AC/DC drives give crane overhaul specialist a lift

When a Texas/Louisiana-based customer was seeking an electrical contractor to help upgrade the drive systems on 10 LeTourneau oilfield cranes, JC’s Marine Power & Distribution was in prime position to secure the order thanks to its technical support and AC/DC capabilities. As a long-standing advocate and user of drive technologies from Control Techniques, the company proposed the use of a Unidrive SP AC variable speed drive for the boom, and two Control Techniques Mentor MP series DC regenerative drives for the swing and hoist.

“The technical advice offered by Control Techniques is one their best selling points,” stated John Costanza, President at ‎ JC's Marine Oilfield Services.

Costanza added: “Their technicians always address problems quickly and comprehensively, which means a lot to a business such as ours, and is certainly better than we have experienced elsewhere. We exclusively use Control Techniques drives on our projects, ranging from 75-750kW, both AC and DC.”

Around 1,600 LeTourneau cranes are currently in service on oil and gas rigs around the world. Although they were originally fitted with large motor-generator sets, these do not offer variable speed, meaning there is total reliance on the skill of the boom operator to lower heavy loads.

Costanza continued: “By changing to a Control Techniques variable speed drive for the boom we can ensure complete control over the speed and rate at which the boom moves, so that loads up to 50 tonness are ‘feathered’ rather than ‘banged’ to the ground.”

The boom motor drive system comprises an SP5402 Unidrive variable speed AC drive rated at 210A continuous, while the hook motor drive system features a Mentor MP420A4R DC drive rated at 420A continuous. A Mentor MP210A4R, rated at 210A continuous, is fitted to the swing motor drive system. All of the drives are purposely sized for twice the normal power required, which means the system never runs at its maximum capacity.

LeTourneau crane operator on Atlantic 7 rig, Justin Hillard commented: “I’ve been operating with the new system for 12 months and have not had one issue.”

Hillard added: “The controls are user friendly, very smooth and have a wide variable speed in hook, swing and boom. In my opinion the boom is the biggest operating improvement. With its variable speed you can ease into boom and keep the load stable and personnel safe on deck.”

Hillard also praised the increased safety afforded as a result of the new system: “The crane is also much quieter without the motor generator sets running; you can hear what the crane is doing and what’s going on around you. I’ve also noticed that if you’re in a position where you cannot see the hook, you can actually hear the hook motor running and know how fast the hook is travelling. I highly recommend this system; it’s safer, smoother, quieter and virtually maintenance-free.”

David Powers, fellow LeTourneau crane operator on Atlantic 7 rig, also likes the new control system, which carries a Certificate of Design Conformance from the American Bureau of Shipping (ABS): “The new system gives the crane a better parameter of operation and is more responsive. Most importantly, these changes have made a much safer work environment.”

“Braking is automated, which promotes safety and takes responsibility away from the operator,” added Mr Costanza. “Also, there is better reliability as the load is not being ‘snatched’.”

Further benefits delivered to the end user as a result of AC/DC drive technologies from Control Techniques include conformal coating on the PCBs, which helps impart protection in marine environments, while the large working temperature range is also advantageous.