Selecting a transformer or inductor for a downhole applications requires consideration of more than the component’s electrical specifications. Downhole equipment can operate in environments where temperature, shock, vibration, available space, materials, and other application requirements need to be considered together.
For downhole transformers and inductors, the selection process should begin with a clear understanding of the electrical and physical requirements of the application. The required component characteristics can vary depending on how the magnetic component will be used and the environment in which it will operate.
This guide explains the key considerations involved in selecting transformers and inductors for downhole applications and when a custom magnetic component may be appropriate.
What Are Downhole Magnetics?
Downhole magnetics refers broadly to magnetic components such as transformers and inductors designed for use in downhole applications where electrical requirements need to be considered alongside environmental and dimensional requirements.
Although transformers and inductors are both magnetic components, they perform different functions within an electrical system. A transformer transfers electrical energy between circuits through magnetic coupling, while an inductor stores energy in a magnetic field and opposes changes in current.
Because their functions are different, the specifications used to define a transformer are not identical to those used for an inductor. Component selection should begin with the electrical function required by the application and then consider temperature, dimensions, materials, and other environmental requirements.
The Downhole Transformer and Inductor Selection Process
Step 1: Define the Electrical Requirements
The first step in selecting a downhole transformer or inductor is to establish the electrical requirements of the application. These requirements provide the foundation for determining the appropriate magnetic component and its design characteristics.
For a transformer, the specification may include input and output voltage, turns ratio, current, frequency, insulation requirements, operating temperature, and available space. For an inductor, the specification may instead focus on inductance, current, frequency, core characteristics, temperature, and available space.
Defining these requirements at the beginning helps establish a clear starting point for the magnetic design.
Transformer Electrical Requirements
Transformer selection begins with understanding the voltage relationship required between the circuits. Voltage, turns ratio, frequency, current, insulation, and available space all contribute to the transformer specification.
The required operating conditions should be established before selecting the core, wire, winding arrangement, and other construction characteristics.
Inductor Electrical Requirements
Inductor selection starts with defining the required inductance and current characteristics. Frequency, core characteristics, operating temperature, and available space also need to be considered.
The specific requirements depend on the intended function of the inductor within the downhole system.
Step 2: Establish the Operating Temperature
Operating temperature is an important consideration when selecting a magnetic component for a downhole application. Temperature requirements can influence the selection of the core, wire, insulation, solder, compound, and other materials used in the component.
Custom Coils’ existing downhole information identifies designs for applications at 200°C and 220°C, with some designs operating at 240°C. This demonstrates why the required temperature specification should be established early in the design process.
The temperature requirement should be treated as part of the overall component specification rather than considered separately from the electrical and dimensional requirements.
Why Temperature Matters in Material Selection
Different materials have different temperature specifications, so the required operating temperature can influence which combinations of core, wire, insulation, solder, and compound can be considered. For a high-temperature downhole transformer or high-temperature downhole inductor, the complete component design should be evaluated according to the intended operating conditions. A material’s individual temperature specification should not automatically be treated as the operating rating of the finished component.
Step 3: Consider Shock and Vibration
Downhole equipment can be exposed to shock and vibration, making these environmental conditions relevant when defining a magnetic component specification.The component’s construction and materials should be evaluated according to the requirements of the intended application. These requirements should be established along with the electrical and temperature specifications rather than treated as an afterthought.
For Custom Coils, this means the transformer or inductor design can be considered around the specific requirements provided for the application rather than relying on a single standard configuration.
Step 4: Determine the Available Space
Available space is another important consideration when selecting a downhole magnetic component. Downhole equipment can require compact component geometries, so the maximum allowable dimensions should be established before selecting the component configuration. The available length, width, height, mounting space, and connection requirements can influence the geometry that can be considered for the design.
Custom Coils’ existing downhole information identifies small geometries including toroids down to 4 mm, EE5 and ER9.5 E-cores, and potcores down to 7 × 4 mm.
The appropriate geometry ultimately depends on the electrical requirements, available space, operating temperature, materials, and other specifications of the application.
Step 5: Select Appropriate Core, Wire, and Insulation Materials
Material selection is an important part of transformer and inductor design for downhole applications. Core material, wire, insulation, solder, and compound should be considered together with the expected operating environment.
