GB2162391A

GB2162391A - Electric fault detection device

Info

Publication number: GB2162391A
Application number: GB8513905A
Authority: GB
Inventors: Heihachiro Umemura
Original assignee: Shinko Electric Co Ltd
Current assignee: Shinko Electric Co Ltd
Priority date: 1984-06-04
Filing date: 1985-06-03
Publication date: 1986-01-29
Also published as: GB8513905D0; DE3520257A1; FR2565430A1; CA1263144A; FR2565430B1; DE3520257C2; GB2162391B

Abstract

A relay malfunction detecting device 6 which at the occurrence of any fault in a relay 4 (including a magnet switch type) detects such fault immediately and gives an alarm by means of a lamp LP, or operates a cut-off switch 12. The device is provided with a sensor 7 for detecting driving current flowing in a driving circuit 2 to a load 3 and a judging circuit 8 to which signals from the sensor 7 and operation signals from a relay operating circuit 5 are input. The judging circuit 8 stores a signal representative of the mutual relationship between the two signals in normal condition and actuates fault response circuit 10 when the mutual relationship between the two signals shows a value outside the standard. <IMAGE>

Description

SPECIFICATION Fault detecting device for relays This invention relates to a relay malfunction detecting device which detects automatically any fault in a relay or magnetic switch (hereinafter referred to simply as "relay") provided in a driving circuit for a motor or other load.

High-tension heavy current is used for driving the motors of hoist cranes and large size processing machines. Therefore, it is dangerous to do switching operation manually for starting and stopping. In order to avoid such danger, relays which open and close a driving circuit of high-tension and heavy current by low-tension light current are adopted. The life of these relays depends upon the frequency of use, values of tension and current, etc. Especially in three-phase alternating circuits, when any one of the three phases has become bad in connection, we have the so-called singlephase running, with the result of such trouble as burning. In the case where relay contacts become fused together, "runaway" running results and does much damage to persons and things.With this in view, it has been the practice to set a permissible time for use of each relay and to change relays with new ones after their use for this permissible time.

This, however, involves uneconomical use of relays because some are still usable safely at the time of change. On the other hand, depending upon the environment under which relays were used, some go wrong earlier than usual due to gas, water content, etc. Thus, a safe countermeasure is needed.

The present invention seeks to provide a device whereby any fault or malfunction in a relay is detected automatically as soon as it occurs, thereby preventing trouble such as burning and runaway running.

In accordance with the invention there is provided a relay malfunction detecting device comprising a sensor for detecting driving current provided in a driving circuit which connects a power source with a load and a judging circuit to which detecting signals from said sensor and operation signals of a relay operation circuit are applied, said sensor being operable to apply detecting signals corresponding to applied load current to said judging circuit, which judging circuit is operable to examine the mutual variation relation between the detecting signal and the operation signal and operate an alarm circuit selectively.

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a drawing illustrating the basic concept of the present invention; Figure 2 is a perspective view of the sensor for detecting driving current; Figure 3 is a perspective view of another example of the sensor for detecting driving current; Figure 4 is an overall circuit diagram showing a first embodiment of the present invention; Figure 5 is an overall circuit diagram showing a second embodiment of the present invention; Figure 6 is an overall circuit diagram showing a third embodiment of the present invention;; Figures 7 and 8 relate to a fourth embodiment of the present invention, in which Figure 7 is an overall circuit diagram and Figure 8 is a plan view of the main device from which an upper lid is removed; and Figure 9 is an overall circuit diagram of a fifth embodiment of the present invention.

Figure 1 is a drawing showing the basic concept of relay malfunction detecting device according to the present invention. In Figure 1, a power source 1 is connected to a load 3, such as a motor, via a relay 4. The relay 4 is opened and closed by a relay operating circuit 5. Numeral 6 denotes a relay malfunction detecting device which comprises a sensor 7 for detecting driving current flowing in a driving circuit 2 and a judging circuit 8 to which detecting signals from said sensor 7 and operating signals from the operating circuit 5 are applied. As the means of inputting operating signals, a sensor 9 for detecting operating signals is fitted to the operating circuit 5, for example. The judging circuit 8 is composed of an IC, for example.This circuit compares the relay operating signals with the detecting signals from the sensor for detecting driving current and in the case of three-phase alternating current, it detects whether or not the electric current of each phase is uniform and thus judges whether the relay 4 is good or bad. When abnormality occurs, an alarm circuit 10 is actuated to give an alarm or a switch 1 2 for cutoff provided in the driving circuit 2 is operated to open the driving circuit 2.

