IE20010271A1 - Residual Current Device - Google Patents
Residual Current DeviceInfo
- Publication number
- IE20010271A1 IE20010271A1 IE20010271A IE20010271A IE20010271A1 IE 20010271 A1 IE20010271 A1 IE 20010271A1 IE 20010271 A IE20010271 A IE 20010271A IE 20010271 A IE20010271 A IE 20010271A IE 20010271 A1 IE20010271 A1 IE 20010271A1
- Authority
- IE
- Ireland
- Prior art keywords
- neutral
- mains
- solenoid
- winding
- residual current
- Prior art date
Links
- 238000004804 winding Methods 0.000 claims abstract description 54
- 230000007935 neutral effect Effects 0.000 claims abstract description 46
- 239000004020 conductor Substances 0.000 claims abstract description 20
- 238000001514 detection method Methods 0.000 claims abstract description 4
- 238000002070 Raman circular dichroism spectroscopy Methods 0.000 description 23
- 238000010586 diagram Methods 0.000 description 5
- 230000001419 dependent effect Effects 0.000 description 4
- 230000007246 mechanism Effects 0.000 description 4
- 230000004913 activation Effects 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 230000000670 limiting effect Effects 0.000 description 3
- 239000003990 capacitor Substances 0.000 description 2
- 230000003213 activating effect Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
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
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Breakers (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
A residual current device for an A.C. includes a circuit (16) for detecting an earth fault current and contacts (14A,14B) operated by current flowing in a solenoid winding (W1) for disconnecting the mains in response to such detection. The circuit (16) is powered from the mains live (L) and neutral (N) conductors and also has a connection to the earth conductor (E) via a second solenoid winding (W2) to maintain power to the circuit means if there is a loss of neutral. The second solenoid winding is connected between the mains neutral and earth conductors to disconnect the mains in the event of a reverse live-neutral mains connection. <Figure 4>
Description
^^i^KSfi^TURRENT DEVICE
This invention relates to a residual current device(RCD) having a loss of neutral circuit.
RCDs can be of voltage independent (VI) type or voltagedependent (VD) type. VI types depend on the faultcurrent energy to activate a tripping mechanism whereasthe VD types use the mains supply for their sensing andtripping functions. The use of VD type RCDs hasincreased substantially over recent years because ofadvantages of size, performance and cost.
A drawback of VD type RCDs is that on a single phase l mains installation they require the presence of bothlive and neutral supplies for their operation. If aloss of supply neutral occurred it is possible that theRCD maybe disabled. Some manufacturers have addressedthis problem by providing a separate connection fromthe RCD to the system earth. This connection, often..referred.-to as a functional earth. (FE) connection, can-act as an alternative neutral in the event of loss ofsupply neutral.
The provision of a connection to earth will result in•the flow of a current from live to earth within the RCDwhich could cause problems such as nuisance tripping,etc. Manufacturers generally place some form ofImpedance syithin the RCD in mrt-Ji.rnnnpnl-inn circuit to limit such current flow to earth. Theimpedance can be a resistor, capacitor, zener diode, SCR, etc. Whilst all of these circuits and componentsprovide varying degrees of success, they share a commonproblem in that they all require additional space onthe printed circuit board (PCB) where the RCD circuitelements are assembled..
Also, under loss of supply neutral conditions thecurrent limiting effect of the impedance within the RCDearth circuit can substantially reduce, the forcegenerated by the solenoid to enable the RCD to trip.
The reduced efficiency of the solenoid usually resultsin the minimum operating voltage of the RCD under aloss of neutral condition being substantially higherthan that when the neutral is present. Thus the degreeof protection provided by the RCD under a loss ofsupply "neutral condition will be less than that undernormal supply conditions.
