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9.1 Cell venting in operation
The probability for a cell venting during operation in the Evolion is very low. When considering the redundant and independent safety
mechanisms included on the cell level and the system level, there is a zero probability that an external influence of voltage or current
will force the cells in the Evolion to an unsafe state to vent. Based on history and experience, the only mechanism that would cause a
cell to vent and release gas is an internal cell short.
9.2 The probability of an internal short
If a cell shorts, it will discharge rapidly and cause the temperature to rise quickly. At one point the maximum cell pressure will be
exceeded and the cell will vent gas.
The calculated probability of a single cell to experience an internal Short Circuit (SC) is linked to the number of cell in the module and is
equal to,
λ
cell SC
= 4.9x10
-10
per hour
The probability for an internal SC event for a single Evolion module is equal to,
λ
Evolion module SC
= (4.9 x 10
-10
) x (14 cells) = 6.9 x 10
-9
per hour
Important note: The electrolyte is flammable.
Important note: Never expose the Evolion to a temperature higher than 80°C (176°F). The electrochemistry may become unstable.
In the very low probability case of a cell internal short and venting, the Evolion’s cell pack is designed to prevent propagation of a cell
venting event to an adjacent cell.
9.3 Released gas characteristics
In case of a cell venting event and the released gas is assumed to combust completely (worst case assumption), the gas composition
released through the Evolion vent ports is given in the following table.
Gas element
Symbol
% by volume
Nitrogen
N
2
65 %
Carbon dioxide
CO
2
27 %
Carbon monoxide
CO
3 %
Combustion residue
-
5 %
Assuming the worst case of total combustion, the total gas volume is estimated to be 500 liters to 800 liters with a venting rate of
approximately 40 to 110 liters/second and it releases at approximately 300°C to 500°C (572°F to 932°F).
Important note: The combustion residue (conductive carbon dust) and high temperatures during a cell venting event may contaminate
or cause damage to other equipment in the same zone. To prevent contamination or possible damage, it is recommended to contain or
to exhaust the released to a safe area. Contact your Saft representative for further details.
The service life of the Evolion depends on calendar time usage and the cyclic duty. As the Evolion ages in use, the available capacity
decreases and its internal resistance increases. Both mechanisms are irreversible. For life estimations, the calendar aging and cyclic
aging are considered separately when discussing factors that affect each. It is considered that 20 % loss of capacity represents end of life.
The factors that impact the calendar aging are:
•
%SOC
•
Module temperature
10. Service life
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