LP is an alarm lamp. The sensor 7 for detecting driving current is composed of a current transformer, for example, and is so constructed that it detects the electric current of each phase separately in the case where the power source is three-phase AC. An example of it is shown in Figure 2. In a sensor 1 5 for detecting driving current shown in Figure 2, conductors Ra, Sa, Ta which are connected to each phase R, S, T respectively are wound round a winding 1 6 (in the drawing Ra is shown to be passed through) so as to generate induced current at the winding 1 6. The number of turns of each phase is different from each other. Numeral 1 7 is an output terminal which is connected to the judging circuit 8.The judging circuit 8 compares induced current induced at the winding 16 of each phase and detects any variation of induced current caused by interruption or poor conducting of any one of the three phases.

Figure 3 shows a sensor of a different type for detecting driving current. This type is applicable to the case where each conductor of the driving circuit 2 is thick and is unsuitable for winding round the winding 16 as shown in Figure 2. A sensor 20 for detecting driving current comprises current transformers 21 a, 21 b (the current transformer for R phase is omitted from the drawing) for detecting each phase provided for conductors R, S. T for each of the three phases and a main current transformer 24. Conductors 23a, 23b are wound round a winding 25 of the main current transformer 24 from the secondary sides of the current transformers 21 a, 21b for detecting each phase.As will be described later, it is possible to have the current transformers 21a, 21b for detecting each phase serve as a sensor for detecting driving current and output signals of each transformer are applied to a judging circuit via a conversion circuit.

The sensor 9 for detecting- operation signals is composed of a current transformer, for example, and detects electric current flowing in the relay operating circuit 5 when the circuit 5 is working. However, in the case where the operating circuit 5 is DC, operating signals are applied to the judging circuit 8 by other proper means as will be described later.

Embodiment 1 The first embodiment 1 is shown in Figure 4. In a three-phase driving circuit 30, a plurality (three, for example) of loads 31a, 31b and 31c are arranged in parallel. Each load is a driving motor, for example, and for normal and reverse turn of the driving motor, each load is fitted in relating to the driving circuit 30 via the relays 32a, 32b, 32c .... 32f.

Numeral 33 is a relay operating circuit which is provided with solenoid coils MC1, MC2, MC3 MC6 for relays 32a, 32b, 32c ......

respectively and interlock type push buttons Pb2, Pb3, Pb4 for the solenoid coils. The push button Pbl is the main push button.

A relay malfunction detecting device 40 comprises a sensor 41 for detecting driving current provided in the driving circuit 30 and an operating box 42. The operating box 42 is provided with a sensor 43 for detecting operation signals for the relay operating circuit 33 and a switching contact 45 for a judging circuit 44 and an alarm circuit 46. The alarm circuit 46 is connected to a no fuse breaker (hereinafter referred to as NFB) having a trip circuit provided in the driving circuit 30. Both the sensor 41 for detecting driving current and the sensor 43 for detecting operation signals are composed of current transformers.

The sensor 41 should preferably be constructed as shown in Figure 2 or Figure 3. In Figure 4, 48a, 48b ...... 48f are normally closed contacts for preventing erroneous operation and are opened when the solenoid coils MC2, MC1, MC4 ...... operate.

In the above construction, when the relays 32a, 32b ...... are in normal condition, loads 31 a, 31 b, 31 c are driven by input of relays and the amount of electric current flowing in the driving circuit 30 is detected by the sensor 41 for detecting driving current. In this case, according to the horsepower of a load to be worked and the number of loads, the amount of electric current flowing in the driving circuit 30 should vary but the amount of alternating current in each of the three phases is uniform. By pressing the push buttons Rb2, Pb3, Pb4 to work the relays 32a, 32b ......, the amount of electric current flowing in the relay operating circuit 33 is detected by the sensor 43 for detecting operation signals. In this case, the amount of electric current flowing in the operation circuit 33 is proportionate to the number of closed push buttons.

