YEDITEPE UNIVERSITY
ENGINEERING & ARCHITECTURE FACULTY
INDUSTRIAL ELECTRONICS LABORATORY
EE 432 – INDUSTRIAL ELECTRONICS
Deniz
Yildirim
Digitally signed by Deniz
Yildirim
DN: CN = Deniz Yildirim,
C = TR, O = Istanbul
Technical University, OU
= Electrical Engineering
Reason: I am the author
of this document
Date: 2011.10.30
08:38:43 +02'00'
EXPERIMENT 5
CONTROLLING A SQUIRREL-CAGE
INDUCTION MOTOR WITH SIMATIC S7-300 PLC
Introduction:
The main objective in this experiment is to:
• Understanding the programmable logic controller and its peripherals.
• Programming the PLC with the STEP 7 software.
• Applying the PLC to drive a squirrel cage motor.
Equipments:
726 75
727 41
732 54
732 55
732 59
735 24
730 800
732 804
3RT1016-1BB41
3SB14 00-0A
Metra Hit 25S
Table 1. List of Equipments
Three-Phase Supply Unit with FCCB
Measurement Indicator
Magnetic Powder Brake
Control Unit for the Magnetic Powder Brake
Tachogenerator
AC Current Transformer (2V/1A)
PLC Basic Unit
Squirrel-Cage Induction Motor, 1.6kW
24V DC Relays (x2)
Normally Open (NO) Push-button switches (x3)
Multimeter (x 2)
Siemens SIMATIC S7-300
General Information:
THREE-PHASE INDUCTION MOTOR
An induction motor is one in which alternating current is supplied to the stator
directly and to the rotor by induction or transformer action from the stator. When
excited from a balanced three-phase source, the stator winding will produce a
magnetic field in the air gap rotating at synchronous speed as determined by the
number of stator poles and the applied stator frequency f e . The rotor of a three-phase
induction machine may be one of two types. A wound rotor is built with a three-phase
winding similar to, any wound with the same number of poles as, the stator. The
terminals of the rotor winding are connected to insulated slip rings mounted on the
shaft as shown in Figure 1(a). Carbon brushes bearing on these rings make the rotor
terminals available external to the motor. The second type is squirrel-cage rotor with a
winding consisting of conducting bars embedded in slots in the rotor iron and shortcircuited at each end by conducting end rings. The three-phase induction motor with
squirrel-cage rotor is shown in Figure 1(b).
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 1/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
brushes
Three phase
windings on
rotor
Slip rings
(a)
Short
circuiting
ring
Aluminum rotor
bars embedded in
rotor iron
(b)
Figure 1. Cutaway view of a three-phase (a) wound-rotor and (b) squirrel-cage
induction motor.
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 2/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
The quantity slip is the difference between the synchronous speed and the actual
speed of motor, as measured in rpm. Slip is more usually expressed as a fraction of
synchronous speed.
The fractional slip s is
s=
ns − n
120 ⋅ f
, where ns =
ns
p
(1)
Where f is the frequency of applied voltages, p is the pole number and n is the
mechanical speed of rotor.
The rotor terminals of an induction motor are short circuited; by construction in the
case of a squirrel-cage motor and externally in the case of a wound-rotor motor. The
rotating air-gap flux induces slip-frequency voltages in the rotor windings. The rotor
currents are then determined by the magnitudes of the induced voltages and the rotor
impedance at slip frequency. At starting, the rotor is stationary (n=0), the slip is unity
(s=1), and the rotor frequency equals the stator frequency f e . The field produced by
the rotor currents, therefore, revolves at the same speed as the stator field, and a
starting torque results, tending to turn the rotor in the direction of rotation of the
stator-inducing field. If this torque is sufficient to overcome the opposition to rotation
created by the shaft load, the motor will come up to its operating speed. The operating
speed can never equal the synchronous speed however, since the rotor conductors
would then be stationary with respect to the stator field; no current would be induced
in them, and hence no torque would be produced.
MAGNETIC POWDER BREAK
Magnetic powder break is mechanically connected to the three-phase induction motor
for loading purposes. It applies breaking torque to the induction motor. The amount of
breaking torque can be adjusted from the break control unit (732 55). Control unit also
takes speed information from the tachogenerator (732 59) and displays the speed with
an analog panel meter on the break control unit.
SIMATIC S7-300 PLC
SIMATIC S7-300 PLC will be used to drive the squirrel-cage induction motor. More
information can be obtained from the Experiment 2 laboratory handout.
