INNO glasvezel temperatuursensoren ,temperatuurbewakingssystemen.
- Analyse van opgelost gas (DGA) is the single most effective diagnostic technique for detecting internal faults in oil-filled stroomtransformatoren — including partial discharge, oververhitting, and arcing — before they escalate into catastrophic failures.
- A full-spectrum online DGA-monitoringsysteem continuously tracks seven key fault gases (H₂, CO, CO₂, CH₄, C₂H₆, C₂H₄, C₂H₂) with detection cycles as short as two hours, replacing slow and labour-intensive laboratory oil sampling.
- Diagnostic interpretation methods such as the IEC three-ratio method En Duval-driehoek translate raw gas concentrations into actionable fault-type identification, enabling condition-based maintenance strategies.
- Modern DGA monitors integrate seamlessly with SCADA platforms via Modbus, DNP3, En IEC 61850, feeding transformer health data into the utility’s broader asset-management workflow.
- Het juiste selecteren dissolved gas analysis equipment depends on gas coverage, meetnauwkeurigheid, communicatie protocollen, environmental rating, and whether the application calls for a standalone unit or a multi-parameter transformatorbewakingssysteem.
Inhoudsopgave
- What Is DGA Analysis and What Role Does It Play in Transformer Condition Monitoring?
- What Do the 7 Key Fault Gases in Transformer Oil Mean?
- What Is the Difference Between Online DGA Monitoring and Traditional Offline Oil Sampling?
- What Components Make Up a Complete Online DGA Monitoring System?
- How Does a DGA Monitor Automatically Detect Dissolved Gases?
- How Do the Three-Ratio Method and Duval Triangle Help Identify Fault Types?
- Key Technical Specifications of an Online DGA Monitor
- How Does a DGA Monitoring System Integrate with SCADA and Transformer Monitoring Platforms?
- Which Transformers Need Online DGA Monitoring the Most?
- How to Choose the Right DGA Monitoring Equipment — A Buyer’s Selection Guide
- What International Standards Apply to DGA?
- Veelgestelde vragen (Veelgestelde vragen)
1. What Is DGA Analysis and What Role Does It Play in Transformer Condition Monitoring?
Analyse van opgelost gas, commonly known as DGA, is a diagnostic technique that identifies internal faults inside oil-filled stroomtransformatoren by measuring the types and concentrations of gases dissolved in the insulating oil. When electrical or thermal faults occur inside a transformer — even at a very early stage — the insulating oil and cellulose paper decompose and release characteristic gases. Each fault type produces a distinct gas signature, which makes DGA one of the most reliable early-warning tools available to asset owners.
The technique has been used in laboratory settings since the 1960s, but the shift toward online DGA monitoring over the past two decades has transformed it from a periodic check-up into a continuous surveillance capability. By tracking gas trends around the clock, een online DGA-monitoringsysteem lets operators catch developing faults weeks or months before they would have been noticed through routine oil sampling. This is why DGA is widely regarded as the cornerstone of any modern bewaking van de toestand van de transformator programme.
2. What Do the 7 Key Fault Gases in Transformer Oil Mean?
International standards — including IEC 60599 En IEEE C57.104 — define seven gases as the primary indicators of transformer health. Each gas is associated with specific fault mechanisms, and their relative concentrations help engineers pinpoint the nature and severity of the problem. The table below summarises the relationship between each gas and its corresponding fault indication.
| Gas | Formula | Primary Fault Indication |
|---|---|---|
| Waterstof | H₂ | Gedeeltelijke ontlading, kroon, low-energy electrical activity |
| Methane | CH₄ | Low-temperature thermal fault (<150 °C) |
| Ethane | C₂H₆ | Medium-temperature thermal fault (150–300 °C) |
| Ethylene | C₂H₄ | High-temperature thermal fault (300–700 °C) |
| Acetyleen | C₂H₂ | Boogvorming, very high temperature (>700 °C) |
| Carbon monoxide | CO | Degradation of cellulose (papier) isolatie |
| Carbon dioxide | CO₂ | Thermal decomposition of paper insulation |
Why Seven Gases Matter
A simplified monitor tracking only one or two gases — typically hydrogen or acetylene — can indicate that something is wrong, but it cannot tell the operator what type of fault is developing. Full seven-gas coverage is essential for applying standard diagnostic methods such as the three-ratio method en de Duval-driehoek, both of which require multiple gas inputs to differentiate between thermal faults, gedeeltelijke ontlading, and arcing conditions.
