SAMPLING
The insulating fluid samples should be taken by qualified personnel in accordance with IEC 60475. During his storage and transport, samples should be protected from direct light.
LABELLING
Insulating liquid samples must be properly labeled before being sent to the laboratory.
The following information is required:
- Customer or facility;
- Fluid identification (type and class);
- Identification of the equipment;
- The date and time of sampling;
- Temperature during sampling;
- sampling point;
- Other relevant information.
PROCEDURES
In order to obtain a meaningful measure of the dissipation factor is essential to follow exactly the rules with respect to:
- Careful cleaning of the test cell;
- Careful filling test cell and the careful handling of liquid samples and the very test cell.
Cleaning test cell
Procedure. Depending on the cleanliness of the test cell and the level of conductivity liquid to be analyzed, the cleaning of the test cell will be more or less sophisticated and more or take less time.
If the cleanliness of the cell is unknown, or if there is any doubt, you should have a cleaning process.
You can follow many cleaning procedures if they prove to be effective.
Checking the cleanliness of the empty cell. For a significant extent, it is necessary that
Cell electrical losses are much smaller empty the fluid to be measured.
Checking the cleanliness of the full cell for measurements at room temperature. If the cell trial is perfectly clean and fluid temperature is constant, and are independent of time. The measure can therefore be performed as soon as practically possible. In fact, this can be done in less 1 min. Moreover, a single measurement of a single sample is sufficient to obtain the correct value.
It may happen that, at constant temperature, conductivity(or so to increase or decrease over time, but no more than 2% at two minutes to fill the cell. In this case can be seen that the cell is sufficiently clean and the first measured value, ie a minute or so to fill the cell, can be registered.
Otherwise, it is recommended after cleaning the cell again, take a second sample of the same liquid and a second measure. It is considered the lowest value of the two, as recommended in IEC 60247.
Checking the full cell for measurements at temperatures above room temperature.
Before taking any action at high temperatures, make sure that the temperature of the liquid in the cell is constant. Except in cases in which the cell is perfectly clean, the measurement result depends on the way in which the cell and the liquid had been heated.
If the test cell is perfectly clean and the liquid temperature is constant, conductivity and are independent of time. The measure can thus be made immediately. In practice, the measure may do as soon as the temperature may be considered constant. Moreover, a single measurement of a single sample is enough to get the correct value.
It can happen, even if the liquid and the cell are at a constant temperature, conductivity (o de tan increase or decrease over time. This may be due to different causes: for example, heating to high temperatures can alter the composition of certain liquids, or modify the moisture content of the particles.
In practice, the temperature is not perfectly constant and their variations induce variations or conductivity,liquids varies more or less depending on the temperature nature of the liquid, typically up to 5% per degree centigrade. Therefore, the origin of variations.
If the test cell is not perfectly clean, the heating time affects the measured values, even the first, because the cell impurities dissolve in the liquid. The first measured value should, therefore, be discarded and the cell must be cleaned again.
Precautions when filling the test cell
When the cell is filled with liquid, you must ensure that the ambient atmosphere is, as far as possible, free of gas fumes that can be dissolved in the liquid.
The electrodes must be completely submerged in the liquid.
Test temperature
The measurement of conductivity and dissipation factor of a liquid can be made at any temperature.
Room temperature is recommended for its simplicity and time savings. Since the ambient temperature is essentially variable, you must remember a fixed value (eg 25 ° C).
There is nothing to stop the test is done at higher temperatures (eg 40 ° C 1 ° C, 90 ° C 1 º C or more).
Methods of heating
To make a measurement at high temperatures can be used several methods of heating. The time required to reach the test temperature depends on the method used and typically varies between 10 min and 60 min. If the test cell is not perfectly clean, the increase in conductivity due to the dissolution of impurities will depend on the duration of heating and the measured conductivity will depend, in turn, the heating method.
Thus, heating test cell as quickly as possible.
A suitable method to achieve this can be heated separately from the test cell and the liquid in a clean container. Another method is to rapidly heat the liquid in the test cell itself.
Measure
Fill the sample cell with avoiding contamination of the fluid or the cell (see 8.2).
Cleaning is checked as described in 8.1.3 or 8.1.4. If the cell is clean enough (see 8.1), is
Note the values of G and C.
15:13
Allison
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