winding, Water-filled; Open-winding, Oil- 

 filled; and Hermetically sealed motors. 



Open-Winding, Water-Filled Motors: 



In this design the machinery is open to the 

 sea and operates within the ambient sea- 

 water environment where circulating sea- 

 water both cools and lubricates the motor. 

 The stator coils are magnet wire insulated 

 with a heavy-duty waterproof coating, such 

 as polyvinyl chloride (PVC). The advantages 

 to this system are that no dynamic seals are 

 required and a supply of machinery fluid is 

 always available. On the debit side, the poor 

 lubricating, electrical and corrosive proper- 

 ties of seawater call for a very high degree 

 of reliability in components (standard ball or 

 roller bearings would have a limited life- 

 span). To restrict the inti'oduction of large 

 particles and organic materials, a shaft seal 

 can be installed and internal water compen- 

 sated to ambient pressure, but, as Thomas 

 points out, some biological growth and corro- 

 sion is still likely. 



Open-Winding, Oil-Filled Motors: 



The stator coils of this motor are wound of 



standard varnish insulated magnet wire. 

 The machinery system may be filled with a 

 dielectric fluid which provides protection 

 against corrosion, and also cools and lubri- 

 cates. Also, the entrained fluid acts as a 

 pressure-compensation system where a shaft 

 seal keeps water out and the pressure differ- 

 ential across the seal can be minimal. This 

 system is one of the more popular types used 

 in submersibles with DC motors. Its reliabil- 

 ity is strongly influenced by the effective- 

 ness of the seal. The simplest system uses 

 one seal and one pressure compensator to 

 maintain the machinery compartment at am- 

 bient pressure or slightly higher. The major- 

 ity of seal systems on electric drives uses two 

 axial face seals at the machinery-shaft-sea 

 interface and two pressure compensators. An 

 example of this type of seal design in a system 

 is shown in Figure 8.21. If seawater leaks into 

 the system the motor may fail quickly by 

 short circuiting. However, DOT studies of 

 such seals concluded (6 Feb. 1973) that no 

 serious problems with these seals have been 

 reported to date, and tests they performed 

 substantiated this observation. Static leak- 

 age immediately after assembly has been re- 



MACHINERY CAVITY COMPENSATOR 



SEAL CAVITY COMPENSATOR 

 SIMPLE ELASTOMER DIAPHRAGM 



INBOARD SEAL OUTBOARD SEAL SLINGER 



Fig. 8.21 Double seal, redundant arrangennent (AP Nominally Zero). (From Ref. (14)1 



390 



