14-05-2012, 04:58 PM
Fault Detection and Protection of Induction Motors Using Sensors
[attachment=22029]
INTRODUCTION
AC INDUCTION MOTORS (IMs) are used as actuators in
many industrial processes [1]. Although IMs are reliable,
they are subjected to some undesirable stresses, causing faults
resulting in failure. Monitoring of an IM is a fast emerging
technology for the detection of initial faults. It avoids unexpected
failure of an industrial process. Monitoring techniques can be
classified as the conventional and the digital techniques.
Classical monitoring techniques for three-phase IMs are generally
provided by some combination of mechanical and electrical
monitoring equipment. Mechanical forms of motor sensing
are also limited in ability to detect electrical faults, such as stator
insulation failures. In addition, the mechanical parts of the
equipment can cause problems in the course of operation and
can reduce the life and efficiency of a system [2].
PROGRAMMABLE LOGIC CONTROLLER
APLC or a programmable controller is a small computer used
for automation of real-world processes, such as control of machinery
on factory assembly lines. A PLC can be programmed
to sense, activate, and control industrial equipment. Therefore,
a PLC incorporates a number of I/O points, which allow electrical
signals to be interfaced. Input and output components of the
processes are connected to the PLC; and the control program is
loaded on the PLC memory. The basic structure of the PLC is
illustrated in
In this study, the PLC measures the current, the voltage, the
temperature, and the speed of an induction motor through analog
inputs. In addition, it continuously monitors the inputs and
activates the outputs according to the program.
CONTROL SYSTEM OF INDUCTION MOTOR
In Fig. 3, a block diagram of the protection system is illustrated.
It consists of the measurement of the current, the
voltage, the rotor speed, and the winding temperature. The protection
system proposed can be analyzed in three categories as
the hardware, the instrumentation, and the software. The tasks
of these categories are explained in the following sections.
Hardware
The protection system used in this study consists of a
1.5 kW/2800 r/min three-phase IM, three voltage transformers
with transformation ratio of 220/5 V, three current transformers
with current ratio of 1000:1, a temperature sensor with transformation
ratio of 10 mV for each 1 ◦C increasing temperature,
and an incremental encoder with 360 pulse per revolution used
for measuring the rotor speed, a true rms to dc conversion card,
a Siemens CPU 224, and S7 200 series PLC. A photograph of
the proposed system is demonstrated in Fig. 4.
Instrumentation
The currents and the voltages of the motor in the protection
system were measured using the measurement card available
in the laboratory including three current transformers and three
voltage transformers, as shown in Fig. 5. This card includes
an amplifier with opamps, a gain potentiometer, and a filter
circuit used to change the current value.
[attachment=22029]
INTRODUCTION
AC INDUCTION MOTORS (IMs) are used as actuators in
many industrial processes [1]. Although IMs are reliable,
they are subjected to some undesirable stresses, causing faults
resulting in failure. Monitoring of an IM is a fast emerging
technology for the detection of initial faults. It avoids unexpected
failure of an industrial process. Monitoring techniques can be
classified as the conventional and the digital techniques.
Classical monitoring techniques for three-phase IMs are generally
provided by some combination of mechanical and electrical
monitoring equipment. Mechanical forms of motor sensing
are also limited in ability to detect electrical faults, such as stator
insulation failures. In addition, the mechanical parts of the
equipment can cause problems in the course of operation and
can reduce the life and efficiency of a system [2].
PROGRAMMABLE LOGIC CONTROLLER
APLC or a programmable controller is a small computer used
for automation of real-world processes, such as control of machinery
on factory assembly lines. A PLC can be programmed
to sense, activate, and control industrial equipment. Therefore,
a PLC incorporates a number of I/O points, which allow electrical
signals to be interfaced. Input and output components of the
processes are connected to the PLC; and the control program is
loaded on the PLC memory. The basic structure of the PLC is
illustrated in
In this study, the PLC measures the current, the voltage, the
temperature, and the speed of an induction motor through analog
inputs. In addition, it continuously monitors the inputs and
activates the outputs according to the program.
CONTROL SYSTEM OF INDUCTION MOTOR
In Fig. 3, a block diagram of the protection system is illustrated.
It consists of the measurement of the current, the
voltage, the rotor speed, and the winding temperature. The protection
system proposed can be analyzed in three categories as
the hardware, the instrumentation, and the software. The tasks
of these categories are explained in the following sections.
Hardware
The protection system used in this study consists of a
1.5 kW/2800 r/min three-phase IM, three voltage transformers
with transformation ratio of 220/5 V, three current transformers
with current ratio of 1000:1, a temperature sensor with transformation
ratio of 10 mV for each 1 ◦C increasing temperature,
and an incremental encoder with 360 pulse per revolution used
for measuring the rotor speed, a true rms to dc conversion card,
a Siemens CPU 224, and S7 200 series PLC. A photograph of
the proposed system is demonstrated in Fig. 4.
Instrumentation
The currents and the voltages of the motor in the protection
system were measured using the measurement card available
in the laboratory including three current transformers and three
voltage transformers, as shown in Fig. 5. This card includes
an amplifier with opamps, a gain potentiometer, and a filter
circuit used to change the current value.