Consider that your manufacturing process runs into troubles every afternoon, as the local distributed supply system is unable to cope with peak loads — while the engines are still moving, the voltage falls below the required value of +/-5% indicated by variable speed drives, and you have to choose between purchasing the entire new substation and implementing the less expensive solution. In most cases, the better solution is a booster transformer — the device transforming the existing supply by means of voltage adjustment, which helps to solve the problem with sagging line voltage without impacting the electrical machines. In this piece, we will discuss the best types of the booster transformers suitable for operation in 2026 in detail.
Quick answer: Booster transformer is a type of transformer that is designed to work together with other transformers in a series circuit where its secondary winding is connected directly to a load circuit, so it increases the voltage level above the original voltage at the input of the transformer, ensuring the maintenance of the voltage without making any modifications in the configuration of the substation and its operation. The most widely used types include fixed ratio boosters, OLTC boosters, autotransformer boosters, buck-boost transformers, and phase shifting boosters.
What Is a Booster Transformer?
A booster transformer is a unique power transformer that is hooked up in series to a feeder line instead of in parallel. Its primary winding derives energy from a regulating source (often this line itself, via a tap or through a small control transformer) while its secondary circuit is connected directly to the load circuit. The voltage generated in the secondary circuit is added to the line voltage to generate an overall boost. The booster acts as a series step-up transformer and is able to increase the supply voltage by an exact value that can be predicted. Since the booster only handles the boost, its kVA rating is very low in comparison with the load it supports, which is normally just 5 percent to 25 percent of the load kVA, thus making the booster much cheaper in comparison to a supply transformer.
How a Booster Transformer Works
An example helps to understand the working of the booster better. Consider the case of feeder voltage dropping from 480 V down to 448 V under full load, which is 6.7% of the voltage drop. However, a booster secondary can be added to add back 32 volts to bring back the voltage to 480 V. Therefore, for a 200 A load, the boost kVA becomes 32 × 200 = 6.4 kVA, to manage a 200 kVA circuit. The primary side receives power from the power line (either with a fixed tap or with an ON load tap changer), and the secondary side is connected in series with the line conductor in such a way that the voltage gets added. With the help of a reversing switch or buck mode connection, it could be possible to remove the voltage from the power line.
The 5 Main Booster Transformer Types
| Тип | Working principle | Типичное применение | Indicative price (US$) |
|---|---|---|---|
| Fixed-ratio booster | Adds a constant voltage increment via fixed taps | End-of-line sag correction on long feeders | $1,500–$15,000 |
| OLTC booster | Variable boost set by on-load tap changer | Fluctuating industrial and commercial loads | $6,000–$45,000 |
| Auto-transformer booster | Single-winding design, lighter and cheaper | Moderate boost in constrained footprints | $1,200–$12,000 |
| Buck-boost transformer | Adds or subtracts voltage by reconnecting windings | Line voltage too high or too low | $800–$9,000 |
| Phase-shifting booster | Adjusts both magnitude and phase angle | Power-flow control in utility networks | $15,000–$120,000 |
Type-by-Type Comparison Table
| Критерий | Fixed-ratio | OLTC | Автотрансформатор | Buck-boost | Phase-shifting |
|---|---|---|---|---|---|
| Boost range | Fixed (e.g., +10%) | Variable, on load | Fixed or tapped | ±5–20% | Variable with angle |
| Handles fluctuating load | Нет | Yes | Нет | Partial | Yes |
| Corrects over-voltage | Нет | Optional | Нет | Yes | Yes |
| Relative cost | Низкий | Высокий | Lowest | Низкий | Highest |
| Typical duty | Stable sag | Variable supply | Small boosts | Residential/commercial | Grid power flow |
Key Features to Look for in 2026
- A large, authentic range of boost. Check that it can cover your maximum sag without issue; a unit that can provide a boost of 10% cannot cover a sag of 15%.
- On-load tapping can be done when the voltage fluctuates continuously to avoid shutting down for adjusting the tap manually.
- Low impedance. The booster works in series with the load and causes its own impedance to drop, hence it is important to keep it low to solve the problem.
- Good insulation quality. A clear separation needs to be kept between the two parts of the system so that insulation is designed according to the operating voltage not boost voltage.
- Compliance with IEC 60076 for temperature rise and short circuit withstand and routine report with the measurement of losses.
