Oil Transformer Temperature Controller

Working Principle

• thermal simulation: A current proportional to the load is taken out through the current transformer, adjusted by the converter and fed into the electric heating element inside the elastic element of the winding temperature controller. The heat generated by the electric heating element causes the elastic element to generate additional displacement, thus generating a temperature indication value that is one temperature difference higher than the oil temperature, and indirectly obtaining the average indication value of the winding temperature.
• Pressure temperature control principle: It is mainly composed of elastic element, capillary tube, temperature package and microswitch. The temperature-sensitive medium in the temperature package is subjected to thermal expansion, the volume increment is transferred to the elastic element through the capillary tube, so that the elastic element produces displacement, which is amplified by the organization to indicate the measured temperature and drive the microswitch to work, so as to control the input or output of the cooling system.
• Fiber Grating Temperature Sensing PrincipleBased on fiber optic grating temperature sensing technology, the fiber optic sensor is directly immersed in the transformer oil, detects the temperature through the wavelength change of light, collects the oil temperature data, and then analyzes it through the internal intelligent algorithm to automatically control the startup and shutdown of the oil pump and cooling fan.

Functional characteristics

• Temperature monitoring and display: Real-time monitoring of the transformer's oil and winding temperatures, and converting the temperature signals into electrical signals for transmission to the control unit and displaying the temperature values on the display unit.
• automatic control function: When the transformer temperature reaches the preset start value, the cooling system is automatically activated; when the temperature drops to the preset stop value, the cooling system is automatically shut down to keep the transformer temperature within the appropriate range.
• Alarm function: When the transformer temperature exceeds the preset safety value, sound and light alarm signal will be issued to prompt the staff to deal with it in time, and the alarm signal can also be transmitted to other monitoring system or equipment through the output contact or communication interface to realize remote alarm.
• protective function: When the transformer appears abnormal conditions, such as winding short circuit, oil temperature is too high, cooling system failure, etc., according to the different situations to take appropriate protective measures, such as tripping, shutdown, etc., to avoid equipment damage or accident expansion.
• Data logging and storage: It has a data recording function, which can record the temperature change of the transformer, the operation status of the cooling system and other information, and these data can be exported through the communication interface or memory card, which can provide the basis for the subsequent analysis and processing.
• Remote control and monitoring: Connected to other monitoring systems or equipment through the communication interface, the staff can perform temperature setting, start-stop control and other operations on the transformer in the remote control center, improving the maintainability and management efficiency of the equipment.

typology

• Mechanical Thermostat: Relying on bimetal temperature sensing, simple structure, lower cost, but limited precision and response speed, applicable to ordinary oil-immersed transformers.
• Electronic thermostatThe electronic temperature measurement by thermistor or PT100 sensor has higher precision and can be linked with PLC or remote monitoring system, which is suitable for intelligent substation.
• Fiber optic temperature measurement system: Used in large or important occasions, it can realize the distributed monitoring of winding temperature, strong anti-electromagnetic interference ability, suitable for high-voltage, large-capacity transformers.

Main technical indicators

• Normal operating temperature range: Generally around - 30°C to + 55°C, may vary from model to model.
• Measurement range: Commonly available are - 20°C to + 80°C, 0°C to + 100°C, 0°C to + 120°C, 0°C to + 150°C, and many other specifications.
• Indication accuracy: Usually about 1.5 levels.
• output signalThe signal, such as Pt100 platinum resistance signal, can be transmitted remotely to the control room, or converted to DC standard signals, such as 0-5V, 1-5V, 4-20mA, etc., which can be networked with computers.

Installation and Maintenance

• mounting: Temperature sensors are usually installed on the wall of the transformer's tank or in the oil pillow to accurately measure the oil temperature; for the winding thermostat, its related current transformer and other components need to be correctly installed in the transformer's high-voltage side casing and other locations.
• safeguard: Regularly check whether the display of the thermostat is normal or not, whether the sensor connection is firm or not, and whether there is any loosening, corrosion and other phenomena; clean the shell and display of the thermostat to ensure that its heat dissipation is good and the display is clear; calibrate the measurement accuracy of the thermostat, which can be compared with the standard thermometer, and calibrate and adjust it if necessary.

First, first look at the transformer "its own conditions": the basic parameters to determine the bottom line of adaptation

Second, clarify "what to measure": oil temperature or winding temperature?

• Oil Temperature Measurement::
  Oil temperature is a visual reflection of the overall heating state of the transformer, the measurement point is usually in the oil tank or oil pillow, the technical threshold is low.
  • Scenario: All oil-immersed transformers need to monitor the oil temperature as a basic monitoring indicator.
  • Recommended type: Mechanical (low cost), electronic (medium-high precision) are available, choose according to the precision needs.
• Winding Temperature Measurement::
  The winding is the part of the transformer that is most likely to overheat (e.g., a sudden rise in local temperature in the event of a short circuit), but it is difficult to measure it directly (high-voltage environmental limitations), and special techniques are required.
  • Indirect measurement: Derived from "oil temperature + load current simulation" (e.g. thermal simulation method), suitable for low and medium pressure, common occasions, commonly used in mechanical or electronic thermostats.
  • Direct measurement: embedded in the winding with fiber optic sensors, real-time monitoring of the real temperature, strong anti-electromagnetic interference, suitable for high-voltage, large-capacity, important occasions (such as the main transformer of power plants).

III. Matching "feature lists" to needs: from basic to smart

IV. Environment and cost: balancing reliability and economy

• environmental adaptation::
  • High / low temperature environments (e.g. outdoor extreme cold areas): thermostats are required to cover the operating temperature range of - 40℃~+60℃ (e.g. industrial grade electronic).
  • Dusty/humid environments: Select housings with protection class IP54 and higher to avoid sensor corrosion.
  • Vibration occasions (e.g. vehicle transformer): mechanical type is susceptible to vibration, give priority to the electronic type (fixed firmly).
• Cost & Maintenance::
  • Low-cost priority: Mechanical (hundreds of dollars per unit, simple maintenance, accuracy ±2℃~±5℃).
  • Medium cost-effective: electronic (unit price thousands of dollars, accuracy ±1 ℃ ~ ±2 ℃, support linkage, long maintenance cycle).
  • High reliability is preferred: fiber optic systems (tens of thousands of dollars per unit, 10+ year lifespan, virtually maintenance free, for critical equipment).

V. Don't ignore "compliance": meet the standards before you use them

• Power industry: need to comply with "DL/T 540-2010 Power Transformer Room Layout Design Regulations" "JB/T 7631-2016 Transformer Temperature Controller", etc., to ensure that the measurement range, the alarm value (such as oil temperature ≥ 85 ° C alarm, ≥ 95 ° C trip) meet the requirements.
• Explosion-proof: If the transformer is located in a flammable and explosive environment (e.g. gas station), an explosion-proof thermostat (Ex approval) is required.

In summary: three steps to lock in the right thermostat

1. lay the foundation: Determine the measuring range and anti-interference requirements of the thermostat according to the transformer capacity and voltage level;
2. select core: Specify whether the oil or the winding temperature is to be measured, and decide whether to use indirect measurement (mechanical/electronic) or direct measurement (fiber optic);
3. complementary function: Balance cost and reliability by overlaying automation, remote monitoring and other functions according to O&M needs.