In addition to loss of neutral protection, a reversewired live-neutral supply is generally considered to bedangerous and unacceptable. To overcome this problemmanufacturers often provide their RCDs with additionalcircuitry to detect such conditions and bring aboutautomatic tripping of the RCD, thereby alerting theuser to the wiring defect. The additional circuitryrequired for detection of a reverse live-neutral adds further to component cost and space demands which canprove onerous to the RCD manufacturer.
Additional components and circuitry required to performthe various ancillary functions of the RCD such asreverse L-N sensing, etc., add to the cost, complexityand size of the RCD and reduce its overall reliability.In addition, the reduced performance of the RCD under aloss of neutral condition may not be acceptable to theuser.
The purpose of the present invention is to overcome ormitigate some or all of the above problems.
Accordingly, the present invention provides a residualcurrent device for an A.C. mains having live, neutraland earth conductors, the residual current deviceincluding circuit means for detecting an earth faultcurrent and contact means operated by current flowingin a solenoid winding for disconnecting the mains inresponse to the detection of an earth fault current bythe circuit means, wherein the circuit means is poweredfrom the mains live and neutral conductors and furtherhas a connection to the earth conductor via animpedance to maintain power to the circuit means ifthere is a loss of neutral, and wherein the impedancecomprises a further solenoid winding.
Preferably the further solenoid winding is connectedbetween the mains neutral and earth conductors and isoperative to disconnect the mains in the event of areverse live-neutral mains connection.
Most preferably the further solenoid winding isdisposed on the same solenoid body as the firstwinding. In such case the further solenoid windingshares the same coupling mechanism to the contact meansas the first winding.
Embodiments of the invention will now be described, byway of example, with reference to the accompanyingdrawings, in which: t
Fig. 1 is a circuit diagram of a typical prior artvoltage dependent (VD) type RCD with an FE connection;
Figs. 2A and 2B are examples of single and doublewinding solenoids respectively;
Fig. 3 is a circuit diagram of a first embodiment ofthe invention using the double winding solenoid ofFig. 2B; •Fig. 4 is a circuit diagram of a second embodiment ofthe invention, also using the double winding solenoidof Fig. 2B; and
Pig. 5 is a circuit diagram of a third embodiment ofthe invention.
Fig. 1 is a circuit diagram· of a typical prior artvoltage dependent RCD for an A.C. mains supply havinglive L, neutral N and earth E conductors. Such devicesare very well known, and therefore will only bedescribed briefly for the purposes of the presentspecification.
On the load 10 side of the RCD the live and neutralconductors L and N respectively are passed through acurrent transformer CT having a secondary winding 12.Under normal conditions, when relay contacts 14A, 14Bin the live and neutral conductors are closed, thecurrent flowing in the live conductor L from the mainssupply to the load 10 will equal the current returningin the neutral conductor N from the load to the supply.There are, therefore, equal and opposite currentsflowing through the transformer CT so that the currentinduced into the secondary winding 12 is zero.
However, if an earth fault occurs on the load side ofthe RCD there will be some current flow to ground,leading to an imbalance in the currents flowing in thelive and neutral conductors. This induces a non-zerocurrent in the secondary winding 12 which is measuredby electronic circuit 16. If the current induced inthe secondary winding 12 exceeds a pre-determinedthreshold, indicative of an unacceptable level of earth fault current, the circuit 16 will cause a siliconcontrolled rectifier SCR 18 to be triggered (turnedon) .
Power is supplied to the electronic circuit 16 from thelive conductor L via a solenoid SI and full waverectifier bridge Dl—D4 with a return to the neutralconductor N. An FE connection is provided by twoadditional diodes D5 and D6 which form a third arm ofthe bridge and whose junction is connected to earth Evia an impedance Z which can be a resistor, capacitor,zener diode, SCR, etc., as described above. Theelectronic circuit 16 is powered via a dropper resistorR from the positive side of the bridge. The impedance Z limits the standing current flowing to earth bypresenting a higher impedance in that path than that ofthe neutral return path. SCR 18 is connected acrossthe positive and negative sides of the bridge.
