マレーシアの病院のプロジェクトマネージャーは、1,000 kVA 定格の変圧器に対する2つの見積もりを評価していました。安価な油浸変圧器は$16,000で、より高価なキャストレジン変圧器は$26,000で価格が設定されていました。安価な選択肢は$10,000の節約になります。しかし、病院は電気設備が設置されている場所から2階上に位置しているため、火災規制により漏れが発生した場合に油を保持するためのピットが必要とされました。さらに、保険会社は病院が屋内で使用できない鉱油を使用するつもりかどうかをすでに尋ねています。したがって、この場合、乾式変圧器が必ずしも優れているわけではなく、むしろ病院の建設上の問題によるものです。上記の質問は、乾式変圧器と油浸変圧器の比較に関連する問題の本質を理解するのに役立ちます。この点に関しては、問題は優位性とは関係がなく、サイト、火災リスク、負荷要件、予算制約に関するプロジェクト特有の状況に関連していることを述べるべきです。.
この質問に対する簡単な答えは、設備が屋内で使用される場合、火災安全が最も重要である場合、または利用可能なスペースが限られている場合には、乾式変圧器を選択すべきということです。例えば、建物、病院、トンネル、データセンターなどのケースです。設備を屋外に設置する必要がある場合、過負荷容量が重要な要件であるか、予算制約が影響する場合には、油浸変圧器がより適した選択肢となります。例えば、通常は公共の変電所、工業施設、太陽光発電所で見られます。.
の技術の主な違い
名称は冷却および絶縁材料を示しています。油浸変圧器は鉱油（またはエステル流体）を使用して絶縁し、タンクの壁を通じて熱を除去します。乾式変圧器は、通気性のあるコイルまたはキャストエポキシ樹脂で封入されたコイルで空気を使用します。この1つのことがすべてを可能にします：故障の仕方、冷却の仕方など。.
油は最高の絶縁体および冷却剤であり、油浸技術が公共および外部産業を支配している理由は、kVAあたりのコストと過負荷機能が重要だからです。しかし、油は非常に可燃性で漏れの問題があるため、乾式技術は価格が高いにもかかわらず、建物や火災に敏感な地域で使用されます。.
安全性と火災挙動
火災リスクに関する最初の決定は、鉱油および絶縁油の発火点が約140-150 °C、火点が約160 °Cであることです。油ベースの装置は、故障が発生した場合に漏れたり点火したりする可能性があります。これが理由で、ほとんどすべての建物および電気コードは、油浸装置を屋内で使用することを禁止しています。火災耐性のある壁の囲いを持つか、追加の排水機能を持つ防火囲いがない限り、油の保持が許可されていません。.
ドライタイプ変圧器は、IEC 60076-11の火災試験で燃焼せず、可燃性の油を放出しないため、火災リスクを伴いません。そのため、ドライタイプ変圧器は屋内用途に最適な選択肢です。.
| 安全性の側面 | 油浸型 | ドライタイプ（キャストレジン） |
|---|---|---|
| 冷却媒体 | ミネラルオイル / エステル（可燃性） | 空気 / エポキシ樹脂（自己消火性） |
| 油の引火点 | 140–150°C（ミネラル） | 該当なし |
| 火災リスク | 屋内でのバルトまたは containment が必要 | 非常に低い、IEC 60076-11の火災試験に合格 |
| 屋内設置 | コードによって制限される | 標準 |
| 環境リスク | 油の流出は containment が必要 | 液体なし — クリーン |
各定格でのコスト比較
ドライタイプ変圧器は、同じkVA容量の油浸型変圧器よりも40-80%高価です。ドライタイプ変圧器の価格が高くなる要因には、銅巻線の使用（ドライタイプは油冷却に比べて効率の悪い空気冷却のため、必ず銅を使用します）、ヘラルディングおよびキャスティングレジンの封入、100Kの温度上昇で運転する際に必要な優れた熱設計が含まれます。.
| 定格 | 油浸型（FOB中国） | ドライタイプ / キャストレジン | プレミアム |
|---|---|---|---|
| 100 kVA | $2,500–$6,000 | $4,000–$9,000 | +40–60% |
| 250 kVA | $4,500–$11,000 | $7,000–$16,000 | +45–55% |
| 500 kVA | $8,000–$16,000 | $12,000–$24,000 | +50% |
| 1,000 kVA | $15,000–$32,000 | $22,000–$46,000 | +45–60% |
| 2,500 kVA | $38,000–$75,000 | $58,000–$110,000 | +50–70% |
The prices are estimates and depend on specifications, manufacturers, and geographic locations. As the power increases, the differences between oil units narrow, as opposed to when they use an ester fluid that is fireproof. In the case of the hospital, the additional charge of $10,000 originally included in the price of the dry-type unit turned out to be misleading, as when the vault, containment pit, and fire-fighting system of the oil power system were included, it was found out that it was more expensive to install the “cheap” solution.
Performance: Overload, Efficiency, and Life
Oil-immersed transformers stand out when it comes to overload performance. The oil heats up while the transformer is in use, which allows it, in accordance with IEC 60076-7 standards, to work while carrying 1.3 to 1.5 of recommended load for several hours after previous use. As for dry-type transformers, they are only able to carry slightly more than their rated capacity (typically 1.1) because they have little thermal capacity.