Custom Coils identifies several material options for its downhole designs. These include powdered iron and MPP cores for applications up to 200°C and ferrite cores for applications up to 300°C. Wire options identified include MW35-C for 200°C and ML16 for 240°C. The existing Custom Coils information also identifies Kapton at 180°C, Teflon at 200°C, Nomex at 220°C, and Teflon/GC at 260°C as insulation options with specific temperature specifications. Solder types and compounds also have their own specifications.
These values should be considered as material specifications within the overall design process. The appropriate combination depends on the requirements of the individual transformer or inductor.
Step 6: Evaluate the Transformer or Inductor Design
Once the electrical, temperature, dimensional, and material requirements have been established, the next step is to evaluate the component-specific design requirements.
A transformer and an inductor should not be selected using exactly the same criteria because their electrical functions are different.
Transformer Design Considerations
For a downhole transformer, the design requirements can include voltage, turns ratio, frequency, current, insulation, core material, wire, operating temperature, and available space.
These requirements should be considered together to establish the transformer specification for the intended application.
Inductor Design Considerations
For a downhole inductor, the design requirements can include inductance, current, frequency, core characteristics, wire, operating temperature, and available space.
The required combination of characteristics depends on the function of the inductor within the system and the conditions under which it will operate.
Step 7: Match the Component to the Downhole Applications
After defining the component requirements, the next step is to consider the application in which the transformer or inductor will be used.
Custom Coils identifies MWD, LWD, rotary steerable motors, wireline, and completion equipment among its downhole applications.
These applications can have different temperature, dimensional, electrical, and environmental requirements. Therefore, the component should be specified according to the requirements of the actual application rather than selected solely because it is intended for a particular downhole category.
Choose Custom Coils for Your Downhole Transformer and Inductor Requirements
Selecting the right magnetic component for a downhole application starts with clearly defined requirements. When your application requires a specific combination of electrical specifications, temperature range, compact dimensions, core materials, wire, insulation, or other design requirements, a custom approach can help align the component design with the application. Custom Coils specializes in custom transformers and inductors for downhole applications, with downhole designs addressing requirements such as high operating temperatures and compact component geometries. Discuss your downhole transformer or inductor requirements with Custom Coils.
Whether you need a component designed around specific electrical specifications, temperature requirements, compact dimensions, core materials, wire, or insulation, provide your application requirements to the Custom Coils team to begin the design discussion.
Explore Custom Coils’ Down Hole Applications or contact the Custom Coils team at sales@customcoils.com or 605.934.2460 to discuss your requirements.
Frequently Asked Questions About Downhole Transformers and Inductors
What factors should be considered when selecting a downhole transformer or inductor?
The selection process should consider the electrical requirements of the application together with temperature, available space, materials, shock, vibration, and other environmental requirements. For transformers, voltage, turns ratio, current, and frequency can be important specifications. For inductors, inductance, current, frequency, and core characteristics can be relevant.
Why is operating temperature important for downhole magnetics?
Operating temperature can influence the selection of the core, wire, insulation, solder, compound, and other materials used in the component. Custom Coils’ downhole information identifies designs for applications at 200°C and 220°C, with some designs operating at 240°C.
What is the difference between a downhole transformer and an inductor?
A transformer transfers electrical energy between circuits through magnetic coupling, while an inductor stores energy in a magnetic field and opposes changes in current. Because their functions differ, their design and selection requirements also differ.
What materials can be used for downhole transformers and inductors?
Material selection depends on the requirements of the specific design. Custom Coils identifies powdered iron, MPP, and ferrite core options, along with wire and insulation options having different temperature specifications. The appropriate combination depends on the complete application requirements.
Why are dimensions important when selecting a downhole magnetic component?
Downhole equipment can have limited available space, so the component’s dimensions and geometry should be established early in the selection process. Custom Coils’ downhole information identifies compact geometries including small toroids, E-cores, and potcores.
When should a custom transformer or inductor be considered?
A custom transformer or inductor may be considered when an application requires a specific combination of electrical, physical, material, temperature, or environmental specifications. Defining those requirements provides the starting point for the custom design process.
What applications use downhole transformers and inductors?
Custom Coils identifies MWD, LWD, rotary steerable motors, wireline, and completion equipment among the downhole applications for its magnetic components. The specific requirements can vary between applications.