DE970618C - Contact converter with means to relieve the contacts from switching lights - Google Patents

Description

(WiGBl. P. 175)

ISSUED OCTOBER 9, 1958

from Sclialtfeuer

(Ges. Of July 15, 1951)

For some purposes it is desirable or possible in the commutation circuit of mechanical Converters (contact converters) to accommodate large ohmic resistances, z. B. if you want to have steeply sloping characteristics, such as B. with welding converters, or when it comes to low power or low duty cycle, in which the efficiency is irrelevant plays. In these cases you can use the cross-section

of the windings choose small so that the desired resistance is in the windings themselves lies. This has the advantage that the performance of the transformer and any switching chokes or inductor-like transformers becomes small. The resistances have the consequence that the commutation voltage, d. H. the difference in the voltages of alternating phases, compared to operation without resistors, is changed, in

809 632/43

part of this voltage is needed to drive the current through the resistors. Act If it is the ohmic voltage drop in the emitting phase, then the Instantaneous values of the commutation voltage are increased, while the voltage drop in of the newly added phase, the instantaneous values of the commutation voltage compared to the Operation without resistors can be reduced. Overall, the voltage-time integral of the commutation voltage can be increased or decreased over the commutation period depending on the circumstances.

The invention relates to a contact converter with means for relieving the contacts from switching lights, e.g. B. switching chokes, and for applications where one is beyond the usual A characteristic curve that is inclined to the extent required is greater than that of conventional contact converters Resistance in the commutation circuit. According to the invention this is achieved in that the increased Resistance, which is a fixed resistance in the commutation circuit, in the windings of the transformer and switching throttles and one of the

like size has that the desired slope of the characteristic curve by the voltage drop of the load current is effected on them, and that when operated as a rectifier, the time of contact closure is placed before the point in time when the phase voltages are equal.

In the drawing, the concept of the invention is explained using the example of a six-phase rectifier. e _x and e ₂ are the voltages of two alternating phases. The resistors R in the commutation circuit reduce these voltages to the values e / and e ₂ when the full direct current flows in the relevant phase. It is assumed that the contact of phase 2 is closed at time t _etn , ie by the time period t _a -t _a before the point of intersection of the phase voltages. At this point in time e _{2 is} already greater than e (. The inductance in the commutation circuit is relatively small. If there is no smoothing in the DC circuit, the current of phase 2 jumps to a value such that the voltage e _v reduced by the ohmic voltage drop of this current, becomes just as great as the instantaneous value of the voltage e '. The currents % _x and i ₂ of phases ι and 2 may flow in the further course of the commutation, as indicated in the drawing below. Let Igi be the At the end t _{ms of} the commutation time, phase 2 carries the full current. Its voltage is therefore reduced to e ₂ , while phase 1 is de-energized. Its voltage therefore assumes the instantaneous value of voltage e _t . During the commutation time, minus of the ohmic voltage drop, the voltage of phase 1 according to the curve ^ ₁ ", the voltage of phase 2 according to ^ ₂ ". Both curves enclose an area F ₃ , which e represents the voltage time integral of the commutation time; it can be seen that part of this area lies in front of the intersection of the phase voltages e _x and e _2.

With a small load, the commutation voltage around the area Fj is initially negative. When using switching chokes, for example, this voltage area pushes the magnetization of the phase 2 chokes in the negative direction opposite to the load current. Before commutation can begin with a small load, the magnetization of the phase 2 choke must first be driven to positive saturation according to area F _2. Only then can the commutation of the small current begin. So you can see that the commutation is delayed quite considerably in the case of small currents. Since, in contrast, the commutation is moved forward for large currents (area .F ₃ ), the overall result is that, for. B. when using switching chokes, the position of the currentless break does not shift with the load or not shift as much with increasing load at larger times, as is usually the case with rectifiers with small resistances in the commutation circuit. However, this has the consequence that with a given idle safety the possible load cycle is increased or with a given load cycle the idle safety is increased or with a given load cycle and given idle safety the required size of the switching throttles is reduced. The illustration in the drawing applies in the event that a material with a sharp saturation knee is used for the iron in the switching reactors. It is also possible to use a less high-quality material and to provide for complete smoothing of the direct current.

The invention is particularly important for rectifiers with simple contact devices with relatively imprecise contact times. By bringing the commutation forward, as the experiment has shown, the voltage drop under load is reduced; z. For example, the current of a rectifier working on resistance was increased from 460 to 530 A by bringing the switch-on time forward by about 20 ^{° C.} The voltage drop at Soo A was slightly greater than half the peak value of the phase voltages, and the commutation duration was around 70 ^° C. By bringing the switch-on time forward, the no-load voltage of the rectifier was reduced from around 59 to 54 V.

Claims (1)

PATENT CLAIM: Contact converter with means to relieve the contacts of switching lights, z. B. Switching chokes, and for applications in which one inclined beyond the usual extent Characteristic curve is desired, with increased resistance compared to conventional contact converters in the commutation circuit, characterized in that the increased resistance, as a fixed resistance in the commutation circuit is placed in the windings of the transformer and switching reactors and such Size has that the desired slope of the characteristic curve due to the voltage drop of the load current is effected on them, and that when operated as a rectifier, the time of contact closure is placed before the point in time when the phase voltages are equal. Considered publications: Swiss patent specifications No. 222 060, 229051. 1 sheet of drawings © 809: 632/43 10. ES