrical circuits

All electrical circuits are presented in the form of an image or drawing, where, along with the equipment, the links of the electrical circuit are indicated. The circuits differ in purpose, on the basis of which a classification of different electrical circuits has been developed:

• primary and secondary circuits.

Primary circuits are created to supply the main electrical voltage from the current source to consumers. They generate, transform and distribute electricity during transmission. Such circuits require a main circuit and circuits for various needs.

In secondary circuits the voltage is not higher than 1 kW; they are used to provide automation, control and protection tasks. Thanks to secondary circuits, electricity consumption and metering are monitored;

• single-line, full-line.

Full line diagrams are designed for use in three-phase circuits and show devices connected across all phases.

Single line diagrams show only the devices in the middle phase;

• fundamental and installation.

The basic general electrical diagram involves indicating only the key elements; it does not indicate minor details. Thanks to this, the diagrams are simple and understandable.

Wiring diagrams contain more detailed images, since these are the diagrams that are used for the actual installation of all elements of the electrical network.

Expanded diagrams indicating secondary circuits help to highlight auxiliary electrical circuits and areas with separate protection.

Designations in diagrams

Electrical circuits consist of elements and components that ensure the flow of electric current. All elements are divided into several categories:

• devices generating electricity - power sources;
• converters of electric current into other types of energy act as consumers;
• parts responsible for transmitting electricity from the source to the devices. Also included in this category are transformers and stabilizers that ensure voltage stability in the network.

Each element has a specific graphic designation on the diagram. In addition to key symbols, the diagrams indicate power transmission lines. Sections of an electrical circuit through which the same current flows are called branches, and at the places where they are connected, dots are placed on the diagram to indicate connecting nodes.

The circuit of an electrical circuit assumes a closed path of movement of electric current along several branches. Most simple circuit consists of a single circuit, and for more complex devices, circuits with several circuits are provided.

On an electrical diagram, each element and connection has an icon or symbol. To display insulation pins, single-line and multi-line diagrams are used, the number of lines in which is determined by the number of pins. Sometimes, for ease of reading and understanding of diagrams, mixed drawings are used, for example, stator insulation is described in detail, and rotor insulation is described in general form.

Designations of transformers in electrical circuits are drawn in general or expanded form, using single-line and multi-line methods. The method of displaying devices, their pins, connections and nodes on the diagram directly depends on the detail of the image. So, in current transformers primary winding reflected by a thick line with dots. The secondary winding can be displayed as a circle in a standard diagram or two semicircles in the case of an expanded diagram.

Other elements are displayed on the diagrams with the following symbols:

• contacts are divided into make, break and switch contacts, which are indicated by different symbols. If necessary, contacts can be indicated in mirror image. The base of the moving part is indicated as an unshaded dot;
• switches - their base corresponds to a point, and for circuit breakers the category of the release is drawn. Switch for open installation, as a rule, has a separate designation;
• fuses, fixed resistors and capacitors. Safety elements are depicted as a rectangle with taps, fixed resistors may be designated with or without bends. The moving contact is drawn with an arrow. Electrolytic capacitors are designated based on polarity;
• semiconductors. Simple diodes with a pn junction are shown in the form of a triangle and a cross circuit line. The triangle represents the anode and the line represents the cathode;
• incandescent lamp and other lighting elements are usually designated

Understanding these icons and symbols makes reading electrical diagrams easy. Therefore, before proceeding with electrical installation or disassembly household appliances, we recommend that you familiarize yourself with the main symbols.

How to read electrical diagrams correctly

A schematic diagram of an electrical circuit displays all the parts and links between which current flows through conductors. Such diagrams are the basis for the design of electrical devices, so reading and understanding electrical diagrams is a must for any electrician.

A competent understanding of diagrams for beginners makes it possible to understand the principles of their composition and the correct connection of all elements in electrical circuit to achieve the expected result. In order to correctly read even complex diagrams, it is necessary to study the main and secondary images, symbols of the elements. Symbols indicate the general configuration, specifics and purpose of the part, which allows you to get a complete picture of the device when reading the diagram.

You can start familiarizing yourself with circuits with small devices such as capacitors, speakers, resistors. Circuits of semiconductor electronic parts in the form of transistors, triacs, and microcircuits are more difficult to understand. So in bipolar transistors There are at least three pins (base, collector and emitter), which requires more symbols. Thanks to a large number of different signs and patterns, it is possible to identify the individual characteristics of the element and its specificity. The designations contain encrypted information that allows you to find out the structure of the elements and their special characteristics.

Often symbols have auxiliary clarifications - next to the icons there are Latin letter symbols for detail. It is also recommended that you familiarize yourself with their meanings before starting to work with the diagrams. Also, near the letters there are often numbers that display the numbering or technical parameters of the elements.

So, in order to learn to read and understand electrical circuits, you need to become familiar with the symbols (drawings, alphabetic and numerical symbols). This will allow you to obtain information from the diagram regarding the structure, design and purpose of each element. That is, to understand the circuits you need to study the basics of radio engineering and electronics.