1. A method of teaching students the physical modern relay programming and operation ABSTRACT: A microprocessor relay is configured as a portable, self-contained, low cost learning tool to supplement academic textbooks and classroom lectures on mainstream power system protection technology. The presenter’s inspiration to assemble the demo was the result of the motivation of the students who would benefit from this educational tool, especially those who learn best by the “hands-on” 3-D experience. Analogies and comparisons aid students in understanding new concepts, especially the merging of logic programming and system protection engineering. Learning is not just strictly for students as the presenter is surprised to learn something new about the behavior of common electrical appliances.

2. A method of teaching students the physical modern relay programming and operation by Dan L. Glaser, BSEE, MSE, P.E. Southeast Symposium on Contemporary Engineering Topics Electrical and Computer Engineering September 19, 2014

3. A method of teaching students the physical modern relay programming and operation My INSPIRATION – Local community college with ABET accredited program in need of industry support to demonstrate continuous improvement and to introduce student to modern technology. The CONSTRAINTS – College’s engineering and electronics technology curriculum has limited budget to acquire newer technology. Their MOTIVATION – Many students who enroll in the 2-year technology program already have employment, but are seeking better opportunities by dedicating time In participating 3 hour class sessions each week night.

4. A method of teaching students the physical modern relay programming and operation How to satisfy needs? INSPIRATION – Volunteer to lecture students on aspects of the electric utility industry, especially with emphasis on electrical and computer engineering applications. CONSTRAINTS – Seek donations from vendors who are willing to provide modern technology equipment for educational purposes. MOTIVATION – Demonstrate near “real-life” experience with industry tools used “day-to-day.”

5. A method of teaching students the physical modern relay programming and operation Needs were met. INSPIRATION – Annual “one evening” lecture on protective relaying has been offered to students enrolled in summer session for past 3 years. CONSTRAINTS – Prominent vendor of relay protection equipment donated microprocessor relay to college. MOTIVATION – “Hands-on” demonstration of microprocessor relay using simple setup now included in annual “one evening” lecture.

6. A method of teaching students the physical modern relay programming and operation How do we learn? Everyday “life experiences” are learning experiences. Our five senses – seeing, hearing, touching, tasting, and smelling – are key to receiving and understanding (learning). Do each of us have a different way of learning? Yes, some learn better by seeing – reading or watching. Others rely on hearing – attending class or listening to lectures. Some need touching as a 3-D experience or “hands-on” approach for learning. Tasting and smelling are often learning approaches to keep us safe from harmful substances.

7. A method of teaching students the physical modern relay programming and operation So, here’s my solution to appealing to the seeing, hearing, and touching “learning” senses: A self-contained demonstration of a microprocessor relay setup that introduces electrical & computer engineering technology to the classroom or lab.

8. A method of teaching students the physical modern relay programming and operation I suppose our smelling sense helps us learn when too much current goes through a resistor. What about tasting? I would think that eating a sandwich at a workbench would not be a good idea. What do solder balls and stripped wire taste like?

9. A method of teaching students the physical modern relay programming and operation Here is the wiring diagram and the programming assignments for the microprocessor relay demo.

10. A method of teaching students the physical modern relay programming and operation A view of the finished product.

11. A method of teaching students the physical modern relay programming and operation Safety is a vital “learning” concept. Safe work practices and hazard identification are emphasized during the demonstration. Insulating tape over terminal blocks with “live” AC power. Use of power strip with 15 amp circuit breaker.

12. A method of teaching students the physical modern relay programming and operation A key method to “learning” is use of analogies. This is when a similarity is made between a new concept and something that most people have already encountered. like this This is

13. A method of teaching students the physical modern relay programming and operation Another key method to “learning” is use of comparisons. This is when a difference is emphasized between new concept and something that most people have already encountered. These are both switches. Both can isolate electricity. That is how they are similar. The wall switch can break low voltage & current, but the utility switch cannot at high voltage. SIMILARDIFFERENT

14. A method of teaching students the physical modern relay programming and operation A better “analogy” or “similarity” is that the house circuit breaker panel (left) and the high voltage substation circuit breaker (right) both can isolate and interrupt normal load or short circuit current. SIMILAR

15. A method of teaching students the physical modern relay programming and operation MOTOR OP SWITCH CURRENT TRANSFORMER CIRCUIT BREAKER Here’s the analogy of a “real” station layout to the demo relay.

