DE411225C - Overcurrent time relay serving to selectively switch off faulty line sections - Google Patents

Description

With overcurrent relays for selective shutdown of faulty line sections with double earth fault (this is simultaneous earth fault of different phases on different Points of the network) the overcurrents that occur are roughly equivalent to those which occur in the event of a two-phase short circuit. However, the voltage is not affected as much as in the case of a short circuit. While namely in the latter case the voltage at the short-circuit point equals zero, is in the case of an earth fault always only the earth-closed conductor at the earth connection point without voltage, the However, conductors that are not connected to earth have the voltage over their entire length is imprinted on them at the head office. All relays receive at least this tension. This means that the tripping times are longer in the case of a double earth fault

ao than with a short circuit, which is generally undesirable.

The object of the invention is, instead of for the correct graduation of the release time insufficient voltage drop

as another caused by the earth fault Use the change of state to achieve the correct graduation, namely the disturbance of the equilibrium of the currents in the individual, which occurs in the earth fault, Phases. While the sum of the phase currents is equal to zero in a healthy state, it is known to be one in the event of a ground fault; non-zero value. This current is now used according to the invention, around the overcurrent flowing in the strox winding of the selective relay in the sense to support an increase in the torque, i.e. an acceleration of the release.

Two exemplary embodiments are shown in the figures. In Fig. 1, the current transformers α of phases a, V, W feed the current modules b of the overcurrent relays. On the same core as these coils sit auxiliary coils c, which are connected to Hüfsstrojnwandter d . These auxiliary converters can be accommodated in the housing of the associated relay. The secondary sides j of the auxiliary transducers are connected by compensating lines e , the transducers are thus connected in the known asymmetry circuit, so that the auxiliary coils c

are de-energized as long as the sum of the phase currents u, v, w is equal to zero. If this condition is disturbed by an * earth fault, currents flow in c which support the currents flowing in coils b .

Fig. 2 shows another embodiment, u, b, c have the same meaning as in Fig. I. D instead of the Hilfswandkr but down in the main lines,

ίο Current transformers that are usually present and connected in an asymmetrical circuit are used to connect the earth fault relays. The asymmetry current sifted out during the earth fault is fed to the coils c connected one behind the other.

The for feeding the windings b and c

The two current transformer sets used for this purpose can also be combined into a single set.

Instead of arranging the coils c on the same core as the coils b , they can also be attached in any other way so that they generate a torque which is added to that originating from b.

Claims (2)

Patent claims: ^a 5 j. Overcurrent time relay used to selectively switch off faulty line sections, characterized by devices that are dependent on the disturbance of the equilibrium occurring in the event of an earth fault of the currents generate a torque which is the same as that of the currents in The torque dependent on the individual. · phases is increased. 2. Relay according to claim 1, characterized in that the generation of the additional torque used devices from that occurring in the event of a ground fault Asyrnmetriestnom or a current proportional to it controlled or are flowed through. //66.2