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Current Supply to Battleship Fire Control System By William Hetherington Jr. cuits are today fairly common in the supply and utilization of electricity. And these circuits will increase in extent and complexity as the automatization of industry pro- ceeds and the human element be- comes decreasingly a labor factor and increasingly a directive one. For pointers on details of this utilization of electricity as, actually, an exten- sion of the human mind, the electri- cal engineer in industry and in the central station may profitably go to the modern battleship. Here details of function and assurances of con- trol energy supply are worked out to almost the ultimate degree. An in- stance is afforded by this description of the control scheme for current supply to a battleship fire control system. In the fire control stations, intri- cate problems of ballistics, including corrections for ship speeds, degrees of ship roll, wind velocity and other factors are quickly and automatically worked out and their results in terms of gun elevation, direction and firing time are electrically transmitted to the gun crews. In the most modern schemes of fire control the complex system of calculators, transmitters, indicators and receivers is operated by alternating current. Obviously, the current supply must be under perfect control at all times and must not fail. The latest answer to these requirements is embodied in instal- lations on U. S. S. PENNSYLVANIA and ARIzONA which were lately modernized. Both installations include three motor generator sets converting from direct to alternating current. The motors are 25 horsepower direct cur- rent and the single phase, 60-cycle generators are rated at 25 kilovolt- amperes at 0.2 to 0.4 power factor. The three units are independently controlled from a central board which is designed on the basis of 40 degrees Centigrade ambient tempera- ture. It is of the open type, meeting class A shockproof requirements of the United States navy. Each unit section has a magnetic contactor type controller, semi-automatic, designed as a motor starter, with automatic bus transfer provision for change from power to battery supply and vice versa. The power supply to the unit panel is selected by a double pole double throw knife switch being closed in one position for supply from the for- GS cuee control and signal cir- 26 ward main distribution panel and in the opposite position for supply from the after main distribution panel. From the knife switch, the connec- tions are made to one of the double pole magnetic contactors which com- prise the bus transfer unit. This unit is controlled by a voltage relay which has its operating coil connected to the main direct current supply. If the voltage of this supply falls to a predetermined value, for which the relay is set to open its contacts, the double pole contactor in the gener- ator supply circuit opens. Immedi- ately a circuit is completed which closes the contactor connecting to the battery circuit. These two contac- tors are mechanically interlocked to prevent simultaneous connection to generator and battery lines. If at some later period the generator volt- age rises to a predetermined value, the voltage relay contacts function to open the battery line contactor and reclose the generator line contactor. Illuminated white and red lenses show, whether connection is to the generator or battery lines. The three-motor starting units are Control board for U. 8S. 8. Pennsylvania MARINE REvIEw—March, 1932 identical in operation. A single-pole single-throw knife switch controls starting and stopping the equipment. When the knife switch is closed, all functions of starting and accelerating the motor to full speed are automatic. The operating coil circuit of the field failure relay and the motor shunt field circuit is closed when the con- trol knife switch is closed. This causes the relay contacts to close the operating coil circuit of the main magnetic contactor which closes and connects the motor to the power lines with all starting resistance in circuit with the motor armature. If the motor field circuit be interrupted by a field failure, the field failure relay will open and cause the equipment to shut down. : As the motor accelerates and the starting current inrush falls to values of approximately 85, 90 and 105 per cent normal motor current the three steps of starting resistance are short circuited consecutively under control of the series accelerating relays until the motor is connected to the supply lines. A generator field rheostat is provided for regulating the voltage of each generator unit, the values of voltage being read from two volt- meters suitably connected through voltmeter selector switches. Speed of Merchant Ships A survey made by the National Council of American Shipbuilders shows that more than 37 per cent of the gross tonnage of passenger and combination vessels owned by Italy is composed of vessels which operate at speeds of 18 knots or over. The United States stands sec- ond among the nations in the per- centage of such vessels, and Great Britain stands fifth. More than 18 per cent of the gross tonnage of passenger and combination vessels throughout the world consists of vessels which operate at speeds 0 18 knots or over. ce Thirteen per cent of the gross ton- nage of ocean-going freighters owned by Great Britain consists of vessels which operate at speeds of 14 knots or over. Norway stands second in the percentage of such vessels, and the United States seventh. About 7 per cent of the gross tonnage of ocean-going freighters throughout the world consists of vessels which operate at speeds of 14 knots or over. While Italy, the United States and Sweden are well represented in high- speed passenger and combination vessels, they own little or no high- speed freighters. Norway, which stands second in the percentage of high-speed freighters, owns no high- speed passenger and combination vessels. Great Britain alone of all the nations is well represented in the percentage of high-speed ton- nage of both classes of vessels.