DC Power Systems.
The electrical system on the Ross Revenge is officially 220 volts DC. The AC systems which today provide the source of all the power were installed purely to run the broadcasting equipment when she was converted to a radio ship in 1982. Much of the ships original equipment still runs from DC mains, which is now derived from the AC through a transformer and rectifier system. However, modern living necessitates an AC supply, which is essential for convenience items such as
electric kettles, microwave ovens, toasters, television sets, radios, and many other items we take for granted such as fluorescent lighting none of which were a reality onboard a trawler in 1960.
DC Power can be sourced from one or more of four sources: There are two Deutz 6 cylinder generators rated at 120kw each, and an auxiliary fuel efficient MWM "harbour" genset, rated at 35kw to keep essential services running whilst in port between fishing trips. There is also a shaft generator driven from the main engine, which is double wound with both 220 volt and 440 volt DC windings. The 440 volt winding is exclusively used to provide energisation for the ships main trawling winch motor.
The two Deutz sets are located on the port and starboard sides of the main engine and thus known as port and starboard gen sets. The Deutz engines are coupled onto AEG generators, more correctly termed simply as Dynamo's. Each dynamo can provide 600 amps of power. Bear in mind that in the DC world there is no such thing as single or three phase, real or apparent power, or power factor, so there is just one feed from each genset to the main distribution switchboard. Like all main equipment in the engine room, these generators are started by compressed air,
though prior to starting, a manual pump handle has to be used to pump oil pressure round the system to minimise start-up wear. As the ships electrical system pre-dates semiconductor electronics and automatic regulators, stabilisation of the generators outputs has to be undertaken manually. The output of any rotary driven generator depends upon two factors: the magnetic flux density within the windings and the speed of rotation. In an AC system, the rotational speed will also affect the output frequency (normally 50 or 60 cycles) but this is irrelevent to
DC generators. The voltage output of the genset will also depend to some extent upon the load presented to the set - the more current which is taken, the more the voltage will tend to "sag". This simplest means to provide some basic form of stabilisation or regulation is to vary the speed of the diesel engine driving the dynamo. However, this is not an all encompassing solution, as reducing the speed too far will cause the available power (horsepower) to drop, thus not providing an optimum performance characteristic.
Increasing the engine speed will incease the fuel consumption, and if run at excessive speeds without the correct load, will lead to premature engine wear. The second means to provide regulation then, is to be able to vary the magnetic field within the generator unit. In the modern world, everything from a simple car alternator to a nuclear power station utilises semiconductor electronics to vary the magnetic field by adjusting the current through a set of electromagnetic field windings to give precise control over the output.
However, this technology was not available in 1960, so although the electromagnetic current is varied, control is performed manually by means of a large control wheel connected to a large variable resistance "rheostat" to adjust the current. The current passed through the electromagnetic field windings is also produced by the same generator, so a high degree of skill is required to vary both the engine speed and field current to provide the correct 220 volts output for whatever load is required to be supplied with power without over or under revving the engine or using excessive fuel.
As large, heavy consumption equipment is switched on and off, interactive adjustment of the two controls will be required. The rotational speed of the Deutz engines is approx 900 rpm.
|The starboard Deutz.|
Both Deutz diesel engines are cooled by by means of circulated pumped freshwater supplied from individual header tanks. The hot water from this can then either coupled into the main engine water system, to pre-heat the main engine prior to starting, or can simply be passed through a heat exchanger along with sea-water whereby the heat is simply discharged over the side.
|A voltage regulator wheel on the switchboard.|
In a DC system is is quite simple to have more than one generator powering the ship simultaneously, or to perform a hitless switch between the two. In an AC system it is necessary to syncronise the speeds and phases of both generators before they can be applied to the same load, but this is not necessary in a DC environment.
It is simply necessary to bring both gensets to the same output voltage, by means of either the speed or magnetic flux controls, and place both online by closing the relevent main circuit breaker. The voltage can then be fine adjusted such that the load is taken equally by both sets. As well as providing the means of connection and disconnection, the main breakers also provide over-current protection, and by means of a holding coil, under voltage protection.
The latter will prevent a genset being put online unless it is producing an adequate output, and in the event of loss of output will take the set off-line so it is not reverse fed from another unit. In an operating environment, all four of the DC generators (two Deutz, MWM and shaft) could be switched on and off line in this manner without causing loss of power to the ship.
As the output of the shaft generator depends upon the rotational speed of the main engine, it could not be used to power the ship whilst manouvers were in progress and at these times one of the Deutz's would be in service. However, when cruising for hours, or days at a time at a constant speed both Deutz could be stopped, and the shaft generator used to provide all of the ships electrical requirements.
The shaft generator is double wound with 220 and 440 volt DC windings. The 220 volt winding, rated at ??? watts can be used to provide all of the ships electrical power when the main engine is operating at a constant speed. The 440volt winding, rated at an impressive 1000 amps (nearly half a megawatt) is used solely to power the ships main trawling winch.
