GB2218286A

GB2218286A - Malfunction indicator with reset arrangement

Info

Publication number: GB2218286A
Application number: GB8903298A
Authority: GB
Inventors: Minoru Nakahata; Nobuyuki Orito
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1988-04-21
Filing date: 1989-02-14
Publication date: 1989-11-08
Anticipated expiration: 2009-02-14
Also published as: GB8903298D0; CN1010911B; GB2218286B; DE3913180A1; KR910005246B1; CN1037243A; DE3913180C2; JPH01270723A; KR890016496A

Description

MD6550 1 2218286

TITLE OF THE INVENTION

Malfunction indicator for electric utility line FIELD OF THE INVENTION AND RELATED ART STATEMENT 1. FIELD OF THE INVENTION

The present invention relates generally to a malfunction indicator for electric utility lines, and more particularly to a malfunction indicator for indicating occurrence of ground fault or short-circuit in the electric utility lines. 2. DESCRIPTION OF THE RELATED ART

FIG.4 is the circuitry of a malfunction indicating apparatus in a conventional art. Referring to FIG.4, a short-circuit detecting coil 1 is composed of two windings 1X and 1Y, and the windings 1X and 1Y are connected to current transformers 2X and 2Y which are mounted on two electric utility lines, respectively. Furthermore, a ground fault detecting coil 3 is connected to a zero-phase current transformer 4 which is mounted on three electric utility lines. A normal-open contact 1-1 which is activated by excitation of the short-circuit detecting coil I is coupled in series with a limiting resistor 7 between a positive terminal P-1 of a power source and a voltage dividing resistor 8 which is coupled in series with a resistor 9, and the resistor 9 is coupled at the other terminal thereof with the negative terminal N of the power source. In a similar manner, a normal-open 1 contact 3-1 which is activated by excitation of the ground fault detecting coil 3 is coupled in series with a resistor 14 between the positive terminal P-1 of the power source and a voltage dividing resistor 15 which is coupled in series with a resistor 16. The resistor 16 is coupled at the other terminal thereof with the negative terminal N of the power source. A capacitor 10 which functions as a time delay circuit is connected across the voltage dividing resistors 8 and 9 which are connected in series. A Zener diode 11 is coupled at the cathode with the junction between the voltage dividing resistors 8 and 9, and is coupled at the anode with the base of a transistor 12. An auxiliary relay 13 is connected between the collector of the transistor 12 and the positive terminal P-1, and the emitter of the transistor 12 is coupled with the negative terminal N. The positive terminal P-1 is connected with a positive terminal P of the power source through a diode 38, and a capacitor 39 is connected across the positive terminal P-1 and the negative terminal N.

A similar circuit described above is composed of a limiting resistor 14, voltage dividing resistors 15 and 16, a capacitor 17, a Zener diode 18, a transistor 19 and a auxiliary relay 20, and coupled-across the positive terminal P-1 and the negative terminal N. Flag indicators 21 and 22 of magnetic holding-type are provided with activating windings 21S and 22S and reset windings 21R and 41 1 t 22R, respectively.

A latch relay 23 is connected across the activating winding 21S and the negative terminal N, and the normal-open contact 13-1 which is activated by the excitation of the auxiliary relay 13 is coupled at one terminal with the activating winding 21S. The normal-open contact 13-1 is coupled in series at the other terminal with a normal-close contact 13-2 which is connected in series with a normal-close contact 23-1 which is activated by excitation of the latch relay 23. The normal-close contact 23-1 is connected to the positive terminal P-2 which is connected to the positive terminal P of the power source through a limiting resistor 27 and a diode 28.

A capacitor 29 is coupled across the negative terminal N and the junction between the normal-open contact 13-1 and the normal-close contact 13-2.

