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Matching AC Power Sources

  1. May 2, 2012 #1
    Not being an electrical engineer, I have always wondered how sources of AC power are matched when joining a common grid. I assume the power is generated at 60 hertz from each source but how is the match made so sources are in phase with one another?

    For instance, suppose an individual could generate his own electrical power. I have heard of the situation where the unneeded power is passed to the utility company for a credit. I assume the phases must be synchronized. How is this done?
  2. jcsd
  3. May 3, 2012 #2


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    Staff: Mentor

    This was explained well in a thread a few weeks back. I can't find it though. For big generators: Basically, you set your generator running at precisely the right speed, and connect a light bulb between your RED phase and the grid's RED phase, and same for YELLOW phases. When the phases are nowhere near synchronized, the bulbs glow steadily. As the phases approach sync the bulbs brightness glows and dims periodically, with a longer and longer period as you approach sync. When the speeds and phases are perfectly in sync, the bulbs are unlit. That's the point at which you connect the two systems.
    For you home photovoltaic system: there are no moving parts. The inverter that converts the DC to AC is synchronized to the grid and produces its AC in phase. It's not a 3 phase system.
  4. May 3, 2012 #3
    Instead of using light bulbs it is better to use a synchroscope, (google it for details).
  5. May 3, 2012 #4
    Thanks for replies.
  6. May 3, 2012 #5

    jim hardy

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