TIMER TYPES
Timer format:
S5T# aH_bbM_ccS_ddMS
a. where a = hours, bb = minutes, cc = seconds, and dd = milliseconds
b. The time base is selected automatically, and the value is rounded to
the next lower number with that time base.
For example: 500ms = S5T#500MS,
1min 10sec = S5T#1M_10S
There are five different timer types in Simatic Ladder programming as depicted in
Figure 2 where each timer starts with an input signal.
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 3/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
Figure 2. Timer types
CONTACTOR
A contactor is a simple electromechanical relay that is used to connect loads to the
power supplies – the contactor illustrated in Figure 3 will be used to connect a threephase induction motor to a three-phase voltage source in this experiment. This
contactor has four normally open (NO) contacts and contacts are activated (closed) by
applying 24V DC voltage to terminals A1+ and A2- (relay coils). A freewheeling
diode must be connected across the relay coil terminals (cathode of diode is connected
to A1+ and anode is connected to A2-) in order to prevent PLC output from
destructive inductive-kick overvoltages.
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 4/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
Figure 3. Contactor for switching motor (see Appendix A for data sheet)
Procedure of Experiment:
Circuit Set-up: Assemble the circuit shown in Figure 4.
First, connect the power circuit cables of the motor. Then, connect the control circuit
cables for an easy set-up. Do not forget to connect the PE (ground) connections!
•
Connect the 24 V DC Relay to the three-Phase Supply Unit (726 75). Connect a
multi-meter to measure the line current.
•
Connect the Relay to the stator windings of the induction motor. The windings
connections can be plugged to the connection box on the induction motor. The
stator must be WYE connected.
•
Connect the tachogenerator to the breaker control unit (732 55).
•
Make sure that the torque knob in the brake unit is at minimum, i.e., rotate all the
way to the CCW direction.
•
Connect the NO and NC switches to the digital input module of the PLC via PLC
Basic Unit (730 800). For each switch, connect one end to 24 V socket on PLC
Basic Unit, and connect other end to the corresponding input sockets on PLC
Basic Unit.
•
Connect the voltage output of current sensor (735 24) to the analog measurement
indicator.
•
Connect the PLC output from the PLC Basic Unit (730 800) to the 24 V DC
Relay. Connect A2- end of relay to zero volt on PLC Basic Unit and connect other
end to the corresponding output socket.
Open the STEP 7 software to program the PLC:
•
Make an online connection between the PLC and the software by running the
command from “File/Connect Online”.
•
Create a new project. Then, in “Program/OB1” write your code in FBD/LD or
STL.
•
Right Click on OB1 and choose “Download to CPU” command.
•
When file transfer is finished, switch PLC to RUN mode.
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 5/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
Figure 4. PLC control of induction motor operation..
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 6/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
5
vw
6
4
2
4
0.0
3SB14 00-0A
OFF
0.1
3
(red color)
S2
0.2
0.3
3SB14 00-0A
contactor KM
0.0
A1+
L+
735 24
U+
0.2
current transducer
~
0
0.1
4
3
W2
W1
732 804
V2
V1
θ>
U2
U1
U1
+
732 59
tachogenerator
measurement indicator
727 41
+ 10V -
3-phase induction motor
wye-connected
W1
V1
0.3
delayed
ON/OFF
S3
(yellow color)
PLC Digital Input/Output Module
M
S1
3RT1016-1BB41
3
vv
A2-
1N4001
+24VDC
1
726 75
4
3SB14 00-0A
ON
3
(green color)
vu
+
380V-50Hz AC
-
Deniz Yildirim
Mar 24, 2010
e4_plc.eps
push-button
switch (NO)
+24VDC
nm
6
5
732 54
contactor KL
3RT1016-1BB41
4
2
3
1
magnetic brake
A2-
24V coil
1N4001
Lamps
+
tacho
temp
732 55
brake
729 09
indicator light
Ld
magnetic brake control unit
A1+
1. Unlatched Circuit Configuration with Indicator:
Write a program in STEP 7 such that when S1 button is pushed on momentarily, it will
start the motor, and when S2 button is pushed on momentarily, it will deenergize
motor. When motor is operating, the indicator light Ld must be turned on
continuously, otherwise it must be in off position.
Motor must be initially loaded with minimum torque, therefore, torque adjustment
knob must be set to low value. Start the motor and write down the starting current
(peak value), running current (using the analog measurement unit), torque, and speed
in Table 1.
