Current Transformers perform two critical roles in the power supply eco-system. They are used as current measurement devices and as protection relays. However, there are different types of Current Transformers and several factors govern the appropriate choice of the Current Transformer.
The objective of this study is to understand the key considerations before choosing the right Current Transformer for a particular application.
If you are looking to read about the basic function of Current Transformers, compliance standards, and applications, read our earlier blog here.
These Current Transformers are employed to detect a fault, not for measuring the current of a power system or the connected equipment. The fundamental difference in the requirement of a measuring and a protective transformer is in terms of accuracy, saturation level and VA burden.
Unlike a measuring CT, a protection CT has a high saturation level to allow high primary current to transform substantially to the secondary as required, depending on the current setting of the protective or tripping relays. Therefore for protection CTs, accuracy class is of little relevance up to the primary rated current, but a true reflection in the secondary is more important of a fault condition in the primary.
Generally, it is not feasible to meet both requirements of metering and protection by one CT. Two sets of transformers are usually employed for a power circuit, one for measurement and the other for protection.
Protection CTs are generally available in wound or ring type. They find wide application in Control Panels, Monitoring Systems and Protective Systems.
KWP Series are a range of Protective Current Transformers. These CTs are used to activate the protective relay in case of a fault current and isolate a part of or the full system from the main supply.
Learn more: KWP Series – Wound Primary Protective Current Transformers from KSI
KRP series of Ring type also called as window type, allow bus bars or cables to be passed through the CT and act as a Primary for the CT. These CTs are used to activate the protective relay in case of a fault current and isolate a part of or the full system from the main supply.
Learn more: KRP SERIES – Ring Type Protective Current Transformers from KSI
Read related blogs on
Summation Measuring Current Transformers for Power Systems
Selection of Current Transformers for Metering and Measurement Applications