Abstract: Energy storage devices have gained significant attention from application of electrified railways for the capability of energy conservation. Therefore, models of electrified railways with energy storage devices (ESD) need to be built for investigation on the effect of ESD on traction systems and power networks. This paper analyzes the effect of the electrical double layer capacitor (EDLC) ESD on the power quality of the traction and the network when EDLC is connected to the locomotive. An integrated electromagnetic transient model composed of the traction substation, the transmission line, the locomotives with control systems, and the energy storage devices with control systems is build based on the topology of the real network. With the real data from the network, power quality at the grid side will be analyzed and compared with the one before EDLC is connected to assess the effect of EDLC on power quality. The performance of power quality of the network will be assessed by an analytical hierarchy process.