Current is conveyed from the main dynamos by means of heavy rubber insulated cables, each 1·5 sq. in. in section and 2 1/4 in. in diameter, to the dynamo control switches situated on the front of the switchboard gallery.
The main switchgear which is arranged on somewhat novel lines has been manufactured by Messrs. Dorman & Smith. Nearly all the gear is placed on an orlop deck across the forward end of the generator room. It consists of four sets of main switchgear, each set controlling one of the four main generators, combined with a set of four pairs of equalising switches, and also of a main feeder switchboard of 25 panels equipped with gear for controlling two circuits on each panel, making 50 circuits in all, each of 600 amps. capacity. All main circuit breakers and switches are capable of continuously passing 6,000 amps. Each of these circuit breakers is capable of being operated by hand release or by a Ferranti overload control with an inverse time element equipment. In designing the circuit breakers, very careful attention has been given to the question of reliability. Every possible detail, such as the throw-out springs, trigger springs, cushion springs, auxiliary metallic and carbon breaks, &c., has been arranged in duplicate, so that the breakage of any one part cannot spoil the working efficiency of the breaker.
In series with each circuit breaker is the main instrument, which is about twice the usual size to ensure a low temperature rise, and also a pair of main selector switches, permitting each generator to be connected to either the power or lighting ‘bus bars, or to both.
All the main generator switches, shunts and connections are carried on steel bars, insulated with hard micanite. The supporting bars are in turn carried on steel frame casting, and the whole gear for each machine is enclosed in a neat steel casing, supported on a cast frame.
Each set of main switchgear is operated by a row of five interlocked handle levers (see Fig. 4). The two outer handles are connected mechanically with the lighting and power equalising switches, respectively, and are interlocked so that they must be closed before the next handles, which operate the lighting and power main ‘bus-bar selector switches, can be worked. The central handle is for closing and gripping the circuit breaker, and is also interlocked with the selector switch handles, so that the circuit breaker can only be closed and gripped when the selector switches are both in the “off” position.
Fig. 4 shows the complete switchgear of dynamos Nos. 1 and 2. At the side of the casing are seen two devices for tripping the main circuit breaker; the top one closes the electrical circuit of the trip coil and the lower one mechanically trips the toggle grip and lifts the trigger. On the right-hand side of each gear is a small panel with the fuses of the pilot lamps, wattmeter, shunt, &c. On the upper right hand is the engine room signal knob. Fig. 5 is a view of a main generator control pillar during construction, showing the circuit and the two selector switches below.
The selector switches themselves are very massive, and have a long rubbing contact to avoid dirt being squeezed in under the contact faces. The section is 13·7 sq. in. and the contact surface 21 sq. in. The link connecting these switches to the operating lever handle is so arranged that no great effort is required on the part of the switchboard attendant.
Pilot lights are provided as follows: On any machine being excited the dial of the ammeter is illuminated; on closing a circuit breaker two pilot lights across the machine illuminate the inside of the casing containing the switchgear; on closing either a power or lighting selector switch two more pilot lights illuminate a bold sign at the back and front of the switchgear casing, intimating whether that machine is connected to the power or lighting ‘bus bars.
The equalising switches called for very special consideration in their design. They are placed in the centre of the generator room and are as nearly as possible equidistant from the four machines. There is a power and lighting equalising switch for each machine, and these are mechanically operated from the switchgear deck by levers interlocked with the other main switchgear, so that no machine can be connected to a power or lighting ‘bus bar until after its equalising switch is connected to the power or lighting equalising bar respectively.
These switches are very compactly constructed for such heavy gear, being identical with the main selector switches in capacity and construction. The contacts are combined with the equalising ‘bus bar, so that the minimum amount of space is taken up, and the whole eight switches and two ‘bus bars are carried on a massive steel frame, being insulated therefrom with micanite. This frame is arranged so that it is bolted and stayed to the ship construction work. A neat sheet steel casing to protect the switches is built round the eight switches and forms part of the steel foundation frame. A view of the equalising switchgear is given in Fig. 6. The enclosing case is arranged to open in two parts, the left-hand half being here shown open. The connecting links of some of the switches are shown on the right-hand side.
The main voltmeters (Fig. 7), which are used also for paralleling, are carried on a cast-iron pillar amidships between the main dynamo control gear. The voltmeters themselves are mounted in pairs, each pair being arranged so that they can swing round through 220 deg.
The two outside instruments are used to give machine voltages and the two centre instruments ’bus bar voltages, the former being controlled from the plugging arrangements on the main dynamo panels, and the latter on the voltmeter pillar itself.
The voltmeter plugs are all three-pin and are fool-proof, so that machines cannot be put in parallel on to any one instrument. The third pin on each voltmeter plug is connected to the lamp circuit automatically illuminating a sign, so that the insertion of a voltmeter plug in any socket causes an indicator on the voltmeter pillar to be illuminated, intimating to the operator to what the voltmeter is connected.
Special attention has been paid to the transmitting of instructions from the switchgear deck to the engine attendant, and a signaling arrangement has been provided for this purpose. Placed in the centre of the engine room, where it can be easily seen and read from both sides, is an illuminated signal device. This can be operated from a control knob on each of the dynamo control gears. On turning the knob to the instruction required to be given, and pressing it, the corresponding signal is illuminated and a bell is rung, drawing the attendant’s attention. The signs, reading “start,” “ raise speed,” “lower speed” and “stop,” combined with the number of the machine to which the signal applies, are visible in white letters on a red background when the lamps are illuminated by pressing a signal knob (Fig. 8).
From the main dynamo switches the current passes by insulated cables below the gallery to a massive feeder switchboard, which consists of 25 black polished slate panels for 50 separate circuits. Each circuit is controlled by a circuit-breaker and a large main “handle” type fuse. Each circuit has a moving coil ammeter, and each panel a pilot light bracket.
The main ‘bus bars for the power circuit are of 8·4 sq. in. section, and for the lighting circuits 3 sq. in. section. The latter run the full length of the board, the power circuits being arranged on the centre panels, and the lighting circuits in two parts—at the port and starboard ends, respectively.
The main dynamo cable connections from the main selector switches are connected to the ‘bus bars through massive copper connectors bolted up with steel clamps, and the surfaces of connection are spread along the central part of the ‘bus bar, so that the current density is kept low.
From the feeder switchboard no fewer than 48 cables, ranging in size up to 61/12 S.W.G., radiate, passing vertically up two steel trunkways port and starboard and terminating in master fuse boxes on each deck, from whence branch the individual circuit cables. These ramify along the main passages of the different decks throughout the vessel and feed, in turn, distribution boxes. From these run branch cables supplying current to the individual lights, motors, heaters and other plant.
The system adopted is known as the single-wire, the returns being carried back, however, and bonded in such a way as to avoid stray currents. The power and heating can, if desired, be run entirely independently of the lighting, there being power and light ’bus bars on the switchboard, which can be paralleled if desired. The circuits are further so split up that passenger accommodation, saloons, crew, cargo, machinery spaces and individual motors or groups of motors, are independent, and can be switched on or off to suit the varying conditions when en voyage or in port. In addition, there are, of course, local switches in the cabins, and generally throughout the ship, for turning on or off individual lights or machines. The main cables and branch wires are of tinned copper covered with rubber and heavily braided, and in the machinery spaces are lead-sheathed, armoured and externally braided. In the boiler rooms they are run in steel pipes for protection against damp and mechanical injury. Considerably more than 200 miles of cable have been employed.