Reverse TURN OF AN Automatic Three- Phase Motor WITH PLC PDF

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Reverse TURN OF AN Automatic Three- Phase Motor WITH...

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REVERSE TURN OF AN AUTOMATIC THREE-PHASE MOTOR WITH PLC

1. OBJECTIVE Understand how the PLC works. Know the general structure of these devices, main components and their functions; Know the types of PLCs that exist in the industry. Design a control circuit to reverse the rotation of an automatic three-phase motor (without going through S0). 2. THEORETICAL FRAMEWORK Turning reversal of three-phase motors To reverse the direction of rotation of an induction motor, the direction of the rotating magnetic field generated by its coils must be reversed, this is accomplished by reversing two of the three phases of motor power. By reversing two supply phases, what you are actually doing is reversing the phase sequences of the three-phase supply line to the motor. If the three phases are inverted, the same phase sequence is maintained and, therefore, the motor does not change its direction of rotation. In reference to the circuit of image 1 that we see below, when a three-phase motor is connected as the motor on the left, that is, with its terminals U, V and W to phases L1, L2 and L3 (or R, S and T) respectively, the motor always rotates clockwise, while if any two phases are interchanged and is connected as in the case of the motor on the right to the phases in the order L1, L3 and L2 (or R, T, S) the direction of rotation is the opposite, that is, counterclockwise [1].

Figure 1. Turning reversal

PLCs A Programmable Logic Controller (PLC) is a computer, used in automatic engineering or industrial automation, to automate electromechanical processes, such as controlling factory machinery on assembly lines or mechanical attractions. However, the most precise definition ofthese devices is given by the NEMA (National Association of Electrical Manufacturers), which says that a PLC is: “Electronic instrument, which uses programmable memory to store instructions on the implementation of certain functions, such as operations logic, action sequences, time specifications, counters and calculations for control by analog or digital I / O modules on different types of machines and processes ”[2].

Fig.1 esquema de un PLC Programming languages When speaking of programming languages, reference is made to different ways of writing the user program. The current softwares allow to translate the user program from one language to another, thus being able to write the program in the language that is most convenient. The increasing complexity in the programming of the programmable controllers requires more than ever of the standardization of the same. Under the direction of the IEC the standard IEC 1131-3 (IEC 65) for PLC programming has been defined. It achieved international standard status in August 1992. With the idea of making the right model for a wide range of applications, five languages have been defined in total: • Sequential graph of functions (Grafcet) • List of instructions. • Structured text. •

Flowchart.

• Ladder Logic or Ladder Logic or Ladder Logic. However, the most widely used programming languages today are: the list of instructions and the ladder or Ladder Logic [3].

Table 1. Advantages and disadvantages of the PLC [4] Advantages • More precise control. • Faster response time. • Flexibility Control of complex processes. • Ease of programming. • Security in the process. • Use of little space. • Easy installation. • Less energy consumption. • Better performance monitoring. • Less maintenance. • Rapid detection of breakdowns and dead times. • Less time in the elaboration of projects. • Possibility of adding modifications without raising costs. • Lower cost of installation, operation and maintenance. • Possibility of controlling several actuators with the same automaton.

Disadvantages • Skilled labor. • Centralizes the process. • Appropriate environmental conditions. • Higher cost to control very small or simple tasks.

Fig 2. Zelio SR3B261FUTable 2. Zelio SR3B261FU Features local display

Con

control scheme number or lines

0 ... 500 with FBD programming 0 ... 240 with ladder programming

Cycle time

6 ... 90 ms

backup time

10 years at 77 ° F (25 ° C)

drift clock

6 s / monthat 77 ° F (25 ° C) 12 min / yearat 32 ... 131 ° F (0 ... 55 ° C)

checks

Program memory at every power up

[Us] rated supply voltage

100 ... 240 V

supply voltage limits

85 ... 264 V

supply frequency

50/60 Hz

supply current

100 mAat 100 V (without extension) 50 mAat 240 V (without extension) 60 mAat 240 V (with extensions) 80 mAat 100 V (with extensions)

power consumption in VA

12 VA without extension 17 VA with extensions

insulation voltage

1780 V

protection type

Against investment of terminals (control instructions not executed)

discrete entry number

sixteen

discrete input voltage

100 ... 240 V CA

discrete input current

0.6 mA

discrete input frequency

47 ... 57 ... 63 Hz

voltage status 1 guaranteed

> = 79 V for discrete input

voltage status 0 guaranteed

= 0.17 mA for discrete input

current status 0 guaranteed

= 10 mAat 12V (relay output)

operating rate in Hz

0.1 Hz (at Ie) for the relay output 10 Hz (no load) for relay output

mechanical durability

10,000,000 cycles (relay output)

[Uimp] rated impulse withstand voltage

4 kV according to EN / IEC 60947-1 and EN / IEC 60664-1

watch

Con

response time

connections - terminals

10 ms (from state 0 to state 1) relay output 5 ms (from state 1 to state 0) relay output 50 ms with ladder programming (from state 0 to state 1) discrete input 50 ms with ladder programming (from state 1 to state 0) discrete input 50 ... 255 ms with FBD programming (from state 0 to state 1) discrete input 50 ... 255 ms with FBD programming (from state 1 to state 0) discrete input Screw terminals, clamping capacity: 1 x 0.2 ... 1 x 2.5 mm² AWG 25 ... AWG 14 semisolid Screw terminals, clamping capacity: 1 x 0.2 ... 1 x 2.5 mm² AWG 25 ... AWG 14 solid Screw terminals, clamping capacity: 1 x 0.25 ... 1 x 2.5 mm² AWG 24 ... AWG 14 flexible with cable end Screw terminals, clamping capacity: 2 x 0.2 ... 2 x 1.5 mm² AWG 24 ... AWG 16 Solid screw terminals, clamping capacity: 2 x 0.25 ... 2 x 0.75 mm² AWG 24 ... AWG 18 flexible with cable end

Torque

4.42 lbf.in (0.5 Nm)

Overvoltage category

III conforming to EN / IEC 60664-1

Product Weight

0.88 lb (US) (0.4 kg)

PROCESS Brief explanation of the operation of the circuit: In the control circuit we have S1, S2, S0 with which we control the motor; with S1 the motor turns clockwise, S2 is pressed and the motor automatically changes direction; with S0 we stop the motor running.

CONCLUSIONS With PLCs we can reduce the wiring of a control circuit, but the wiring of the power circuit must continue to be done. When choosing one of these devices, you must be very clear about the work to be done, the number of inputs and outputs that will be needed for the job. As for the PLC programmer used in the laboratory, it can be said that it is an easy environment to understand and has a simulation tool with which we can check if the circuit is going to work correctly. It should be noted that at the time of making the program in the PLC programmer, care must be taken that there is no short-circuit in the design of the control circuit....