On-line incipient fault detector

During recent years, studies and investigations have attributed increased significance to the gases generated in a transformer relative to incipient faults. Early detection of incipient faults has prevented equipment failures and thus potential power outages. The generated gases can result from arcing, corona, electrolysis of water or general overheating of the insulation. Unless a failure occurs, these incipient faults will go undetected electrically. However, the faults do cause deterioration of solid and/or liquid insulation and this deterioration results in a greater likelihood of equipment failure as gases are generated. The composition of the gases formed varies with the type and magnitude of fault but nearly always includes hydrogen and/or carbon dioxide and quite often the lower molecular weight hydrocarbons such as methane, ethane, ethylene, etc. Improvements have been made in the gas detection and evaluation techniques for transformers and a very reliable procedure consists of carefully drawing a gas or oil sample into a special container with the analysis being performed later. However, this method is impractical on a daily basis even though it is desirable to have continuous monitoring of the conditions inside a power transformer. This paper describes a method developed under a contract with the Electric Power Research Institute which permits continuous monitoring of a transformer for the presence of certain gases whose presence motivates a search for the source of the gas. The oil from the transformer is continually moved past a polymeric membrane, the gases present are defused through the membrane and collected. Once a day, a measured portion of the collected gases are transferred to the detection system for analysis. While all the gases present in the oil are collected by the permeation cell, the analytical system is specifically sensitive to hydrogen and carbon dioxide. The device will sound an alarm when a predetermined level of these gases are present. The following sections discuss the various components of the extraction-analytical system and the development program by which the operating parameters were determined.