GB2072443A - An earth fault detector - Google Patents
An earth fault detector Download PDFInfo
- Publication number
- GB2072443A GB2072443A GB8105638A GB8105638A GB2072443A GB 2072443 A GB2072443 A GB 2072443A GB 8105638 A GB8105638 A GB 8105638A GB 8105638 A GB8105638 A GB 8105638A GB 2072443 A GB2072443 A GB 2072443A
- Authority
- GB
- United Kingdom
- Prior art keywords
- earth
- earth fault
- detector
- fault detector
- resistance
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/32—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
- H02H3/33—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers
- H02H3/338—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers also responsive to wiring error, e.g. loss of neutral, break
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
- G01R27/18—Measuring resistance to earth, i.e. line to ground
Abstract
A resistance detection module 7 is provided for measuring the resistance of the loop formed between the earth 9 and a pilot conductor 8 in an electrical supply through an earth leakage circuit breaker 2 to give protection in the event of incorrect connection of the breaker and/or the existence of an imperfect earth connection on the apparatus being supplied. The module 7 operates relay contacts 10 when the current in the earth/pilot loop reaches a certain threshold value due to an increase in resistance in the loop. Operation of the contacts 10 simulates an earth fault to open the circuit breaker 2. <IMAGE>
Description
SPECIFICATION
An earth fault detector
The present invention relates to an earth fault detector.
In industry it is frequently necessary to use heavy portable electrical equipment which is supplied with electrical power via a plug and socket arrangement. To protect the equipment and the personnel, it is normal to earth any bare metal on the apparatus and to protect the apparatus from over-loads and short circuiting with some form of automatic interrupter.
However, should the earth connection to the apparatus become disconnected or otherwise become a high resistance, it is possible that an earth fault in the apparatus could result in bare metal attaining a dangerously high voltage. It is common practice to offer a degree of protection should any person touch such "live" metal by utilising an earth leakage circuit breaker (E.L.C.B.), which is a commonly used piece of electrical switchgear.
According to the present invention, there is provided an earth fault detector for determining the existence of an earth fault in electrical equipment comprising an earth leakage circuit breaker adapted to be connected in the electrical supply to the equipment, a pilot conductor means for detecting the resistance of the loop formed with the earth and pilot conductor and means responsive to the resistance detection means for tripping the circuit breaker in the event the resistance is above a certain predetermined value.
An E.L.C.B. is therefor utilised to offer a degree of protection should anybody touch a "live" conductor, and in addition the correct earth connection of the apparatus is monitored. Should the earth not be correctly connected power is automatically disconnected from the apparatus by the E.L.C.B.
In order that the invention may be more clearly understood, two embodiments thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a circuit diagram of an earth fault detector for a three phase system,
Figure 2 shows a circuit diagram of an earth fault detector for a single phase system, and
Figure 3 shows a detailed circuit diagram of a part of the arrangements shown in Figs. 1 and 2.
Referring to Fig. 1, an earth fault detector is shown for a three phase three wire system.
The red, yellow and blue phases are respectively referenced R, Y and B.
An earth conductor is shown referenced E and a pilot conductor is provided ending in a terminal 8. The three phases and the pilot conductor are connected to an earth leakage circuit breaker (E.L.C.B.) 2. The supply to the detector is therefore through this circuit breaker and is turned off when the circuit breaker is tripped. A miniature circuit breaker 3 is connected to the three phases R,Y and B and acts as a normal ON/OFF switch to protect the outgoing supply from overload and short circuit. The input terminals to the detector are referenced 1 and the output terminals from the detector are referenced 4.
A resistance detection module 7 is provided with a low voltage supply via an auxiliary supply transformer 5 fed from the red and yellow phases via fuses 6. This module 7 incorporates contacts 10 and a test resistance 1 5. The test resistance forms with a test operating switch 14 disposed in series with the pilot conductor connected to the terminal 8 a test circuit. An indicator lamp 11 is connected to an output of the resistance detection module 7.
Referring more particularly to Fig. 3, the transformer 5 comprises two secondary windings 50 and 51. The output from the secondary winding 50 is fed through a full wave bridge rectifier 49 and supplies circuitry comprising an operational amplifier 53 whose output controls, via a base resistor 48, a PNP transistor 47. The coil 55 of a relay RY is disposed in the selector circuit of the transistor 47 and a light emitting diode 46 is connected to this relay coil 55. Winding 51 is connected to terminal 50 via a limiting resistor 52. Terminal 50 is the pilot wire connection through which current circulates around the pilot/earth loop supplied by winding 51.
A push-button switch 1 2 and indicator lamp 1 3 are provided to enable the supply of power through the detector to be checked.
The operation of the detector is as follows.
Power is fed to the detector through the terminals 1 and thence on to the piece of electrical equipment being supplied through the terminals 4. In a correctly functioning installation, the resistance between the pilot terminal 8 and the earth terminal 9 will be sufficiently low and the contacts 10 of the relay RY will be open. This will be indicated by the illumination of the indicator lamp 11.
The existence of the supply at the terminals 4 is checked by the iliumination of lamp 1 3.
The circuit to this lamp is closed by switch 1 2 which is automatically closed when breaker 3 is closed. Of course under these conditions the earth leakage circuit breaker 2 is closed as well as the miniature circuit breaker 3.
Should the resistance between the pilot terminal 8 and the earth terminal 9 rise to a sufficiently high value to operate the module 7 by switching on the transistor 47 to energise the coil 55 of the relay RY, the contacts 10 of the relay RY will close and a simulated earth fault will be applied to the earth leakage circuit breaker 2. The circuit breaker 2 will then trip out to disconnect the supply. The supply cannot be reconnected until the resis tance is sufficiently low. The module 7 may be tested by opening the normally closed switch 1 4 to insert the resistance 1 5 in series with the pilot conductor thus simuiating a high resistance in the pilot/earth loop. In the module 7, the current threshold in the pilot/ earth loop at which the amplifier 53 acts to switch on the transistor 47 to energise the relay coil 55 may be varied by means of the variable resistance 54.
