Why is aviation power 400Hz?

400Hz is the power frequency used by most aircraft. Aircraft use AC generators to generate electricity, providing stable and efficient power for avionics equipment, onboard systems, cockpit equipment, auxiliary power units, etc. Why do most aviation power supplies use 400Hz frequency instead of 50 or 60Hz?

1. Lower weight

One of the reasons why many aircraft use 400Hz power is that it allows for lower weight. The higher the frequency of the electrical system, the less copper and steel materials used in the generator and transformer, and the correspondingly lighter weight and lower cost. The disadvantage is that the inductive reactance of electrical equipment and lines increases, the capacitive reactance decreases, the loss increases, and the transmission efficiency decreases. On the contrary, low frequency will increase the materials used in electrical equipment, increase weight, and increase costs. There is a famous saying in the aviation industry: "Strive to reduce every gram of weight!" Therefore, in order to reduce the size and weight, the aviation power supply is required to use a high frequency. The transmission line on the aircraft is not too long, and the loss is not the main contradiction, so most aircraft use 400Hz power.

2. Reduce EMI(electromagnetic interference)

High-frequency power supply can reduce EMI in the power supply system. Electromagnetic compatibility is a very important issue on aircraft because there are a large number of electronic equipment and communication equipment on aircraft, which are very sensitive to EMI. Using high-frequency power supply can reduce the electromagnetic interference generated by the power supply system, thereby improving the performance and reliability of electronic equipment on the aircraft.

3. Power output stability

High-frequency power supply can provide more stable and reliable power output. High-frequency power supply can better filter out harmonics and noise in the power supply system, thereby providing more stable and clean power output, which is very important for various electronic equipment and aviation systems on aircraft.

4. Balance

The choice of 400Hz frequency as aviation power supply is not accidental. Increasing the frequency can reduce the core volume and weight of static electromagnetic equipment. Through many tests, it is found that the rotating motor has an optimal frequency value to minimize the volume weight coefficient of inverter, motors and other equipment. This frequency is 400Hz, as shown in the figure below.

Too low a frequency will increase the size and weight of the inductor and capacitor components in the power system, while too high a frequency will increase the loss and heat of the power system. A frequency of 400Hz has a better balance in power transmission and conversion. Too low a frequency may require larger cables and transformers, while too high a frequency may require more complex electronic devices to achieve power conversion, which will increase the complexity and cost of the system.

5. Standardization and historical accumulation

The 400Hz frequency aviation power supply is widely used in the aviation field, which is also related to historical reasons. In the past few decades, many countries and aviation manufacturers have established aviation power supply standards and equipment based on the 400Hz frequency. This uniformity makes the power systems between different aircraft interchangeable and easy to maintain and update. In addition, the production and supply chain of aviation power supply equipment have also adapted to the needs of the 400Hz frequency, making replacement and maintenance more convenient and cost-effective.

Summary

400Hz power supply has advantages in size and weight, electromagnetic interference control, stable power output, excellent balance, standardization and historical accumulation on aircraft, making it a universal frequency for aerospace systems. 

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