5,000 kVAの容量を持つ変圧器は、水曜日の午前11時20分に差動保護でトリップします。工場の電気技師が到着すると、ブクホルツリレーに明らかなガスの蓄積とタンクに小さな膨らみがあることがわかります。その間に、生産管理者は電気技師に運転に戻ることができるのはいつかと尋ねています。これは、一般的な変圧器の故障とその原因、さらには迅速な処理技術の知識が冷静な反応とパニック反応を分ける時です。変圧器の故障のほとんどはランダムではなく、よく知られた変圧器の故障とタイプのいくつかのグループに分類され、簡単に認識、理解、技術的に事前に定義された方法で修正できます。.
記事では、一般的な変圧器の故障がどのように分類されるか、異なる故障の原因、一般的な変圧器の問題を認識する方法、そしてステップバイステップで何をすべきかについて説明しています。損害修理のための通常の値、新しい機器の購入に対するコスト、問題が発生した際に製造業者に連絡する方法とタイミングに関するヒントも見つかります。.
一般的な知識によれば、変圧器で発生する最も一般的な故障は、絶縁の失敗と湿気の侵入、変圧器の巻線短絡、コアの問題（電流の循環と緩んだクランプ）、タップチェンジャーの欠陥、ブッシングの故障、冷却システムの故障、油の汚染によって引き起こされます。.
変圧器故障ファミリー：概要
IEEE作業グループとCIGRÉは、信頼性調査において変圧器の故障をいくつかのコンポーネントに分散させてきました。故障統計は電圧クラスによって異なりますが、変圧器の故障の主な要因には、絶縁システム、タップチェンジャー、ブッシング、巻線、冷却/アクセサリーが含まれます。優勢なパターンを知ることは、より良い予防と対応につながります：
| 故障ファミリー | 故障の典型的な割合 | 発展速度 | 主な検出 |
|---|---|---|---|
| 絶縁システム（巻線、紙、油） | 30–50% | ゆっくりから中程度 | DGA、油の湿気、IRテスト |
| タップチェンジャー（OLTC/DETC） | 10–25% | 中程度 | OLTC油DGA、機械検査 |
| ブッシング | 5–15% | 突然 | 視覚、PD、タンデルタ |
| 巻線短絡/機械的損傷 | 5–15% | 突然（しばしば通過故障後） | 差動保護、DGA、巻線テスト |
| コアと磁気回路 | 3–8% | ゆっくり | ノイズ、コア接地電流 |
| 冷却システムとアクセサリー | 5–15% | ゆっくり | 温度傾向、視覚 |
データは二つの重要な教訓をもたらします。第一に、変圧器の故障の大多数は回避可能または検出可能であり、最大のファミリーはゆっくりと劣化します。第二に、迅速な故障（ブッシングと巻線短絡）は、雷、切り替えの乱れ、または通過要素などの外部要因から発生することが多く、保護の調整や運用の良い実践がメンテナンスと予防の両方にとって不可欠であることを示しています。.
絶縁破壊と湿気の侵入
絶縁障害は最も一般的な変圧器の故障タイプです。油-filled 変圧器の絶縁システムは、油、紙、プレスボードで構成されており、熱劣化、湿気、部分放電の3つの原因によって劣化します。.
- 熱は紙絶縁の破壊を引き起こし、COおよびCO2を放出し、その機械的強度を弱めます。ユニットの最も熱い部分の温度が通常の運転の必要性を超えて6-8K上昇するごとに、絶縁のサービス寿命は半分に短縮されます。数年間常に加熱されていた機器は、故障する前に予期せず脆くなることがあります。.
- 水は、ブリーザー、漏れ、または不良シールを通じて変圧器に侵入する可能性があります。これにより、油の破壊電圧が低下し、紙の劣化プロセスが加速します。油の湿気に対する通常の警報値は20-30 ppmの範囲内であり、IEC 60156規格に従って30 kV未満の破壊電圧は深刻な脅威を示します。.
- 空気の空洞、気泡、層は局所的な放電を引き起こし、絶縁が短期間で劣化します。結果として得られるDGAの読み取り値は窒素とメタンが支配し、PDが診断を確認します。.
上記の問題が検出された場合、変圧器は運転を停止するか、負荷を減少させ、湿った油を交換し、DGAおよびPDテストを実施する必要があります。絶縁劣化の確認は適切な措置を必要とします。.
