How to make Continuously Transposed (CTC) cable?

Continuously Transposed Cable (CTC) consists of multiple rectangular, film-insulated conductors that are assembled and typically wrapped in multiple layers of insulation. The conductors are arranged side-by-side in two groups and transposed using a special process so that each wire occupies every possible position within a transposition cycle. The number of conductors is typically odd, ranging from 5 to 79 strands (up to 61 strands in a dual-CTC configuration). A dual-CTC is formed by combining two identical CTCs, which improves phase-adjustment performance in high-power transformers. The transposition cycle length depends on the transformer winding diameter and the conductor dimensions.

Here's an expanded and professionally written version of the CTC manufacturing process, with additional technical detail and logical flow:

Manufacturing Process of Continuously Transposed Cable (CTC)

The production of Continuously Transposed Cable (CTC)​ is a precision-driven continuous process designed to minimize eddy current losses and optimize space factor in transformer windings. The manufacturing sequence consists of the following key stages:

1. Stranding of Aluminum Round Conductors (Rigid Strander)

The process begins with a frame stranding machine​ (also known as a tubular or planetary strander), which pays off multiple aluminum round conductor reels arranged around a rotating frame. The individual conductors are fed through a central guide system and twisted together at a controlled lay pitch. The frame strander ensures that each conductor strand continuously changes its radial position within the bundle, which is the fundamental principle of transposition. Key parameters—such as lay direction, lay length, and rotation speed—are precisely synchronized to achieve uniform strand distribution and prevent internal stress buildup.

2. In-Line Compacting / Profiling (Square Compact Device)

As the stranded bundle exits the frame strander, it immediately enters an in-line compacting and profiling unit. This device typically consists of a series of profiled rollers or dies arranged in progressive stages. The round stranded bundle is gradually compressed and reshaped into a rectangular (or square) cross-section​ while the strands continue to transpose. The compaction process eliminates inter-strand voids, significantly improving the space factor​ (filling factor) and ensuring dimensional accuracy. Critical adjustments during this stage include roller gap calibration, compaction force control, and real-time monitoring of width and thickness tolerances. Care is taken to avoid damaging the individual strand insulation during the shaping process.

3. Wrapping / Serving Unit (PE Tape & Protective Layers)

Immediately following compaction, the rectangular transposed conductor passes through a wrapping (serving) machine. This unit applies PE (polyethylene) tape, polyester film, or other specified insulation materials helically around the compacted bundle. The wrapping serves multiple purposes: it binds the transposed strands together to prevent unraveling, provides an additional dielectric barrier, and protects the conductor surface from mechanical abrasion during handling and coil winding. The wrap angle, overlap ratio, and tension are tightly controlled to ensure uniform coverage without wrinkles or gaps. Depending on customer specifications, additional layers—such as semi-conductive tape or crepe paper—may also be applied in this section.

4. Caterpillar Traction & Take-Up

A caterpillar (track-type) puller​ is positioned downstream to provide continuous, non-slip traction. Unlike capstan wheels, the caterpillar system uses two opposed belt or cleated tracks that grip the flat cable evenly across its full width, preventing deformation of the rectangular profile. The puller maintains a constant line speed synchronized with the frame strander and wrapping unit, ensuring consistent lay pitch, compaction ratio, and wrap tension throughout the production run. After traction, the finished CTC is measured for electrical and dimensional parameters, then taken up onto a drum or coil by an automatic traversing take-up system, ready for transformer winding applications.

MAX Xu

China Cable Equipment Specialist | Production Problem Solver

With deep expertise in wire and cable manufacturing machinery, I specialize in helping customers design, optimize, and troubleshoot production lines​ for advanced cable products — including Continuously Transposed Cable (CTC), Litz wire, and other specialty conductors.

From frame stranding and in-line compaction​ to wrapping systems and caterpillar traction, I understand every stage of the process and the challenges that come with it. Whether you're dealing with dimensional inconsistency, insulation damage during compaction, wrap tension issues, or line synchronization problems — I can help you identify the root cause and implement practical, cost-effective solutions.

Email / WhatsApp:​ +86 186 0661 5951 cabletwister@126.com