Transformers are one of the most critical components in electrical power systems, facilitating the safe and efficient transmission of electricity across vast distances. Given their essential role in the infrastructure, the health and longevity of transformers are crucial for ensuring system reliability and avoiding costly downtime. Understanding the overall aging process of transformers is fundamental to their maintenance and operational management, which is why asset management specialists are paying more attention than ever to stresses on the transformer itself.
Transformers age over time due to a variety of factors, both internal and external. Thermal aging is one of the primary drivers, as the materials inside the transformer—especially the insulation—degrade due to continuous exposure to heat. The winding insulation, made of cellulose-based paper, deteriorates as its molecular structure breaks down, which is often accelerated by high operating temperatures.
Among the many factors contributing to transformer aging, through-faults, harmonics and Geomagnetic Induced Currents play a significant role, and monitoring these parameters can provide key insights into the wear and tear on the equipment. Effective monitoring helps asset managers make informed decisions about the lifespan, maintenance schedules, and replacement timelines of transformers, ultimately promoting grid stability and efficiency.
Through-Faults: Stress on the Transformer
Through-faults occur when a short circuit or other fault in the network leads to an abnormal current flow through the transformer. These high-magnitude currents, even for a brief duration, put immense thermal and mechanical stress on the transformer. Each through-fault introduces sudden surges of current that cause heating and mechanical forces inside the windings. While transformers are designed to handle short bursts of fault currents, repeated through-faults over time lead to cumulative damage.
Thermal degradation can occur when high current surges significantly raise the temperature of transformer components, particularly the windings. This heat causes insulation to degrade faster, weakening the internal structure of the transformer.
This leads to mechanical stress, as the high forces generated during through-faults can cause physical displacement or deformation of the windings and other internal parts. This mechanical strain increases the likelihood of internal faults and can lead to catastrophic failure if left unchecked.
Finally, repeated exposure to through-faults accelerates the wear and tear on the transformer, reducing its expected lifespan. Without proper monitoring and preventive measures, the transformer may fail prematurely, leading to costly repairs and unplanned outages.
Not Easily Detected
This degradation is not easily detected. Through faults generate mechanical stress and heating within the transformer windings and core, but transformer monitoring systems are generally focused on electrical measurements like voltage, current, and temperature. These standard sensors may not detect the rapid mechanical forces exerted on the transformer components by through-faults, making it hard to observe their impact.
Additionally, through-faults cause a spike in current similar to heavy load fluctuations. Monitoring systems might interpret through-faults as temporary load surges if the fault resembles typical load behavior, especially if the monitoring system isn’t tuned to differentiate between high-load conditions and fault conditions. This can make it difficult for standard monitoring systems to distinguish between a sudden load increase and a genuine fault.
Harmonics
Meanwhile, higher harmonic content in the electrical grid can significantly affect transformers by increasing their operating temperatures, which in turn strains their mechanical and dielectric strength. Harmonics are distortions in the electrical waveform, occurring at multiples of the fundamental frequency (50 Hz or 60 Hz). These distortions arise due to non-linear loads, such as variable frequency drives (VFDs), uninterruptible power supplies (UPS), and other power electronics.
These harmonics impact transformer performance and longevity in a number of key ways.
Harmonic Resonance and Overheating
Under certain conditions, harmonics can interact with the inductance and capacitance in the power system, leading to harmonic resonance. When resonance occurs, the harmonic currents are amplified, causing extreme levels of current and voltage distortion. This condition can result in localized overheating of transformer components, such as windings or the core.
Resonance-induced overheating poses a significant risk of damaging the transformer’s insulation, as the amplified currents can quickly raise temperatures beyond safe operating limits.
Straining Dielectric Strength
Transformers rely on insulating materials, such as oil and cellulose paper, to separate electrical conductors and withstand high voltages. Harmonics introduce higher-frequency voltage stress across the transformer windings, which can degrade the dielectric strength of the insulation through increased electrical stress and the occurrence of partial discharge.
The non-sinusoidal voltage waveform created by harmonics places additional electrical stress on the transformer’s insulation. Insulating materials are typically rated for smooth, fundamental-frequency voltage. When exposed to the rapid voltage fluctuations introduced by harmonics, the insulation experiences more frequent, high-magnitude electrical stresses, leading to faster degradation.
The higher frequency of harmonic voltages can also trigger partial discharge within the insulation. Partial discharges are small electrical sparks that occur in voids or impurities in the insulation material. Over time, these discharges erode the insulation, reducing its dielectric strength and increasing the risk of a dielectric failure or transformer breakdown.
As harmonics stress the dielectric properties of the insulation, the transformer’s ability to handle high voltages without failure diminishes, increasing the likelihood of insulation failure or dielectric breakdown.
Wind and PV Sources
Additionally, Wind and photovoltaic (PV) sources impact higher harmonic generation in power systems due to their inverter-based design and the non-linear nature of their power conversion processes. Unlike conventional generators, which produce a smooth, sinusoidal AC output, wind and PV systems use power electronics, specifically inverters, to convert their DC output into AC for grid compatibility. This conversion process introduces higher harmonics into the grid, impacting both power quality and system stability.
Geomagnetic Induced Currents
Geomagnetic Induced Currents (GICs) are low-frequency currents induced in power systems by geomagnetic disturbances (GMDs), such as solar storms. GICs can flow into transformers through grounding connections, leading to significant heating, mechanical stress, and insulation degradation that accelerate transformer aging and can prematurely age other equipment.
