This example shows the use of the Machine Initialization tool of Powergui to initialize machine currents.
Louis-A. Dessaint and R. Champagne (Ecole de Technologie Superieure, Montreal)
A three-phase generator rated 200 MVA, 13.8 kV, 112.5 rpm is connected to a 230 kV, 10,000 MVA network through a Delta-Wye 210 MVA transformer. At t = 0.1 s, a three-phase to ground fault occurs on the 230 kV bus. The fault is cleared after 6 cycles (t = 0.2 s).
1. Open the Powergui and select 'Machine Initialization'. A new window appears. The machine 'Bus type' is initialized as 'PV generator', indicating that the initialization is performed with the machine controlling the active power and its terminal voltage. The desired terminal voltage parameter is set to 13800 and the active Power to 150e6.*
Press the 'Compute and Apply' button. The phasors of AB and BC machine voltages as well as the currents flowing out of phases A and B are updated. The machine reactive power, mechanical power and field voltage requested to supply the electrical power is also be displayed: Q = 3.4 Mvar; Pmec = 150.32 MW (0.7516 pu); field voltage Ef = 1.291 pu.
2. In order to start the simulation in steady state with the HTG and excitation system connected, these two blocks are initialized according to the values calculated by the Machine Initialization tool. This initialization is automatically performed as long as you connect at the Pm and Vf inputs of the machine either Constant blocks or regulation blocks from the machine library (HTG, STG, or Excitation System). Open the HTG block menu and note that the initial mechanical power was set to 0.7516 pu (150.32 MW) by the tool. Open the Excitation System block menu and note that the initial terminal voltage and field voltage have been set respectively to 1.0 and 1.29071 pu.
3. Open the 4 scopes and restart the simulation. Observe that the terminal voltage Va is 1.0 p.u. at the beginning of the simulation. It falls to about 0.4 pu during the fault and returns to nominal quickly after the fault is cleared. This quick response in terminal voltage is due to the fact that the Excitation System output Vf can go as high as 11.5 pu which it does during the fault. The speed of the machine increases to 1.01 pu during the fault then it oscillates around 1 p.u. as the governor system regulates it. The speed takes much longer than the terminal voltage to stabilize mainly because the rate of valve opening/closing in the governor system is limited to 0.1 pu/s.