Speaking of efficiency, state-of-the-art transformers have similar performance, though it must be noted that amorphous-core oil-immersed transformers have the least level of no-load losses — it serves well where transformers are working around the clock. Lifetime-wise, both types are designed for 20 to 30 years, but lifetimes will depend on insulation temperature. Moisture in oil, sludge formation, and gases dissolved in oil are sources of maintaining oil-based units; while dry-type transformers have their own issues as they do not get affected by oil-based problems but are under the threat posed by dust accumulation on windings and by the start of partial discharge in humid conditions.
| Performance Metric | 油浸型 | Dry-Type |
|---|---|---|
| Short-term overload (IEC 60076-7) | 1.3–1.5× for hours | ~1.1× briefly |
| Temperature rise (rating) | 55–65 K | 100 K |
| Typical efficiency (500 kVA) | 98.2–98.8% | 98.0–98.6% |
| Insulation life target | 20–30 years | 20–30 years |
| Main failure mode | Oil degradation, moisture, DGA events | Partial discharge, dust tracking |
Installation and Space Requirements
Space and civil work selection normally takes place before pricing. For an oil type of transformer inside a building, a fire-rated vault will be needed (at the very least, with two hour resistant walls); also, an oil containment pit will be necessary that will be able to contain the full volume of the oil plus 10 % of the fire-fighting water, as well as ventilation be provided in compliance with the regulations with a required minimum flow.
However, outside the situation reverses – while oil transformers are normal since a simple lined pad is required for them, you can hardly expect to find a dry-type transformer outside without affecting its price and having the risk of overheating. There is noise as well: while oil transformers are quiet since the tank absorbs the core vibration, dry-types are noisier not less than by 5-10 dB(A) due to the same power rating (according to IEC 60076-10 sound level measurement standards).
| Installation Aspect | 油浸型 | Dry-Type |
|---|---|---|
| Indoor clearance | Vault + oil pit + fire rating | 300–600 mm air clearance |
| Outdoor weatherproofing | Integral (tank sealed) | Needs enclosure (IP54+) |
| Foundation | Containment liner, heavier base | Flat pad, lighter |
| Noise at 1 m (500 kVA) | ~55–62 dB(A) | ~60–70 dB(A) |
| Floor loading | Higher (tank + oil) | Lower |
Maintenance and Total Cost of Ownership
When it comes to transformers that involve oil, maintenance is undeniably a real and ongoing requirement, which consists of yearly inspections, the sampling of the oil (every 1 to 3 years in accordance with how critical the transformer is), checking of the oil level and temperature, the completion of a replacement of the silica gel in the breather, and eventually filtering of the oil. Dry transformers need virtually no maintenance when indoors and have only minimal dust cleaning and thermal checks. However, because of a higher initial cost, dry-type transformers tend to be more problematic as they may end up leading you to get a higher capacity than you require.
In terms of the total costs of ownership over a period of twenty years, oil transformers may cost less initially, but they would involve ongoing costs associated with oil maintenance (around $150-600 per year) unlike dry transformers that have a high initial cost (around 40-80% higher) and almost no operational costs. This means that with a device installed, both solutions will be getting very close to each other in terms of the costs, with the difference being not more than 10-20%. Consequently, decisions must be made according to impossible conditions (where it will be located, fire code, overload characteristics, etc.) rather than the cost.
Side-by-Side Comparison Table
| Dimension | 油浸型 | Dry-Type |
|---|---|---|
| Best location | Outdoor, substations, industrial | Indoor, buildings, tunnels |
| Fire safety | Needs vault/containment | Self-extinguishing |
| Price (500 kVA) | $8,000–$16,000 | $12,000–$24,000 |
| Overload tolerance | 1.3–1.5× for hours | ~1.1× briefly |
| Maintenance | Oil, DGA, inspections | Minimal |
| Noise | Lower (55–62 dB) | Higher (60–70 dB) |
| 環境リスク | Oil spill containment | None |
| Indoor code compliance | Restricted | 標準 |
For starters, please refer to this table: if the row shows “indoor building” you can proceed to dry-type; if it mentions “outdoor substation” then you will require oil. After this, most of the projects have the direction confirmed from the fire code and overload profile.
A Decision Framework for Your Project
Follow these five questions in order — the first question that dictates the responses to the following:
- Where is it located? Indoors → dry-type, unless vaulting is possible. Outdoors → oil-immersed, unless compactness is required.
- What do fire safety codes and the insurer say? If mineral oil is banned in the building code, opt for dry-type or ester-filled equipment.
- What kind of loads does it deal with? As with growth, repetitive loads or usage of large motors → benefits of oil-immersed overloading should be taken into account; consider one class higher for dry-type.
- What constraints are on noise and space? If there are tight space and noise constraints → prefer dry-type over oil equipment in terms of space, and vice versa when it comes to noise.
- What are the budget constraints? If the most cost-effective equipment is favored → use oil-immersed (given the location permits it). If long-term costs and regulatory issues are a priority → provide a comparison of the cost of equipment after installation.