巻線短絡と機械的損傷
巻線故障は一般的に突然かつ激しく発生します。巻線故障の従来の誘発要因は通過故障であり、LV側の短絡は変圧器の巻線を通過する巨大な機械的力を生成し、コイルを圧縮、曲げ、または移動させます。クランプシステムが不十分で、絶縁が長期間使用されている場合、通過故障は巻線の故障を引き起こし、その後の起動時にターン間短絡が発生します。DGA分析はエチレンのレベルが上昇していることを示し、多くの場合、アセチレンも確認され、差動または過電流保護がオフになります。.
トリップ後は直ちに行動を起こしてください。スイッチをすぐに閉じることは避けてください。保護のフラグを観察し、油とガスのサンプルを取り、各相の巻線抵抗を測定する必要があります（2-3 %を超える差異はターン故障を示します）。欠陥が発見された場合、変圧器は点検または巻き直しのために運転を停止する必要があり、コアまたはタンクが損傷している場合は交換の可能性もあります。.
コア故障：クランプ、循環電流、および接地
コア欠陥は静かに成長します。十分でないコアクランプは振動や機械的摩耗を引き起こし、ハミングや「ガタガタ」音の変化を引き起こします。層間の絶縁の故障や意図しない二重接地によるコア内の循環電流は、メタンやエチレンなどのガス形成とともにコアの過熱を引き起こします。コアの単点接地が望ましく、必要ですが、二点接地は加熱を引き起こすループを作ります。.
問題が疑われる場合は、コア接地電流を測定する必要があります（正常値はミリアンペアであり、値がアンペアの電流と等しくなると、二点接地があることを意味します）、DGAテストを実施し、タンクが開いている場合はコアクランプを確認します。二重接地に関連する欠陥を修正するには多くの時間がかかる可能性があるため、コアの取り外しが必要になることを考慮する必要があります。.
タップチェンジャーの故障
負荷時タップチェンジャーはトランスの可動部であり、5年以上経過したトランスの故障の主な原因の一つです。一般的な故障モードには、接点の摩耗や焼損、駆動機構の詰まり、OLTCコンパートメント内の油の汚染、位相の不整合が含まれます。潜在的な問題の症状には、電圧の故障、タップ変更中の騒音、OLTC油中の高濃度のガスが含まれます。.
OLTCが正しく動作しない場合は、シャットダウンし、駆動モーターの電流を確認し、DGAを使用して油を別途テスト用にサンプリングする必要があります。通常、接点を交換するか、OLTCを再生する必要があり、そのコストはOLTCのサイズに応じて$5000-$40,000です。.
ブッシングの故障
ブッシングはいつでも故障する可能性があり、ブッシング故障の結果は非常に深刻です。爆発すると油が飛散し、火災や隣接する位相に問題を引き起こす可能性があります。ブッシングの問題の原因はさまざまで、陶器の亀裂からの湿気、トラッキングを引き起こす表面汚染、誤った静電容量グレーディング、過負荷による熱影響が含まれます。故障はブッシングが爆発するまで隠れていることがあり、重要なブッシングに対して定期的なPD診断とタンデルタ測定を推奨する理由です。.
迅速に対応する必要があります：ブッシングがひび割れているか、重度に汚染されている場合は、即座に交換する必要があります（交換コストは$3,000から$30,000の間です）。損傷がある場合は、ブッシングの交換を先延ばしにしないでください。激しい故障がいつでも発生する可能性があります。.
冷却システムと油の汚染故障
Cooling defects are the most frequent “slow” issue: clogged radiators, faulty fans, locked pumps, and insufficient oil content. They do not themselves damage the transformer, but their presence forces hot operation, thus hastening insulation deterioration and, on certain occasions, resulting in the protection being triggered in times of high power consumption. In the meantime, oil pollution hides water intrusion, sludge formation, acidity, and dissolved metals, which all have a negative impact on the insulation.
Immediate response: with cooling issues, fix the fan and pump, clean the radiators and check the oil level, and for oil pollution perform the suite of oil quality tests (breakdown voltage, moisture, acidity, IFT) and cleanse or change oil costing $2000-15000 depending on the volume. The true root cause of contamination, usually a leak, breather malfunction, or overheating, should always be detected and eradicated.