The judging circuit 44 can find the number of closed push buttons by the amount of electric current induced at the sensor 43 for detecting operation signals. When, for example, the push button Pb2 is pressed to work only the load 31a and the relay 32a or the relay 32b is actuated, if any one of the relay contacts becomes faulty and does not conduct, operation signals are applied to the judging circuit 44 via the sensor 43 for detecting operation signals but induced current generates at the sensor 43 for detecting driving current only for the electric current which generates between two phases which are conducting. The judging circuit 44 detects this and judges that the relay is faulty on the basis of signals from both sensors 41, 43 and opens the NFB 47 via the alarm circuit 46.

When two or three (all) contacts are badly conducting, no electric current flows in the driving circuit 30 and only operation signals are applied to the judging circuit 44, from which bad conducting of the relay can easily be found. At the termination of operation, if the load 31 a continues to be driven due to fusing together of contacts, despite the release of the push button Pb2, signals are applied to the judging circuit 44 only from the sensor 41 for detecting driving current and no signals are applied from the sensor 43 for detecting operation signals, whereby malfunction of the relay can be recognised.

While both the load 31a and the load 31b are working normally by pressing the push buttons Pb2 and Pb3, if the push button Pb4 is pressed to work the third load 31 c but the relay 32e (or 32f) is faulty and one of the contacts is conducting badly, electric current flows to the phase connecting to the remaining two contacts. Therefore, electric current among the three alternating phases becomes out of balance and this unbalance can be recognised by the induced current induced by the sensor 41 for detecting driving current. If two or three contacts are connecting badly, electric current in the operation circuit 33 increases due to closing of the push button Pb4, but the increase of electric current is not recognised in the driving circuit 30. This indicates that the relay is faulty.

Embodiment 2 This embodiment is shown in Figure 5. The relay malfunction detecting device 50 shown in this embodiment is so designed that a main electromagnetic contactor 52 is opened by the operation of an alarm circuit 51. The alarm circuit 51 is connected to the side of the normally closed terminal 45a of the switching contact 45 provided in the operation box 42 (as in the case of Embodiment 1) and carries a push button Pb5 and a solenoid coil MC7 of the main electromagnetic contactor 52. Under this arrangement, at starting, the push button Pb5 is first pressed to close the main electromagnetic contactor 52. If bad contact took place at the relay contact, such fault is detected in the same way as Embodiment 1 and the switching contact 45 is switched over to release the main electromagnetic contactor 52.In Embodiments 1 and 2, an example of using three-phase AC is shown as a driving power source but it is applicable to the case of using single phase AC. In the embodiments, AC is adopted for the relay operation circuit 33 and a current transformer is used for the sensor for detecting operation signals, but in the case where DC is used for the operation circuit, electric current flowing in the operation circuit can be detected by a DC galvanometer or other proper means.

Embodiment 3 This embodiment is shown in Figure 6. In the preceding embodiments, driving current flowing in the driving circuit 30 and operating current flowing in operation circuit 33 are detected by the detecting sensors 41 and 43 respectively and detecting signals from both sensors 41, 43 are input to the judging circuit 44. In this embodiment, however, a sensor for detecting operation current is omitted and with the operation of a relay, operation signals are input directly to the judging circuit. The relay 60 provided in the driving circuit 30 connecting to the load 31 is of the semiconductor element type (hereinafter referred to as solid-state relay, abbreviated as SSR), using a light shielding system as a switch 61.

In the above relay 60, from the construction of SSR voltage generates at its secondary side by the influence of leakage current, even if input signals are in OFF state, and therefore it is not suitable to use a relay for detecting the secondary side.

