Schemes for controlling electric drives of technological mechanisms
In the general case, the control and automation schemes of electric drives are developed in projects for power electrical equipment and power supply of industrial enterprises. However, the automation of most objects is inextricably linked to the management of technological mechanisms with electric drives. In this case, it is necessary to develop separate control schemes for these electric drives as part of a project for automation of technological processes.
Reversible and irreversible asynchronous electric motors with a squirrel-cage rotor are mainly used as electric drives of mechanisms of automated technological equipment (pumps, fans, valves, valves, etc.), the control schemes of which will be considered further. The construction of these control schemes is carried out mainly on the basis of relay contact devices.This is due to the availability of a large selection of commercially available relay contact equipment with contact devices of different designs and coils operating at different voltages.
The analysis of the control schemes, including the most complex ones, shows that the control schemes of electric drives of technological mechanisms are specific combinations of a limited number of introduced nodes and the simplest electrical circuits connecting these nodes. Knowing the typical solutions makes reading specific control schemes much easier.
Reading the schematic diagrams for controlling electric drives of technological mechanisms should begin with studying the technical requirements for the circuit and establishing the conditions and sequence of the circuit. At the same time, an important place is occupied by the study of the accepted scheme for organizing the management of electric drives, on which it is advisable to dwell in more detail.
Examples of control schemes for electric drives of technological mechanisms:
Three control circuits of an asynchronous electric motor
Control of automatic start and stop of electric motors
Schemes of automated electric drive of lifting and transporting machines
Electrical diagram of the irrigation pumping station
Electric drive control schemes from multiple locations
Scheme of the organization of the control of the electric drive
The scheme of the organization of the control of electric drives can provide for local, remote and automatic control. All three types of control are used in all possible combinations.The most widespread are the management structures that provide for: local and remote management; local and automatic control; local, remote and
Automatic control. In some cases, as a rule, at significant distances to the control object, teleautomatic control is used. Local control of the electric drive is carried out by the operator with the help of controls, for example, buttons with buttons located in close proximity to the mechanism. Control over the operation of the mechanism is carried out by the operator visually or by ear, and in production premises, where such control is impossible, light signaling for position is used.
With remote control, the start and stop of the electric drive of the mechanism is carried out by the control station. The object is outside the field of vision of the operator, and its position is controlled by signals: "Enabled" - "Prohibited", "Open" - "Closed" and so called
Automatic control is provided by automation of technological parameters (regulators or alarms for temperature, pressure, flow rate, level, etc.), as well as with the help of various software devices that provide automatic control of the electric drives of the mechanisms of the technological equipment in compliance with the specified functional dependencies (simultaneity, certain sequence, etc.).
The type of electric drive control (local, automatic or remote) is selected using circuit switches (control type switches), which are installed on local, aggregate and dispatch panels and control panels.
Continuing to read the diagram, they find out which unknown means of automation and electrical equipment are involved in the work and study the principle of their work.
You should take very seriously the consideration of diagrams and tables of switching contacts of electrical devices and devices, explaining technological diagrams, diagrams of blocking dependencies on the operation of technological equipment, tables of applicability and other explanatory inscriptions. The success of all further work to clarify the principle of action of the considered scheme depends on how carefully and seriously the listed recommendations are implemented.