Frequency and Cost of Each Fault Family
When a fault is confirmed, the response cost depends heavily on the family and the speed of detection. The table below summarizes typical repair and replacement costs:
| 故障ファミリー | Typical Repair Cost | Replacement Cost (20–60 MVA unit) | Cost Multiplier if Detection Delayed |
|---|---|---|---|
| Insulation / moisture (caught early) | $5,000–$30,000 (oil treatment, dry-out) | $250,000–$1.2M | 5–20x |
| Winding short circuit | $20,000–$150,000 (rewind) | $250,000–$1.2M | 2–4x if secondary damage |
| Core fault | $15,000–$80,000 | $250,000–$1.2M | 3–8x |
| Tap changer | $5,000–$40,000 | OLTC assembly $15,000–$60,000 | 2–5x |
| Bushing | $3,000–$30,000 per phase | — | 10x+ if bushing explosion |
| Cooling / oil contamination | $2,000–$15,000 | — | Indirect, via accelerated aging |
The pattern is global: early detection through DGA, temperature trending, and regular inspections cuts costs by a factor of ten compared with waiting until after a trip. This is the complete business case for condition monitoring.
Rapid Handling Strategy: The 6-Step Response
Whenever a transformer indicates a fault or trips, a certain procedure must be followed:
- Secure the equipment. Open the circuit breaker, lock it out, and put a tag on the equipment. It is extremely important not to power it again until the reason for the trip is established, except in the case of a known nuisance trip (external cause) where a confirmation must take place before performing the re-closure operation.
- Collect all the data. Record all the information including the flags registered by the protection relay, gas and oil readings, temperature at the time of the event, sounds, and notes from the operator. This data will become the backbone of the future analysis of the cause and consequences of the thing happened.
- Make a sample right away. Prepare oil and Buchholz gas samples as soon as possible after the event, instead of waiting for several days recuperating from the shock. DGA analysis is usually rather expensive (about $200-500) yet very fast and efficient in answering major “what happened” questions.
- Analyze according to the standards. Use IEEE C57.104 and IEC 60599 standards for fault classification.
- Perform necessary electric tests. These include winding resistance check and insulation resistance testing.
- Make a decision. Depending on the conclusions made from analytical procedures, monitoring, repairs, or replacement interventions must be selected.
Set response targets by severity so the sequence has time discipline:
| Severity | Indication | Response Target |
|---|---|---|
| 警告 | TDCG 720–1,920 ppm, stable | Investigate within 1–2 weeks |
| Alert | Rising gas rate or acetylene > 35 ppm | Sample weekly, plan intervention |
| Emergency | Buchholz trip, acetylene > 80 ppm, tank bulge | Isolate now; decide within 48–72 hours |
Two important pieces of advice: if acetylene is present in concentrations greater than 35-50 ppm, treat the system as being in a potentially hazardous condition and investigate prior to restarting the equipment; if the Buchholz relay has tripped rather than only raised an alarm, then some internal damage is to be suspected and the unit may need to be opened.
Below is a simple troubleshooting chart that connects the fault description with the proper trouble-shooting test and recommended first action.
| Symptom | Likely Fault | Decisive Test | First Action |
|---|---|---|---|
| Buchholz gas alarm | Thermal or discharge fault | Gas + oil DGA | Sample within hours, classify |
| High hydrogen, low acetylene | 部分放電 | PD measurement | Monitor, inspect insulation |
| High ethylene, no acetylene | Thermal fault | DGA ratios, load check | Find overload or cooling cause |
| High acetylene | Arcing / discharge | DGA, winding tests | Do not re-energize; plan inspection |
| Tripped differential protection | Winding short circuit | Winding resistance, ratio | Isolate; internal inspection likely |
| Rising top-oil temperature | Cooling or overload fault | Load and fan check | Restore cooling, reduce load |
Repair vs. Replacement Decision
The decision of whether to repair or replace is a matter of both economics and technology. The following measures are to be considered:
- Age and condition: A unit that was built 35 years ago and is known to suffer from both paper aging and a winding defect should be replaced. A unit that is 10 years of age and has one of the OLTC defects or a bushings fault should be repaired.
- Extent of damage: A localized issue such as failure of one bushing, a tap changer, or presence of oil contamination is indicative of a repair and a fault which is more widespread (damage of both windings and the core) is an indication for replacement.
- Cost of repairs as a percent of replacement: As a rule of thumb, if repair costs exceed 50-70% of replacement costs, or if repairs will delay larger failures, replacing should become the preferred option.
