current transformers (CTs)

Protection class current transformers (CTs) are designed to work with protective relays, which isolate circuits during current surges. Unlike metering CTs, focused on measurement accuracy, protection CTs prioritize a higher burden and knee point voltage. In IEC standards, the class P protective current transformer is relevant. These CTs are crucial for safeguarding electrical systems from faults by quickly disconnecting downstream circuits when excessive current is detected.

Below are some helpful PDF files related to the Current transformers:

• What is a protection class CT? A current transformer designed to drive protective relays during faults, prioritizing reliability and fast response over absolute metering precision.
• Key features:
  • High burden capability and knee-point voltage to handle fault currents without saturating.
  • Higher accuracy class and insulation level suitable for protection schemes.
  • Common standards: IEC 61869 (and parts related to protection CTs), ANSI/IEEE references in the U.S.
• Parameters to specify: primary current, secondary rating, burden (VA), knee-point voltage, accuracy class (e.g., 5P, 10P), insulation level, transformation ratio, and thermal/short-circuit withstand.
• Typical applications: feeder protection, transformer protection, busbar protection, relay tripping schemes.