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Rev. A1 (30–05–12) MFC-300/T-Dry Technical Manual 3
2 Operating principle
2.1 General principle
The MFC-300/T-Dry’s main purpose is to monitor transformer temperatures and acti-
vate cooling systems whenever necessary. It features up to 6 RTD inputs, which are
automatically compensated for cable length and linearized for each sensor’s standardized
temperature response.
The standard MFC-300/T-Dry configuration for dry transformers features 4 relays, as-
sociated with cooling, alarm, trip and failure events. Each RTD has associated cooling,
alarm and trip set points. For instance, if the cooling set point associated with RTD 2 is
configured to 80 ◦Cand this RTD’s temperature exceeds this value, the MFC-300/T-Dry
activates the forced cooling relay, regardless of the states of the other RTDs.
Each relay features a hysteresis, whose purpose is to prevent intermittent activations
whenever the temperature oscilates around a configured set point. For example, if the
cooling hysteresis is configured to 2 ◦C, then in the example above the cooling relay will
only be deativated once RTD 2’s temperature drops below 80 −2 = 78 ◦C.
Relays dedicated to cooling functions may also be activated once per day at a configurable
time and remain active for a configurable duration. The daily activation of cooling pumps
or fans is desirable in cold climates in order to keep mechanical parts well lubricated and
to prevent the accumulation of dirt.
During normal operation, the temperature maximum for each RTD is registered in non-
volatile memory. These values may be reset with a user command.
The MFC-300/T-Dry can feature up to 6 current loop outputs with a 16-bit resolution
(one for each RTD measurement), and with scales configurable to 0-1, 0-5, 0-10, 0-20 or
4-20 mA.
2.2 RTD operation
The MFC-300/T-Dry continuously monitors the state of each RTD and its connection,
and automatically ignores sensors which are absent or which present abnormal behavior.
If the user wishes to install less RTDs than the maximum allowed by the equipment, the
parameter Qty. of Active RTDs should be set.
The following events are identified as RTD faults:
