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Introduction: The Microchip Guardian

A dry-type transformer (Articles 12–14) is sealed in air, not oil — so it has no oil-temperature gauge or Buchholz relay to fall back on. Its only early-warning signal is winding temperature. The smart temperature control system is the device that watches that signal around the clock: it reads three embedded platinum sensors, starts the cooling fans before the coil overheats, raises an alarm as the margin thins, and finally trips the breaker before insulation fails. It is the quiet "microchip guardian" that turns a passive piece of iron and copper into a self-protecting, remotely observable asset. This article walks through how it works, what it protects against, and how to specify one.

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Technical Principle: Sense, Decide, Act

The system is built around three Pt100 platinum RTD sensors pre-buried in the three-phase windings (the A, B, C coil packages) during manufacturing. Each Pt100 has a resistance of 100 Ω at 0 °C and rises predictably with temperature, so the controller reads resistance and converts it to °C — typically with 0.1 °C resolution and class 0.5 accuracy over a −30 to 240 °C range. A microcontroller compares each phase against user-set thresholds and drives the outputs: fan contactors, alarm and trip relays, and a digital link. The whole unit is designed to JB/T 7631 and built for strong EMC immunity (common-mode, fast-transient, ESD, RF) so it keeps working in a noisy switchroom.

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Key Features

• Three-phase PT100 sensing: Reads all three coil packages continuously, with scan and max-value display so an operator can spot a single overheated phase at a glance.

• Automatic fan control: Starts/stops the cooling fans at setpoints (often fan-off 80 °C, fan-on 100 °C) and supports manual override plus timed exercise to keep fans healthy.

• Two-stage protection — alarm then trip: A ~130 °C alarm gives early warning (audible/visual + relay); a ~150 °C trip opens the breaker before insulation breaks down. Both are redundant relays, not software-only.

• RS485 / Modbus remote link: Half-duplex RS485 carries the three-phase temperatures and status to SCADA/DCS — up to 31 controllers on one bus, ~1200 m away, 300–9600 bps. Optional 4–20 mA analog output maps 0–200 °C to a gauge.

• Black-box recorder: On power loss it retains the last temperatures of the three windings plus its own state, so engineers can reconstruct what happened before a trip or blackout.

• Self-diagnosis: Detects an open or shorted sensor, forces the fan on, and flags the fault (A/B/C) instead of going silent — so a broken probe never hides a real overheat.

3.1 How the Pieces Connect

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Application Scenarios

The controller matters most wherever a transformer runs unattended or where a trip is expensive. It is standard on the dry-type units from Articles 12–14 and on the prefabricated substations of Article 9:

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Selection Guide: Five Checks Before Specifying

• Communication: If the unit feeds a SCADA/BMS, choose an RS485 / Modbus model (or 4–20 mA analog); confirm the protocol and bus length (up to ~1200 m) and node count.

• Protection grade: The controller itself is typically IP40 — house it in a panel door or cabinet; verify supply (100–240 V AC/DC) and operating band (−25 to +55 °C).

• Sensor match: Confirm Pt100, 3-wire probes are embedded in the windings at the factory; mismatched probes break accuracy and self-diagnosis.

• Thresholds & relays: Set fan-on / alarm / trip to the coil's class (e.g. 100 / 130 / 150 °C for F/H); check relay contact rating (often 7 A / 220 V) for the fan and trip coils.

• Black-box & certification: Ask for the fault recorder and JB/T 7631 compliance, and source from a full-capability supplier such as XIAOPAI Electric that bundles the controller with the transformer and type-test reports.

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Conclusion: A Brain for the Coil

The smart temperature control system is the difference between a dry-type transformer that merely sits there and one that watches, cools, warns, and protects itself. Three embedded Pt100 sensors feed a controller that runs the fans, sounds the alarm, opens the breaker, logs to a black box, and reports over RS485 — covering the gap that oil-less, air-cooled designs leave behind. Specified well, it is what lets the dry-type and prefabricated units of this series (Articles 9, 12–14) run unattended in data centers, hospitals, and substations with confidence. XIAOPAI Electric supplies the controller as an integrated part of its transformer and substation packages — built to JB/T 7631, backed by ISO 9001, CE, and UL, and ready for global delivery.

For wiring diagrams, setpoint sheets, and Modbus register maps, contact the XIAOPAI Electric technical team.

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