Hydraulics: Virtually all hydraulically-pow- 

 ered devices require electricity to pump hy- 

 draulic fluid. 



There are exceptions to the above, but 

 they only accentuate the widespread and 

 essential role electricity plays in deep sub- 

 mergence, generally, and manned submers- 

 ibles, specifically. It is not surprising, then, 

 that the recent literature on submersibles 

 contains an inordinate amount of discussion 

 regarding electrical power and the means to 

 increase its output and endurance. It is in- 

 teresting to observe that the majority of 

 early literature on submersible design dealt 

 with pressure hull materials and later with 

 power sources. Apparently the first order of 

 business was to dive safely; the next item 

 was to accomplish something once safety was 

 attained. 



Terminology and General 

 Considerations 



The only general statement which may be 

 made regarding power supply and distribu- 

 tion in submersibles is that they most often 

 use lead-acid batteries which are usually re- 

 charged from a surface support ship after 

 each dive. While approaches to electrical 

 power distribution vary widely, system re- 

 quirements are similar, and it is around such 

 requirements that basic submersible electri- 

 cal terminology is defined. 



In many respects, electric power genera- 

 tion and distribution aboard a submersible is 

 similar to that aboard a surface ship, but the 

 problems are compounded in a submersible 

 by the operating environment: High pres- 

 sure, low temperature and an operating me- 

 dium which itself is an excellent electrical 

 conductor, namely seawater. The character- 

 istics of the operating environment and the 

 constraints imposed by occupant safety com- 

 bine to make problems of electric power gen- 

 eration and distribution in submersibles and 

 submarines quite unique. A basic definition 

 of terms follows, while Figure 7.1 presents a 

 graphical representation of the components 

 cited: 



Power Generation: This requirement is met 

 primarily by Secondary Batteries Consisting of 

 lead-acid (Pb-acid), nickel-cadmium (Ni-Cd) 

 or silver-zinc (Ag-Zn) cells which are re- 

 chargeable to their rated capacity (measured 



in ampere-hours) for many cycles. In sub- 

 mersibles the Pb-acid batteries are conven- 

 tional and similar to automobile batteries. 



Power Distribution: Connectors and cables are 

 used to carry the power from the batteries. 

 Cables provide a waterproof, insulated cas- 

 ing for the current-carrying conductor(s), 

 and connectors are devices, generally 

 molded to either end of a cable, consisting of 

 a plug and receptacle which provide a water- 

 proof attachment to the energy source or, 

 more commonly, to a penetrator. An electri- 

 cal hull penetrator is a specially designed 

 receptacle which permits passage of current 

 through the pressure hull or any other cas- 

 ing containing an electrical component. 



Power Changers: Batteries generate direct 

 current (DC). Many instruments and propul- 

 sion systems however, operate on alternat- 

 ing current (AC). Consequently, inverters are 

 used to change DC power to AC. The invert- 

 ers may be carried within or external to the 

 pressure hull. Other components or sub-sys- 

 tems may operate on DC voltages which are 

 lower than that generated by the batteries. 

 In this case a converter is used. Basically a 

 converter provides the functions of a step- 

 down transformer and an inverter — that is, 

 it lowers the voltage and changes AC to DC. 

 This is a more energy conserving approach 

 than placing a series resistor in the circuit. 

 In practice, then, an inverter first changes 

 battery DC to AC which is then acted on by 

 the converter to yield DC power at the re- 

 quired voltage. 



Power Protection: Three approaches are used 

 in protecting batteries from seawater and 

 pressure: 1) pressure-compensation (Fig. 7.1) 

 wherein the battery is placed within a sealed 

 and vented case filled with a dielectric fluid 

 (usually oil) and connected to a compensat- 

 ing fluid reservoir which acts to maintain a 

 zero or slightly positive pressure differential 

 across the enclosed oil/seawater face; 2) pres- 

 sure-protection wherein the battery is en- 

 closed in a pressure-resistant pod outside the 

 pressure hull and maintained in a dry, 1- 

 atmosphere environment; 3) interior location 

 where the battery is placed within the pres- 

 sure-hull to protect it from seawater and 

 pressure. No provisions are made to main- 



314 



