The Arrangement and Meaning of Letters in Power Transformer Models | Yawei Transformer

When you first come across a power transformer model, the combination of letters and numbers can look a little confusing. Something like S11-M-1000/10 or SCB14-2000/10 may seem like a string of codes with no obvious meaning.

But there is usually a logic behind it.

A transformer model number is often used to describe the transformer's basic type, design series, insulation or construction method, rated capacity, voltage level, and sometimes its voltage regulation arrangement. Once you get familiar with the common symbols, reading a transformer model code becomes much easier.

For engineers, EPC contractors, project managers, and purchasing teams, this is useful when comparing equipment or checking whether a transformer matches the initial project requirements. Manufacturers such as Yawei Transformer also use model designations to distinguish between different transformer designs and applications.

What Does a Power Transformer Model Number Mean?

A transformer model is usually made up of several letters and numbers arranged in a specific order. Each section tells you something about the equipment.

Take S11-M-1000/10 as an example:

S → 11 → M → 1000 → 10

A general interpretation would be:

This kind of breakdown is helpful, but there is one thing to keep in mind: transformer model codes are not completely universal. The same letter can mean something different under another standard, manufacturer, or product series. So the model number should always be checked together with the technical datasheet and nameplate.

Common Letters in Power Transformer Models

S - Three-Phase Transformer

The letter S is commonly used to identify a three-phase transformer in Chinese transformer model systems.

Three-phase transformers are used almost everywhere in modern power systems, from industrial plants and utility substations to commercial buildings and renewable energy projects.

For example, S11-1000/10 generally refers to a three-phase transformer with a rated capacity of 1000 kVA and a 10 kV high-voltage rating.

D - Single-Phase Transformer

In some model naming systems, D is used to indicate a single-phase transformer.

Single-phase transformers are often found in applications where the electrical load or system arrangement calls for a single-phase design. They can be used in residential, commercial, railway, control, and other specialized electrical systems.

Still, it is better not to assume the meaning of D without checking the manufacturer's naming convention.

O - Oil-Immersed Transformer

The letter O can be associated with an oil-immersed transformer in certain transformer model systems.

An oil-immersed transformer uses insulating liquid for both electrical insulation and heat transfer. This construction is widely used for medium- and high-capacity transformers because it provides effective cooling and reliable insulation performance.

For larger substations and industrial facilities, oil-immersed transformers are still a very common choice.

C - Cast Resin

The letter C is commonly associated with cast-resin insulation in dry-type transformer models.

One familiar example is SCB14-2000/10. This type of transformer uses cast-resin insulation instead of liquid insulation.

That makes cast-resin dry-type transformers a good fit for many indoor installations, including industrial facilities, commercial buildings, metro stations, hospitals, and other locations where fire safety, environmental protection, and installation conditions need to be considered carefully.

B - Dry-Type Transformer Structure

In a model such as SCB14, the letter B forms part of the designation for the dry-type transformer structure.

It is worth looking at the complete model rather than trying to assign a meaning to one letter in isolation. Transformer model codes work as combinations, and the actual definition depends on the applicable naming standard.

Z - On-Load Voltage Regulation

The letter Z is commonly used to indicate a transformer with on-load voltage regulation.

For example:

SZ11-50000/110

can generally describe a three-phase transformer with on-load tap-changing capability, a Series 11 design, a rated capacity of 50,000 kVA, and a 110 kV high-voltage rating.

In practical terms, an on-load tap changer (OLTC) allows the transformer to adjust its voltage ratio while the transformer is energized and carrying load. That's particularly useful in transmission substations and large industrial power systems where maintaining a stable output voltage is important.

Understanding the Numbers in Transformer Models

The numbers in a transformer model are not just there for identification. Several of them provide quick information about the transformer's rating and product series.

Series Number

Numbers such as 11, 13, and 14 can identify a particular product series or design generation.

For example, you may see models such as:

Depending on the product and applicable standard, the series designation may be related to the transformer's design characteristics, loss levels, energy-efficiency requirements, or product generation.

So, for example, 11 should not be mistaken for an 11 kV voltage rating. It is generally a series designation.

Rated Capacity

A number such as 630, 1000, 1600, 2000, or 50000 normally represents the transformer's rated capacity in kVA.

For example:

S11-M-1000/10

indicates a rated capacity of:

1000 kVA

Likewise:

SZ11-50000/110

indicates:

50,000 kVA = 50 MVA

Rated capacity tells you how much apparent power the transformer is designed to handle under its specified operating conditions. It is one of the first things engineers look at when selecting a transformer for an electrical system.

Rated Voltage

The number after the capacity commonly indicates the high-voltage rating.

For example:

S11-M-1000/10

can be understood as:

Rated capacity: 1000 kVA

High-voltage rating: 10 kV

For a larger power transformer:

SZ11-50000/110

can indicate:

Rated capacity: 50,000 kVA

High-voltage rating: 110 kV

The low-voltage rating is normally provided separately in the transformer specification.

CommonYawei Transformer Model Examples

Looking at several examples side by side makes the naming system easier to understand.

These are simplified examples intended to explain the basic naming logic. Actual transformer models from Yawei Transformer may contain additional letters, numbers, or application-specific designations depending on the product.

How to Read a Transformer Model Correctly

Reading the model is a useful first step, but you should not stop there.

Start by identifying the transformer type. Is it an oil-immersed transformer, dry-type transformer, cast-resin transformer, pad-mounted transformer, grounding transformer, or another special design? That immediately narrows down the application and installation requirements.

Next, check the rated capacity and voltage level. A 1000 kVA, 10 kV distribution transformer is obviously intended for a very different duty from a 50 MVA, 110 kV power transformer.

The voltage regulation method is another important point. A transformer with an off-circuit tap changer is different from one equipped with an OLTC. When voltage needs to be adjusted while the transformer remains energized, on-load voltage regulation can be a major requirement.

After that, the full technical specification needs a closer look. Important parameters include impedance voltage, no-load loss, load loss, insulation level, cooling method, temperature rise, vector group, short-circuit withstand capability, enclosure protection, and the applicable standards.

In other words, the model number gives you the first picture. The datasheet fills in the rest.

Choosing the Right Transformer with Yawei

Understanding power transformer model numbers can make the selection process much less complicated, especially when you're comparing several products with similar capacities.

Yawei Transformer manufactures a wide range of transformer products, including oil-immersed transformers, dry-type transformers, power transformers, distribution transformers, renewable energy transformers, and customized transformer solutions for utility, industrial, infrastructure, commercial, and renewable energy projects.

The right model depends on much more than its letters and numbers. Rated voltage, rated capacity, frequency, cooling method, installation environment, load characteristics, harmonics, altitude, ambient temperature, voltage regulation requirements, and applicable standards all have to be considered.

So, next time you see a transformer model like S11-M-1000/10 or SCB14-2000/10, don't treat it as a random product code. There is useful information packed into those few characters. Once you know how to read them, comparing transformer products and communicating technical requirements with a manufacturer becomes a whole lot easier.

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