Index

# RELAYS 101

### RELAYS 101 Lecture Notes

Screen Shots of various concepts presented on classroom whiteboard.
Extra Stuff at Beginning of Class
1. A calculation to find the amount of VARs in a metered circuit form the olden days. A KWH Meter measures only the real power provided to a load. In the olden days, before solid-state circuitry or microprocessors, a KWH meter could be wired competely "wrong" and the measurement would have been known as "Q-Hr" ("Q" for Quality of circuit.) then the number of "Q-Hrs" measured would be put into a simple calculation to determine the amount of VARs. So, a KWH meter can be used to determine amount of VARs. Note that there must be a KWH meter also in service. Of course nowadays with solid-state or microprocessor metering VARs (and so much more) can be found with the same device that measured the Watts. 2. The calculation to determine frequency of a generator. This too will become more and more archaic as it only applies to "spinning power resources". With DC generation run through an inverter the calculations are just not needed. 3. Fibonacci Sequence starts with "1,1..." Add the last two numbers together and you get "2". Now the sequence is "1,1,2..." Add the last two numbers together and you get "3". "1,1,2,3,5,8,13,21,34,55..." (Goes on forever) Take any 4 consecutive numbers from the sequence (such as 2,3,5,8). Multiply the two outer numbers of the sample (2x8 = 16) and take the two internal numbers multiply them together and multiply that product by 2 (3x5x2=30). Now use those two products (16 & 30) as the two sides of your right triangle. This yields a hypotenuse that is a whole number (34) AND THE HYPOTENUSE ALSO IS A NUMBER IN THE FIBONACCI SEQUENCE!! So cool. 4. & 6. Method(s) to find whole numbers that can be applied to the sides of a right triangle that will produce a hypotenuse that is also a whole number. With a series of ODD numbers (3,5,7,9,11,13...) take any two consecutive numbers, add their reciprocals, the answer provides the values of the two sides of a right triangle that produce a whole number hypotenuse. Examples shown ODD: 1/5+1/7 = 12/35 (yields hypotenuse of "37"). EVEN: 1/4+1/6 = 5/12 (yields hypotenuse of "35") three methods to get numbers that I use in class to put into X-Y rectangular - polar conversions or R-X rectangular - polar conversions or into P-Q rectangular - polar conversions. After all you cannot always use the 3,4,5 triangle and it's just easier to have whole numbers for the calculations. 5. A nonsense demonstration of "REDUCING FRACTIONS" - a joke. 7. Fancy math. i eight sum pi. 8. Refresher for the class to recall calculating parallel resistances and adding currents in a circuit. This same circuit is shown later in class as a way to understand zero sequence compensation and accurate distance measurements for a phase-to-ground fault. See second diagram below.
Phase to Phase Fault
A simple diagram showing distance measurement in a phase-to-phase fault.
3-Phase Fault
A simple diagram showing distance measurement in a 3-phase fault.
Example Phase-to-Ground Equivalent Circuit
A simple diagram showing distance measurement in a phase-to-ground fault. Wait, maybe not so simple- but this diagram shows how accurate distance measurment can be achieved in a phase-to-ground fault. Here, two measurements and two programmed inputs (relay settings) make the relay work. "Z0" & "Z1" are the relay settings. "V" & "A1" are the measurements. Everything else is a calculation. But the final result is distance to the fault measurement that is as accurate as the relay settings. To me this underscores how so much of microprocessor relay testing is nonsense because "How many times must you test the programming?" Test it once in acceptance testing then test the measuring units of the relay (is one way to do this).
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