If there is a gas accumulation in the Buchholz relay, it is advisable to take a sample of the gas immediately!
The free gas in the Buchholz relay and the transformer oil are in close contact. Therefore some gas constituents will dissolve in the oil, modifying the composition of the gas collected. Typical fault gas patterns will disappear.
Due to the analysis can be distinguished, if the incident was caused by a serious fault in the transformer or has been occured due to air accumulation in the Buchholz relay.
The BGT 4.1 is used to measure the hydrogen concentration in the Buchholz gas. To make a decision „Fault gas or Air“ the measurement of the hydrogen concentration in the Buchholz gas is enough. Any kind of fault in the oil causes the formation of hydrogen.
The gas to be measured is sampled by the Buchholz gas sampler BGS and fed into the BGT 4.1. A BGS is included in the scope of supply.
The BGT 4.2 allows the measurement of hydrogen, carbon dioxide, carbon monoxide, total hydrocarbon and ethyne concentrations in the Buchholz gas. The determination of the various fault gases allows to draw conclusions from the different causes of fault.
The gas to be measured is sampled by the Buchholz gas sampler BGS and fed into the BGT 4.2. A BGS is included in the scope of supply.
Causes of fault
|Cause of fault||Gases evolved|
|Fault gas pattern measurement by BGT 4.2|
|Discharges of high energy|
(e.g. arcs, break downs, short circuits)
|Discharges of low energy|
(e.g. partial discharges, sparking discharges, corona discharges)
|Thermal faults||C2H4, CH4, H2, C2H6||x||-||-||x||-|
|Involvement of the solid (cellulosic) insulation||CO, also: CO2||-||(x)||x||-||-|
It is generally difficult to distinguish between faults caused by discharges of low energy and thermal faults on the knowledge of the Buchholz gas composition only. Both faults cause the formation of the less soluble gases hydrogen and methane. On the other hand the very soluble key gases for thermal faults ethylene and ethane may not reach the gas collecting relay. Also in Buchholz gases caused by air accumulation can be low fault gas concentrations. These fault gases evaporated out of the oil into the gas bubbles during the bubble rise to the collecting relay. In oil transformers do not exist faults which affect the solid insulation only.