Effect of Voltage Frequency Dependence on an Isolated Power System

Jawad Talaq


Supplementary control, Power system stabilizer, Power system dynamics, Isolated systems


Excitation supplementary control is used in power systems to enhance the damping of low frequency oscillations due to the mechanical modes of the generators. Traditionally, frequency deviation is fed back to the exciter through phase lag-lead compensators to form the supplementary control. This supplementary control is known as power system stabilizer (PSS). A wash out block is usually included with the stabilizer to get rid of any DC offset in the frequency deviation. This is helpful if the machine is connected to an infinite bus as the angular speed deviation of the machine eventually vanishes. However, this is not true for isolated systems as the angular speed deviations tend to stabilize to a final value depending on the perturbation. The terminal voltages are proportional to angular speed deviations of the machines. This phenomenon tends to destabilize the system due to the negative feedback of voltages to the exciters. A feedback of angular speed deviations to the exciters can stabilize the system. In this paper, the effect of angular speed deviation feedback to the exciter on the stability of a single machine isolated system is investigated.

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