Temperature Rise for Class F Insulation

Just some addition:

Ins Class E: Max Temp 180°C,

Temperature Rise (Max temp - Amb Temp). Here temp rise is inclusive of hot spot allowance.

Thus if amb temp is 25°C, permitted temp rise (total) will be (180-25)= 155°C.

As I recall, The stator slot RTD temperature shutdown was set at 250F on the hydro generators with class F insulation.

Max temp. rise permisible inclusive of ambient by resitance method is 140 DegC earlier .The max temp allowed is 155 Deg with 10 Deg for hot spot .If ambient is 40 rise by resistance method to be limited to100 deg C.By thermometer method it is to be limited to 95Deg C.If ambient temp is 50 then temp rise will be 90 deg. Ambient depends upon motor manufacturer's design.Normally availble standard motors are designed for 40Deg .Motors are designed specifically for 45 and 50 deg against requirements.

Further to my post ,I would state that max temp including ambient is 145 DEg C now .therefore the max.temp rise over ambient of let's say 40 Deg will be 105 by resistance method of measurement and 95 for thermometer.It is the temp rise that the designer has allowed facilitates one to use the motor on higher ambient without reducing the out put.For example if a motor is having a temp rise of 90 DEG over 40Deg amb then with class F and class F rise one can use it up to 55DEG amb or at 40 It can be overloaded.However in India the temp rise is restricted to that of class B which means a total of 120DEG C Including ambient that is 80Deg rise over 40DEG by resistance .So while specifying one has to be clear about the requirement.