Guide 05 Naval electrical power
Why Do Navies Use 400 Hz Power?
Warships run part of their electronics, radar, weapon, communication and navigation equipment, on 400 Hz rather than the 50 or 60 Hz that feeds the rest of the ship, because rectifying a 400 Hz supply leaves far less noise on the DC rails those systems actually use. Aircraft on deck draw the same 400 Hz through the same family of converters.
- Topic
- Naval electrical power
- Checked
- 23 September 2026
- Sources
- 3
- Questions
- 5
01
What actually runs on 400 Hz
On a warship, 400 Hz supplies feed naval radar, weapon, communication and navigation equipment, alongside the aircraft that operate from the ship. Aircraft on the ground or the deck, which are commonly built around a 400 Hz standard, are supplied through frequency converters that step the ship's or the airfield's 50 or 60 Hz down to 400 Hz for them, using the same conversion technology fitted for the ship's own 400 Hz loads.
Radio and combat systems equipment on naval ships is often powered by 400 Hz specifically to reduce noise on the DC signal after rectification. Ripple frequency on a rectified supply rises with the AC input frequency, so a 400 Hz source produces ripple at a correspondingly higher frequency than a 50 or 60 Hz one, which a filter of a given size can remove more completely.
02
How the 400 Hz supply is produced
400 Hz is generated either by a static converter, rectifying the ship's supply and inverting it electronically with no moving parts, or by a rotary converter, a motor-generator set in which a 50 or 60 Hz motor drives a generator wound to deliver 400 Hz on a common shaft. Both arrangements are in service on Indian naval bases and dockyards, according to converter suppliers, fitted either on the jetty to supply a ship alongside or on board the ship itself.
03
Why isolation and stability matter for this supply
Where the 400 Hz feeds radar, weapon or navigation equipment, the quality of that supply matters more than for ordinary ship's power. A rotary converter's shaft electrically separates the ship's own, sometimes noisy, generation from the 400 Hz output, and its rotating mass rides through brief transients and dips rather than passing them on to the load. Static converters give a smaller, quieter alternative with very high output accuracy, and many navies use both, choosing rotary or static equipment against what each piece of 400 Hz equipment's own specification calls for.
04
The same idea powers aircraft on the ground
Aircraft electrical systems are widely built around 400 Hz because it is lighter for a given power output than 50 or 60 Hz equipment, so ground power units for aircraft carry the same 50 or 60 Hz to 400 Hz conversion found on a warship, whether at a naval air station or on a ship's own flight deck or hangar supply.
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Questions people also ask
Why Do Navies Use 400 Hz Power?
What equipment on a warship runs on 400 Hz?
400 Hz supplies commonly feed naval radar, weapon, communication and navigation equipment, along with aircraft operating from or embarked on the ship. It sits alongside the ship's main 50 or 60 Hz supply rather than replacing it, and is produced locally by static or rotary frequency converters rather than generated directly at 400 Hz.
Why does a 400 Hz supply leave less noise on a DC signal after rectification?
Ripple frequency on a rectified supply rises with the AC input frequency, so 400 Hz produces ripple at a much higher frequency than 50 or 60 Hz does. A filter of a given size removes higher frequency ripple more completely, which is why radio and combat systems equipment on naval ships is often powered at 400 Hz specifically to reduce noise on the DC side.
How is 400 Hz power supplied to a ship alongside a jetty?
Ships alongside take shore power at the local 50 or 60 Hz standard, and frequency converters, static or rotary, on the jetty or on board the ship itself, produce the 400 Hz needed for radar, communication and weapon systems. Both static and rotary 400 Hz converters are in use for this purpose at Indian naval dockyards and shipyards, according to converter suppliers.
Why do some 400 Hz loads use rotary rather than static converters?
A rotary converter's motor-generator shaft electrically separates the ship's own supply from the 400 Hz output, so disturbances on the ship's generation do not reach the load, and its rotating mass rides through brief dips and switching transients. That tolerance matters for radar and weapon systems that are sensitive to power quality, though static converters are also used depending on the equipment's own specification.
Do aircraft need a 400 Hz supply on the ground?
Yes. Aircraft on the ground are commonly built around 400 Hz electrical systems, so ground power units, whether at an airfield or on a ship's flight deck, take the local 50 or 60 Hz supply and convert it to 400 Hz using the same frequency converter technology fitted for a ship's own combat and navigation systems.
Checked against
Sources
- 01Frequency changer, Wikipedia
- 02Frequency converters for defence applications, Energiaa
- 03SOLAS Chapter II-1, electrical installations on merchant ships (warships are exempt from SOLAS), International Maritime Organization
This guide explains how the system works in general, as the documents above describe it, and was last checked on 23 September 2026. Rules and thresholds change: the governing document is the authority, not this page.
On this site
Where this meets the work
- The DQA(N) type approved rotary frequency converter
- Defence contract works
- The two type approvals on record
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