What is required to be connected to a protective relay for a bus with 24kA fault current?

To determine the appropriate current transformer configuration needed for a protective relay, it's important to consider the fault current levels at which the relay will operate effectively. In the case of a bus with a fault current rating of 24kA, the current transformer must be able to accurately sense the current flowing through it in order to protect the bus from damage during fault conditions.

For a system carrying a fault current of 24kA, a current transformer ratio must be chosen that allows the relay to measure this fault current within its operational range. The ratio provided indicates how the full load current is transformed into a secondary current that is typically 5A for relays.

Using the choice of current transformers rated at 400/5A, we can determine their applicability to the system. The primary current of these transformers (400A) means that they can handle a maximum of 400A on the primary side, which relates to the expected fault currents. If we consider the scaling factor (400A on the primary transforming down to 5A), we can confirm that these transformers will provide a significant portion of 24kA fault current.

This option allows the protective relay to effectively monitor and react to fault conditions within the bus. The ratio chosen provides enough coverage