Page 147 - Offshore Electrical Engineering Manual

134 CHAPTER 13 Subsea Supplies and Cathodic Protection

24 Vdc. Heater elements, including supply cables, should be screened with the screen
continuity continuously monitored.
A line insulation monitor (LIM) designed on fail-safe principles should be incor-
porated into the supply circuit to detect any deterioration in the supply cable or heater
element insulation resistance. The sensitivity of the LIM should be such as to ensure
a tripping response in a few milliseconds to a significant fall in resistance.
By far the most common form of diver’s suit heating in the North Sea, however,
is the ‘hot water machine’ from which heated seawater is pumped from the surface.
The heated water is directly in contact with the diver’s skin and escapes from wrist
and ankle bands in the suit. There is a remote possibility that an earth leakage current
could travel down the heated water via the hose and be earthed via the diver, but if
the heater element tank in the hot water machine is adequately earthed, there should
be no danger, especially as the incoming cold water also provides a conducting path.
If the diver is to use any handheld electrical equipment, sensitive earth leakage
current (RCD) protection will be required. RCDs with a trip current of 4 mA are
recommended (see Codes of Practice in Bibliography).

SUBSEA COMPLETION MODULES
With the development of remotely operated vehicles (ROV’s) and with oil and gas
exploration in deeper waters, subsea completions are now both more robust and also
far more complex, due to the well monitoring and control telemetry facilities avail-
able. Fig. 2.13.1A–H is a series of CAD 3D pictures of various modules and connec-
tors. Some connectors have special keys/implements to allow mating of connectors
using ROV tools.

FIGURE 2.13.1
(A) Subsea Christmas Tree (XMT) with Twinlock subsea control module (SCM) integrated
in the foreground. (B) 199098_POD-01 – Twinlock SCM with top cover removed for clarity.
(C) 199098_POD-02 – Twinlock SCM with top cover shown as built. (D) Module mount-
ing base. (E) Older generation Monolock SCM with cover shown as built. (F) Oil filled EFL
(Tronic) (2) – typical remotely operated vehicle (ROV) mateable Tronic electrical flying
lead (EFL). (G) Older generation Monolock SCM hydraulic/electrical connection detail for
SCMMB interfacing. Optical iConSEM_with new logo_original_1035 × 1057 (2) – iCon sub-
sea electronics module (SEM) as built with optical and electrical connection interfaces. (H)
Optical iConSEM, with new logo original_1035 × 1057 (2) – iCon SEM as built with optical
and electrical connection interfaces.
(A) Courtesy Aker Solutions, Dyce, Aberdeen. (B) Courtesy Aker Solutions, Dyce, Aberdeen. (C) Courtesy Aker
Solutions, Dyce, Aberdeen. (D) Courtesy Aker Solutions, Dyce, Aberdeen. (E) Courtesy Aker Solutions, Dyce,
Aberdeen. (F) Courtesy Aker Solutions, Dyce, Aberdeen. (G) Courtesy Aker Solutions, Dyce, Aberdeen. (H)
Courtesy Aker Solutions, Dyce, Aberdeen.