CT on any star winding of a transformer are connected in delta that CTs on any delta winding connected in star. CTs in order to compensate for the phase difference in the primary and secondary current of transformer.

The type of connection employed for current transformers (CTs) for the protection of star-delta connected 3-phase transformers is Star-Delta connection.

Explanation:
- Transformers are used in power systems to step up or step down voltage levels. In certain cases, it is necessary to protect the transformers from faults such as overcurrent or short circuits. Current transformers are used for this purpose.
- Current transformers are designed to measure the current flowing through a conductor and provide a reduced current output proportional to the primary current.
- The connection of current transformers depends on the transformer's winding configuration. In the case of a star-delta connected 3-phase transformer, the primary winding is connected in star (wye) configuration, and the secondary winding is connected in delta configuration.
- For the protection of the transformer, current transformers are connected in the secondary side of the transformer's delta winding.
- The reason for using a star-delta connection for current transformers in this configuration is to ensure proper measurement and protection during both normal and fault conditions.
- During normal operation, the star-delta connection allows the current transformers to accurately measure the currents flowing through the delta-connected winding.
- In the event of a fault, such as a phase-to-phase or phase-to-ground fault, the current transformers will detect the fault current and provide a proportional output to the protection relays.
- The star-delta connection ensures that the fault current is accurately measured and relayed to the protection system for appropriate action, such as tripping the circuit breaker to isolate the faulty section.
- Additionally, the star-delta connection helps to reduce the magnitude of fault currents flowing through the current transformers, making it easier to design the CTs and the associated protection system.
- It is important to note that the primary side of the current transformers should always be connected in the direction of the primary current flow to ensure accurate measurement and protection operation.