Timed Starting for Three Motors with Instrumentation.pptx

This presentation provides a detailed exploration of a control circuit designed to manage the timed starting of three large motors in a machine. The core challenge addressed is the excessive current surge that occurs when all three motors start simultaneously. To mitigate this, the circuit implements a time-delay mechanism, ensuring a 10-second interval between the starting of each motor.

The presentation begins with an overview of the problem and then delves into the schematic of the start-stop push-button control system. It explains how the circuit is designed to control three motor starters and two time-delay relays. The sequence of operations is described in detail, illustrating how the circuit starts motor 1, followed by motor 2 and motor 3, each with a 10-second delay.

The presentation also covers the safety features of the circuit, highlighting that an overload on any motor will stop all motors. This ensures the protection of the system and prevents potential damage.

In addition to the timed starting sequence, the presentation includes a section on developing wiring diagrams from schematic diagrams. It emphasizes the importance of correctly labeling and connecting components, using a simple numbering system for clarity.

Overall, this presentation is a comprehensive guide for understanding and implementing a timed starting circuit for multiple motors, ensuring both operational efficiency and safety.

1. Timed Starting for Three Motors

2. A machine contains three large motors. The current surge to start all three motors at the same time is too great for the system. Therefore, when the machine is to be started, there must be a. delay of 10 seconds between the starting of each motor. Circuit 2, shown in Figure 20–1, is a start–stop, push button control that controls three motor starters and two time-delay relays. The circuit is designed so that an overload on any motor stops all motors.

3. When the START button is pressed, a circuit is completed through the START button, M1 motor starter coil, and TR1 relay coil. When coil M1 energizes, motor 1 starts and auxiliary contact M1, which is parallel to the START button, closes. This contact maintains the current flow through the circuit when the START button is released

4. After a 10-second interval, contact TR1 closes. When this contact closes, a circuit is completed through motor starter coil M2 and timer relay coil TR2. When coil M2 energizes, motor 2 starts

5. Ten seconds after coil TR2 energizes, contact TR2 closes. When this contact closes, a circuit is completed to motor starter coil M3, which causes motor 3 to start

6. If the STOP button is pressed, the circuit to coils M1 and TR1 is broken. When motor starter Ml de-energizes, motor 1 stops and auxiliary contact Ml opens. TR1 is an on-delay relay; therefore, when coil TR1 is de-energized, contact TR1 opens immediately When contact TR1 opens, motor starter M2 de-energizes, which stops motor 2, and coil TR2 de-energizes. Because TR2 is an on-delay relay, contact TR2 opens immediately. This breaks the circuit to motor starter M3. When motor starter M3 de-energizes, motor 3 stops. Although it takes several seconds to explain what happens when the STOP button is pressed, the action of the relays is almost instantaneous. If one of the overload contacts opens while the circuit is energized, the effect is the same as pressing the STOP button. After the circuit stops, all contacts return to their normal positions, and the circuit is the same as the original circuit

7. Float Switch Control of a Pump and Pilot Lights

8. In circuit 3, a float switch is used to operate a pump motor. The pump is used to fill a tank with water. When the tank is low on water, the float switch activates the pump motor and turns a red pilot light on. When the tank is filled with water, the float switch turns the pump motor and red pilot light off, and turns an amber pilot light on to indicate that the pump motor is not running. If the pump motor becomes overloaded, an overload relay stops the pump motor only. The requirements for this circuit indicate that a float switch is to be used to control three different items: a red pilot light, a motor starter, and an amber pilot light. However, most pilot devices, such as float switches, pressure switches, and limit switches, seldom contain more than two contacts. When the circuit requires these pilot devices to use more contacts than they contain, it is common practice to let a set of contacts on the pilot device operate a control relay. The contacts of the control relay can be used as needed to fulfill the requirements of the circuit.

9. The float switch in circuit 3 is used to operate a control relay labeled FSCR. The contacts of the control relay are used to control the motor starter and the two pilot lights. In the circuit shown in Figure 21–2, current can flow through the normally closed FSCR contact to the red pilot light and through a second normally closed FSCR contact to the coil of motor starter M1. When motor starter M1 energizes, the pump motor starts and begins to fill the tank with water. As water rises in the tank, the float of float switch FS rises also.

10. When the tank is sufficiently filled, the float switch contact closes and energizes relay FSCR When the coil of relay FSCR energizes, all FSCR contacts change. The normally closed contacts open and the normally open contact closes. When the normally closed contacts open, the circuits to the red pilot light and to coil M1 are broken. When motor starter M1 de-energizes, the pump motor stops. When the normally open FSCR contact closes, current flows to the amber pilot light. When the pump motor turns off, the water level begins to drop in the tank. When the water level drops low enough, the float switch opens and de-energizes relay coil FSCR.