16. A method of teaching students the physical modern relay programming and operation Now it’s time to define attributes of the demo relay physical I/O mapping and programming AUX1 PB toggles OUT103 & OUT105 contact (close/open) AUX2 PB toggles OUT104 & OUT106 contact (close/open) AUX3 PB enables 50 instantaneous overcurrent TRIP AUX4 PB enables 51 inverse time overcurrent TRIP AUX3 & AUX4 PB enables definite time overcurrent TRIP Vb energized causes AUX1 LED to illuminate Vc energized causes AUX2 LED to illuminate 50 instantaneous overcurrent element enabled causes AUX3 LED to illuminate 51 inverse time overcurrent element enabled causes AUX4 LED to illuminate Definite time overcurrent element enabled causes AUX3 & AUX4 LED to illuminate

17. A method of teaching students the physical modern relay programming and operation Unless default settings and logic are used, the microprocessor relay is dumb. It needs to be programmed. This includes the pushbuttons, the LED lamps, and input/output behavior. TR = 50P1 * LT10 * !LT11 + 51P1T * !LT10 * LT11 + 67P1T * LT10 * LT11 SET8 = !LT8 * PB7SET10 = !LT10 * PB9 RST8 = LT8 * PB7RST10 = LT10 * PB9 SET9 = !LT9 * PB8SET11 = !LT11 * PB10 RST9 = LT9 * PB8 + /TRIPRST11 = LT11 * PB10 67P1TC = 151P1TC = 1 OUT103 = LT8OUT104 = LT9 * !TRIP OUT105 = LT8OUT106 = LT9 * !TRIP LED7 = 59B1 LED8 = 59C1 LED9 = LT10 LED10 = LT11

18. A method of teaching students the physical modern relay programming and operation LOGIC TERMINOLOGY: Assert – Logical 1, energized, true, closed contact Deassert – Logical 0, de-energized, false, open contact ! – Inverted logic, output state opposite of input state * - AND function, all inputs must be Logical 1 for output to be Logical 1 + - OR function, any input (at least one) is Logical 1 for output to be 1 / - Rising edge trigger, asserts when Logical 0 changes to Logical 1 \ - Falling edge trigger, asserts when Logical 1 changes to Logical 0 The microprocessor relay uses some fundamental logic expressions which offer the user flexibility in applying the relay.

19. A method of teaching students the physical modern relay programming and operation Let’s follow the programming for pushbutton 7 (PB7): Since we want PB7 to latch “on” or “off” each time we depress PB7, we will need a latch bit to retain a continuous “on” or “off” state. Since latch bit 7 (LT7) has already been used elsewhere by default logic, we will use latch bit (LT8) to hold the “on” or “off” status that toggles each time we depress PB7. SET8 = !LT8 * PB7 So, when PB7 is depressed and if LT8 is NOT “on” (but “off”), then latch bit 8 (LT8) will turn “on” by making SET8 logic “1” (asserted). Conversely, the next logic statement will turn “off” LT8 if it is already “on” and PB7 is depressed. RST8 = LT8 * PB7 When LT8 is “on” (asserted), output contacts 103 and 105 will close on the relay as defined in the next two logic statements. OUT103 = LT8 OUT105 = LT8

20. A method of teaching students the physical modern relay programming and operation Be aware that the LED lamps adjacent to the pushbuttons are not automatically illuminated when a pushbutton is depressed. The behavior of the LED must be programmed! Recall how LT8 is programmed from the following statements. SET8 = !LT8 * PB7 RST8 = LT8 * PB7 Remember that LT8 controls the position of OUT103 and OUT105 contacts. OUT103 = LT8 OUT105 = LT8 LED7 = 59B1 Notice that LED7 does not “directly” follow PB7 logic state. LED7 follows PB7 logic only as an “indirect” result LT8 closing OUT103 and OUT105 contact. Closure of these contacts energize the circuit section connected to “Vb,” the voltage input measuring element. When “Vb” voltage exceeds 60 volts AC (as per the 59P1P setting, then the 59B1 logic variable “asserts” to cause LED7 to illuminate.

