溶存ガス分析 (DGA) は、電源変圧器の内部状態を評価するための重要なツールです。水素 (H₂) は最も一般的な特性ガスの 1 つですが、その発生源は通常の材料の化学反応から部分放電や過熱などの初期故障に至るまで多岐にわたります。水素源を正確に特定することは、変圧器の状態評価とメンテナンスの意思決定に不可欠です。
This article systematically reviews the main sources, generation mechanisms, and identification methods for hydrogen in transformer oil, and highlights the drawbacks of relying solely on single‑gas hydrogen monitoring.
ガス発生メカニズムと関連特性に基づいて、水素供給源は内部欠陥、材料化学反応、外部要因の 3 つのカテゴリに分類されます。
Mechanism: Weak discharge causes oil molecule cracking → H₂ generation.
Gas signature: H₂ dominates (>80%), trace CH₄ and C₂H₆ possible, almost no C₂H₂.
Key indicator: Isolated H₂ rise with very low other hydrocarbons.
Mechanism: Thermal breaking of C‑H bonds releases H₂.
Gas signature: CH₄, C₂H₆, C₂H₄ appear depending on temperature; H₂ level usually lower than in discharge cases.
Key indicator: H₂ rise accompanied by significant hydrocarbon gases (especially C₂H₄).
| Type | Mechanism | Typical Scenario | Gas Signature |
|---|---|---|---|
| Moisture‑involved reaction | Fe + H₂O → FeO + 2H → H₂ | High humidity, poor sealing | H₂↑ + moisture↑ |
| Cyclohexane catalytic dehydrogenation | Cyclohexane → Benzene + H₂ (Ni catalyst) | Stainless steel bellows expanders | Isolated H₂↑ (up to thousands ppm) |
| Metal corrosion | Electrochemical rusting produces H₂ | Rust in tank, core, coolers | Isolated H₂↑, possible moisture↑ |
Residual hydrogen in new oil: Dissolved during refining, transport, or filling – common in newly commissioned transformers, decreases with operation.
Improper oil treatment: Insufficient vacuum, short processing time, or poor temperature control can increase dissolved gases including H₂.
Core principle: Never rely on hydrogen concentration alone – combine multi‑dimensional information.
| H₂ Trend | Accompanying Gases | Moisture | Most Likely Source | Action |
|---|---|---|---|---|
| Isolated rise | No hydrocarbons, CO normal | Normal | Cyclohexane dehydrogenation, residual H₂ | Monitor only |
| Isolated rise | No hydrocarbons, CO normal | Elevated | Moisture‑related corrosion | Check sealing, treat moisture |
| Rise | CH₄, C₂H₄ etc. | Normal or elevated | Overheating | Electrical tests, plan inspection |
| Rise (dominant) | Trace CH₄, C₂H₆, no C₂H₂ | Normal | Partial discharge | PD measurement, consider outage |
| Rise | C₂H₂ present | Normal | Arcing (severe) | Immediate outage |
H₂↑ + 水分↑ → 水分反応または腐食
H₂↑ + 水分通常 → 放電、接触脱水素、または残留H₂
Rapid continuous increase → Active fault, need outage
Peak then stable/declining → Commissioning “break‑in” or catalytic equilibrium
Seasonal fluctuation → Moisture‑related reactions
高 PD、超音波異常 → 部分的放電
アンバランスなDC抵抗、異常なコア接地電流、IRホットスポット → 過熱
すべてのテストは正常+耐用年数が短い → 材料/プロセス要因
Principle: CO is a specific byproduct of solid insulation (cellulose) thermal decomposition. Material/chemical hydrogen sources do not involve insulation heating, so CO remains normal.
意思決定ロジック:
H₂↑ + CO 通常 → 良性水素 (材料/プロセス) – 不必要なものなし停止。
H₂↑ + CO↑ → 固体絶縁体 (複数のコア接地など) を伴う過熱 – 警戒してください。
CO↑ + H₂ 正常 → 通常の熱老化 – 異常ではありません。緊急.
Practical value: Using H₂ and CO as a paired indicator significantly reduces false alarms and avoids costly unnecessary inspections.
Situation: 220kV transformer, 3 months in service, H₂ = 1500 μL/L, other gases <1 μL/L, moisture normal, all electrical tests normal.
Diagnosis: Cyclohexane catalytic dehydrogenation.
Outcome: After 1 year, H₂ stabilized at ~800 μL/L – no action needed.
Situation: 110kV transformer, 10 years in service, H₂ = 380 μL/L, CH₄ = 45 μL/L, C₂H₄ = 28 μL/L, moisture rose from 12 to 25 mg/L.
Diagnosis: Moisture‑induced rust reaction with mild overheating.
Outcome: Internal inspection revealed core rusting; after treatment, H₂ returned to normal.
Relying solely on hydrogen monitoring carries significant false‑alarm risks because:
水素源は多様であり、良性 (材料/プロセス) および故障関連 (放電/過熱) は H₂ と区別できません。単独。
単一ガスのデータでは、障害の種類、重大度、または位置を特定できません。
It can lead to two extremes: missing major faults (assuming benign) or frequent false alarms → unnecessary outages and wasted resources.
推奨事項:
Prefer multi‑component DGA (at least H₂ + CH₄ + C₂H₂ + CO + moisture).
新たに稼働するガスの上昇を許容する変圧器ですが、傾向を追跡して CO.
For isolated H₂ rise with normal CO – do not rush to outage; enhance monitoring or perform degassing.
Q: What is the typical alarm threshold for hydrogen in transformer oil?
A: Usually >150 μL/L warrants attention, but thresholds vary by voltage class and asset type – trend analysis is more important.
Q: How long does it take for hydrogen to drop in a new transformer?
A: Typically 1‑3 months of operation or hot oil circulation. If H₂ remains high with hydrocarbon gases, further investigation is needed.
Q: Are single‑gas hydrogen monitors still useful?
A: They can provide basic early warning for distribution‑class transformers, but for critical assets, upgrade to multi‑component DGA is strongly recommended.
HERTZINNO’s online DGA systems (DGA900, DGA500, DGA300) support multi‑component gas plus moisture monitoring, effectively avoiding false alarms caused by single‑gas hydrogen monitoring. Learn more →
