Мониторинг изоляции трансформаторов: что можно контролировать в режиме онлайн?

Дата публикации:7 октября 2026 г., 15:54:38

  • Measurable online: dissolved gases (DGA), moisture in oil, partial discharge (PD), bushing capacitance and tan delta, winding hot-spot temperature and core/clamp ground current.
  • Estimated online: moisture in paper (calculated from oil data) and loss of life (calculated from hot-spot history). Both are indirect values.
  • Offline only: insulation resistance and polarization index, winding power factor, FDS/DFR, SFRA, furan analysis, paper DP and laboratory oil quality tests.
  • Best first sensors: online DGA with moisture, then fiber optic hot-spot sensing, then bushing monitoring, then PD and core ground current.
  • Practical rule: online data detects change early and continuously, while offline tests confirm alarms and supply accurate baselines. Both are needed.

Содержание

1. Insulation System Components: Winding Paper, Pressboard, Oil, Bushing Cores and Cast Resin

Transformer Insulation Condition Matters

Six parts of an oil-immersed insulation system

Copper and steel rarely wear out. Paper, pressboard, oil and resin age continuously from the day of energization, and their failure usually ends in a short circuit, an internal arc and a long outage.

  • Conductor insulation: paper wrapped around winding conductors, separating turns and discs.
  • Major insulation: pressboard barriers, spacers and oil ducts between windings, and between windings and the core or tank.
  • Insulating oil: fills every gap, impregnates the paper and carries heat away.
  • Bushing insulation: oil-impregnated or resin-impregnated paper condenser cores that carry conductors through the tank wall.
  • Tap changer insulation: insulation inside the OLTC selector and diverter.
  • Core insulation: laminations and the insulation between the core and its clamping structure.

Dry-type units replace oil and paper with cast resin or vacuum-pressure-impregnated (VPI) insulation, and air handles cooling. Monitoring principles stay similar, but parameters change, as covered in section 12.

2. Insulation Aging Stresses and the Online Sensors That Track Them

Stress and indicator reference

Stress Effect on Insulation Online Indicators
Thermal Breaks cellulose chains, reduces paper strength Hot-spot temperature, CO and CO₂, loss-of-life calculation
Влажность Speeds up aging, lowers dielectric strength, risk of bubbles Moisture in oil, estimated moisture in paper
Oxygen and oxidation Forms acids and sludge, accelerates paper aging Mostly laboratory tests, some indirect signs from DGA
Electrical PD erodes insulation, leading to tracking and breakdown PD monitor, hydrogen and acetylene in DGA, bushing tan delta
Mechanical Short-circuit forces and vibration loosen or crack insulation Limited online options, mainly offline tests

Stresses act together

Heat accelerates moisture release, moisture lowers the discharge threshold, and discharge produces gas and more heat. Reviewing transformer failure modes and detection methods shows how these chains end in actual failures.

3. Online vs Offline Indicator Table: DGA Monitor, Moisture Sensor, PD Sensor and FDS Tester

Quick answer table

Показатель Онлайн-мониторинг Что это показывает
Растворённые газы Yes, mature Active faults in oil and paper: PD, arcing, overheating
Moisture in oil Yes, mature Wetness of oil and, by estimation, of paper
Частичный разряд Yes, mature, needs expert setup Localized insulation defects before breakdown
Bushing capacitance and tan delta Yes, mature Condition of bushing condenser insulation
Winding hot-spot temperature Yes, mature Thermal aging rate and cumulative loss of life
Core and clamp ground current Yes, simple Core insulation faults and unintended grounding
Oil dielectric properties Limited, emerging sensors Oil contamination and aging
Paper degree of polymerization (DP) No, estimated indirectly Mechanical strength and remaining paper life
Furans in oil Mainly laboratory Paper degradation
Insulation resistance and polarization index No, offline Overall dryness and cleanliness of insulation
Winding power factor / tan delta No, offline Overall winding insulation condition
Frequency domain spectroscopy (FDS/DFR) No, offline Moisture content of solid insulation

How the methods fit together

Each online method covers one slice of the insulation picture. A structured мониторинг изоляции трансформатора program combines several of them and ties the results to offline test dates.

4. Online DGA Monitor: Dissolved Gas Signatures of Oil and Paper Faults

Индикаторы уровня газа

DGA is the most widely used online insulation indicator. Faults in oil and paper produce characteristic gases that dissolve in the oil, and an online monitor measures them continuously.

