DE2036497B2 - Residual current circuit breaker - Google Patents

Description

The invention relates to a residual current circuit breaker with a summation current transformer, the primary windings zui coupling to an alternating current circuit to be monitored and a secondary winding has, on which the excitation winding acts on a switch mechanism for a switching direction Tripping magnet is connected, as well as with one between the secondary winding of the summation current transformer and the excitation winding of the tripping magnet switched on capacitor, with secondary winding, The excitation winding and the capacitor form an oscillating circuit, which is based on one of the operating frequency frequency is matched in the monitored circuit.

The German patent 716 585 relates in principle such a residual current circuit breaker, with the secondary winding, excitation winding and capacitor form an oscillating circuit. There, however, the resonant circuit is only at a frequency that is dependent on the operating frequency in the monitored circuit tuned to achieve an increase in the sensitivity of the residual current circuit breaker.

The detection of direct current residual currents with those for alternating current has always been problematic usual means. This increases the AC response current of a conventional residual current circuit breaker with a summation current transformer if the switch is also influenced by a direct current transformer due to the premagnetization of the transducer due to the DC residual current, so that its release behavior is disturbed. Furthermore, such a residual current circuit breaker triggers at all not off if it is only traversed by a direct current fault current, as it is known to be for induction a voltage in the secondary winding of the summation current transformer an alternating current in the primary winding is required. But even the river change that one by one way glide direction of Alternating current generated chopped direct current in the converter of one with one or more primary windings summation current transformer is not so large that one triggers the residual current circuit breaker Sufficient voltage is induced in the secondary coil of the summation current transformer.

The invention is based on the object of providing a remedy here and the use of fault current Schulz switches of the above type also in circuits with DC residual currents, such as them

ίο, for example, with thyristor-controlled DC motors, in which, due to the thyristor control, not only AC residual currents but also DC residual currents can occur.
The solution to the task at hand is thereby

achieved by improving the known switch so that it responds even to DC fault currents, such as those that occur in thyristor-controlled circuits. The solution is that the resonant circuit is tuned ^{to the frequency of the voltage ahee r.}

those flowing in the secondary winding of one in the primary windings of the summation current transformer DC residual current is induced.

The invention is based on the knowledge that by connecting a capacitor in series or in parallel to the secondary winding of the summation current transformer of a residual current circuit breaker through a fault current consisting of a pulsating direct current generated in the secondary circuit Voltage oscillations one to actuate the

Trigger magnets and thus can have sufficient amplitude to trigger the switch. This means that the resonant circuit is tuned to resonance at least approximately for the frequency which has the voltage that is in the secondary winding of one in the primary winding residual current flowing through the summation current transformer is induced.

The invention is explained in more detail below with reference to the drawing using an exemplary embodiment.

It shows

Fig. 1 schematically shows a residual current circuit breaker.

Fig. 2 the magnetic characteristic of the total current

converter in the switch according to Fig. 1,
Ed. 3 and 4 oscillograms.
Fig. 1 shows a residual current circuit breaker 2 for monitoring the lines RU and M _{p of} an electrical system.

This residual current circuit breaker 2 has a summation current transformer 3 with primary windings 4 and a secondary winding 5. The primary windings 4 are in the lines to be monitored RU and M _p . The secondary winding 5 of the summation current

converter 3 is connected to an excitation winding 9 of a tripping magnet 8. This release magnet 8, which can be a holding magnet or a working magnet, acts through a mechanical connecting part 8a on a switch lock 10, which over

a switching rod 10a actuates a circuit-breaker 11 located in the lines Ri t / and M _{p to be monitored.}

In parallel with the secondary winding 5 of the summation current transformer 3 and the excitation winding 9 of the tripping magnet 8, a capacitor 6 is switched on. Instead of the capacitor 6, a capacitor 7, indicated by dashed lines in FIG. 1, can be connected in series with the Secondary winding 5 and the excitation winding 9

be trained. The one from the capacitor 6 or 7, the Secondary winding 5 and the excitation winding 9 existing oscillating circuit is at resonance or at least approximately matched to the response.

The mode of operation of the capacitor 6 or 7 is explained with reference to Figs. 2 to 4:

In the ordinate of the diagram according to Fin 2, the flux / or the time / and in Abs, se the fault current I _{1 are} plotted. If an alternating current fault current flows through the summation current transformer 3 in accordance with the dashed curve 12 in FIG. 2, this is magnetized in accordance with its magnetic characteristic curve 13 shown in dashed lines. At a corresponding level of this alternating current, the entire magnetic characteristic curve 13 consisting of the hysteresis loop is passed through and the flux change A $ _{x that occurs} is very large, so that the voltage induced in the secondary winding 5 of the summation current transformer is so large according to the induction law that it corresponds to the response voltage of the Trip magnet 8 exceeds and the residual current circuit breaker trips without difficulty. This triggering of the switch would also take place if the capacitors 6 or 7 were not present in the above-mentioned circuit. If, on the other hand, the fault current has the character of a pulsating direct current according to the solid curve

14 in Fig. 2 (one-way direct current), the magnetization of the summation current transformer 3 would result in the hysteresis loop in Fig. 2 only up to the resonance point

15 run through. The change in flux A <ß ₂ would remain small, and the voltage induced in the secondary winding 5 of the summation current transformer 3 did not reach the response value of the tripping magnet 8, so that the switch would not trip. This case is shown graphically in the oscillogram according to FIG. The curve 16 shows the time profile of the fault current I ₁ , the curve 17 located between the trigger lines 18 and 19 represents the time profile of the voltage

U ₁ , on the excitation winding 9 of the tripping magnet 8. As can be seen, the curve 17 would nowhere protrude beyond the tripping line 18 and 19.

By switching on the capacitor 6 in parallel with the secondary winding 5 and the excitation winding 9

ίο or the capacitor 7 in series with the secondary winding 5 and the excitation winding 9 creates an oscillating circuit, and when this oscillating circuit is tuned at least approximately to resonance, the voltage U ₁ on the excitation winding 9 of the triggering

»5 magnets 8 raised so far that the switch is triggered even with a fault current consisting of pulsating direct current. These relationships are illustrated by the ozsillogram according to FIG. 4, in which the same curves have the same reference symbols as in FIG. 3. As can be seen, curve 2 (1. Indicates the dL · time dependency of the 'voltage L _1. At the excitation winding 9 of the Ai ..-; release magnet 8 indicates the tripping line 19, so that <" pulsating DC current corresponding to the curve 16 in Fig. 4. The shape and height of the curve 20 depends on the size of the capacitor 6 or 7 in Fig. 1 used.

Is the trigger magnet 8 a holding magnet, in which the trigger from the Strornrichlung in the exciter winding! depends, it is advantageous to dimension the capacitor 6 or 7 so that the amplitudes the curve 20 in Fig. 4 on both sides of the zero line approximately are equal, which avoids the aperiodic limit case in the secondary circuit.

For this 1 sheet of drawings

Claims (1)

Claim: Residual current circuit breaker with a summation current transformer, the primary windings for coupling to an AC mains circuit to be monitored and a secondary winding, to which the excitation winding acts on a switch mechanism for a switching device Trigger magnet is connected, as well as with a between the secondary winding of the Summation current transformer and the field winding of the tripping magnet switched on capacitor, with secondary winding, excitation winding and capacitor form an oscillating circuit which is monitored at one of the operating frequencies in the Circuit-dependent frequency is tuned, characterized in that the Resonant circuit is tuned to the frequency of the voltage in the secondary winding (5) of a direct current fault current flowing in the primary windings (4) of the summation current transformer (3) is induced.