IES84850Y1 - A residual current device - Google Patents
A residual current deviceInfo
- Publication number
- IES84850Y1 IES84850Y1 IE2007/0390A IE20070390A IES84850Y1 IE S84850 Y1 IES84850 Y1 IE S84850Y1 IE 2007/0390 A IE2007/0390 A IE 2007/0390A IE 20070390 A IE20070390 A IE 20070390A IE S84850 Y1 IES84850 Y1 IE S84850Y1
- Authority
- IE
- Ireland
- Prior art keywords
- housing
- load
- core
- supply
- neutral
- Prior art date
Links
- 239000004020 conductor Substances 0.000 claims abstract description 64
- 230000005611 electricity Effects 0.000 claims abstract description 4
- 230000007935 neutral effect Effects 0.000 claims description 36
- 238000004804 winding Methods 0.000 abstract description 8
- 238000002070 Raman circular dichroism spectroscopy Methods 0.000 description 17
- 238000009434 installation Methods 0.000 description 6
- 239000007787 solid Substances 0.000 description 6
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000005355 Hall effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000005405 multipole Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H83/00—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current
- H01H83/20—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by excess current as well as by some other abnormal electrical condition
- H01H83/22—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by excess current as well as by some other abnormal electrical condition the other condition being imbalance of two or more currents or voltages
- H01H83/226—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by excess current as well as by some other abnormal electrical condition the other condition being imbalance of two or more currents or voltages with differential transformer
Abstract
ABSTRACT A residual current device for an AC electricity supply comprises a housing 10 and a first load conductor L inside the housing connected in series between the supply and a load and including a set of contacts 18 by which an electrical connection between the supply and the load may be made or broken. A current transformer inside the housing and has a toroidal core T, the first load conductor passing through the core and forming one primary winding of the current transformer. At least one further load conductor N outside the housing passes through the core T via an opening 32 in the housing and forms a further primary winding of the current transformer. A secondary winding W on the core produces an output in response to a residual current, and a circuit RCC inside the housing is responsive to the output on the secondary winding to open the contacts if the residual current is above a predetermined level.
Description
A Residual Current Device
This invention relates to a residual current device (RCD).
RCDs can be divided into two categories based on the technology used:
- Voltage independent (VI) RCDs, which use the residual current as the source
of energy for operation of the RCD. These are sometimes referred to as
conventional or electromechanical RCDs
- Voltage dependent (VD) RCDs which use the mains supply voltage as the
source of energy to operate the RCD. These are sometimes referred to as
electronic RCDs.
RCD is a generic term which includes both RCCBs and RCBOSZ
— RCCB: a residual current circuit breaker without overcurrent sensing.
- RCBO: a residual current circuit breaker with overcurrent sensing.
An RCCB will open automatically only in response to a residual current. An
RCBO will open automatically in the event of a residual current or an overload
or overcurrent condition.
Figure 1 shows an AC electricity supply which is protected by an RCD, also
known as a ground fault interrupter (GFI). Figure 1 represents a typical single
phase TN installation comprising live L and neutral N conductors supplying a
load LD. The supply neutral N is connected directly to earth E, and a solid earth
conductor is distributed throughout the installation. The installation is protected
by an electronic type residual current circuit RCC based on a WA050 IC
produced by Western Automation and powered via leads M from the mains
supply.
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In operation a current IL flows from the supply in the live conductor L to the load
LD and returns to the supply as a current IN in the neutral conductor N. The live
L and neutral N conductors pass through the toroidal core T of a current
transformer CT, and serve as primary windings for the CT. The CT includes a
secondary winding W on the core T whose output is connected to the RCC.
Under normal conditions the currents IL and IN flowing through the core T in the
conductors L, N are equal in magnitude but opposite in direction, and as a result
the vector sum of these currents is zero and no current is induced into the
secondary winding W.
However, if a person touches a live part, as shown in the figure, a current IR will
flow through the person’s body to earth and return to the supply via the earth
return path. The current IL will now be greater than IN and consequently the
secondary winding W will produce an output in response to this differential or
residual current. This output will be sensed by the RCC, and if it meets
predetermined criteria as to amplitude and/or duration a mechanical coupling
between the RCC and a set of contacts 8 in the live and neutral conductors will
cause the contacts 8 to open and disconnect the supply from the load LD to
provide protection. This is all very well known and no further description is
deemed necessary.
RCDs are often based on miniature circuit breakers (MCBs) to ensure
compatibility in terms of mechanical and electrical properties and aesthetics,
etc. In many cases, the basic MCB design is modified to provide for inclusion of
the RCD function so as to produce an RCBO - an RCD with overcurrent
protection. Such RCBOS can comprise 1 pole with solid neutral, 1 pole with
switched neutral (1P + N), 2 pole, 3 pole, 3 pole with solid neutral or 3 pole with
switched neutral (sometimes referred to as a 4 pole device). The term “pole”
signifies a pair of contacts that can make and break a fault current, whereas the
term "switched neutral” is used to indicate that the neutral pole comprises a pair
of contacts that can open and close but that this pole is not fully rated to make
and break a fault current because it does not have overcurrent sensing.
