Current Transformers

Current transformers (CT's), also known as Core Balance Current Transformers or Current Transducers, are instruments that are used to reduce or multiply the current from a high current into a lower current or vice versa. Current transformers, however, work in a slightly different way from voltage transformers. Plus, the amount of reduction in current is dependent upon the turn ratio. Whereas, connecting an ammeter to the CT's terminals will allow you to measure the current easily.

Current Transformers (CT) consist of a core, a primary 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" .

It is possible, however, that the secondary winding contains many coil turns which are wound atop a laminated core made out of magnetic material that is low-loss. With this core, the cross-sectional area is large, resulting in a low magnetic flux density when coupled with a wire of a smaller cross-section, no matter if it has to step down the current, whatever the load.

The secondary winding supplies current either to a short circuit, such as an ammeter or a resistive load, up to the point when the secondary becomes saturated or breaks down due to excessive voltage.

RS offers an extensive range of highly accurate Core Balance Current Transformers in various transformer types, current ratings, CT ratio supply voltages and mounting types to suit every application. Supplied by industry-leading brands including Siemens, Murata Power Solutions LEM and of course RS PRO.

How does a current transformer 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 Ammeters

Types of current transformer (CT meter)

#1 - Toroidal Current Transformer

In the shape of a doughnut, these transformers are designed without having a primary winding as part of their construction. Rather, a toroidal transformer has a window or hole through which the current flowing in the network passes.

#2 - Wound Current Transformer

Transformers have primary windings that are connected physically line to line with the conductor bringing the measured current through the circuit.

#3 - Bar-type Current Transformer

This type of transformer uses the cable, or busbar, of the main circuit as its primary winding, effectively one turn of the transformer. In most cases, they are bolted directly to current-carrying devices and are fully insulated from high operating voltages.

Where would I use a Current Transducer?

CTs are used in a wide range of industrial and commercial measurement applications. Some of the most common are:

1. Generating Stations
2. Electrical Substations
3. Commercial Electric
4. Power Distribution
5. Electrical Panels

Usually, ammeters and current transformers are used in conjunction, with the current transformer being designed to deliver a maximum secondary current equivalent to the ammeter deflection at full scale. It is common for current transformers to have inverse turn ratios between their primary and secondary windings. Therefore, CT calibrations are usually geared towards a specific type of ammeter.

Browse the broad range of Current Transformers RS have to offer and order today for next-day delivery.