Industrial Automation: Control, Switching, and Protection Devices
Automatism is a system that controls a single machine or production process, reducing human intervention. Commonly used devices include sectioning, switching, and protection devices.
Sectioning Devices: These isolate a part of the network electrically for maintenance. Examples include disconnectors, switches, and circuit breakers or contactors.
Switching Devices: These establish or interrupt the power supply to receptors automatically or remotely. Examples include electromagnetic contactors, relays, and circuit breakers.
Protection Devices: These protect equipment from current surges caused by electrical faults.
Overload Protection
Overload is a small but continuous increase in current, causing overheating. Protection is ensured by thermal relays, sensors, and electronic relays.
Short Circuit Protection
Short circuits are a sudden, significant increase in current due to direct contact between points of different potential (e.g., two phases, phase to neutral, phase to ground). Protection is ensured by fuses and magnetic circuit breakers.
Starters
There are three types of starters:
- On-off: For nominal and constant velocity regimes.
- Electronic: Controls acceleration and deceleration, maintaining constant velocity.
- Electronic Variable Speed Drives: For variable speed control.
Disconnector | Switch | Interrupter-Sections | |
In Cargo Handling | No | Yes | Yes |
Insulation in Position | No | No | Yes |
Switching Devices Details
Switching devices connect or disconnect supply circuits to actuators. They must allow connection and disconnection under load, execute switching in a single movement, and cut all active circuits (phase and neutral). Manual switching is done directly by an operator.
Electromagnetic Contactor
An electromagnetic contactor is a switch that establishes or interrupts electrical current to open or close contacts. Its characteristics include robustness, reliability, quick adjustment to circuit supply voltage, safety against unexpected starts, facilitation of emergency stop positions, protection against voltage drops, and suitability for complex equipment. Main parts include the coil, contacts, and power contacts. Advantages include automation of motor starting and stopping, control from various points, handling high currents with low currents, worker safety, and control of complex processes.
Contactor Categories
- AC1: Resistive receptors with cos > 0.95 (heating).
- AC3: Three-phase motors reaching stable speed.
- AC2: Wound rotor motors (special conditions).
- AC4: Squirrel cage motors (special conditions).
Fuses
Two types of fuses based on fusion time:
- Fast: Type gL or gG.
- Slow: Type aM (motor).
Man-Machine Dialogue Devices
These devices enable operator intervention in automated processes.
Push Button
An on-off device for dialogue between man and machine, with two stable positions (resting and temporary actuation). It can have multiple associated contacts.
Types of Push Buttons:
- Flat: For start commands.
- Outbound: For stop commands.
- Retained: For stop commands that cannot be voluntarily canceled.
- Emergency: Red, large, and easily accessible.
- Double: For start and stop functions.
Other drives include levers and locks.
Interlocked Buttons: Pressing one button disconnects the others, preventing simultaneous operation.
Push Button Contacts: Can be overlapping or non-overlapping.
Selector
A rotary actuator with various stable or return positions.
Manipulative Cradle
Controls movement of a process on one or two axes.
Pilot Lights
Signal the status of various processes.
Light-Selector Buttons
Incorporate a pilot light into the button.
Hanging Button Boxes
Made of tough materials (rubber) to house mobile man-machine dialogue devices.
Beacons and Lighting Columns
Allow visual or acoustic signaling of process status over long distances and at 360 degrees.