A relay malfunction detecting device 62 in this embodiment comprises the sensor 41 for detecting driving current (same as the sensor 41 of the preceding embodiment provided for the driving circuit 30 to the load 31), a relay operating circuit 63, such as an interface circuit for the relay 60 (SSR) for switching the driving circuit, and a judging circuit 64. Operating signals of the switch 61 are input to the judging circuit 64 from the relay operating circuit 63. The switch 61 is of light shielding type and comprises a light emitting element LEC, a light receiving element PD and a light shielding plate 65 which is interposed between the two elements and is shifted to and from the light shielding position. Switch signals are transmitted to the relay operating circuit 63 in the a control box 67 via a signal transmitting circuit 66.While the relay operating circuit 63 gives operating signals to the relay (SSR) 60, the operating signals are input to the judging circuit 64. In Figure 6, LP and RSW are a lamp for information and a resetting switch respectively for the judging circuit 64 and numeral 70 is a switch circuit for a contact 72 to be provided in an alarm circuit 71. The alarm circuit 71 operates the NFB 47. Under this arrangement, detecting signals from the sensor 41 for detecting driving current and the switch closing signals from the switch 61 are compared at the judging circuit 64 to judge whether the relay 60 is good or bad. If a fault occurs, the alarm circuit 71 is closed immediately and the driving circuit 30 is opened.In this embodiment, the relay 60 provided in the driving circuit 30 and the switch 61 are of non-contact type but the switch is not necessarily required to be of non-contact type and a switch device of contact type may be used.

Embodiment 4 This embodiment is shown in Figure 7 and Figure 8. In this embodiment, a relay malfunction detecting device is composed of a plurality of sending members, one of which is called a main device and the others are called supplemental devices. While the main device alone has breaking function of NFB, the supplemental devices have terminals (for signal transmitting) to the main device. On the basis of relay malfunction signals detected by the main device, by the supplemental device or by both the main device and the supplemental device, trouble signals (for breaking the NFB at the main device) are issued. A plurality of loads, for example, three loads 31a, 31b, 31c are connected to the common driving circuit 30. Also, the NFB 47 is provided in the common driving circuit 30.Relays for circuit switching 80a, 80b, 80c are provided in branch driving circuits 30a, 30b, 30c respectively connected to the load 31a, 31b, 31c.

MC shows a magnet coil and PB shows a push button.

A relay malfunction detecting device 81 for relays 80a, 80b, 8Cc comprises a plurality of sensing members 82, 83, 84, of which the sensing member 82 is called a main device and the sensing members 83, 84 are called supplemental devices. The main device 82 is equipped with a sensor 85 for detecting driving current provided in the branch driving circuit 30a, a sensor 87 for detecting operation current provided in an operation circuit 86a for the relay 80a, a judging circuit 88 to judge whether the relay 80a is good or bad by the input signals from both sensors 85, 87 and a switching means 89 for an alarm circuit 90. The sensor 85 for detecting driving current is composed of a current transformer as in the case of the preceding embodiments.In this embodiment, a power source for driving the main device 82 is electric current obtained from the sensor 85 for detecting driving current and therefore the driving power source circuit for the main device 82 can be omitted.

The sensor 87 for detecting operation current detects presence of operation current by utilising a current transformer. An output terminal is connected to the judging circuit 88.

The alarm circuit 90 is for opening the NFB and the switching means 89 mainly comprises SSR, such as triac, and makes the alarm circuit 90 ON when abnormality occurred.

Both the supplemental device 83 and the supplemental device 84 are of the construction and therefore explanation is made below about the supplemental device 83. Similarly to the main device 82, the supplemental device 83 carries a sensor 91 for detecting driving current for the branch driving circuit 30b, a sensor 92 for detecting operation current provided in the operation circuit 86b of the relay 80b and a judging circuit 93 but lacks the alarm circuit switching means 89 which is provided for the main device.

Similarly to the case of the main device 82, sensors 91 and 92 are provided with a current transformer and terminals 95 for transmitting signals and are connected to the main device 82 by means of connecting cords 94. When abnormality is detected in the relay 80b, the switching means 89 provided in the main device is operated. Similarly to the main device 82, the supplemental device 83 takes output from the sensor 91 for detecting driving current as its driving power source.

For the other supplemental device 84, like symbol numbers are given to like parts and explanation of it is omitted. However, 86c is the operating circuit for the relay 80c.