A latch"relay 30 is connected in parallel with the activating winding 22S, and in a similar manner mentioned above, a normal-close contact 30-1 which is activated by the latch relay 30 and is connected in series with a normal-close contact 20-2 which is activated by the auxiliary relay 20 is connected with the positive terminal P-2. A normal-open contact 20-1 which is also activated by the auxiliary relay 20 is connected between the normalclose contact 20-2 and the activating winding 22S. The latch relay 23 comprises a reset winding 23A, which 3 activates a normal-open contact 23-3 and a normal-close contact 23-4 for controlling external devices. Moreover, a normal-open contact 30-3 and a normal-close contact 30-4 for controlling external devices are activated by the latch relay 30.

A capacitor 34 is connected across the negative terminal N and the junction between the normal-open contact 20-1 and the normal-close contact 20-2. Diodes 35 and 36 are coupled at the cathode with the reset windings 21R and 22R, respectively, the anodes of both the diodes are connected together with each other, and is connected with the positive terminal P-2 through a normal-open contact 64-1.

The capacitor 39 is charged in normal operation state of the power source, and when the power source falls in malfunction, an electric power for activating auxiliary relays 13 and 20 is supplied from the capacitor 39. The reset windings 23A and 30A are coupled in parallel with a diode 42, and are connected between one terminal of a capacitor 43 and the negative terminal N. The capacitor 43 is connected at the other terminal with the positive terminal P through a normal-open contact 64-2 of the reset relay 64, and a resistor 52 is coupled across the negative terminal N and the junction between the capacitor 43 and the normal-open contact 64-2. The reset 4 winding 23A for resetting the latch relay 23 is mounted in the latch relay 23, and the reset winding 30A for resetting the latch relay 30 is mounted in the latch relay 30.

Normal-open contacts 23-2 and 30-2 which are coupled in parallel are activated by the latch relays 23 and 30, respectively, and are coupled at one terminals with the positive terminal P-2 and at the other terminal with the anode of a diode 47. The cathode of the diode 47 is coupled with the cathode of a Zener diode 48, and the anode of the Zener diode 48 is connected to one terminal of a charging resistor 49, and the other terminal thereof is coupled with a resistor 51 and a capacitor 50 which are coupled in parallel. The other terminals of the resistor 51 and the capacitor 50 are connected with the negative terminal N. A capacitor 53 is connected across the positive terminal P-2 and the negative terminal N.

A Zener diode 54 is coupled at the cathode with the junction between the charging resistor 49 and the capacitor 50 and is coupled at the anode with the base of a transistor 55. An integrating circuit for delaying time is composed of the charging resistor 49 and.the capacitor 50. The transistor 55 is connected with a transistor 56 in Darlington connection and the transistor 56 is coupled at the emitter with the negative terminal N. The collector of the transistor 55 is connected with the positive terminal P of the power source through a resistor C_ 57, and the collector of the transistor 56 is connected with the positive terminal P through normal-close contacts 13-3 and 20-3, which are'connected in series, and the reset relay 64, which are connected in series with the normal close contact 13-2.

In the above-mentioned malfunction indicator in the conventional art, when the detected current of the ground fault detecting winding 3 or the short-circuit detecting windings 1X and 1Y exceeds a predetermined value, the normal-open contact 1-1-or the normal-open contact 3-1 is closed, and the capacitor 10 or the capacitor 17 is discharged, respectively.

When the capacitor 10 or 17 is charged and hence a voltage of the junction between the voltage dividing resistors 8 and 9 or a voltage of the junction between the voltage dividing resistors 15 and 16 exceeds a Zener voltage of the.Zener diode 11 or the Zener diode 18, respectively, the transistor 12 or 13 turns ON, and thereby the auxiliary relay 13 or 20 is activated, respectively. Corresponding to operation of the auxiliary relay 13 or 20, the normal-open contact 13-1 or 20-1 and the normal-close contact 13-2 or 20-2 are activated, and electric charge of the capacitor 29 or 34 is discharged to the activating winding 21S or 22S of the indicator 21 or 22 and the latch relay 23 or 30, and the latch relay 23 or 30 is activated, respectively. The normal- close contact 6 C_ 23-1 or 30-1 is opened by activation of the latch relay 23 or 30, respectively, and the latch relay 23 or 33 is isolated from the positive terminal P-2. Consequently, electric charge of the capacitor 29 or 34 is discharged into the indicator 21 or 22 and the latch relay 23 or 33. Moreover, close of the normal-open contact 23-2 of the latch relay 23 or the normal-open contact 30-2 of the latch relay 30 results in discharging of the capacitor 53 into the capacitor 50 through the diode 47, Zener diode'48 and the charging resistor 49.

