Figure 2

4. Artificial mechanical characteristic of the motor of a constant independent excitation with magnetic flux attenuation

Artificial mechanical characteristic of an independent engine excitements is the dependence of the velocity on the moment of loading at a constant value of the voltage at the motor clamps and introduction of additional resistance in the excitation winding circuit: U_H=const, i_B=const.

The experiment is carried out in the following sequence:

- switch on the QF1 and QF2 automata of the MPS and MP modules, respectively;

- apply for the operation of the TP (SA6) and, setting the direction of rotation, set the voltage of the potentiometer RP1 to 200V;

- switch SA2 of the module MDS2 set to a nonzero position, make the first measurement;

- Switch SA1 of the module MDS1 to enter resistance, the thus, loading of the DC motor as long as the armature current reaches 1.5A MDS1, thereby loading the DFT until the armature current reaches 1.5A or the stator current reaches I_C=I_N.

The data of the experiment are listed in table. 3.

Table 3 Results of the experiment

RдB=220
n, rpm	1720	1698	1668	1565	1485	1370
Iя, А	0.3	0.33	0.35	0.5	0.63	0.95

After the experiment, set all the module switches to their original state.

According to Table 3, we construct the characteristics n = f (I_Я).

Figure 3

5. Performance characteristics of DC motor of independent excitation Workers characteristics motors are the dependence of the rotational speed, electromagnetic moment, armature current and efficiency of useful power on the motor shaft at constant value of the voltage at motor clamps n or ω; M, I_я, ŋ=f(P2) with U_я=U_ян=const, i_B=const. The experience is in the following sequence: 6. Performance characteristics motor directly current independent excitation workers characteristics motors are the dependence of the rotational speed, electromagnetic moment, armature current and efficiency of useful power on the motor shaft at constant value of the voltage at motor clamps n or ω; M, I_я, ŋ=f(P₂) with Uя=U_ян=const, i_B=const.

The experience is in the following sequence:

- turn on automata QF1, QF2;

- to file a permit on the work of the TP (SA6) and, setting direction of rotation, potentiometer RP1 set the voltage U_Я=0,75·U_ЯН;

- switch SA1 module MDS1 introduce resistance, thereby loading the DС motor, until the armature current will not reach   or stator current will not reach I_С=I_Н=1,3А. - as you increase load potentiometer RP1 of the TP module support the weekend converter voltage at the level given. Record the experience data in Table 5. Table 5 Results of the experiment

Experimental data			Calculation data
Uя	IЯ	n		iв	Ря				М		М0	М2	Р2
V	А	rpm	1/с	А	W	W	W		Nm	А	Nm	Нm	W	%
180	0.3	1354	141.7	0.22	54	39.69	93.69	0.15	0.045	0.183	0.027	0.018	25.51	27.2
178	0.4	1350	141.3	0.217	71.2	38.6	109.8	0.148	0.059	0.181	0.0268	0.0322	45.5	41.4
160	0.5	1218	127.5	0.195	80	31.18	111.18	0.135	0.067	0.175	0.0236	0.044	56.1	50.4
158	0.7	1161	121.5	0.193	110.6	30.54	141.14	0.13	0.091	0.174	0.0226	0.068	82.62	58.5

After the experience set all module switches into the initial state. Calculation data. Power, supplied to the motor armature, W

Р_Я = U_Я·I_Я.

Electrical losses in the excitation circuit, W

where r_В - resistance of the excitation winding (Appendix B); i_В is the excitation current of a DC motor, A

Power supplied to the DC motor, W

Р₁=Р_Я+ .

Electromagnetic moment, N*mМ = С_М*I_Я,

where CM is adopted depending on from angular rotation speed (Appendix B). The moment of idling engine, proportional mechanical losses and losses in steel, N*m,

М₀=С_М·I_Я0,

where I_Я0 - is adopted depending on the angular frequency of rotation (Appendix B).

Useful moment on the shaft of the DC motor, N*m

М₂=М-М₀.

Useful power on the motor shaft, W

Р₂=ωМ₂.

Efficiency,%

Figure 4— Working characteristics

Conclusion

Control questions

1. How to change the direction of rotation of the DCM?

2. Why does the DCM(Direct current motor) increase the armature current with increasing load on its shaft?

3. Why, with a decrease in the excitation current, the rotational speed of the DCM is increasing?

4. How should the armature current change with decreasing excitation current and constant resistance moment on the motor shaft?

5. How will the appearance of the mechanical characteristics of the engine change if an additional resistance R_ДЯ is introduced into the armature circuit?

List of references

1 Копылов И.П. Электрические машины.-М.: Высшая школа, Логос, 2000. -607 с.

2 Брускин Д.Э., Зорохович А.Е., Хвостов В.С. Электрические машины. Ч. 1,2. -М.: Высшая школа, 1987.

3 Копылов И.П. Электрические машины.-М.: Энергоатомиздат, 1986.-360 с.

4 Вольдек А.И. Электрические машины.-Л.: Энергия, 1978.-832 с.

5 Костенко М.П., Пиотровский Л.М. Электрические машины. Ч.2 Машины переменного тока.- Л.: Энергия, 1973. - 412 с.