21. A method of teaching students the physical modern relay programming and operation Now that “programming” of the microprocessor relay has been introduced, how to you get the “program” into the relay? Communication with the microprocessor relay is achieved with a PC, communications cable (serial or USB), and the relay’s communication port. The user can either use “terminal mode” that supports simple messaging or use the relay vendor’s communication software.

22. A method of teaching students the physical modern relay programming and operation COMMUNICATION TOOLS FOR RELAY: AcSELerator Quick Set – relay setting data entry tool SEL-5601 Analytic Assistant – captured event and waveform viewing tool Quickset Communications – send terminal commands to interrogate relay The “terminal command” interface has a language of its own. The vendor’s communication software is quite powerful, supports storing files as a database, and retrieves event reports. NOTABLE TERMINAL COMMANDS: ACC – Access Level 1 (password is OTTER) 2AC – Access Level 2 (password is TAIL) BAC = Access Level B SHO n = Show settings in Group n SHO n 1 = Show settings in Logic Group n CON n = Control Remote Bit n, then SRB n (set), CRB n (rest), PRB n (pulse) MET = Meter command SET n = View or change individual setting in Group n SET n 1 = View or change individual logic settings in Group n END = End editing with option to save, X to abort without saving

23. A method of teaching students the physical modern relay programming and operation Now that we’ve introduced “computer engineering,” now its time for some “electric engineering” for the demo relay. The demo relay will illustrate two principles – control and protection. The control part is easier to tackle. We just want the ability to close and open OUT103 & 105 to energize and de-energize the section between OUT103 to OUT104 (and OUT105 to OUT106). This is done with pushbutton 7 (PB7), then observe LED7.

24. A method of teaching students the physical modern relay programming and operation Understanding the protection portion of the relay will require some background information about relaying. We need to measure the voltage and current to determine if something is abnormal about the circuit. We need to SCALE down the high voltage (as much as 500 kV) and large current (up to 65,000 amps) to a lower magnitude we can use in a measuring device. PTs (potential transformers) and CTs (current transformers) scale down the voltage and current to a safe, measurable value. CT PT

25. A method of teaching students the physical modern relay programming and operation For the microprocessor relay, PTs would be connected to voltage inputs Va, Vb, and Vc, whereas CTs would be terminated to current inputs I a and I b. For demo purposes, no PTs or CTs are used for this simple single phase loop circuit, but instead, the actual voltage and current from the AC source are directly measured.

26. A method of teaching students the physical modern relay programming and operation The protective relay must be set such that it can differentiate normal load from a short circuit – this is Sensitivity. This can be achieved with an overcurrent setpoint – current below the setpoint is ignored, but when over, the current must be interrupted. An improperly set relay can either fail to detect a short circuit or it can cause an unwanted outage.

27. A method of teaching students the physical modern relay programming and operation How does a relay decide to operate for a nearby short circuit but ignore a short circuit beyond its protection zone? Use Selectivity. Remember the 2-second driving rule? The “time” cushion between cars “selectively” avoids collisions. What’s the difference between normal traffic flow and a fender bender?

28. A method of teaching students the physical modern relay programming and operation An overcurrent relay with an instantaneous element and a time curve characteristic can provide both “sensitivity” and “selectivity,” respectively. A nearby fault (short circuit) will exhibit greater current magnitude than a distant fault. This also allows a nearby fault to be cleared faster than a distant fault by using a time curve delay characteristic. The time delay for lower magnitude distant faults should be selected to permit relays closer to the fault to operate first.

29. A method of teaching students the physical modern relay programming and operation With relay protection theory explained, we’re ready to demonstrate the overcurrent protection feature on our demo microprocessor relay. We have already discussed the “analogy” of the demo relay to a “real life” substation switch, CT, and circuit breaker, but we have not mentioned how we will simulate normal load vs. short circuit current. Our simulated load and short circuit current will use two 150 watt incandescent light bulbs (for resistive load) and a 3-speed fan (to introduce some reactive load plus represent fault current when fan operates at high speed). Let’s get ready to measure.

