Current transformers play a vital role in a wide range of industrial applications today. They can carefully monitor electrical current in a circuit, providing overload protection and keep current within a safe level. When you order current transformers, you should be aware of ratings and classes. Here is a closer look at relay class ratings for CT applications.
Accuracy
Accuracy is extremely important when it comes to metering and controlling electrical current. Many components in control circuits are very small, and when current levels get too high, you run the risk of burning out components or even starting a fire. When a current transformer is working, you may not know just how accurate it measures current. This is where relay class ratings for CT applications play an important role.
What the Letters Mean
You may notice a rating beginning with the letter “C.” C stands for calculation, and this means the transformer ratio may be calculated. This type of transformer has evenly spaced windings. C rated units have low reactance. Reactance is electrical component opposition to AC current flowing through a circuit. Although reactance is similar to electrical resistance, it is not the same. Both reactance and resistance together are called impedance.
“T” means the CT has been tested. Testing is essential because, in this type of CT, reactance cannot be fully guaranteed. A typical rating may be C100 or T100. This number is derived by multiplying the secondary current rating by 20 and then by the burden, so a C100 would have 5 amps rated secondary current and a 1.0-ohm burden. Burden refers to the secondary CT load as opposed to the primary load.
To fully understand your needs for current transformers, and relay class ratings for CT applications, talk to your current transformer specialists. They can answer all your questions and also offer custom applications.