Ten rules for drawing up electrical diagrams
Purpose of electrical circuits
A schematic diagram is an extended circuit diagram. This is the main diagram of the electrical equipment project of the production mechanism and gives an overview of the electrical equipment of this mechanism, reflects the operation of the automatic control system of the mechanism, serves as a source for drawing up connection and connection diagrams, developing structural units and making a list of items.
According to the schematic diagram, the correctness of electrical connections is checked during the installation and commissioning of electrical equipment. The accuracy of the production mechanism, its performance and reliability in operation depend on the quality of the development of the concept.
Ten rules for drawing up electrical diagrams
1.The drawing up of a basic circuit diagram of the production mechanism is carried out based on the requirements of the technical specification... In the process of drawing up a schematic diagram, the types, versions and technical data of electric motors, electromagnets, limit switches, contactors, relays, etc. are also specified.
Recall that in the schematic diagram all the elements of each electrical device, apparatus or device are shown separately and are placed for ease of reading the diagram in different places, depending on the functions performed. All elements of the same device, machine, apparatus, etc. are supplied with the same alphanumeric designation, for example: KM1 - first line contactor, KT - time relay, etc.
2. The electrical schematic diagram shows all the electrical connections between the electrical components of the manufacturing mechanism included in it. In schematic diagrams, power circuits are usually placed on the left and depicted with thick lines, and control circuits are placed on the right and drawn with thin lines.
The schematic diagram is designed using existing typical assemblies and circuits for automatic control of electrical wires (for example, magnetic controller circuits and protective panels - for faucets, circuits of assemblies for transition from commissioning mode to automatic using separate buttons for control or mode switch — for metal cutting machines, etc.).).
3.Relay contact circuits must be made taking into account the minimum load on relay contacts, contactors, motion switches, etc., using amplifier devices to reduce the power they switch: electromagnetic, semiconductor amplifiers, etc.
4. To increase the reliability of the circuit, you should choose the simplest option that has the least number of controls, devices and contacts. For this purpose, for example, general protection devices should be used for electric motors that do not operate simultaneously, as well as to control auxiliary drives from the main drive devices if they operate simultaneously.
5. Control circuits in complex circuits must be connected to the network through a transformer that lowers the voltage to 110 V. This eliminates the electrical connection of the power circuits with the control circuits and eliminates the possibility of false alarms of relay-contact devices in the event of earth faults in the circuits of their coils. Relatively simple electrical control circuits can be connected directly to the mains.
6. The voltage supply to the power circuits and control circuits shall be by means of an input pack switch or circuit breaker. When using only DC motors on machine tools or other machines, DC equipment must also be used in the control circuit.
7. It is recommended, if possible, different contacts of the same electromagnetic device (contactor, relay, command controller, limit switch, etc.) to be connected to the same pole or phase of the network.This allows more reliable operation of the devices (there is no possibility of damage and short circuit on the surface of the insulation between the contacts). It follows from this rule that one output of the winding of all electrical devices, if possible, should be connected to one pole of the control circuit.
8. To ensure reliable operation of electrical equipment, means of electrical protection and blocking must be provided. Electric cars and the devices are protected against possible short circuits. and unacceptable overloads. In the control circuits of electric drives of metalworking machines, hammers, presses, bridge cranes, zero protection is required to eliminate the possibility of self-starting of electric motors when the supply voltage is removed and then applied.
The electrical circuit must be designed so that when the fuses are blown, the coil circuits are broken, the contacts are welded, there are no emergency modes of operation of the electric drive. In addition, the control circuits must have blocking connections to prevent emergency modes in case of wrong actions of the operator, as well as to ensure the specified sequence of operations.
9. In complex control schemes, it is necessary to provide for alarms and electrical measuring devices that allow the operator (driver, crane operator) to monitor the operating mode of the electric drives. Signal lamps are usually switched on at reduced voltage: 6, 12, 24 or 48 V.
10.For easier work and correct installation of electrical equipment, the brackets of all elements of electrical devices, electrical machines (main contacts, auxiliary contacts, coils, windings, etc.) and wires are marked on the diagrams.
Sections (clamps of circuit elements and connecting wires) of DC circuits with positive polarity are marked with odd numbers, and negative polarity with even numbers. AC control circuits are marked in the same way, that is, all terminals and wires connected to one phase are marked with odd numbers and the other phase with even numbers.
Common connection points of several elements in the diagram have the same number. After passing the circuit through the coil, contact, warning lamp, resistor, etc., the number changes. To emphasize certain circuit types, indexing is done so that control circuits are numbered 1 to 99, signal circuits 101 to 191, and so on.