Construction Of A Direct Online Starter

1.0 INTRODUCTION

1.1 BACKGROUND OF THE STUDY

A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults. 

A small motor can be started by simply plugging it into an electrical receptacle or by using a switch or circuit breaker. A larger motor requires a specialized switching unit called a motor starter or motor contactor. When energized, a direct on line (DOL) starter immediately connects the motor terminals directly to the power supply. Reduced-voltage, star-delta or soft starters connect the motor to the power supply through a voltage reduction device and increases the applied voltage gradually or in steps. In smaller sizes a motor starter is a manually operated switch; larger motors, or those requiring remote or automatic control, use magnetic contactors. Very large motors running on medium voltage power supplies (thousands of volts) may use power circuit breakers as switching elements.

1.2 STATEMENT OF THE PROBLEM

i. It will put high thermal stress on the motor and that will reduce the motor life.

ii. High starting current will leads to dips in voltage. 

iii. The unnecessary high starting torque required by the load may cause increasing mechanical stress on motor mechanical parts as well as the load.

1.3 RESEARCH OBJECTIVE 

i. To construct an electrical device that can be used to start and control the direction of AC motor.

ii. To test the constructed starter.

1.4 CONTRIBUTION TO KNOWLEDGE

i. This project helps us to understand the working principle of a direct online starter.

ii. It helps us to understand how each components works.

1.5 LIMITATION OF THE PROJECT

This motor starter is simply manual switches designed to control larger current loads typical of motor control. They may be small and similar to the light switches in your home, or they may be much larger dedicated switches designed for control of high amperage circuits. This motor starter is Triple Pole devices (switch 2/3 lines). This device was built using Normally Closed (STOP) and Normally Open (START) momentary contact switches and normally close (reversing) switch. 

1.6 METHODOLOGY

This project contains detailed analysis of the working and the construction of a Direct Online Starter, and also the books that were consulted and the site that was visited to get materials for the successful completion of this project report (Direct Online Starter).

1.7 DEFINITION OF TERMS

Overload relay: This is an electromechanical protection device for the main circuit.it offer reliable protection for motors in the event of overload or phase failure.it can make up a compact starting solution together with the contactors.

Contactor: A contactor is an electrically-controlled switch used for switching an electrical power circuit. A contactor is typically controlled by a circuit which has a much power level than the switched circuit, such as a 20-volt coil electromagnet controlling a 230-volt motor switch.

Miniature circuit breaker: A miniature circuit breaker [MCB] automatically switches off electrical circuit during an abnormal condition of the network means in overload condition as well as faulty condition. Nowadays we use MCB in low voltage electrical network instead of a fuse.

Direct online starter: A direct online starter is the simplest kind of starter that connect the motor directly to the power supply through a three phase contactor.