Page 161 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

Stationary GRIN lens
GRIN lenses
7.1 Electrical considerations 149
FIGURE 7.9
Diagram of a single-pass FORJ.
Stationary GRIN lens
Cell #1
FIGURE 7.10
Diagram of a multi-mode multi-pass FORJ.
Cell #2
Stationary mirror
Stationary mirror
7.1.5 The ubiquitous ground fault
It is said that electricity is lazy as it will take the least possible resistance within a circuit. The con- ductive properties of seawater are such that as the salinity increases so does its conductivity. Any break of the insulation through the power circuit of an ROV will (instead of continuing through the circuit) immediately seek ground state by faulting to ground. It is essential for electrical safety to have grounding protection by way of a ground fault interrupt (GFI) circuit to protect the vehicle from dangerous circuit leakage.
In Figure 7.11, the basic concept of operation of a GFI circuit is depicted. During normal opera- tions, the live (energized) line (L) conducts the same current as the return via the neutral line (N). As the flows are balanced, no magnetic flux is generated into the transformer core (3). Should an imbalance occur between the L and N lines, flux is generated in the core (3) and a current is thus induced into the surrounding coil (2). Should the current exceed the nominal value, the sensor unit (1) will then break the circuit. The tester switch (4) completes the unit. The GFI is also referred to as a ground fault circuit interrupter, residual-current device, or residual-current circuit breaker depending upon local preference.