In the above composition, when the relays 80a, 80b, 80c are in normal condition, any one (for example, 86a) of the relay operating circuits 86, 86b, 86c is made ON and when driving current is applied to the load 31a, both the sensor 85 for detecting driving current and the sensor 87 for detecting operation current give signal current, which the judging circuit 88 judges and the switching means 89 is not operated. Thus, SSR is not operated.

This applies to the case where all relay operation circuits 86a, 86b, 86c are made OFF and also branch driving circuits 30a, 30b, 30c are made OFF. However, even if any one (80b, for example) of the relays 80a, 80b, 80c has become faulty and the relay operating circuit 86b is in OFF state, so long as electric current flows in three phases or two phases of the branch driving circuit 30b, the supplemental device 83 judges it at the judging circuit 93 and makes the alarm circuit switching means at the main device 82 ON, whereby putting the alarm circuit in conducting state and opening the NFB 47.

Figure 8 is a plan view of the main device 82. In Figure 8, terminals 96a, 96b are connecting terminals for the operation circuit 86a; 96c, 96d are connecting terminals for the switching means 89; and 96e, 96f, 96g are connecting terminals for the supplemental devices 83 and b4.

Embodiment 5 This embodiment is shown in Figure 5.

Thick wires are used for the driving circuit 30 common to loads 31a, 31b, 31e to flow heavy current.

A relay malfunction detecting device 100 comprises two sensing members 101, 102 (hereinafter the sensing member 101 is referred to as a main device and the sensing member 102 is referred to as a supplemental device). The main device 101 is provided with a current transformer 104 for an arbitrary one phase (Rphase, for example) in the driving circuit 30, a switching means 108 for a judging circuit 30 and an alarm circuit 109, and a sensor 111 for detecting operation current provided in a relay operation circuit 110. The alarm circuit 109 composes an operation circuit for a NFB 107. The switching means 108 is mainly composed of SSR as in the preceding embodiments.The supplemental device 102 is provided with a current transformer 105 for the other one phase (Tphase, for example) in the driving circuit 30, a judging circuit 11 3 to judge whether the relay is good or bad by input signals of a sensor 11 2 for detecting operation current provided in a relay operation circuit 110 and terminals 11 5 for transmitting signals connected to the main device 101 by connecting cords 114. Relays 120a, 1 20b 1 20f for normal and reverse driving of each load 31 a, 31b, 31 c are arranged in parallel in the relay operation circuit 110 and when any one of the relays became ON, operation current is detected by the sensors 111 and 11 2 for detecting operation current.

A current transformer is applied to the sensors 111, 11 2 for detecting operation current as in the case of the preceding embodiment.

In Figure 9, PBI, PB2 ..... PB4 are push button switches of interlock type. In this em bodiment, a driving power source for the relay trouble detecting device 100 is electric current obtained from the sensor 103 for detecting driving current.

In the above arrangement, in the case where relays 120a,. 1 2orb 1 2Of are in normal condition, if any one of the relays (the relay 120a, for example) is made ON and driving current is applied to the corresponding load 31 a, the sensor 103 for detecting driving current and the sensors 111, 11 2 for detecting operation current generate signal current, which is applied to the judting circuits 106, 11 3. In the case where all the relays 120a, 120b 1 20f are OFF, no electric current flows in the driving circuit 30. In either case, judging circuits 106, 11 3 do not make the alarm circuit 109 (namely, SSR) ON.

Even when any one of the relays 120a, 1 20b .. . 1 20f has become faulty and the relay operation circuit 110 is OFF, so long as electric current flows to three phases or two phases of the driving circuit 30, the sensor 103 for detecting driving current operates and applies signal current to the judging circuits 106 and 113 or any one of 106 and 113.

Thus, the judging circuits 106, 11 3 make the switching means 108 ON and open the NFB 107.

In the above described embodiments, when a relay provided in a driving circuit for a load has gone wrong and the connection of one or more relay contacts is inaccurate and current does not flow at the operation of relays or when the relay contacts of plural phases do not break and in conducting state at releasing the relay, such malfunction is detected by the value and state of electric current flowing in the driving circuit and by the existence of relay operation and an alarm is given. Thus, unforeseen accidents can be prevented.

