鉄鋼工場では、アーク炉用変圧器が白熱した鋼からわずか数メートルの位置に配置されており、二次電流は40,000 Aです。半導体工場では、主変圧器が110 kVを20 kVに降圧し、計画外のダウンタイムを一瞬も許容できない施設に供給します。主変圧器は、実際には産業界のバックボーンであり、電力会社のラインから高電圧供給を転送し、それをいわゆる低電圧でプラントのスイッチギア、エンジン、炉に供給します。.
この記事では、主変圧器とは何か、配電変圧器やユニット変圧器との違いを見分ける方法、産業施設に適したサイズと仕様の決定方法、効率、インピーダンス、冷却、保護、価格の観点からのコストについて説明します。あなたが電気技術者であろうと、プラントエンジニアであろうと、購買マネージャーであろうと、このガイドは正しい選択をするために必要なすべての技術的および商業的データを提供します。.
主変圧器とは何ですか？（定義）
産業、商業、または公共施設における主変圧器は、最大の電力変圧器であり、施設を電力網に接続し、すべての内部配電ネットワークに電力を供給する装置です。例えば、鉄鋼工場では40MVA/110kVユニットである可能性があり、中規模の工場では2.5MVA/11kVユニットを使用し、病院キャンパスでは冗長性を提供するために複数の2MVAユニットを適用する可能性があります。この装置が主変圧器と呼ばれる理由は、電圧値ではなく、プラントの主要な電気コンポーネントとしての変圧器の位置にあります。.
主変圧器は、損失に関する最良の解決策、高品質の絶縁、機能するタップチェンジャー、適切な保護ソリューションを含むため、最大の信頼性で動作するように製造されています。主変圧器の故障によるコストは、修理費用だけでなく、プロセスプラントの場合、故障による損失は数百万ドルに達する可能性があります。.
産業電力システムにおける主変圧器の役割
現代の産業施設の電力構造は、主に類似のパターンに従います：
公共電力接続 — 33 kVから220 kVの範囲で、施設の境界に位置しています（外部電力供給が施設の電気システムに接続されるポイント）。.
主変圧器 — 施設自体に供給電圧を6.6 kVから35 kVに生成します。.
中電圧配電システム — 変電所、モーター制御センター、主要駆動装置への電力接続を含みます。.
ユニット変圧器 — 供給電圧を6.6 kVから35 kVに降圧し、400 Vおよび230 Vを生成して建物や小負荷に電力を供給します。.
重要な負荷 — 無停電電源装置（UPS）、バックアップ発電機、冗長スイッチが設置されています。.
この枠組みの中で、主変圧器は電圧を変換するだけでなく、そのインピーダンスによって回路全体を故障から保護し、タップの利用可能性によって電圧を制御し、施設を電力網から分離します。.
施設の主変圧器のサイズを決定する方法
サイズ決定は他のすべての仕様を決定する要因です。エンジニアリングの手順：
| ステップ | 方法 | 一般的な結果 |
|---|---|---|
| 負荷インベントリ | カテゴリごとに接続された負荷を合計 | 例：接続された8 MW |
| 需要係数 | 多様性を適用（通常0.6〜0.85） | 例：最大需要6 MW |
| 力率補正 | 9〜0.95に補償 | ≈6.5〜7 MVAの見かけ |
| 成長マージン | 将来のために15%〜25%を追加 | ≈8〜8.5 MVAを選択 |
| 冗長性の決定 | NまたはN+1構成 | 重要な場合は2×8 MVA |
工業施設に対する確固たるガイドラインは、主変圧器のサイズを、通常のピーク負荷がその定格の60％から80％の間に収まるようにすることです。これにより、過負荷の余裕が確保され、効率が最大化され、モーター起動時の電力低下に対する十分なマージンが確保されます。重要なプラントでは、緊急時に両方の変圧器が全負荷を管理できるN+1構成で2つの変圧器を使用することが一般的になっています。.
主変圧器の種類と構成
| 構成 | 電圧ステップ | 典型的な定格 | 使用場所 |
|---|---|---|---|
| 二次巻線、油浸型 | 110/20 kV | 60 MVA | ほとんどの工業サイト |
| 二次巻線、乾式 | 11/0.4 kVまたは20/0.4 kV | 5〜10 MVA | 屋内、火災に敏感な施設 |
| 三次巻線 | 110/20/6.6 kV | 60 MVA | 複数の電圧レベルを持つプラント |
| N+1 twin bank | 110/20 kV ×2 | 2×5–2×30 MVA | Data centers, hospitals, refineries |
Three-winding main transformers are popular where a site needs both a medium-voltage process bus and a separate auxiliary bus; the third winding also provides a harmonic path and reduces the need for a separate unit transformer.