30. A method of teaching students the physical modern relay programming and operation To set demo relay display for better resolution, depress METER (CANCEL) button, next push CNTRL (down arrow), then push EVENTS (SELECT). Now the up or down arrow scrolls display. Push AUX1 button. Read VB voltage and observe AUX 1 LED. VB energizes when OUT103 & OUT105 close. Make sure that AUX3 & AUX4 LEDs are not illuminated. If so, push AUX3 & AUX4 to extinguish those LEDs. Now push AUX2 and observe VB and its LED.

31. A method of teaching students the physical modern relay programming and operation Use the demo microprocessor relay to measure each of our simulated loads and fault current with the protection disabled. We could estimate the bulb current. Using 150 watts with 120 VAC, the current should be I = P / V, or 150 W / 120 V = 1.25 Amps Not too bad. The actual measured light bulb current is 1.239 Amps. Take note that the light bulb has a power factor (PF) = 1. This implies a resistive load.

32. A method of teaching students the physical modern relay programming and operation Let’s take more loading measurements with demo relay. Two 150 watt bulbs measure about 2.5 Amps. Notice that I b current is 180 degrees relative to I a current. This is true since the current input polarity of I b is wired opposite of Ia. Note current for each fan speed: Low speed = 0.633 Amps Medium speed = 1.044 Amps High speed = 1.94 Amps Notice the fan produces current that lags voltage. Reactive load introduced.

33. A method of teaching students the physical modern relay programming and operation Pretend that with both 150 watt bulbs on and the fan set to medium speed represent maximum normal load. The load current is 3.29 Amps. Now pretend that with the two bulbs on and the fan set at high speed will represent a short circuit or fault. The fault current is 4.13 Amps. So what would be a suggested setpoint that distinguishes maximum load and minimum fault current? Let’s choose 3.5 Amps.

34. A method of teaching students the physical modern relay programming and operation We could have used terminal commands or vendor’s software to capture of measurements using the MET (meter) command. Notice the Low speed fan measurements that were captured using the meter command.

35. A method of teaching students the physical modern relay programming and operation Now that we know the characteristics of our test load and identified what we declare as fault current, we are ready to apply the protection scheme to the demo relay. The following setpoints and TRIP logic will be applied. KEY SETTINGS FOR DEMO: Group 1, Group Settings: CTR = 1 PTR = 1 E50P = 1 E51P = 1 E32 = N EVOLT = Y 50P1P = 3.50 67P1D = 30.00 51P1P = 3.50 51P1C = U1 51P1TD = 2.00 59P1P = 60.00 67P1TC = 151P1TC = 1 TR = 50P1 * LT10 * !LT11 + 51P1T * !LT10 * LT11 + 67P1T * LT10 * LT11

36. A method of teaching students the physical modern relay programming and operation Examine the instantaneous & time curve overcurrent setpoints: CTR = 1 PTR = 1 No CTs or PTs are used in the relay demo because the voltage and current inputs will be directly measuring the AC waveforms, so scaling ratios are not needed. Hence, both ratios are 1:1. E50P = 1 50P1P = 3.50 67P1D = 30.00 Let’s have one instantaneous overcurrent (50P1) element available to use. It’s pickup values will be 3.5 amps. We may want to have a definite (fixed) time delay of 30 cycles applied to it. E51P = 1 51P1P = 3.50 51P1C = U1 51P1TD = 2.00 We also want one time curve delay overcurrent (51P1T) element. It’s pickup value will also be 3.5 amps. However, this time delay is specified by a family of curves (or a math formula). We have selected curve U1 (moderately inverse) and a time dial of 2.

