Advance Power Solution

A Current Transformer (CT) is an electrical device used to measure the current flowing through a conductor in an electrical circuit. It is widely used in power systems, electrical protection, and measuring instruments to safely monitor and record high currents by converting them into a lower, more manageable value that can be easily measured by meters, relays, or other protection equipment.

1. Primary Winding:

   • The primary winding consists of a single conductor or a few turns through which the current to be measured flows. In some cases, this conductor is the actual power line carrying the high current. The primary winding of a CT typically carries the full load current, which can be several hundred or thousand amps, depending on the application.

2. Secondary Winding:

   • The secondary winding is wound around the core of the CT and provides a reduced current that is proportional to the primary current. This current is usually in the range of 1A or 5A, making it safe to be measured by meters, instruments, or relays.

3. Magnetic Core:

   • The core is made of a magnetic material (usually laminated steel or ferrite) and serves to direct the magnetic flux generated by the primary current. The core enables the transformation of the high primary current into a much lower secondary current.

4. Insulation:

   • The CT is designed with insulation to ensure safety and avoid short circuits. The insulation prevents direct contact between high-voltage components and the measurement system, protecting the operator and the equipment.

5. Burden:

   • The burden refers to the load (e.g., meter or relay) connected to the secondary winding of the CT. It is important to match the CT’s secondary winding with the burden for accurate measurement and safe operation.

• The working principle of a current transformer is based on electromagnetic induction. When the current flows through the primary conductor, it generates a magnetic flux in the CT’s core. This magnetic flux induces a current in the secondary winding of the CT, proportional to the primary current.
• The relationship between the primary current and the secondary current is determined by the turns ratio of the primary and secondary windings. For example, if the primary winding has 100 turns and the secondary winding has 1 turn, the current is stepped down by a factor of 100.

• Primary Current Rating: This is the current level in the primary circuit (e.g., 200A, 1000A) that the CT is designed to handle.
• Secondary Current Rating: This is the current on the secondary side of the CT (usually 1A or 5A) that is proportional to the primary current.
• Accuracy Class: CTs are also rated by their accuracy class, which defines how closely the secondary current tracks the primary current under various load conditions. Common accuracy classes are 0.5, 1.0, or 3.0 (with 0.5 being the most accurate).
• Burden: The maximum load the CT can handle without distortion of the output signal is specified as the burden. It is typically expressed in VA (volt-amperes).