Characteristics of Overcurrent Stage

Do the relay coordination and see which curve fits for the protection of the motor.

For detail about the relay coordination, see this link: http://epowerengineering.com/guides-part-5.pdf.

Since Siemens SIPROTEC 7SJ600 is the motor protection relay, I would suggest you to look into the 'MV Motor Sample Problem' (page 28 through 30).

For proper coordination, it is better to use the software such as ETAP.

- MS

You said Definite Time Ovecurrent Protection, but have mentioned IDMT (Inverse Definite Minimum Time) Curves. Contradictory!!

However, if the protected equipment is a motor, it is advisable to go for an extremely inverse curve, because it follows the formula K = I (squared) t, which closely resembles the Thermal Curve of the motor.

However, I would also like to into co-ordination requirements with other upstream and/or downstream protective devices.