DE3230047A1 - Circuit for short-circuit monitoring of circuits - Google Patents

Abstract

In order to monitor circuits for an overload, especially circuits in which the short-circuit current is limited (e.g. generator circuits in mains-standby systems), a threshold value switch (ZD, S) is provided, which is coupled to the load circuit via current transformers (W1, W2, W3) having loads (R1, R2, R3) connected downstream from them, which threshold value switch trips in the event of an excess current which is considerably higher than the rated current and breaks the supply lines (L1, L2, L3) to the loads, via a contactor. Any desired number of circuits can inherently be monitored by using a plurality of such threshold value switches for individual circuits or a sequencing circuit. By allocating different time constants to the individual threshold value switches, a specific sequence for disconnecting the circuits in the event of a disturbance can be predetermined. The circuit is suitable for monitoring both single-phase and multi-phase networks and reacts to single-phase or multi-phase short-circuits in the same manner. <IMAGE>

Description

Circuit for short-circuit monitoring of electric circuits

The invention relates to a circuit for short-circuit monitoring of circuits, in particular generator circuits, and for load disconnection in the Short-circuit case using current transformers connected to the circuits as well as contactors for switching consumers on and off.

To protect power supply systems and electrical consumers it is common practice in the circuit to the consumers more or less to lay fast fuses that respond to an impermissibly high supply current and, for example, by melting the connection from the consumer to the power supply system cut open. A certain period of time is required to blow the fuses. This period of time can sometimes be too long, even with over-fast backups. to endanger the power supply device and / or the consumer To be able to exclude security. The meltdown time of a fuse is essential depending on their dimensioning and in the event of a malfunction compared to the nominal current occurred current increase; in circuits in which there is a possible short-circuit current cannot be arbitrarily high, for example in generator circuits of emergency power systems, the meltdown time can be on the order of ten or more seconds lie. During this time, both the power supply device, i. primarily the emergency power supply unit driving a generator, as well as the switched on Loads can be damaged by overcurrent.

Another disadvantage of such fuses is the fact that they only trigger when there is a relatively significant increase in current compared to the rated current. Slight excesses of the nominal current have no effect on the fuses, although these current increases at least when they are over long periods of time pending, certainly to damage to the power supply device and to the consumers being able to lead. To detect a relatively low increase in current, it is known in addition to the faster switching fuses in the circuit consumers still have bimetal switches or switching means controlled by bimetal relays to lay. These fuses neither protect the power supply device the consumers are still sufficient, since they are also in the lower range of their characteristic curve have a characteristic that is too sluggish. But especially in this area, i.e. at The short-circuit currents of generators are three to five times the nominal current a.

For operational reasons it is desirable to have a short circuit as possible can be recognized quickly and by disconnecting the connection between the power supply device and to make it ineffective for consumers.

So far, this has only been possible by using power protection switches with specially trained electromagnetic short-circuit protection quick releases. These circuit breakers are in the power circuit and are therefore correspondingly large and expensive. Their disadvantage is also a very imprecisely defined response threshold, the use of such devices in systems with upwardly limited short-circuit currents doesn't always make sense.

The object of the present invention is to provide a circuit according to the The preamble of claim 1 to indicate a simple space-saving and inexpensive short-circuit protection can be achieved, while being sufficiently sensitive is, can be used for both single-phase and multi-phase networks and also if there are several feed outputs, selective shutdown in the event of a fault of the disturbed output.

The invention solves this problem through the characterizing features of claim 1. Advantageous training and further developments of the invention are specified in the subclaims.

The invention is illustrated below with reference to one in the drawing Embodiment explained in more detail.

FIG. 1 shows the circuit according to the invention in its implementation for a three-phase generator circuit and FIG. 2 several of these circuits for the selective or joint shutdown of individual outputs.

Figure 3 of the drawing shows a generator circuit with two separate ones From feeds and a common short-circuit monitoring circuit and Figure 4 an additional circuit that works in conjunction with the common monitoring circuit according to Figure 3, the selective shutdown of the two feeds takes over.

The generator circuit shown in Figure 1 consists of one three-phase generator G1 driven, for example, by a diesel unit, lines L1 to L3 and N1 and one not shown placed load, which is connected to the lines at A = exit. Included in the lines are current transformers W1 to W3, via which the in the lines L1 until L3 flowing current is to be measured; the symbolically indicated are used for this Ammeter J1 to J3. Each current transformer is on the secondary side except for the associated one Ammeter led to a low-resistance measuring resistor R1, R2 or R7, which is used for this serves, a voltage drop proportional to the supply current flowing in each case provide a downstream switching arrangement.

The switching arrangement essentially consists of an overcurrent relay S and a Zener diode ZD connected in series with this. The switching arrangement is on the one hand to one connection of the three measuring resistors and on the other hand over a series resistor RV and decoupling diodes D1 to D3 to the other terminal of the three measuring resistors connected.

