Troubleshooting & Function Guide:  Dry-Type Transformer Temperature Controllers

Dry-type transformer temperature controllers are the "brain" of your transformer's thermal protection system, monitoring temperatures, controlling cooling fans, and preventing catastrophic overheating. Even the most reliable BW10 Series controllers may encounter common operational issues, and understanding how to resolve them is critical for minimizing downtime and ensuring transformer safety. This guide breaks down core product functions and step-by-step troubleshooting for the most common problems, tailored for power distribution professionals and facility managers.

BW10 Series: Product Types & Core Functions

The BW10 Series offers multiple variants to match different transformer monitoring needs, with standardized functions across the line plus specialized features for advanced applications:

Common Troubleshooting for BW10 Series Controllers

Even with proper installation, controllers may experience occasional issues. Below are step-by-step solutions for the four most common problems encountered in field operation:

Problem 1: The Controller Does Not Light Up / No Display

If the screen remains dark after power is applied, follow these steps based on your controller type:

Universal (Black Shell) Temperature Controller (bw10-RS485):

Check that 220V power is connected to terminals 1 and 2. If voltage is present but the controller still does not display, disconnect the cabinet door travel switch wiring at terminals 9 and 10, then reapply power.

This resolves 70–80% of no-display issues caused by switch malfunctions. If the problem persists, replace the temperature controller.

Flip-Over (White Shell) Temperature Controller (bw10-RS485):

Verify 220V power at terminals 11 and 12. If voltage is present but no display, disconnect the cabinet door travel switch wiring at terminals 9 and 10, then reapply power.

If the display still does not light up, replace the controller.

Embedded (Gray Shell) Temperature Control Box:

Confirm power is connected to the lower and upper terminals of the air switch microcontroller. If power is present but the display is off, disconnect the cabinet door travel switch wiring at terminals 7 and 8, then reapply power.

If the issue remains unresolved, replace the temperature control box.

Final Check: Ensure all wiring connections are secure and there are no signs of damage to the controller's power supply terminals.

Problem 2: Temperature Controller Alarm / Abnormal Readings

If the controller displays error codes or inconsistent temperature readings, troubleshoot as follows:

All three phases (A, B, C) display "H" / High Temperature Alarm:

Check if the DB9 sensor plug is securely connected to the controller. If the sensor is disconnected or loose, reconnect it firmly.

One phase displays "H" while others show normal temperatures:

The sensor for the faulty phase is damaged or disconnected. Replace the corresponding temperature sensor probe.

All three phases display "L" / Low Temperature Alarm:

The sensor type is incompatible with the controller. Replace the sensor with a compatible PT100 probe matching the BW10 Series specifications.

Phase temperatures are normal, but the controller displays "H":

Check if the transformer cabinet door travel switch is closed properly. If the switch is open, the controller may trigger a false high-temperature alarm.

Disconnect the travel switch wiring and test again. If the alarm clears, repair or replace the faulty cabinet door switch.

Special Reminder: If the controller has been operating normally for a period and suddenly triggers an alarm, check the travel switches on the front and rear of the transformer enclosure first. Loose or damaged switches are a common cause of false alarms in field environments.

Problem 3: Cooling Fan Does Not Start

If the fan fails to start when the controller triggers it (manual start does not work, or temperature reaches the 80°C fan start threshold with no response):

Diagnosis: This indicates a fault in the fan circuit, most commonly excessive current (>15A) passing through the fan load, or a short circuit in the fan motor.

Solution:

Inspect each cooling fan one by one, especially older units that have been in service for a long time.

Check for signs of burnt wiring, damaged motor windings, or seized fan impellers.

Replace any faulty fans, then test the controller's fan output function again.

If multiple fans are connected, disconnect them one at a time to identify which unit is causing the circuit overload.

Problem 4: Unable to Communicate with RS485 / MCGS

If the controller cannot connect to the MCGS monitoring system or other RS485 devices:

Pre-Test Check: Before testing, disconnect the wiring on the 485 interface of the on-site temperature controller. Loose, damaged, or incorrectly wired connections are the most common cause of communication failures.

Troubleshooting Steps:

Verify the A/B line polarity of the RS485 connection (incorrect polarity is a frequent issue in field installations).

Check for voltage or signal interference on the communication cable, especially in industrial environments with high electrical noise.

If the connection still cannot be established after verifying wiring and polarity, replace the temperature controller.

Pro Tips for Long-Term BW10 Controller Reliability

Preventative Maintenance: Inspect sensor wiring and fan connections every 3–6 months to catch loose connections before they cause alarms or failures.

Environment Protection: Install the controller in a dry, dust-free enclosure to prevent moisture or debris from damaging the circuit board.

Calibration Checks: Perform annual temperature calibration using a reference thermometer to ensure readings remain accurate within the 0.5% FS tolerance.

Spare Parts: Keep a spare controller and PT100 sensor probes on hand for quick replacement during critical outages.

The BW10 Series temperature controller is a critical component of your dry-type transformer's thermal protection system. By understanding its functions and following these troubleshooting steps, you can resolve common issues quickly, minimize downtime, and extend the service life of your transformer.