Fast evaluation methods for voltage sags in ship electrical power systems

Induction motors are widely used in ship electrical power applications as they are frequently switched-on into the supply system, consuming about 70% of the electrical energy generated. Voltage sag produced by the starting current of induction motors is one of the main causes of sensitive equipment dropout and has been recommended to be considered in ship electrical system designs to comply with class societies´ rules. Before making a decision about which mitigation method to choose, a simple/fast method that is able to estimate the expected magnitude of disturbing sags and provide information about the effectiveness of the various mitigation methods is essential and important. This paper aims at presenting a faster evaluation method for voltage sags due to motor starting in ship electric power systems. Performance of the proposed method is validated by measurements gathered from several motor starting designs in practical ship power applications by using a Riemann summation principle based evaluation method. The proposed method can provide the engineers useful information about the actual magnitude of disturbing sags and about the effectiveness of motor starters for ship electrical power applications for assisting them in determining proper motor starting designs.