When selecting instrument transformers, various parameters must be considered, such as rated primary current/voltage, rated secondary current/voltage, accuracy class, and rated burden. Accuracy classes are typically categorized as 0.1, 0.2, 0.5, 1, 3, etc., with lower numerical values indicating higher accuracy. Furthermore, installation and operation must comply with relevant standards and specifications-such as IEC and GB-to ensure safety and reliability. For instance, the secondary side of a current transformer must not be left open-circuited, as this creates a risk of high voltage; conversely, the secondary side of a voltage transformer must not be short-circuited, as this can cause equipment damage.
Rated Voltage and Current: The rated voltage of the transformer should exceed the line's rated voltage; the primary current should be selected at 1.2 to 1.5 times the maximum load current.
Transformation Ratio and Secondary Current: Standard secondary currents are 5A or 1A; a 1A rating is recommended for long-distance transmission or high-voltage applications (330kV and above) to reduce power loss.
Accuracy Class: Select Class 0.2S or 0.5 for metering purposes, and Class 5P or 10P for protection purposes; ensure the secondary burden does not exceed the rated capacity.