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Petronas Gas

Project Summary

Background

Petronas Gas Berhad are involved in gas processing and gas transmission. Natural gas from the offshore fields of Terengganu is processed before being piped into the pipeline network, delivering gas to customers in the power, industrial and commercial sectors throughout Peninsular and East Malaysia. The company has recently evolved to include the generation of electricity and have developed a 300 MW gas power plant in Kimanis to meet the growing demand for electricity in the state of Sabah.

Quartzelec had been chosen to investigate and repair a major failure to one of their nine similar bearingless rotating diode exciters. Investigation indicated that one of the flexible connections to the rotor up-shaft leads had failed, most likely due to the connection dovetail joint failing from tin migration within the soldered joint. Quartzelec recommended and Petronas concurred that all the exciters should be modified to avoid such failure.    

The Project

Quartzelec worked on site to refurbish the rotating diode exciter hubs by fitting new jointless laminated connections between the current rings and the main rotor ‘D’ leads. The rotating diode exciter is rated at 164kW, 119V, 1398 A and 3000 rev/min.

The connections were designed and manufactured at the Rugby workshop along with a fitting kit and shipped to site for Quartzelec engineers to install.

On site, work commenced by removing the diodes and their connection straps and extracting the current ring assembly. The exciter hub and the current ring assembly was cleaned, the old connection leads were removed from the current rings and the original soldered dovetail joint examined. New joinless leads were fitted to the current rings. The exciter was re-assembled by screwing in new insulation studs and mounting a new insulation disc over the studs.New epoxy-glass insulation, Nomex insulation paper and epoxy resin was used to insulate the outer current ring connection and the refurbished current ring assembly was pressed back into the exciter hub flange. All insulation nuts were tensioned and locked-off and the insulation resistance from rings to hub was measured.

Over 50% of the eight exciter hubs modified showed clear signs of tin migration and cracking to the soldered dovetail joints of the connection leads. All of the leads were failing / would have failed leading to costly forced generator downtime and damage to the exciters. Quartzelec supplied a solution to remove the certain failures in a planned and relatively inexpensive manner. 

CS10