The decoupling diodes D1 to D3 are in the reverse direction of the zener diode ZD switched. Parallel to the series connection of Zener diode ZD and relay S is a capacitor C is arranged, which together with the adjustable series resistor RV a defined response delay for the relay S can be achieved and thus ensures that overcurrents that occur only briefly, for example when switching on of consumers, have no effect on the short-circuit monitoring circuit.

With normal high current in the lines of the generator circuit voltages drop across the measuring resistors R1 to R3 which are below the Zener voltage the Zener diode ZD, i.e. the relay S is not energized. As long as this is so the switching arrangement does not draw any power from the generator circuit; in the a Phase position of the supply current blocking decoupling diodes, with the other phase position the Zener diode ZD the current path through the relay S. Now increases the current in one or in several lines of the generator circuit, increases in correspondingly the voltage drop across one or more of the measuring resistors R1 to R3. This charges through the decoupling diodes Di to D3 and the series resistor RV the capacitor C on until the voltage applied to its terminals finally leads to the Zener diode ZD being driven through. As a result, the relay S picks up and thus causes the shutdown in a manner not shown in detail here a generator contactor, also not shown, which then has its switching contacts g, 5 and t opens and thus disconnects the load from the generator. Thereby the relay S de-energized; it drops out and is ready again for short-circuit monitoring of the generator circuit after the generator contactor has been switched on again.

By suitably dimensioning the circuit according to the invention it is possible for the relay S for both single-phase and three-phase short circuits to achieve almost the same pull-in delay. In the case of a three-phase short circuit, increases the voltage applied to the measuring resistors to about three times the value of Nominal voltage, with a single-phase short circuit to about five times the value of this voltage. The diode decoupling acts in the first case as a single-phase one-way circuit and at three-phase short-circuit as a one-way star connection.

By suitably dimensioning the capacitor C and series resistor RV existing delay element can be used in the circuit according to the invention suitable assign the appearing delay time, i.e. the circuit only reacts to the presence of overcurrents after a specified period of time.

In addition to short-circuit monitoring, the circuit according to the invention detects also the state of failure of their burden, which is dangerous for current transformers. at If the load fails, the current transformer (s) go like a short circuit in the supply circuit into saturation and give about five times the voltage related to the at Nominal current from the voltage drop across the measuring resistors. The consequence of this is that the overcurrent relay S then picks up and the shutdown of the main circuit is initiated.

The circuit according to the invention reacts to significant increases in current, given for example by doubling or tripling the rated current are. By now also less significant, but longer pending current increases to be able to capture is provided in an advantageous embodiment of the invention, the measuring resistors at which the voltage drop controlling the overcurrent relay is tapped is designed as a bimetal relay and via this bimetal relay to the circuit switching contactor with its contacts i, 5 and t. That way will E.g. the circuit for the consumers is disconnected when the supply current is supplied via a Hour is 10% higher than the rated current.

When it comes to supplying energy to electrical consumers, it happens frequently stipulate that separate feed circuits are to be provided for certain consumers.

The reason for this can be, for example, in the joint monitoring similar consumer or also in spatial separation the consumer lie.

The provision of various feed circuits can also be justified therein be that in the event of a fault, for example in the event of a power failure, from a power supply unit at least temporarily only certain consumers should be switched on, which can just about be handled by the emergency power supply. In such cases it is desirable that in the event of a fault, that is, in the event of a short circuit in one of the feed circuits, only the feed circuit concerned is switched off will. How this can be achieved is indicated in the exemplary embodiment according to FIG.

Figure 2 of the drawing shows a generator circuit with two separate feed-outs Ai and A2.

There is a separate branch for each branch of the generator circuit Circuit X1 and X2 are provided, which are connected to the individual via associated current transformers branching parts of the common feed circuit are coupled. The structure the circuits X1 and X2 corresponds to the circuit of Figure 1. The two Response delays assigned to circuits X1 and X2 may or may not have to be be the same size. In the illustrated embodiment it is assumed that the switching delay is about one second; this is through a next to the relevant overcurrent relay S1 or S2 indicated symbol indicated.

The two overcurrent relays SI and S2 are not shown Contactors for disconnecting the respectively assigned supply circuits in the event of a short circuit Separation takes place via switching means M / 1, ß / 1 and or ob / 2, ß / 2 and g / 2 of from the overcurrent relay controlled contactors.

In addition to the selective monitoring of the two outputs Circuits X1 and X2 is still a circuit that monitors the entire circuit X provided.

It is used to prevent short circuits between the common power supply device and to record the feeds (central busbar) and it also takes over the failure protection for the downstream circuits X1 and X2. In advantageous The response time impressed on it is greater than that of the two circuits X1 and X2 each impressed switching time.

