Page 54: of Offshore Engineer Magazine (Sep/Oct 2014)

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Drilling

The perils of offshore power

Unacceptable power quality quality can have signi? cant impacts on safety, the productivity of operations and pro? tability.

Ian C. Evans explains. lectrical power

E E quality is routinely taken for granted by oil and drilling industries irrespective of the irrespective of the conclusion that the quality fact that it is absolutely of electrical power therefore fundamental to the safety and operational requires serious consider- integrity of drilling rigs, offshore ation by safety and regula- platforms and installations worldwide, tory authorities worldwide, without exception. including in the EU and

Electrical variable speed drives; DC the US. However, the drives (SCR drives in offshore par- new European Directive, lance) drives and AC variable frequency (2013/30/EU), govern- drives (VFDs) are fundamental to most ing the safety of offshore operations. However, their use signi? - oil and gas installations, cantly degrades the quality of electric ignores it.

power, increases equipment failure,

The author has been and disrupts control systems, resulting in discussion with UK’s in production losses and compromised

Health and Safety Executive safety.

(HSE - HID Energy Division,

The electrical power quality offshore Offshore) since 2006, is rarely monitored and, even after a regarding offshore power serious incident or disaster, it is rarely quality. Two years ago HSE investigated nor considered to be a con- drafted, with assistance tributing factor. Rules and recommen- from the author and others,

Left: An Ex motor. Above: Typical jackup type drilling rig. Photos from Harmionic Solutions.

dations for the limitation of harmonic a document entitled “HSE voltage distortion have been in place for information sheet - Harmonic Voltage

Occidental platform, Piper Alpha. 167 originates. Little or no training is pro- many years, via the marine classi? ca- Distortion in Electrical Systems. Offshore men perished. The Cullen Enquiry failed vided for rig electricians and little or no tion bodies, IEE (Institute of Electrical Information Sheet No. xx/2011.” The to establish the initial source of ignition harmonic or power quality measurements Engineers) and the IEC (International draft document stated: “The objective is which ignited the escaping condensate. taken. Electrotechnical Commission) but often to limit the THDv (total harmonic volt-

Some engineers now believe that har- Some consequences of poor power given scant regard. Harmonic volt- age distortion), most commonly to 5% monic voltage distortion could have been quality can appear relatively minor (e.g. age distortion offshore can exceed the or 8%. To achieve this, the magnitude a signi? cant contributory factor, but this the repeated failure of control relays, VFD recommended limits by a factor of 4-7 of the harmonic currents drawn by the was never considered by the commission. capacitors or electric motors) but are often times. non-linear load(s), which otherwise ? ow

At that time there was only rudimentary expensive operationally. The potential for US$100 millions are lost annually in the system, has to be reduced signi? - harmonic measurement equipment avail- something more serious also lurks. across the industry, directly and indi- cantly.” (This compares to THDv levels able and problems of harmonics were In July 1988, the world’s worst oil- rectly, due to poor power quality. The up to 35% witnessed by the author on largely unknown to most of the industry. ? eld disaster, as far as human life was industry is often unaware of where the many installations). The draft document

The reader may start to come to the concerned, occurred off Scotland on the damage or disruption to equipment concluded saying: “This guidance is

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