Offshore critical power supplies

Paul Boughton

Mark Burslem looks at how to improve inherent safety and reducing cost

Critical control and safety systems of offshore oil and gas installations are protected against electrical disturbances by stored energy in strings of batteries within uninterruptible power supply systems (UPS). These provide security of power for the periods of time as specified by each asset’s Design Safety Case.

Ensuring these batteries remain able to perform their function during a real situation throughout the life of the asset demands regular capacity testing, which can present its own safety challenges working with live electricity.

Alternative technology offered by Dale Power Solutions can achieve reduced operating costs and provide an inherently safer design.

Dale Power Solution’s UPS with its regen feature, permits inherently safer management of the primary hazards associated with battery capacity testing by eliminating them, or reducing their likelihood of occurrence.

The simplified process gives less scope for human errors, reduces the need for live working and requires fewer personnel-days offshore while more frequent or more flexible testing schedules can readily be performed.

Over the 20-30 year design life of a regen equipped UPS, less live working and reduced offshore labour and logistics can realise significant cost benefits.

Capacity testing of a UPS battery requires defined current to be drawn for a period of time according to the battery manufacturer’s data.

Traditionally this manual activity involves a test load bank temporarily connected via trailing cables to an electrically isolated battery while platform loads are first switched onto alternative power supplies.

The operation is relatively complex to arrange, requiring specialist UPS/battery technicians and bulky load banks to be mobilized offshore. The activity must be coordinated around any operational constraints or other on-going work scopes and the heat output of the load bank may dictate additional temporary ventilation. All of which have obvious impacts on helicopter seats, cargo space and offshore manning levels.

Manual working on live equipment carries inherent safety hazards. Stringent work methods and safety measures must be adhered to if the task is to be completed safely (Blackouts can and do happen as a result of human errors during UPS load switching operations). Personnel safety and asset integrity significantly relies on ‘add-on’ measures including detailed procedures, insulated tools, personal protective equipment, etc.

However, UPS technology advancements now enable a simpler way to capacity test a battery; Insulated Gate Bipolar Transistor (IGBT) chargers with regeneration (regen) allows energy from the UPS battery under test to be ‘regenerated’ instead of dumping the energy into a temporary load.

A battery test is initiated, simply, using the UPS operator screen. The required battery test current is automatically established by controlling energy fed back into the network as the platform load remains ‘on line’ whilst still being supported by the battery.

After the required capacity has been drawn from the battery, the battery test data is recorded and the UPS automatically reverts to normal operation. With regen, the requirement for specialist technicians to switch UPS loads or connect trailing cables onto live circuits during battery capacity testing is eliminated.

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Mark Burslem is with Dale Power Solutions Ltd, Scarborough, North Yorkshire, UK.

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