In case that the electric power is supplied to the malfunction indicator, a current for charging the capacitor 50 is supplied from the positive terminal P through the diode 28 and the resistor 27. However, in case that the electric power is not supplied from the electric power source, the electric charge of the capacitor 53 is.supplied to charge the capacitor 50. When the voltage of the capacitor 50 exceeds the Zener voltage of the Zener diode 54, a base current of the transistor 55 flows through the Zener diode 54, and the transistors 55 and 56 which are connected in Darlington connection turn ON. Consequently, the reset relay 64 is activated under impression of the power source.

In the above-mentioned state, if the electric utility line is continuously under malfunction, the reset relay 64 is not activated, since the normal-close contact 7 C_ 13-3 or 20-3 of the auxiliary relay 13 or 20 is opened. When the malfunction is restored and the normal-close contacts 13-3 and 20-3 of the auxiliary relays 13 and 20 are closed, the reset relay 64 is activated and the normal-open contacts 64-1 and 64-2 are closed. Consequently, the reset windings 21R and 22R of the indicated 21 and 22 and the reset windings 23A and 30A of the latch relays 23 and 30 are activated, respectively, and thereby the respective displays and the contacts are reset to initial state.

Transmission of control signals for external apparatus is accomplished by close of the contacts 23-3 and 30-3 or open of the contacts 23-4 and 30-4. In a monitoring room for monitoring the electric utility lines, condition of the various electric utility lines are monitored or controlled by activation of these contacts 23-3, 23-4, 30-3 and 30-4.

In the above-mentioned malfunction indicator in the conventional art, the reset-relay 64 for resetting automatically the malfunction indicator is activated by turning the transistors 55 and 56 to ON when the Zener voltage of the Zener diode 54 exceeds a charged voltage level of the capacitor 50. As shown in FIG.5(a), the terminal voltage of the capacitor 50 rises gradually corresponding to charge of the capacitor 50, and when the terminal voltage of the capacitor 50 exceeds the Zener 8 1 1 1 1 voltage of the Zener diode 54, as shown in FIG.5(b), a base current of the transistor 55 flows through the Zener diode 54. The electric charge of the capacitor 50 is discharged through the Zener diode 54 and the transistors 55 and 56, and the voltage falls rapidly. Consequently, a collector current of the transistor 56 flows during an infinitesimal time period as shown in FIG.5(b). Accordingly, the reset relay 64 connected between the collector of the transistor 56 and the positive terminal P is activated during the infinitesimal time period, and the contact thereof is closed or opened during the infinitesimal time period. On the other hand in order to surely reset the indicator, an electrifying time period of the activating current which is applied to the reset windings 21R and 22R of the latch relays 23 and 30 must be maintained over a predetermined time period. Therefore, in case that the activated time period of the reset relay 64 is infinitesimal as mentioned above, and it is feared that the indicator can not be surely reset. In order to avoid the failure of the reset, an indicator having especially high response speed must be employed. OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a malfunction indicator for electric utility lines which can be surely reset after restoration of malfunction.

The malfunction indicator for electric utility 9 lines in accordance with the present invention comprises:

at least one current transformer for detecting a current of an electric line.

a zero-phase current transformer for detecting ground fault of the electric lines, malfunction indicating means for indicating an abnormal state of the electric utility lines after a predetermined time period from detection of an abnormal current value by one of the current transformer and the zero-phase current transformer, reset means for resetting the malfunction indicating means when abnormal current value of neither the current transformer nor the zero-phase current transformer is detected any more, wherein the reset means further comprises reset relay for resetting the malfunction indicating means, transistor switching circuit for activating the reset relay, an integrating circuit having a series connection of a resistor and a capacitor wherein junction point between the resistor and the capacitor is connected to the base of the transistor switching circuit through a Zener diode coupled in reverse direction with respect to a base current of the transistor switching circuit, and contacts of the reset relay are coupled across A r i C_ the cathode and the anode of the Zener diode.