- Guilty motion of switching is allowed for an easy bypass.
| Specification item | Typical value / choice | Примечания |
|---|---|---|
| Line voltage class | 480 V, 600 V, or MV up to 34.5 kV | Determines insulation and BIL |
| Boost range | +5–15% (buck-boost: ±5–20%) | Match to measured worst-case sag |
| Booster kVA | Boost V × Line A / 1000 | Usually 5–25% of load kVA |
| Охлаждение | AN/AA (dry), ONAN (oil) | Continuous series duty |
| Стандарт | IEC 60076-1, -3, -5 | Routine test report required |
| Аксессуары | Bypass switch, protection relay | Bypass essential for maintenance |
Where Boosters Solve Real Problems
Booster transformers are used in different situations where the electric power supply is not sufficiently high enough to operate appliances properly such as when a factory is located 5 km from the power station, or when a warehouse is sharing the same transformer with other machines, or where a cold-storage facility is running the compressors during the daily dip in voltage levels. They could also be employed temporarily at the construction sites or during the electric power supply for a particular event. When used in electric utility sectors, phase-shifting booster transformers control the flow of electricity between two lines of electric circuits thus reducing power. It does not matter which situation we consider, the matter of costs will be the same: the individual will have to spend a few thousand dollars on the series booster transformer rather than on the feeder, transformer, or stabilizer installation that will cost him or her tens of thousands of dollars.
| Применение | Symptom | Best booster type | Typical size |
|---|---|---|---|
| Long rural feeder end | Stable low voltage at distance | Fixed-ratio | 5–50 кВА |
| Industrial plant with fluctuating load | Voltage swings with production | OLTC | 25–500 kVA |
| Commercial/residential supply | Line runs high or low | Buck-boost | 1–75 kVA |
| Diesel-genset site supply | Droop under starting load | Fixed-ratio | 10–100 kVA |
| Parallel utility circuits | Uneven power sharing | Phase-shifting | 100–2,000 кВА |
Sizing and Specification Basics
The kVA rating of the booster is obtained by multiplying the necessary boost voltage by the load current. The formula is Boost kVA = Boost voltage (V) x Line current (A)/1000. For example, for a 480 V feeder with 400 A that needs a 24 V boost, the required series kVA would be 24 x 400/1000 = 9.6 kVA while actually controlling a load of 192 kVA. After establishing the kVA rating, the following parameters must be determined: the line voltage level (480 V and 600 V or something from the medium-volume market (up to 34.5 kV) for effective use of utility boosters), the boost range (e.g. 240V to 63 kV), the gradient of the boost range, the current vector group and polarity, the cooling technology (dry types should use cooling using air AN/AA or oil cooling ONAN), and environmental features of its use (temperature, altitude, indoor or outdoor usage). In case of using medium voltage boosters, do not forget to confirm the BIL and the excursion that could support the unit’s operation.
| Example system | Line voltage | Load current | Required boost | Booster rating |
|---|---|---|---|---|
| Factory end-of-feeder | 480 В | 200 A | +24 V (5%) | 4.8 kVA |
| Warehouse with VFDs | 480 В | 400 A | +32 V (6.7%) | 12.8 kVA |
| Cold-storage plant | 400 В | 500 A | +30 V (7.5%) | 15 kVA |
| Medium-voltage rural feeder | 11 kV | 80 A | +550 V (5%) | 44 kVA |
| Utility power-flow regulator | 33 кВ | 150 A | Variable 0–10% | Up to 500 kVA |
Топовые бренды и ценовые категории
| Бренд | Страна | Product focus | Ориентировочный диапазон цен (US$) |
|---|---|---|---|
| ABB | Швейцария/Швеция | OLTC and phase-shifting regulators | $8,000–$120,000 |
| Сименс | Германия | Voltage regulators and booster units | $7,000–$100,000 |
| Schneider Electric | Франция | Buck-boost and small boosters | $800–$12,000 |
| Итон | США | Buck-boost transformers for 480 V systems | $700–$9,000 |
| GE Grid (part of Hitachi Energy) | USA/Switzerland | Utility-grade regulators | $10,000–$130,000 |
| Jiangsu Subian Electric Power | Китай | Custom boosters, buck-boost, OLTC types | $1,500–$45,000 |
The prices given are references and depend on the type, boost range, voltage class and accessories. ABB, Siemens, Schneider Electric, Eaton and Hitachi Energy are manufacturers of highly reputable products, and they provide the most comprehensive guidelines on how to use the products previously mentioned. For those that value the same engineering capability but at a lower price, Jiangsu Subian Electric Power Co., Ltd. provides the manufacture of custom booster and buck-boost transformers according to IEC 60076 in dry and oil immersion forms with on-load tap-changing mechanisms the client may need. The engineers of Subian assist with sizing the transformers, testing, and providing documentation needed for export.For a 2026 project where budget and lead time matter, this makes Subian a practical partner. Review the product range on the сайте Subian Electric.
