How to confirm the new energy vehicle high voltage wire diameter?
Influencing factors of wire diameter
1.Transmission capacity: Simply put, it is the amount of electricity that the cable needs to transport. The greater the transmission power, the larger the wire diameter required, which is like to transport more water, you must use a thicker water pipe.
2. Allowable voltage drop: When electrical energy is transmitted in the wire, the voltage will drop to a certain extent. The allowable voltage drop in the industry is clearly defined, and in order to meet this standard, the cable diameter must be adjusted according to the cable length and transmission power. In general, the longer the cable, the smaller the voltage drop allowed, and the larger the required cable diameter.
3.Ambient temperature: Temperature has a significant effect on the resistance of the wire. As the temperature increases, the wire resistance increases. In high temperature environment, in order to ensure the normal operation of the wire, it is necessary to appropriately increase the diameter of the wire.
4.Electromagnetic compatibility requirements: there are many electronic devices inside new energy vehicles, and electromagnetic interference generated by high-voltage wiring harnesses can not affect the normal operation of other equipment. Thicker wires can reduce the current density and reduce electromagnetic radiation, so the choice of wire diameter will also be affected when meeting electromagnetic compatibility standards. For example, in high-voltage harnesses close to sensitive electronic components such as on-board computers, larger wire diameters may be required to ensure electromagnetic compatibility.
5.Space layout limitation: the interior space of the car is limited, and the high-voltage wiring harness needs to be rationally arranged in the limited space. This requires that when determining the wire diameter, both the electrical performance should be satisfied and the spatial adaptation should be considered. If the wire diameter is too large, it may not be possible to route in the narrow gap of auto parts, affecting the vehicle assembly.
Basic requirements and information input
The High Voltage Cable shall comply with the requirements specified in SAE J1654 (High Voltage Primary Cable) and SAE J1673. On this basis, it is necessary to combine the following factors to determine the diameter selection of high-voltage wire cable.
1). Wire diameter selection should meet LV216-1/2, ISO19642 and other standards.
2). Determine the load characteristics of the electrical components to which the high voltage cable harness is connected, including steady-state current strength, voltage requirements, transient conditions and current strength and current waveform (smooth, pulse, frequency, etc.).
3). The cross-sectional area of the conductor is determined according to the steady-state current intensity
4). Adjust the cross-sectional area of the conductor according to the working environment temperature
The operating temperature of the high-voltage wire cable is -40℃~125℃, and it needs to pass the voltage resistance test of AC2500V/min and 50Hz.
If the layout environment of the high-voltage conductor exceeds the allowable operating temperature of the conductor, the conductor with a larger cross-sectional area must be selected. When the ambient temperature is up to 180 ° C, the cross-sectional area of the conductor should be increased by one step. When the ambient temperature is up to 250 ° C, the cross-sectional area of the conductor increases by two levels.
Figure: External high voltage wiring harness and assembly connection schematic diagram
Method and procedure of determining wire diameter
3.1 Method 1, use the product specification to determine
- Check the working voltage platform of the high-voltage wire, the current general voltage platform is below 1000V DC, so the high-voltage wire resistant to 1000V DC is more used;
- Select the wire diameter according to the temperature rise curve combined with the carrying capacity of the wire and the working environment temperature;
- Comparing the peak current, peak duration and wire smoke curve (see figure below), the peak duration is less than the wire smoke time;
- Comparing the fuse time with the wire smoke time, the wire smoke time is longer than the fuse time.
- After the above steps to initially determine the wire diameter, combined with the high-voltage plug-in model and specifications, to confirm whether the wire can be applied, especially the need to check the high-voltage plug-in on both sides of the wire to meet its requirements.
Figure 1:35 square silica gel cables in the flow temperature rise and smoke curve
3.2 Method 2, calculation formula of wire diameter selection
The current intensity and cross-sectional area are calculated as follows:
- The current intensity of the electrical equipment is: I=P/U.
*P is the load power, *U is the rated voltage
- The cross-sectional area of the conductor is calculated as follows: A=IρL/UVL.
*A is the cross section of the wire, *I is the current value, *ρ is the resistivity of the copper wire (0.0172Ω · m at standard atmospheric pressure and room temperature), *L is the length of the wire, *UVL is the allowable voltage drop of the wire
- Current density S=I/A. Check the current density to avoid excessive heating of the wire.
*I is the current intensity and *A is the cross section of the wire
Current density is a very important concept in the field of electricity, and it plays a key role in determining the diameter of a high-voltage cable. The current density refers to the size of the current passing through a unit area, which reflects the distribution of the current across the cross section of the conductor in amperes per square meter.
The value of current density will be affected by the service life of the cable, load nature and electricity price. For example, for cables with long-term operation and stable load, lower current density values can be selected to reduce cable losses and operating costs; For cables with short-term use or large load fluctuations, the current density value can be appropriately increased to reduce the initial investment cost.
The current density of high-voltage wiring harnesses of new energy vehicles is relatively special, and the current density of general copper wires is 3-6A /mm². This is because the car space is limited, there are strict requirements on the size of the wire, and it is necessary to minimize the volume and weight of the wire harness under the premise of ensuring electrical performance and electromagnetic compatibility. However, in some high-power fast charge or high-performance drive motor harness, in order to meet the demand for instantaneous large current, the current density upper limit may be close to or even exceed 6 A/mm² for a short time, but this requires more advanced heat dissipation and electromagnetic shielding measures to ensure the normal operation of the wiring harness.
Examples
When the maximum current is 150A, the high voltage harness of 35mm² is used at 125 ° C; At 180℃, 50mm² wiring harness is selected; At 250 ° C, use a 70mm² high voltage harness.
Determining the diameter of high voltage wire is a work with high technical content, which needs to consider many factors. I hope that through today's sharing, you can have a deeper understanding of this field. If you encounter related problems in actual work or have wire, wire harness needs, welcome to Email us: sales03@aichie.com, we will try our best to help you solve the problem!
Supplement, confirm the type of wire
| Conductor type | Material characteristics | advantage | shortcoming | Applicable environment | Special requirements |
| Silicone conductor | Soft, good temperature resistance | Soft, good temperature resistance | Poor tear resistance and oil resistance |
1. The operating temperature is greater than 150 ° C 2. The wiring harness layout space is small, the complete radius does not meet the 5D area, or the flexibility of the wiring harness is strictly required 3. High voltage harness protection is better, no oil no wear area
|
The high voltage plug-in has clear requirements for use |
| Cross-linked polyolefin wires | Hard material | Good wear resistance and tear resistance, low cost | Poor softness, poor temperature resistance |
1. The working environment temperature is not more than 150℃ 2. The wiring harness layout space is large, the bending radius is <5D, or the wiring harness assembly is not difficult 3. The wiring harness may have oil contact, or wear vibration amplitude is large |
The high voltage plug-in has clear requirements for use |
| Other wires | - | Can meet different special needs | - | - |
1. There are flame retardant requirements, HB or V0 grade wires can be selected. 2. There are shielding requirements, unshielded wires, single shielded wires, double shielded wires can be selected, and the shielding density is generally above 85% |