Exploring the Types of Current Transformers with Examples

Current transformers (CTs) are critical components in electrical systems, used to measure and monitor electrical currents safely and accurately. Various types of current transformers exist, each with distinct features and applications. This article delves into the four main types of current transformers, providing detailed explanations and practical examples for each type.

1. Wound-type Current Transformer

Wound-type current transformers are widely used in various electrical installations, especially in high-voltage environments. The primary winding is directly connected in series with the line conductor that carries the entire current to be measured. These transformers have a fixed primary and secondary winding, which cannot be disconnected. One of the notable applications of wound-type CTs is in switchyard high-voltage current transformers (HVCT).

Example: Switchyard High Voltage CTs are used in power substations to accurately measure the current flowing in high-voltage circuits, ensuring the efficiency and safety of the electrical infrastructure.

2. Toroidal Current Transformer

Toroidal current transformers, also known as ring-type transformers, do not have a primary winding. Instead, the line that carries the current is threaded through a window or hole in the toroidal transformer. This design makes them highly versatile and portable. Toroidal CTs can be easily installed and removed, making them ideal for testing and maintenance.

Example: A digital tongue tester is an example where toroidal current transformers are used. These devices can quickly and accurately measure current without the need for permanent installation, making them convenient for temporary testing scenarios.

3. Bar-type Current Transformer

Bar-type current transformers are designed to have the primary winding as the line, cable, or busbar of the load circuit. The primary is a single straight line that is considered a primary winding. These CTs are designed with a hollow core that does not have any physical contact, allowing for easy installation and maintenance. However, the secondary winding cannot be removed in a live condition, which can be a drawback for some applications.

Example: Core-balanced current transformers (CBCTs) are commonly used to sense unbalanced current flows in electrical circuits. These transformers provide accurate measurements of current imbalances without direct physical contact with the live circuits.

4. Summation Current Transformer

Summation current transformers combine the outputs of multiple current transformers into a single output. This approach simplifies the metering process and reduces the installation and wiring costs associated with multiple individual current transformers. Summation CTs are particularly useful in applications requiring precise and efficient current measurement for multiple circuits.

Example: In a power distribution system, multiple summation current transformers can be used to measure the combined current from various sources, providing a more accurate and cost-effective solution than installing individual CTs for each circuit.

Comparison of Basic Types of Current Transformers

When considering the three basic types of current transformers—wound, toroidal, and bar—it is important to understand their unique characteristics. Wound-type and toroidal transformers have been discussed extensively. Here’s a brief comparison:

Wound-type current transformers have a primary winding directly connected in series with the conductor, with a fixed primary and secondary winding. Toroidal current transformers feature a window or hole through which the current-carrying line is threaded, and can be split for easier installation and removal without disconnecting the circuit. Bar-type current transformers use the actual cable or busbar as the primary winding, offering full insulation from the high operating voltage of the system and bolted to the current-carrying device.

In conclusion, the choice of current transformer depends on the specific application requirements, such as accuracy, installation ease, and the need for portability. Understanding the types of current transformers and their applications is crucial for effective electrical system design and maintenance.

Keywords: Current Transformer, Wound Transformer, Toroidal Transformer