Choose the right current transformer

Current transformers are generally used to make measurement currents greater than 5A suitable for kilowatt-hour meters and analysers. We can distinguish between 3 types of current transformers:

• Traditional current transformers (CTs)
• Low power current transformers (LPCTs)
• Rogowski coils

Traditional current transformers, in a split core version, are ideally suited for use in existing installations without disconnecting the primary conductor. fortop has an extensive range of split core current transformers.

Low power current transformers are mainly used for low measurement currents with high accuracy requirements. They are cost-effective, and the use of short-circuit terminals is not necessary.

Rogowski coils are ideal for measuring high measurement currents and for use around copper busbars.

On this advice page, you will find, by type of current transformer, a handy overview to easily and quickly find the right current transformer for your application or meter/analyser.

View current transformers in the Product Portal

In addition to conventional current transformers, it is also possible to opt for low power current transformers. Low power current transformers are safer and easier to use than standard current transformers. They contain an internal resistor that prevents the occurrence of high voltages, thereby reducing the risk of sparking and making a short-circuit block unnecessary. Additionally, they provide an output of 333mV, making the installation safer.

Beyond the safety benefits, low power current transformers offer several other advantages. They allow the use of thinner and longer cables without affecting the measurement results. Furthermore, the use of connectors is possible, and they are cheaper and more compact.

Specialist low power analysers or current measurement modules are required for connecting low power current transformers. Below is a clear overview of the different low power current transformers and the analysers or current measurement modules they can be connected to.

Rogowski coils are a special type of current measuring device without a magnetic core. This clearly distinguishes Rogowski coils from traditional current transformers. The Rogowski coils, named after Walter Rogowski, use a wire wound in a helical structure. This coil generates a voltage corresponding to the change in current through the conductor.

One of the advantages of Rogowski coils is that they can measure very high currents without saturating. They are therefore linear over a wide range, with an output signal that is proportional to the measured current. Other advantages include easy installation in difficult locations, the possibility of large through-hole openings, the coils being electrically isolated from the circuit being measured, and a wide frequency range.

Despite the many advantages, Rogowski coils also have disadvantages. For example, they are sensitive to external magnetic fields, and their accuracy can depend on the exact positioning around the conductor. Additionally, their performance can be (adversely) affected by temperature fluctuations.

The table below provides a clear overview of the Rogowski coils.

Current measurement at a lower level is necessary in many installations. Relatively low values ​​are measured at this low level and the available space is minimal. In addition, the measurements must meet high accuracy (minimum class 1).

Most compact IEC transformer for accurate current measurement

The compact RM27 current transformer is the smallest current transformer on the market and has been specially designed for use in combination with digital measuring systems. The small current transformer is also suitable for use on a three-phase automatic switch with a 17.5 mm distance between the phases. The RM27 is supplied with a connector with terminal technology for mounting on secondary connections. Optionally, mounting on a DIN rail or clip for screw mounting is possible.

Features RM27 compact current transformer:

• Ideal for detailed current measurements at level 4, where no direct energy meters can be used
• Easy to integrate with the Wago Picomax connector
• Meets the requirements of IEC61869-2
• Ideal for detailed flow measurements up to automatic level
• Primary lead-through opening suitable for cable Ø7.5 mm
• Super compact, suitable for use on a 3-phase machine
• Accuracy class 1, suitable for energy monitoring
• Output power tailored to modern meters such as Janitza
• Available in 35/1A and 64/1A transfer ratios
• Also suitable for mounting on a DIN rail with optional adaptor

View RM27 compact current transformer in the Product Portal

Quickly perform accurate flow measurements in small spaces or existing installations with the TQ line split core current transformers from ELEQ.

Simple and efficient flow measurement

Current transformers are easy to install due to the compact design, the hinge construction, and the supplied cable tie around the transformer to mount the insulated conductor. The long color-coded secondary connections ensure that the transformer is seamlessly connected to the energy meter.

The specified power rating applies at the end of the secondary branches and is adjusted to modern energy measurement devices such as the Janitza meters. The transformers meet the requirements of IEC61869-2, which guarantees accuracy.

Features of the TQ series split core current transformers:

• Compact and hinged for easy installation
• Suitable for the insulated conductor
• Suitable for energy measurement
• Colour-coded connections simplify assembly
• Available in different variants and transfer ratios (see table)

View TQ series current transformers in the Product Portal