- Availability: If lead times for replacement reach up to 30 months and an increase in the supply cannot wait, a repair with proper documentation regarding remaining lifespan would become the ideal option.
- Strategic considerations: While it is still possible to make repairs, improvement criteria, network development, and load predictions can suggest replacement as being preferable.
It is important to document such numbers as repair costs, estimated remaining life, replacement costs, lead times, and downtime. This would create a coherent case for the decision itself.The criteria mentioned when applied in order may serve as a quick filter.
| 基準 | Repair | Replace |
|---|---|---|
| Unit age | Under 20 years | Over 30–35 years |
| Damage extent | Localized (bushing, OLTC, oil) | Winding or core widespread |
| Repair cost vs replacement | Below 50% | Above 50–70% |
| Remaining life | 10+ years expected | Short or unknown |
| Spare lead time | Load can wait | 12–30 month wait unacceptable |
よくある質問
What is the most common cause of transformer failure?
The standard cause of failure in electrical components is insulation breakdown, which accounts for approximately 30–50% of total failures in IEEE and CIGRÉ surveys. This damage is usually attributed to heat and moisture damage as well as partial discharge issues. Other minor causes include faults in tap changers, bushings, and windings. Majority of insulation failure cases are detected before the failure happens, because it happens over months or years.
How quickly should I respond to a transformer fault?
Isolate and lock out the unit as soon as possible; sample the oil and gas as soon as possible within hours. Carry out the DGA within 24 to 72 hours after the event; it will almost always identify the fault family and costs around $200-500. By diagnosing the issue within 24-72 hours, the total fault cost would typically be reduced by half compared to waiting for a second event to occur.
Can a transformer be repaired after a winding short circuit?
Certainly in most cases. The cost of rewinding a medium power transformer is in the range of $20,000 to $150,000 depending on its rating, while replacing it would cost between $250,000 and $1.2 million. The choice between the two depends on the condition of the core and tank, their age and the cost of rewinding as a percentage of replacement. Units below 20 years in age that have localized winding damage have a high chance of successful rewinding.
What does a high acetylene reading mean in DGA?
The presence of acetylene (C2H2) in the transformer signals an electric arc. As stated in IEEE C57.104, levels higher than 35 ppm will elevate the transformer into the caution level, and levels higher than 80 ppm will elevate the transformer into the urgent level requiring immediate action. Even the trace levels of acetylene require screening due to the risk of rapid escalation of an electric arc.
How much does a failed transformer cost to replace?
In the case of a 20–60 MVA transformer, it would take between $250,000 and $1.2 million value of the equipment alone to repair it. Emergency logistics, crane leasing, and downtimes have to be added. If it is a transformer above 100 MVA the price would range from $1.5 million to $4 million. Unplanned losses of outages will make you pay between $50,000 and $2 million depending on the load.
参考文献
- IEEE C57.104: Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers — The reference for classifying DGA results and setting response priorities.
- IEC 60599: Guide to the Interpretation of DGA in Mineral Oil-Impregnated Equipment — International gas interpretation framework used with ratio and Duval methods.
- IEC 60422: Supervision and Maintenance Guidance for Mineral Insulating Oils — Oil quality limits and maintenance practice for in-service transformers.
- IEC 60076-5: Ability to Withstand Short Circuit — Standard covering winding mechanical strength against through-faults.
- CIGRÉ — Technical brochures on transformer failure statistics and reliability (A2 committee).
- IEEE — Source of transformer reliability working group data and maintenance standards.
- 江蘇省蘇辺電力 — IEC 60076-compliant transformer manufacturer offering fault diagnosis support and replacement supply.
結論
Faults in transformers can be classified into unique types, and all types demonstrate common symptoms, have known diagnostic tests, and are managed using standard procedures. What distinguishes the case that involves an investment of $5,000 from a case that entails an expense of $1 million is usually the speed and method of response: isolate, document, gather samples, interpret, test, and decide.
- Insulation problems prevail in statistics on failures and are detectable through DGA and testing of oil quality.
- Problems with bushings and windings appear unexpectedly and can be prevented through coordination and monitoring.
- Never energize transformers again after a Buchholz trip or if an indication of high acetylene exists without diagnosis.
- Run DGA within 24–72 hours of the incident at a cost of $200–$500 per sample.
- Make a decision concerning repair or replacement depending on the age and extent of damage.