As mentioned, if there is a residual current (earthfault current) exceeding a predetermined threshold theelectronic circuit 16 will turn on SCR 18, effectivelysubjecting the solenoid SI to the full supply voltage.
A large current will now flow from live L through therelatively low impedance winding of the solenoid SI,via diodes Dl—D4 and SCR 18, and back to neutral N,activating the solenoid SI. The solenoid SI is coupledin known manner to the contacts 14A, 14B in the liveand neutral conductors L, N such that activation of the solenoid causes the contacts 14A, 14B to open andthereby disconnect the mains from the load 10. Thecoupling mechanism (not shown) typically comprises aplunger slidable in the solenoid body and. linked to thecontacts.
In the event of a loss of supply neutral and asubsequent residual current fault, the current flowingthrough the solenoid SI will now pass via diodes Dl, D2, D5 and D6 and SCR 18 through the impedance Z toearth.
D5 and D6 are required to provide rectified DC power tothe electronic circuit 16 under the loss of neutral t condition. Alternatively, a single diode could be usedto provide power to the electronic circuit 16 via liveL and neutral N, and a second diode could be used toprovide'*' power to the electronic circuit via live L andearth E under a loss of neutral condition. The bridgearrangement has the advantage of using both half cyclesof the mains supply to provide power to the electroniccircuitry 16 and the SCR 18.
As explained previously, regardless of the form that ·impedance Z may take, it will require space on the PCB,and it may contribute to other problems such as cost,size, solenoid performance and overall reliability.
An embodiment of the present invention, whose circuitdiagram is shown in Fig. 3, takes advantage of the factthat in many cases the solenoid SI which operates thecontacts 14A, 14B has room for a second winding to beplaced on the same body, and this second winding can beused as the impedance Z. Examples of single and doublewinding solenoids are shown in Figs. 2A and 2Brespectively.
Fig. 2A shows a conventional solenoid as used, forexample, as the solenoid SI in the RCD of Fig. 1. Inthis case the solenoid body 20 has only a singlewinding Wl, connected between the live conductor L andthe junction of the diodes D1 and D2. Fig. 2 shows asolenoid which may be used in the embodiment of theinvention shown in Fig. 3. In this case, in additionto the original winding Wl there is a second winding W2overlyrhg the first (alternatively, Wl could overlieW2). This second winding W2 is connected between theearth conductor E and the junction of the diodes D5 andD6, and the impedance of W2 can be optimised to performthe function of the impedance Z in figure 1.
In figure 3, the second winding W2 replaces Z in theearth path. Under normal supply conditions, the RCDbehaves substantially the same as before, but with W2now acting as the current limiting impedance. Under aloss of neutral condition, when SCR 18 is turned oncurrent will flow from live L via solenoid winding Wl, diodes Dl, D2, D5 and D6, SCR 18 and solenoid windingW2 to earth, thereby opening the contacts 14A, 14B (thesolenoid comprising the body 20 and windings W1,W2 iscoupled to the contacts 14A, 14B as before). Ofcourse, the impedance and number of turns of thewinding W2 must be such that the standing currentthrough the winding W2 is insufficient in itself tocause opening of the contacts 14A and 14B under nonfault conditions.
The two windings W1 and W2 can be overlaid as shown inFig. 2 or disposed end to end or in any otherconvenient arrangement on the body 20. The polarity ofthe winding W2 is preferably such as to reinforce themagnetic field generated by the winding Wl, for reasonsto be discussed later, but this is not absolutelynecessary provided the net magnetic field generated bythe two* windings when the SCR 18 is tripped issufficient to open the contacts.
In the embodiment of Fig. 3 it is necessary to providemeans for rectifying the mains supply via live andearth when the . neutral is disconnected. Thisrectification is provided by the diodes D5 and D6.
Such components add considerably to space, cost andreliability problems for the RCD manufacturer.
These additional components can be avoided byconnecting the windings Wl and W2 as shown in theembodiment of Fig. 4.
