Abstract: After the pulverized coal feeder of Boiler No. 1 at the Xicun Thermal Power Plant of Guangzhou Power Plant Co., Ltd. was replaced with a YCT-160-4A slip-ring motor and controlled by a TYPEY100-L1-4 motor and an ACS 140 (0.12~2.2 kW) frequency converter, a short-circuit fault occurred on the user side of a 35 kV external line. Although the relay protection operated correctly, Boiler No. 1 still experienced flameout. Through analysis of the cause of the incident, reasonable improvement methods are derived, thus providing relevant references for the design and improvement of similar equipment. Keywords: boiler; powder feeder; frequency converter; flywheel; mechanical inertia[b][align=center]Analysis of boiler flameout caused by an external line fault ZENG Ling-jun, SHI Feng (Ouangzhou Power Plant Co., Ltd,, Guangzhou 51{}160, China)[/align][/b] Abstract : The pulverized fuel feeder was changed from YCT-160—4A motor to TYPEY100—L1—4 motor and ACS 140 (0.12～2.2 kW) transducer for Unit 1 boiler in Xicun Cogeneration Power Plant under Ouangzhou Power Plant Co,, Ltd． In an accident caused by the outside 35 kV feeder line short-circuit damage, though the relay-set acted correctly, the pulverized fuel feeder still caused flameout in the bo iler． This paper analyzes the accident and brings forward rational improving measures． This can be used as a reference in the design and improvement of similar equipment. Key words : boiler; pulverized coal feeder; transducer; flywheel; mechanicalineria. The No. 1 boiler at the Xicun Thermal Power Plant of Guangzhou Power Plant Co., Ltd., model WGZ220, 9.8.13, was put into operation in May 1989. Until the end of 2003, the feeder previously used a YCT160.4A slip-ring motor for speed regulation. During this period, it encountered several short-circuit faults in the 35 kV system, but never caused the No. 1 boiler to extinguish. At the end of 2003, after the No. 1 boiler feeder system was converted to frequency converter speed regulation and TYPEY100.L1-4 motors, the effect of mechanical inertia was not adequately considered. After the modification, the mechanical inertia was too small. When a short circuit fault in the 35 kV external line caused the ACS140 (0.12~2.2 kW) frequency converter to stop output due to undervoltage or momentary power loss (the frequency converter control of the pulverizer restarted normally after simulating the above phenomenon through the electrical test team), it was found that the speed of the No. 1 boiler pulverizer fluctuated greatly, affecting the pulverizer feed rate and seriously threatening the safe operation of No. 1 boiler. On April 30, 2005, a short circuit fault on the user side of the 35 kV external line occurred at Xicun Thermal Power Plant, causing the No. 1 boiler of Xicun Thermal Power Plant to extinguish. The lessons learned from the analysis of the cause of this boiler extinguishing are summarized here for reference. [b][align=center]For details, please click: Analysis of the Causes of a Boiler Flame-Out Caused by an External Line Fault[/align][/b]