3. What Is the Difference Between Online DGA Monitoring and Traditional Offline Oil Sampling?
Offline DGA involves an engineer extracting an oil sample from the transformer, shipping it to a laboratory, and waiting for results. The total turnaround time — from sampling to report — typically ranges from several days to two weeks. This approach has served the industry well for decades, but it has inherent limitations: the snapshot frequency is low (often quarterly or annually), sample handling errors can introduce inaccuracies, and a rapidly progressing fault may be missed entirely between sampling intervals.
Een online DGA-monitoringsysteem automates the entire process. The instrument mounts directly on the transformer, draws oil through an internal circuit, extracts and analyses dissolved gases, and uploads results to the control room — all without human intervention. Detection cycles can be as short as two hours, providing near-real-time visibility into gas trends. This continuous data stream enables operators to observe the rate of gas generation, which is often a more important diagnostic indicator than the absolute concentration.
When Does Offline Sampling Still Make Sense?
Offline laboratory analysis remains valuable for confirmatory testing, for transformers that are not critical enough to justify online monitoring costs, and for parameters beyond the scope of field instruments — such as furan analysis, interfacial tension, and detailed oil-quality testing. Many utilities adopt a hybrid strategy: online DGA monitors on their highest-risk transformers and periodic laboratory sampling on the rest of the fleet.
4. What Components Make Up a Complete Online DGA Monitoring System?
Een typisch DGA monitoring system consists of three functional layers that work together to deliver actionable data.
Front-End Monitoring Device
This is the field-mounted instrument installed directly on the transformer. It contains the oil-gas separation unit (using dynamic vacuum extraction or membrane technology), de gas chromatography analysis module with separation column and detectors, and the onboard microprocessor for data acquisition and local processing. The device connects to the transformer’s oil circuit via copper tubing and flanged valves.
Backend Software Platform
The centralised software collects data from one or more field devices and provides real-time dashboards, automated fault diagnosis (three-ratio method, Duval-driehoek, key-gas algorithms), historische trend, statistische analyse, and multi-level alarm management with email and SMS notifications.
Communication Infrastructure
Reliable data transmission between the field device and the backend platform is achieved through RS-485 serial cables, Ethernet, or fibre-optic links. Standard protocols include Modbus RTU/TCP, IEC 61850, En DNP3, ensuring compatibility with virtually any substation automation architecture.
5. How Does a DGA Monitor Automatically Detect Dissolved Gases?
The detection process in a gas chromatography DGA analyser follows a fully automated six-step cycle that repeats at a user-configurable interval.
Step-by-Step Workflow
Eerst, the instrument circulates transformer oil through its internal loop to obtain a representative sample. Seconde, a measured volume of oil enters the degassing chamber, where dynamic vacuum extraction releases dissolved gases from the oil matrix with high efficiency. Derde, the extracted gas mixture is injected into a chromatographic separation column, where individual gas components separate based on their molecular properties. Vierde, a high-purity nitrogen carrier gas pushes the separated components through sensitive detectors that generate proportional electrical signals. Vijfde, onboard electronics digitise the signals and apply calibration algorithms to calculate the concentration of each gas in parts per million (ppm). Sixth, the results are uploaded via the configured communication protocol to the backend platform for storage, trending, diagnostic interpretation, and alarm evaluation.
The entire cycle — from oil intake to data upload — completes within approximately two hours on a well-configured system. Operators can extend the interval to four, eight, or twenty-four hours depending on the transformer’s risk profile and carrier-gas conservation requirements.
6. How Do the Three-Ratio Method and Duval Triangle Help Identify Fault Types?
Raw gas concentration data becomes truly valuable when it is interpreted through established diagnostic frameworks. The two most widely used methods are the IEC three-ratio method en de Duval-driehoek.
IEC Three-Ratio Method
Defined in IEC 60599, this method calculates three ratios — C₂H₂/C₂H₄, CH₄/H₂, and C₂H₄/C₂H₆ — and maps the results to a fault-type code. The table below shows the primary diagnostic codes.
| C₂H₂/C₂H₄ | CH₄/H₂ | C₂H₄/C₂H₆ | Fouttype |
|---|---|---|---|
| <0.1 | <0.1 | <1 | Normal ageing |
| <0.1 | 0.1–1 | <1 | Gedeeltelijke ontlading (kroon) |
| <0.1 | 0.1–1 | 1–3 | Low thermal fault <150 °C |
| <0.1 | 0.1–1 | >3 | Thermal fault 150–300 °C |
| <0.1 | >1 | 1–3 | High thermal fault >700 °C |
| >3 | <0.1 | <1 | Low-energy discharge |
| >3 | 0.1–1 | <1 | Arc discharge |
Duval-driehoek
De Duval-driehoek plots the relative percentages of methane, ethyleen, and acetylene onto a triangular graph divided into fault zones — PD (gedeeltelijke ontlading), T1/T2/T3 (thermal faults of increasing severity), D1/D2 (low- and high-energy discharge), and DT (mixed thermal and electrical). It is visually intuitive and handles borderline cases more gracefully than ratio methods alone, which is why many DGA software platforms include both approaches for cross-verification.
