Question 6.AE.11: The temperature rise equation is written for a drip-proof mo......
The temperature rise equation is written for a drip-proof motor [48, Section 13.7]. This equation is based on the following assumptions:
1. The ohmic losses in the embedded part of the stator winding produce a temperature drop across the slot insulation.
2. The iron-core losses of the stator teeth, the ohmic losses in the embedded part of the stator winding, and the ohmic losses of the rotor bars and half of the iron-core losses of the stator back iron generate temperature drops across the stator back iron and the motor frame. The thermal network of this drip-proof motor based on the above assumptions is depicted in Fig. E6.11.1. In this figure P_{em} stands for the ohmic losses in the embedded part of the stator winding.
From the thermal network of Fig. E6.11.1 one obtains for the temperature drop across the stator winding insulation
\Delta T_i=P_{e m} \frac{\beta_i}{\lambda_i \cdot S_i}, (E6.11-1)
and the temperature drop across the stator back iron is
\Delta T_{y 1}=\left(P_{e m}+\frac{1}{2} P_{y 1}+P_{t 1}+P_{s p 1}+P_b+P_{s p 2}\right) \frac{h_{y 1}}{\lambda_c \cdot S_{y 1}} (E6.11-2)
where P_b are the ohmic losses in the rotor bars.
Finally, the temperature drop from the motor frame to the ambient temperature is
\Delta T_f=\frac{\left(P_{e m}+P_b+P_{t 1}+P_{s p 1}+P_{s p 2}+\frac{1}{2} P_{y 1}\right)}{\alpha_o \pi\left(D+2 h_1+2 h_{y1}+2 h_f\right)\left(L+L_e\right)} (E6.11-3)
where h_1 is the radial height of stator tooth, h_f is the radial thickness of stator frame, h_{y1} is the radial height of stator back iron, L is the embedded (cylindrical) length of stator winding, and L_e is the length of the two stator end windings.
The temperature rise of the stator winding is therefore
\Delta T=\Delta T_i+\Delta T_{y_1}+\Delta T_f (E6.11-4)