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Auxiliary Plant Upgrade

Rig upgrades to meet the demands of deeper well drilling


Jack-Up Drilling Rig

The existing switchboard was a 30 year old GE system, which had been expanded by the addition of three Tech power SCRs. This meant that it was not possible to simply add the new equipment to the end of the line-up.

As usual, space was extremely limited. The design called for a Bus Coupler/Feeder Section to be inserted between the Tech Power SCRs and the original switchboard in place of an existing Bus Transition section. The additional generator control section could then be spliced on to the end of the Tech Power SCRs.

The Bus Coupler section also included two feeder circuit breakers, and fitting the equipment in with the 5000A rated busbars was a difficult engineering challenge, with the left and right-hand sides having to match two different busbar configurations from two different manufacturers. The new equipment was designed and modelled by Contrelec using AutoCAD 3D.

The installation also presented a number of control and interlocking problems. In order to keep the system fault levels to within the design specification of the existing equipment, it should not be possible to parallel all 6 generators. However, certain combinations of old and new equipment with no more than 5 generators in parallel were allowed. A key interlocking system was devised to address this restriction.

It was important to ensure that the new generator control section could load share in parallel with the existing generators, and a considerable amount of analogue signal switching and scaling was required to ensure that the SCR Power Limit Circuits (a regulation circuit to ensure that the SCRs do not overload the SCRs) operated correctly depending on the switchboard configurations. This was accomplished with a Siemens S7 PLC controller to allow flexibility and avoid potential longer term problems with relay contacts switching low-level analogue voltages and currents.

Also included in the project was a 480V feeder switchboard, and a complete fault level and time-current co-ordination study was completed for the 600 and 480V busbars.

The installation was completed early in 2014.


New Bus Coupler & Feeder Copperwork

Time-Current Co-Ordination Curves

General Arrangement

ENSCO 70 Switchroom Before Modifications