7. Key Technical Specifications of an Online DGA Monitor
When evaluating dissolved gas analysis equipment, the specification sheet can be overwhelming. The table below highlights the parameters that matter most, using representative values from a full-spectrum gas chromatography DGA system designed for outdoor substation deployment.
| Parameter | Specificatie |
|---|---|
| Detected Gases | H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, CO, CO₂ (7 gassen); optional H₂O |
| Detectiebereiken | H₂: 2–2 000 ppm; CH₄/C₂H₆/C₂H₄/C₂H₂: 0.5–1 000 ppm; CO: 25–5 000 ppm; CO₂: 25–15 000 ppm |
| Meetfout | ±30 % of een vaste absolute limiet (per IEC 60567 / DL/T 722) |
| Oplossing | 0.1 ppm voor alle gassen |
| Herhaalbaarheid | RSD ≤5 % over 6 opeenvolgende testen |
| Minimale detectiecyclus | ≤2 uur (door de gebruiker configureerbare langere intervallen) |
| Methode voor het ontgassen van olie | Dynamische vacuümextractie |
| Draaggas | Zeer zuivere stikstof (N₂ ≥99,999 %); ≥400 analyses per cilinder |
| Mededeling | RS-485 / Modbus RTU, Ethernet / Modbus-TCP, IEC 61850, DNP3; 4–20 mA-uitgang |
| Voeding | AC 220 V±15 %, 50/60 Hz; of gelijkstroom 110 V / 220 V |
| Stroomverbruik | ≤800 VA (standaard) / ≤1 200 VA (uitgebreide configuratie) |
| Bedrijfstemperatuur | -40 °C tot +65 °C |
| Beschermingsgraad | IP55 (buiten installatie) |
| Afmetingen | 650 × 500 × 1 300 mm |
| Weight | Approx. 110 kg |
| Gegevensopslag | ≥10 jaar meetgeschiedenis |
| Diagnostische algoritmen | Methode met drie verhoudingen, Duval-driehoek, key-gas trending |
Waarom dynamische vacuümextractie belangrijk is
Sommige goedkopere DGA-instrumenten maken gebruik van membraangebaseerde olie-gasscheiding, die eenvoudiger is, maar lijdt aan verminderde gevoeligheid voor gassen met een lage concentratie – met name waterstof en acetyleen – en aan membraanveroudering in de loop van de tijd. Dynamische vacuümextractie zorgt voor een completere gasterugwinning, better long-term stability, en universele toepasbaarheid voor alle zeven doelgassen, waardoor het de voorkeursmethode is voor kritische transformatortoepassingen.
8. How Does a DGA-bewakingssysteem Integreer met SCADA- en Transformer Monitoring-platforms?
Op zichzelf staande DGA-gegevens zijn nuttig, maar de waarde ervan vermenigvuldigt zich wanneer het in het bredere operationele ecosysteem van het nutsbedrijf terechtkomt. Een goed ontworpen DGA monitoring system ondersteunt meerdere communicatietrajecten om deze integratie eenvoudig te maken.
Op onderstationniveau, de DGA-monitor wordt aangesloten op de Remote Terminal Unit (RTU) of baycontroller via RS-485 (Modbus RTU) of Ethernet (Modbus-TCP / IEC 61850). De RTU stuurt gasconcentratiewaarden door, alarm states, en diagnostische codes voor de SCADA master station, where they appear alongside load current, wikkel temperatuur, oliepeil, and other conventional measurements. Dispatchers can set high-priority alarms for gases like acetylene that indicate severe faults, ensuring immediate visibility during storm loading or abnormal operating conditions.