37. A method of teaching students the physical modern relay programming and operation Remember how we defined the instantaneous (50P1) overcurrent element? E50P = 1 50P1P = 3.50 67P1D = 30.00 We can use an instantaneous overcurrent tripping element if we want the quickest operate time possible – no intentional time delay. This is achieved with the 50P1 relay element. But, we may want to add a definite (fixed) time delay to allow for temporary higher current due to magnetizing current inrush on energizing transformers or to locked rotor current during motor starting. The 67P1D setting defines the amount of delay which is 30 cycles (1/2 second) for the relay demo. The definite (fixed) time logic element is labeled as 67P1T. Instantaneous overcurrent vs. Definite (fixed) time overcurrent

38. A method of teaching students the physical modern relay programming and operation 1.18X 6.3 sec Time Dial M = 4.13 / 3.5 = 1.18 TD = 2.00 tp = 6.32 sec * Normally M > 1.5 Get operate time for 51P1T time curve overcurrent element: 2.0

39. A method of teaching students the physical modern relay programming and operation E32 = N67P1TC = 151P1TC = 1 These three settings deal with torque control, or relay directionality. Since we not interested in having the overcurrent element being directional for our demo, we’ll use the settings as depicted which allow for non-directional operation. EVOLT = Y59P1P = 60.00 The next two settings enable the voltage supervision element and the setpoint for detecting when an overvoltage measurement is detected. For the demo, we are interested in knowing when the voltages are 120 VAC nominal, which happens to be above the threshold of 59P1P setting (of 60 VAC). Let’s check out the remaining setpoints:

40. A method of teaching students the physical modern relay programming and operation And finally, the ultimate purpose of the protective relay – the establishment of the trip logic which sends signals to open substation circuit breakers to clear a faulted circuit. TR = 50P1 * LT10 * !LT11 + 51P1T * !LT10 * LT11 + 67P1T * LT10 * LT11 Notice inclusion of the instantaneous overcurrent element (50P1), the inverse time curve delay overcurrent element (51P1T), and the definite (fixed) time delay ovecurrent element (67P1T). Be aware that there are latch bits that define conditions when these overcurrent elements become enabled or disabled. SET10 = !LT10 * PB9RST10 = LT10 * PB9 SET11 = !LT11 * PB10RST11 = LT11 * PB10 Essentially, LT10 and LT11 latch bits respond to PB9 & PB10 which are used to enable/disable selected protection elements.

41. A method of teaching students the physical modern relay programming and operation Now that the “textbook” theory is out of the way, let’s do some “hands-on” learning with the demo microprocessor relay. STEP 1 Make sure AUX1, AUX2, AUX3, and AUX4 LEDs are extinguished. If not, depress pushbutton near the illuminated LED. STEP 2 Enable AUX1, AUX2, and AUX4 (but not AUX 3). Turn both 150 watt bulbs “on” and turn fan “on” to “Medium” speed.

42. A method of teaching students the physical modern relay programming and operation Now that the “textbook” theory is out of the way, let’s do some “hands-on” learning with the demo microprocessor relay. STEP 3 With LEDs illuminated near AUX1, AUX2, and AUX4 pushbuttons, increase fan to “High” speed and start counting seconds until you observe the relay “trip” (open) the circuit to de- energize the light bulbs and the fan. If you correctly followed the steps, you have just observed your first protective “trip” with the demo microprocessor relay. BOTH LAMPS ON FAN ON HIGH SPEED

43. A method of teaching students the physical modern relay programming and operation Examine what happens after the relay “tripped” the circuit. STEP 4 You should observe “target” LEDs. The TRIP, 50, and 51 LEDs should be illuminated. This is an immediate visual indication of which STEP 5 Notice that AUX2 LED is not illuminated. If you depress the AUX2 pushbutton, nothing should happen since the TRIP target is still engaged which “locks out” the ability to CLOSE OUT104 & OUT106 via the AUX2 pushbutton. relay elements operated. The 51 target is evidence there was a time delayed trip.

44. A method of teaching students the physical modern relay programming and operation Reset the “targets” to disable “lock out” of control to OUT104 And OUT106 to restore and reenergize the circuit. STEP 6 Press the TARGET RESET (LAMP TEST) button to clear the “targets” and “unlock” control of OUT104 & OUT106. STEP 7 The AUX4 LED should still be illuminated. This means that the protection remains enabled. Now, depress AUX2 pushbutton and the circuit will be restored – temporarily. Why? Fault is still there.

