It was at one time considered necessary, before connecting a machine into parallel, to run the incoming machine up on an artificial load approxi

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B

FIG. 130.-500 K. W. horn break circuit-breaker closed.

mately equivalent to the load on the working generators. Practically all modern machines can, however, be paralleled without difficulty.

CHAPTER VII.

GENERAL ARRANGEMENT OF CONTROLLING APPARATUS FOR HIGH-TENSION SYSTEMS.

Examples of compact directly controlled switchgear: 'Ferranti' standard high-tension and extra high-tension switchgear, 'Cowan' hinged panel gear, ‘Hastings' gear, and Brush' standard switchgear-Examples of isolated directly controlled gear: 'Glasgow' cubicle switchgear, ‘Raworth' pillar gear-Indirectly controlled systems: 'Berlin' mechanically controlled switchgear, New York Metropolitan Street Railway,' and 'Niagara' pneumatically and electrically controlled switchgear. HAVING now considered, in detail, some of the apparatus required for a complete switchboard, attention may be turned to the general arrangement and assembling of this apparatus.

The various designs that have been adopted are so widely different that it is extremely difficult to classify them. Mr Clothier, in his paper before the Manchester section of the Institution of Electrical Engineers on "High-Tension Switchgear," divides the various constructions into those with spaces behind them, and those without. There are, however, many other distinct divisions; in fact, almost every different design appears to belong to a class of its own.

One very notable difference is in the spacing of the apparatus. Some designers have aimed at getting everything into as small a compass as possible, whereas others have arranged the apparatus controlling each generator, or feeder, in such a manner as to isolate it from its neighbours. Isolated switchgear may be again divided into directly and indirectly controlled gear. In the case of the former the switchboard attendant has to walk from one panel to another, and can as a rule only see the instruments on one panel at a time, whereas in the latter case the actual operating handles and instruments are usually arranged in a very small space, so that the attendant can control everything from one point.

Compact Directly Controlled Switchgear.-An excellent example of this class is the well-known Ferranti high-tension switchgear, a section of which is illustrated in fig. 131. The essential features of this design are its simplicity and the entire absence of any earthed metal framework, between which and the high-tension conductors a dangerous arc might

be established. The various switches and instruments are mounted in cells, or compartments, isolated from each other by slate slabs imbedded in the glazed brick wall which forms the background of the switchgear. It will be noticed that there are no cable

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connections between the various controlling arrangements. The concentric cable from the generator terminates in a cable box A. The outer conductor of the cable is connected to the outer casing of the cable box, and a copper bar bolted directly on to the cable box constitutes the outer 'bus bar of the system. The inner conductor is continued through the cable box to the lower fuse contact B. From this point the current passes through the fuse C, main switch D, and ammeter E, to the main inner 'bus bar F. On a shelf above the main inner 'bus bar the synchronising transformer and voltmeter, the 'bus bar voltmeter, and incoming generator voltmeter are usually mounted. The 'bus bar voltmeter and one side of the synchronising transformer are permanently connected between the 'bus bar and earth, whereas the second voltmeter and the other half of the synchronising transformer are connected to the swinging contact G. Before switching a generator into parallel the main switch is set at half-cock. In this position the moving blade of the switch makes connection with the swinging contact, thus completing the circuit between the incoming generator and earth through the voltmeter and synchroniser. To finally connect the generator to the 'bus bar the switch is pushed home, thus automatically disconnecting it from the swinging contact connected to the synchroniser 'bus bar. Care must be taken to guard against two of the generator switches being set at halfcock simultaneously, as to do this would parallel the two generators through the synchroniser 'bus bar. To prevent a serious accident from this cause, the precaution is sometimes taken of inserting light fuses between this 'bus bar and the swinging contacts.

B

FIG. 131.-Section of Ferranti
H.T. switchgear.

The method adopted of locking a switch open, to guard against its

being accidentally closed when men are working upon the generator or feeder, is very neat. A small wooden panel H just fits the front of the switch compartment, and when this is locked into the position shown, it is impossible for the switch to be operated. Fig. 132 is a front view of

a standard single-phase switchboard, each panel of which is capable of controlling 300 kilo-watts at a pressure of 2000 volts.

The field regulating resistances are usually placed below the switchboard gallery and controlled by a handle projecting through the top of the panelled desk in front of the switchboard. The field switches and field voltmeters are also usually mounted on these panels.

A modification of the above is the Ferranti extra high-tension switch

gear, illustrated in fig. 133. The general arrangement is practically similar to that shown in fig. 131, the chief difference being that it is adapted to receive the extra high-tension multiple break switches and fuses referred to in Chapter III. The illustration shows a 20,000 volt, 100 K.W.

FIG. 133. Ferranti extra high-tension switchgear.

per panel, two-phase board. The switches on the two phases are linked together so that they may be operated by the movement of one handle.

Cowan Hinged Wall Type Switchgear.-Another compact type of switchgear is illustrated in fig. 134. Two further important features of this arrangement are its accessibility for overhauling or extensions, and the very effective precautions that have been taken to guard against an