A hospital has chosen dry-type because question 2 has decided everything in this case. A solar farm has chosen oil-immersed equipment because questions 1 and 3 seem to prevail. A hospital that is located in the basement may opt for ester-filled oil in order to save money.
Brands and Price Benchmarks
Both technologies belong to the same brand spectrum and have the same price ratios among different brands. International brands take charge of mission-critical dry-type supply, while IEC-certified companies from China successfully compete in both categories at lower levels.
| Brand | Strength | Oil 500 kVA | Dry-Type 500 kVA |
|---|---|---|---|
| ABB | Full range, global service | $18,000–$30,000 | $26,000–$44,000 |
| Siemens | Efficiency, digital monitoring | $18,000–$32,000 | $27,000–$46,000 |
| Schneider Electric | Dry-type leadership | $15,000–$28,000 | $24,000–$40,000 |
| Hitachi Energy | Grid and industrial | $17,000–$30,000 | $25,000–$42,000 |
| Eaton | North America compliance | $14,000–$26,000 | $20,000–$36,000 |
| Jiangsu Subian Electric Power | IEC 60076, both types, test reports | $8,000–$16,000 | $12,000–$24,000 |
Prices are presented as FOB China or ex-works and depend on several parameters, including specifications, name, and location. The international names mentioned above serve as benchmarks for reliability in terms of the technologies. Jiangsu Subian Electric Power is involved in any project of technology choice but seeks the most reliable price because the company produces oil-immersed and dry-type transformers with the power from 10 kVA up to 100 MVA with the direct compliance to IEC 60076 (which means IEC 60076-11 for dry types). The company provides its clients with the test report for every order and uses copper-wound units as the standard. If you have chosen dry-type for assuring hospital functioning or oil-immersed for a solar power station, you will still be presented with the same certifications, losses measurements, and the report of the test, as the technology choice defines what you purchase, and the documents define whether you have received it.
Frequently Asked Questions
Which is better: dry-type or oil-immersed transformer?
Oil-immersed and dry-type transformers have pros and cons for both types. The oil-immersed variant is cheaper (40-80% cheaper than dry type with same kVA rating), deals with overloads of 1.3-1.5× for hours, and is suitable for outdoor substations, factories, and solar farms. The dry-type is fire-safe, does not require presence of oil, and can work inside buildings, hospitals, and data centers.
Are dry-type transformers more expensive than oil-immersed?
Yes, generally speaking 40–80% higher at a comparable kVA: a 500 kVA dry-type costs $12,000–$24,000 and an oil-immersed type $8,000–$16,000. However, when considering the oil type’s indoor vault, containment pit, and fire suppression, the installed costs may end up being similar.
Can oil-immersed transformers be installed indoors?
Yes, according to the code: fire-resistant vault construction is a must in most areas; there should also be a pit for collecting the entire oil volume, and fire extinguishing systems have to be installed. Alternatively, it is possible to consider the use of an ester-filled unit.
How long do dry-type and oil-immersed transformers last?
They are both made with a time span of the range of 20-30 years. The life expectancy of the oil units is adversely affected by moisture or overheating which can be caught by regular DGA sampling. In the case of dry type transformers, they can be utilized the longest in perfect clean and dry conditions, however, dust and humidity can cause partial discharge resulting in shorter life spans.
Which transformer type is quieter?
Oil-filled transformers create less noise as the weight of the tank absorbs vibrations of the core, registered as a noise level 5-10 dB(A) lower than that of an air-cooled transformer of the same type (about 55-62 dB(A) as compared to 60-70 dB(A) for a transformer with a rating of 500 kVA). According to IEC 60076-10, before making your choice for residential and hospital locations, it is necessary to confirm the sound strength of your transformer.
References
- IEC 60076-1: Power Transformers — General — the base standard for ratings, temperature rise, and testing.
- IEC 60076-11: Dry-Type Power Transformers — the specific standard for dry-type design, fire testing, and ratings.
- IEC 60076-7: Loading Guide for Oil-Immersed Power Transformers — overload and cyclic-loading guidance for oil units.
- IEEE C57.12.00: General Requirements for Liquid-Immersed Transformers — North American equivalent framework.
- NFPA 70: National Electrical Code — installation and vault requirements for oil-immersed transformers indoors.
- Electrical4U — Transformer Types — background on dry-type, cast-resin, and oil-immersed construction.
- Wikipedia — Transformer Types — a reference on the major transformer classifications.
Conclusion
Choosing between a dry-type transformer and an oil-immersed one is not so much about which one is better as which solution fits within all constraints. You can find constraints such as fire codes and location that will dictate whether to go for oil units, which are more effective with overloads and under outdoor conditions, or dry-types, which beat their rivals in terms of fire safety indoors — and the 40–80% price difference substantially vanishes once installed cost is calculated.
- Conduct your location and fire code analysis first; technology will follow.
- Evaluate installed price, including vaults and containment materials, rather than just appliance price.
- Choose a model suitable for overloads, that is, select dry-types according to specific overload requirements.
- Confirm your choice with IEC 60076 test results and verified losses.