Main vs. Distribution vs. Unit Transformer
| 視点 | メイン変圧器 | Distribution Transformer | Unit Transformer |
|---|---|---|---|
| Position | Utility boundary to plant MV | MV feeder to end user | Plant MV to LV loads |
| 一般的な定格 | 2.5–60 MVA | 50 kVA–2,500 kVA | 100 kVA–3 MVA |
| 主電圧 | 11–220 kV | 2.4–35 kV | 6–35 kV |
| Duty profile | Continuous high load + overload | Variable partial load | Building/process loads |
| Typical price | $35k–$300k+ | $1.5k–$45k | $5k–$70k |
The line between “main” and “unit” can blur in small facilities where a single transformer does both jobs, but the engineering priorities differ: main transformers optimize for reliability and continuous load, unit transformers for cost and flexibility.
Key Specifications for Industrial Main Transformers
| パラメータ | 典型的な値 |
|---|---|
| 定格電力 | 20 MVA |
| Voltage ratio | 110 / 20 kV |
| ベクトルグループ | YNd11 |
| インピーダンス電圧 | 10% |
| Tap changer | OLTC ±12% in 13 steps, or off-circuit ±5% |
| 冷却 | ONAN/ONAF (20/28 MVA) |
| 無負荷損失 | ≈14 kW |
| 負荷損失 | ≈98 kW |
| 絶縁レベル | 550 kV BIL (110 kV side) |
| 標準 | IEC 60076-1/-5 |
These numbers are the contract between buyer and manufacturer. Any deviation — higher losses, different impedance, weaker tap range — changes the price and the performance, so they must be locked before production.
Efficiency, Losses & Total Cost of Ownership
Most industrial main transformers operate with efficiency levels between 99.0% and 99.6%. For example, at an efficiency of 99.4% for a 20 MVA transformer, the heat loss amounts to around 120 kW for full load operation, which comes out to about 1,000 MWh of total consumption in one year of operation. That means costs amounting to $80,000–150,000 per year at average tariffs of $0.08–0.15/kWh, not counting the losses that occur during standby time.
The effective cost assessment should be carried out over a period of 20–30 years in other words. The creation of low-loss models takes about 5%–10% more to produce, but they save money on operational costs in the long run. Cutting off 5 kW of losses for the 20 MVA transformer unit means savings of approximately 44 MWh annually, which gives savings of somewhere around $4,400–6,600 per year, $90,000–130,000 in 20 years at normal industrial pricing solutions.
Protection & Safety Engineering
The most significant approach of multi layer protection is towards a transformer which has the highest valuation in the location.
Starting with the different protection schema:
Differential protection (87T) which compares currents in primary side of transformer with currents on the secondary side (corrected for ratio and vector groups) to detect internal faults quickly.
Overcurrent protection (50/51) assists in phase and earth fault backup.
Restricted earth fault (REF, 64) assists in detecting winding to ground fault.
Buchholz relay detects failures at early stages due to gas formation; it can also produce surge and wave impulse alarms.
Temperature alarms indicate that the transformer has reached its temperature limit in accordance with the standards set by IEC 60076-2.
Pressure relief, OLTC protection and surge arresters protect transformer from mechanical forces and lightning.
The experience of commissioning and maintenance is adopted from the standards set by IEEE C57.140 (maintenance guide) and IEC 60076-7 (loading guide).
Applications Across Modern Industry
Steel and metallurgy — main + furnace transformers which deal with loads in the range of 30-120 MVA along very arduous duty cycles.
Computer centers — twin main transformers with guaranteed redundancy, often in the range of 2×10-2×30 MVA at the voltage level of 110/20 kV.
Pharmaceuticals & semiconductors — connecting to adverse loads and demanding high-quality voltage in addition to dry-type option choice for installations indoors.
Mining — remote areas with need for specific designs responding to difficult environmental factors, high ambient temperature, bad accessibility conditions.
Chemicals and refining — continuous load technologies usually work on N + 1 basis and support significant excess load capacity.
Commercial buildings and hospitals — 5-20 MVA that are subject to stringent redundancy requirements.
In each situation, the logic behind the purchase will be similar: matching sizes with the characteristics of the loads, optimizing losses with the investments, adding redundancy where downtime means losses, and adding protection with the connections of relays.
