CHAPTER 6
for acceleration of the motor to avoid high
Controllers are commonly used for starting motors
starting current.
aboard ship. They can be designed to limit the amount
of current applied when starting motors by slowly
MANUAL
incrementing the starting process, allow the user to
select the speed at which the motor will operate, allow
A manual (nonautomatic) controller is operated by
the operator to reverse the direction of rotation of a
hand directly through a mechanical system. The
motor, remove the motor from service if conditions exist
operator closes and opens the contacts that normally
which may damage the motor or other connected
energize and de-energize the connected load.
equipment, allow the user to operate the motor under
adverse conditions in an emergency, and so forth. In all
MAGNETIC
cases, the basic function of motor controllers is to
govern the operation of and protect the motors they
In a magnetic controller, the contacts are closed or
serve.
opened by electromechanical devices operated by local
or remote master switches. Norman y, all the functions
LEARNING OBJECTIVES
of a semiautomatic magnetic controller are governed by
one or more manual master switches. Automatic
Upon completing this chapter, you should be able
controller functions are governed by one or more
to do the following:
automatic master switches after the motor has been
1. I d e n t i f y t h e d i f f e r e n t t y p e s o f e l e c t r i c
initially energized by a manual master switch. All
controllers.
magnetic controllers can be operated in either mode,
depending on the mode of operation selected.
2. Recognize the principle of operation of various
types of motor controllers.
ACROSS-THE-LINE CONTROLLER
3. Identify the procedures for troubleshooting
motor controllers.
An across-the-line controller (fig. 6-1) throws the
connected load directly across the main supply line. The
4. Identify the procedures to use when performing
across-the-line controller may be either manual or
corrective maintenance on motor controllers.
magnetic, depending on the rated horsepower of the
In this chapter, you will learn the characteristics, the
motor. Norman y, across-the-line dc controllers are used
uses, and the operating principles of the various kinds
to start small (fractional horsepower) motors. However,
of shipboard motor controllers, including their relays
they may be used to start average-sized, squirrel-cage
and switches. The techniques for maintaining and
induction motors without any damage because these
troubleshooting motor controllers are also discussed.
TYPES OF MOTOR
CONTROLLERS
Motor controllers are classified as manual or
automatic (magnetic). They are further classified b y the
methods by which they are started-across-the-line and
reduced voltage.
Across-the-line motors are started with full-line
voltage being immediate] y applied to the motor.
Reduced voltage motors are started by applying
Figure 6-1.--Schematic of a simple across-the-line controller.
line voltage to the motor in increments to allow
6-1
