Low-Cost Humidity Sensor for Transformer Oil

What it does

This project features a low-cost, real-time capacitive humidity sensor system designed to monitor moisture levels in transformer oil. It detects early signs of insulation degradation, enabling preventive maintenance and improving transformer reliability.

Your inspiration

The inspiration for this project arose from the need to monitor moisture in transformer oil more affordably and efficiently. Excess humidity can lead to insulation failure and reduced transformer lifespan, yet most existing solutions are costly or require laboratory analysis. This project aims to develop a simple, low-cost, and real-time monitoring system using a capacitive humidity sensor combined with basic electronics. By converting changes in capacitance into measurable signals, the design offers an accessible solution for early moisture detection, supporting preventive maintenance and improved transformer reliability.

How it works

The design features a capacitive humidity sensor consisting of two metal plates separated by a moisture-sensitive material. When exposed to transformer oil, the material absorbs water molecules, altering the sensor’s ability to store electrical charge, a property known as capacitance. Since capacitance is difficult to measure directly, the sensor is connected to a 555 Timer IC, which converts capacitance changes into electrical pulses. As moisture levels increase, the timing or frequency of these pulses shifts accordingly. By measuring this frequency, the system can determine the level of humidity in the oil. A custom circuit board ensures compactness and reliability, while calibration using saturated salt solutions allows for accurate and consistent readings. This enables real-time monitoring of moisture content in transformer oil, providing early warnings of potential insulation issues and supporting preventive maintenance strategies.

Design process

The design process began with identifying the need for a low-cost, real-time humidity monitoring solution for transformer oil, where excess moisture can degrade insulation and reduce operational lifespan. A detailed literature review was conducted to evaluate existing sensing methods, leading to the selection of a capacitive humidity sensor for its simplicity, affordability, and compatibility with oil environments. A humidity-to-frequency conversion circuit was then developed using a 555 Timer IC, which transforms changes in capacitance into a frequency signal. An initial breadboard prototype was constructed and tested, followed by iterative circuit refinements to improve accuracy and signal stability. Calibration was performed using saturated salt solutions in accordance with ASTM E104-20a, allowing for reliable correlation between frequency and humidity levels. A custom PCB was then designed and fabricated to integrate the sensor and circuitry into a compact, stable platform. The final prototype was validated through controlled testing, confirming its effectiveness in providing accurate, real-time moisture readings. The complete system demonstrates a practical and affordable approach to continuous humidity monitoring in transformer oil applications.

How it is different

What makes this design unique is its combination of simplicity, low cost, and suitability for real-time humidity monitoring directly in transformer oil environments. Unlike commercial humidity sensors that are often expensive, bulky, or not oil-compatible, this system uses a compact capacitive sensor paired with a 555 Timer IC to convert subtle changes in capacitance into frequency signals, eliminating the need for complex or costly signal processing. The system is built on a custom PCB for stability and can be calibrated easily using saturated salt solutions, ensuring reliable and accurate measurements. Its modular design also allows for integration into existing monitoring systems. Most importantly, it offers a practical, affordable alternative to laboratory testing methods, enabling continuous, on-site monitoring and supporting proactive maintenance strategies—something not commonly found in standard humidity sensing solutions for transformer oil.

Future plans

Based on test results, improvements will focus on enhancing the sensor’s packaging to increase oil resistance and ensure long-term reliability. Another key development is the integration of digital output features, such as microcontroller-based data logging or wireless transmission, to improve compatibility with modern transformer monitoring systems. Looking ahead, the goal is to create a fully integrated, plug-and-play humidity monitoring module that offers a low-cost, scalable solution for preventive maintenance in power systems— reducing unexpected failures and supporting more reliable energy infrastructure.

Awards

Best Research Paper