Influence of a Step-Voltage Regulator on Synchronous DG Anti-Islanding Protection

The performance of anti-islanding frequency and voltage protections is strongly affected by the power imbalance between the islanded loads and distributed generators, which is altered by changes of load demand. Since the voltage-dependent loads change the demand as the voltage profile changes, automatic step-voltage regulator on the distribution grid can impact on the islanding detection performance. In this context, the main goal of this paper is to investigate the influence of the automatic step-voltage regulator on the performance of under/overfrequency and under/overvoltage protections applied for islanding detection of a synchronous distributed generator. The simulations were performed on the Alternative Transients Program. As this software does not have a model of a step-voltage regulator, a second contribution of this paper is to propose the full modeling of an on-load tap-changer of a voltage regulator using MODELS and controlled voltage and current sources, which was not observed in the literate so far. The behavior of the step-voltage regulator is validated by simulation. Then, the anti-islanding protection is analyzed, as different operational conditions are considered to simulate island events with constant impedance loads. The results have shown the performance of the protection scheme can be strongly affected by the steady-state voltage, and such issue should be considered to correctly adjust the anti-islanding protection.