Page 207 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition
P. 207
196 CHAPTER 8 Cables and Connectors
• Amps
• Duration
Transmitting electrical signals through a cable involves four different factors:
• Frequency
• Bandwidth
• Impedance
• Capacitance
When determining the power (P 5 IE) a cable can transmit, it all comes down to amperes. The current capacity of a particular wire gauge does not reference volts. Thus, to increase power down a given size wire, a designer needs to step up the voltage as current is fixed. For each ampere it is necessary to have enough material to conduct the power to the far end. Most conductors have resis- tance to electrical energy flow. This creates a voltage drop, and it is necessary to keep this value as small as possible to provide power to the source. Therefore, it is necessary to use material with as low a resistance as possible.
The most common material for providing power through a cable is copper. The most common form for electrical cable conductors in ROV cables is electrolytic tough pitch copper with a tin coating. Other coatings are available for special purposes, but most increase the resistance to elec- trical current. Oxidation of bare copper makes terminations more troublesome.
Another consideration is insulation on the conductors to contain the electrical energy. There are two general insulation families: thermoplastic and thermoset.
Thermoplastic is a material that repeatedly softens or melts when heated and hardens when cooled. Some examples are as follows:
Polyethylene (PE)
Polypropylene (PP)
Polyvinyl chloride (PVC)
Polyurethane (PUR)
Nylon
Fluorocarbons (Tefzelt and Teflont)
A thermoset material reacts to heat, changing forever into its final molecular form. Some exam- ples are as follows:
Cross-linked PE (XLPE)
Chlorosulfonated PE (Hypalont)
Chlorinated rubber (Neoprenet)
Ethylene propylene rubber (EPR)
Ethylene propylene diene rubber (EPDM)
Styrene butadiene rubber (SBR)
ROV cables usually use thermoplastic materials. They process more easily than thermoset materi- als and thermoplastics cover a broad range. Thermoset materials require special processing equipment. However, because thermoplastics soften or melt with heat, it is important to know both the operating environment and the current requirements. The cable designer needs to look at all these parameters in choosing the proper material.
