Diagnostic Tools / Equipment

Dissolved gas analysis, or DGA, is a diagnostic and maintenance tool used in machinery. more...

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The study of gases from transformers can be used to give an early indication of abnormal behavior of transformer and may indicate appropriate action that may be taken on the equipment before it suffers great damage. The DGA as a maintenance tool must become a part of the routine practice in the industry.

Usage

The conventional Buchholz relay and gas collector relay are universally used. However, they have limitation that enough gas must be generated, first to saturate the oil full and then to come out of solution and collect in the relay, typically 10 – 15 % of gas by volume of oil, has to be generated for it to come out of the solution, often by the time the buchholz relay was never meant to be a diagnostic device. The D.G.A. is a very sensitive technique and detect gas in PPM of oil.

Faults

There are four basic types of faults, which can occur in the transformer:

Arcing or high current break down; Low energy sparking or partial discharges.; Localized overheating or hot spots and; General overheating due to inadequate cooling or sustained overloading;

Each of the fault result in thermal degradation of the oil ether alone or in combination with paper insulation. This gives rise to the evaluation of various hydrocarbon gases, hydrogen and oxides of carbon, in quantities depending on the type of fault.

Heavy current arcing is characterized by the evolution of significant quantities of hydrogen and acetylene (C2H2). If the arcing also involves paper insulation, the oxide of carbon will also be present.; Partial discharge usually results in evolution of hydrogen and lower order hydrocarbons.; Localized heating or hot spot gives rise to methane and Ethane in appreciable amount.; Prolonged overloading or impaired heat transfer can cause CO and CO2 to be generated due overheating paper insulation.;

To ensure uninterrupted and economical supply the trouble free performance of vital electrical equipments like power transformers during service is a matter of great importance. They are often subjected to complex environmental condition and variable thermal and electrical stresses. Efforts have been made to assess the health of the transformer during service through a series of diagnostic tests. Major Emphasis of these diagnostic tools is to detect the incipient fault prior to their developing into major faults which has obvious advantages.

Testing

Various diagnostic-testing techniques can be grouped as either traditional or non-traditional. Within these categories the testing equipment or systems used can be conventionally grouped into three types:

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