GIC-related heating causes the expansion and contraction of transformer materials due to temperature fluctuations. This cycling, especially during intense geomagnetic storms, can lead to mechanical wear over time.
The periodic thermal cycling causes mechanical deformation of the transformer’s internal components, particularly the windings, which may loosen or shift from their original positions. Over time, this strain can create partial discharges or even internal faults.
Meanwhile, core saturation can also lead to increased vibrations within the transformer, stressing its structural components and fasteners. Repeated mechanical stress shortens the transformer’s structural integrity, further accelerating aging.
The flow of GIC in transformers is the root cause of all GMD related power system problems.
- The magnitude of the GIC current and the associated DC offset is superimposed on the excitation current which forces the transformer into part-cycle saturation.
- GIC can result in increased reactive power requirements and large harmonic currents during GMD events.
- The harmonics can result in tripping of VAR compensation devices at times when additional VARS are needed most. This results in system disturbances and instability. Large GMD events are often associated with a variety of system alarms.
The Importance of Monitoring
Monitoring through-faults, harmonics, and GIC is essential for understanding the overall health and aging process of a transformer.
Early identification of excessive through-faults or harmonic levels can prevent catastrophic transformer failures. Since both factors accelerate aging, real-time electrical usage monitoring helps operators intervene before significant damage occurs. By responding to early warning signs, operators can take action to prevent faults that could otherwise lead to transformer explosions, fires, or long outages.
By tracking through-faults and harmonic distortion levels, operators can implement predictive maintenance strategies. Regular monitoring allows asset managers to understand how much stress the transformer has been subjected to over its operational life. Based on the frequency and severity of through-faults and harmonics, maintenance teams can schedule repairs or replacements at the right time, avoiding unexpected failures. Condition-based monitoring enables more efficient maintenance, extending the life of the transformer and optimizing costs by preventing over-maintenance or deferred maintenance, both of which can be expensive in the long run.
Condition Based Monitoring Solutions from Dynamic Ratings
The E3 Transformer Monitor harmonics and fault counter card is designed with the latest industry standards to capture the total fault count, maximum fault current, accumulated fault current, THD, and the ratio in percent of even/odd harmonics.
E3 Transformer Monitoring
The E3 Transformer Monitor measures and calculates current waveform harmonics and operates within the latest industry standards, and our E3 Transformer Monitor analytics provide an optimal platform for condition-based maintenance.
The E3 Transformer Monitor utilizes field-proven technology in data collection, analysis and visualization to communicate and notify changes in transformer conditions to prevent aging and extend the life of your assets.
Combining the E3 monitoring solution with an online transformer monitoring system as effective as LIFESTREAM® provides a comprehensive, data driven approach to condition monitoring for bushings, windings, OLTC, cool system and insulation of power transformers.
Though transformer failure most commonly occurs as the result of a through fault, it is typically not a single through fault which leads to failure, but the cumulative effects of a multitude of through faults to which the transformer is exposed during its lifetime.
The E3 Transformer Monitor harmonics and fault counter card is designed with the latest industry standards to capture the total fault count, maximum fault current, accumulated fault current, THD, and the ratio in percent of even/odd harmonics. Additionally, installing a circuit breaker monitor can help limit the number of faults that occur and provide additional protection for your transformer.
The E3 Transformer Monitor Improves Reliability
With online condition-based data, users receive alarms when problems first arise allowing earlier detection so that appropriate actions can be taken before problems arise and escalate. Transformer failure can be catastrophic, and knowing the condition of assets allows users to reduce failure rates and unplanned outages.
Reduce Maintenance Costs with the E3
The advanced analytics within the E3 monitoring system filters through the condition data to automatically identify issues requiring maintenance attention. This allows the Operations & Maintenance crews to focus on resolving problems rather than manually collecting data for offline condition assessment.
GIC Sensors
GIC sensors can also be installed to measure GIC events and communicate to the E3 in a matter of minutes without the need to de-energize equipment and without making modifications to the transformer neutral ground connection. The GIC Sensor split core design allows for easy installation, and provides a means to sense, measure and communicate DC ground currents in harsh utility environments.
Our GIC Sensor Features
- Range of the sensor can be easily adjusted
- Hall affect sensor provides excellent response time and is linear over the entire operating range
- Senses pure DC and quasi-DC up to 3Hz
- Bracket design allows for centering the sensor around the conductor and provides conduit support for 4-20mA output
- Core material is stable over a wide temperature range
- Hall effect sensor has excellent response time and is linear over the entire operating range
Active Monitoring Solutions
Understanding and monitoring the aging process of transformers is critical to maintaining their reliability, longevity, and efficiency.
By actively monitoring through-faults, harmonics, and GIC levels, operators can implement predictive maintenance strategies, optimize load distribution, and take preventive measures to extend the operational life of transformers.
Moreover, such monitoring helps avoid costly unplanned outages and catastrophic failures, while also ensuring compliance with industry regulations. For asset managers and power system operators, the insights gained from monitoring through-faults and harmonics are invaluable in preserving the health of transformers and ensuring the reliability of the electrical grid.
If you’d like to know more about how our hardware and software solutions can help you extend the life of your assets, contact us today and we’ll be happy to help.
Author: Tyler Willis, Dynamic Ratings