GB2031239A - Interfaces of control devices - Google Patents

Abstract

In an interface of a control device capable of transmitting and receiving control signals through a disconnectable connector 15, a first circuit element 12a is provided in the control device for delivering an output of the control device therethrough. A sink load 21 and a source load 16 are both connected to the output of the first circuit element 12a. A second circuit element 23 is further connected to receive the output signals of the two loads thereby delivering different control signals in response to the presence or absence of the output signals of the two loads. <IMAGE>

Description

SPECIFICATION Interfaces of control devices Background of the invention Field of the invention This invention relates to an interface provided for a control device, and more particularly to an interface of, for instance, a protective relaying device for an electric power system, wherein the transmission and reception of the output signals must be carried out with high reliabilities.

Description of the prior art In a typical arrangement of conventional protective relaying means used in an electric power system, the transmission and reception of electric signals between a relay and a sequential control unit which applies trip signals to circuit breakers, etc. have been carried out as shown in Figure 1. In this figure, a protective relaying means 11 comprises a protective relay 12 and an output circuit 16.The protective relay 12 itself comprises a circuit 13 for judging whether the relay 12 should operate or not, and an output transistor 14 for delivering an output of the protective relay 12 in accordance with the judgement of the circuit 13 The collector terminal of the output transistor 14 is connected through a detachable connector 15 to the output circuit 16, thereby permitting to replace the relay by another protective relay of a different kind or to provide it for maintenance.

Herein it is assumed that the output of the protective relay 12 is the output signal of the output circuit 16 is B1, and the transistor 14 is completely turned off when the protective relay 12 is operative, and turned on when the relay 12 is inoperative. When the relay 12 is operative, the output A1 is approximately equal to +E volts and hence it is assumed to be in a "1" state. Conversely, when the relay 12 is not operative, the output A1 is approximately equal to 0 volt, and hence is assumed to be in a "0" state.

The output circuit 16 in this example may otherwise be termed a source load. When the output A1 of the relay 12 is "0", a current i, flows from the power source of the circuit 16 through the connector 15 to a point between the collector and emitter electrodes of the transistor 14 now conducting. The base current ib of a transistor included in the source load 16 is thus interrupted, and the output B1 from the transistor 17 (or from the source load 16) is thereby brought into "1". When the output A1 of the relay 12 is "1", the base current flows, and the output B1 of the source load 16 is brought to "0".

The above described arrangement of the protective relaying means 11, however, is found to be disadvantageous because of its difficulty in discriminating the operative state of the relay 12 from the state in which the relay 12 has been disconnected. That is, even when the relay 12 is disconnected from the means 11 the current i5 flowing from the source to the collector electrode of the transistor 14 would be interrupted just in the same manner when the relay 12 is operative. The transistor 17 in the source load 16 is thus turned on, and the output signal B1 of the source load 16 is brought into "0". This difficulty in discriminating the two different conditions has resulted in a serious drawback of the conventional arrangement of the relaying means.

For the purpose of eliminating the above described disadvantage, there has been proposed a construction, wherein after the connector has been disconnected for removing the protective relay, the remaining part of the connector 15 is mechanically connected to a point of 0 volt. This construction, however, gives rise to further drawbacks of requiring a great number of short-circuiting mechanisms for relays having a multitude of outputs, thus complicating the construction, reducing the reliability, and increasing the manufacturing cost of the relaying means.

Summary ofthe invention An object of the present invention is to provide an interface of a control device wherein the above described disadvantages can be substantially eliminated.

Another object of the invention is to provide an interface of a control device through which the transmission and reception of important signals can be carried out correctly and accurately.

Still another object of the present invention is to provide an interface of a control device wherein any erroneous effect caused in the interface can be eliminated without fail.

According to the present invention there is provided an interface of a control device capable of transmitting and receiving control signals through a disconnectable connector, the interface comprising a first circuit element included in the control device for delivering an output of the control device through the circuit element, a sink load and a source load both connected to the output of the first circuit element, and a second circuit element connected to receive the output signals of the sink load and the source load for delivering different control signals in response to the presence or absence of the output signals of the two loads.

The sink load is provided in its input circuit with a threshold voltage level high er than a threshold voltage level provided in the input circuit of the source load.

The first circuit element in the control device may comprise a first switching element to conduct when the control device is in an operative state, and a second switching element which interrupts when the first switching element conducts, thereby passing a current from the source load through the disconnectable connector to the first switching element.

