How to Write Transformer Specifications

Transformers are integral pieces of equipment in electrical systems, using inductive coupling to transmit electrical energy between circuits. Power transformers convert power-level voltages from one phase to another, either decreasing or increasing the voltage based on the application's unique needs.

To ensure expected performance, safety, compliance, and clarity in procurement, it's necessary to learn how to write transformer specifications. For project managers, electrical engineers, and spec writers, this guide will provide practical information to help clarify the specific requirements needed to begin each new project.

Understand the Purpose of the Transformer

First, understand the intended application of the transformer, whether it's for power distribution, isolation, control, or another purpose. Consider whether the transformer is intended for indoor or outdoor use, along with the load requirements and operating environment.

Other considerations include relevant industry regulations, including ANSI, IEEE, IEC, NEMA, and UL standards. Ultimately, various transformer types will require different types of specification information.

Power Transformers

These transformers require documentation covering:

• Electricals. Consider electrical specifications for power transformers, such as output and input voltages, output VA or current, frequency of operation, efficiency, voltage regulation, single or multi-phase operation, and isolated or non-isolated operation.
• Other characteristics. Other power transformer specifications will cover dielectric withstanding voltage (DWV), Hipot, insulation resistance, leakage current, operating temperatures, DC resistance, maximum temperature rise, and different types of encapsulation (e.g., potted, molded, varnished, open, or conformal coated).
  

Signal Transformers

Specifications for these transformers will go over:

• Topology. Specify the transformer’s audio, impedance matching, data, or pulse topology.
• Input requirements. Detail insertion loss, impedance ratio, DC isolation, frequency range, and power rating.
• Other characteristics. Include Hipot and DWV, insulation resistance, leakage current, DC resistance, center taps, temperature rise, operational temperature, and encapsulation type.
  
  

Switch Mode Transformers

Specification info for these transformers will go over:

• Topology. List specs such as flyback, gate drive, H-bridge, forward converter, push-pull, and LLC.
• Electrical parameters. Specify factors like DC bias inductance, inductance fields, input voltage range, leakage inductance, duty cycle, switching frequency range, RMS and DC current, DC resistance, and tolerance.
• Other characteristics. Documentation will also cover Hipot/DWV, leakage current, test points, storage and ambient temperature ranges, insulation resistance, maximum temperature rise, and encapsulation type.
  
  

Current Sense Transformers

Specs for current sense transformers should cover:

• Electrical parameters. Documents could state max voltage, inductance, phase shift, current range, burden resistor, duty cycle, operating frequency, turns ratio, volt-second, accuracy, and W1 and W2 DCR.
• Other characteristics. Information should also cover Hipot/DWV, insulation resistance, leakage current, test points, operating temperature ranges, temperature rise, encapsulation type, and ambient and operating temperature.
  
  

Standards and Compliance

The next considerations are standards and regulatory compliance, which will vary across industries and applications.

For example, you may need your transformers to comply with national or international standards, like IEC 60076 or IEEE C57. They may also need to comply with UL, RoHS, REACH, or other safety and environmental regulations.

Documentation and Testing Requirements

Also, consider requirements for proper documentation and testing, which may include routine or special factory test reports based on transformer type. Other key considerations will include compliance and certification documentation, as well as manuals for transformer operation, installation, and maintenance.

Optional and Custom Features

Transformers could come with additional features if needed for a particular application. These features include sound level limits, special branding or labeling requirements, and finishing requirements for corrosion resistance, such as paints or other coatings.

Tips for Writing Clear Specifications

To write proper transformer specifications, here are a few tips to keep in mind:

• Maintain consistent units and terminology to avoid confusion
• Clearly define all of the terms used within the documentation, including abbreviations.
• Incorporate visuals when possible, such as drawings and diagrams.
• Collaborate with manufacturers or suppliers early on in the process to keep everyone on the same page.

Learn More About Writing Transformer Specifications

Knowing how to write transformer specifications is important in creating safe, precise, and compliant transformers that function properly in their intended applications. To get started with writing these specifications for your transformer, download our design templates and use them as checklists:

At Triad Magnetics, we help our customers get the best results from their transformers and other magnetics. We can customize any product from our inventory of over 1,000 standard products.

For more information about our transformers and other products, contact us or request a quote today.