IEC TR 61946:2007 pdf free download

IEC TR 61946:2007 pdf free download Mineral insulating oils – Characterization of paraffinic/naphthenic nature – Low temperature differential scanning calorimetry (DSC) test method
4 Test method
The method consists of heating (or cooling) the test specimen at a controlled rate in a controlled atmosphere through the region of melting (or crystallization). The difference in heat flow between the test specimen and the reference material due to energy changes in the material is continuously monitored and recorded as a function of temperature. A transition is marked by the absorption (or release) of energy by the test specimen resulting in a corresponding endothermic (or exothermic) peak in the heating (or cooling) curve. Integration of the energy of the recorded peak area as a function of time (or temperature) results in a measurement of the energy of the transition. Observation of the position of the transition on the temperature axis provides the necessary temperature information.
NOTE 1 This method is only for the purpose of distinguishing between paraffinic and naphthenic oils. To do so it is not necessary to make any calculation of temperature nor enthalpy.
NOTE 2 If, despite the previous note, there is still an interest in calculating the temperature or the enthalpy of the process, it should be taken into account that the melting or crystallization of paraffins follows a very complex kinetics and depends on the time the sample is maintained at very low temperature.
5 Interference
Test specimens that release volatiles on heating will change mass and this may invalidate the test. It is recommended not heating the oil samples at temperatures above 50 °C to 1 00 °C.
6 Apparatus
The test method uses the following apparatus:
a) differential scanning calorimeter having the following performance:
− heating or cooling rate up to 20 K/min;
− automatic recording of differential heat flow between the test specimen and the reference material;
− heat flow sensitivity to provide an accuracy of ± 1 %;
− time base precision of ± 1 % over the time base range from 0,1 min/cm to 2,0 min/cm (1 0,0 cm/min to 0,5 cm/min) of chart;
− temperature sensitivity sufficient to provide a specimen temperature accurate to at least ± 0,1 K;
− cooling device able to cool the oven at least at –80 °C. Preferred operating range – 1 00 °C to + 1 00 °C;
b) planimeter, or other means of area measurement with an accuracy and precision of ± 0,1 %;
NOTE 1 Most modern equipment has built-in area integration systems.
c) specimen holders, inert to the oil specimen over the prescribed temperature range,composed of aluminium or other material of high thermal conductivity;
d) dry nitrogen (at least 99,9 % purity) or other inert gas supply for purging purposes. The dew point of the selected gas shall be below the lowest operating temperature;
NOTE 2 Due to its high thermal conductivity, helium may be used very efficiently at very low temperatures.
However, the use of helium at temperatures above 1 00 °C may cause damage in the equipment.
e) analytical balance, accurate to the nearest 0,01 mg.