IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 49, NO. 1, JANUARY/FEBRUARY 2013 233 Fast Evaluation Methods for Voltage Sags in Ship Electrical Power Systems Chun-Lien Su, Member, IEEE, Ching-Jin Chen, and Ching-Cheng Lee Abstract—Induction motors are widely used in ship electrical power applications as they are frequently switched on into the supply system, consuming about 70% of the electrical energy gen- erated. Voltage sag, which is produced by the starting current of induction motors, is one of the main causes of sensitive equipment dropout and, as such, must be considered in ship electrical system designs to comply with classification societies’ rules. A simple and fast method that is able to estimate the expected magnitude of voltage sag disturbances and provide information about the effectiveness of the various mitigation methods is essential. This paper aims at presenting a faster evaluation method for voltage sags due to motor start-ups in ship electrical power systems. The performance of the proposed method is validated by measure- ments gathered from several motor starter designs in practical ship power applications using the Riemann-summation-principle- based evaluation method. The proposed method can provide en- gineers with useful information about the actual magnitude of sag disturbances as well as on the effectiveness of motor starters for ship electrical power applications, which will assist them in determining proper motor starter designs. Index Terms—Motor starter design, power quality, ship electri- cal power system, voltage sags. I. I NTRODUCTION I NDUCTION motors are widely used in ship electrical power applications as they are frequently switched on into the ship supply system, consuming about 70% of the electrical energy generated. Voltage sag produced by the starting current of induction motors is one of the main causes of sensitive equipment dropout, particularly if the motor is large when compared with the supply short-circuit power [1]. Ship owners and shipyards have been faced with rising numbers of ship accidents and incidences related to the quality of power due Manuscript received June 29, 2011; revised November 14, 2011, December 16, 2011, and March 22, 2012; accepted May 7, 2012. Date of publication November 21, 2012; date of current version January 16, 2013. Paper 2011-PSEC-275.R3, presented at the 2011 IEEE Industry Applications Society Annual Meeting, Orlando, FL, October 9–13, and approved for publication in the IEEE TRANSACTIONS ON I NDUSTRY APPLICATIONS by the Power Systems Engineering Committee of the IEEE Industry Applications Society. This work was supported in part by CSBC Corporation, Taiwan, under Grant CSBC-RD-558.2 and in part by the National Science Council of Taiwan and Taiwan Power Company under Grant NSC 99-2221-E-022-012 and Grant NSC 100-3113-P-110-004. C.-L. Su is with the Department of Marine Engineering, National Kaohsiung Marine University, Kaohsiung 80543, Taiwan (e-mail: cls@ webmail.nkmu.edu.tw). C.-J. Chen is with the Electrical Design Section, Department of Design, CSBC Corporation, Kaohsiung 81234, Taiwan (e-mail: 094224@csbcnet. com.tw). C.-C. Lee is with the Basic Design Section, Department of Design, CSBC Corporation, Kaohsiung 81234, Taiwan (e-mail: 085745@csbcnet.com.tw). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIA.2012.2229255 TABLE I ACTUAL EXAMPLES OF PROBLEMS CAUSED BY MOTOR STARTING SAGS IN SHIPS to sags [2]. There are a number of reasons for this, with the most important being that all modern ships have more sensitive loads and rely on automated equipment to reduce manpower and achieve maximum loading so as to remain both economic and competitive. An important cause of voltage sags on ships is directly related to the starting of the onboard large motor. However, there is little discussion in the literature regarding this problem. There have been several relevant observations and comments reported by ship owners to shipyards concerning motor starting sags, some of which are shown in Table I and described as follows. 1) Example I: During the simultaneous starting of any two big (82 and 105 kW) and one small (28 and 35 kW) induction motors for the windlass and mooring winch in a container vessel at berth, the large starting currents were measured and the sags generated caused the contactors in the molded-case circuit breakers (MCCBs) connected to these pumps to drop out, but other protection relays remained closed, which resulted in frequent electric arcs that destroyed the electrical contacts and the MCCB casing. 2) Example II: During the starting of the main engine lu- bricating oil pumps in a buck carrier in a situation when the number of working generator sets was small, the starting sag disturbed the pumps’ electrical parts, such as contactors and electronic control devices, and sometimes, the malfunction of other pumps occurred. 0093-9994/$31.00 © 2012 IEEE