"We used LabVIEW graphical programming tools and the NI CompactRIO platform to develop an oil aging temperature regulation and monitoring test system to achieve quick measurement and control with predetermined accuracy."
The Challenge: Developing a system that continuously monitors, logs, and regulates transformer oil temperature during the aging process and maintains temperature consistency within strict limits.
The Solution: Using an NI cRIO-9073 controller, NI 9217 temperature analog-input modules, NI LabVIEW software, and an NXP ARM7 LPC2148 ARM 32-bit microcontroller to develop the system.
The controller system (Figure 1), based on the NXP ARM7 LPC2148 ARM 32-bit microcontroller, performs the following functions:
Measures temperature using two PT100 temperature sensors—one for the oil and another for the aluminum-block cuvettes containing the oil samples
Regulates oil temperature to maintain values set between 40 ºC and 200 ºC, with a tolerance of 0.5 ºC for temperatures of 40 ºC to 140 ºC, and 1 ºC for temperatures between 140 ºC and 200 ºC
Heats the oil automatically using three 320 W heaters with PWM regulation
Sets temperature value and experiment duration, and displays measured oil temperature and remaining time (Figure 2) on a 2x16-character LCD with a standard 12-way keyboard connected to the controller with an RS232 device
Figure 1. Controller With Oil Samples
Figure 2. Controller Front Panel
Temperature Monitoring
We chose the NI cRIO-9073 because we knew we could quickly set it up and perform accurate measurements based on our previous experience with using it for thermal imaging of two power transformers at the coal-fired power plant TENT-B in Obrenovac, Serbia. We instrumented this controller with NI 9217 temperature modules and used LabVIEW software to monitor the set temperature of 12 transformer oil samples simultaneously. The cRIO-9073 controller measures the oil sample temperature when the temperature is above or below the set limits, or has an out-of-range temperature alarm during the pretest period. Temperature measurement history, with all relevant parameters for each sample, is stored in a database for further analysis. The process displays graphically on a monitor attached to the cRIO-9073 controller (Figure 3).
Figure 3. Temperature Monitoring System With a cRIO-9073 Controller and NI 9217 Analog-Input Modules
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