Page 302 - Electronic Mechanic - TP - Volume - 2

ELECTRONICS MECHANIC - CITS

EXERCISE 206&209&212: Construct a DoL starter with

self hold contactor circuit and

run a 3 Phase Induction Motor

Objectives

At the end of this exercise you shall be able to:
• To Connect contactors , Relays and contacts
• To Connect , operate and demonstrate an using DoL starter for 3 phase induction motor
• To Demonstrate function of self Holding contact in the DoL starter.
Requirements

Tools/ Equipments/ Instruments Materials/ Components
• Combination Plier 250mm - 1 No. • Induction Motor - 1 No.
• Screwdriver Set 150mm - 1 No. • Circuit Barker - 1 No.
• Wire Stripper - 1 No. • Push Button NO/NC - 1 No.
• Overload Relay - 1 No.
• Contactor - 1 No.

Procedure

A Direct On Line (DOL) or across the line starter applies the full line voltage to the motor terminals.
This is the simplest type of motor starter. A DOL motor starter also has protection devices and, in some
cases, condition monitoring. Smaller sizes of direct on-line starters are manually operated; larger sizes use an
electromechanical contactor (relay) to switch the motor circuit. Solid-state direct on line starters also exist.
A direct on line starter can be used if the high inrush current of the started motor does not cause excessive voltage
drop in the supply circuit. The maximum size of a motor allowed on a direct on line starter may be limited by the
supply utility for this reason. For example, a utility may require rural customers to use reduced-voltage starters
for motors larger than 4KW (5HP).
DOL starting is sometimes used to start small water pumps, compressors, fans and conveyor belts.
In the case of an asynchronous motor, such as the 3-phase squirrel-cage motor, the motor will draw a high starting
current until it has run up to full speed. This starting current is typically 6-7 times greater than the full load current.
To reduce the inrush current, larger motors will have reduced- voltage starters or variable speed drives in order to
minimize voltage dips to the power supply, or series resistance and inductance can be added.

Instruments & Equipments

Name Figure

Three phase induction motor

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