What is 400Hz System?

It is a system whereby the power generator using the high-frequency of 400Hz to generate the AC power instead of the normal 50Hz or 60Hz. This system is normally used by airliners due to its advantages.

The History

In1920s when planes routinely carried radios and navigation gear powered by direct current (DC) batteries, the demand of self-powered generator becoming a major concerned. In the early days, planes had no need for electrical power since they carried no devices that required it. Later advances led to the development of small generators that supply DC power, typically at 28 volts.

By the beginning of the jet age, aircraft were becoming increasingly more complex and operated a vast array of electrical devices. It is a must for commercial airliners to provide power for environmental systems, galley equipment, cockpit displays, communication gear, weather radar, and in-flight entertainment systems whereby the current DC power supplies are insufficient to meet the demands for electricity to operate flight instruments, actuators, heating equipment, avionics, and internal/external lighting on these large aircraft. These planes instead use alternating current (AC) systems that usually supply 115 volts at 400 hertz.

Modern military aircraft however are equipped with powerful radars, sensors, weapon systems, and sophisticated cockpit displays that require large amounts of electricity to operate. Aircraft are equipped with a number of power generation systems including both primary and redundant backup systems to continue supplying power to vital equipment in an emergency.

Primary power is usually provided by AC generators directly connected to the jet engines. Commercial aircraft and many military planes are also equipped with an auxiliary power unit (APU). These generators provide AC power using an alternator that supplies 115 volts at 400 Hz frequency.

The advantages

The advantage of running an electrical system at 400 Hz rather than 60 Hz is that the power supplies are smaller and lighter.

The alternators that run in high-frequency are only requiring fewer copper coils in order to generate the necessary electrical current. This reduction in material allows the alternator to become much smaller such that it takes up less space and weighs much less than it would otherwise.

This benefit is essential for an aircraft since space is always limited, and it is imperative to minimize weight in order to maximize performance.

The reductions in weight will absolutely reducing the fuel consumption for an airplane thus makes the flight trip is more economical.

Disadvantages

High-frequency electrical systems are less efficient.

Equipment operating at 400 Hz systems is more likely to suffer voltage drops. As the frequency increases, the larger the voltage drop becomes.

The most significant of these losses results from reactive drops. Reactive drops are caused by the inductive properties of the conducting cables or wires through which the electrical current is transmitted. This type of loss is affected both by the length of the conductor as well as the frequency of the power flowing through it.

Since the distance of the conductor is not a major issue in the airplane, this voltage drop is considered as minimal and less significant compared to the reduction in weight of the generation equipment.

What will happen if using the 400Hz equipment in 60Hz systems?

This is something that I’m not encouraging you to experiment it. Theoretically, running 400 Hz equipment on a 60 Hz electrical system is not advised since it will damage the device by means of overheating the metal in the 400 Hz unit.

The end result will almost surely be smoke and possibly a fire.

Is there any way to operate the 400 Hz equipment into the 60 Hz system?

Actually there is! By reducing the voltage supplied to the device by a ratio of 60/400, or 0.15. A reduction in voltage to 15% of its original value at the same current will allow most 400 Hz devices to operate safely on a 60 Hz electrical system.