## 2 Description of the Measurement System
### Switch Cabinet, Control Desk and Load Resistor  
To operate the electric devices (analyzed motor, load/drive motor, frequency converters, sensors, battery charger) in the MS, appropriate power sources are necessary. A multifunctional switch cabinet and a control desk were developed to ensure them. Figure 7 shows a photo of the above equipment.  
Figure 6: Shunt resistors for measuring the electric current intensity.  
Figure 7: The electrical switch cabinet and control desk.  
In Figure 8, photos of the inside (**a**) and outside (**b**) of the switch cabinet are presented. The photos have been labelled for a more straightforward description.  
The contacts S1-S4, S6-S9 and S10, the fuses F1-F10, and the rectifier are built in the switch cabinet. Contactor S5 is built into the control desk. The user can operate the switch cabinet from the control desk (Figure 9).  
In Figures 10 and 11, the wiring diagrams of the switch cabinet and the control panel are presented.  
Figure 11: Wiring diagram of the switch cabinet and control panel (diagram 2).  
Figure 10: Wiring diagram of the switch cabinet and control panel (diagram 1).  
1. If switch \(K_{0}\) is closed, sockets 1-3 are supplied with 230 V 50 Hz AC.
2. If switches \(K_{0}\) and \(K_{5}\) are closed, sockets 8-13 are supplied with 220 V one-phase 50 Hz AC.
3. If switches \(K_{0}\) and \(K_{1}\) are closed, socket 4 is supplied with 400 V three-phase 50 Hz AC.
4. If switches \(K_{0}\) and \(K_{2}\) are closed, sockets 6-7 are supplied with 400 V three-phase 50 Hz AC.
5. If switches \(K_{0},\ K_{4}\) and \(K_{7,2}\) are closed, socket 5 is supplied with 400 V three-phase 50 Hz AC.
6. If switches \(K_{0}\), \(K_{4}\) and \(K_{7,4}\) are closed, socket 5 is supplied with 400 V three-phase AC with a variable frequency between 0 and 50 Hz. Changing the frequency is solved by the frequency converter in Figure 8a.
7. If switches \(K_{0}\), \(K_{4}\) and \(K_{7,6,1}\) are closed, socket 5 is supplied with three-phase AC with a variable voltage between 0 and 400 V. Changing the voltage is solved by the variable toroidal transformer in Figure 9.
8. If switches \(K_{0}\), \(K_{4}\) and \(K_{7,6,1}\) are closed, socket 5 is supplied with DC with a variable voltage between 0 and 400 V. Changing the voltage is solved by the variable toroidal transformer in Figure 9. The rectifier can be seen in Figure 8b.
9. If switches \(K_{0}\) and \(K_{3}\) are closed, we can use DC, which is obtained from four car batteries. Changing the resistance of the load resistor (0-7 \(\Omega\)), the intensity of the electric current in the circuit can be varied.  
The load resistor is a high-power resistor originally used as a starting resistor of a tram. Thus, it can be applied at very high current intensities.  
Combinations C1-C5 can be used for everyday applications, while C6 and C8 can be used when we use the three-phase induction motor (Figures 2 and 3) as a drive and load motor, respectively. Combination C7 can be used to provide supply voltage to an AC, while C6 and C9 to a DC motor. It must be emphasized again that the analyzed motor can be any type of AC or DC motor. Combination C9 can also be used for investigations when a direct current with strictly constant--but wide-range variable--intensity is necessary. One example is the measurement of the mutual dynamic inductance between the stator and rotor windings of a series-wound DC motor [26]. Another example is when an electric current with a strictly constant intensity is necessary for the measurement of the pure electric resistance of a winding.