IE930319A1 - Circuit for detecting a faulty mains neutral - Google Patents
Circuit for detecting a faulty mains neutralInfo
- Publication number
- IE930319A1 IE930319A1 IE930319A IE930319A IE930319A1 IE 930319 A1 IE930319 A1 IE 930319A1 IE 930319 A IE930319 A IE 930319A IE 930319 A IE930319 A IE 930319A IE 930319 A1 IE930319 A1 IE 930319A1
- Authority
- IE
- Ireland
- Prior art keywords
- circuit
- neutral
- earth
- mains
- current
- Prior art date
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
-
- 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
- H02H3/334—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 with means to produce an artificial unbalance for other protection or monitoring reasons or remote control
- H02H3/335—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 with means to produce an artificial unbalance for other protection or monitoring reasons or remote control the main function being self testing of the device
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Emergency Protection Circuit Devices (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
Abstract
A circuit for detecting a faulty mains neutral comprises a current transformer 10 having a primary winding T2 and a secondary winding T1. The mains live L is connected via an impedance Z1 to a first circuit branch 1 connected to mains earth E via the primary winding T2 and to a second circuit branch 2 connected to mains neutral N avoiding the primary winding T2. The total impedance in the second circuit branch 2 is less than the total impedance in the first circuit branch 1, such that when earth and neutral are at the same potential the current from mains live flows preferentially to neutral. The circuit further includes means 12 for detecting a current induced into the secondary winding T1. The circuit is also responsive to earth leakage current, and missing earth and live-neutral reversal through the provision of resistive connections A, B.
Description
CIRCUIT FOR DETECTING A FAULTY MAINS NEUTRAL
This invention relates to a circuit for detecting a missing neutral or other faulty conditions of the mains.
A missing neutral detection circuit is described in our UK patent application number 8908385, which gives the general background to the present invention.
According to the invention there is provided a circuit for detecting a faulty mains neutral comprising a current transformer having a primary winding and a secondary winding, the mains live being connected through an impedance to first and second circuit branches of which the first circuit branch is connected to one of mains earth and neutral via the primary winding and the second circuit branch is connected to the other of mains earth and neutral avoiding the primary winding, the impedance in the circuit branch connected to neutral being less than the impedance in the circuit branch connected to earth such that when earth and neutral are at the same potential the current from mains live flows preferentially to neutral, the circuit further including means for detecting a current induced into the secondary winding.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a circuit diagram of a first embodiment of the invention, met (/θ!a ί ^flllTIM·----.. . .. Ϊ
I OPEN TO PUBLIC INSPECTION j LNDER
I SECTION 23 AND RULE 23 /jM......
JNL. No
^930319
Figure 2 is a circuit diagram of a second embodiment of the invention, and
Figure 3 is a circuit diagram of a third embodiment of the invention,
In figure 1 the faulty neutral detection circuit comprises a current transformer 10 having a primary winding T2 and a secondary winding Tl. The mains live L is connected through an impedance Z1 to first and second circuit branches 1 and 2 respectively, the first circuit branch 1 being connected to mains earth E via the primary winding T2 and a further impedance Z2 and the second circuit branch 2 being connected to mains neutral N avoiding the primary winding (the diodes DI and D2 will be described later). The total impedance in the second circuit branch 2, consisting essentially only of the impedance of the diode DI, is low compared to the total impedance in the first circuit branch 1, consisting essentially of sum of the impedance Z2, the impedance of the winding T2 and the impedance of the diode D2.
The circuit operates on the principle that under normal mains supply conditions earth E and neutral N will be at approximately the same potential with respect to each other, so that the current IL from mains live L will flow preferentially to neutral N via the low impedance second circuit branch 2, with minimal current flowing through the first circuit branch 1 to earth E, and hence through the primary winding T2, due to the higher total impedance in this branch. However, under missing neutral conditions IL will be diverted to earth E via the winding T2 and impedance Z2. This earth current flowing in the primary winding T2 will induce a current in the secondary winding Tl. The resultant output current from the winding Tl can be fed to a »030319 detection circuit 12. The detection circuit may compare the induced current to a threshold level and when the magnitude of the induced current exceeds the threshold level an alarm may be raised and/or a relay used to disconnect the mains from an appliance, as for example in a residual current device. Alternatively, it may be sufficient in some applications just to monitor the output of the transformer secondary Tl.