Multi-Parameter Correlation
The greatest diagnostic accuracy comes from correlating DGA trends with data from complementary sensors — fibre optic winding temperature monitors, detectoren voor gedeeltelijke ontlading, bushing capacitance and tan-delta monitors, core grounding current monitors, En on-load tap changer monitors. Bijvoorbeeld, a simultaneous rise in ethylene and a hot-spot temperature spike strongly confirms a thermal fault, while coincident hydrogen elevation and partial-discharge UHF pulses point to an electrical fault. Geïntegreerd transformer monitoring platforms automate this cross-verification, reducing reliance on manual expert interpretation.
9. Which Transformers Need Online DGA Monitoring the Most?
Not every transformer in a fleet requires continuous dissolved gas surveillance. The investment is best directed at assets where the consequences of an undetected fault are highest.
High-Priority Applications
Transmission-voltage main power transformers at utility substations top the list, omdat het falen ervan wijdverbreide storingen veroorzaakt en de levertijden voor vervanging meer dan twaalf maanden kunnen bedragen. Generator step-up transformers at power plants — thermal, waterkracht, and nuclear — are equally critical because an unplanned trip removes generation capacity from the grid. Large industrial process transformers serving petrochemical plants, staalfabrieken, faciliteiten voor de fabricage van halfgeleiders, and data centres also justify online monitoring due to the enormous cost of production downtime.
Increasingly Common Applications
De uitbreiding van hernieuwbare energie heeft een nieuwe vraag gecreëerd. Collector- en verbindingstransformatoren bij windparken En zonneparken operate under highly variable loading and are often located in remote areas where manual oil sampling is expensive and infrequent. Tractiestroomtransformatoren voor elektrificatie van het spoor systems carry safety-critical loads where service continuity directly affects public safety. Ageing transformers operating beyond their original design life are another strong candidate — continuous DGA trending supports risk-based lifetime extension decisions rather than conservative early replacement.
10. How to Choose the Right DGA Monitoring Equipment — A Buyer’s Selection Guide
With several products on the market — from single-gas hydrogen sensors to full seven-gas chromatography systems — choosing the right dissolved gas analysis equipment can be confusing. The following criteria will help narrow the field.
Gas Coverage
If the goal is comprehensive fault diagnostics, insist on full seven-gas detection. Single-gas or three-gas monitors are suitable only for basic screening on lower-priority assets.
Measurement Accuracy and Degassing Method
Look for compliance with IEC 60567 nauwkeurigheidseisen. Instruments using dynamic vacuum extraction generally outperform membrane-based designs on low-concentration gases and long-term stability.
Ondersteuning voor communicatieprotocollen
Ensure the device supports the protocol already in use at your substation — Modbus RTU, Modbus-TCP, DNP3, of IEC 61850. Retrofitting a protocol converter adds cost and a potential point of failure.
Milieubeoordeling
For outdoor installation, specify IP55 or higher and verify the operating temperature range covers your site’s climate extremes. Units rated from -40 °C tot +65 °C suit the vast majority of global locations.
Carrier Gas Strategy
Cylinder-based carrier gas is simpler and cheaper upfront, but cylinders require periodic replacement. A built-in nitrogen generator eliminates replacement visits — an important advantage for remote sites or large fleets where logistics costs add up.
Software and Diagnostics
The backend software should include three-ratio analysis, Duval Triangle plotting, customisable alarm thresholds, historische trend, en het genereren van rapporten. Cloud or web access for mobile viewing is increasingly expected.
11. What International Standards Apply to DGA?
Three documents form the backbone of DGA practice worldwide. IEEE C57.104-2019 (Guide for the Interpretation of Gases Generated in Mineral-Oil-Immersed Transformers) is the primary reference in North America; it introduced a four-level status classification based on individual gas concentrations and rates of change. IEC 60599 (Mineral Oil-Filled Electrical Equipment in Service — Guidance on the Interpretation of Dissolved and Free Gases Analysis) provides the internationally recognised three-ratio and Duval Triangle diagnostic frameworks. IEC 60567 (Oil-Filled Electrical Equipment — Sampling of Gases and Analysis of Free and Dissolved Gases — Guidance) defines the measurement methodology and accuracy requirements that online DGA instruments must meet.
Aanvullende referenties zijn onder meer CIGRE Technische brochure 771 (Advances in DGA Interpretation) and regional standards such as China’s DL/T 722 and DL/T 1498. When specifying a DGA monitoring system, referencing these standards in the procurement document ensures that the supplied equipment meets internationally accepted performance benchmarks.
12. Veelgestelde vragen (Veelgestelde vragen)
Q1: Can a DGA monitor detect all transformer faults?
