PLC

Simple Single phase AC motor starter using PLC

             PLC used                                  Siemens S7-200

S7-200 CPU Detail

PC software used     Step 7-Microwin V4.0.5.08  

              

 PC to PLC USB / PPI Multimaster Cable 

( ip 6ES7 901-3DB30-0XA0 )

Connecting PLC with PC

Electrical Connection Diagrams of PLC

This PLC has 14 input in two groups (I0.0 to I0.7 and I1.0 to I1.5) outputs in two groups.

Q0.0 to Q0.7 and ( Q1.0, Q1.2) see the I/ O diagram below.
This Cpu is operated by 24 Volts DC.
All its inputs are source inputs (You have to connect +ve of the supply to the inputs)
DC supply connections are M (-ve) and L+ (+ve) can be seen upper right corner.

Induction Motor

Cut view of  induction Motor

Motor terminal block Connections 

Winding connections arrangement

Pictorial view of Motor terminal block

Simple Induction Motor Starter Circuit

PLC Ladder Program for the Above Circuit
with addition of overload flashing indication

In the above ladder program Network 1 is the one which is doing the main job, as switch on  and switch off the motor.In this program input are shown with "I" and output with "Q" this is Siemens notation system different manufacturer have different notation system as Mitsubishi co mention with "X" for input  and "Y" for output.

How to make your first Program

When first you start the Step-7 Micro/Win program you will see the following window.Double click on CPU-

224 or what ever CPU is there on the left side as shown in the image below.

Another window will pop-up, as shown below. click Read PLC tab to select the CPU type.

It will select the CPU then press O.K Now press Communication tab.

You will get following window , now double click the to refresh the communication.
it will communicate with plc and set the comm port.

Now  PLC is ready to make and test the program

Star- Delta connection arrangement

  Traditional Star-Delta circuit of Motor

Star Delta Starter Theory

     Electrical motors have been used in industries for quite a long period of time to convert electrical energy into mechanical energy. Three phase induction motors, also called asynchronous motors, are most extensively used motors in industries because of certain advantages like self starting, robust design, simple construction, less maintenance, efficient and comparatively low cost, though there is a problem of peak starting current associated with these motors. Peak starting current can be up to 5 to 7 times of full load current (flc) and sometimes it may become as high as 10 times of full load current. However, the problem of peak starting current remains only for few seconds till the motor attains its speed, this problem may become severe especially with the motors above 10 HP. To deal with the problem of peak starting current or inrush current associated with three phase induction motors, many different starters having different mechanism and principle of operation are used. Star-delta starters are used for motors ranges from 5 hp or 3.5 kW. Star delta starters first configure windings of 3 phase motors in star thereby reduce voltage across each winding and then after few seconds these starters configure windings in delta and motors start run at full load voltage without any difficulty.