# Synchronous Homopolar Generator without Permanent Magnets for Railway Passenger Cars
## 5 Performance Comparison of the Optimized Design with a Commercially Available Undercar Generator  
This section compares the characteristics of the proposed optimized design of the generator with a serially produced undercarriage generator with an excitation winding on the stator EGV.08.1 with a rated power of 35 kW [31]. Table 4 shows the comparison results of the considered generators.  
The results of comparing the calculated optimized characteristics of the SHG with the characteristics of a commercially produced generator allow us to draw the following conclusions:  
1. The volume of the active part of the optimized SHG is 0.04/0.019 = 2.1 times smaller than that of a mass-produced generator. It is expected that the mass and the cost of the optimized SHG will be less than that of the mass-produced generator;
2. The calculated efficiency of the optimized SHG neglecting mechanical losses is much greater than the efficiency of the mass-produced SHG over the entire range of operation. The mechanical losses that are mainly small losses in the bearings cannot reduce the efficiency significantly;
3. The reduced input (mechanical) power due to the reduction of power loss of the SHG results in reducing the load on the transmission elements and wheels of the car, which will increase their lifetime.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Parameter** & \multicolumn{2}{c}{**Initial Design**} & \multicolumn{2}{c}{**Optimized Design**} \\ \hline Operating point & 1 & 2 & 1 & 2 \\ \hline Rotational speed \(n\), rpm & 3450 & 750 & 3450 & 750 \\ \hline Amplitude of the armature phase current \(l_{arm}\), A & 388.6 & 1001.7 & 369.5 & 676.2 \\ \hline Efficiency \(\eta\) *, \% & 93.7 & 71.1 & 90.4 & 79.8 \\ \hline Input mechanical power \(P_{mech}\), kW & 40 & 40 & 40 & 40 \\ \hline Active electrical power \(P_{1}\), kW & 37.67 & 29.33 & 36.58 & 33.12 \\ \hline Output electrical power \(P_{1}-P_{ex}\), kW & 37.5 & 28.4 & 36.2 & 32.0 \\ \hline Armature DC copper loss \(P_{arm\,DC}\), kW & 1.55 & 10.30 & 1.90 & 6.37 \\ \hline Armature eddy current copper loss \(P_{arm\,AC}\), W & 123 & 51 & 417 & 131 \\ \hline Stator lamination loss \(P_{iron\,st}\), W & 663 & 359 & 961 & 403 \\ \hline Rotor lamination loss \(P_{iron\,st}\), W & 51 & 10 & 192 & 26 \\ \hline Excitation copper loss \(P_{ex}\), W & 129 & 837 & 368 & 1169 \\ \hline Total loss \(P_{loss}\) **, kW & 2.52 & 11.56 & 3.84 & 8.10 \\ \hline Average loss \textless{}+P_{loss}\textgreater{}, kW & 7.04 & & 5.97 & \\ \hline Number of turns in armature winding & & 5.14 & & 7.75 & \\ \hline Required rectifier power, kW & & 100.6 & & 67.9 & \\ \hline Power factor & 0.969 & 0.668 & 1.000 & 0.747 \\ \hline Line-to-line voltage amplitude \(V_{arm}\), V & 116.0 & 51.3 & 116.0 & 75.3 \\ \hline Nonsymmetrized torque ripple, \% & 49.7 & 33.7 & 97.8 & 47.0 \\ \hline Symmetrized torque ripple, \% & 13.1 & 5.0 & 11.3 & 4.5 \\ \hline Magnetic flux density in the housing and the sleeve \(B_{h}\), T & 1.00 & 1.91 & 0.84 & 1.60 \\ \hline \end{tabular}  
* Note: the generator efficiency was calculated as \(\eta=(P_{1}-P_{ex})/P_{mech}\), where \(P_{1}\) is the active power in armature winding; \(P_{ex}\) is the loss in the excitation winding; \(P_{mech}\) is the input (mechanical) power. Mechanical losses, namely bearing and windage losses, were neglected; ** the total loss is the sum of all individual loss components \(P_{loss}=P_{arm\,DC}+P_{arm\,AC}+P_{im\,st}+P_{im\,st}+P_{ex}\).  
\end{table}
Table 3: Optimization results.