26-04-2012, 10:37 AM
ELECTRONIC MOTOR CONTROL
[attachment=20839]
Once the proper motor is selected, understanding the many various control devices available and
their uses and limitations becomes an important part related to reliable operation and protection of
the motor and the personnel using the motor.
Motor Control Topics
There are four major motor control topics or categories to consider. Each of these has several
subcategories and sometimes the subcategories overlap to some extent. Certain pieces of motor
control equipment can accomplish multiple functions from each of the topics or categories.
The four categories include:
1) Starting the Motor
Disconnecting Means
Across the Line Starting
Reduced Voltage Starting
2) Motor Protection
Overcurrent Protection
Overload Protection
Other Protection (voltage, phase, etc)
Environment
3) Stopping the Motor
Coasting
Electrical Braking
Mechanical Braking
4) Motor Operational Control
Speed Control
Reversing
Jogging
Sequence Control
• An understanding of each of these areas is necessary to effectively apply motor control
principles and equipment to effectively operate and protect a motor.
MOTOR STARTING
All motors must have a control device to start and stop the motor called a “motor controller”.
Motor Controller
A motor controller is the actual device that energizes and de-energizes the circuit to the motor so
that it can start and stop.
• Motor controllers may include some or all of the following motor control functions:
S starting, stopping, over-current protection, overload protection, reversing, speed
changing, jogging, plugging, sequence control, and pilot light indication.
S Controllers range from simple to complex and can provide control for one motor,
groups of motors, or auxiliary equipment such as brakes, clutches, solenoids, heaters,
or other signals.
Motor Starter
The starting mechanism that energizes the circuit to an induction motor is called the “starter” and
must supply the motor with sufficient current to provide adequate starting torque under worst case
line voltage and load conditions when the motor is energized.
• There are several different types of equipment suitable for use as “motor starters” but only
two types of starting methods for induction motors:
1. Across the Line Starting
2. Reduced Voltage Starting
Across the Line Starting of Motors
Across the Line starting connects the motor windings/terminals directly to the circuit voltage “across
the line” for a “full voltage start”.
• This is the simplest method of starting a
motor. (And usually the least expensive).
• Motors connected across the line are capable
of drawing full in-rush current and
developing maximum starting torque to
accelerate the load to speed in the shortest
possible time.
• All NEMA induction motors up to 200
horsepower, and many larger ones, can withstand full voltage starts. (The electric
distribution system or processing operation may not though, even if the motor will).
[attachment=20839]
Once the proper motor is selected, understanding the many various control devices available and
their uses and limitations becomes an important part related to reliable operation and protection of
the motor and the personnel using the motor.
Motor Control Topics
There are four major motor control topics or categories to consider. Each of these has several
subcategories and sometimes the subcategories overlap to some extent. Certain pieces of motor
control equipment can accomplish multiple functions from each of the topics or categories.
The four categories include:
1) Starting the Motor
Disconnecting Means
Across the Line Starting
Reduced Voltage Starting
2) Motor Protection
Overcurrent Protection
Overload Protection
Other Protection (voltage, phase, etc)
Environment
3) Stopping the Motor
Coasting
Electrical Braking
Mechanical Braking
4) Motor Operational Control
Speed Control
Reversing
Jogging
Sequence Control
• An understanding of each of these areas is necessary to effectively apply motor control
principles and equipment to effectively operate and protect a motor.
MOTOR STARTING
All motors must have a control device to start and stop the motor called a “motor controller”.
Motor Controller
A motor controller is the actual device that energizes and de-energizes the circuit to the motor so
that it can start and stop.
• Motor controllers may include some or all of the following motor control functions:
S starting, stopping, over-current protection, overload protection, reversing, speed
changing, jogging, plugging, sequence control, and pilot light indication.
S Controllers range from simple to complex and can provide control for one motor,
groups of motors, or auxiliary equipment such as brakes, clutches, solenoids, heaters,
or other signals.
Motor Starter
The starting mechanism that energizes the circuit to an induction motor is called the “starter” and
must supply the motor with sufficient current to provide adequate starting torque under worst case
line voltage and load conditions when the motor is energized.
• There are several different types of equipment suitable for use as “motor starters” but only
two types of starting methods for induction motors:
1. Across the Line Starting
2. Reduced Voltage Starting
Across the Line Starting of Motors
Across the Line starting connects the motor windings/terminals directly to the circuit voltage “across
the line” for a “full voltage start”.
• This is the simplest method of starting a
motor. (And usually the least expensive).
• Motors connected across the line are capable
of drawing full in-rush current and
developing maximum starting torque to
accelerate the load to speed in the shortest
possible time.
• All NEMA induction motors up to 200
horsepower, and many larger ones, can withstand full voltage starts. (The electric
distribution system or processing operation may not though, even if the motor will).