In the present invention, when a voltage of the junction between the resistor and the capacitor exceeds a Zener voltage of the Zener diode. the base current of the transistor for activating a reset relay flows through the Zener diode, and the transistor turns ON, and the reset relay is activated. Then a contact of the reset relay which is connected across the anode and cathode of the Zener diode is closed, and the Zener diode is shortcircuit across the anode and the cathode, and thereafter, the electric charge of the capacitor flows into the base of the transistor via the contact. BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 is a circuitry of a first embodiment of the present invention; FIG.2 is a circuitry showing the relevant parts of a second embodiment of the present invention; FIG.3(a) is a waveform chart showing terminal voltage of a capacitor 50 in FIG.1; FIG.3(b) is a waveform chart showing state of a transistor 55 in FIG.1; FIG.3(c) is a waveform chart showing operation of a reset relay in FIG.1; FIG.4 is the circuitry of the malfunction indicator in the conventional art; FIG.5(a) is a waveform chart showing terminal 11 g voltage of capacitor 50 in FIGA; FIG.5(b) is a waveform chart showing state of the transistor 55 in FIGA; FIG.5(c) is a waveform chart showing operation of the reset relay in FIGA; DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1 is a circuitry of a first embodiment of a malfunction indicator in accordance with the present invention. Referring to FIGA, a short-circuit detecting coil 1 is composed of two windings 1X and 1Y, and the windings 1X and 1Y are connected to current transformers 2X and 2Y which are mounted on two electric utility lines, respectively. Furthermore, a ground fault detecting coil 3 is connected to a zero-phase current transformer 4 which is mounted on three electric utility lines. A normal- open contact 1-1 which is activated by excitation of the shortcircuit detecting coil 1 is coupled in series with a limiting resistor 7 between a positive terminal P-1 of a power source and a voltage dividing resistor 8 which is coupled in series with a resistor 9, and the resistor 9 coupled at the other terminal thereof with the negative terminal N of the power source. In a similar manner, a normal-open contact 3-1 which is activated by excitation of the ground fault dttecting coil 3 is coupled in series with a resistor 14 between the positive terminal P-1 of the power source and a voltage dividing resistor 15 which 12 1 is coupled in series with a resistor 16. The resistor 16 is coupled at the other terminal with the negative terminal N of the power source. A capacitor 10 which functions as a time delay circuit is connected across the voltage dividing resistors 8 and 9 which are connected in series. A Zener diode 11 is coupled at the cathode with the junction of between the voltage dividing resistors 8 and 9, and is coupled at the anode with the base of a transistor 12. An auxiliary relay 13 is connected between the collector of the transistor 12 and the positive terminal P-1, and the emitter thereof is coupled with the negative terminal N. The positive terminal P-1 is connected with a positive terminal P of the power source through a diode 38, and a capacitor 39 is connected across the positive terminal P-1 and the negative terminal N.

A similar circuit described above is composed of a limiting resistor 14, voltage dividing resistors 15 and 16, a capacitor 17, a Zener diode 18, a transistor 19 and a auxiliary relay 20, and coupled across the positive terminal P-1 and the negative terminal N. Flag indicators 21 and 22 of magnetic holding-type are provided with activating windings 21S and 22S and reset windings 21R and 22R, respectively. A latch relay 23 is connected across the activating winding 21S and the negative terminal N, and the normal-open contact 13-1 which is activated by the excitation of the auxiliary relay 13 is coupled at one 13 C_ C_ terminal with the activating winding 21S. The normal-open contact 131 is coupled in series at the other terminal with a normalclose contact 13-2 which is connected in series with a normal-close contact 23-1 which is activated by excitation of the latch relay 23. The normal-close contact 23-1 is connected' to the positive terminal P-2 which is connected to the positive terminal P of the power source through a:limiting resistor 27 and a diode 28.

