DE454128C - Protection arrangement for transformers in economy circuit - Google Patents

Description

The serious endangerment of transformers in economy circuit when Mains short circuits can be avoided by removing the main circuit of the transformer is automatically interrupted. However, this contradicts the demand to be more selective Disconnection of short circuits.

"If instead the circuit of the excitation winding b in the illustrations is interrupted when a short circuit occurs, the excessive current load is probably prevented; however, there are relatively severe overvoltages at the terminals of this winding, which not only cause flashovers over the cover, but also endanger the In addition, the choke effect of the main current winding α in the figures, which remains in operation alone, has an unfavorable influence on the voltage regulation of the network.

If a resistor is switched on in the excitation circuit when a mains short-circuit occurs, better conditions result, but this solution can only be used as Compromise between the two extremes: full mains short-circuit current in the transformer or full overvoltage on the field winding. The present invention aims, the Protection of the autotransformer through automatic shutdown of the same without interruption of the mains circuit.

For this purpose is determined by the open in normal operation switch c of pictures when overcurrents occur of certain magnitude the auxiliary winding α (for example, by the action of the overcurrent relay / in connection with the current transformer e) short-circuited and then the circuit of the exciter winding b with very small time lag by the switch d interrupted so that the mains current can continue to flow past the autotransformer undisturbed.

The two «switches can either electrically or mechanically coupled in a suitable manner or to a changeover switch be united. It is advantageous to use both switches or switch parts as pre-stage switches to train and to coordinate their alternating switching activity so that the pre-stage resistors in the middle position are switched on in both circuits at the same time.

If the interruption point <L of the excitation circuit is in front of the excitation winding b , as in Fig. 1, common ballast resistors can also be arranged for both circuits.

So that the circuit responds even if the transformer itself is defective it is necessary that the relays are installed on the side of the incoming energy. If the transformer can receive energy from both sides, then there is a corresponding doubling the relay required.

Claims (3)

Patent claims: 1. Protection arrangement for transformers in economy circuit against network short-circuits, characterized in that switches are arranged are the first the main current winding automatically when mains overcurrents of a certain magnitude occur short-circuit and then inevitably interrupt the circuit of the excitation winding. 2. Protection arrangement according to claim 1, characterized in that both switches are equipped with pre-stage resistors and the alternating switching activity is matched so that in a central position both circuits over simultaneously the pre-stage resistors are closed. 3. Protection arrangement according to claims ι and 2, characterized in that that the switches are arranged so that they go under after the mains current drops automatically return to the starting position a certain size.