In Fig. 4 the winding Wl has been connected between theoutput of the bridge rectifier circuit (junction ofD3/D4) and neutral N and the winding W2 has beenconnected between neutral N and earth E. In addition,diodes D5 and D6 of the previous embodiment have beenomitted.
When the neutral N is present and the SCR 18 is turnedon, current will preferentially flow from live L via the bridge rectifier circuit, the SCR 18 and winding Wl ( to neutral N, and the resultant activation of Wl willcause the contacts 14A, 14B to open. The winding W2provides an impedance in the earth circuit which limitsany current flow to earth before or after the SCR 18 isfired. If the SCR 18 is turned on under a loss ofneutral condition, current will flow from live Lthrough the bridge rectifier, the SCR 18 and bothwindings Wl and W2 to earth, and the resultantactivation of both solenoid windings will cause thecontacts 14A, 14B to open.
With the arrangement of Fig. 4 there is no need fordiodes D5 and D6 because either solenoid winding can beactivated through the four diode bridge rectifier.
This obviates the need for rectification circuitry tobe provided specifically for loss of neutral operation.
Under a reverse live-neutral condition, the winding W2will be connected across the mains supply and willautomatically be activated causing the contacts to openprovided the winding W2 has the correct polarity on thebody 20. The winding W2 effectively provides thereverse live-neutral sensing and activation functionsfor this circuit.
The arrangement of Fig. 4 suffers from a possibledisadvantage in that when contact 14B starts to openthe impedance in the neutral line starts to increaserapidly due to arcing and the widening gap in contact14B. Dependent on the speed of opening, the point ontheA.C. wave of opening, etc., and the impedance ofW2, sonife of the current flowing through W1 may flowthrough W2, with the resultant risk of trippingupstream RCDs. This problem can be overcome by thearrangement of Fig. 5 which shows an alternative meansfor connection of the two solenoid windings on the body20. In this arrangement the electronic circuit 16 andwinding W1 are connected on the supply side of contacts14A and 14B, while winding W2 remains connected on theload side as for Fig 4. The current through winding W1will no longer see an increase in the impedance in theneutral path and current will be less likely to bediverted through winding W2.
In conventional loss of neutral circuits typified byFig. 1 the provision of an impedance in the earth pathnot only limits the current flow in that path but alsoreduces the efficiency of the solenoid under a loss ofneutral condition. The energy produced in a solenoidis dependent on the ampere turns generated in itswindings. When the solenoid is energised with the liveand neutral present, the ampere turns produced by thesolenoid will be a maximum. Under a loss of supplyneutral condition the solenoid will be activated viathe earth circuit, but the current limiting impedancein the earth circuit will reduce the current flow t through the solenoid. This in turn reduces the ampereturns and reduces the efficiency of the solenoid.
In the circuits of Figs. 3 to 5 the impedance m theearth circuit comprises the second winding W2 on thesolenoid and when the neutral is present this impedancelimits the current in the earth circuit, as normal.However, under a loss of neutral condition current willflow through both windings W1 and W2 when the SCR 18 isturned on. Now, instead of behaving as a powerdropping impedance which reduces the efficiency of thesolenoid, the additional winding W2 supplements thewinding W1 so as to increase the overall number ofturns such that the ampere turns of the solenoidremains much the same as that produced under normal supply conditions. Thus the efficiency of the solenoidis substantially the same whether it is activated vianeutral or earth.
Furthermore, in respect of the Figs. 4 and 5embodiments, the dual winding solenoid obviates theneed for rectification circuitry to be providedspecifically for loss of neutral operation, and itprovides automatic tripping under a reverse live-neutral condition. It is highly cost effective, spaceefficient, and improves the overall reliability of theRCD.
In the foregoing embodiments the additional winding W2 is disposed on the same solenoid body as the windingW1. As discussed, this has advantages of saving spaceas well as allowing the winding W2 to share the samecoupling mechanism to the contacts 14A, 14B as thewinding W1. However, the winding W2 could be disposedon a separate solenoid body and independently coupledto the contacts 14A, 14B for disconnecting the mains inthe event of a reverse live-neutral mains connection.
