SYSTEM OVERVIEW

The Shell Brent Field comprises four Platforms located in the North Sea, 115 miles off Shetland. Brent, Britain’s largest oilfield, has been producing oil and gas for 30 years and provides the benchmark price for North Sea crude.

Shell UK raised with GAI-Tronics the requirement for a phased change-out of the Public Address and General Alarm Notification equipment on all four of its Offshore Platforms starting with Brent Charlie.
A standardised design philosophy was determined, that would satisfy the requirements of all four Installations, whilst allowing platform specific operational features to also be retained. GAI-Tronics’ Visual Applications Software package was of special interest, offering Shell the ability to remotely monitor, in real time, the equipment operation and to record and download system status records.

SYSTEM FUNCTIONALITY

GAI-Tronics was chosen because it could offer a totally flexible design solution with the equipment capable of operating from a variety of input voltages and offering significantly increased operational reliability and integrity.

Brent Charlie required a duplicated PA/GA System with system ‘A’ equipment housed in two 2000x800x800mm cabinets, including 21 power amplifiers, and system ‘B’ occupying a single cabinet with only 7 amplifiers.
In accordance with the need to minimise system down-time, the two A cabinets were designed to instantly connect together via a heavy-duty plug & socket arrangement. In addition each equipment cabinet was provided with castors allowing temporary ‘live’ operation to be quickly achieved prior to removal of the existing equipment.

System A provides complete coverage of all Platform Areas whilst B only provides partial coverage, broadcasting into designated critical areas only (accommodation, muster stations and drilling). Operating voltage is from a negative 24V DC (nominal) UPS. This non-fully duplicated operation prompted development of new software by GAI-Tronics which would automatically identify either system (A or B) and operate accordingly.

Brent Delta followed, and specified a 12 amplifier and 9 amplifier dual system with the A Equipment operating from Mains 254V AC & 24V DC whilst system B operated from only 240V AC. Brent Bravo required operation from 254V AC & 24V DC on system A with system B operating on 24V DC only. Brent Alpha is a duplicated 12 amplifier system operating on 254V AC and 24V DC. The design has customised elements with system B cabinet being only 600mm wide.

Being able to maintain the agreed delivery programme was of vital importance to Shell as they faced up to the logistical issues of an Offshore Change-out of a First Line Safety System on each Operational Platform