Holdfast Training Services Trial Blog

I stumbled across an interesting building last week whilst out on a Fire Compliance Survey. Within the Devonport Dockyard, Babcock have a building called the Central Frequency Changing Station (CFCS). This feature is responsible to the provision of “Shore Power” electrical supplies across the dockyard and HMS Drake Naval Base.

Devonport Dockyard showing CFCS building

Once large ships and subs are docked, there is obviously still a requirement to run auxiliary systems such as HVAC, lighting, battery charging, communications centre, computers and navigation systems. The vessels can provide their own power with their on-board diesel generators, but this results in noise, vibration and emissions as well as driving up running hours and using up vast amounts of fuel. The obvious choice is to just “plug them in” to a “shore supply”.

There is one slight issue; as the vessels make their way from international port to international port; the local power grid supplies can, and do, vary. Most vessels are designed to receive a shore supply of 6600 Volts at a frequency of 60 Hz. “Oh no” I hear the E&Ms cry! Here in the UK we use 50 Hz and generally a HV supply of 11 kV.

World wide electrical frequency standardisation 50 vs 60 Hz

So how do we get around this? Each “Shore Supply” is converted to 6.6kV at 60 Hz by motor-generator units. The CFCS building houses 12 x 10 MVA “common-shaft” synchronous-motor frequency converters.

Rotary “Common-shaft” Frequency Converter Units

Frequency Converter Front Panel

Each of the sets uses a 50 Hz supply to produce an output of 60 Hz through the use of a “common-shaft” converter. Frequency conversion is achieved by winding the motor with a different number of electrical poles than the generator. A 10-pole motor and 12-pole generator are used to provide the conversion from 50-60 Hz . Using a synchronous drive motor ensures the frequency is maintained at a constant level to ensure power quality. Rotary units are selected as they are more reliable than solid state converters which create a synthesised output voltage and are prone to unwanted harmonics.

The sets give off a lot of heat which means the building requires heavy ventilation and the units themselves are served by a water cooling system which can be seen by the pumps and green pipework shown dotted around the installation.

Circulation pumps for Frequency Converter cooling system

The 60 Hz supplies are then distributed via what I was told is the largest switch-room in Europe (citation needed!).

Dockyard Shore-to-Ship Electrical Supply Control Room

Just as a side note – A higher frequency is the preferred choice for many applications as motors and generators which run faster, have a better power to weight/size ratio and therefore take up less space. The same reason is why the aviation industry uses 400 Hz – smaller, lighter components for the same shaft power output.

What other locations or facilities are people aware of that have different supply requirements? Have you seen any “funnies” on your travels so far?