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Battery knowledge · High-voltage and functional safety

Fuse coordination

Choosing the ratings of fuses and breakers in series so that a fault opens only the device nearest to it and the remainder of the system keeps running. For fuses, the downstream fuse’s total clearing I²t must stay below the upstream fuse’s pre-arcing I²t; in a pack, a cell or module fuse should act before the main fuse or pyrofuse.

Also called
selectivity, discrimination, protection coordination
Relationship
I²t_clearing(downstream) < I²t_pre-arcing(upstream)

Example

Compare clearing and pre-arcing energy

If a downstream fuse has 500 A²s clearing I²t and the upstream fuse has 1000 A²s pre-arcing I²t under the specified fault conditions, the inequality is satisfied. The full time-current curves and manufacturer coordination rules are still required.

Explore the graph

Compare an illustrative fault integral with two hypothetical device limits.

Illustrative fault integral
Illustrative fault integralFault duration (s) versus Accumulated I²t (A²·s). Constant-current integral; Example downstream clearing = 1000; Example upstream pre-arcing = 3000. Interpretation follows the graphs.009000.251,8000.52,7000.753,6001Fault duration (s)Accumulated I²t (A²·s)
Constant-current integralExample downstream clearing = 1000 (dashed)Example upstream pre-arcing = 3000

At 60 A, an integral of 1000 A²·s is reached in 0.2778 s.

I²t = ∫ I(t)² dt

Illustrative model. Both thresholds are invented teaching values. Constant fault current is assumed; no arc, current-limiting behavior or validated protection design is modeled.

Use in Lemonergy

Relate protection to faults, detection and response.

This is a reference concept. No executable Lemonergy block has been verified for this term.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

  1. ISO 26262-1:2018 — Road vehicles — Functional safety — Part 1: Vocabulary

    International Organization for Standardization · 2018

    Topic background · Scope and terminology of automotive electrical/electronic functional safety. The catalogue is not the full standard.

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