The HV Definitions & Glossary is an A to Z extension to our website that just gives you an alternative way of finding information.
Arcing – a luminous, sustained discharge of current through air or another normally-insulating medium once a gap’s dielectric strength is exceeded; a key hazard that the HV system’s creepage, clearance and interlock design must prevent.
Battery Disconnect Unit – contains the contactors, fuses, pre-charge circuit and current sensors. This unit sits inside/on top of the battery pack and has all of the components for monitoring, activating, and deactivating the high-voltage battery system.
Blanking Delay (Blanking Time) – a deliberately short pause built into overcurrent or short-circuit protection circuitry immediately after it arms, during which brief and harmless current transients are ignored so they don’t trip protection unnecessarily.
Busbars are the main electrical connections between cells, modules and connect all of the HV system to the outlet connector. Normally made from copper or aluminium.
Clearance – the line-of-sight distance between two conductors through the air.
Charge Voltage – voltage that the battery is charged to when charged to full capacity.
Comparative Tracking Index (CTI) – a standardized measurement that quantifies an insulating material’s resistance to surface “tracking”. Tracking is the progressive degradation of a material’s surface, where moisture, dust, and continuous voltage stress cause localized leakage currents that slowly carbonize the material, eventually forming a permanent conductive path.
Current Interrupt Device (CID) – installed in cells to ensure their safety. The CID disconnects the cell electrically when the pressure inside the cell increases above the design level.
Contactor – a switch that can be operated by the control system. They are essentially a relay.
Creepage – the distance between two conductors on the surfaces of the parts or along the surface of the insulating material.
Current Rating – shorthand for a component’s or pack’s continuous and peak current capability, the figure that sizes busbars, contactors, fuses and connectors.
Current Sensor – can include resistive or magnetic elements based on their structure. We use these elements for sensing the current to be measured.
Cut-off Voltage – the minimum allowable cell voltage defines this lower voltage limit.
Electrical Breakdown – the point at which an insulating gas or solid dielectric, under a strong enough electric field, rapidly loses its insulating properties and becomes conductive.
Extra-Low Voltage (ELV) – the voltage class below the low-voltage threshold, split into Safety, Protective and Functional categories (SELV/PELV/FELV) depending on how the circuit is isolated from higher-voltage sources.
Fuse – device that protects electrical circuits against undesired high currents. We can use passive fuses and pyro fuses in battery design.
Fuse Coordination (Selective / Layered Fusing) – designing the fuses at cell, module and pack level so each tier blows only for a fault local to it and at a current below the tier above it, meaning a single cell fault takes out one cell fuse rather than the whole pack.
HIPOT Test – a quality-control test that applies a high potential across a cell or HV system to measure leakage current and detect insulation failures or latent short circuits.
HV – abbreviation of High Voltage and in automotive world this means above 60V DC.
HVIL – High Voltage Interlock Loop.
HV Battery Junction Box – the assembly that brings together the measurement, control and connection functions of the battery’s HV system, typically housing the contactors and pre-charge circuit alongside the Battery Disconnect Unit.
Impedance – the total opposition a cell presents to alternating current, combining resistive, capacitive and inductive components; it grows with ageing and is commonly characterised by EIS as a state-of-health indicator.
Inrush Current – the brief, high-magnitude current surge at the moment of contactor closure or charge initiation, driven by the charger’s or inverter’s capacitive input stage when pre-charge doesn’t fully manage it.
Insulation and Isolation – electrically we need to insulate and isolate the battery.
IR Drop – the fall in terminal voltage under load caused by current flowing through a cell’s or pack’s internal resistance, per Ohm’s Law.
Isolation Resistance of a Pack – for the complete HV system to ground with the contactors closed should be >500Ω/V and hence for a battery pack its resistance target must be specified by the HV System designer, typically >1,500kΩ.
LV – abbreviation of Low Voltage and in automotive world this means below 60V DC.
Nominal Energy – a cell’s measured charge/discharge energy over the same standard cycle used for Nominal Capacity, at a given C-rate and temperature.
Nominal Voltage – reference voltage of the battery at 50% state of charge and at the defined discharge rate.
Open Circuit Voltage (OCV) – the cell terminal voltage measured at rest with no current flowing, a direct function of state of charge and chemistry.
Pre-Charge Resistor – when the battery pack contactors are closed onto a motor and inverter there will be an inrush of current into the inverter capacitor. This very high current is at a minimum likely to age the contactors, it could permanently damage the contactors.
Pyro Fuse – a fuse that can be blown by a signal.
Voltaic Efficiency – the ratio of a cell’s average discharge voltage to its average charge voltage over a cycle; distinct from Coulombic Efficiency, which compares charge in against charge out rather than voltage.
See also: Cell Definitions & Glossary, Pack Definitions & Glossary, System Definitions & Glossary