Have you ever thought that the “grounding” of electric vehicles is the same as that of household appliances, which guides current into the earth ground?
The truth may overturn your perception – the so-called “grounding” in the car is not truly connected to the ground, but rather a sophisticated “potential balancing” system inside the vehicle that safeguards safety.
When your car is speeding, the rubber tires completely insulate it from the ground, forming a suspended metal castle. If the insulation of high-voltage components is damaged at this time, the vehicle body may be electrified.
But don’t worry, the engineers resolved the crisis with clever “potential balancing” design.
- Why?
Because the real grounding is to bury the grounding wire under the ground. Physical limitations Real grounding requires the ground wire to be buried underground, which cannot be achieved while the vehicle is moving.
Insulated quarantine rubber tires are natural insulators that keep the vehicle in suspension and in electrical quarantine with the ground.
- Vehicle grounding is actually “potential equalization”
The vehicle is “” potential equalized “” by equipotential bonding-all metal parts (e.g. body, high voltage enclosure) are connected by wires or metal structures to ensure that there is no potential difference between the parts.
3.Resistance requirements
The resistance value of the high-voltage component shell and the vehicle body is ≤ 100mΩ, and the resistance value of the two high-voltage component shells that can be touched at the same time is ≤ 200mΩ. Of course, the requirements for the resistance value are not exactly the same, so it is necessary to pay attention to the target market and the special requirements of customers.
- Potential equalization: to achieve fault protection between the high-voltage part and the metal shell.
General requirements for protection: basic protection + fault protection
Basic protection refers to the protection under normal working conditions, that is, our basic insulation design between the high-voltage part and the metal enclosure.
Fault protection means that in the event of a single fault, the human body can still be protected from the risk of electric shock.
When an insulation fault occurs, the human body touches the high-voltage component and the vehicle body at the same time, and when the vehicle body and the vehicle body, as well as two different high-voltage components, due to the equipotential between them, there is no potential difference between the two sides of the human body, so no current will be generated, and the human body is safe.
However, if a person touches the car body while touching the ground, the car body is suspended and in a high potential state when the insulation fault occurs. Even if there is a potential balance, there is a potential difference between the two sides of the human body, which will form a current and have the risk of electric shock.
- Connect the PE cable when charging, which is really connected to the ground.
When the vehicle is inserted into the charging pile, the body is connected to the ground through the PE line of the charging socket, and then the real grounding is realized.
- Fault detection
Vehicle side fault
If the high-voltage positive insulation is damaged → the vehicle body is charged → the charge flows into the ground through the PE line → the vehicle body is equipotential with the ground → there is no risk of electric shock; At the same time, the leakage current triggers the RCD (residual current protector) to cut off the charging circuit.
Fault on charging pile side
If the positive/negative pole insulation of the charging pile fails → the fault current flows back to the neutral point of the power grid through the PE line → the current is prevented from flowing into the vehicle → the RCD synchronously cuts off the circuit.
Therefore, the potential equalization of the vehicle itself only ensures that there is no potential difference in the vehicle, but it cannot quarantine the ground; when charging, the PE line must be connected to build a “vehicle-ground” safety circuit to cover all the risks of electric shock.
