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  • Tom Gray
    This discussion from another list may be of interest. ... From: Andrew Tuckey [mailto:tuckey@ieee.org] Sent: Friday, July 06, 2001 5:23 AM Subject: SPINNING
    Message 1 of 1 , Jul 6, 2001
      This discussion from another list may be of interest.

      -----Original Message-----
      From: Andrew Tuckey [mailto:tuckey@...]
      Sent: Friday, July 06, 2001 5:23 AM

      A few comments below

      > I think the real function of spinning reserve is to be a pro-active
      monitor/stabiliser of grid frequency, which is inherently unstable and
      influenced by dynamic load changes. Any spinning reserve ("wind turbine"?) must
      therefore be programmed to increase its power output when the grid frequency
      drifts slightly below 50 Hz, and conversely decrease its output when the
      frequency drifts above 50 Hz.
      > Large wind farms forming say 20 per cent of a system's generating capacity
      will actually perform the exact opposite function: for example a squall front
      entering a compact wind farm would cause a big surge in generation with no
      reference to the grid frequency, and unless matched by a similar increase in
      system load, would inevitably tend to increase the system frequency. I regret to
      say that this is really the opposite of spinning reserve, and a potentially
      destabilising influence on the grid.
      > Does anyone know of a wind farm which modulates its output second-by-second
      inversely with reference to grid frequency? I have never heard of such a place,
      but perhaps we should start developing them. Just need a mighty big load dump
      and some fancy electronics.


      You are exactly right that spinning reserve is there to stiffen the grid by
      being "a pro-active monitor/stabiliser of grid frequency." And yes, a wind
      turbine can do the opposite. We have found that the problem is not when a
      sudden squall hits the wind turbine, since modern wtg have good dynamic
      maximum output power control (they can limit their output power very quickly
      and accurately). The problem occurs when there is a lull in the wind and the
      output power drops. Then the frequency of the system decreases since supplied
      power < load power.

      Therefore utilities often request (demand) that there is enough spinning
      reserve in the system to cover all or 2/3 of the total wind power. This may
      not be a problem in a large stiff grid, but in smaller grids, like minigrids
      in Australia, it may mean that generators must run to supply spinning reserve
      when there is no need for them; i.e. you can never turn them off, even if
      there's enough wind, just in case the wind drops for 30 seconds. Further,
      some rotating plant requires a minimum load to avoid excessive maintenance.
      In this case, you can't use the wind power even if it's there.

      What we are developing is spinning reserve to cover wind fluctuations. This
      stiffens the (mini)grid, and allows enough storage for extra plant to come
      online. So you can effectively turn off rotating plant when there is enough
      wind, and you don't have to fear a blackout if there is a wind drop.

      >It would make more sense to contract with distribution network owners to
      modulate their bus voltage according to grid frequency, to provide a matched
      number of MW of load control to offset the fluctuating generation of a local
      wind farm. Do they make tap changers that respond quickly enough? Customers
      would get a bit suspicious if their light globes always failed on windy nights!

      I don't know about varying the voltage, but in some minigrids you do have the
      freedom to do some load shedding so less spinning reserve is needed. This is
      the ideal solution. We use this where we can.

      Dr Andrew Tuckey
      Renewable Energy R&D
      Powercorp Pty Ltd

      Ph: +61 8 8947 0933
      Fax: +61 8 8947 0925
      Email: Tuckey@...
      Web: www.pcorp.com.au

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