1. A relay malfunction detecting device comprising a sensor for detecting driving current provided in a driving circuit which connects a power source with a load and a judging circuit to which detecting signals from said sensor and operations signals of a relay operation circuit are applied, said sensor being operable to apply detecting signals corresponding to applied load current to said judging circuit, which judging circuit is operable to examine the mutual variation relation between the detecting signal and the operation signal and operate an alarm circuit selectively.

2. A detecting device as defined in claim 1, wherein the sensor for detecting driving current is a current transformer.

3. A detecting device as defined in claim 1, wherein the driving circuit is a single phase or threephase AC type and the sensor for detecting driving current is composed of a current transformer.

4. A detecting device as defined in claim 1, wherein the sensor for detecting driving current is a current transformer and output signals of said current transformer form a power source for operation.

5. A detecting device as defined in claim 1, wherein the driving circuit is a three-phase AC type and the sensor for detecting driving current is a current transformer which is common to each phase and is equipped with a judging circuit to judge the applied current of each phase.

6. A detecting device as defined in claim 1, wherein the driving circuit is a single-phase or three-phase AC type, the sensor for detecting driving current comprises a plural current transformers for detecting each phase, each provided for conductors of at least two phases, and a main current transformer and a secondary side output circuit of the transformer for detecting each phase is connected to the main current transformer.

7. A detecting device as defined in claim 1, wherein a relay operation circuit is provided with a sensor for detecting operation signals.

8. A detecting device as defined in claim 7, wherein the sensor for detecting operation signals is a current transformer.

9. A detecting device as defined in claim 1, wherein an alarm circuit is connected to a nofuse breaker (NFB) operating circuit provided in the driving circuit.

1 0. A detecting device as defined in claim 1, wherein the alarm circuit forms an operating circuit for an electromagnetic contactor for switching the driving circuit ana is closed normally but is opened by a signal from the judging circuit.

11. A detecting device as defined in claim 1, wherein the alarm circuit includes a switching means in the form of a solid-state relay.

1 2. A detecting device as defined in claim 1, wherein the alarm circuit includes a switching means in the form of a contact relay.

1 3. A detecting device as defined in claim 1, further comprising a plurality of sensing members, one of which is a main device and the others are supplemental devices, said main device being provided with the sensor for detecting driving current, the judging circuit and a circuit for operating the alarm circuit and the supplemental device being provided with the sensor for detecting driving current, the judging circuit and output terminals to transmit output signals of the judging circuit to the main device.

14. A detecting device as defined in claim 13, wherein a plurality of loads are connected in parallel to the driving circuit, the main device being arranged in a branch driving circuit for one load and each supplemental device being arranged in a respective branch driving circuit for the other loads.

1 5. A relay malfunction detecting device substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. bodiment, a driving power source for the relay trouble detecting device 100 is electric current obtained from the sensor 103 for detecting driving current. In the above arrangement, in the case where relays 120a,. 1 2orb 1 2Of are in normal condition, if any one of the relays (the relay 120a, for example) is made ON and driving current is applied to the corresponding load 31 a, the sensor 103 for detecting driving current and the sensors 111, 11 2 for detecting operation current generate signal current, which is applied to the judting circuits 106, 11 3. In the case where all the relays 120a, 120b 1 20f are OFF, no electric current flows in the driving circuit 30. In either case, judging circuits 106, 11 3 do not make the alarm circuit 109 (namely, SSR) ON. Even when any one of the relays 120a, 1 20b .. . 1 20f has become faulty and the relay operation circuit 110 is OFF, so long as electric current flows to three phases or two phases of the driving circuit 30, the sensor 103 for detecting driving current operates and applies signal current to the judging circuits 106 and 113 or any one of 106 and 113. Thus, the judging circuits 106, 11 3 make the switching means 108 ON and open the NFB 107. In the above described embodiments, when a relay provided in a driving circuit for a load has gone wrong and the connection of one or more relay contacts is inaccurate and current does not flow at the operation of relays or when the relay contacts of plural phases do not break and in conducting state at releasing the relay, such malfunction is detected by the value and state of electric current flowing in the driving circuit and by the existence of relay operation and an alarm is given. Thus, unforeseen accidents can be prevented.