8.4.6 Moisture Readings Remain at 0%
Probable causes:
1. If there is no display (see Figure 3-1), the 24-Vdc power supply of the Hydran
M2-X has failed. Verify the wiring at both ends of the dc power supply cable.
2. The analog output cable is disconnected or broken.
8.4.7 Irregular Readings (Moisture and Temperature)
On a transformer in operation, it is normal to observe variations in the moisture
of the oil. This parameter is sensitive to the temperature as the quantity of water
that can be absorbed by the oil increases logarithmically with the temperature. For
a constant water concentration (ppm), the moisture drops rapidly as the oil
temperature rises. For example, in a relatively dry transformer (1 % moisture in the
paper), a 15 °C (27 °F) variation between day and night can produce a variation in
moisture of 2 to 3 %; this effect is stronger in a wet transformer. The oil warming
causes a reduction of its moisture, thus resulting in a water transfer from the paper
into the oil. When the oil is hot (70–100 °C [158–212 °F]), this transfer is significant
and contributes to stabilize the moisture reading; at low temperatures, this transfer
is very slow and has a low impact over a 24-hour cycle.
The probable cause of irregular readings is electric interference. Verify the
grounding and shielding of the analog output cable.
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