I would appreciate feedback [negative, like the T-shirt says] and any bullshit detection
from anyone for my open source synchrophasor PMU (phasor measurement unit) project. The project goal is to develop an open source hardware sensor device (or kit) for measuring frequency and phase in AC power grids. It is designed to be compatible and used with the openPDC open source software project.
I am Open to suggestions, critique, and negative feedback for all aspects of the project. From your reply(s), I hope to figure out how to take the project to the next level.
The current project site is:
http://gridtrak.codeplex.com//AJ
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Update Nov 6, 2014:
Here is an example of how to observe AC power grid phasor:
1) use an AC/AC transformer to step down your mains voltage to a safe level for your oscilloscope to measure.
2) observe the AC sine wave on the scope on channel 1
3) input a function generator signal to channel 2 which will be used as a trigger
4) set the function generator's frequency to an even division of your mains frequency. For 50Hz, set the trigger signal to 10Hz
5) observe the position of the sine wave with respect to the trigger point. If the mains frequency is not exactly 50Hz, then you will observe the sine wave drift on the screen.
Now, get one of your friends in a location a 100km away and perform the same setup.
1) If your friend is on the same power grid, her/his mains frequency will be the same.
2) the phase angle offset from the trigger will be different because you two are not "synchronized"
Why?
The SynchroPhasor is the measurement of the phasor when you synchronize the measurements to a common time source - like a GPS PPS (pulse per second) or another signal.
When your PMU (phasor measurement units) are precise enough (synchronized to GPS or not), when the measurements are plotted on the same chart for Phase Angle VS Time, the 2 signals will be parallel while the power grid is working normally. In abnormal conditions (high loads in a section of the grid), the signals will drift apart or together. As the grid tries to balance itself, the signal separation will oscillate. If the corrective oscillation is observed to be increasing - you don't want that to happen.
How this particular Open Source PMU works:
* Converts the sine wave to complimentary half waves then to square waves triggered at a fixed voltage reference point on the sine curve. It does this using an OpAmp to avoid hysteresis (e.g. TTL transition or Schmitt trigger).
* Measures the frequency based on the square wave timing
* Measures the phase angle from the last PPS and timer increments in between
* Computes the magnitude of the "ideal" signal - in case anyone is interested in that
Feedback I would like:
I designed this as a EET student and later refined the design. However, there are probably a bunch of artifacts in the circuit that either reduce its accuracy or efficiency. I figure you EEVBlog engineers can spot these artifacts or problems right away!
The reason the project uses thru-hole components is that it is mostly intended to be a kit and the entire concept can be reproduced on a prototype board without soldering and allowing the experimenter more flexibility to change the circuit - i.e. to troubleshoot any of my mistakes!