RTD Problems at Darlington

Abstract

Resistance Temperature Detectors (RTDs) and their measurement circuit components have been a significant maintenance item at Darlington. Analysis of the problems has shown that RTDs and electrical penetrations (EPs) have been the largest sources of faults. A failure mechanism in which the RTD electrical resistance shifts upward was identified as a major source of RTD failures, which prompted a detailed failure investigation by Ontario Hydro Technologies (OHT). The investigation concluded that the root cause failure mechanism is chlorine contamination of the platinum wire during manufacture which resulted in surface damage to the wire and flaking of the wire surface during operation. Electrical penetrations in Darlington are of a pre-built modular design with two crimps internal to the EP. Spurious resistance in poor quality crimps in the EPs lead to errors in resistance measurement. The problem led to a complex and costly job to insert new modules in existing spare EPs.