BHP Titanium Minerals have a minerals sand mine at Beenup in Western Australia, approximately 300km South of Perth. The total installed capacity of VSD's is over 15 MW with the majority of these being voltage source inverter drives supplied by PDL Electronics. Approximately three months after the initial installation, a number of failures with the DC link capacitors occurred, causing considerable downtime and disruption to production.
The failures were limited to the Beenup site only, hence BHP Engineering and PDL Electronics jointly investigated a number of potential causes ranging from inadequate ventilation, poor voltage regulation, to inrush current and harmonics whilst the failures continued. PDL's capacitor supplier alluded to the possibility of the cause being the result of an ingress of a foreign substance, experienced by the supplier approximately six years earlier.
Four subsequent independent analyses of the capacitor electrolyte showed the presence of Bromide ions (Br-) in solution. The failure mechanism was identified as the Br- ions corroding the Al terminals in the electrolyte. The cause of the ingress of the Bromide was determined to be through fumigation of the shipping containers with Methyl Bromide gas, as required by the Australian Quarantine and Inspection Service
(AQIS).
As all PDL Electronics AC drives are normally airfreighted into Australia from it's New Zealand manufacturing base, the exposure to fumigation of container loads to Australia has provided an expensive lesson to PDL. Other electronics suppliers should also take note.
PDL are pleased to report that since the fumigated capacitors have been replaced, the installation at BHP's Beenup site is now operating reliably without failure.
|
