The Rationale Behind Aircraft Voltage and Frequency: 115V and 400Hz Explained
The design and operation of aircraft require specific electrical parameters to ensure safe and efficient performance. Two key characteristics of the electrical system in aircraft are voltage and frequency. Commonly, aircraft utilize 115V 400Hz, whereas household power is typically 230V 60Hz. This article will explore the rational behind these specific standards.
Understanding the Differences
There are several reasons why aircraft use 115V and 400Hz for their electrical systems, while households commonly use 230V and 60Hz. These differences are not just arbitrary but have practical, safety, and efficiency benefits.
1. Voltage and Safety
The voltage chosen for aircraft is crucial for both safety and power delivery. 115V is considered relatively safe for power transmission over long distances without becoming lethal. This choice allows sufficient power to be delivered to all parts of the aircraft, even over very long wires.
For comparison, household voltage in North America is 110V, while the rest of the world often uses 230V. 230V proves to be an efficient option for single-phase power supply, offering lower current and smaller wires, although this can come with its own trade-offs when it comes to frequency.
2. Frequency and Size
The 400Hz frequency in aircraft systems offers advantages in terms of size and weight. 400Hz transformers and filters are smaller and lighter than their 60Hz counterparts, making them more suitable for installation within the confines of an aircraft. Additionally, at 400Hz, the power can be more easily filtered out of radio and audio systems, reducing interference.
This lower interference is a significant factor in the design of aircraft, where sensitive electronic systems need to function without disruptions. At 60Hz, there is a higher risk of radio frequency (RF) interference, which can be hazardous in an aircraft environment. Thus, 400Hz also results in less interference and greater reliability of the aircraft’s electronic systems.
3. Weight and Wire Efficiency
Aircraft use 115V 400Hz for weight savings. The frequency is high enough to allow the use of smaller and lighter cores in generators and transformers, which reduces the overall weight of the aircraft. Furthermore, the skin effect at high frequencies (400Hz) is pronounced, meaning that the current flows on the surface of the wire. This effect allows for the use of thin, lighter conductors, further reducing the weight of the wiring harness throughout the aircraft.
On the other hand, while 230V can be more efficient in terms of current, it requires larger conductors to achieve the same power transmission. This increases the weight and bulk of the wiring, which is a critical consideration in the design of aircraft, where every gram counts. Therefore, not only does 115V 400Hz save weight, but it also simplifies the overall design and reduces costs.
4. Historical and Practical Considerations
The use of 115V 400Hz for passenger electronics and equipment on aircraft has deep historical roots. This standard was chosen during World War II, as it allowed for the production of smaller and lighter transformers and generators. This was a critical consideration given the ongoing war effort and the need for lightweight, efficient equipment.
During this period, the conversion of DC ships' power to 115V 400Hz AC was done using solid-state inverters to ensure smooth operation of gyros and the accurate functioning of heading and attitude indicators. Despite the arbitrary nature of the voltage and frequency choices, they were made with the practical needs of aircraft in mind.
Conclusion
The choice of 115V 400Hz for aircraft is rooted in a combination of safety, efficiency, and practical considerations. These parameters allow for the creation of smaller and lighter components, reduced interference, and improved reliability of the avionics systems. While different commercial aircraft manufacturers may have slight variations in their standards, the principles remain the same, ensuring that the aircraft are safe, efficient, and capable of performing at their best.