Газ Типичные признаки неисправности
Водород (H₂) Partial discharge, early sign of many faults
Ацетилен (C₂H₂) Arcing or high-energy discharge, serious even at low levels
Methane, ethane, ethylene Thermal faults of increasing temperature
CO, CO₂ Paper involvement, which is irreversible damage

Interpretation and selection points

5. Online Moisture-in-Oil Sensor: Relative Saturation and Paper Moisture Estimates

Why moisture matters

Wet paper can age several times faster than dry paper at the same temperature. Very wet insulation can also release bubbles during overloads, risking dielectric failure.

How online moisture sensing works

  • Измеренные значения: relative saturation (%RS) of the oil and oil temperature, from which water content in ppm is calculated.
  • Paper estimate: most water sits in the paper, not the oil, so systems estimate paper moisture from oil moisture and temperature using equilibrium relationships.
  • Reliability condition: estimates are best after the transformer has run at fairly steady temperature, because water moves slowly between paper and oil.

What trends reveal

  • Gradual moisture increase from leaking seals or a saturated breather.
  • Wet paper releasing water as the transformer heats up.
  • Effectiveness of drying treatments over time.
  • Bubble formation risk during planned overloads.

Moisture is usually measured by the DGA unit or by a dedicated probe. Combined oil readings fit into мониторинг состояния трансформаторного масла, alongside temperature, level and pressure data.

6. Partial Discharge Sensors: UHF Antenna, HFCT, Bushing Tap Coupler and Acoustic Probe

What PD is

Partial discharge is a localized electrical breakdown that does not bridge the full insulation gap. It occurs at voids, sharp edges, contaminated surfaces and weak spots. Each pulse is tiny, but continuous PD erodes insulation and is among the most common precursors to dielectric failure.

Online PD detection methods

Метод Sensor and Location Сильные стороны Ограничения
УВЧ Antenna through drain valve or dielectric window Good noise immunity, tank shields interference Needs tank openings, harder to calibrate in pC
HFCT Clamp-on sensor on neutral, core or tank ground lead Easy retrofit More sensitive to external noise
Bushing tap coupling Measurement through bushing test taps Close to IEC 60270 principles, shares bushing monitor hardware Needs tap adapters and noise suppression
Acoustic Piezoelectric sensor on tank wall Helps locate the PD source Signal attenuates, affected by mechanical noise

Setup requirements

Successful monitoring depends on noise suppression, pattern recognition and baseline measurements. Combining several techniques in one Система онлайн-мониторинга частичных разрядов трансформатора improves detection and source identification, and мониторинг частичных разрядов в трансформаторах explains each method in depth.

7. Bushing Tap Adapter: Capacitance and Tan Delta Monitoring

Why bushings deserve a dedicated monitor

Bushings are among the most failure-prone insulation components, and failures are often violent. Bushing insulation is also one of the easiest to monitor online, because the test tap gives direct access to the current through the main insulation.

Measured values

  • Capacitance (C1): increases when condenser layers short-circuit, showing progressive core breakdown.
  • Tan delta: rises with moisture, contamination and thermal aging.
  • Leakage current: combines both effects, and sum-current or reference methods use it to detect changes in any phase.

Continuous comparison against baselines and between phases is what makes the method sensitive. A система мониторинга проходных муфт трансформатора automates this comparison and raises trend alarms.

8. Fiber Optic Temperature Sensor: Winding Hot-Spot and Thermal Aging Rate

Temperature governs aging speed

Heat does not damage insulation suddenly, but it sets how fast insulation ages. Per IEC 60076-7, the aging rate of non-thermally upgraded paper roughly doubles for every 6 K rise in hot-spot temperature above 98 °C. Hot-spot measurement is therefore the most direct online way to track how quickly insulation life is being consumed.

Why fiber optic probes suit windings

Calculated outputs

  • Instantaneous relative aging rate.
  • Cumulative loss of life since commissioning.
  • Safe overload capacity for a given duration.
  • Bubble formation risk when combined with moisture data.

Limits and loading rules are summarized in Предельные значения нагрева трансформатора и номинальные характеристики.

9. Clamp-On Current Sensor: Core and Clamp Ground Current Monitoring

What the signal shows

Power transformer cores are grounded intentionally at a single point. When core insulation fails and a second ground path forms, circulating currents cause local overheating and gas generation.

Measurement and thresholds

  • Sensor: clamp-on current sensors on the core and clamp ground leads, simple and inexpensive.
  • Normal values: very small. Many utilities investigate above roughly 100 mA, although the right threshold depends on the design.
  • Confirmation: a rising core ground current together with thermal gases in DGA is a strong sign of a core insulation fault.

