DE515767C - Arrangement to improve commutation in three-phase DC cascades for changing loads - Google Patents

Description

GERMAN EMPIRE

ISSUED ON
JANUARY 14, 1931

REICH PATENT OFFICE

PATENT LETTERING

CLASS 21 d 2 GROUP

General Electricity Society in Berlin ")

for changing loads

Patented in the German Empire on March 22, 1928

The invention relates to three-phase direct current cascades for strongly changing loads. In the case of three-phase direct current single-armature converters, which do not have to perform any mechanical work, a noteworthy one is known to form resulting anchor field. The reversing pole winding therefore essentially only needs to generate the Commutation voltage required lines of force across the magnetic resistance of the reversing pole circuit to drive, since there are no significant counter-amperage windings of the armature. As is well known, it is different with Single-armature converters that have to perform mechanical work, especially with single-armature converters, which are used for three-phase direct current cascades.

The following considerations also apply to such three-phase DC cascades,

ao where the power of the DC rear motor is not fed to the main shaft, but to any alternating current or direct current network after conversion.

Fig. Ι shows a three-phase direct current cascade according to Krämer; it is ν the front motor, h the rear motor, ti the single armature converter, α the driven machine, s the flywheel, 11 the speed of the front motor, η, ι that of the single armature converter and w the reversing pole windings of the cascade.

The rear motor h has a main current field winding to achieve strong flywheel buffering. In steady-state conditions, the currents /, / and J _{g have} a fixed ratio. With an increase in the load • the currents / and J _{g increase} . It will

but the ratio -γ- is greater. In the stationary

State corresponds to the single armature converter 11 of a connection between three-phase motor and direct current generator, in which the electrical power of the generator results in the only load on the motor. With increasing load, the speed tt of the front engine v decreases, and therefore the slip frequency of its rotor increases and thus the speed n _{u of} the single-armature converter. The single-armature converter ti must have a driving torque. The armature field of the three-phase current / must therefore be greater than that of the direct current J _e . Now the armature ampere turns of the direct current / _ff counteract the flow of the reversing poles, while the ampere turns originating from the three-phase current / increase the reversing pole flux. As a result, when the load increases, that is, when the armature field of the current / is greater than that of the current J _g , the reversing poles are too strongly excited, and the current reversal is consequently worsened.

■ '·) Has been indicated by the patent seeker as the inventor;

Dipl.-Ing. Wilhelm Weiler in Berlin-Niederschönhaiisen,

According to the invention, as illustrated in Fig. 2, the reversing pole winding of the converter at all speeds of the cascade with an invariable parallel resistance was b provided without self-induction, so that the reversing poles are properly excited in the steady state. The current J _g now flows partly through the reversing pole winding w and partly through the resistor b. In the steady state there is between the current J _w flowing through the reversing pole windings and the current Jb flowing through the resistor b

a fixed relationship -? - . When the

^J b

Stromes / _e is created by the action of the

Self-induction of the reversing pole winding w that

Ratio '-γ smaller. There now the growth

^J b
of the current J _{e is} always associated with a decrease in the speed n, i.e. with an increase in the speed n _a and an increase in the * three-phase current /, the above-described inadmissible increase in the reversing pole flux due to the predominant three-phase armature field can be compensated for by the resistance h.

When the load decreases, the speed / z of the front motor increases and the speed ß _{a of} the single armature converter and thus the three-phase current / decreases. The equal armature field of the single-armature converter predominates and, on the other hand, the self-induction of the reversing-pole windings of the single-armature converter α tries to increase the current component /, "compared to Ji. As a result, the parallel resistance b now counteracts a too weak excitation of the reversing poles.

Three-phase DC cascades for sub-synchronous speeds are considered here ■ been. Three-phase direct current cascades for However, oversynchronous speeds result in the same advantageous effect of the parallel resistance.

The effect of the parallel resistance can be used to suppress oscillations attached damper cage can still be supported, if this is the reversing pole wraps around.

The parallel connection of resistors to the reversing pole winding; of DC machines is known per se. It is used for the precise setting of the reversing pole winding Namely where a setting occurs. Changing the reversing air gap makes difficulties. For DC machines with However, the arrangement was subject to greatly changing loads precisely because of the change in the ratio - ~ not usable, and man

^J b

connected a resistor with a choke coil in series and for such machines both of the reversing pole winding in parallel.

Claims (1)

Claim: Arrangement to improve the grain mutation in three-phase direct current cascades for strongly changing loads, consisting of asynchronous front motor, single armature converter and a DC rear motor that delivers its power to the Output shaft of the front engine or another wave, characterized in that at all speeds of the cascade to the reversing pole winding of the single armature converter an invariable non-inductive resistor is connected in parallel. 1 sheet of drawings