This ensures that the common circuit actually works only in the event of a defect in one of the downstream circuits or in one Short circuit in the common part of the feed circuit can respond.

By correspondingly increased use of the invention Circuit, a reliable selectivity of the short-circuit protection can be achieved for any number of circuits achieve; this selectivity is used alone in the practice of the invention limited by the effort involved.

However, the selectivity can also be achieved without corresponding duplication achieve the circuit according to the invention by a common for all consumers Short-circuit monitoring circuit using a sequential circuit, the individual Consumer switches off.

This process continues until the one causing the problem Load is switched off, the short-circuit monitoring circuit in again reaches its starting position. At this point at the latest, they are about to be switched off of the actually defective consumer switched off again to turn on. But it is also possible to continue fenden shutdown the consumer switches off the previously switched off when a consumer is switched off To switch consumers on again.

Like such a sequential circuit for one on two consumers dividing circuit could look advantageous is shown in Figure 4 of the drawing shown.

For the explanation of FIG. 4, reference is made to FIG. 3, in the arrangement of the short-circuit monitoring circuit common to both consumer circuits is shown.

FIG. 3 essentially corresponds to FIG. 1 with the difference that that as in Figure 2 instead of a single now two separate feeds from Al and A2 are provided and that the common short-circuit monitoring device does not affect the contactor that switches the entire circuit. The switching means «, ß and For example, this contactor will only be used by those in the common Part of the supply circuit switched or indirectly from the current flowing there influenced bimetal relays RI to R3 controlled. They are used to switch off of the supply network in the event of an overcurrent below the Response limit of the short-circuit monitoring circuit.

The individual outlets A1 and A2 are through the contacts A / 2 to A / 4 or B / 3 to B / 5 of these feeds assigned contactors for to or. For the common short-circuit monitoring of the outlets A common short-circuit monitoring circuit is used for loads connected to A1 and A2 as shown in FIG.

Has the overcurrent relay S of the short-circuit monitoring circuit responded and so signals a short circuit in one of the two consumer circuits, so the circuit shown in Figure 4 is effective, which disturbed the respective Loads localized and switched off. This is done via contactors A and B, whose switching contacts are in Figure 3 in the circuits of the two consumers. With proper functioning of the connected to the two outlets The overcurrent relay S has dropped out and has its contact S / 1 in the supply circuit of the two contactors A and B closed.

In this switch position of the contact S / 1, both Switch on the contactors by pressing the assigned button contacts TA or TB. At the When the contactors are switched on, contacts A / 1 and 3/1, among other things, close and switch at the same time Holding circuits for the contactors.

The short-circuit monitoring circuit shown in FIG. 1 now speaks on, the contact S / 1 of the overcurrent relay S opens in the supply circuit of the contactors A and B. Contactor A then drops out, while contactor B initially still over its RC element for a certain delay time, for example one second, remains excited. When contactor A drops out, its contacts change, with the Contacts A / 2 to A / 4 switch off the consumers of the outfeed Al, during the Contact A / 1 in the already disconnected holding circuit of the contactor an automatic Switching on contactor A again when contact S / 1 closes at a later date is prevented. If namely the cause of the response of the short-circuit monitoring device was to be looked for in the switched-off consumers of the feed-out Al, this is the one Short-circuit after switching off these consumers no longer detectable bar and the overcurrent relay drops out again. It closes its contact S / 1 im Feed circuit of the two contactors A and B and contactor A would respond again, if the holding circuit has not been disconnected by the normally open contact A / 1 in the meantime were.

As soon as the overcurrent relay S in the assumed short circuit case (short circuit in the outfeed Al) its contact S / 1 in the circuit of contactors A and B again closes, contactor B, which is still excited via the RC circuit, is again removed from the supply voltage U operated; it remains switched on via its hold circuit and thus has the effect that the consumers of outfeed A2 via contacts B / 3 to B / 5 (Figure 3) from the generator continue to be supplied.

If the cause of the response of the overcurrent relay S is not in the exit A1 but in the exit A2, then after the expiry of the specified Delay time also the contactor B. So it first separates with his Contacts B / 3 to B / 5 are the previously connected consumers of feed-out A2 from the generator and prevents the contactor with a later closing of the contact S / 1 can automatically tighten again.

