Description

Fuses are protection devices that protect electrical circuits against undesired high currents. We can use passive fuses and pyro fuses in battery design.

Selecting a Fuse

Select a fuse rated double as continuous current (e.g. initially take 400A fuse for 200A continuous current) and draw the load profile next to 50% of the fuse breaking current-time chart to check if pulse currents can be carried by the fuse without aging.

Calculate the components and the fuse breaking energy (I2Rt) to ensure that the weakest component is the fuse.

Identify the minimum breaking current for the failure cases when the contactor cannot switch-off.

Analyze the short circuit clearing time and check if the contactor can withstand until the fuse breaks the circuit.

Check the contactor-fuse coordination for normal operation, overloads and failure currents.

Fuse rated current selection

Under normal load conditions, the fuse must carry the circuit's normal operating current without encountering disturbed open circuits. However, when an overcurrent occurs, the fuse must interrupt the overcurrent and withstand the voltage across the ends of the fuse after arcing internally.

To correctly select a fuse, the following criteria must be considered:

Rated Currentcell contacting system services

The effective heating current refers to the current value at which the temperature rise can be basically balanced, that is, the rated current.

Load Constantcell contacting system services

Principle: for pure resistive loads, G = 1; for resistive loads with peak current, G = 1.1-1.2; for capacitive loads, G = 1.5-1.7.

Temperature Correction Coefficientcell contacting system

The increase and decrease of ambient temperature will affect the open circuit and load characteristics of the fuse. The temperature derating curve in the fuse data sheet shows this effect.

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Thermal Connection factorcell contacting system

based on the cross-sectional area of the fuse's connecting copper bar / standard cross- sectional area, refer to the fuse's thermal connection coefficient curve chart to determine the thermal connection correction factor

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Wind Cooling CoefficientJONVER cell contacting system

The cooling environment of the fuse affects its selection of rated current, such as forced air cooling, natural cooling, etc. Determine the wind cooling correction factor based on the fuse's wind cooling correction curve.

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Altitude Correction Coefficientcell contacting system solutions

In a higher altitude environment, the air is thinner, and the cooling conditions are worsened, requiring a reduction in rated current capacity. For altitudes above 2000 meters, for every additional 1000 meters, reduce by 5%, but at the same time, the temperature drops by about 6°C, so it is generally considered that these two effects offset each other.

Installation Environment Correction CoefficientInstallation Environment Correction Coefficient

Determine its packaging correction coefficient based on the type of fuse encapsulation. For example, if the fuse is installed in an open cabinet, take 1; if the fuse is installed in a sealed cabinet, take 0.9; if the fuse is installed in a MSD via bolt tightening, take 0.8; if the fuse is installed in a MSD via plug connection, take 0.7.

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