How Insulation Resistance in EV Vehicles measured and Why?.

Measuring Insulation Resistance in EV Vehicles

                                    

EV high-voltage systems are designed to be extremely safe, and insulation integrity is a cornerstone of this safety. Regulations such as ISO 6469-3 and IEC 61557-8 set stringent requirements for isolation resistance in EVs. The use of IMDs and such resistor networks is a direct implementation of these safety standards to

1. Prevent electric shock: By ensuring that a single fault does not create a dangerous path for current through a person touching the vehicle.
2. Mitigate fire risk: By detecting and addressing insulation failures that could lead to arcing or overheating.

Insulation Resistance in EV Vehicles 

The primary reason for these high-value resistors is to enable continuous monitoring of the insulation resistance between the high-voltage lines (DC+ and DC-) and the vehicle chassis (earth/ground).

There are no direct connection between HV lines to the chassis, meaning the HV system "floats" relative to the vehicle's metal structure. However, over time, insulation can degrade due to factors like vibrations, temperature changes, moisture, or physical damage. A drop in insulation resistance can lead to a ground fault, which poses a severe risk of electric shock or fire.

The Secondary reason for thses resistors are to discharge the power from Link Capacitors safely, its main function is not rapid discharge, they contribute to the slow discharge of the link capacitor if the system is de-energized, making it safer for maintenance over an extended period. Dedicated pre-charge and discharge circuits are usually in place for quicker and safer discharge during normal operation or shutdown.

The Insulation Monitoring Device (IMD) typically connects between HV system and chassis ground, and injects a small test signal to measure leakage resistance.