GB2036476A - Improvements in or Relating to Earth Leakage Circuit Breakers - Google Patents
Improvements in or Relating to Earth Leakage Circuit Breakers Download PDFInfo
- Publication number
- GB2036476A GB2036476A GB7847616A GB7847616A GB2036476A GB 2036476 A GB2036476 A GB 2036476A GB 7847616 A GB7847616 A GB 7847616A GB 7847616 A GB7847616 A GB 7847616A GB 2036476 A GB2036476 A GB 2036476A
- Authority
- GB
- United Kingdom
- Prior art keywords
- earth leakage
- earth
- circuit breaker
- potential difference
- current
- 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.)
- Granted
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
-
- 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
- H02H3/16—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 fault current to earth, frame or mass
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Emergency Protection Circuit Devices (AREA)
- Breakers (AREA)
Abstract
A device for increasing the sensitivity of an earth leakage circuit breaker comprising a resistor R1 connected in the earth lead to detect earth leakage current. The potential difference which occurs across the resistor in the event of an earth leakage is amplified by an amplifier A and used to close a switch 6. When switch 6 is closed the live lead is connected through a resistor R2 to the earth lead, thus causing current to flow from the live lead into the earth lead and hence through the coil 2 of the circuit breaker to cause positive operation of the circuit breaker. Resistor R1 may be replaced by the coil 2 or by a current transformer embracing the live and neutral leads. <IMAGE>
Description
SPECIFICATION
Improvements In or Relating to Earth Leakage
Circuit Breakers
This invention relates to earth leakage circuit breakers.
Earth leakage circuit breakers are placed in single and multi-phase power supply leads in order to detect the occurrence of faults leading to current flow in the earth lead. Conventional earth leakage circuit breakers generally comprise an electromagnetic relay coil which may be situated in the earth lead and arranged such that any earth current which flows will flow through the coil. The relay contacts are each arranged in a respective live and neutral lead to thereby cut off the supply should the current flowing in the relay coil rise to a sufficient magnitude to trip the relay. In an alternative arrangement, a current transformer enclosing the live and neutral leads senses the occurrence of a fault by a difference in current flow as between the two leads, and energises the relay coil to cut off the supply.
Existing earth leakage circuit breakers require a relatively large leakage current to trip and the present invention seeks to overcome this disadvantage by providing a device which is operable to increase the sensitivity of the conventional earth leakage circuit breakers.
According to the invention there is provided a device for increasing the sensitivity of an earth leakage circuit breaker, said device comprising means for detecting leakage current flow in an electrical power supply system, and switch means operable to connect an impedance element between one of the power leads of the supply and the earth lead when the detecting means detects an earth leakage current above a predetermined level, said impedance element being such as to cause sufficient current to flow in the earth lead to operate the earth leakage circuit breaker.
The leakage current detecting means may comprise a resistance element in the earth lead.
The potential difference which appears across the element as a result of earth leakage current flow may be used to operate said switch means.
Alternatively, the detecting means may comprise all or part of the electromagnetic relay coil of the earth leakage circuit breaker itself. In either case, the potential difference which arises as a result of earth leakage current flow is preferably amplified before being used to operate the switch means.
By such an arrangement trip sensitivities for the earth leakage circuit breaker in the order of milliamperes and microamperes can be achieved.
In an alternative embodiment, the leakage current detecting means comprises a current transformer enclosing the live and neutral leads and operable to detect a difference in current flow as between the two leads, which indicates leakage of current to the earth lead. The output of the transformer is amplified and used to operate said switch means.
The switch means may be of the mechanical or electronic type and is operable to connect an impedance element from the live lead to earth in order to artificially increase the earth leakage current to a level sufficient to ensure positive operation of the earth leakage circuit breaker.
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 circuit diagram of one embodiment of a device according to the present invention, showing also the earth leakage circuit breaker with which it is associated; and
Figures 2 and 3 are circuit diagrams similar to
Figure 1, but showing further embodiments of the invention.
In the drawings the device according to the invention for improving the sensitivity of earth leakage circuit breakers is shown under the reference 1. In all the illustrated embodiments, the circuit breaker itself is of the type comprising an electromagnetic relay coil 2 and two normally closed relay contacts 3 and 4. The relay coil 2 is connected in the earth line between the power supply source (i.e. the a.c. mains) and the load, which latter may be a single appliance or a complete industrial or domestic premises. The contacts 3 and 4 are connected in the live and neutral leads respectively and operate, in conjunction with the relay coil 2 to cut off the supply of power to the load.Such cut-off of power occurs when, as a result of a fault or other malfunction on the load side of the circuit breaker, leakage current from the live or neutral leads, or both, is caused to flow in the earth line, and hence through the coil 2, thus tripping the relay. The type of earth leakage circuit breaker shown requires a relatively high leakage current to flow before it will trip, and its safety function is thus impaired.
