Ministry of Trade, Industry and Energy (MOTIE) publicized results of investigation on ESS (Energy Storage System) fire accident carried out by ‘Private and Public Joint ESS Fire Accident Investigation Committee’ and specified four causes of 23 ESS fire accidents that had occurred nationally between August of 2017 and end of last month.
This committee, which is comprised of 19 experts from universities, research institutes, testing certificate agencies, and fire service agencies held its first meeting on the 3rd of January and had carried out investigations over the course of five months.
‘Inadequate battery protective system’ indicates fire accidents caused by second short circuit accidents that happen inside of a bus bar of a battery protective system or an enclosure of a battery protective system as DC contactor that has its performance reduced from rack fuse, which is a battery protective system, not being able to prevent short circuit current when electrical impact such as overvoltage or overcurrent from short circuit is introduced to a battery system explodes.
Fire accidents caused by ‘inadequate management of operating environment’ happened when an insulator near ground connection is broken as condensation and dryness occur repeatedly inside of a battery module of an ESS that is operated in an environment that is prone to condensation from wide range of daily temperature and accumulation of dust.
There were also fire accidents that occurred due to ‘negligence of ESS installation’. ‘Inadequate comprehensive protective system and management system’ were also seen as potential causes. Fact that EMS (Energy Management System, PMS (Power Management System), and BMS (Battery Management System) with different manufacturers were not operated organically by a SI (System Integration) business was seen as the main cause for inadequate comprehensive protective system and management system.
The committee had carried out its investigations after initially assuming that ‘faulty battery system’ was one of the causes. After finding out that many accidents were caused by batteries that were produced by a same plant of a particular manufacturer at a similar time, it broke apart corresponding battery and found many defects such as bent pole plates, faulty cutting, and faulty active material coating from few batteries. However, after not seeing internal short circuit that can lead to battery ignition from demonstrations, it ultimately decided that ‘inadequate battery protective system’ was one of the causes of fire accidents caused by ESS.
However, some people within relevant industries point out that that a mechanism that led to these fire accidents was not clearly defined by the investigation. There is a possibility that ESS that is currently operating and ESS that will be installed in the future may cause fire accidents.
“This investigation only checked possibilities of fire accidents that may be caused by electric impact or environment issues and investigation on conditions for ignition, causes of fire accidents, and relevance are still insufficient.” said Professor Park Cheol-wan of Seojeong University. “Although there is many data that can be obtained from the investigation from an aspect of fire prevention, effectiveness of data is questionable.”
Some point out that investigation on dangerousness of fire accidents cause by ‘overcharge’ was insufficient as 14 fire accidents out of 23 fire accidents happened while ESS was in idle mode. There have been constant criticisms about overcharge as South Korean ESS operators have been impractical with SOC (State of Charge) standard by setting it between 5 and 95% of entire capacity to increase effectiveness of ESS.
“Systems such as ESS that uses hundreds of cells at once can experience an issue where voltage can fluctuate due to different internal resistance of cells. If SSD operators forcefully operate SOC to increase effectiveness of SSD, thermal runaway phenomenon can occur from overcharge during cell balancing process.” said a representative for the industry. “While it is recommended to limit DOD (Depth of Discharge) to about 70% to prevent fire accidents caused by overcharge, fire accidents will ultimately reoccur again even if safety measures are set up as this issue is entangled with effectiveness and compensation issues and is not publicized.”
However, the committee does not see fire risks from overcharge as a major issue. The committee however decided to enforce installation of software that prohibits additional charge when a battery is completely charged as one of safety measures in case of emergency situations.
“Although we cannot see additional charge, which is done by some operators to increase profitability, as direct cause of a fire accident, it can be an extremely dangerous act and we can solve such issue through software installation.” said a representative for the committee. “Although we assumed that this issue could be a cause of a fire accident, we did not specify it as a direct cause because we found that it is an extremely small case after our investigation and there is not much to worry about as it is not a common case.”
Staff Reporter Jung, Hyunjung | & Staff Reporter Choi, Jaepil |