What is the protection devices that you have to fix it on the motor?

on the stator you can fix these devices

1) Phase &Ground fault protection.2) Inter turn fault protection.3) Over&Under voltage protection.4) Temperature (Thermal) protection.

and on the rotor you can fix these devices

1) Ground fault on rotor winding.2) Loss of excitation.3) Over speed.4) Motoring of generator.

PTC(Positive Temperature Ceoff.) Thermistors, NTC ( Negative Temp. Ceoff) or Thermostats, If you mean the protection devices that you fix on or inside the motor. These devices provide winding over-heating pfotection.

The thermal protector or thermal relay is in a place to turn the moter off when excessive heat