Current Transformers

Current transformers (CT's), also known as core balance current transformers (CBCT) or current transducers, are instruments that are used to reduce the current from a high current into a lower current or vice versa. The amount of reduction in a current is determined by the turn ratio.

Current transformers consist of a core, a primary winding, and a secondary winding. In some current transformers, the primary winding has a limited number of turns, making it possible for current to be measured without disconnecting it from the supply or load. Since it is arranged in this manner, the current transformer is sometimes called a "series transformer".

In some cases, the secondary winding contains many coil turns which are wound atop a laminated core made out of magnetic material that is low-loss. The cross-sectional area of this core is large, resulting in a low magnetic flux density when coupled with a wire of a smaller cross-section. The secondary winding supplies current either to a short circuit, such as an ammeter, or a resistive load, until it becomes saturated or breaks down from excessive voltage.

How Current Transformers Work

When an alternating current flows through the primary winding, a magnetic flux is created, which then induces an alternating current in the secondary winding. This alternating current is proportional to the current in its primary. Current transformers are also known as "step-down transformers". Once the current has been reduced, it can be safely monitored and measured using an ammeter.

Current Transformer Types

Toroidal Current Transformer

Toroidal current transformers, also known as ring-type current transformers, have a distinctive doughnut shape. They are constructed without a primary winding. Instead, a toroidal transformer has a window or hole through which the current passes. Toroidal CTs are often used in applications where high accuracy and minimal heat generation are required.

Wound Current Transformer

Wound current transformers have primary windings that are physically connected in series with the conductor carrying the measured current. Wound current transformers are commonly used in applications such as metering for billing purposes.

Bar-type Current Transformer

Bar-type current transformers use the cable, or busbar, of the main circuit as their primary winding. They are often bolted directly to current-carrying devices, useful for high-current applications where it may be impractical to disconnect the conductor for installation. They are fully insulated from high operating voltages to ensure safety and prevent electrical shock.

Core Balance Current Transformer (CBCT)

CBCT current transformers are designed to detect and measure current imbalances in a three-phase system. They are typically used for earth fault protection. A CBCT encircles all three phase conductors and the neutral conductor. Under normal balanced conditions, the magnetic fluxes generated by the currents cancel out. However, if an earth fault occurs, an imbalance in current flow is detected, and the CBCT produces a secondary current that triggers a protective device.

Split Core Current Transformer

Split core CTs offer a convenient solution for measuring current without interrupting the circuit. Unlike CBCTs, which are designed for earth fault protection, split core current sensors are used for general current measurement applications. Their core can be opened and clamped around the conductor, eliminating the need to disconnect the conductor for installation. This makes them ideal for retrofitting in existing installations or temporary monitoring setups.

Current Transducer

Like current transformers, current transducers measure current. However, they have the additional capabilities of converting the measured current into various output signals, including voltage, current, frequency, or even digital signals. This makes them more versatile for integration with different monitoring and control systems.

Benefits of Using Current Transformer Metres

Safety

CT transformers provide electrical isolation between the high-current primary circuit and the low-current secondary circuit, enhancing safety for personnel and equipment.

Accuracy

Current transformers offer high accuracy in measuring currents, making them suitable and reliable for various applications, including metering and protection.

Easy Installation

Electronic current transformers are relatively easy to install and maintain, making them generally accessible across users.

Cost-Effectiveness

Compared to other current measurement methods, current transformer prices are relatively cost-effective, especially for high-current applications.

Industrial Applications of CT Transformer

Generating Stations

Current transformers are used in power plants to monitor generator output, transformer currents, and overall power flow, ensuring efficient and safe operation.

Electrical Substations

In substations, CTs are crucial in metering, protection and control of high-voltage equipment, ensuring reliable power distribution.

Commercial Electric

Commercial buildings utilise CTs for energy monitoring, load balancing and tenant sub-metering, optimising energy usage and reducing costs.

Power Distribution

CTs play a critical role in power distribution networks, enabling accurate metering, protection against overloads, and fault detection.

Electrical Panels

Current transformers are commonly found in electrical panels to monitor individual circuit currents, providing data for energy management and overload protection.

Trusted Current Transformers Manufacturers, Suppliers and Distributors in Australia

As a leading provider and manufacturer of electrical and industrial products, RS Australia offers highly accurate Core Balance CTs in various transformer types, current ratings, CT ratio supply voltages and mounting types. Our current transformers come from reputable brands such as ABB, Eaton and Schneider Electric.

We also provide other essential electrical components, such as multimeter test leads and interlock switches. Whether you’re planning the perfect home office setup or installing industrial high bay lighting, you’ll find all your essential electrical components at RS Australia.

Buy Current Transformers from RS Australia

RS Australia offers efficient delivery of current transformers for online and offline orders, with self-collection options available as well. Read our Delivery Page to find out how our various delivery services can help meet your requirements.