The detector circuit 12 could also be used to detect out of balance currents flowing in load-carrying live and neutral conductors 14 and 16 respectively. This is achieved by passing the conductors through the toroidal core 18 of the current transformer 10. Under normal conditions, the current flowing in the load-carrying conductors will be balanced, and therefore the vector sum of the currents induced into the secondary winding Tl by the live and neutral conductors 14 and 16 will be substantially zero. However, if there is an earth fault condition, some current will flow to earth, and the vector sum of the currents induced into the secondary winding Tl by the live and neutral conductors will become greater than zero. This induced current in the winding Tl can be detected by the detection circuit 12.
The impedance Zl could comprise the detection circuit 12, as shown in figure 2. Under normal conditions the supply current IL will flow via live L and neutral N, and when the neutral is disconnected, the supply current will flow between live L and earth E. In either case the detection circuit is powered by the current IL. The resultant current induced into the secondary winding Tl in the case of a missing neutral or earth fault can be detected by the circuit 12, thereby facilitating detection of these conditions.
-030319
It is not essential that neutral be disconnected in order to activate the detection circuit 12. If for example a sufficiently large impedance existed in the neutral line or between earth and neutral, the supply current IL could preferentially flow from live to earth, thereby activating the detecting circuit. In this way, it can be seen that the circuit will be responsive to abnormal neutral conditions in addition to a loss of neutral, such as a high impedance neutral or a high voltage neutral.
The impedance Z2 could comprise a resistance, a semiconductor device such as a diode or zener diode, a voltage dependent device such as a varistor, or an inductor, or other electronic device. Its function is simply to encourage most of the supply current IL to flow between live and neutral under normal supply conditions.
The diodes DI and D2 may be included in the circuit to ensure that a low impedance path is not inadvertently provided between earth and neutral via impedance Z2 if this latter impedance is of a low value. The diodes would thereby provide protection against a reverse live-neutral condition by preventing current flow from the high voltage neutral terminal to earth which could possibly damage Z2.
From the foregoing it is clear that the circuit may be considered a current diverting and detecting circuit, in that under abnormal supply conditions such as loss of neutral, the current flowing from live is diverted to earth specifically to facilitate its detection. There is no interruption in current flow, nor is there any increase, but there will be some reduction in current flow due to the impedance Z2.
»30319
As a variation on the above embodiments, it is possible to have the impedance Z2 include the detection circuit 12 rather than the impedance Zl. In this case the detection circuit would only be powered when the supply current is flowing to earth, but this is the condition one wants to detect so it is satisfactory. However, one could not detect an earth current fault in this way.
Figure 3 shows a further development of the circuit of figure 1, adapted to detect missing earth and reverse live-neutral conditions. As compared to figure 1, figure 3 has a first resistor A connected across the diode DI and a second diode B connected across Zl, T2 and D2. As before, when earth and neutral are at the same potential there will be minimal current flow through the winding T2 due to the much lower impedance through A and DI in parallel, and when neutral is missing current will be diverted through T2. In both cases there will be a current through B and Z2, but this always bypasses the winding T2 so it does not affect the detection of the missing neutral.
However, in the case of a missing earth there will be a current flow, on negative half cycles of the L, from live L through resistor B, diode D2, winding T2 and resistor A to neutral N, which will induce a current in the winding Tl for detection by the circuit 12. In the case of a reverse live-neutral, there will be a current flow through resistor A, winding T2, diode D2 and impedance Z2 to earth E, likewise inducing a current in the winding Tl. Thus the additional resistors A and B permit detection of missing earth and reverse live-neutral.