The invention is not limited to the embodimentsdescribed herein which may be modified or variedwithout departing from the scope of the invention.CLAIMS
Claims (7)
1. A residual current device for an A.C. mains havinglive, neutral and earth conductors, the residualcurrent device including circuit means for detecting anearth fault current and contact means operated by-current flowing in a solenoid winding for disconnectingthe mains in response to the detection of an earthfault current by the circuit means, wherein the circuitmeans is powered from the mains live and neutralconductors and further has a connection to the earthconductor via an impedance to maintain power to thecircuit means if there is a loss of neutral, andwherein the impedance comprises a further solenoidwinding.
2. A residual current device as claimed in claim 1,wherein the further solenoid winding is connectedbetween the mains neutral and earth conductors and isoperative to disconnect the mains in the event of areverse live-neutral mains connection.
3. A residual current device as claimed in claim 2,wherein the first solenoid winding is in the pathbetween the circuit means and the neutral conductor.
4. A residual current device as claimed in claim 1, 2•or 3, wherein the circuit means is powered from themains live and neutral conductors on the supply side ofthe contact means.
5. A residual current device as claimed in any-preceding claim, wherein the further solenoid windingis disposed on the same solenoid body as the firstwinding. >
6. A residual current device as claimed in claim 5,wherein the first and further windings are overlaid onthe body or disposed end to end on the body.
7. A residual current device as claimed in claim 6,wherein the polarity of the second winding is such asto reinforce the magnetic field generated by the firstwinding.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IE20010271A IE20010271A1 (en) | 2000-03-22 | 2001-03-21 | Residual Current Device |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IE20000222 | 2000-03-22 | ||
| IE20010271A IE20010271A1 (en) | 2000-03-22 | 2001-03-21 | Residual Current Device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| IE20010271A1 true IE20010271A1 (en) | 2001-10-03 |
Family
ID=11042585
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| IE20010271A IE20010271A1 (en) | 2000-03-22 | 2001-03-21 | Residual Current Device |
| IE20010272A IES20010272A2 (en) | 2000-03-22 | 2001-03-21 | Residual current device |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| IE20010272A IES20010272A2 (en) | 2000-03-22 | 2001-03-21 | Residual current device |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB2366676A (en) |
| IE (2) | IE20010271A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2377834B (en) * | 2001-05-31 | 2003-09-17 | Shakira Ltd | Residual current device |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2162708B (en) * | 1984-07-27 | 1988-12-14 | Technology Res Corp | Ground fault current interrupter circuit with open neutral, and ground lead protection |
| GB2224404B (en) * | 1988-10-25 | 1993-03-17 | Shakira Ltd | Residual current device |
| US4933801A (en) * | 1989-04-19 | 1990-06-12 | Square D Company | Ground fault circuit interrupter |
| GB2268011B (en) * | 1992-06-18 | 1995-11-29 | Shakira Ltd | A residual current device |
| CA2093061C (en) * | 1992-07-22 | 2005-02-15 | Raymond H. Legatti | Leakage current protection device adapted to a wide variety of domestic and international applications |
| GB2311177B (en) * | 1996-03-13 | 2000-08-02 | Crabtree Electrical Ind Ltd | Residual current devices |
-
2001
- 2001-03-21 IE IE20010271A patent/IE20010271A1/en not_active IP Right Cessation
- 2001-03-21 IE IE20010272A patent/IES20010272A2/en not_active IP Right Cessation
- 2001-03-21 GB GB0107121A patent/GB2366676A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| IES20010272A2 (en) | 2001-10-03 |
| GB2366676A (en) | 2002-03-13 |
| GB0107121D0 (en) | 2001-05-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MM9A | Patent lapsed through non-payment of renewal fee |