The aforementioned sink load and source load may include respective output switching elements through which the outputs of the two loads are delivered to the second circuit element in a manner such that any intentional or faulty disconnection of the connector can be clearly discriminated from any of the operational outputs of the control device.

Briefdescription of the drawings In the accompanying drawings: Figure 1 is a circuit diagram showing a conventional interface of a control device; Figure 2 is a circuit diagram showing an embodiment of the present invention; and Figure 3 is a circuit diagram showing an example of a control circuit shown in Figure 2.

Description of the preferred embodiment Referring now to Figure 2, there is illustrated a preferred embodiment of the present invention, wherein members and parts similar to those shown in Figure 1 are designated by like reference numerals, or like numerals with suffixes, and the detailed descriptions thereof are omitted. In this embodiment, a relaying means 1 la includes a protective relay 12a which in turn includes a circuit 13, as in Figure 1, judging whether the relay 1 2a should deliver an outut for tripping a circuit breaker or not. The judged result of the circuit 13 is applied to the base electrode of an output transistor 18.The collector electrode of the transistor 18 is connected directly to the base electrode of a transistor 20 and through a diode 19 to the emitter electrode of the transistor 20, which, in turn, is connected to a detachable connector 15 as described with reference to Figure 1.

The other side of the detachable connector 15 is connected to a source load 16 and a sink load 21, so that the output A2 of the relay 1 2a is applied to the two loads 16 and 21. In order to prevent circulation of a current from the source load 16 to the sink load 21, the threshold voltage of sink load 21 is selected to be higher than that of the source load 16. Since the threshold voltages for the inputs of the two loads 16 and 21 are determined by Zener voltages VZD, and VZD2 of Zener diodes ZD1 and ZD2 provided in the input circuits of the two loads, the above described relation can be achieved when the Zener voltages are selected as VZDX S VZD2 The source load 16 and sink load 21 include transistors 17 and 22 which deliver the output signals B1 and B2, respectively.A control circuit 23 is further provided in the relaying means 11 a for receiving the output signals B1 and B2.

The embodiment described above operates as follows.

When the protective relay 1 2a is inoperative and the output A2 is "0", that is, when the transistor 18 is in the ON state, a current is flows from the positive bus +E2 Of the source load 16 to the ground voltage of the relay 12a, through the connector 15, a diode 19, and the transistor 18. Thus, the base current of the transistor 17 in the source load 16 is interrupted, and the output B1 is thereby brough to "1". Reversely, when the output A2 of the relay 1 2a is "1", the current i5 is supplied to the base electrode of the transistor 17, and the output B1 thereof is brought to "0" as described with reference to Figure 1.

As for the sink load 21, when the transistor 18 of the protective relay 1 2a becomes off (or A2 = "1"), a current iR flows from the positive bus +E1 of the relay 1 2a to the base electrode of the transistor 22 of the sink load 21, through the transistor 20 in the relay 12a, connector 15, and the Zener diode ZD2 in the sink load 21.

Thus, the transistor 22 conducts and the output B2 thereof is brought to "0". Conversely, when the transistor 18 of the protective relay 12a is ON, and the output A2 is "0", the current iR flows through the diode 19 and the transistor 18, and the flow of the base current of the transistor 22 of the sink load 21 is thereby interrupted. The output B2 Of the sink load 21 is thus brought to "1".

In case where the protective relay 12a is removed from the relay means 1 lea, the conductor 15 is in the disconnected state. The current i, in the source load 16 thus flows through the Zener diode ZD1 to the base electrode of the transistor 17 thereby causing the output B1 to become "0". On the other hand, no base current flows into the transistor 22 in the sink load 21, and the output B2 of the sink load is brough to "1"; The variations in the state of the outputs B1 and B2 Of the source load 16 and the sink load 21 are summarized in the following table for the cases where the output of the protective relay 1 2a is varied to "1" and "0", and where the protective relay 1 2a is removed from the relaying means 11 a.

TABLE Output A2 or state of pro- Output B1 of Output B2 of tective relay source load sink load "1" "0" "0" "0" "1" "1" removed "0" "1" As is apparent in the Table, the combinations of the outputs B1 and B2 Of the source load 16 and the sink load 21 are all different for the different outputs A2 of the protective relay, and therefore the output states of the protective relay 12a can be discriminated from the removal of the same from the relaying means.