Realistic Prices & Top Brands
Main transformer pricing follows rating, voltage, losses, tap changer, and brand. Planning-level ranges for oil-immersed units:
| Rating / Voltage | Chinese Factory (e.g. Subian, TBEA) | European/US Brand |
|---|---|---|
| 2.5 MVA / 11 kV | $35,000–$70,000 | $70,000–$130,000 |
| 5 MVA / 33 kV | $55,000–$90,000 | $120,000–$200,000 |
| 20 MVA / 110 kV | $160,000–$300,000 | $430,000–$700,000 |
| 40 MVA / 110 kV | $300,000–$550,000 | $800,000–$1,300,000 |
Prices vary by specification, loss level, and region. For industrial buyers who need a main transformer engineered to their load profile without the international brand premium, 江蘇省蘇辺電力 is a strong option: a Chinese transformer manufacturer producing distribution and power transformers from 50 kVA to 220 kV class, including 2.5–60 MVA industrial main transformers with custom impedance, tap ranges, and cooling configurations. Units ship with IEC 60076 type-test reports and full factory test documentation, and their engineers support protection interface design and site commissioning. Factory-direct pricing is typically 30%–50% below European equivalents, and OEM/ODM customization is available for complex projects.
よくある質問
What is the difference between a main transformer and a unit transformer?
A main transformer connects the facility to the utility grid at 11–220 kV and feeds the whole plant’s MV distribution at 6.6–35 kV. A unit transformer is smaller (usually 100 kVA–3 MVA) and steps the plant’s MV bus down to 400/230 V for buildings, lighting, and small loads. A large site has one or two main transformers and dozens of unit transformers.
How do I size the main transformer for my factory?
Sum the connected loads, apply a demand factor of 0.6–0.85, correct power factor to 0.9–0.95, add 15%–25% growth margin, then select the nearest standard rating so normal peak load sits at 60%–80% of rating. For critical facilities, use N+1 twin units each capable of full load. A 6 MW maximum demand typically leads to an 8–10 MVA transformer.
What efficiency should an industrial main transformer achieve?
Expect 99.0%–99.6% at full load, with no-load loss around 0.05%–0.1% of rating and load loss 0.4%–0.7%. A 20 MVA unit might show 14 kW no-load and 98 kW load losses. Request guaranteed loss values and run a capitalized-loss comparison over 20–30 years before choosing between bids — loss differences usually outweigh price differences.
How much does a main transformer cost for a factory?
Budget $35,000–$90,000 for a 2.5–5 MVA / 11–33 kV unit, $160,000–$300,000 for 20 MVA / 110 kV from Chinese factories (or $430,000–$700,000 from European brands), and up to $1.3 million for 40 MVA class from premium brands. Add 20%–40% for protection, installation, testing, and civil works.
Should my main transformer have an on-load tap changer?
If the utility voltage varies more than ±5% or your loads cause meaningful voltage swings, yes — an OLTC holds plant MV within ±2% automatically over a ±12% to ±16% range. If supply is stable and load is constant, an off-circuit tap changer at ±5% is cheaper and adequate. The OLTC typically adds $15,000–$60,000 depending on rating.
参考文献
- IEC 60076-1: Power Transformers — General — Ratings, tolerances, and tests for main transformers.
- IEC 60076-5: Ability to Withstand Short Circuit — Short-circuit withstand requirements essential for industrial duty.
- IEC 60076-7: Loading Guide for Oil-Immersed Power Transformers — Overload capability and thermal aging guidance.
- IEEE C57.12.00: General Requirements for Liquid-Immersed Transformers — North American companion standard.
- IEEE C57.140: Guide for Transformer Maintenance — The maintenance and condition-assessment reference for industrial units.
- Hitachi Energy Transformers — Industry reference for large transformer technology.
結論
- The main transformers are the critical components in the electrical system of modern industries, as they form the basis of the energy structure of the enterprise. The parameters of size, optimization of losses, type of protection, and redundancy determine the performance and cost of the site for the years to come.
The size should be selected so that normal maximum load is 60%–80% of the rated capacity with a growth margin of 15%–25%.
The losses should be optimized using a 20–30 year capitalized-loss model.
The protection should be provided by means of differential protection, REF, Buchholz relay, and temperature control while maintenance should follow the DGA.
The budget for these transformers should range from $35k to $90k for 2.5–5 MVA and from $160k to $300k for 20 MVA/110 kV (factory-direct).
If you are planning a new plant or upgrading an existing substation, 江蘇省蘇辺電力 can engineer and supply main transformers from 2.5 MVA to 60 MVA with IEC 60076 certification, custom tap and cooling configurations, and factory-direct pricing to match your budget.