So if the short circuit registered by the overcurrent relay S in from A2 is to be looked for, this means that after switching off the there Consumer the overcurrent relay S drops out and thereby its contact S / 1 in Figure 2 closes again. In the case of the assumed fault (from feed A2 is short-circuited afflicted) the consumers of the output Al can safely return to the power supply be connected. It is therefore an automatic restart in an advantageous manner This consumer is provided. A break contact B / 6 of the contactor is used for this B, wel- cher when switching off the contactor there B a connection circuit prepared for contactor A. Is the contactor B and then also the overcurrent relay S dropped, then pulls when the contact S / 1 closes the capacitor C of the dem switched off contactor B associated delay element RC via a decoupling diode D, the break contact B / 6 of contactor B and the winding of contactor A briefly one considerable charging current. This charging current is dimensioned so that the contactor A to above its response limit is excited. As soon as contactor A has responded, it switches it creates a holding circuit with its contact A / 1, which makes it independent of the charging current flowing through the capacitor C and it also switches with its Contacts A / 2 to A / 4 the consumers of the not disturbed outfeed Al again at. This means that after only a small switching gap, the power supply is still available for the properly working outfeed Al restored and the work on Elimination of the malfunction at the switched off discharge can begin.

4 figures 10 claims

Claims (10)

Claims S circuit for short-circuit monitoring of circuits, in particular generator circuits, and for load disconnection in the event of a short circuit, using current transformers and contactors connected to the circuits for switching consumers on and off e t that each current transformer (W1, W2, W3) on the secondary side to an associated measuring resistor (R1, R2, R3) is performed that the measuring resistor or resistors the series connection a relay (S) and a Zener diode (ZD) is connected in parallel, the Zener diode a Zener voltage above that which can be tapped off at the measuring resistor or resistors at nominal load Has voltage drop and that the switching means of the relay (S) when responding of the relay directly or indirectly (via O (,) to the monitored Separate circuits. 2. A circuit according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that the series connection of relay (S) and zener diode (ZD) is a capacitor (C) is connected in parallel and that this parallel connection is preferably adjustable Resistance (RV) is connected upstream. 3. A circuit according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the zener diode (ZD) is a diode operated in the reverse direction (e.g. D1) is connected upstream. 4. Circuit according to one of claims 1 to 3, d a -d u r c h g e it does not indicate that it is used for monitoring and switching multiphase circuits a very common, from relay (S), Zener diode (ZD) and possibly capacitor (C) and series resistor (RV) existing switching arrangement is provided, which via in Reverse direction of the Zener diode (ZD) operated decoupling diodes (D7 to D3) to the The measuring resistors (R1 to R3) fed by the current transformers are connected. 5. Circuit according to one of claims 1 to 4, d a -d u r c h g e It is not stated that for monitoring and switching individual also multi-phase Circuits from a plurality of fed from the same supply device Circuits a corresponding number of switching arrangements (X1, X2 in Figure 2) is provided, which via associated measuring resistors and current transformers to the individual Circles are connected. 6. A circuit according to claim 5, d a d u r c h g e -k e n n z e i c h n e t that an additional common switching arrangement (X) is provided for monitoring and switching the common circuit part. 7. A circuit according to claim 2 and 5 or 2 and 6, d a -d u r c h g e k e n n n e i c h n e t that the switching arrangements (X, X1, X2) of the individual feed circuits Different switching times are permanently assigned due to different series resistors. are. 8. A circuit according to claim 6 and 7, d a d u r c h g e k e n n z e i c h n e t that the switching time assigned to the common switching arrangement (X) is greater than the switching times assigned to the other switching arrangements (X1, X2). 9. Circuit according to claim 1 or one of claims 4 to 6, d a It is indicated that the measuring resistors (R1 to R3) are through Bimetal switches or bimetal relays are shown, their switching means when responding the switch or relay directly or indirectly monitored the one or more Disconnect circuits. 10. Circuit for the selective shutdown of one with a short circuit affected consumer from one consisting of two consumers, from the same Supply device fed consumer arrangement using the contactors assigned to both loads for selective switching on and off of the relevant consumer and a circuit common to both consumers according to claim 1 or 4, d a -d u r c h g e k e n n z e i c h n e t that the excitation windings of the two contactors (A, B) via one if the operating behavior is correct Consumer closed contact (S / 1) of the relay (S) and one with each of them Assigned key contact (TA, TB) connected in series to a DC supply voltage (U), via which they respond when the button contacts (TA, TB) are closed and a holding circuit connected in parallel via the button contacts own normally open contacts (A / 1, B / 1) switch so that one of the contactors (B) is opposite the other Contactor (A) is designed with dropout delay and that for the dropout delay on RC element (RC) is provided, the C of which has one connection via one in the forward direction operated diode (D) to a tap between the contact (S / 1) of the relay (S) and the normally open contact (A / 1) of the non-dropout delayed contactor (A) and a connection the field winding of the drop-out delayed contactor (B) closed and with its other connection via an NC contact (B / 6) of the drop-out delayed contactor (B) to a tap between the normally open contact (A / 1) of the non-off-delay contactor (A) and its field winding as well as via the R to the other connection of the field winding of the drop-out delayed contactor (B) is connected.