This paper is the sequel to a previous paper presented at the IEEE PClC Conference in 1994 [l]. . The original paper focused on the design, testing, and commissioning of-the 15 000 hp adjustable speed drive (ASD) system. This paper describes the operating experience of this ASD system during its first ten years of sewice. Several unplanned trips of the ASD, two failures of the input transformer, failure of the motor lead cables, and overheating of the motor that led to its eventual replacement are discussed. The incidents are described, the root causes are examined, the corrective measures are discussed, and the lessons learned are presented. The success of the ASD in dealing with the many utility voltage disturbances experienced by the refinery electrical system is also addressed. motor, operating experience, lessons learned.lndex Terms -Adjustable speed drive, ASD. high speed INTRODUCTIONThe ASD system is installed at the user's refinery located in Pascagoula. MS. The driven equipment is a hydrogen recycle centrifugal compressor in a benzene production facility. The ASD was originally started up in December 1993 and except for brief periods has been in continuous sewice since then.As described in more detail in [l], the high-speed motor (greater than 3600 dmin) and ASD were selected as a cost effective alternative to a steam turbine driver. Use of the ASD system avoided the need to purchase a new boiler and also had environmental and maintenance advantages. The existing electrical system had sufficient capacity to supply the new ASD system, so minimal capital investment in me electrical system was required. The high-speed motor was selected over a conventional speed motor with a gearbox to avoid the maintenance, torsional issues, and losses associated with the gearbox. The estimated capital cost savings of approximately $16 million dollars, along with the maintenance, environmental. and process control benefits, convinced project management to accept the ASD option over the steam turbine option. Even though the user's company had not applied large high-speed ASDs at that time, investigations concluded the technology was suitable for application in critical refinery sewice if the system was property designed, tested, commissioned, and maintained for reliability. Unfortunately, it would take several years after plant startup to complete this process. II. BASIC ASD SYSTEM DESIGNThe ASD system is a load commutated inverter (LCI) type drive which supplies a 15 000 hp synchronous motor. The basic ASD system design is discussed in more detail in [l] and will be only briefly described here. Fig. 1 shows a simplied diagram of the ASD system including the electrical system from which it is supplied.The input transformer is a three winding oil filled rectiier duty transformer with a delta primary winding and two three-phase secondary windings, one connected in delta and the other in wye, to provide suitable input to the 12-pulse line converter. It is rated 18.5 MVA at 65% rise and steps the voltage from 13.2 kV to 3.2 kV....
The electrical Variable Speed Drive (VSD) system presented is designed for installation on the sea floor to drive nearby electric motors for pumps and gas compressors. A modular concept of the VSD is developed and intended to operate a wide range of subsea motors of powers from 0.5 to 18 MVA, with voltages from 2.0 kV to 7.2 kV or more, and fundamental frequencies up to 300 Hz. Step-out distances from a few km to over 600 km can be accommodated. The pressure compensated design effectively removes limits as to the depth of deployment. Pressure compensation is achieved by submerging the drive hardware including the drive transformer in a dielectric liquid which also acts as coolant. The electric power components, including capacitors, semiconductors, and the control electronics are designed with increased margins and redundant hardware, pressure resistance, and materials chosen for compatibility with the dielectric liquid, to achieve a highly reliable design of the overall VSD. The drive was deployed into shallow water in a harbor in Vaasa Finland for testing. A top side station was built implementing a "Power-In-the-Loop" approach, where the VSD output energy is recovered back into the drive input such that the grid supply only provides the lost power, but not the much higher circulated power. The drive operated more than 1000 h at 22 kV input and 6.9 - 7.2 kV output voltage at different power levels. We conclude from this first shallow water test, that all components of the VSD system work properly together up to 1000 A output current. Different operation conditions reflecting the envisioned application, including redundancy capability were successfully tested. The thermal performance was extensively verified, including an optional external heat exchanger to achieve high ratings even in warm waters. To our knowledge this is the first time a medium voltage drive is operated at 9 to 12 MVA for an extended time submerged in a sea water environment. All its modules are designed to operate down to depths of 10’000 ft / 3000 m or more and are concluding qualification according to API17F and SEPS 1002.
This paper gives an overview of the Ormen Lange LongStep-out Power Supply (LSPS) system which shall provide power and communication over the 120 km step out distance from Nyhamna west coast of Norway to the subsea gas compression station. The document will present status including technical description and qualification programmes. Transmitting 65 MW over a distance of 120 km is challenging not only related to voltage and power loss at full load, but also to the voltage stability at number of different load scenarios, such as reactive power production in the cable which is also present in no load situation. The subsea mounted Variable Speed Drive (VSD) dictates stringent requirements to voltage variation and stability of the power supply system. Limited track record and maturity of components and equipment meant that development and qualification testing would be necessary to ensure sufficient reliability of the subsea power supply system. On this basis StatoilHydro decided to include the LSPS system in the pilot testing of the subsea gas compression at Nyhamna west coast of Norway. The LSPS pilot project was kicked off in July 2006. Since then development and testing of LSPS equipment and components has been ongoing. The status of the Long Step-out Power Supply project is that all the qualification programs have been successfully completed together with most of the manufacturing for the pilot LSPS. System test for the LSPS pilot system is scheduled to take place during October 2009. Hook up and mechanical completion at the Nyhamna test site is scheduled for first quarter of 2010.The purpose of the LSPS pilot system is to test and qualify components and equipment to be used in the LSPS permanent system as far as practical.
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