The control circuit 23 may be constructed in various ways so that the circuit ce n accomplish various functions. For instance, the control circuit 23 may be constructed to issue an instruction to trip a circuit breaker only when the outputs B1 and B2 are both "0". Such a construction can eliminate any possibility of misunderstanding the removal of the protective relay 12a as one of the operating results of the same relay.

The control circuit 23 may otherwise be so constructed that the output B2 Of the source load 21 is used for tripping a circuit breaker, and the output B1 of the sink load 16 is used for the constant supervision of the output of the protective relay 12a.

Figure 3 illustrates a construction of the control circuit 23 where both the highly reliable trip signal to a circuit breaker and the supervised output signal of the conditions of the protective relay are obtainable. With this construction, only when the outputs B1 and B2 are both "0", an instruction for tripping circuit breaker is issued from inverters 24 and 25 and an AND gate circuit 26, and an alarm signal is issued through an exclusive OR gate circuit 27 when the outputs B1 and B2 are different from each other. By the above described construction of the control circuit 23, it is possible to readily find out the removal of the protective relay 12a or the occurrence of a fault in the connector 15, and any possibility of issuing an erroneous tripping instruction for the circuit breaker in either of the two cases can be completely eliminated.

When the above described embodiment of the invention is compared with the hereinbefore described conventional example shown in Figure 1, where the removal of the protective relay has caused a similar effect as that caused by a faulty connector, and when it is considered that the possibilities of occurrence of faults in the connectors in the conventional device and in the embodiment of the present invention are equally high, the advantage of the present ianvention over the conventional device will be quite clear.

Although the invention has been described in terms of a preferred embodiment thereof, it will be apparent to one skilled in the art that various modifications will be obvious within the scope of the present invention.

For instance, the output part of the protective relay 12a may be of any suitable construction so far as it can be connected to the source load and the sink load. The source load and the sink load may also be constructed other than those described above so far as the threshold level of the sink load is selected to be higher than that of the source load.

Furthermore, although in the above description, the control device having the interface has been described with respect to a protective relaying device, it is apparent that the invention is also applicable to any kind of control device having a detachable component element similar to the protective relay in the described embodiment.

Claims (12)

1. An interface of a control device capable of transmitting and receiving control signals through a disconnectable connector, said interface comprising a first circuit element included in said control device for delivering an output of the control device through said circuit element, a sink load and a source load both connected to the output of said first circuit element, and a second circuit element connected to receive the output signals of said sink load and said source load for delivering different control signals in response to the presence or absence of the output signals of said two loads.

2. An interface of a control device as set forth in claim 1 wherein said sink load is provided in its input circuit with a threshold voltage element higher than a threshold voltage in the input circuit of said source load.

3. An interface of a control device as set forth in claim 1 wherein said first circuit element in said control device comprises a first switching element to conduct when the control device is in an operative state, and a second switching element which interrupts when the first switching element conducts, thereby passing a current from said source load through said disconnectable connector to said first switching element.

4. An interface as set forth in claim 1 wherein said first switching element interrupts when the control device is in an inoperative state, and said second switching element conducts when said first switching element interrupts, thereby passing current from said second switching element in said control device through said disconnectable connector to said input of said sink load.

5. An interface as set forth in claim 1 wherein said sink load and said source load include respective output switching elements through which the outputs of the two loads are delivered to said second circuit element.

6. An interface as set forth in claim 3 wherein said current flowing from said source load to said first switching element in said control device causes, in said source load, to interrupt an output switching element, thus delivering a logic signal "1" to said second circuit element.

7. An interface as set forth in claim 6 wherein said current flowing from said source load to said first switching element in said control device causes, in said sink load, to interrupt an output switching element, thus delivering a logic signal "1" to said second circuit element.

8. An interface as set forth in claim 4 wherein said current flowing from said second switching element in said control device to said sink load causes, in said sink load, to conduct an output switching element, thus delivering a logic signal "0" to said second circuit element.

9. An interface as set forth in claim 8 wherein said current flowing from said second switching element in said control device to said sink load causes, in said source load, to conduct an output switching element, thus delivering a logic signal "0" to said second circuit element.

10. An interface as set forth in claim 1 wherein in either of the cases where the control device is removed or the disconnectable connector is disconnected, an output switching element in said source load conducts thus delivering a logic signal "0" to said second circuit element, while an output switching element in said sink load is interrupted, thus delivering a logic signal "1" to said second circuit element.

11. An interface as set forth in claim 7 wherein said second circuit element operates a device controlled by said control device.

12. An interface as set forth in claim 10 wherein said second circuit element issues an alarm.