Requirements for high voltage cables for electric vehicles

- Oct 03, 2019-

Innovative electric vehicle designs present new challenges to high voltage cables and system components that do not fully utilize existing solutions. The specific requirements are analyzed as follows.


1. Voltage

The basic difference from conventional automotive cables is that the structure needs to be designed for a rated voltage of 600 V, and if used on commercial vehicles and buses, the rated voltage can be as high as 1000 V. In comparison, it is even higher. Cables currently used in automobiles driven by internal combustion engines are designed to have a rated voltage of 60 V.

      

In the case where the generated power (P = U × I) is constant, the high voltage can reduce the power loss in the transmission system (PLOSS = I2 × R) due to the use of a lower current.

      

2. Current

Since the cable connects the battery, the inverter and the motor, the high voltage cable needs to transmit a high current. Current can reach 250A to 450A depending on the power requirements of the system components. Such high currents are difficult to find on conventionally driven vehicles.

      

3. temperature

The result of high current transmission results in high power consumption and heating of the components. High voltage cables are therefore designed to withstand higher temperatures. It can be seen that there is a tendency for further increase in temperature requirements.

      

In contrast, current vehicles typically use a cable rated temperature of 105 ° C, as long as the cable is not used in the engine compartment or other areas that are resistant to higher temperatures. Electric vehicle high voltage cables are usually higher than this temperature, such as 125 ° C or 150 ° C.

      

If the route passed through the electric car is unfavorable, the OEM will even propose higher temperature resistance requirements. Such as near the exhaust pipe, the front of the motor, the back of the battery, etc.

      

4. life span

The automotive industry typically has a designed service life of 3000 h at a specified temperature grade. In recognized cable standards (eg ISO 6722, ISO 14572), this value is typically used for long-term aging tests. Special requirements for customers in high-voltage applications may exceed 3000 h, and the cumulative operating time at specified temperatures may even reach 12,000 h.

     

5. Shielding effect

The high voltage cable itself does not need to be shielded because it does not transmit data like a coaxial cable, but it is necessary to prevent or reduce the high frequency radiation generated by the switching power supply in the system from being induced to the peripheral components through the cable.

      

Unlike fuel-driven vehicles, three-phase alternating current that controls the electric motor's motors becomes a must. The sinusoidal voltage carrying energy is equivalent to a square wave pulse signal of different frequencies. Since the high frequency pulse has a steep edge, it generates a very strong harmonic emission to the surrounding area.

      

The EMI problem can be completely solved by using an appropriate shielding method. In some cases, a combination of different shielding types is required to meet the different requirements of the shielding effect.

      

6. Flexibility

The challenge in the development of hybrid vehicles in many cases is that the existing series of platforms originally only designed the space for loading the gasoline engine and its components into more electrical components. Even if wiring is not considered, space limitations can be expected. In addition, cables and connectors also require space for routing. The usual consequence is the bending radius that leads to tension.

      

Due to the inherent design of conventional cables, high bending forces are difficult to overcome. To solve this problem, the high flexibility of high voltage cables is critical. Only a more flexible design can be easily implemented by routing the vehicle.

      

7. Resistance to bending

If the motor is located close to the moving part of the vehicle and then causes the connected high-voltage cable to continuously vibrate, it is required to be designed to withstand high cyclic bending to ensure good bending endurance.

      

8. Identification

Because of the increased application risk due to high voltages, various standards define that high-voltage cables must be visually distinguished from ordinary automotive cables, and the designated surface must be bright orange.

At the same time, warning content and special marks can also be printed, such as "Caution! High voltage 600V", high voltage lightning logo.

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