ELECTRICAL ENGINEERING DESIGN AND DRAWING II Electrical Engineering

ELECTRICAL ENGINEERING DESIGN AND DRAWING - II Electrical Engineering Fourth Semester

Contactor • A contactor is an electrically controlled switch (relay) used for switching an electrical power circuit. A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24 -volt coil electromagnet controlling a 230 -volt motor switch. • Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads. • A contactor has three components. The contacts are the current carrying part of the contactor. This includes power contacts, auxiliary contacts, and contact springs.

Contactor

DOL starting of 3 -phase induction motor

Forwarding/reversing of a 3 -phase induction motor

Star delta starter for 3 -phase Induction Motor

Electrical Earthing • Definition: The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire is known as the electrical earthing. • The electrical earthing is done by connecting the non-current carrying part of the equipment or neutral of supply system to the ground. • To protect human lives as well as provide safety to electrical devices and appliances from leakage current we use earthing. • To avoid the risk of fire in electrical installation systems.

Methods of Earthing Pipe and plate earthing

Pipe Earthing: • A galvanized steel and a perforated pipe of approved length and diameter is placed vertically in a wet soil in this kind of system of earthing. It is the most common system of earthing. • The size of pipe to use depends on the magnitude of current and the type of soil. The dimension of the pipe is usually 40 mm (1. 5 in) in diameter and 2. 75 m (9 ft) in length for ordinary soil or greater for dry and rocky soil. • The moisture of the soil will determine the length of the pipe to be buried but usually it should be 4. 75 m (15. 5 ft).

Plate Earthing:

Plate Earthing: • In plate earthing system, a plate made up of either copper with dimensions 60 cm x 3. 18 mm (i. e. 2 ft x 1/8 in) or galvanized iron (GI) of dimensions 60 cm x 6. 35 mm (2 ft x ¼ in) is buried vertical in the earth (earth pit) which should not be less than 3 m (10 ft) from the ground level. • For proper earthing system, follow the above mentioned steps in the (Earth Plate introduction) to maintain the moisture condition around the earth electrode or earth plate.

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