Electrical Circuit Classification, Protection, and Automation
Electrical Circuit Classification
Electrical circuits can be classified, from an electrical standpoint, into DC circuits and AC circuits. AC circuits may be single-phase or three-phase.
From a technical point of view, electrical circuits can be classified into the following categories:
Scope
- Power circuits: For high consumption devices other than lighting.
- Lighting circuits: For providing electric light in premises and homes.
- Safety and emergency circuits: Legally required in many buildings, such as exit lights and fire detectors.
- Auxiliary power circuits: Provide immediate power replenishment during power loss.
Technical Function
- Power circuits: Involved in the supply and consumption of electrical energy.
- Control circuits: All electrical circuits of an installation, other than the main power circuit.
Line Calculations
Low-voltage lines can be direct current or alternating current, and within these, single-phase or three-phase. Lines can be open or ring connections.
Electrical Circuit as a Control Element
Electrical Protection Systems
Electricity involves physical processes that can be hazardous. The first protection system is suitable electrical isolation of live parts. There are different degrees of protection, from mechanical isolation to watertight systems.
Safety devices against overloads and short circuits include circuit breakers and fuses. Fuses are expendable, while circuit breakers can be reset after an overload or short circuit.
Automatic Disconnect Switches
Automatic disconnect switches have two main protection mechanisms:
- Thermal device: Activates a spring upon warming, disconnecting the device.
- Magnetic device: High instantaneous current generates a magnetic field, attracting a spring and disconnecting the device.
Types of Automatic Switches
- H-type (Domestic): Magnetic trigger acts between 2.5 to 3 times the rated current, with a downtime of less than 0.2 seconds.
- L-type (Lines): Used for protecting drivers in maneuvering lines and lighting.
- G-type (Motor): Used for protecting motors and appliances sensitive to thermal overloads.
Differential Protection
Another important protection system disconnects a circuit when a fault occurs between a phase insulation and the casing or ground. This is achieved by connecting to ground and using fault current protection switches, also called differentials.
Differentials are characterized by:
- Number of poles: Bipolar, tripolar, or tetrapolar.
- Maximum current: 25 A, 40 A, 63 A, 100 A.
- Tripping current: 30mA, 300mA, 500mA.
Electrical Automation
The basis of electrical automation is the contactor. Electromagnetic contactors are the most important switchgear in the industry.