«30319
The circuit of figure 3 also includes an indicator 20 in the form of a neon lamp connected across earth E and neutral N. Under normal conditions, the earth and neutral are at the same potential, and the neon lamp will not be lit.
However, if the earth or neutral is disconnected, or the live and neutral are reverse wired, a voltage will appear across the neon lamp 20 causing it to be lit. On the other hand, if the mains is correctly wired but an earth fault current flows in the load, the neon lamp 20 will not be lit. Therefore, the neon lamp 20 indicates mains wiring fault conditions as distinct from earth fault current conditions. Instead of a neon lamp the indicator 20 can be any device which can be activated in the case of a mains wiring fault, such as an LED, a buzzer, or a relay.
Claims (6)
1. A circuit for detecting a faulty mains neutral comprising a current transformer having a primary 5 winding and a secondary winding, the mains live being connected through an impedance to first and second circuit branches of which the first circuit branch is connected to one of mains earth and neutral via the primary winding and the second circuit branch is 10 connected to the other of mains earth and neutral avoiding the primary winding, the impedance in the circuit branch connected to neutral being less than the impedance in the circuit branch connected to earth such that when earth and neutral are at the same potential 15 the current from mains live flows preferentially to neutral, the circuit further including means for detecting a current induced into the secondary winding.
2. A circuit as claimed in claim 1, wherein the first 20 circuit branch is connected to earth.
3. A circuit as claimed in claim 1 or 2, wherein live and neutral conductors for a load are also inductively coupled to the transformer such that in the absence of 25 an earth current fault the vector sum of the currents induced into the secondary winding by the live and neutral conductors is substantially zero.
4. A circuit as claimed in claim 1, 2 or 3, wherein the 30 firstmentioned impedance includes the detecting circuit.
5. A circuit as claimed in any preceding claim, further including respective diodes in the first and second circuit branches. fc 93 0 3 '
6. A circuit for detecting a faulty mains neutral, substantially as described herein with reference to the accompanying drawings.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IE930319A IE930319A1 (en) | 1993-04-27 | 1993-04-27 | Circuit for detecting a faulty mains neutral |
| GB9404435A GB2277646B (en) | 1993-04-27 | 1994-03-08 | Circuit for detecting a faulty mains neutral |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IE930319A IE930319A1 (en) | 1993-04-27 | 1993-04-27 | Circuit for detecting a faulty mains neutral |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| IE930319A1 true IE930319A1 (en) | 1994-11-02 |
Family
ID=11039951
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| IE930319A IE930319A1 (en) | 1993-04-27 | 1993-04-27 | Circuit for detecting a faulty mains neutral |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB2277646B (en) |
| IE (1) | IE930319A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2992449B2 (en) * | 1994-11-15 | 1999-12-20 | 松下電工株式会社 | Circuit breaker |
| CN104426128B (en) * | 2013-09-05 | 2018-01-19 | 西门子公司 | Broken neutral line detects circuit and corresponding residual current circuit breaker |
| CN203983940U (en) * | 2014-05-04 | 2014-12-03 | 西门子公司 | Earth leakage protective device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4598331A (en) * | 1984-07-30 | 1986-07-01 | Technology Research Corporation | Ground fault current interrupter circuit with open neutral and ground lead protection |
| GB2178916B (en) * | 1985-06-22 | 1989-09-06 | Ashley Accessories Ltd | Detecting abnormal neutral line conditions in electrical circuits |
| GB2244398B (en) * | 1990-05-25 | 1994-03-16 | Mk Electric Ltd | Electrical protection devices |
-
1993
- 1993-04-27 IE IE930319A patent/IE930319A1/en not_active Application Discontinuation
-
1994
- 1994-03-08 GB GB9404435A patent/GB2277646B/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| GB2277646B (en) | 1997-04-09 |
| GB2277646A (en) | 1994-11-02 |
| GB9404435D0 (en) | 1994-04-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FJ9A | Application deemed to be withdrawn section 31(3) |