A latch relay 30 is connected in parallel with the activating winding 22S, and in a similar manner mentioned above, a normal-close contact 30-1 which is activated by the latch relay 30 and is connected in series with a normal-close contact 20-2 which is activated by the auxiliary relay 20 is connected with the positive terminal P-2. A normal-open contact 20-1 which is also activated by the auxiliary relay 20 is connected between the normalclose contact 20-2 and the activating winding 22S. The latch relay 23 comprises a reset winding 23A, and a normal-open contact 23-3 and a normal-close contact 23-4 for controlling external devices are activated by the reset winding 23A. Moreover. a normal-open contact 30-3 and a normal-close contact 30-4 for controlling external devices are activated by the latch relay 30.

14 i A capacitor 34 is connected across the negative terminal N and the Junction between the normal-open contact 20-1 and the normal-close contact 20-2. Diodes 35 and 36 are coupled at the cathode with the reset windings 21R and 22R, respectively, the anodes of both the diodes are connected together with each other, and is connected with the positive terminal P-2 through a normal-open contact 64-1.

The capacitor 39 is charged in normal operation state of the power source and when the power source falls in malfunction, an electric power for activating auxiliary relays 13 and 20 is supplied from the capacitor 39.

The reset windings 23A and 30A are coupled in parallel with a diode 42, and are connected between a capacitor 43 and the negative terminal N. The capacitor 43 is connected at the other terminal with the positive terminal P through a normal-open contact 64-2 of the reset relay 64, and a resistor 52 is coupled across the negative terminal N and the Junction between the capacitor 43 and the normal-open contact 64-2. The reset winding 23A is mounted in the latch relay 23, and the reset winding 30A is mounted in the latch relay 30.

Normal-open contacts 23-2 and 30-2 which are coupled in parallel are activated by the latch relays-23 and 30, respectively, and are coupled at one ends with the C_ c I- positive terminal P-2 and at the other terminal with the anode of a diode 47. The cathode of the diode 47 is coupled with the cathode of a Zener diode 48, and the anode of the Zener diode 48 is connected to one terminal of a charging resistor 49,-and the other terminal thereof is coupled with a resistor 51 and a capacitor 50 which are coupled in parallel. The other terminals of the resistor 51 and the capacitor 50 are connected with the negative terminal N. A capacitor 53 is connected across the positive terminal P-2 and the negative terminal N.

A Zener diode 54 is coupled at the cathode with the junction between the charging resistor 49 and the capacitor 50 and is coupled at the anode with the base of a transistor 55. An integrating circuit for delaying time is composed of the charging resistor 49 and the capacitor 50.

Moreover, a normal-open contact 64-3 of the return relay 64 which is coupled in series with a-limiting resistor 66 is connected across the anode and the cathode of the Zener diode 54.

The transistor 55 is connected with a transistor 56 in Darlington connection and the transistor 56 is coupled at the emitter with the negative terminal N. The collector of the transistor 55 is connected with the positive terminal P of the power source through a resistor 57, and the collector of the transistor 56 is connected 16 1 with the positive terminal P through normal-close contacts 13-3-and 20-3 which are connected in series and the reset relay 64 which are connected in series with the normalclose contact 13-2.

In the above-mentioned malfunction indicator in the preferred embodiment of the present invention, when the detected current of the ground fault detecting winding 3 or the short-circuit detecting windings 1X and 1Y exceed a predetermined value, the normal-open contact 1-1 or the normalopen contact 3-1 is closed, and the capacitor 10 or the capacitor 17 is discharged, respectively.

