Current transformers (CTs) are essential components in modern electrical systems, enabling accurate current measurement and system protection across different voltage levels. In medium- and high-voltage switchgear environments, CTs are widely used for monitoring, metering, and relay protection.
At 11kV to 36kV systems, CTs are typically installed inside switchgear or mounted on bushings. These CTs are designed to deliver precision under demanding conditions, ensuring the reliable functioning of protection relays and measurement equipment. For example, in RMU (Ring Main Unit) applications, resin-cast or toroidal CTs are integrated into compact spaces, where both thermal stability and insulation performance are critical.
In high-voltage substations (66kV and above), oil-immersed or gas-insulated CTs are used. These units are built to handle larger currents and withstand environmental stress. Their output is connected to digital relays or SCADA systems for real-time monitoring and remote protection control. The use of multi-ratio CTs allows flexibility for different load conditions, helping utilities manage grid stability with improved efficiency.
When selecting a CT, it is important to consider:
·Rated primary and secondary current
·Burden and accuracy class
·Insulation material and method of installation
·Compliance with IEC or ANSI standards
By understanding the application environment and voltage level, engineers can choose the right CT type—be it window-type, bar-type, or wound-type—to ensure system accuracy and longevity.
