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dinos:
You have an interesting interpretation of the translation of your data to the ITIC boundary curves.
In retrospect the definitions may not be as clear as I thought.
3.5) Voltage Sags
Two different RMS voltage sags are described. Generally, these transients result from application of heavy loads, as well
as fault conditions, at various points in the AC distribution system. Sags to 80% of nominal (maximum deviation of 20%)
are assumed to have a typical duration of up to 10 seconds, and sags to 70% of nominal (maximum deviation of 30%) are
assumed to have a duration of up to 0.5 seconds.
3.6) Dropout
A voltage dropout includes both severe RMS voltage sags and complete interruptions of the applied voltage, followed by
immediate re-application of the nominal voltage. The interruption may last up to 20 milliseconds. This transient typically
results from the occurrence and subsequent clearing of faults in the AC distribution system.
I believe what the Voltage Tolerance Envelope says is that if a sag or dropout occurs for less than 20 milliseconds, 1.2 cycles, that no matter how you measure the voltage (peak, RMS, average) during that period it does not matter what the voltage is, it can be zero. Their discussion would seem to imply that on either side of the 20 millisecond problem that the voltage needs to be nominal based on section "3 Discussion" in the ITI Application Note.
I do not believe that RMS voltage is the really important consideration for sags or dropouts. Since this is directed at IT applications it is most likely related to DC capacitor input filter power supplies. These will be designed with a time constant that probably allows a 1 cycle loss of power input. This also means that near full voltage is needed at the end of the 1.2 cycle period. Basically a whole cycle could be lost, but then the following cycle needs to be nominal. Really would be not less than 90% od nominal. So you could lose one positive peak followed by a loss of the following negative peak or vice versa.
A capacitor input filter power supply essentially uses the peak of the input voltage to charge the capacitor. Current only flows for a short time.
Assume a bridge rectifier off of the line feeding a capacitor input filter. Apply a 120 V sine wave input. Capacitor voltage will be 169.7 V minus diode drop. I apply this 120 V RMS for a while, and then switch to 120 V DC (same RMS voltage). The capacitor voltage drops to 120 V minus diode drop. This does not fail the criteria using RMS as the means of measuring the input voltage. Yet from a functional point of view at the output of the DC supply there is failure.
How should "3.5 Voltage Sags" be interpreted? I think for your distorted waveform RMS is not the correct measurement. However, assume RMS is a valid measure, measurements are quantized to start on a zero crossing, the RMS value is calculated for a 2 cycle period (meaning the time period of averaging is 2 cycles --- 32 milliseconds), and a running measurement is made every 1/2 cycle, then any RMS value obtained below 70% of nominal is failure. This is a tough criteria and may not really address the problem. I believe your waveform would fail this test.
Now consider your data. To put points on the ITIC plot from your data I believe you have to set a starting time reference point that will correspond to the left coordinate of the ITIC curve. I would pick the first negative zero crossing on your original plot, This is above the 122.2 V dot. Your first RMS value from this reference is 59.4 V because you have whole cycle calculations of RMS. Thus, at 16.6 MS on the ITIC I would plot 59.4 V. Next I need an RMS value from the first negative zero crossing to 1.5 cycles later. This will not be as large as 91.3 V and occurs at 25 MS. I believe your waveform fails the ITIC lower limit.
When longer times for sags are considered I conclude that this means you drop from nominal to a fixed steady value for that long time, like 70%, and this can last for 0.5 seconds and then must return to nominal.
One item missing from the ITI definitions is the meaning of their usage of RMS and its integration time period.
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