BA2070/03/16
Messko
13
2 Product specification
The dehydrating breather can be mounted either on the pipe of
the oil conservator with a flange (Fig. 1/1) as standard or with
2 side mounting rods (appendix, Fig. 7) as an option.
2.1 Function specification
Dehydrating breathers work according to the following principle.
When the oil conservator suctions in air (e.g., due to the reduced
load), the air flows through a filter made of high-grade steel
wire mesh (Fig. 1/4) to the inside of the device. This filter and
the dust cap (Fig. 1/5) filter dust, sand and other dirt particles
from the air. The filtered air flows through the desiccant cham-
ber (Fig. 1/8) filled with colorless, moisture adsorbing pellets
and is dehydrated. The dehydrated air rises further via the pipe
in the oil conservator.
A sensor (Fig. 1/10) monitors the air flowing by to determine the
saturation degree of the desiccant. Depending on its state, the
desiccant is regenerated with the heating elements integrated
in the desiccant container. A temperature sensor monitors the
function of the heating elements.
The water vapor created by the baking process condenses by
convection in the dehydrating breather on the bottom metal
flange (Fig. 1/7). The condensed water exits the device through
the high-grade steel filter.
No maintenance is required for replacement and regeneration
of the desiccant.
2.2 Twin Dehydrating Breather
The twin dehydrating breather (DB 200 D-T) uses the same
principle as the „single“ dehydrating breather. This is equipped
with two parallel desiccant containers to enable them to
handle the air exchange of greater amounts of oil.
2.3 Desiccant
Colorless, non-poisonous, moisture-adsorbing Silicagel pellets
which do not change their color when a moisture saturati-
on occurs are used as desiccant material in the dehydrating
breather. Silicagel pellets which do change their color have a
limited lifetime due to the chemical additives used.
2.4 Control of the heater
The following 3 types are available for controlling the heater.
α-controller: Recommended for use on tap changers, arc su-
pression coils and traction transformers. Here the dehydrating
breather is baked out based on its state which is monitored for
humidity.
β-controller: A self-learning system that is recommended for
use on transformers with cyclic loads (see applications, table
2). In addition to monitoring the humidity, a time window is
determined here during which the oil conservator exhales and
the dehumidification chambers are regenerated.
γ-controller: Recommended for special applications such as
transformers installed in caverns, furnace transformers and GSU
machine transformers with non-periodic breathing behavior. If
the moisture content of the air flowing in the direction of the
transformer exceeds a specified value, the silica gel chambers
are regenerated alternately.
For redundancy, a time control is also present which starts the
regeneration of the desiccant at predetermined intervals should
the moisture sensor fail.
The control unit and the terminals for the electrical connec-
tions are located in the terminal box (Fig. 1/9).
Table 2 lists the recommended application areas for the
different MTraB versions.
2.5 Self-monitoring function
The dehydrating breather has a self-monitoring function. When
the device malfunctions, this is reported by a relay contact. The
following malfunctions are detected:
- Failure of the power voltage
- Failure of the silicon gel heater
- Failure of a sensor
- Internal error
- Failure of the ball valve (only with the γ-controller)
2.6 Outputs
Analog output:
Temperature in the pipe -40 to +80 °C;
Signal 4 to 20 mA standard, others optional;
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