Referring to Figure 1 , the device 1 comprises an impedance element in the form of a resistor R1 connected in series with the relay coil 2. The ends of the resistor are connected to the input of an amplifier A so that the potential difference across the resistor may be amplified. The output of amplifier A is passed to a rectifier and relay unit 5 which contains a normally-open mechanical or electronic switch 6. The switch 6 is connected at one side to the live lead and at the other side is connected, via a resistor R2, to the earth lead. It is to be noted that the connection of resistor R2 to the earth lead is at a point 7 on the load side of the relay coil 2.
In the event of a fault causing an earth leakage current to flow, an a.c. potential difference will appear across resistor RI. This potential difference is amplified in amplifier A and rectified in unit 5. The rectified voltage is then used to close the switch 6, thus connecting the resistor
R2 from the live to the earth leads. The value of resistor R2 is chosen such that, upon closure of switch 6, the magnitude of the current flowing from the live lead to the earth lead, and hence through relay coil 2, is sufficient to cause the circuit breaker to trip, thus opening contacts 3 and 4 and making the load side of the circuit breaker safe. Clearly, resistor R2 can be connected on the "live" side of switch 6 if this is preferred.
Sensitivity can be aitered by changing the amplification of amplifier A; however, it will be seen that the device 1 may ensure positive operation of the contact breaker at earth leakage currents well below those normally required to trip the breaker.
Referring now to Figure 2, the device 1 is modified in that the resistor R1 is replaced by the electromagnetic relay coil 2 of the circuit breaker itself. The ends of the coil 2, or an intermediate tapping, are taken to the input of amplifier A so that any potential difference appearing across the coil 2 by virtue of a flow of earth leakage current is amplified and used to operate the device, as described above.
Referring now to Figure 3, there is shown a current operated earth leakage circuit breaker which is modified by the device of the present invention. In Figure 3, a current transformer 8 which encloses the live and neutral leads is used to sense earth leakage current by detecting any difference in the current flowing as between the live and neutral leads. The sense winding 9 of transformer 8 is connected to the input of amplifier A, and the circuit operates as previously described.
The device herein described may be used in association with voltage or current operated earth leakage circuit breakers, or with electronic circuit breakers. The device may be remote from the circuit breaker, both electrically and physically, or may be attached hereto, possibly forming part of the circuit breaker itself.
Claims (8)
1. A device for increasing the sensitivity of an earth leakage circuit breaker, said device comprising means for detecting leakage current flow in an electrical power supply system, and switch means operable to connect an impedance element between one of the power leads of the supply and the earth lead when the detecting means detects an earth leakage current above a predetermined level, said impedance element being such as to cause sufficient current to flow in the earth lead to operate the earth leakage circuit breaker.
2. A device as claimed in claim 1 wherein said leakage current detecting means comprises a resistance element connected in the earth lead of the supply system to produce a potential difference thereacross as a result of earth leakage current flow, and means for applying such potential difference to said switch means in order to operate the switch means at a predetermined potential difference.
3. A device as claimed in claim 1 wherein said leakage current detecting means comprises the electromagnetic coil of the earth leakage circuit breaker, means for detecting the potential difference which appears across the coil when earth leakage current flows, and means for applying such potential difference to said switch means in order to operate the switch means at a predetermined potential difference.
4. A device as claimed in either one of claims 2 or 3 further comprising amplifier means for amplifying said potential difference before application to the switch means.
5. A device as claimed in claim 1 wherein said leakage current detecting means comprises a current transformer enclosing the live and neutral leads of the supply system and operable to detect a difference in current flow as between the two leads, and means for applying the output of said transformer to said switch means in order to operate the switch means when a predetermined difference of current as between the live and neutral leads is detected.
6. A device as claimed in claim 5 further comprising amplifier means for amplifying the output of said current transformer prior to its application to the switch means.
7. A device for increasing the sensitivity of an earth leakage circuit breaker substantially as hereinbefore described with reference to any one of the accompanying drawings.
8. An earth leakage circuit breaker including a device as claimed in any one of the preceding claims.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7847616A GB2036476B (en) | 1978-12-07 | 1978-12-07 | Earth leakage circuit breakers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7847616A GB2036476B (en) | 1978-12-07 | 1978-12-07 | Earth leakage circuit breakers |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2036476A true GB2036476A (en) | 1980-06-25 |
| GB2036476B GB2036476B (en) | 1982-10-13 |
Family
ID=10501575
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7847616A Expired GB2036476B (en) | 1978-12-07 | 1978-12-07 | Earth leakage circuit breakers |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2036476B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19946098C2 (en) * | 1999-09-27 | 2003-05-22 | Prodex Technologie Gmbh | RCD |
-
1978
- 1978-12-07 GB GB7847616A patent/GB2036476B/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19946098C2 (en) * | 1999-09-27 | 2003-05-22 | Prodex Technologie Gmbh | RCD |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2036476B (en) | 1982-10-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |