Study on Distribution Reliability Considering Voltage Sags and Acceptable Indices.pdf

IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 2, APRIL 2007 1003 Study on Distribution Reliability Considering Voltage Sags and Acceptable Indices Xiao Xiangning, Member, IEEE, Tao Shun, Bi Tianshu, and Xu Yonghai Abstract— In modern power systems, more sensitive loads ap- where the manufacturing machine is driven by adjustable speed pear. The impact of voltage sags on customers cannot be ignored. drives (ASDs) is almost the same as those of an interruption With the opening of electricity markets, it is necessary to modify lasting 2 h [3]. and supplement the reliability indices to consider the influences of voltage sags. In this paper, three supplementary indices are pro- However, currently used distribution reliability indices do not posed, that is: 1) event time; 2) sag energy; and 3) cost of events. consider short duration voltage disturbances. According to [4], Furthermore, we try to redefine the traditional reliability indices it is clearly stated that momentary interruptions, caused by the on service. These indices may be useful today and in the future as operation of a recloser, or by the commissioning of a standby well. Computer simulation results show that voltage sags do affect source automatically, are not “interruptions” and are ignored reliability indices, which change the value of the third digit of the decimal part of reliability indices. The higher the reliability level when calculating the reliability indices. So, the traditional re- is, the larger the impact of sags on reliability is. liability indices cannot illustrate the impact of voltage sags and short-duration int