Power Transformer Monitoring

Power transformer health status & reliability monitoring

MISTRAS’ power transformer monitoring solutions provide operators with a complete and accurate condition analysis and health assessment of their power transformers.

By merging decades of substation reliability and transformer monitoring experience, along with a comprehensive suite of online/offline, onsite and laboratory diagnostic screening services, MISTRAS helps maximize transformer & substation reliability.

MISTRAS' comprehensive inspection, testing, and monitoring solution is offered as a four-step transformer reliability assessment program: SAMPLE, SCREEN, OBSERVE, and MONITOR. Each of the services listed below are offered as individual services, or as part of an integrated program.

Onsite and laboratory testing

In Dissolved Gas Analysis (DGA) tests, MISTRAS analyzes the insulating oil within a transformer, which creates gas as it breaks down. Studying gas distribution and rate of generation yields information about the presence, type, location, and severity of faults within the transformer.

Determining the health of your power transformer begins with the SAMPLE testing programs. Technicians perform Dissolved Gas Analysis (DGA) and Oil Quality Tests to assess the transformer's real-time condition and identify potential issues such as overheating, arcing, partial discharge, and other active or slow-evolving faults.

Oil quality tests are traditional testing methods that provide power transformer operators with an economical, yet marginal alternative to more advanced testing techniques. Our SAMPLE programs are utilized only as reliable first indicators, allowing specialists to further investigate areas of concern using advanced SCREEN spot inspection programs.

Transformer spot inspection services

SCREEN spot inspection services provide an advanced level of instantaneous fault detection and location capabilities. Issues that can be identified and characterized at this stage include loose connections, arcing, partial discharge, core clamping problems, unintentional core grounds, circulating currents, blocked radiators, localized overheating, mechanical defects, and high-temperature faults.

As industry-leading inspection experts, MISTRAS deploys a unique and purposeful range of advanced of field inspection techniques methods:

Acoustic emission (AE) accurately detects, measures, and locates flaws by “listening” to the frequencies of internal defects.
Vibration analysis (VA) measures and identifies signs of irregular or excessive in-service movement occurring within a unit.
Infrared imaging (IR) precisely identifies hot-spots and heat signatures caused by faults and defects.
High-frequency current transformer testing (HFCT) detects and measures partial discharge impulse activity. The combination of AE and HECT allows for optimal detection of electrical faults.

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Transformer overnight baseline testing

While the SCREEN stage helps to identify issues that are present at the time of inspection, symptoms may come and go. OBSERVE overnight baseline testing services place your transformers in the care of our certified specialists for a 24-hour observation period that captures fault activities as they occur.

In this stage, MISTRAS specialists review all compiled inspection data and issue a summary of their findings to transformer operators, in addition to a comprehensive condition-ranking summary that provides a clear overview of the transformer’s condition and outlines recommended courses of action.

Transformer acoustic and vibration monitoring

Finally, MISTRAS offers power transformer monitoring solutions, because early detection of potential faults is paramount. With 24/7 continuous health monitoring using MISTRAS’ industry-proven acoustic emission (AE) technology, MISTRAS enables transformer operators to track one, a few, or an entire fleet of power transformers.

MISTRAS’ transformer monitoring solutions offer a robust and easy-to-use web-based monitoring application that generates real-time health and condition based summaries designed to help improve your transformer's in-market availability.

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Online transformer testing services

Aside from our reliability programs shown above, MISTRAS offers a comprehensive line of a la carte online testing services, including:

Acoustic emission (AE): Acoustic Emission is a powerful tool used to "listen" and register acoustic signals of different frequencies generated within a power transformer. Utilizing around-the-clock proprietary AE technology, AE monitoring provides continuous condition readings, processed and analyzed though proprietary software.

Dissolved Gas Analysis (DGA) and Oil Quality Tests (Laboratory): Provides valuable and reliable diagnostic information about the condition of the insulating system allowing the identification of internal faults by analyzing the insulating oil. Combustible gas concentrations (PPM), as well as gas generating trends are calculated. Physical and dielectric properties of the oil are tested.

High-frequency current transformer testing (HFCT): Electrical Partial Discharge detection uses high-frequency current transformer testing (HFCT). These sensors measure high frequency currents produced by partial discharge and/or arcing though a transformer ground cable. The simultaneous use of AE and HFCT technologies allow the detection of electrical faults verses other sources.

Infrared imaging (IR): Through thermographic imaging technology, Infrared imaging generates quick and accurate readings, locating and detecting abnormal heating signatures, or ’hot spots’.

Sound Measurements Services: Measurement of audible sound from transformers originating from core and windings and transmitting through the dielectric fluid and/or structural supports to outer shell and/other solid surface, where it radiates as airborne sound. The frequency spectra of the audible sound consist primarily of the even harmonics of the power frequency.

Ultrasonic Testing (UT) Services: Ultrasonic wave measurements are performed to determine if activity associated with a defect has been detected. A quick measurement that allows operators to determine the condition of the asset.

Vibration Diagnostic Testing Services and Continuous Monitoring: Performed on in-service power transformers, Vibration tests serve as an additional method of continuous health status monitoring for the detection of mechanical failures, such as core/winding loosening.

Offline Transformer Testing Services

Has your power transformer been taken offline? Not a problem, as MISTRAS offers a a selection of offline testing services as well, including:

Dielectric Frequency Response Analysis (DFR)

Dielectric Frequency Response Analysis (DFR) is an offline testing method used to determine the moisture level in power transformers. Moisture can result in partial discharge, generate bubbles in the oil, and negatively impact the integrity and effectiveness of insulation . This test uses a lower-voltage level than power factor testing in its overall conductivity assessment in order to measure a wide range of temperatures.

Insulation Resistance Testing Services

The insulation resistance test uses a megohmmeter to study the internal insulation of power transformers. Insulation degrades with age, often accelerated by extreme temperatures and conditions, and this degradation can both create dangerous conditions and increase the likelihood of transformer faults or failure.

Transformer Turn Ratio (TTR) Testing Services

The Transformer Turns Ratio (TTR) is the number of turns in one transformer winding compared to the number of turns of other windings of the same phase in the transformer. The purpose of TTR is to help operators diagnose problems within their transformer’s winding turns and other components. This test detects short-circuits within windings, in addition to the detection of load tap changer alignment issues.

Sweep Frequency Response (SRFA) Testing Services

Movement of windings and conductors changes the capacitance created between transformer conductors. Sweep Frequency Response Analysis (SFRA) is an offline test in which different frequencies are injected to measure frequency response, and these results are plotted against baseline measurements to test transformer health and operation.

Winding Resistance Testing Services

An offline winding resistance test uses DC electric currents to check for differences between windings and for openings in their connections. Shorted turns, loose connections, deteriorating contacts, and other transformer faults will alter winding resistance and can be identified with this test.

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