DGA excels at detecting thermal faults, gedeeltelijke ontlading, and arcing inside the oil-filled tank. Echter, it does not directly detect external faults such as bushing failures, tap-changer contact wear, or cooling-system blockages. Een veelomvattend transformatorbewakingssysteem combines DGA with complementary sensors for full coverage.
Vraag 2: How often should an online DGA system run its detection cycle?
A two-hour cycle provides near-real-time awareness for high-risk transformers. Voor stabiel, lower-risk units, an eight- or twenty-four-hour interval conserves carrier gas while still capturing meaningful trends. Most systems allow operators to adjust the interval remotely.
Q3: Does an online DGA monitor eliminate the need for laboratory oil analysis?
Nee. Laboratory analysis covers additional parameters — furan content, diëlektrische doorslagspanning, zuurgraad, interfacial tension — that field instruments do not measure. Industry best practice is to use online DGA for continuous surveillance and laboratory sampling for periodic comprehensive oil-quality assessment.
Q4: What does a sudden rise in acetylene (C₂H₂) indicate?
Acetylene is produced by high-energy arcing at temperatures above 700 °C. A sudden spike is one of the most serious DGA alarms and typically warrants immediate investigation, load reduction, and — depending on the magnitude — emergency de-energisation.
Vraag 5: Is a seven-gas monitor always better than a single-gas hydrogen sensor?
A single-gas hydrogen sensor costs less and requires less maintenance, making it suitable for basic screening on non-critical assets. Echter, it cannot differentiate between fault types. For any transformer where accurate diagnostics and standards-based interpretation are needed, a full seven-gas DGA analyser is the recommended choice.
Vraag 6: How long does it take to install a DGA monitoring system on an existing transformer?
Most installations require connecting oil inlet and outlet tubing to existing transformer valve ports, mounting the instrument enclosure on a platform or concrete pad, routing communication cables, and performing calibration verification. Ervaren technici kunnen het werk doorgaans binnen één ploegendienst voltooien – vaak zonder transformatoruitval als er al geschikte kleppoorten beschikbaar zijn.
Vraag 7: Wat is TDCG en waarom is het belangrijk??
TDCG staat voor Total Dissolved Combustible Gas – de som van H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, en CO. IEEE C57.104 gebruikt TDCG-drempels om de toestand van de transformator in vier statusniveaus te classificeren. Een stijgende TDCG-trend, zelfs als geen enkel afzonderlijk gas de alarmdrempel heeft bereikt, kan duiden op een zich ontwikkelende fout en zou tot verder onderzoek moeten leiden.
Vraag 8: Kunnen meerdere DGA-monitoren rapporteren aan één backendplatform?
Ja. De meeste systemen ondersteunen een N:1 architectuur waarbij meerdere in het veld gemonteerd zijn DGA monitors communicate with a single centralised software platform. This is the standard configuration for substations or industrial facilities with several transformers, reducing total system cost and simplifying fleet-wide data management.
Vraag 9: How often does a DGA monitor need calibration?
Manufacturers typically recommend calibration verification every six to twelve months using a certified standard gas mixture. Some units include an automatic self-check function that flags drift between scheduled calibrations. Annual calibration is the most common practice across the industry.
Q10: What is the typical lifespan of an online DGA monitoring system?
With regular maintenance — calibration, carrier gas replacement, and periodic inspection of oil tubing and seals — a quality DGA monitoring system operates reliably for ten years or more. Data storage capacity of ten-plus years ensures that the full trend history remains available throughout the instrument’s service life.
Vrijwaring: De informatie in dit artikel is uitsluitend bedoeld voor algemene educatieve en referentiedoeleinden. FJINNO (www.fjinno.net) geeft geen garanties, expliciet of impliciet, wat betreft de volledigheid, nauwkeurigheid, of de toepasbaarheid van de inhoud op een specifiek project of installatie. De technische specificaties waarnaar hierin wordt verwezen, vertegenwoordigen typische waarden en kunnen variëren afhankelijk van het transformatortype, oil condition, en siteomgeving. Engineering decisions should always be based on site-specific assessments conducted by qualified professionals in accordance with applicable standards including IEEE C57.104, IEC 60599, IEC 60567, en lokale netcodes. Productnamen van externe fabrikanten zijn handelsmerken van hun respectievelijke eigenaren en worden uitsluitend ter informatie vermeld. FJINNO is niet aansprakelijk voor verlies of schade die voortvloeit uit het gebruik van of het vertrouwen op deze informatie.
Glasvezel temperatuursensor, Intelligent monitoringsysteem, Gedistribueerde glasvezelfabrikant in China
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