Intern turn winding fault can be easily detect by differential protection relay.
Also detect by buchholz relay (gas operated relay), cause buchholz relay is used to detect the internal fault of transformer.
It is usually associated with system faults but can also be caused by energization of heavy loads or starting of large motors.
Voltage sag is the short reduction in the RMS voltage between 0.1 to 0.9 pu for a duration of 0.5 cycle to 1 minute
Thermistors are ideal when measuring a single point temperature that is within 50°C of ambient.
If the temperatures are excessively high or low, a thermistor will not work.
Most thermistors work best in the range between -55°C and +114°C.
Sensitivity of thermistor is high.
Span value of thermistor is low.