Although there is some control over the power developed by this winding, most of the control over the winchs torque and speed would be performed by varying the speed of the main engine. In these cirumstances, the provision of the vulcan coupling and the vari-pitch propeller would be essential in keeping the ship in position. Whilst trawling, and operating the winch, a Deutz set would provide the rest of the ship with power.
Due to the immense power involved in the shaft generator, an external electric air blower has to be used to keep the windings and innards cool under operation. The smaller gensets use a simple shaft mounted fan to keep the windings cool, much like a car alternator does.
|A view of the shaft generator.|
The DC systems thus described have one fascinating ability, which is simply not possible in an AC environment. As every high school physics student knows, a dynamo and electric motor are very nearly reverse processes of each other. Thus, it is inheritently possible to use a dynamo as a motor and vice versa. The switching arrangements upon the Ross Revenge are such that one of the Deutz gensets can be used to "reverse feed"
the shaft generator, thus forcing it to act as a motor. This can provide an extra boost of propulsion power in the event of everything being needed, or in the event of total failure of the main engine, it can provide emergency electric propulsion. The power thus developed would be no more than a few hundred horsepower, resulting in a speed of a handful of knots at most, but is a uniquely useful arrangement none the less.
The main switchboard in the engine room controls all original power distribution around the ship. Smaller sub-boards are fitted in other heavy use areas such as the Galley, the Bridge and the accomodation area, which are fed from circuit breakers on the main panel. From this position it is possible to operate and isolate any original electrical system on the ship. Some services are deemed essential, such as engine room systems, and others non-essential such as cabin lighting and heating.
In the event of partial catastrophic failure of the electrical systems the non essential services can be quickly and easily dropped, thus allowing any available power to be used for the ships safety. The switchboard is open to the rear and it is perfectly feasible to step inside for maintenance or to replace a fuse. A design such as this would definitely not meet modern Health and Safety requirements as there are huge "knife" type switches and bare copper busbars several inches thick in here.
Large panel meters along the top allow the engineers to see exactly how much power is flowing and where its going to
|A partial view of the main switchboard|
with the starboard Deutz pipework
in the foreground.
When originally converted for use as radio ship and fitted with AC generator facilities, it was obviously sensible to derive DC power from the new generators to avoid the need to simultaneously run AC gensets to power the broadcast equipment and DC gensets to power the ships systems. The first means of achieving this was by means of a motor-generator or "rotary converter", which quite simply is an AC motor directly shaft-coupled to a dynamo.
Although simple, this arrangement is not particularly efficient and the need to have a motor and generator spinning 24 hours a day has other maintenance issues. A year or so into her broadcasting career, the Ross Revenge was fitted with a three-phase transformer and rectifier system to derive 220 volts DC from the 460 volt, three-phase 60 cycle broadcast feed. However, in the very early days of her broadcast career neither of these systems was operating, which necessitated running the DC gensets in the engine room.
As these generators are directly below the studio, some significant generator rumble was readily apparent whenever the microphone was live!
|The Rotary Converter.|
Currently, the starboard side Deutz is in fine running order, despite the many thousands of hours of duty is has performed over the last 40 years. It is run up and put online for at least a few minutes a couple of times each year. The MWM is also believed to be in good working order, although it has not run for a few years. A fault with the air pipework for starting this set prevented it from running for a long time and although this has now been repaired, the opportunity has not arisen to start it up.
Sadly the portside Deutz is not in such good condition and was in fact an early casualty in the ships broadcasting role. Due to a most unfortunate oversight it was run with a partly open oil drain cock, and bearing damage ensued. As by that time the majority of the ships electrical power was provided by the AC generators either directly or through the converter/rectifier, and two other DC gensets remained operational repairs were not unertaken. During the 1990's a well meaning volunteer decided the time was right
to attempt to repair this genset, and it was extensively dismantled to allow access to the crankshaft bearings. However at this point the crew member lost enthusiasm in the project and in the follwoing years no-one had the inclination to either complete the repair or re-assemble the engine. Thus for several years now, the generator has been in pieces and parts of it have been scattered around the engine room. Whether all the parts could ever be located to rebuild the set remains to be seen.
As the marine safety agency require all generator sets to be operable for a ship to be certified seaworthy, action will one day be required. Either the original engine can be repaired and rebuilt, or it can be removed and replaced with a new engine, but with the original dynamo. This would not be easy due to the limited access to the engine room and the weight and bulk of the headblock and other components. An alternative would be to remove the entire plant, and replace it with a modern AC genset,
but this would require a new feed to the AC switchboard in the transmitter hold. However, an AC genset here would have the advantage of producing hot water which could be pumped round the central heating system.
|The remains of part of the port-side Deutz. |