Impacts Of Induction Motor Load On Voltage Sag Characterization

Due to the fast development in electrical devices,which depend on converting AC power system from the grid to DC,those devices become more sensitive to power quality problems and they affected easily by small disturbances in the system.In addition,people definition of power quality has changed through last decades.They do not just want electrical supply to be reliable,they also need their power supply to be highly compatible with their devices and do not cause any shut down to the load.The most common power system disturbance is voltage sag(dip).Because industrial loads are the most common and sensitive load in power system,therefore their impacts of power system disturbance are simulated and studied.This thesis is a research work on impacts of induction motor load on voltage sag characterization caused by faults.A model was chosen to be simulated through DigSilent PowerFactory software and the output data was analyzed using Mathworks MatLab.A fault event happened with the induction motor plant is in its area of vulnerability.The system was used to study the impacts in two sides.First,study the impacts of induction motor existence on voltage sag characterization and impact of voltage sag on induction motor slip,induced torque and power consumption.Second,study the impact of the quantity of induction motor load on voltage sag characterization.An industrial system was simulated and assumed to have identical 7 production lines.It is also assumed that every line has the same mechanical load.Then,the number of production lines in the time of voltage sag was increased from 0 to 7.In every load number the voltage sag was simulated and it characterization was studied.The results of this simulation indicate that that duration and depth of voltage sag are severely increased by the existence of voltage sag.On the other hand,phase-shift and frequency are slightly affected by the voltage sag.For motor side,slip becomes higher after transient which means that the motor is operating at a lower speed in steady state.In addition,the motor is generating power to the system in the transient.But,in steady state torque and active power consumption are low and reactive power is high.That means that motor is working with low power factor and high current magnitude.This current could cause induction to overheat and damage if it lasts for a long time or the sag is repeated many times in short period.For induction motor load quantity impacts,the results show that the depth of voltage sag and duration is directly proportional to induction motor load quantity.This means that as more production lines working in the time of voltage sag the deeper and longer voltage sag.Also,phase-shift was increased when the number of working production lines in time of voltage sag increased but the difference is very low so its value can be considered as constant value.In summary,induction motor existence and quantity has impacts to voltage sag characterization and those impacts have to be considered when designing power systems that contain industrial loads.