DE1956526A1 - Activation circuit to protect an electrical system - Google Patents

Description

Activation circuit to protect an electrical system

For the protection of electrical systems, e.g. for cables from transformers, machines or the like, the Measure the currents flowing at a certain point on the line and measure the voltage present there and, depending on the over- or The system to be protected can be switched off if certain critical measured values are not reached or - e.g. in the case of distance protection, a Protective device for measuring the fault distance are switched on, which in turn either immediately or after a delay time, a switch-off command for Disconnection of the electrical system to be protected.

The simplest starting circuit consists of an overcurrent relay, which emits an output signal when a certain current value is exceeded. Such an overcurrent relay has the advantages that it can detect errors very quickly and is relatively simple in structure. However, must the response value must be set to a value that will not be exceeded in the event of brief operational overloads will. Particularly when protecting a double line, it is necessary to set the response value of the overcurrent release to a The value to be set is greater than twice the nominal current of a line, otherwise the Double line due to the resulting current overload of the second line, this would also be switched off.

It is therefore known to excite distance protection devices, not only the current in a line, but also the voltage the line to use to the overload case of a J? ehlerfall to be able to distinguish. In these known circuits, the excitation depends on whether the value falls below a certain value Impedance value obtained by forming the quotient of current and

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Tension is formed. In addition, such an underimpedance excitation circuit can also be made dependent on the phase angle between current and voltage Increase the response sensitivity with increasing conduction angle without the risk of a faulty response in the event of an overload consists.

However, there is also a short-term overload of a line with twice the rated IT current and the associated low voltage lowering the impedance is relatively low, such a TInterimpedanzanreschaltung must be set so that it is Range of low currents only responds when the operating impedance is not reached.

In addition, the formation of quotients in a TInterimpedance pickup circuit is necessary because of the necessary smoothing devices that it takes considerably more time to respond than this is the case with a simple overcurrent relay.

The task of the Anregeschaltxmg according to the invention is, with simple Build up a quick response with high currents and a high sensitivity of the excitation circuit for errors to achieve low currents (remote short-circuit fault or low machine use in the network).

The invention thus relates to an excitation circuit for the protection of an electrical system with voltage and current-dependent excitation elements which respond when certain, voltage-dependent, fixed current values are exceeded and influence downstream signaling devices or circuit breakers directly or via one or more protective devices voltage-dependent and two current-dependent exciter elements set to different overcurrent values are provided and are connected on the output side to the inputs of a logic circuit, which consists of an "and" circuit connecting the outputs of the voltage-dependent and current-dependent exciter element with the lower overcurrent value and one the output of the "and ¹¹ Linking circuit with the See output st priority, 3-at higher overcurrent value on-

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pointing stimulator connecting "Or" logic circuit consists.

An exemplary embodiment of the new device is shown in FIG shown * A phase voltage U1 of the system to be protected is applied to the primary winding of a converter W2. In the same way the current I1 belonging to the same phase flows through the primary winding of a converter W3, while the primary winding of a converter W1 from which the full current JO of the system flows will. The secondary winding of the converter W2 is on via a switchover device U and an overcurrent release ÜA voltage-dependent excitation element UG1 connected. This voltage-dependent exciter UG1 always gives an output signal when a certain voltage value is exceeded at the input.

The secondary winding of the converter TV3 is in series with two current-dependent ones Suggest members IGM and IG2. Of these, the current-dependent exciter IG2 is set to a higher response value than the current-dependent excitation element IG1. Both then emit an output signal when the corresponding response value is not exceeded by the input current.

The output of the voltage-dependent exciter UGI and the output of the current-dependent exciter IGI are led to the inputs of an NGR-G-atters N1. The output of this NOR gate is connected to the input of a command generator B via the contact of the overcurrent relay ÜA. In addition, the output of the current-dependent exciter IG2 with the larger response value is also connected to the input of the command generator B via a NOR gate ΪΓ2.

The changeover device U, which is shown here as a heater with a changeover contact, is connected to the secondary winding of the converter W1 and a changeover will be heard, wsan the zero current one? exceeds certain Wsrt. If the UmsGhaltei-.ri2lrf-.Tmg is switched over by a fleJeiiüsK liulictiwiii 10 - the ^ amiungs ^ Dt ^ gigeii Suggesteglisu 1131 a Iz ^ .my ^ t U1 is simulated, so that it is already with a lower

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Voltage drop of voltage -TJ1 responds and no output signal gives more to the downstream NOR gate N1. A particular advantage - especially for more distant errors - results if the switching device U has a selection circuit for selecting the largest phase current and / or the smallest Upstream phase voltage. This selection circuit then actuates the switching device in the phase with the greatest current or the lowest voltage, so that the excitation circuit is switched to greater sensitivity in that phase, in which the presence of an error is most likely.

