DE292750C - - Google Patents

Description

IMPERIAL

ΡΑΤΕΝΤΑλΙΤ.

PATENT LETTERING

Vi 292750 CLASS 2 \ d. GROUP

of the motor.

Patented in the German Empire on June 3, 1913.

By the invention, the influence of network fluctuations on the speed of a Shunt motor can be reduced or eliminated entirely.

In order for a shunt motor to keep its speed constant when the voltage changes, the excitation current must change more than proportionally with the voltage because of the iron saturation. As is known, this is achieved in that (Fig. I) a constant or almost constant back EMF e is switched into the excitation circuit of the motor, so that the normal excitation current corresponds to the value (E - ■ e). is proportional. As shown in Fig. 2 too

¹ S , the excess Ai over the proportional value of the excitation current is around

the larger, the smaller - -p - is.

The necessary constant EMF e is supplied by the battery B in a known arrangement (FIG. I). This is very costly and requires careful operation to produce a constant or near constant emf.

In order to avoid these disadvantages, according to the invention, as shown in FIG. 3, the battery is replaced by a small auxiliary converter M ₁ , m ₂ . Given certain ratios of the field sizes f _x and f _{2 of} the two auxiliary machines m _ls m ₂ , it can be achieved that the back EMF that m ₂ supplies remains constant or almost constant.

For the sake of simplicity, the iron and friction losses of the unit should be disregarded when proving this fact. M ₁ , m ₂ , fi and f ₂ should be chosen so that m _{2 runs} as a motor and M ₁ as a generator; then one has the following equation:

E + I ₁ W ₁ f j '

in which f _x and f ₂ should not only contain the corresponding field values, but also other constants of the machine, such as the number of conductors of the runners, etc.; furthermore, W ₁ and w _{2 are} the total ohmic resistances of the corresponding circuits.

On the other hand, the energy equation for the present case reads:

(2.) i ₂ [E - i ₂ W ₂ ) - I ₁ [E -f I ₁ W ₁ ).

From these equations we get:

W ₂ +

So that i _{2 is} positive, i.e. m _{2 runs} as a motor, J- must be a proper fraction, except-

Jl

where W _{1 is} smaller than W ₂ . So one can also write with great approximation:

ίο =

fx

W ₉ ,

The field f ₁ should now be weakly saturated, that is to say approximately f ₁ = K ₁ E , and the field f ₂ , which in this exemplary embodiment of

a generator G coupled to the motor M is fed, is kept constant by any means, such as iron resistances or by saturation or by both means at the same time.

So f ₂ = K ₂ . Then:

W ₀

This is exactly the relationship required by FIG.

In order for equation 4 to be completely true, it is necessary that the field f _{x be} completely proportional to the voltage E and that the field f _{2 be} completely constant. In practice, however, this is associated with difficulties, since one has to work on the straight part of the magnetization curve for perfect proportionality between E and f _x , whereby the utilization of the machine is impaired, while a perfect constancy of f _{z is} practically impossible to achieve.

In practice, however, it is not absolutely necessary to have a completely constant back EMF . into the excitation circuit of the main motor. A sufficiently constant one Back EMF is achieved when the field and number of revolutions of the auxiliary engine change so that their product is approximately constant.

This is achieved if (FIG. 4) a counter compounding / "'is applied to m ₂ or a compounding f [ or both means j at the same time _{to W 1} Wg adds a shunt winding that works in the same way as f _2. In these cases, the generator can still work on the knee of the magnetization curve and the motor does not have an absolutely constant field, which means that the machine can be better utilized or the other of the windings indicated earlier can be omitted.

Claims (4)

Patent Claims: 1. Arrangement to keep the number of revolutions constant · by electric motors Counter-connection of a constant or almost constant EMF in the excitation circuit of the motor, characterized in that a running independently of it in the excitation circuit of the motor Auxiliary motor is switched on, def "one Auxiliary generator. drives, both of which are excited so that the motor part the desired Back EMF delivers. 2. Circuit according to claim 1, characterized in that the auxiliary motor is strong, the auxiliary generator is weakly saturated. 3. Arrangement according to claim 1 and 2, characterized by counter compounding of the auxiliary engine and compounding of the auxiliary generator. 4. Arrangement according to claim 2 or 3, characterized by an additional self-excitation of the auxiliary engine. 1 sheet of drawings.