How to Choose the Right Type
- Measure the worst case for your voltage baselines. Log voltage levels as close to your point of utilization as possible for a minimum of one full week, preferrably including mid summer peaks to arrive at your lowest and highest voltage levels.
- Calculate how much boost you need. Determine how much you need to raise your voltage as the difference between your true voltage and your predetermined/target voltage (which should generally be between 95 and 105%).
- Select whether to use fixed voltage or adjustable voltage. If your voltage is generally stable but low, a fixed ratio booster is the most cost effective choice; if voltage levels are variable, a buck-boost or OLTC device should be used.
- Verify rating of the voltage class. Because the low voltage booster is a common item, medium voltage boosters must go through avalanche ratings (BIL) and short-circuit analysis.
- Provide polarity and vector group. Use alternative connection design so that voltage is converted from boost modes to bucking circuits (ensuring winding orientation is safe).
- Get the latest IEC 60076 reports and review test reports to see if ratio, efficiency, and thermal state of design work out.
- Organize installation details. Make sure there is a bypass switch, proper ventilation of devices, and protection arrangement in accordance with existing installation standards.
Часто задаваемые вопросы
Is a booster transformer the same as a step-up transformer?
This is not the correct interpretation. A transformer increases the level of the entire voltage supply and is used in a similar way to a transformer installation. A booster is used in series and provides only a small increase in voltage and thus has a kVA rating significantly lower than the load being fed. Their operation principle is the same.
What size booster do I need for a 200 kVA load with a 10% sag?
Calculate voltage boost by multiplying received power by load current; for 200 kVA at 480 V, receiving approximately 240 A, voltage boost is calculated as 10% of 480 V, which is 48 V, thus, booster size is equivalent to 48 × 240 / 1000 similar to11.5 kVA. Always leave an appropriate margin of between 10% and 20%, so let’s say go with 14 kVA, which you may need to adjust depending upon voltage data you provide to a vendor.
Can a booster transformer correct over-voltage as well as under-voltage?
The buck-boost variety is the only transformer capable of achieving both functions. It allows you to reconfigure the windings so that the resulting voltage can either be added or reduced from the supply voltage. In contrast, a conventional ratio transformer is only capable of boosting the supply voltage. If your location is subject to both high and low supply voltage at different times throughout the year, then you should choose a buck-boost device.
How much does a buck-boost transformer cost?
In the case of low voltage systems (240 to 600 V), the price of a small buck-boost transformer (1 to 10 kVA) is about $800 to $3,000 while that of bigger installations (10 to 50 kVA) costs between $3,000 and $9,000. Medium-voltage booster transformers that come equipped with an on-load tap changer have a price range from $15,000 to $45,000 and more. This price for every installation varies with the standard, rated power, manufacturer and should be quoted according to the requirement.
Does Subian supply custom boosters for export?
Absolutely. Jiangsu Subian Electric Power makes fixed ratio OLTCs and buck-boosts in line with IEC 60076 standards, and ships worldwide along with necessary test certifications and export documentation. Please share your electrical voltage details and load requirement to receive the sizing recommendations.
Ссылки
- IEC 60076-1 — Силовые трансформаторы: Общие сведения — the governing standard for transformer rating, losses, and testing.
- IEC 60076-5 — Способность выдерживать короткое замыкание — the verification standard for series-connected windings under fault conditions.
- IEC 60076-3 — Уровни изоляции и диэлектрические испытания — sets the insulation requirements for medium-voltage boosters.
- Eaton — Buck-Boost Transformer Application Guide — practical guidance on sizing and connecting buck-boost units.
- Hitachi Energy — Продукты трансформаторов — reference documentation for utility-grade regulation transformers.
- UL 1561 — Стандарт безопасности для трансформаторов сухого типа — safety standard commonly cited for low-voltage booster and buck-boost products in North America.
Заключение
One of the cheap and fast ways to deal with a supply voltage that droops is to make use of a booster transformer; since this device works as a series device along with the power line, it lifts the voltage a bit, and costs several times less than a new transformer or feeder. Namely, there are 5 types of booster transformers: fixed ratio, OLTC, auto-transformer, buck-boost, and phase-shifting, which can be used in cases of a constant sag in the voltage output, operational problems with the fluctuating voltage, and grid applications, usually requiring the transformer that shifts the phases. One should consider real operational performance of the transformer provided by the manufacturer. Jiangsu Subian Electric Power offers custom boosters at competitive factory-direct pricing with full engineering support — contact the company via the официальный сайт with your voltage data for a specification-matched quotation.