Fire at a generator of a power plant

The incident occurred at a power generator during the shutdown of one reactor unit. Hydrogen leaked from the cooling circuit of the generator due to damaged sealing. The hydrogen ignited. The fire was extinguished after 1 hour 40 minutes.

The INITIATING cause of the accident was the release of hydrogen from a sealing on the generator. The root cause is related to an electrical fault that caused the generator speed to suddenly rise from a still state to 1145 r/min, causing violent vibration of the generator rotor which lead to wear of the sealing leakage of hydrogen gas and the consequent hydrogen explosion. The cause of the ignition is probably an electrostatic spark.

cooling cirucit of generator, sealing

Just before the hydrogen leak an electrical fault caused the generator speed to suddenly rise from a still state to 1145 r/min

unknown (probably just internal fire-fighting action).

A stronger focus on safety management of equipment is needed. There are several incidents related to hydrogen explosions in a hydrogen-cooled generator in power plants, (for further examples see for example this Chinese online source https://www.gg-lb.com/asdisp-65b095fb-35521.html ).

The National Energy Group Co., Ltd. National Thermal Power Industry Operation control centre issued the following preventive measures and requirements (google translation):
1. Learn lessons from the accident. The company should carry out a comprehensive investigation of hidden dangers in booster stations, focusing on rectifying hidden dangers of high-voltage equipment such as switches, isolating switches, transformers, and lightning arresters, especially strengthening the monitoring of high-voltage combinations. Check the status indication of electrical switches and knife switches to prevent similar accidents from happening.
2. Strengthen equipment management. In view of the problems exposed by this accident, each power generation enterprise should strengthen equipment management and implement various requirements and measures in light of the actual conditions of the unit. Problems such as unclear instructions should be given great attention, and defects should be eliminated in time.
3. Strengthen operation management. To implement two and three-step control procedures , by which each step of equipment operation must be confirmed on site and the next operation is strictly prohibited before the operation is confirmed. Improve operating procedures, strengthen the training of operating personnel, so that operating personnel can clearly understand the content and requirements of inspection and operation work. Carry out accident prediction and anti-accident drills to improve emergency response capabilities and levels.
4. All power generation companies should carefully check the start-up and stop operation steps, and check the opening and closing positions of switches and knife gates before operation. In addition to personnel inspection and confirmation, they should also ensure that the switch and knife gate opening and closing positions are confirmed by contact instructions.