{ "node": { "id": "term:fuse-coordination", "type": "Term", "label": "Fuse coordination", "properties": { "id": "fuse-coordination", "name": "Fuse coordination", "aka": [ "selectivity", "discrimination", "protection coordination" ], "section": "topic-hvsafety", "definition": "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.", "formula": "I²t_clearing(downstream) < I²t_pre-arcing(upstream)", "related": [ "fuse", "pyrofuse", "battery-disconnect-unit", "external-short-circuit", "series-parallel" ], "example": { "title": "Compare clearing and pre-arcing energy", "text": "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." }, "url": "https://lemonergy.com/learn/glossary/fuse-coordination/", "mentions": [] } }, "edges": [ { "id": "edge:5094", "source": "term:fuse-coordination", "target": "topic:topic-hvsafety", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:5095", "source": "term:fuse-coordination", "target": "term:fuse", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5096", "source": "term:fuse-coordination", "target": "term:pyrofuse", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5097", "source": "term:fuse-coordination", "target": "term:battery-disconnect-unit", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5098", "source": "term:fuse-coordination", "target": "term:external-short-circuit", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5099", "source": "term:fuse-coordination", "target": "term:series-parallel", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:5100", "source": "term:fuse-coordination", "target": "visual:fuse-integral", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-hvsafety", "type": "Topic", "label": "High-voltage and functional safety", "properties": { "id": "topic-hvsafety", "name": "High-voltage and functional safety", "lede": "Keeping people safe from the pack’s voltage and keeping its electronics safe when they fail: insulation, switching, fusing and the functional-safety process.", "context": "Relate protection to faults, detection and response.", "example": "Normal-operation current limits do not demonstrate correct contactor behavior under a welded-contact or sensor fault.", "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-basics/", "lesson_label": "Open battery basics" } }, { "id": "term:fuse", "type": "Term", "label": "Fuse", "properties": { "id": "fuse", "name": "Fuse", "section": "topic-hvsafety", "definition": "A link that melts and opens the circuit when current exceeds its rating. Packs use a main fuse in the high-voltage path and often a small fuse on each parallel cell connection, so one shorted cell does not drain its neighbours into the fault.", "related": [ "external-short-circuit", "pyrofuse", "battery-disconnect-unit", "series-parallel", "cell-level-fuse" ], "url": "https://lemonergy.com/learn/glossary/fuse/", "mentions": [] } }, { "id": "term:pyrofuse", "type": "Term", "label": "Pyrofuse", "properties": { "id": "pyrofuse", "name": "Pyrofuse", "aka": [ "pyrotechnic disconnect" ], "section": "topic-hvsafety", "definition": "A high-voltage disconnect fired by a small pyrotechnic charge on command, typically from the airbag controller in a crash. It cuts the pack from the vehicle in milliseconds, faster and more reliably than a contactor can open under fault current.", "related": [ "fuse", "contactor", "battery-disconnect-unit", "high-voltage-interlock" ], "url": "https://lemonergy.com/learn/glossary/pyrofuse/", "mentions": [] } }, { "id": "term:battery-disconnect-unit", "type": "Term", "label": "Battery disconnect unit", "properties": { "id": "battery-disconnect-unit", "name": "Battery disconnect unit", "abbr": "BDU", "aka": [ "battery junction box" ], "section": "topic-hvsafety", "definition": "The box inside the pack that holds the contactors, pre-charge circuit, main fuse or pyrofuse and current sensor, where the pack’s high-voltage connections are made and broken.", "related": [ "contactor", "pre-charge", "fuse", "pyrofuse", "current-sensor" ], "url": "https://lemonergy.com/learn/glossary/battery-disconnect-unit/", "mentions": [] } }, { "id": "term:external-short-circuit", "type": "Term", "label": "External short circuit", "properties": { "id": "external-short-circuit", "name": "External short circuit", "section": "topic-safety", "definition": "A low-resistance connection between the terminals outside the cell, driving currents of hundreds of amperes. Fuses, the current interrupt device and a positive-temperature-coefficient element are the layers of protection against it.", "related": [ "internal-short-circuit", "fuse", "current-interrupt-device", "ptc", "short-circuit-test" ], "url": "https://lemonergy.com/learn/glossary/external-short-circuit/", "mentions": [] } }, { "id": "term:series-parallel", "type": "Term", "label": "Series and parallel connection", "properties": { "id": "series-parallel", "name": "Series and parallel connection", "aka": [ "xSyP" ], "section": "topic-pack", "definition": "Cells in series add their voltages; cells in parallel add their capacities and share current. A pack is described as, for example, 96s4p: 96 groups in series, each of 4 cells in parallel. Series strings need balancing; parallel groups self-balance through their shared terminals.", "formula": "V = n_s·V_cell, Q = n_p·Q_cell", "related": [ "module", "cell-balancing", "pack-voltage", "volt", "fuse" ], "lesson": "fundamentals/battery-basics/#cell-module-pack", "example": { "title": "Assemble an ideal 4s2p pack", "text": "Eight identical 3.6 V, 5 Ah cells arranged as four series groups with two cells in parallel give 14.4 V nominal, 10 Ah and 144 Wh. Interconnect losses, cell variation and usable voltage limits are additional constraints." }, "url": "https://lemonergy.com/learn/glossary/series-parallel/", "mentions": [] } }, { "id": "visual:fuse-integral", "type": "Visual", "label": "Accumulated current stress is an integral", "properties": { "title": "Accumulated current stress is an integral", "summary": "Compare an illustrative fault integral with two hypothetical device limits.", "readout": "At 60 A, an integral of 1000 A²·s is reached in 0.2778 s.", "formula": "I²t = ∫ I(t)² dt", "note": "Both thresholds are invented teaching values. Constant fault current is assumed; no arc, current-limiting behavior or validated protection design is modeled.", "software": { "status": "reference", "label": "Reference concept", "body": "This explains I²t accounting. Actual fuse coordination needs manufacturer time-current curves, clearing and pre-arcing data, DC voltage and prospective fault-current conditions.", "href": "../chapter-1/" }, "html": "
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
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