What Technical Parameters Do You Need to Specify Before Purchasing a Transformer?

What Technical Parameters Do You Need to Specify Before Purchasing a Transformer?

Introduction

“I want to buy a transformer. Please give me a quote.”

This is the most common way customers ask for a quotation. But a transformer is not like buying a light bulb — where you only need to know the wattage. If you don‘t provide complete parameters, the quote you get may be inaccurate or even completely unsuitable for your needs.

Too many parameters and customers get overwhelmed. Too few and the quote is meaningless.

This article helps you understand: what technical parameters do you need to specify before purchasing a transformer?

1️⃣ Why Does an Incomplete Parameter List Lead to Inaccurate Quotes?

The price of a transformer is determined by multiple factors:

• Capacity affects price

• Voltage level affects price

• Copper vs. aluminum windings affect price

• On-load vs. off-load tap changers affect price

• Oil-immersed vs. dry-type affects price

If you only say “I need a 1000kVA transformer,” the supplier doesn‘t know the voltage level, the connection group, or the installation environment — the quote they give you could be far from what you actually need.

The more complete your parameters, the more accurate your quote.

2️⃣ Core Parameter Checklist

The following are the 7 most critical parameters. You should clarify them before purchasing:

① Rated Capacity (kVA)

• The “power” rating of the transformer

• Common ratings: 100, 200, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500kVA

• How to determine it? Based on actual load + reasonable margin

② Voltage Rating (Primary / Secondary)

• Primary side: 10kV, 35kV, or other

• Secondary side: 400V, 380V, or other

• Example: “10kV / 0.4kV” means 10kV on the primary side and 400V on the secondary side

③ Frequency (Hz)

• Most countries: 50Hz (China, Europe, most of Africa)

• Some countries: 60Hz (USA, parts of Japan)

• Don‘t get this wrong — incorrect frequency means the equipment won‘t work

④ Connection Group (Dyn11, Yyn0, etc.)

• Tells the supplier how the transformer windings are connected

• Most common: Dyn11 (widely used, handles unbalanced loads well)

• Second most common: Yyn0 (requires balanced three-phase loads)

⑤ Tap-Changing Method: On-Load vs. Off-Load

• Off-load (off-circuit): Requires a power outage to adjust voltage — lower cost

• On-load: Adjustable without power outage — more expensive, suitable for areas with voltage fluctuations

• For most projects, off-load tap-changing is sufficient

⑥ Insulation Type: Oil-Immersed vs. Dry-Type

• Oil-immersed: lower cost, suitable for outdoor use

• Dry-type: higher cost, suitable for indoor and fire-sensitive locations

• Depends on the installation environment

⑦ Impedance Voltage (Uk%)

• A technical parameter that affects short-circuit current and voltage regulation

• Standard values are typically 4%, 6%, or 8%

• Suppliers usually configure this to standard specifications — generally not something the customer needs to specify, but good to be aware of

3️⃣ Environmental Parameters Are Also Important

4️⃣ Frequently Asked Questions

Q: What if I can‘t fill in all the parameters?

• Just fill in what you can. Your supplier can help confirm the rest.

Q: Who determines these parameters?

• Capacity, voltage, and frequency are project-specific

• Connection group and tap-changer type can be recommended by the supplier

• Insulation type depends on the installation environment

Q: Why do different suppliers quote very different prices for the same capacity?

• Key reasons: copper vs. aluminum windings, component brands, and manufacturing standards

• For more details, refer to our earlier article on price differences

Conclusion

Before purchasing a transformer, spending 10 minutes to clarify the parameters will make all subsequent communication much smoother.

If you‘re unsure how to fill in the details, feel free to send us your project information — we‘ll help you figure it out. No charge.

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