Meaning
Failure of insulating materials when subjected to high voltage differences across a series connection of cells can lead to electrical arcing and systemic failure. When a series string dielectric breakdown occurs, the high voltage overcomes the electrical resistance of the cell holders or potting compounds. This failure creates a conductive path that can bypass the protection circuitry and cause a severe short circuit.
Sourcing teams must ensure that all insulating materials are rated for the maximum system voltage of the series string.
Electrical Test
Dielectric strength testing is performed by applying a high voltage across the insulating barriers of the pack. This test verifies that the insulation can withstand voltages well above the nominal rating without allowing current to leak. If a series string dielectric breakdown is detected, the pack design must be modified to increase the physical spacing or to use materials with higher dielectric ratings.
These tests are essential for high-voltage battery systems used in electric vehicles or grid storage.
Material Degradation
Thermal and mechanical stress can degrade the insulating properties of the pack materials over time. Continuous thermal cycling and vibration can cause cracks in the insulating plastics or wear down the thin polymer coatings on the busbars. Sourcing materials that are resistant to these environmental factors prevents premature insulation failure during the operational life of the battery.
Voltage Boundary
High-voltage systems require generous physical clearance and creepage distances to prevent surface tracking. These design rules are particularly important in humid or dusty environments where surface contamination can compromise the insulation.
