DE279545C - - Google Patents

Description

IMPERIAL

PATENT OFFICE.

With current transformers, the accuracy of the work is not just about the correctness of the Gear ratio is important, but also the lowest possible phase deviation against 180 ° between the primary and secondary currents. It has become known to reduce this size by referring to the secondary or a third Winding connects a capacitor. The process is that the magnetizing current of the converter is more or less compensated by the capacitance current. A very perfect balance of the However, phase deviation cannot be achieved as a result, since the magnetizing current according to the variable permeability of iron, the E.M.K. changes while the capacitance current corresponds to the constant capacitance of the capacitor proportionally to the E.M.K. increases. In Fig. Ι the course is in the right half of the magnetization current as a function of the E.M.K., while the left side the (proportional) change in the capacitor current with change in the E.M.K. shows. As can be seen from FIG. 1, the magnetizing current can be determined by the capacitance current not fully compensate, there remains a difference that depends on the E.M.K. applied, sometimes lagging behind and sometimes leading values results.

A much better compensation and thus an improvement or cheaper Current transformer could be achieved if the curve of the capacitance current is more of that

of the no-load current would be similar. This is achieved according to the invention in that the capacitor is not connected directly to the secondary or third winding of the current transformer, but rather through the intermediary of a small auxiliary transformer. The auxiliary transformer must be dimensioned in such a way that it shows signs of saturation when the current transformer is fully loaded, i.e. when the largest values of the EMF occur. The ohmic or the scattering of the magnetizing current of this auxiliary transformer in its primary circuit then ensures that the capacitor current increases to a different extent than the EMF of the current converter. The capacitance current in Fig. 1 must then form a curve that is too convex along the abscissa axis as a result, it is able to almost completely compensate for the no-load current of the current transformer, which only works in the lower part of the magnetization curve. The arrangement is shown in Fig. 2, where α denotes the core of the current transformer, b denotes the auxiliary transformer, c denotes the third winding to which it is connected and k denotes the capacitor.

For example, the saturation in the useful field can be greater than in the primary stray field choose to increase the capacitance current more slowly at higher E.M.K. reach. But you can also if the magnetizing current of the auxiliary transformer occurs strongly, the proportions must be reversed in order to enter to achieve a faster increase in the capacitance current at higher loads. Fig. 3

shows for this case that the sum of the no-load current to be compensated / iy of the current transformer and the magnetizing current Ih of the auxiliary transformer forms a curve which is too concave along the abscissa axis. The capacitance current must therefore have the same curvature, ie grow faster than the EMF. If necessary, a special secondary spread can also be provided;

ίο in all of these arrangements is the floor do not leave the invention. It's just a matter of properly sizing that Scatter, the ohmic drop and the saturation ratios of the auxiliary transformer like this to be dimensioned so that the capacitance current exceeds the empty! on current of the current transformer plus of the no-load current of the auxiliary transformer as completely compensated as possible.

With the relatively high saturations with which the auxiliary transformer works, can make the magnetic circuits in a particularly simple and cheaper way ever Make a bent sheet metal strip, which at the joint with consideration can be welded together electrically to a low magnetic resistance. The position of the metal sheets is shown in FIG. 4.

As a special advantage it should be mentioned that in the case of a secondary option Current transformer of the capacitor due to the high saturation of the auxiliary transformer none has to endure much higher tension than in normal operation. As a result of this lesser Requirements on the dielectric strength, the capacitor can be manufactured considerably cheaper, so that because of the applied high saturation does not outweigh the very large cost of the auxiliary transformer will.

Claims (3)

Patent-to sayings: 1. Current transformer, characterized in that in order to reduce the phase deviation an auxiliary transformer between the primary and secondary currents to the secondary or a third winding connected, which is secondarily loaded with a capacitor and which is at full load of the current transformer in sloping branch of the permeability curve is working. 2. Current transformer according to claim 1, characterized characterized in that the auxiliary transformer has artificially increased dispersion. 3. Current transformer according to claim 1 and 2, characterized in that the iron body of the auxiliary transformer consists of a few bent sheets, whose each is electrically welded together at the joint. 1 sheet of drawings.