Three-Phase LV Auto Transformers

Efficient Voltage Adaptation​

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Omsan three-phase LV autotransformers are designed for high-efficiency voltage conversion in low-voltage systems.

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They offer a more compact, lower-loss, and more economical solution compared to classic isolation transformers in applications that do not require galvanic insulation.

They are particularly suitable for 400V ↔ 690V systems, motor supplies, machine voltage adaptations, and in-factory distribution applications.

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Key Advantages

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Omsan LV autotransformers increase system efficiency and reduce unnecessary energy losses under the right application conditions.

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Main advantages:

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• High efficiency up to 99%

• Low voltage drop

• Compact design

• Lower weight

• Low operating loss

• Application-specific design

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Areas of Application​

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Omsan LV autotransformers are used in the following applications:

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• 400V → 690V motor supply

• 690V → 400V system adaptation

• Imported machine voltage compatibility

• In-factory low-voltage distribution

• High-power industrial systems

• Test systems and process lines

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Why Autotransformers?

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Galvanic isolation is not necessary in every application. Using isolation transformers in systems where isolation is not required means higher losses, larger volume, more weight, and higher costs.

In autotransformers, the primary and secondary windings are shared. Energy transfer occurs through both magnetic and direct conductive connections.

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Thanks to this structure:

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• Less material is used.

• Copper losses are reduced.

• Core size is reduced.

• System efficiency is increased.

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In conclusion, autotransformers are the most efficient voltage-matching solution in the right application.

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Engineering Approach

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In Omsan, autotransformers are not treated as standard catalog products. Each product is designed according to the electrical and thermal conditions of the system in which it will be applied.

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Key parameters considered in the design:

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• Input and output voltages

• Voltage transformation ratio

• Load type and load profile

• Continuous or transient operating regime

• Voltage drop requirement

• Short-term overload conditions

• Ambient temperature

• Cooling conditions

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This engineering approach ensures the product is sized not only based on nominal power but also on actual operating conditions.

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Voltage Stability

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Voltage drop under load can occur in incorrectly selected or inadequately sized transformers. This negatively affects motor performance, process stability, and equipment efficiency.

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In Omsan LV autotransformers, impedance is optimized according to the needs of the application. This ensures a more stable voltage under load and maintains system performance.

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Thermal Performance

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High current and continuous operating conditions make thermal design critical in autotransformers.

In Omsan designs:

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• Current density is controlled.

• Hot-spot temperature is taken into account.

• Loss distribution is balanced.

• The cooling structure is determined according to the application.

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This ensures that the temperature rise is kept under control, insulation life is preserved, and long-term, reliable operation is maintained.

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Dynamic Load Behavior

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Motor starting, sudden load changes, and short-term high current demands can create electromagnetic and thermal stresses on the transformer.

Omsan LV autotransformers are designed taking these conditions into account. The winding structure, connections, and mechanical fastening elements are reinforced against dynamic load effects.

As a result, the system operates more stably, and the stress on the equipment is reduced.

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Production Quality

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Omsan LV autotransformers are manufactured using controlled production processes.

The key quality elements applied in production are:

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• Low-loss core design

• Homogeneous winding distribution

• Low contact resistance connections

• Controlled insulation application

• Vacuum Pressure Impregnation (VPI)

• Structure with increased mechanical strength

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These processes ensure repeatable quality and long-term operational reliability.

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Testing and Verification

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Each transformer undergoes routine testing in accordance with relevant standards.

Tests performed:

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• Winding resistance measurement

• Voltage ratio verification

• Impedance measurement

• No-load loss measurement

• Load loss measurement

• Insulation resistance test

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Temperature-rise tests and special verification tests can also be performed upon request.

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When Not to Use?

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Autotransformers are not the right solution for every application.

Isolation transformers should be preferred over autotransformers in the following situations:

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• If galvanic insulation is required

• If sensitive electronic loads are being supplied

• If the grounding structure is critical

• If electrical separation between the grid and the load is desired

• If EMC or leakage current control is important

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Correct product selection is critical for system safety and long-term performance.

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Technical Specifications

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• Power range:0.1 kVA – 2500 kVA

• Voltage level: ≤ 1 kV

• Frequency:50 / 60 Hz

• Phase: 3-phase

• Cooling: AN / AF

• Insulation class: F / H

• Temperature rise: 80K / 100K

• Protection class: IP00 – IP23, optional IP55

• Efficiency: 98.5% – 99%+

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Conclusion

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Omsan LV autotransformers are designed to reduce energy losses, increase system efficiency, and provide a compact solution in low-voltage applications that do not require insulation.

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In the right application, an autotransformer is not only a more economical option; it is a more efficient, more compact, and more rational engineering solution.

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Engineering Support

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For the correct selection, load information, voltage levels, operating conditions, and system requirements are evaluated together.

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Omsan determines the appropriate autotransformer solution for each project through engineering calculations.