bwr transformer winding thermometer type

Meter body: pointer type or digital display type, dial usually has white real-time pointer, red maximum value pointer, and four-color (red, blue, green, yellow) contact indicator block.

Temperature package: The metal temperature sensing package is placed in the oil on top of the transformer at a depth of ≈ 150 mm and filled with temperature sensing medium.

Capillary/Spring Hose: Connects the temperature package to the gauge head and transmits the medium expansion displacement.

Thermal simulation device:
- Converter: Converts high voltage side casing CT secondary current (0-5 A or 0-1 A) to 0-1 A (typical) heating current at the manufacturer's ratio.
- Heating element: This current flows through a heating wire placed inside the heating pack and generates an additional temperature rise Δt proportional to the load.

Auxiliary components:
- Microswitch: Provides alarm/trip/start/stop cooler contacts for groups K1~K6.
- PT100 platinum resistance: Outputs 4-20 mA or RS-485 (Modbus) remote signals for background monitoring.

At no load or low load: The temperature pack is only affected by the top oil temperature tₒ, which is indicated by the pointer as tₒ.

After carrying a load:
t_winding = tₒ + k-I²
where k is the thermal simulation coefficient, which is determined by the converter ratio in conjunction with the resistance of the heating wire. The additional heat generated by the heating current on the heating wire simulates the temperature rise of the winding copper, thus making the meter value close to the hot spot temperature of the winding.

Output:
- Mechanical pointers are displayed in situ;
- The microswitch closes/disconnects at the set value to actuate the cooler or protection circuit;
- PT100 or 4-20 mA signal to DCS/backend for remote monitoring.

Installation: The temperature package is inserted vertically into the special oil hole, and the bending radius of the capillary tube is ≥40 cm, avoiding twisting and sharp bends.

Electrical: All wiring must be done in a power-off state, with the junction box well sealed and reliably grounded.

Calibration: According to JJF(Jin)XX-2024 and other specifications, the display value and contact action error calibration is carried out at 10 ℃, 20 ℃, 38 ℃ temperature rise points, and the display value error of the remote transmission ≤ 1/2 of the absolute value of the maximum permissible error.

Daily inspection: Check whether the pointer is stuck, the maximum value pointer reset, and the contact action is reliable, to prevent analog failure due to capillary leakage or broken heating wire.

Directly buried sensors: high accuracy, but need to be pre-buried fiber optic or RTD when the transformer is manufactured, and difficult to transform later.

Pure oil thermometer: reflects only the top oil temperature, not the additional temperature rise of the winding caused by the load current.

Winding thermometers: taking into account the economy and engineering implementability, widely used in operating transformers.