The correct answer is: C. Method of average losses
The method of average losses is a method of calculating the temperature rise of a machine under variable load conditions. It does this by calculating the average loss of the machine over a period of time and then using this average loss to calculate the temperature rise. However, this method does not take into account the maximum temperature rise that can occur under variable load conditions. This is because the average loss is calculated over a period of time, and the maximum temperature rise can occur at any point during this time.
The equivalent power method, the equivalent current method, and the equivalent torque method are all methods of calculating the temperature rise of a machine under steady-state load conditions. These methods do take into account the maximum temperature rise that can occur under steady-state load conditions.
The equivalent power method is a method of calculating the temperature rise of a machine by assuming that the machine is a resistor. The equivalent current method is a method of calculating the temperature rise of a machine by assuming that the machine is an inductor. The equivalent torque method is a method of calculating the temperature rise of a machine by assuming that the machine is a motor.
All of these methods are valid methods of calculating the temperature rise of a machine, but the method of average losses is not a valid method of calculating the temperature rise of a machine under variable load conditions.