These AC current sensor devices output 333 mVac at the rated current you select, e.g. 2000A/333mV. These are typically passive devices.
These “true” current transformers output up to 5 Amps AC at the rated current you select. These are all passive devices except for the 5A Rogowski coil kits, which require external power. This type of AC current sensor comes in various forms including solid an split core current transformer styles.
These current transformers output up to 1 Amp AC at the rated current you choose. These are all passive devices. This type of AC current sensor is offered in a couple styles including solid and split core current sensor styles.
These “true” current transformers output up to 5 Amps AC at the rated current you select. These are all passive devices except for the 5A Rogowski coil kits, which require external power. This type of AC current sensor comes in various forms including solid an split core current transformer styles.
These current transformers output up to 1 Amp AC at the rated current you choose. These are all passive devices. This type of AC current sensor is offered in a couple styles including solid and split core current sensor styles.
These current sensors output a 20 mA signal at the rated current and 4 mA at zero. The split-core current sensors are passive but the 4-20 mA Rogowski coil kits require either an external power source, or 9-36 Vdc power from the 4-20 mA loop, depending on the model.
There are two critical things to get right when ordering a current sensor:
1 – The input rating. 2 – The output type.
Input Rating
CTs have input ratings. For example, the SCT-0750-100 has a 100A rating, and the manufacturer has specified that it will operate from 10% to 130% of the rated current with a specified accuracy. IEC 61869-2 states the accuracy from 5% to 120%. Therefore, the SCT-0750-100 would be suitable for a circuit where the current doesn’t drop below 10A often, and that doesn’t exceed 130A.
Output Type
CTs can output AC current, AC voltage, DC voltage, 4-20mA signals, and more. Therefore, it is critical to understand what input your measuring device (e.g. meter) expects. Getting this wrong can result in device failure, incorrect results, and more.
If you are unsure, contact your meter manufacturer to determine the input signal required.
Solid-core current transformers offer a cost-effective and accurate solution for designing power meters dedicated to new equipment and buildings. They are not suitable, however, for the numerous applications involving power monitoring of existing machines and facilities, where it would be necessary to shut down power and disconnect cables before retrofitting the solid core sensors in all the places where they might be used. Installing power metering systems is generally not possible, prohibitively expensive, or even dangerous if it requires a service interruption, even for a short while (e.g. stopping a production line, a telecom or data center power supply, some nuclear plant equipment, etc).
installation and maintenance simple. They can be installed in electrical control panels – thus avoiding complex wiring – to remotely monitor devices that sometimes operate in inaccessible or harsh environments. The beauty of the split core transformers is that they can be retrofitted into a live installation without disturbing it, which often makes them the unique choice for engineers designing power meters.
But these advantages have a price, making the split core current transformers more expensive and less accurate than the solid core transformers. It is thus very important to understand the difference between the various technologies available and make a choice according to specific application constraints.
Ferrite vs. Nickel vs. Silicon Steel
Current sensors can be manufactured with many different types of core materials. The most commonly used materials are:
Ferrite:
The ferrite's qualities puts the high-performance split core current transformers on the market at a very attractive price. Ferrites are ceramic compounds of transition metals with oxygen, which are ferrimagnetic but non-conductive. Ferrite ceramics are a class of ceramic compounds made from iron oxide, and one or multiple metallic elements. The magnetic cores made from ferrite ceramics are used in high-frequency applications. The ceramic materials are produced with different specifications to meet diverse electrical requirements. These ceramic materials serve as efficient insulators and help decrease eddy currents.
Nickel:
Nickel still offers a high accuracy rating with a lower cost but does not have the performance terms of Silicon Steel cores. This metal is glassy or non-crystalline, making it useful for high-performance transformers due to low conductivity.
Silicon Steel:
Silicon steel has high electrical resistivity and long-term performance stability. Silicon steel offers high saturation flux density. A few years ago, the characteristics of silicon steel were altered with chemical changes, and today, the new product is known as AISI type M6. The M6 steel has high permeability and low losses, and it is used in high-performance applications.