10. Oil Level Transmitter, Pressure Sensor, OLTC Monitor and Surge Recorder

Supplementary online indicators

11. Offline Test Equipment: Insulation Tester, FDS/DFR Analyzer, SFRA Set and Furan Lab Analysis

Tests that stay offline

Тест Why It Is Offline When to Perform
Winding insulation resistance and polarization index Needs DC test voltage on a de-energized unit Commissioning, routine outages, after events
Winding power factor / tan delta Needs isolation and controlled test voltage Commissioning and periodic outages
Frequency domain spectroscopy (FDS/DFR) Needs de-energized windings and low-frequency measurement When paper moisture must be quantified accurately
Sweep frequency response analysis (SFRA) Detects mechanical winding deformation, needs outage After short circuits, transport or relocation
Furan analysis and paper DP Needs laboratory analysis of oil or paper sample Periodically for aging, DP during internal inspection
Oil quality tests Breakdown voltage, acidity and interfacial tension are lab tests Every one to a few years

Combining both approaches

Online monitoring detects change early and continuously. Offline tests give accurate baselines, confirm alarms and measure properties sensors cannot reach. Comparing Онлайн-анализ DGA по сравнению с отбором проб нефти shows how the two complement each other.

12. Dry-Type Insulation Monitoring: Temperature Controller, Humidity Sensor and PD Detector

Parameters that replace oil data

Dry-type units have no oil, so DGA and oil moisture do not apply. Monitoring focuses on the following:

  • Winding temperature: governs resin and varnish aging and is limited by insulation class.
  • Частичный разряд: especially in cast resin units, where voids and cracks are the main defects.
  • Humidity and condensation: can cause surface tracking when a de-energized transformer is re-energized.
  • Dust and contamination: promote surface discharge and block cooling airflow.
  • Fan operation: cooling failure raises winding temperature quickly.

Параметры контроллера

Panel controllers such as the IB-S201 — устройство контроля и регулирования температуры сухих трансформаторов handle temperature and fan control locally. Projects needing wider condition data can add an интеллектуальная система онлайн-мониторинга состояния трансформаторов сухого типа.

13. Priority Matrix: DGA Monitor vs Hot-Spot Sensor vs Bushing Monitor vs PD System

Suggested order of installation

Приоритет Online Measurement Reason
1 DGA with moisture Covers the widest range of insulation faults with one instrument
2 Winding hot-spot temperature Governs aging rate and loading capability, specify at purchase for direct measurement
3 Мониторинг втулок High failure consequence, straightforward at higher voltages
4 Частичный разряд Valuable for high-voltage units, suspect units and after DGA shows PD signatures
5 Core ground current Low cost, useful where core faults are a known risk

Adjusting the order

14. FAQ: Transformer Insulation Monitoring Questions

Can insulation resistance be monitored online?

Not in the traditional sense. Insulation resistance and polarization index tests need DC voltage on de-energized windings. DGA, moisture, PD and bushing monitoring supply continuous insulation information instead.

Can the remaining life of paper insulation be measured online?

Not directly. Paper DP requires a physical sample. Online systems estimate paper condition from hot-spot temperature history, moisture and CO/CO₂ trends, and these estimates can be checked against laboratory furan analysis.

Which online measurement detects the most insulation problems?

DGA covers the widest range, including partial discharge, arcing, overheating and paper degradation. Results improve when combined with hot-spot temperature and moisture data.

Is PD monitoring necessary if I already have DGA?

DGA detects PD indirectly through hydrogen and other gases, but cannot locate the source or show the discharge pattern. Direct PD monitoring adds early warning, especially for high-voltage transformers and units with suspected defects.

Does online monitoring replace offline insulation testing?

No. Online monitoring reduces outage frequency and catches fast-developing faults, while offline tests such as winding power factor, FDS and SFRA remain essential for baselines and detailed diagnosis.

How accurate is online paper moisture estimation?

Accuracy depends on steady temperature and equilibrium between oil and paper. Use estimates to rank risk and trend change, and confirm with an FDS/DFR test before any drying decision.

Which sensors can be retrofitted to a transformer in service?

DGA and moisture monitors on drain valves, HFCT and acoustic PD sensors, bushing tap adapters and clamp-on core ground sensors can all be added in service or during a short outage. Winding fiber optic probes are normally embedded during manufacture or rewinding.

How do I choose an insulation monitoring scope for my transformers?

Collect rating, voltage class, age, oil test history and failure consequence, then send the data to the engineering team для согласованной схемы мониторинга.