RCDs with a solid neutral or with a switched neutral must have that pole or
terminal marked N so as to avoid that pole being inadvertently used to provide
protection on a phase. Such RCDs therefore have what is termed a “dedicated"
neutral pole or terminal, and the installer needs to take this into consideration
when fitting such RCDs in an installation.
MCBs based on lEC60898 tend to be supplied with a standard modular width,
1-pole devices being typically 18mm wide (referred to as a single module unit),
2—pole devices being typically 36mm wide (two module unit), 3-pole devices
being typically 54mm wide (three module unit) and 4-pole devices being
typically 72mm wide (4 module unit).
Figure 2 are diagrams showing how a single module MCB, Figure 2(a), can be
converted to a single module RCBO with 1P and solid neutral, Figure 2(b). In
each figure, as well as in Figures 3, 4 and 6, a schematic front view of the
device is shown on the left and a schematic side view on the right. In all figures
the same reference signs have been used for the same or equivalent
components.
The unconverted MCB comprises a narrow housing 10 having opposite
substantially parallel sidewalls 10A, 10B. A conductor 12 extends inside the
housing 10 between an input terminal 14 for connection to the electricity supply
and an output terminal 16 for connection to the load. The conductor 12 includes
a pair of contacts (single pole) 18 by which the electrical connection between
the terminals 14 and 16 can be made or broken. These contacts can be opened
manually by a toggle switch 20, or automatically in response to an overcurrent
flow through the conductor 12. Means to sense the overcurrent and cause
automatic opening of the contacts 18 (tripping) are not shown but are well
known to those familiar in the art of circuit breaker operation.
In the RCBO, Figure 2(b), the MCB housing 10 is extended (while not
increasing its width between the sidewalls 10A and 10B) so as to provide room
to fit a current transformer CT and other RCD circuitry as shown (the RCC
power supply leads are omitted from the side view and all but the core T is
omitted from the front view). The conductor 12 is the live conductor L and a
neutral conductor N is added, passing through the toroidal core T. As before,
the RCC is mechanically coupled to the contacts 18 so as to cause automatic
opening of the contacts in the event of a residual fault current. RCDs are
generally provided with a test button 22 so as to enable the user to verify the
operation of the RCD.
The main advantage of the arrangement of Figure 2(b) is that an RCBO can be
produced which is the same width as a single module MCB. This type of RCBO
can be conveniently used to replace a single pole MCB as part of an upgrade to
add RCD protection to a circuit.
A major disadvantage of the arrangement of Figure 2(b) is that in conventional
RCD designs the 18mm width of the single module places severe constraints on
the RCD designer and the user. Due to space constraints within the 18mm
module width. it is generally not possible to connect two supply and two load
terminals for the L and N conductors because such terminals would be
extremely small and would severely restrict the size and current ratings of
conductors that could be used. Common practice in this arrangement is
therefore to feed the live conductor L from the supply terminal 14 through the
core T en route to the load terminal 16. The neutral conductor N is provided with
a terminal 24 for the load side connection only, from where a conductor is
routed internally via the CT, but which then exits the housing 10 as a wire, often
coiled up like a pigtail.
Note that the L and N conductors must be routed through the core T in the
same direction so that their load currents cancel. Designers and manufacturers
are faced with serious problems of optimising components and parts, assembly
issues, etc. Users are faced with problems of severely limited load current
rating, small terminals, etc. Three-terminal arrangement can also cause
confusion for installers as to supply and load connections, polarity, etc.
Figure 3 shows an arrangement for a 2 module (1P + N) RCBO, In this
arrangement, two single pole MCBs are placed side by side to form a two-
module device. The RCD portion is usually placed in the in N half of the RCBO,
and to accommodate the RCD, various circuit breaker elements such as the
overcurrent sensing and tripping means and the arc stack, etc., are removed
from that half. This arrangement is sometimes referred to as a pod
arrangement because the RCD portion is considered to be like a pod being
carried on the back of the MCB. It will be noted that in this case the neutral
conductor N is switched as well as the live conductor L, and has both supply
and load terminals 28, 30 respectively in its housing 10. Production of 3 and 4
pole RCBOs follows a similar pattern to that of the arrangement of Figure 3,
with the modular width getting wider.
The arrangement of Figure 3 is slightly better than that of Figure 2(b) in that two
modules are used, which facilitates four fully sized supply and load terminals.
However, because the toroidal core T still has to be fitted within an 18mm
module, conductor sizes will still be constrained by the relatively small space
available inside the module which limits the maximum diameter of the core T
that can be used, and assembly problems will still be present.
