Transformer monitoring

Transformer monitoring

Transformer monitoring is essential for ensuring the reliability and efficiency of power distribution networks. As vital components in voltage regulation and energy transmission, transformers require continuous monitoring to detect potential issues early on. From temperature and partial discharge to moisture levels, monitoring provides valuable insights for proactive decision-making, preventing unplanned outages and catastrophic failures.

Transformer temperature monitoring

Monitoring temperature is a fundamental aspect of transformer health, influencing various components. Higher temperatures may signal faults, risking further damage if unattended. It’s crucial to measure temperatures in different areas:

  • Top oil temperature
  • Bottom oil temperature
  • Winding hot spot temperature
  • Ambient temperature
  • External compartment type on load tap changer

Winding insulation, sensitive to temperature and moisture, makes power transformer monitoring the hot spot crucial. This directly impacts the transformer’s aging rate; for every 6˚C increase above the rated maximum of 110˚C, the aging rate approximately doubles.

How to measure transformer temperature

  1. Traditional temperature gauges
    • Oil Temperature Indicator (OTI) and Winding Temperature Indicator (WTI) Gauges, developed in the 1940s, offer reliable control of cooling systems and thermal protection. Regular maintenance and calibration are necessary for accuracy. However, mechanical damage to WTIs can lead to inaccurate readings, impacting cooling efficiency.
  2. Electronic temperature monitors (ETM)
    • ETMs replace analog gauges, consolidating temperature data and cooling control. They enhance accuracy by utilizing transformer design information to calculate winding hot spot temperature. With electronic communication, ETMs provide remote data access, detailed record-keeping, and robust fail-safe designs for added reliability beyond traditional gauges.
  3. Fiber optic temperature probes
    • Providing real-time direct winding monitoring, fiber optic temperature probes validate thermal models. Installed in windings, these probes send light pulse signals to a transformer monitor, enabling direct communication of winding data to utilities. Particularly suitable for critical transformers, the reasonable cost of adding fiber optic probes makes them a viable option for bulk power transformers.

Dissolved gas analysis (DGA)

Dissolved gas analysis (DGA) is a diagnostic technique used to assess the condition of power transformers. Transformers contain insulating oil, and as the transformer operates, various gases are generated within the oil due to the breakdown of insulation materials and other internal processes. By analyzing the composition and concentration of these dissolved gases, DGA provides valuable insights into the transformer’s health and potential issues. 

Bushing monitoring

Bushings serve as the interface between the high-voltage components of the transformer and the external power system, providing insulation and electrical integrity. Monitoring these vital components involves a comprehensive approach that encompasses both electrical and mechanical aspects, allowing for the early detection of potential issues and facilitating timely maintenance.

Electrical monitoring

The focus is on evaluating key parameters such as capacitance, power factor, and partial discharge activity. Changes in these electrical characteristics can be indicative of insulation degradation or other issues within the bushing. By closely monitoring and analyzing these variables, operators can gain insights into the health of the bushing and make informed decisions regarding maintenance or replacement, preventing potential failures that could disrupt the transformer’s performance.

Mechanical monitoring

On the mechanical monitoring front, the assessment shifts towards the physical aspects of the bushing. Parameters such as vibration, oil levels, and temperature are scrutinized to identify signs of mechanical stress or potential failure. Unusual vibrations or deviations in temperature can be early indicators of issues that, if addressed promptly, can mitigate the risk of catastrophic failure. Mechanical monitoring, therefore, provides a proactive approach to bushing health, contributing to the overall resilience of power transformers and the stability of electrical grids.

Partial discharge monitoring

Partial discharges (PD), indicative of localized insulation breakdowns, emit small electrical energy amounts. Effective monitoring is essential for early fault detection, preventing catastrophic failures, and ensuring power transformers’ reliability.

One method for measuring partial discharge is electrical monitoring, involving sensors capturing signals associated with PD. Analyzing parameters like frequency and amplitude provides real-time insights into insulation conditions, enabling proactive maintenance.

Ultra high frequency (UHF) monitoring captures electromagnetic waves from partial discharges in a high-frequency range. This method allows for precise localization of discharge sources, aiding targeted maintenance and offering a non-intrusive approach with high sensitivity.

Ultrasonic monitoring, the third method, detects sound waves produced by partial discharges. Placing sensors strategically on the transformer enables early detection and localization of discharges, contributing to proactive maintenance and overall system reliability.

Moisture monitoring

The insulation system of transformers is highly sensitive to moisture, and excessive moisture levels can lead to insulation degradation, reduced dielectric strength, and an increased risk of faults. Monitoring and controlling moisture levels within transformers ensure transformer reliability and prevent potential failures. Various methods are employed for moisture monitoring in power transformers:

Hygroscopic sensors

Hygroscopic sensors directly measure the moisture content in the insulation oil. These sensors provide real-time data on moisture levels, allowing operators to take prompt action if levels exceed acceptable limits.

Dew point measurement

Dew point measurement involves assessing the temperature at which moisture in the transformer oil would condense. Monitoring the dew point provides insights into the potential for moisture condensation within the transformer.

Effective moisture monitoring allows operators to implement timely maintenance, reduce the risk of insulation failure, and extend the lifespan of power transformers. 

Geomagnetic induced current monitoring

Geomagnetic induced current (GIC) results from solar coronal mass ejections (CMEs) interacting with Earth’s magnetosphere through electromagnetic induction, causing geomagnetic disturbances (GMD). During CME events, the solar wind carries magnetic particles, inducing dynamic magnetic fields on Earth’s surface. These fields interact with Earth’s conductivity, creating ground voltage differences that drive GIC flow. This current traverses through the neutral conductors of interconnected transformers.

GIC is a prime factor in power system issues during Geomagnetic disturbances (GMD). The flow, coupled with a DC offset, overlays on transformer excitation currents, inducing partial-cycle saturation. This leads to increased reactive power demands and substantial harmonic currents during GMD events. Harmonics can trigger the tripping of Voltage-Ampere reactive (VAR) compensation devices at critical moments, causing system disturbances and instability. Significant GMD events often accompany various system alarms.

Monitoring GIC levels helps in understanding potential transformer saturation and implementing preventive measures to mitigate its impact.


To keep the transformer operational and mitigate any risks, transformer monitoring and potential transformer maintenance are essential.

At TTES, we have over 100 combined years of experience manufacturing, maintaining, and repairing transformers. If you’re looking for industry-leading lead times of just 20 weeks on average, don’t hesitate and reach out to us for a free quote!

Categories :

Share This Article :

Satisfaction guarantee

With our OEM network and 100+ years experience, we ship in 20 weeks. Transparency and satisfaction guaranteed on every projects.

Get your transformer at an unrivaled speed