The selection circuit can with difference or quotient formation work. For example, polarized relays with two windings can be provided for the phases. One winding can then be in a DC circuit with one of the Phase current switch on proportional current, while the other winding is in a direct current circuit, its Current is proportional to the sum of the three phase currents.

in the event of a short circuit in the secondary circuit of the Voltage converter will respond to the overcurrent relay. As a result, the secondary circuit of the converter W2 is separated, so that the voltage-dependent excitation element UG1 no longer emits an output signal. In order to prevent this by exceeding the im current-dependent exciter IG1 set overcurrent value of the command generator B 'is switched on, there is a contact of the Overcurrent release ÜA in series with the output of the NOR gate N1. If the secondary circuit of the converter V / 2 is disconnected, the command generator B can only operate if the overcurrent value is exceeded be switched on for the current-dependent exciter IG2.

The NOR gate N1 thus receives at both inputs in the normal state Signal. Only if neither at the output of the voltage-dependent exciter UG1 nor at the output of the current-dependent one Excitation member IG1 an output signal appears when the voltage U1 falls below a certain limit voltage and a certain limit value of the current 11 is exceeded, an output signal is produced at the NOR gate N1. In case of over-

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If a second current value is reached, the signal at the current-dependent exciter IG-2 will also disappear, so that the output signal of the NOR gate N2 a signal appears and turns on the command generator independently of the voltage-dependent exciter UG1.

The response characteristic of the circuit described in FIG. 1 is shown in Mg. Here is the ratio of tension U1 to the nominal voltage Ujj on the ordinate and the ratio of the Current 11 to the nominal current I ^ shown on the abscissa. It is assumed that the response value of the current-dependent exciter IG1, namely the ratio of the current I1 to the rated current Ijj, in which the current-dependent excitation element IG1 just responds, has the value 0.25, while the corresponding response value of the current-dependent control unit IG2 is 2.2. The response characteristic curve K1 resulting from this is shown in FIG. By appropriate selection of the response values for the Excitation members can always be the critical load case represented by point P for a double line, one of which is part of the line has failed, place it in such a way that there is definitely no excitation. Nevertheless, the low response value results of the current-dependent excitation element IGM has a very high sensitivity for small fault currents that occur when Errors are then present if only during a ° oh-wake-up load time few generators on the grid are in operation.

In addition, the sole use of voltage and current-dependent excitation elements and the absence ensures each measuring circuit to form the quotient or to take into account the phase angle that the excitation, i.e. the activation of the command generator B, can take place immediately after the error occurs.

4 claims
2 figures

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Claims (3)

Pat en tans / claims - € - VPA 69/1318 (1.)) Activation circuit to protect an electrical system with - ^ voltage- and current-dependent excitation elements, which respond when certain, voltage-dependent specified current values are exceeded and influence downstream signaling devices or circuit breakers directly or via one or more protective devices, characterized in that a voltage β dependent s (UG1) and two current-dependent exciter elements (IGrI, IG-2) set to different overcurrent values are provided and are connected on the output side to the inputs of a logic circuit that consists of one of the outputs of the voltage-dependent element (UG-1) and the current-dependent exciter element (IG-1) with the lower overcurrent value connecting "and" logic circuit (NOR element N1) and an "or" logic circuit connecting the output of the "and" logic circuit with the output of the current-dependent, the higher overcurrent value having excitation element (IG-2) consists. 2.) Activation circuit according to claim 1 for multi-phase AC systems, characterized in that the voltage-dependent excitation element (UG1) has a switching device (U) for increasing it the voltage value of the phase voltage (U1) at which the voltage-dependent excitation element (UG-1) responds, connected upstream and that the switching device (U) in turn depends on a switched in the zero current path as a function of switching Current transformer (W1) is standing. 3.) Activation circuit according to claim 1 or 2 with an overcurrent release, which is connected upstream of the voltage-dependent exciter, characterized in that one of the overcurrent release (UA) dependent contact is inserted into the logic circuit that after the overcurrent release has responded (UA) only the release connection between the current-dependent starting element (1 (3-2) with the higher response value) and the command generator (B) for evaluating the excitation. 109821/0901 - τ - VPA 69/1318 ■ 4.) Activation circuit according to claim 1 for multi-phase alternating current systems, characterized in that the voltage-dependent excitation element (UGI) has a TJms ehalt device (U) for increasing it the voltage value of the phase voltage (U1) at which the voltage-dependent excitation element (UG-1) responds, connected upstream and that the switching device (TJ) is in turn dependent on switching of a selection circuit for selecting the largest phase current and / or for selecting the smallest The phase voltage is in such a way that only the switching device (U) is actuated by the upstream selection circuit, which is assigned to the phase conductor with the largest phase current and / or with the smallest phase voltage. 109821/0901 Blank page copy