45. A method of teaching students the physical modern relay programming and operation That was a trick. The fault current was still present upon restoring the circuit. We need to remove the fault. STEP 8 Reset the targets. With lamps “on,” change the fan speed to “Medium” before depressing AUX2 pushbutton. Protection should remain enabled, i.e., AUX4 is “on.” STEP 9 With the fault current removed, depress the pushbutton for AUX2. The circuit should return to normal even while AUX4 remains enabled. BOTH LAMPS ON FAN ON MEDIUM SPEED

46. A method of teaching students the physical modern relay programming and operation Let’s try the instantaneous overcurrent “trip” element. STEP 10 With the circuit energized (AUX2 LED still illuminated), depress AUX4 pushbutton to disable the inverse time curve overcurrent protection element. The AUX4 LED will be extinguished. STEP 11 Immediately after disabling AUX4, depress AUX3 pushbutton to enable the “instantaneous” overcurrent tripping element.

47. A method of teaching students the physical modern relay programming and operation The no-delay “instantaneous overcurrent trip. BOTH LAMPS ON FAN ON HIGH SPEED STEP 12 With the circuit energized (AUX2 LED still illuminated) and the “instantaneous” protection enabled (AUX3 LED illuminated), increase fan speed to “High” to simulate a fault. STEP 13 The circuit should “trip” or de- energize without any delay. You should observe the 50 target plus some other targets.

48. A method of teaching students the physical modern relay programming and operation Watch what happens when “instantaneous” element is enabled during motor starting. STEP 14 Press the TARGET RESET (LAMP TEST) button to clear the “targets.” Keep both lamps “on.” Put fan on “Low” speed. STEP 15 The AUX3 LED should remain illuminated to retain “instantaneous” overcurrent protection during reenergization of the circuit. Now depress AUX2 pushbutton to close OUT104 & OUT106 to energize the fan. What happened? The motor start may have caused a current higher than the 3.5 amp pickup of the “instantaneous” element. BOTH LAMPS ON FAN ON LOW SPEED

49. A method of teaching students the physical modern relay programming and operation Let’s try the definite (fixed) time overcurrent “trip” element. STEP 16 Press the TARGET RESET (LAMP TEST) button to clear the “targets” and “unlock” control of OUT104 & OUT106. STEP 17 The AUX3 LED should remain BOTH LAMPS ON FAN ON LOW SPEED illuminated, but now depress AUX4 pushbutton such that both AUX3 and AUX4 LEDs are illuminated. This combination enables a definite (fixed) time delay overcurrent element. If the current exceeds 3.5 amps (as per our setpoint), a “trip” will be delayed by 30 cycles (or ½ second). Now depress AUX2 pushbutton to close OUT104 & OUT106 to energize the fan.

50. The definite (fixed) time overcurrent “trip” element can ride through a motor start. A method of teaching students the physical modern relay programming and operation LAMPS OFF, THEN ON SLOWLY INCREASE FAN SPEED STEP 18 If all went well, nothing should have happened other than the fan starting and the circuit remaining energized. STEP 19 Keep the fan on “Low” speed. Turn “on” both lamps. The circuit should continue to remain energized. We’re still below the 3.5 amp “trip” setpoint. STEP 20 Keep both lamps “on.” Increase the fan speed to “Medium.” Wait 10 seconds. Then, increase the fan to “High.”

51. The definite (fixed) time overcurrent “trip” element also operates for short circuits. A method of teaching students the physical modern relay programming and operation LAMPS OFF, THEN ON SLOWLY INCREASE FAN SPEED STEP 21 With both lamps “on” and the fan at “Medium” speed, the circuit should have remained energized. But once the fan was increased to “High” speed, the simulated fault current was interrupted within ½ second. STEP 22 Turn “off” both lamps and turn “off” the fan in preparation for the last experiment. Depress the TARGET RESET (LAMP TEST) button. Depress AUX4 pushbutton to disable “time delay” trip.

