전기철도 시스템의 불평형 해석

초록

The railway characteristic, which is concerned, as most utilities is unbalance produced by the large single-phase loads. Here are two theoretical concerns associated with unbalanced loads. First, generator rotor heating resulting from unbalanced current flow. Second, there is the possibility of motor overheating in industrial plants, due to the unbalanced voltage. The effects on motors are addressed by the voltage unbalance criteria applying to distribution voltage levels. The effects on generators are addressed by limits on the permissible level of negative sequence currents. The generator is allowed to absorb. The unbalanced single-phase load causes negative sequence currents to flow in the generators and transmission lines. The negative sequence currents produce in the alternator stator a field rotating in a direction opposite to the rotation of the rotor. This field produces rotor core losses and it also induces second harmonics in the rotor. In a salient pole generator, the induced rotor currents cause heating of the amortisseur windings. In a non-salient pole generatorthat does not have amortisseur windings, the induced currents cause heating of the rotor surface particularly in the vicinity of slot wedges at the ends of the rotor [1]. The conventional researches on the voltage unbalance have dealt with connection schemes of the transformers used in AC AT-fed electric railway system and induced formulas to briefly evaluate the voltage unbalance in the system [2, 3]. These formulas are still being used widely due to their easy applicability on the voltage unbalance evaluation. Meanwhile, they do not take into account detailed characteristics of AC AT-fed electric railway system, being founded on some assumptions. The evaluation of voltage unbalance using two-port network model in areas, such as electric railwaydepots was carried out [4]. System of the depot was multi track composed by only contact wire and rails. Hence, two-port network model is fit in electric railway depot. However, four-port network model is fit in general electric railway system composed by contact wires, rails and feeders. Four-port network model has two input ports, two output portsand a basic port. The proposed model is carried out to forecast power qualities at stages of designing and planning for the electric railway system. At this moment, the paper deal with the exact assessment of the voltage unbalance in lots of power qualities The paper proposes a new analysis model to more effectively estimate the voltage unbalance. Numerous distributed circuits in the electric railway system are composed by components. The entire system can be easily modeled by the combination of four-port representation of each component in parallel and/or series. Simulation results using the model are compared with field data, and it verifies the accuracy of the proposed model."