Study On Ignition Characteristics Of Transformer Insulating Oil Under Arc

The fire accidents of oil-filled equipment such as condenser-type terminals usually occur fast and are difficult to extinguish,characterized by their suddenness,explosion and destruction.The transformer insulating oil filled in oil-filled equipment features high calorific value.When being ignited,the oil would release extremely high heat,resulting in the rapid spread of fire.Therefore,whether transformer insulating oil is ignited or not is the key to the development of transformer accidents from partial faults to serious explosions.In this study,the ignition characteristics of transformer insulating oil under arc were tested and analyzed by divided into air and poor-oxygen environments.The ignition characteristics of transformer insulating oil under arc in air environment were studied by designed experiments on hot plate.Two parts of works were accomplished.Firstly,the ignition process of transformer oil under arc was analyzed.Secondly,by controlling the energy of arc and aging degree of transformer oil,the ignition critical temperature and intrinsic safety temperature of transformer oil under arc were counted and calculated by Bruceton method.The results indicate that arc can accelerate the decomposition of transformer oil which would promote the formatio n of flammable oil-gas mixture.The extreme value of arc energy for lowest critical ignition temperature is 13.8 J,corresponding to about 8.1 kV of arc voltage.At this energy and above,the average intrinsic safety temperature is about 124℃.In order to study the ignition characteristics of transformer insulating oil under arc in poor-oxygen environment,experiments focusing on gas production characteristics were completed.The flammable gas mixtures produced by arc in transformer oil under different conditions were collected by self-designed experimental device by controlling arc energy,oil temperature and aging degree of transformer oil.The compositions of gas mixtures were analyzed by infrared gas analyzer.Then we characterize the fire risks of gas mixtures by calculating the explosive limits.The results are as follows:(1)oil temperature was found to have the greatest influence on the gas production rate.When oil temperature increases from 45℃ to 90℃,the gas production rate would increase by more than 10 times.The highest measured value was 23.53mL/s.(2)raises of oil temperature and arc energy will both lead to the decline of lower explosive limited(LEL)to below 2.81%as well as the boost of upper explosive limited(UEL)to above 33%,representing higher risk of ignition.While the increase of aging degree would lead to the rise up of LEL to a maximum value in a period of time,then quickly drop to about 2.80%.(3)changes of specific gas ratios indicate faults evolution trends of transformer oil-filled equipment.The raise of C2H2/C2H4 ratio indicates decline of transformer oil quality.The increase of both C2H2 and C2H4/C2H6 ratios indicates greater energy of arc in the oil-filled equipment.C2H2 proportion fluctuates with increase of C2H4/C2H6 indicates deteriorate of overheating problem.