5.3 ISOLATED BLOCK DIAGRAM REPRESENTATION OF SINGLE AREA FREQUENCY CONTROL

1. Speed governing system: (Fig 4.3 is redrawn as Fig 5.3a)

   K_g = Governor gain constant

   T_g = Governor time constant

   ∆P_C (S) = speed changer setting

   ∆X_T (S) = change in position at point T in linkage mechanism

2. Turbine model representation: (Fig 4.4 is redrawn as Fig 5.3b)

   K_t = Turbine gain constant

   T_t = Turbine time constant

   power flow in the power system:

3. Generator load model representation: (Fig 4.5 is redrawn as Fig 5.3c)

   K_p = Power system gain

   T_p = Power system time constant

   ∆F (S) = Change in frequency

   ∆P_D (S) = Change in power demand.

Models for turbine, speed governor, power system are obtained. In practice a single generator rarely feeds a large area. Several generators located at different places are connected in parallel, to supply the power needs of a geographical area. Normally, all these generators may have the same response characteristics for the changes in load demand. In such a case, it is called as a control area.

Fig 5.3 Block diagram representation of governor, turbine and generator-load models

By combining Figs 5.3 (a, b, c) the block diagram representation for single area control may be shown as in Fig 5.4, where, ∆P_G (S) = ∆P_T (S)

Fig 5.4 Single area load frequency control model