역률의 변화를 이용한 유도전동기의 소프트 기동 특성 해석

Abstract

Induction motors are the most widely used for loads requiring rotational force because they are self-starting, very simple construction, stronger and easier to maintain than other motors. In spite of such various advantages, a large current is generated at the time of direct-on line starting, and a voltage drop is generated. Since the voltage drop may be adversely affected by other facilities connected to the same distribution system, a start-up method is required to reduce the voltage drop as much as possible. The induction motor can select several starting methods by the capacity. Recently, a soft-start starting method using thyristors has been introduced. Induction motors have a lower power factor because the proportion of reactive power for magnetization at startup is relatively higher than the active power, but as the rotation speed increases, the power factor is gradually increased if the active power is higher than the reactive power. That is, when the power factor becomes high in a low state, the phase angle is developed from a high value to a low value. When the change of this phase angle is used at the firing angle of the thyristor, the operation change of the motor can be used as it is to reduce the starting current. In order to reduce the starting current and lower the voltage drop, the power factor change of the induction motor varying from starting to normal speed during operation is used at the firing angle of the thyristor. As a result of analysis using the power factor change of the motor as the firing angle, it is confirmed that the voltage drop is extremely effectively reduced by the reduction of the starting current.