CurrentProtectionDevices copy

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Hennepin Technical College *

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1155

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Mechanical Engineering

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Dec 6, 2023

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CURRENT PROTECTION DEVICES 1-50 BASIC CONTROLS Procedure Summary In the first part of this exercise, you will set up a tripping circuit for the Manual Starter. You will first test the circuit breaker section of the Manual Starter by shorting the circuit. After that, you will intentionally overload the circuit to make the overload relay part trip. In the second part of the exercise, you will use a tripping chart to identify the overload class and theoretical tripping time of the Overload Relay module. You will then implement a circuit with the Overload Relay module to verify the theoretical tripping time value. You will also see that heat has an effect on an overload relay tripping time. Finally, you will compare the Manual Starter and the Overload Relay and observe that the first works directly on the power lines and the latter, on the control circuit. EQUIPMENT REQUIRED Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required for this exercise. PROCEDURE The AC Power Supply provides high voltages. Do not change any AC connection with the power on. Basic setup 1. Perform the Basic Setup and Lockout/Tagout procedures. Overload protection using the Manual Starter 2. Connect the circuit shown in Figure 1-25. 3. Set the Cam Switch to the STOP position. Set the overload potentiometer of the Manual Starter to the lowest value, and the knob to the I position. Clamp an ammeter around a power lead as shown in Figure 1-25. Perform the Energizing procedure. Industrial Controls Training System V21113 Save As ✔ ✔ ✔

CURRENT PROTECTION DEVICES BASIC CONTROLS 1-51 Figure 1-25. Manual Starter tripping circuit. 4. Start the chronometer as you set the Cam Switch to the FWD position. How long does it take for the Manual Starter overload to trip? Explain what happened. 5. Set the Cam Switch to the STOP position. Reset the Manual Starter by turning the knob to the I position. Start the chronometer as the Cam Switch is set to the REV position. Industrial Controls Training System V21113 ✔ Tripped less than a second, a dead overload will go off the moment the power goes on. ✔

CURRENT PROTECTION DEVICES 1-52 BASIC CONTROLS Referring to the ammeter display, what is the current flowing through the circuit? Current: 6. How long does it take for the Manual Starter overload to trip? Tripping time: 7. By how many times is the measured current higher than the Manual Starter's overload current setting? Number of times (ratio): 8. Explain what happened compared to when the Cam Switch is set to the FWD position. The Starting Resistors module may be hot. Please be careful when you handle this module after use. 9. Perform the Lockout/Tagout procedure. 10. Referring to Figure 1-22, determine the overload class of the Manual Starter by using the tripping time and current ratio determined from the Figure 1-25 circuit. Class 10 Class 20 Class 30 11. Referring to Figure 1-22, at six times the overload relay’s current setting, how long should the Manual Starter take to trip? Tripping time: Industrial Controls Training System V21113 4.03A ✔ 25 sec ✔ 2.5x ✔ FWD was going thru one resistor which tripped quicker, REV was going thru three resistor which had more voltage drop and held the curuit longer. ✔ ✔ ✔ ✔ 9.6

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CURRENT PROTECTION DEVICES BASIC CONTROLS 1-53 Overload protection using the Overload Relay 12. In the Figure 1-26 circuit, what would happen in case of a short-circuit (if the only short-circuit protection device is the Fuse Holder)? 13. Calculate the current that will flow through line L3, using the nominal voltage, resistor value, and Ohm's law (E = RI). Current: 14. Calculate the ratio of the current calculated in the previous step to the Overload Relay's current setting (lowest value on the potentiometer) (I CALCULATED / I OVERLOAD ). Ratio: 15. Referring to Figure 1-22, how long should it take for the overload relay to trip, when power is applied to the circuit? Use the current ratio calculated in the previous step. Tripping time: 16. Connect the circuit shown in Figure 1-26. 17. Set the overload potentiometer of the Overload Relay to the lowest value, and the reset button to the A (automatic reset) position. Set the TS toggle switch of the Selector Switches module to the O position. Clamp an ammeter around power line 3 as shown in Figure 1-26. Note: Before installing the Fuse Holder module, make sure that the fuses inside are not blown. Perform the Energizing procedure. 18. Start the chronometer as you set the TS toggle switch to the L position. Referring to the ammeter display, what is the current flowing through the circuit? Current: Industrial Controls Training System V21113 ✔ The fuses would trip/blown. ✔ 4A ✔ 2.5A ✔ 10sec ✔ ✔ ✔ 4.03A

CURRENT PROTECTION DEVICES 1-54 BASIC CONTROLS Figure 1-26. Overload Relay tripping circuit. 19. How long does it take for the overload relay to trip? Tripping time: 20. How long does the Overload Relay take to reset automatically (wait for the current to flow again)? Reset time: Industrial Controls Training System V21113 23sec 2 min

CURRENT PROTECTION DEVICES BASIC CONTROLS 1-55 21. How long does it take for the overload relay to trip a second time? Tripping time: 22. Compare the tripping time measured for the second reset (step 21) to the tripping time measured for the first reset (step 19). How was the tripping time measured for the second reset? Shorter Longer About the same Note: The bimetal strip inside the Overload Relay is still hot after the first reset. 23. Does the theoretical tripping time obtained with the chart correspond to the value obtained experimentally? Yes No 24. What reasons could explain a difference between calculated and experimental results? 25. Do the Manual Starter and the Overload Relay take nearly the same time to trip under similar conditions? Yes No 26. Which device works directly on the power lines? Manual Starter Overload Relay 27. Explain how the two devices make the motor stop. Industrial Controls Training System V21113 >10 sec ✔ ✔ Calculated results are more precise than experimental because most components arent measured as it rated. The fitment in the terminal overload can determine the tripping points by the heat it contains. ✔ ✔ ✔ ✔ ✔ Both have a thermal and trips with the heat and will open the curcuit which will stop the motor.

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CURRENT PROTECTION DEVICES 1-56 BASIC CONTROLS 28. Turn the individual power switch of the AC Power Supply off, disconnect the circuit, remove the magnetic labels, and return the equipment to the storage location. Name Date Instructor's Approval Industrial Controls Training System V21113 ✔ Save As Submit Print