When a voltage of the junction between the voltage dividing resistors 8 and 9 or a voltage of the junction between the voltage dividing resistors 15 and 16 exceeds a Zener voltage of the Zener diode 11-or the Zener diode 18 by charge in the capacitor 10 or 17, respectively, the transistor 12 or 13 turns ON, and thereby the auxiliary relay 13 or 20 is activated, respectively. Corresponding to operation of the auxiliary relay 13 or 20, the normal-open contact 13-1 or 20-1 and the normal-close contact 13-2 or 20-2 are activated, and electric charge of the capacitor 29 or 34 is discharged to the activating winding 21S or 22S of the indicator 21 or 22 and the latch relay 23 or 30, and the latch relay 23 or 30 is activated, respectively. The normal-close contact 23-1 or 30-1 is opened by activation of the latch relay 23 17 C.

or 30, respectively, and the latch relay 23 or 33 is isolated from the positive terminal P-2. Consequently, electric charge of the capacitor 29 or 34 is discharged into the Indicator 21 or 22 and the latch relay 23 or 33. Moreover, close of the normal-open contact 23-2 of the latch relay 23 or the normal-open contact 30-2 of the latch relay 30 results in discharge an electric charge of the capacitor 53 into the capacitor 50 through the diode 47, Zener diode 48 and the charging resistor 49.

In case that the.electric power is supplied to the malfunction indicator, a current for charging the capacitor 50 is supplied from the positive terminal P through the diode 28 and the resistor 27. However, in case that the electric power is not supplied from the electric power source, the electric charge of the capacitor 53 is supplied to charge the capacitor 50. When the voltage of the capacitor 50 exceeds the Zener voltage of the Zener diode 54, a base current of the transistor 55 flows through the Zener diode 54, and the transistors 55 and 56 which is connected in Darlington connection turn ON. Consequently, the reset relay 64 is activated under impression of the power source.

In the above-mentioned state, if the electric utility line is under malfunction continuously, since the 'normal-close contact 13-3 or 20-3 of the auxiliary relay 13 or 20 is opened, the reset relay 64 is not activated.

18 1 1 1 When the malfunction is restored and the normal-close contacts 13-3 and 20-3 of the auxiliary relays 13 and 20 are closed, the reset relay 64 is activated and the normal-open contacts 64-1 and 64-2 are closed. Consequently, the reset windings 21R and 22R. the reset windings 23A and 30A of the latch relays 23 and 30 are activated, respectively, and thereby the respective displays and the contacts are reset to initial state.

Transmission of control signals for external apparatus is accomplished by close of the contacts 23-3 and 30-3 or open of the contacts 23-4 and 30-4. In a monitoring room for monitoring the electric utility line, condition of the various electric utility lines monitored or controlled by activation of these contacts 23-3, 23-4, 30-3 and 30-4.

Furthermore, since the normal-open contact 64-3 of the return relay.64 is closed, the junction between the resistor 49 and the capacitor 50 is directory connected to the base of the transistor 55 through the resistor 66. Consequently, even if the voltage of the capacitor 50 is lowered under the Zener voltage of the Zener diode 54 by discharge of the electric charge of the capacitor 50 into the base of the transistor 55, the base current is not intercepted by the Zener diode 54. All of the electric charge of the capacitor 50 flows into the base of the transistor 55, and thereby the transistor 55 remains ON.

19 The operation described above is shown in FIG.3(b). As a result. an activating time period of the relay 64 is prolonged as shown in FIG.3(c).

FIG.2 is a circuitry of relevant parts showing feature of a second embodiment of the present invention. In FIG.2, the relevant parts including the reset relay 64, the transistors 55 and 56, the Zener diode 54 and the capacitors 50 are shown. Other parts of the circuitry is identical with that of the first embodiment.

In the second embodiment, a combination of a thyristor 67 and a Zener diode 54 is used that the thyristor 67 is coupled at the cathode thereof with the base of the transistor 55, and is coupled at the anode with the junction between the resistor 49 and the capacitor 50. A Zener diode 54 is coupled at the anode thereof with the gate of the thyristor 67, and is coupled at the cathode with the anode of the thyristor 67.

