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College of Engineering and Technology

Electrical and Control Engineering Department

Automated Industrial Systems I

EE512

EX1: Direct Online Motor Starter

Lecturer name: ……………..……………………………………………….…..…………………………...….…… 

Student name : .…………………………………………….…………………..…………………………………….. 

Registration # : …..……..……………………………………………………………………………………………… 

Prepared By: Prof. Hamdy Ashour Eng. Ahmed Al Bashir Mr. Mohamed Samir Mr. Wael Mohamed

September 2014

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Experiment 1

Direct Online Motor Starter

1-  Objective

To start and stop a three phase induction motor by Direct On Line (DOL) Starter.  

2-  Theory

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 timesgreater 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.

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3-  Instruments & Equipments

Three phase induction motor

Main and Sub feeder isolating circuit breakers

(board #5)

Power and control circuits fuses

(board #6)

Three phase electromagnetic contactor with

bi-metal overload relay

(board #2)

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Indicating lamps and Pushbuttons

(board #1)

Multimeter

Digital stroboscope

Wattmeter

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4-  Connection

Power Circuit

F6

L1Q2

K1Start

S1

F4

Stop

S0

K1   H1

Q2

F7

 N

X1

X2

A1

A2

13 13

1414

11

12

95

96

Fuses

F1 F2 F3

Contactor 

K1

Overload

F4

 

3φ

IM

T3T2T1

L1

L2

L3

Circuit Breaker 

C.B

Q1

Control Circuit

Fuse

Fuse

Overload

C.B

C.B

Contactor 

Coil

Pushbutton

Pushbutton

 

Power and Control circuits connections diagram

5-  Procedure

a.  Connect the circuits as shown in the diagram.

b.  Switch on the main and sub feeder isolating circuit breakers (Q1, Q2).

c.  Use the start and stop pushbuttons for motor operation.

d.  Measure the currant, voltage, power and the no load speed of the motor.

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6-  Results

Current =.………..………..A 

Voltage =…………………..V 

Power =……………….….W Speed =……………….....FPS

7-  Connect the power and control circuits on the following figure

8-  Add your own comments

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9-  Use internet resources to provide advantages, disadvantages and then discuss different

applications of DOL motor starter circuit

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