氧化鋁納米變壓器油紙絕緣的電氣性能與改性機(jī)理研究.pdf

1、With the commencement of high voltage alternating current (HVAC) and high voltage direct current (HVDC), the demands on insulating reliability of power transformer is getting more and more imperative.The mineral oil in c

2、onjunction with paper is the main insulation components in oil-immersed transformers; their insulation properties play a significant role in the safe and stable operation of power transformers.To strengthen the insulatio

3、n level of ultra-high voltage transformer and to reduce its size and weight, it is imminent to enhance the insulating performance of transformer oil and oil-impregnated cellulose.Recently, a unique novel effort of suspen

4、sion of nanoparticles (NPs) into mineral oil (MO) has been carried out and the results have exhibited improved insulation characteristics of transformer oil.Nine types ofnanoparticles (Al2O3, Fe3O4, TiO2, ZrO2, Si3N4, Al

5、N, SiC, ZnO, SnO2)bought from a company which are conductive, semi-conductive and insulative in characteristics with same concentration (0.1g/L) and oleic acid modification, were used to modify the transformer oil.The ef

6、fects of nanoparticle types on insulating features of nanofluid (NF) under lightning impulse (LI) voltage were studied.The prepared NFs manifested the enhancement in positive LI breakdown voltages as compared to MO.The A

7、l2O3 NFs showed the maximum improvement (10％) in the positive lightning impulse breakdown voltages followed by the Fe3O4 NFs (7％).The Al2O3, Fe3O4, TiO2 were selected from these nine nanoparticles to study the effect of

8、concentrations (0.05 g/L, 0.1g/L, 0.2 g/L, 0.4 g/L), surface modifications (oleic acid, stearic acid) of these three nanoparticles on dielectric performance of MO under positive and negative lightning impulse.The Al2O3 N

9、Fs manifested approximately 1.11 times enhancement in positive LI breakdown strength at 0.2g/L optimal concentrations followed by Fe3O4 NFs 1.07 at 0.01g/L optimal concentration.It was found with Al2O3 and Fe3O4 NPs modi

10、fication, the positive LI breakdown voltage and chop time of MO were enhanced whereas the negative LI breakdown voltage and chop time of MO was reduced.On the other hand TiO2 NPs has little effects on insulation performa

11、nce of MO.The dielectric properties (permittivity, conductivity) measurement of the prepared three NFs showed that the Fe3O4 and TiO2 NFs manifested high dielectric loss and distinct dielectric constant from pure oil whi

12、ch restricts their practical applications as transformer liquid insulation.The alumina NFs presented low dielectric loss and permittivity close to the mineral oil but they were highly unstable for long term and there bre

13、akdown performance was adversely affected by agglomeration.The Al2O3 nanoparticles with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance.Th

14、e NFs were prepared with different shapes (nanorods, nanoplates), surface modifications (oleic acid, C2, C18) and concentrations (0.6 g/L, 0.8 g/L, 1.2 g/L) of Al2O3 NPs.The positive LI BD voltages of MO were improved by

15、 1.11 times with nanorod shape, oleic acid (OA) surface modification and 0.8 g/L concentration of NPs.The effects of Al2O3 nanoparticle with different gap distances on insulating properties of nanofluid under LI voltage

16、were examined.It was noted that Al2O3 NPs suspension, the positive LI breakdown voltage of transformer oil were enhanced but the negative LI breakdown voltage of were decreased.Surface creeping discharge at oil/liquid in

17、terface is believed as one the major reasons for oil-immersed transformers collapse.In order to curtail the surface creeping discharge, the effects of Al2O3 NPs on creeping discharge and flashover properties of the oil/p

18、ressboard interface under AC and LI voltages.The creeping flashever and partial discharge tests of oil-impregnated pressboards (OIPs) and nanofluid-impregnated pressboard (NIPs) were conducted.The outcomes manifested tha

19、t Al2O3 NPs can enhance both partial discharge inception voltage (PDIV) and creeping flashover strength of OIPs.The positive LI creeping flashover voltage (FOV) of NIPs was 15 ％ higher than those OIPs and the chop time o

20、f NIPs was also prolonged 26.4％ of that of OIPs with gap distance of 30 mm.The negative LI creeping flashover voltage (FOV) of NIPs was 14％higher than those of OIPs whereas the chop time was 35％ higher than those of OIPs

21、 with 30mm gap distance.Moreover, AC creeping FOV and PDIV of NIPs was higher than OIPs.Thermally stimulated depolarization current (TSDC) and Pulse electroacoustic (PEA) test techniques were used to measure space charge

22、 behaviors of oil/pressboard pre and post modification of Al2O3 NPs.It indicated that NIPs has a more uniform intemal electric field and higher decay rate as compared to OIPs, which is caused by the rise of shallow trap

23、density in NPs related to the difference of internal structures, based on the test results of TSC.It was found that NPs can enhance the shallow trap desity.The generated electrons would lose their kinetic energy through

24、repeatedly trapping and de-trapping process, leading to decline in elcetron mobility.The higher trap density of NPs, lower average energy, and lower mobility of electrons are obtained.The electrons with lower energy are

25、convient to be captured by those molecules with high electron affinity, and be converted into negative space charges.These negative space charge decrease the electrical field strength at the front of positive streamer an

26、d therefore reduce the propagating velocity of positive streamer.The streamer velocity in NIPs was higher initially and tends to decline with time and ultimately it was reduced to half as compared to OIPs at particular t

27、ime.Additionally, the prepared insulation system samples of liquid (MO and NFs) and solid (OIPs, NIPs) were thermally aged at 55℃ and 130℃ for 30 days.The effect of alumina NPs on thermal aging of transformer oil and pre

28、ssboard were also investigated.The results showed that Al2O3 NPs can slow down the aging of oil and pressboard.The average AC and positive LI BDV of aged NFs was 11％ higher than aged MOs.The average LI creeping FOVs of N