11. When relay FSCR de-energizes, all FSCR contacts return to their normal positions, as shown in circuit 3. If the pump motor is operating and the overload relay opens the overload contact, only the motor starter is de-energized. The pilot lights continue to operate.

12. Developing a Wiring Diagram

13. Developing a Wiring Diagram Wiring diagrams will now be developed for the three circuits just discussed. The method used for developing wiring diagrams is the same as the method used for installing new equipment. To illustrate this principle, the components of the system will be drawn on paper and connections will be made to the various contacts and coils. Using a little imagination, it will be possible to visualize actual relays and contacts mounted in a panel, and wires connecting the various components.

14. Figure 22–1 shows the schematic for the alarm silencing circuit from Chapter 19, and Figure 22–2 shows the components of the system

15. The connection of the circuit is more easily understood with the aid of a simple numbering system. The rules for this system are as follows: Each time a component is crossed, the number must change. Number all connected components with the same number. Never use a number set more than once. Figure 22–3 shows the schematic of the alarm silencing circuit with numbers placed beside each component. Notice that a 1 has been placed beside L1 and one side of the pressure switch. The pressure switch is a component. Therefore, the number must change when the pressure switch is crossed. The other side of the pressure switch is numbered with a 2. A 2 is also placed on one side of the normally closed S contact, one side of the red warning light, one side of the normally open reset push button, and one side of the normally open S contact. All of these components are connected electrically; therefore, each has the same number

16. W hen the normally closed S contact is crossed, the number is changed. The other side of the normally closed S contact is now a 3, and one side of the horn is a 3. The other side of the horn is connected to L2. The other side of the red warning light and one side of relay coil S are also connected to L2. All of these points are labeled with a 4. The other side of the normally open reset button, the other side of the normally open S contact, and the other side of relay coil S are numbered with a

17. The same numbers that are used to label the schematic in Figure 22–3 are used to label the components shown in Figure 22–4. L1 in the schematic is labeled with a 1; therefore, 1 is used to label L1 on the wiring diagram in Figure 22–4. One side of the pressure switch in the schematic is labeled with a 1 and the other side is labeled with a 2. The pressure switch in the wiring diagram is shown with three terminals. One terminal is labeled C for common, one is labeled NO for normally open, and one is labeled NC for normally closed. This is a common contact arrangement used on many pilot devices and control relays

18. In the schematic the pressure switch is connected as a normally open device; therefore, terminals C and NO will be used. A 1 is placed by terminal C and a 2 is placed beside terminal NO. Notice that a 2 has also been placed beside one side of the normally open reset button, one side of the normally closed contact located on relay S, one side of the normally open contact located on relay S, and one side of the red warning light. A 3 is placed beside the common terminal of relay contact S which is used to produce a normally closed contact, and beside one of the terminal connections of the horn. A 4 is placed beside L2, the other terminal of the horn, the other side of the red warning light, and one side of relay coil S. A 5 is placed on the other side of relay coil S, the other side of the normally open reset button, and on the common terminal of relay contact S, which is used as a normally open contact. Notice that the numbers used to label the components of the wiring diagram are the same as the numbers used to label the components of the schematic.

19. For instance, the pressure switch in the schematic is shown as being normally open and is labeled with a 1 and a 2. The pressure switch in the wiring diagram is labeled with a 1 beside the common terminal and a 2 beside the NO terminal. The normally closed S contact in the schematic is labeled with a 2 and a 3. Relay S in the wiring diagram has a normally closed contact labeled with a 2 and a 3. The numbers used to label the components in the wiring diagram correspond to the numbers used to label the same components in the schematic.

20. After labeling the components in the wiring diagram with the proper numbers, it is simple to connect the circuit (Figure 22–5). Connection of the circuit is made by connecting like numbers. For example, all of the components labeled with a 1 are connected, all of those labeled with a 2 are connected, all of the 3s are connected, all of the 4s are connected, and all of the 5s are connected

21. Developing a Wiring Diagram

22. Circuit 2 Shows the schematic diagram from the first figure shown in the presentation with the component's numbered. Now from this numbered schematic diagram the next figure shows the numbered components in the schematic diagram is converted to a wiring diagram matching the number on each component present.

23. Here is the incomplete wiring diagram converted from the schematic or ladder diagram shown from the previous slide. With matching numbering of each component

24. Wire connections are made by connecting like numbers. Thus completing the conversion from schematic diagram to wiring diagram.

25. Activity Submit it on Friday

26. Now for your activity convert the numbered schematic diagram to a wiring diagram

27. Here the components are numbered to correspond with the schematic. Use this to connect the wires correctly in reference to the schematic diagram shown.

28. Semi-final exam on June 6, 2024 Coverage is After Midterm Topic up to Control Transformer!