52. Check impact of resistive load upon circuit energization with “instantaneous” overcurrent protection enabled. A method of teaching students the physical modern relay programming and operation STEP 23 Turn only one lamp with 150 watt bulb “on” prior to energizing the circuit. STEP 24 With AUX3 illuminated (enabled) and AUX4 extinguished (disabled), this allows only the “instantaneous” (no time delay) overcurrent element to be active. STEP 25 Depress pushbutton for AUX2 to close OUT104 & OUT106. What happens?

53. Result of resistive “light bulb” load upon circuit energization with “instantaneous” overcurrent protection enabled. A method of teaching students the physical modern relay programming and operation Why is “instantaneous” overcurrent operating for resistive load? There should not be “inrush” current for resistive load, or maybe? WHAT??? We measured earlier that the 150 W bulbs exhibited 1.0 PF (Power Factor) which is a purely resistive load.

54. The demo microprocessor relay records events and fault traces to help diagnose protection “misoperations.” A method of teaching students the physical modern relay programming and operation

55. Why did “instantaneous” overcurrent element trip upon energizing an incandescent light bulb? A method of teaching students the physical modern relay programming and operation ANSWER: Even though a light bulb has a “resistive” characteristic, its resistance increases as its tungsten element increase in temperature. All resistors exhibit some change in resistance with temperature, but most stay within a fixed ranged. The resistance of tungsten changes significantly as the temperature of the bulb goes from ambient air temperature (cool) to its operating temperature (hot). Whereas the event report did not explain the reason why the current went dramatically high upon the light bulbs energization, it demonstrated that the current was high (implying low resistance) until the bulb reached its stable operating temperature (and operating resistance and current).

56. A method of teaching students the physical modern relay programming and operation Wait a minute! We’re not done. Remember the setup for the motor start experiment? In STEP 14, we were directed to keep both lamps “on” and put fan on “Low” speed. With AUX3 the “instantaneous” overcurrent element enabled, the circuit tripped without delay. We “assumed” that the trip was caused by a motor start characteristic of the fan. That may have been a “false” inference since we now know that the light bulbs cause a current surge. Hence, the motor start test needs to be redone, but this time we need to make sure both lamps are “off” and only the fan is “on.” BOTH LAMPS ON LAMPS OFF FAN ON LOW SPEED

57. A method of teaching students the physical modern relay programming and operation Let’s do the motor start experiment again – the correct way. What will happen? So we repeat STEP 14 with both lamps “off” and the fan on “Low” speed. With AUX3 the “instantaneous” overcurrent element enabled, the circuit surprisingly remains energized. Try this again with the fan on “Medium” speed, and then on “High” speed with both lamps remaining “off.” There is no current surge for the fan. With the fan “off,” insert a yard stick through the fan’s front and rear grill. Then turn “on” the fan to check for “locked rotor” current. The fan motor may use a split winding exhibiting the same start and run current. BOTH LAMPS OFF FAN ON LOW, MEDIUM, & HIGH SPEED

58. A method of teaching students the physical modern relay programming and operation In conclusion, let’s see what the demo microprocessor relay has done for us. 1.We learn through our five senses. Everyone has a preferred sense for learning. 2.New concepts are easily introduced using “analogies” to show “similarities” and “comparisons” to illustrate “differences.” 3.“Hands-on” experimentation adds “3-D” to learning. 4.The demo microprocessor relay introduces the merger of logic programming and power system protection which is the mainstay of the power industry. 5.The “self-contained” demo relay uses common household items to illustrate protection concepts. It’s a low cost tool. 6.Even the teacher can be the student and learn something new – you can teach an old dog new tricks!

59. A method of teaching students the physical modern relay programming and operation “Their motivation was my inspiration - thanks.” I thank the students of Delgado Community College’s ELET (Electrical and Electronics Technology) program for inspiring me to pursue acquisition of the demo microprocessor relay and make it a useful training tool that introduces students to modern system protection technology. I appreciate the generosity of SEL Engineering Laboratories for donating the SEL-351S relay to Delgado College with special thanks to Sal Jadid for making this happen. I also thank ELET faculty members Ramon Ariza and Mike Nixon for giving me the opportunity to support and improve Delgado’s ELET “ABET” accredited program.