240 ac grid tie issue

Discussion in 'The Projects Forum' started by aac9876, Aug 23, 2008.

  1. aac9876

    Thread Starter Active Member

    Dec 9, 2006
    124
    0
    This is about connecting a wind turbine to your house mains/breaker box.
    There is one commercial turbine that connects simply by wiring the 240 ac leads to a double pole
    breaker 30 amp. In the USA that is a double 120 for 240 total.
    When their is more juice being made than being used, the current backs up into the
    utility service line and spins the meter backward.
    What I am curious about is how much of which source flows up the line at what time??
    I was thinking that the more current that tries to get in the box from the turbine eventually chokes off any current from the utility just because its a larger flow than the utilities..??
    The larger force wins like 50/50 then 60/40 then 70/30 etc etc.
    What do you think....anybody in the know about this like a power company engineer??
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You need at least a licensed electrician to advise you.

    All I can suggest is - don't attempt to hook something like that up yourself.

    I'm not a licensed electrician.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    One of the expensive bits of hardware you need for that is a synchronous inverter. It produces AC from a DC source that is locked in phase with the utility power. If its power output exceeds the house usage, it will drive current towards the utility and run the watt-hour backwards.
     
  4. aac9876

    Thread Starter Active Member

    Dec 9, 2006
    124
    0
    funny how a question often gets way off track in the answer.After asking here and there for years, I know more about sine/square wave/grid issues than I want to.
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    This is a matter of voltage sources in parallel and loads in parallel. Draw your schematic and use the appropriate analysis methods.

    Safety note: The synchronous inverter MUST NOT put power onto the grid when the grid is down. If it does, the lives of linemen are at risk.

    Safety note: The grid, and many stand-alone systems, produce more than enough power to make metal bits explode with permanent detrimental results.

    Safety note: Electricity can kill. When working with multiple sources, insure ALL sources are disconnected before servicing.

    Safety note: If you don't know what you are doing, don't do it. Get an expert. Electrical experts are far less expensive than medical experts or funeral experts.
     
  6. sameerphadke12345

    New Member

    Sep 18, 2008
    3
    0
    HI
    this is not possible unless your frequency mactch with power supply which you have for eg. india we are using 50 hz frequency
    as it is single phase no need to check phase sequence
    But if your volage is more than the supply voltage then meter direction will not change as you may aware that we are converting 3 ph to single phase by chosing 1 ph and neutral connection.
    Dear friend this is also one of the reason why in many places small power genaration project have not got the permision
    this may cause problem to the grid balance
    If entire system is single phase then this is possible.
    this also need lots of protections
    do not try to do this
    If at all you want to do this use relay and contactor and do in house model and check how it works you may cometo know

    For more information you can read BL Thereja or MG says book on parallel operation systems
    byee
     
  7. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    What Sarge said, and these questions..............

    What percentage of time are you able to utilize your wind-turbine at full output ?? Are the winds steady & reliable / gusty / intermittant ??

    Seems it would be far easier ? to design an A or B switching circuit similar to a U.P.S. unit, that will allow the "grid" to kick in, or cause a generator to start...when your turbine ain't cutting it. Bottom line, if your grid watthour meter doesn't run at all, you pay nothing.

    Putting power back onto the grid, sounds a lot like trying to put toothpaste back in the tube post squeeze.......:D.......
     
  8. vetterick

    Active Member

    Aug 11, 2008
    35
    0
    I'm a little curious here, I've heard that generating more power than your using will spin your meter backwards, but I don't believe it, isn't the meter simply a motor across a shunt? If so it can only run one direction, if you made more than you used they would still charge you for the extra.
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    There is no shunt. The meter is more complicated than a simple motor. It is an aluminum disk and a pair of coils. One coil has flux proportional to voltage, the other coil flux is proportional to current. Eddy currents are set up in the disk, making it turn at a rate proportional to power.

    When power goes onto the grid instead of off from the grid, the current is on the opposite phase shift of the voltage. The eddy currents in the disk are backward, so the disk turns backward.

    Newer meters are, of course, solid state.
     
  10. subtech

    Senior Member

    Nov 21, 2006
    123
    4
    Any commercial wind turbine manufacturer will supply the devices necessary to connect the outuput of his turbine with the feed from the power company, IF... that is what you specify when you place your order.
    Almost any size of generator (alternator) can be placed in parallel with the power company mains at your home and can be made to work properly and safely, IF.. you use the proper equipment and it is connected properly and TESTED.
    This undertaking is definitely NOT for the average homeowner. Alot of experienced electricians will not undertake such a project either due to the complexity and liability.
    Having a wind turbine is at your home is a admirable and useful project, BUT... pay a professional and get the job done safely and properly.
    Before you do anything else, check with your power provider. It is likely that they will have a specialist for you to consult with. They will also have requirements and regulations you will need to comply with. Remember, you are connecting your equipment in parallel with their equipment. You need to cooperate and communicate with the powerco. Lives are at stake.
    Good luck with your project, and yes, most older "disc" type wattmeters will spin backward if your generator is producing more power than you home needs at any particular time.
     
  11. vetterick

    Active Member

    Aug 11, 2008
    35
    0
    There is no shunt. The meter is more complicated than a simple motor. It is an aluminum disk and a pair of coils. One coil has flux proportional to voltage, the other coil flux is proportional to current. Eddy currents are set up in the disk, making it turn at a rate proportional to power.

    When power goes onto the grid instead of off from the grid, the current is on the opposite phase shift of the voltage. The eddy currents in the disk are backward, so the disk turns backward.

    Well that makes sense, funny how you can wonder about things for years, I guess I never believed the meter would run backwards because I never saw a need for it.

    Thanks for the info.
     
Loading...