Fig. 2 iilustrates a detector very similar to that illustrated in Fig. 1 but for a single phase system. Corresponding parts of this system to the system of Fig. 1 have been given the same reference numerals. The live and neutral of the single phase have been referenced L1 and N respectively. A four wire adaptation of this system is indicated in dotted line with the other two conductors being referenced L2 and
L3 respectively.
It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention.
Claims (14)
1. An earth fault detector for determining the existence of an earth fault in electrical equipment comprising an earth leakage circuit breaker adapted to be connected in the electrical supply to the equipment, a pilot conductor, means for detecting the resistance of the loop formed with the earth and pilot conductor and means responsive to the resistance detection means for tripping the circuit breaker in the event the resistance is above a certain predetermined value.
2. An earth fault detector as claimed in
Claim 1, in which the resistance detection means comprises a detector for detecting the current flowing in the pilot/earth loop and producing an output signal in dependence thereon, switch means responsive to the output from the amplifier and relay means responsive to the switch means for applying a simulated earth fault signal to the earth leakage circuit breaker when the detected current flowing is above a certain threshold valve.
3. An earth fault detector as claimed in
Claim 2, in which the current detector comprises an amplifier.
4. An earth fault detector as claimed in
Claim 3, in which a variable resistor is connected to the amplifier input for varying the current threshold at which the amplifier acts to operate the switch means
5. An earth fault detector as claimed in
Claims 2, 3 or 4, in which the switch means comprises a transistor.
6. An earth fault detector as claimed in
Claim 5, in which the transistor has its base connected to the output of the current detector and its collector to the coil of the relay means.
7. An earth fault detector as claimed in any of Claims 2 to 5, in which the contacts of the relay means are connected in a circuit for tripping the earth leakage circuit breaker.
8. An earth fault detector as claimed in any preceding Claim, in which the resistance detection means comprises a test circuit comprising a test resistance and a normally closed test operating switch connected in series with the pilot conductor and in parallel with the test resistance, such that on operating the switch the test resistance may be inserted into the earth/pilot loop to simulate a fault to test operation of the resistance detection means.
9. An earth fault detector as claimed in any preceding Claim, in which indicator means are provided connected to the resistance detector means to indicate the existence of a fault/no fault condition.
10. An earth fault detector as claimed in
Claim 9, in which the indicator means comprises a lamp.
11. An earth fault detector as claimed in any preceding Claim, in which a power or indicator circuit comprises a switch and a lamp adapted to be fed from the detector supply, the switch being closed when the earth leakage circuit breaker is closed.
1 2. An earth fault detector as claimed in any of Claims 2 to 7 or in any of Claims 8 to 11 when appendant directly or indirectly to
Claim 2, in which indicator means are provided for indicating energisation of the relay means.
1 3. An earth fault detector as claimed in
Claim 12, in which the indicator means comprises a light emitting diode connected in parallel with the coil of the relay means.
14. An earth fault detector substantially as hereinbefore described with reference to Figs.
1 and 2 or to Figs. 2 and 3 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8105638A GB2072443A (en) | 1980-02-23 | 1981-02-23 | An earth fault detector |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8006192 | 1980-02-23 | ||
| GB8105638A GB2072443A (en) | 1980-02-23 | 1981-02-23 | An earth fault detector |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2072443A true GB2072443A (en) | 1981-09-30 |
Family
ID=26274598
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8105638A Withdrawn GB2072443A (en) | 1980-02-23 | 1981-02-23 | An earth fault detector |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2072443A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2128047A (en) * | 1982-10-05 | 1984-04-18 | Northern Eng Ind | Earth leakage monitor and earth proving apparatus |
| FR2669159A1 (en) * | 1990-11-09 | 1992-05-15 | Barthelemy Louis | SECURITY DEVICE PROCESSING INFORMATION, GIVEN BY THE CONTACT POTENTIAL, ASSOCIATED WITH A SWITCHING OFFICE. |
| WO1995006349A1 (en) * | 1993-08-24 | 1995-03-02 | Metal Manufactures Limited | Load control module |
| CN108483163A (en) * | 2018-04-25 | 2018-09-04 | 广东省特种设备检测研究院珠海检测院 | A kind of elevator door lock safety return circuit earth fault demo system |
-
1981
- 1981-02-23 GB GB8105638A patent/GB2072443A/en not_active Withdrawn
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2128047A (en) * | 1982-10-05 | 1984-04-18 | Northern Eng Ind | Earth leakage monitor and earth proving apparatus |
| FR2669159A1 (en) * | 1990-11-09 | 1992-05-15 | Barthelemy Louis | SECURITY DEVICE PROCESSING INFORMATION, GIVEN BY THE CONTACT POTENTIAL, ASSOCIATED WITH A SWITCHING OFFICE. |
| WO1992009129A1 (en) * | 1990-11-09 | 1992-05-29 | Louis Barthelemy | Device for processing data provided by the contact potential, and cutoff device linked thereto |
| WO1995006349A1 (en) * | 1993-08-24 | 1995-03-02 | Metal Manufactures Limited | Load control module |
| US5721657A (en) * | 1993-08-24 | 1998-02-24 | Metal Manufactures Limited | Load control module |
| CN108483163A (en) * | 2018-04-25 | 2018-09-04 | 广东省特种设备检测研究院珠海检测院 | A kind of elevator door lock safety return circuit earth fault demo system |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |