Transformer Copper Conductor – CTC & PICC

Transformer Copper Conductors are the most important materials used in transformer winding. Copper is preferred because it offers high electrical conductivity, excellent mechanical strength, and superior reliability. In power transformers, windings are mostly made from enamelled rectangular copper conductors, which are formed using multiple strands.

Transformer windings mainly use two types of Transformer Winding Copper:

1. CTC – Continuously Transposed Conductor
2. PICC – Paper Insulated Copper Conductor

Both types are essential for improving transformer performance, efficiency, and durability.

Continuously Transposed Conductor (CTC)

A CTC Conductor is a special type of copper conductor used in medium- and high-voltage transformers. It is made up of several enamelled rectangular copper strands arranged in a pattern where the strands are continuously transposed at fixed intervals.

Why CTC is Used in Transformers

In AC systems, conductors are affected by:

• Skin effect
• Proximity effect
• Uneven current flow

These effects increase resistance and cause energy losses.

By continuously interchanging the position of each strand within the coil, CTC ensures:

• Uniform current distribution
• Lower AC resistance
• Reduced power losses
• Better cooling and lower hot-spot temperature
• Improved voltage regulation

This makes CTC the most preferred conductor for power transformer windings.

Construction of CTC Conductor

A standard Transformer CTC Conductor includes:

• An odd number of enamelled rectangular copper strands
• Continuous transposition of strands
• External insulation using kraft or insulating paper

Epoxy Bonded CTC

In epoxy bonded CTC:

• Each strand is coated with a semi-cured epoxy layer
• During coil drying, the epoxy fully cures
• The winding becomes a solid, strong block
• The conductor can withstand high short-circuit forces

Epoxy bonded CTC is commonly used in large power transformers where mechanical strength is critical.

Paper Insulated Copper Conductor (PICC)

PICC Conductor stands for Paper Insulated Copper Conductor. It is a special type of copper conductor used mainly in oil-filled Power Transformers and Distribution Transformers. PICC is popular because it provides high electrical insulation, mechanical strength, and reliable performance in heavy-duty transformer applications.

Construction of PICC

PICC consists of:

• One to four copper strands
• Wrapped with multiple layers of high-quality kraft paper
• Combined into one insulated conductor

Advantages of PICC Conductor

1. Reliable Electrical Insulation
   Paper insulation prevents contact between copper strands and other windings, reducing the risk of short circuits.
2. Lower Capacitance
   Helps achieve better voltage regulation and reduces energy losses.
3. High Mechanical Strength
   The paper layer supports the conductor and maintains its shape during winding.
4. Thermal Stability
   Paper insulation works well in oil-filled transformers and withstands high temperatures.
5. High Dielectric Strength
   Ensures safety and long life under high voltage stress.

PICC is commonly used in:

• Distribution transformer windings
• Power transformer LV and HV coils
• Dry and oil-filled electrical equipment