GovCT1 : Documentation diagram
Created: |
03/30/2012 09:30:24 AM |
Modified: |
05/26/2012 05:42:39 PM |
Project: |
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Author: |
pcha006 |
Version: |
1.0 |
Advanced: |
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ID: |
{76AAF6CF-5F27-4036-8FC1-DCED1CE49FB3} |
<font color="#0f0f0f"><b>Parameter Notes:</b></font><br /></p><p><ol><li>Per unit parameters are on base of <b>MWbase</b>, which is normally the MW capability of the turbine.</li><br /></p><p><li>The range of fuel valve travel and of fuel flow is unity. Thus the largest possible value of <b>Vmax</b> is 1.0 and the smallest possible value of <b>Vmin</b> is zero. <b>Vmax</b> may, however, be reduced below unity to represent a loading limit that may be imposed by the operator or a supervisory control system. For gas turbines <b>Vmin</b> should normally be greater than zero and less than <b>Wfnl</b> to represent a minimum firing limit. The value of the fuel flow at maximum output must be less than, or equal to unity, depending on the value of <b>Kturb</b>. </li><br /></p><p><li>The parameter <b>Teng</b> is provided for use in representing diesel engines where there is a small but measurable transport delay between a change in fuel flow setting and the development of torque. <b>Teng</b> should be zero in all but special cases where this transport delay is of particular concern.</li><br /></p><p><li>The parameter <b>Wfspd</b> is provided to recognize that fuel flow, for a given fuel valve stroke, can be proportional to engine speed. This is the case for GE gas turbines and for diesel engines with positive displacement fuel injectors. <b>Wfspd</b> should be set to unity for all GE gas turbines and most diesel engines. <b>Wfspd</b> should be set to zero where it is known that the fuel control system keeps fuel flow independent of the engine speed.</li><br /></p><p><li>The load limiter module may be used to impose a maximum output limit such as an exhaust temperature limit. To do this the time constant <b>Tfload</b> should be set to represent the time constant in the measurement of temperature (or other signal), and the gains of the limiter, <b>Kpload</b>, <b>Kiload</b>, should be set to give prompt stable control when on limit. The load limit can be deactivated by setting the parameter <b>Ldref</b> to a high value.</li><br /></p><p><li>The parameter <b>Dm</b> can represent either the variation of the engine power with the shaft speed or the variation of maximum power capability with shaft speed. If <b>Dm</b> is positive it describes the falling slope of the engine speed verses power characteristic as speed increases. A slightly falling characteristic is typical for reciprocating engines and some aero-derivative turbines. If <b>Dm</b> is negative the engine power is assumed to be unaffected by the shaft speed, but the maximum permissible fuel flow is taken to fall with falling shaft speed. This is characteristic of single-shaft industrial turbines due to exhaust temperature limits.</li><br /></p><p><li>This model includes a simple representation of a supervisory load controller. This controller is active if the parameter <b>Kimw</b> is non-zero. The load controller is a slow acting reset loop that adjusts the speed/load reference of the turbine governor to hold the electrical power output of the unit at its initial condition value. This value is stored in the parameter <b>Pmwset</b> when the model is initialized, and can be changed thereafter. The load controller must be adjusted to respond gently relative to the speed governor. A typical value for <b>Kimw</b> is 0.01, corresponding to a reset time of 100 seconds.</li><br /></p><p><li>The parameters <b>Aset</b>, <b>Ka</b>, and <b>Ta</b> describe an acceleration limiter. <b>Ta</b> must be non-zero, but the acceleration limiter can be disabled by setting <b>Aset</b> to a large value, such as 1.</li><br /></p><p><li>The parameter, <b>db</b>, is the speed governor dead band. This parameter is stated in terms of per unit speed. In the majority of applications, it is recommended that this value be set to zero.</li><br /></p><p><li>The parameters <b>Tsa </b>and <b>Tsb</b>, are provided to augment the exhaust gas temperature measurement subsystem in gas turbines. For example, they may be set to values such as 4., 5., to represent the ‘radiation shield’ element of large gas turbines. If both parameters are omitted, they default to 1.0.</li><br /></p><p><li>The parameters <b>Rup</b> and <b>Rdown</b> specify the maximum rate of increase and decrease of the output of the load limit controller (<b>Kpload</b>/<b>Kiload</b>). These parameters should normally be set, or defaulted to 99/-99, but may be given particular values to represent the temperature limit controls of some GE heavy-duty engine controls. If both parameters are omitted, they default to 99 and –99.</li><br /></p><p><li>The fuel flow command <b>fsr</b> is determined by whichever is lowest of <b>fsrt</b>, <b>fsra</b>, and <b>fsrn</b>. Although not explicitly shown in the GovCT1 diagram, the signals that are not in control track <b>fsr</b> so that they do not “windup” beyond that value. This represents GE gas turbine control practice but may not be true for other controller designs.</li><br /></p><p><li>As shown in the GovCT1 diagram, when <b>Kpgov</b> is non-zero, the governor PI control is implemented to “track” <b>fsr</b> to prevent windup when <b>fsr</b> is limited by another signal (<b>fsrt</b>, <b>fsra</b>) or <b>Vmax</b>/<b>Vmin</b>. If <b>Kpgov</b> is zero, the integral path is implemented directly. The same applies to the load limiter PI control with regard to <b>Kpload</b>. </li><br /></p><p><li><b>Pref</b> has units of p.u. speed.</li><br /></p><p></ol><br /></p>