Load the motor using the brake unit by turning the torque adjustment knob slowly in
CW direction. Monitor the motor current and stop when the motor current reaches the
rated value written on the nameplate. Stop the motor. Restart the motor with this
loaded condition and write down the starting current (peak value), running current
(using the analog measurement unit), torque, and speed in Table 2.
2. Delayed Circuit Configuration with Indicator:
Write a program in STEP 7 such that when S1 button is pushed on momentarily, it will
start the motor, and when S2 button is pushed on momentarily, it will deenergize
motor.
The motor will either start or stop (depending on the previous operating condition)
after predetermined delay time when S3 button is pushed on momentarily, i.e., if the
motor is operating, pushing S3 button will stop the motor after 10 seconds. If motor is
at standstill, pushing S3 button will start the motor after 6 seconds.
When starting the motor using S3 button, the indicator light Ld must be flashing
(0.3sec on, 0.8sec off) during the delay time. When motor is energized after this delay
(in operating condition), the indicator light Ld must be continuously turned on. Once
S3 button is pushed on for stopping the motor, the indicator light Ld must be flashing
(0.4sec on, 0.5sec off) during delay time and must be turned off when motor is
denergized.
Conclusion:
Bidirectional operation of an induction motor with Star-Delta starting will be realized
in your report. Use the induction motor nameplate values available in the Industrial
Electronics laboratory. Selection of the contactors will be based on for this motor.
There will be three push buttons (normally open type) for controlling: one stop button,
one clockwise (CW) button and one counterclockwise (CCW) button. Pressing either
CW or CCW button will start the motor in Star-Delta configuration, i.e., stator
windings first will be connected in WYE (star) and then three-phase voltage will be
applied to stator windings. 10 seconds later stator windings will be switched from
WYE connection to DELTAconnection. You must make sure that all safety
precautions are implemented in your program so that no awkward operations result in.
One example of such an operation is short-circuiting of three-phase supply when both
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 7/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
CW and CCW are pressed on. Please note that there may be other unwanted
situations.
a) Describe the operation of the system and draw electrical connection diagram
indicating three-phase supply, induction motor, and contactors.
b) Draw single-line relay logic diagram for this operation.
c) Write a PLC program in ladder diagram form to run this operation properly:
•
Determine the I/O addresses of the PLC which you use for this device.
•
Determine the number of networks and function of each network.
d) Determine all the contactor types (specify model number) and select proper
contactors from a manufacturer’s data sheet. Compare the type of contactor (i.e.,
number of poles) requirements both for relay logic realization and for PLC
implementation. Include data sheet of these contactors to your report (PLC
realization only).
References:
[1] T. E. Kissell, “Industrial Electronics: Applications for Programmable
Controllers, Instrumentation and Process Control and Electrical Machines and
Motor Controls”, Prentice Hall, 3rd edition, 2002.
[2] T. J. Maloney, Modern Industrial Electronics, 5th Ed., Prentice Hall, 2001.
[3] S. J. Chapman, Electric Machinery Fundamentals, 4th ed., McGraw-Hill,
2004.
[4] A. E. Fitzgerald, C. Kingsley, S. D. Umans, Electric Machinery, 6th ed.,
McGraw-Hill, 2003.
[5] T. Bartelt, Industrial Control Electronics, 3rd ed., Thomson Delmar Learning,
2006.
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Experiment 4, page 8/9
Last updated October 30, 2011 8:37 AM by D. Yildirim
EXPERIMENT RESULT SHEET
This form must be filled in using a PEN. Use of PENCIL IS NOT ALLOWED
EXPERIMENT 5: CONTROLLING A SQUIRREL-CAGE
INDUCTION MOTOR WITH SIMATIC S7-300 PLC
STUDENT NO
STUDENT NAME
SIGNATURE
DATE
1
2
3
4
INSTRUCTOR APPROVAL
Table 1: Motor operating with minimum load
starting current
(A)
running current
(A)
torque
(Nm)
speed
(rpm)
Table 2: Motor operating at rated load
starting current
(A)
running current
(A)
torque
(Nm)
speed
(rpm)
Please include flowchart of your program in here indicating inputs and outputs
(ladder diagram code must be included in your report).
EE432 Industrial Electronics, Fall 2011
Experiment 4, page 9/9
Last updated October 30, 2011 8:37 AM by D. Yildirim