Operation of the second embodiment shown in FIG.2 is elucidated hereinafter. When a Zener voltage of the Zener diode 54 exceeds a charged voltage of the capacitor 50, a current flows Into the gate of the thyristor 67 through the Zener diode 54, and the thyristor 67 turns ON. Then, the electric charge of the capacitor 50 flows into the base of the transistor 55 through the thyristor 67, and the transistors 55 and 56 turn ON. Conductive state of the transistors 55 and 56 is i S C.

maintained until the current from the capacitor 55 ceases when the voltage of the capacitor 55 Is almost consumed by the discharge. According to the second embodiment, since the electric charge of the capacitor 50 flows Into the base of the transistor 55 through the thyristor 67, the transistors 55 and 56 maintain conductive state even when the voltage of the capacitor 50 becomes lower than the Zener voltage of the Zener diode 54.

According to the present invention, an indicating device having relatively slow response speed is usable in the malfunction indicator, and thereby expense of the apparatus is reduced.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

21 C_

Claims

WHAT IS CLAIMED IS

1. A malfunction indicator for electric utility lines comprising: at least one current transformer for detecting a current of an electric line, a zero-phase current transformer for detecting ground fault of said electric lines, malfunction indicating means for indicating an abnormal state of the electric utility lines after a predetermined time period from detection of an abnormal current value by one of said current transformer and said zero-phase current transformer, reset means for reset said malfunction indicating means when detection of said abnormal current value of both the current transformer and the zero-phase current transformer is eliminated, wherein said reset means further comprises a reset relay for resetting said malfunction indicating means, a transistor switching said reset relay, an integrating circuit having a seriesconnection of a resistor and a capacitor connected to the base of said transistor switching circuit through a Zener diode coupled in reverse direction with respect to a base current of said transistor switching circuit, and circuit for activating 22 -1 K.

i.

b.

a contact to be activated by said reset relay coupled across the'cathode and the anode of said Zener diode.

2. A malfunction indicator for electric utility lines comprising:

at least one current transformer for detecting a current of an electric line, a zero-phase current transformer for detecting ground fault of said electric lines, a malfunction indicating means for indicating an abnormal state of the electric utility lines after a predetermined time period from detection of an abnormal current value by one of said current transformer and said zero-phase current transformer, reset means for reset said malfunction indicating means when detection of said abnormal current value of both the current transformer and the zero- phase current transformer is eliminated, wherein said reset means further comprises reset relay for resetting said malfunction indicating means, transistor switching said reset relay, an integrating circuit having a series connection of resistor and a capacitor wherein junction point between the resistor and the capacitor is to be circuit for activating 23 connected to the base of said transistor switching circuit through. a thyristor coupled in forward direction with respect to the base of said transistor switching circuit, and a Zener diode coupled in reverse direction with respect to the gate of the thyristor between the gate and the anode of said thyristor.

3. An indicator for indicating the presence of a predetermined state, comprising a reset relay for resetting the indicator after termination of the predetermined state and a circuit for activating the reset relay in accordance with the state of a control input of the circuit, the said control input being connected to an input signal source through a voltage offset means such that an input signal to control the said circuit to activate the reset relay is provided to the control input when the voltage between the input signal source and the control input exceeds the offset.voltage of the voltage offset means, in which following supply of an input signal from the input signal source through the voltage offset means to the control input to cause the circuit to activate the reset relay, the control input is c a - 25 connected to the input signal source such that the control input continues to receive the input signal from the input signal source when the voltage between the input signal source and the control input ceases to exceed the offset voltage of the offset voltage means.

4. An indicator according to claim 3, in which the input signal source is a junction between a resistor and a capacitor of an integrating circuit.

5. An indicator according to any one of claims 3 to 5, in which in the said continuation of the reception of the input signal by the control input, the control input receives the input signal via bypass means which bypass the voltage offset means.

6. An indicator according to claim 5, in which the bypass means comprises a switch activated by the reset relay.

7. An indicator according to claim 5, in which the bypass means comprises a thyristor.

C C i

8. An indicator according to any one of claims 3 to 7, in which the voltage offset means comprises a Zener diode.

1 1

9. An indicator-'substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.

1 Published 1989 atThe Patent Office, State House, 66"71 High Holt orn, London WClR 4TP. Further copies maybe obtainedfrom The Patent Office. Sales Branch. St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques It4d, St Mary Cray, Kent, Con. 1/87