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A permanent magnet based on ferrite for use as components of electrical generators has been fabricated by two different methods: solid–solid mixing and cooprecipitation. The conventional solid–solid mixing method uses Fe 2 O 3 and BaCO 3 as starting materials with mole ratio n=BaO:Fe 2 O 3=1: 6. The mixture is calcinated at 1100 °C and two crystal structures, BaOFe 2 O 3 and BaFe 12 O 19, were obtained with particle size of about 0.5–1.5 μm. Sintering at 1100 °C was followed by a magnetization process. Measurements give the following physical parameter values: remanence, Br=0.0792 T; magnetic saturation, Bs=1.21 T; coersivity, Hc=44.7 kA  m -1; density 3.43 g  cm -3 and porosity 9.16%. On the other hand, the cooprecipitation method uses FeCl 3 and BaCl 2 solution with mole ratio n=BaCl 2:FeCl 3=1:6. After the calcination at 900 °C and higher temperatures a single crystal structure of BaO·6Fe 2 O 3 is formed with particle size of about 30–60 nm. The optimum sintering temperature for the formation of this single phase crystal structure is 1050 °C. The physical parameters of the final product have the following values: Br=0.2673 T; Bs=1.42 T; Hc=89.4 kA  m -1; density 4.34 g  cm -3 and porosity 3.36%.

To implement Condition Based Maintenance (CBM) on power transformer where its accurate condition became necessary and crucial, PLN P3B JB develop condition assessment method. This method starts with FMEA/FMECA generation to define critical failure modes and weighting factor which will be used to give optimal portion of inspections value and typical failure modes in defining condition of transformer.Next step is defining inspection method that accurate to assess those failure modes, whether it is visual inspection, in service measurement or shutdown measurement. Some calculation also used to combine all inspection values in order to generate result value that represents actual condition of transformer.

Transformers are one of some important equipments on electricity network. Each utility, in this case PLN P3B Jawa-Bali, has to assure their reliability in order to maintain electrical power system stability by assessing transformer conditions. Once transformer condition attained, appropriate maintenance and operation strategy can be defined.Based on failure investigation, transformer conditions are influenced by its insulation condition. PLN P3B Jawa Bali has applied dissolved gas and oil characteristic diagnostics. Since the load grows faster than the network expansion, our transformers tend to be operated at their nominal value or even overloaded. We also find out that through fault current is one of transformers failure root causes. Therefore, we are developing on-line thermal monitoring and vibration in order.The oil and winding temperatures are dependant to load. As the load increases to its nominal value, risk due to transformer paper insulation damage caused by disturbances becomes higher. Subsequently the situation will accelerate the transformer to ageing. By recognizing the raise and fall function of these temperatures to load we can identify the thermal characteristics of the transformer. Other characteristic will be identified is dissolved gas increase caused by feeder faults. Based on these characteristics we are able to conduct some actions, for example: maintaining the temperatures in safe range by controlling cooling system (prohibiting ageing) or determining the condition status of the transformer at that particular time.In this paper we would like to describe our experience in developing the thermal statistic characteristics using load and temperature manual data acquisition, and dissolved gas produced by feeder faults.

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