Critically, the arrangements of Figures 2(b) and 3 do not lend themselves
readily to the production of 3 and 4 pole RCDs because of the need to route
three or four conductors through a toroidal core within a single module. Each
load conductor has to be brought from its own pole through the core T and back
to its supply or load terminal within its own module. In addition, 3 and 4 pole
RCBOs may be used on a single phase (L + N) circuit or on a two phase (P + P)
circuit. The RCD circuitry must still function in such cases regardless of which
pair of supply terminals are used on the RCD to supply a load. In the case of a
VD RCD it will be necessary to have a supply connection to the electronic circuit
from all poles of the RCD. This requires routing of wires or terminals from each
pole of the RCD to the location of the electronic circuit.
Production of 1, 2, 3 and 4 module RCDs is usually achieved by having a
dedicated 1, 2, 3 and 4 module RCD housing for each of these variants with the
result that each product has to be produced as a stand alone product. With
conventional assembly processes, it is not possible to convert a 1P RCD into a
2, 3 or 4 pole RCD. Also, given that a 4 module RCD can be used to protect a
three phase circuit without neutral, manufacturers are less inclined to produce 3
module RCDs. Users requiring protection of a three phase circuit therefore often
tend to be burdened with the cost and bulky size of a 4 module RCD rather than
having an optimised product for such applications.
There are RCD products on the market based on the MCB modular principle. In
such case a toroidal current transformer core is located in one of the modules
and all the load conductors, which are external to the module containing the
core, pass through the core by passing through an opening in the module
housing. Thus the module containing the core acts simply as a residual current
detector, but does not in itself perform any circuit breaking function in response
to a detected residual current. This has to be performed in one or more
additional devices, according to the number of load conductors.
it is an object of the invention to provide an improved RCD which mitigates the
above problems associated with conventional devices.
This object is met by the invention claimed in claim 1.
Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
Figures 1 to 3, previously described, are schematic diagrams of various RCDs
according to the prior art.
Figure 4 shows schematic front and side views of a first embodiment of the
invenflon.
Figure 5 illustrates how the embodiment of Figure 4 may be extended for multi-
pole devices.
Figure 6 shows schematic front and side views of a further embodiment of the
invenflon.
In the embodiment of Figure 4, a narrow housing 10 of an extended single
module MCB has opposite parallel sidewalls 10A and 10B and supply and load
terminals 14, 16 respectively. The housing contains a toroidal core T of a
current transformer and other RCD components as shown. To overcome the
constraints of size and wiring arrangements that normally apply to the core
when fitted in an 18mm wide single module housing, the core T is arranged in a
plane parallel to the sidewalls 10A, 10B and disposed in the extended section of
the housing so as to facilitate a core T of substantially greater size than the core
used in the conventional arrangement. Whilst the module width is still nominally
18mm, the extended housing section can be over 30 x 30mm and thus provide
for the use of a core with a substantially larger internal and external diameter
than cores normally used in single module RCBOs.
In the extended housing section an opening 32 is formed in the housing which
extends between the opposite sidewalls 10A, 10B and passes through the
inside diameter of the core T. The live load conductor L, which extends inside
the housing 10 from the supply terminal 14 to the load terminal 16 and contains
the contacts 18, passes through the toroidal core T between the core internal
diameter and the edge of the opening 32 and is therefore not exposed
externally. The section of the internal load conductor L passing through the
core can be formed as a pressed part so as to minimise the gap required to
pass it between the core and the opening. The supply and load terminals 14,
16 for the live internal conductor L are fully sized and rated as for a normal
MCB.
it can be seen that there is no provision for a neutral load conductor or neutral
terminals to be provided as an integral part of the RCD. For installation
purposes, the live supply and load connections are made to the RCD as for a
conventional MCB, but a neutral conductor N is simply taken from the supply
side neutral, passed through the opening 32 and then connected to the load to
complete the RCD-protected circuit. The front view of the RCD shows the
direction for routing of the neutral conductor N so that the L and N load currents
cancel within the current transformer. Operation of the RCD is as for a
conventional RCD in that when a differential current above a predetermined
level flows between L and N, the RCD will trip.
The arrangement of Figure 4 can also be used for a VD RCD. When used as a
VD RCD, it is necessary to connect a lead 34 to the supply neutral so as to
provide power to the internal electronic circuitry of the RCD.
The above arrangement can be extended to provide for 2, 3 or 4-pole RCDs. A
single MCB can be added to produce a 2-pole RCD for single phase or 2 phase
applications. Two MCBs can be added to produce a 3—pole RCD for three phase
applications, and 3 MCBs can be added to produce a 4-pole RCD. Where a
neutral is required, an MCB can be used to provide the neutral pole and
connection, or a solid wire can be fed from the supply N via the RCD opening
32 to provide a neutral connection to the load and thereby obviate the use of an
MCB for that purpose.
For example, Figure 5 shows the case of a 4-pole RCD for a supply having
three phase conductors P1, P2 , P3 and a neutral conductor N. The conductor
P1 extends from the supply terminal 14 to the load terminal 16 inside the
extended MCB housing 10 (LHS of Figure 5), and in doing so passes through
the toroidal core T inside the housing 10 in the manner of the live conductor L in
Figure 4. The other phase conductors P2, P3 and the neutral conductor N
extend through their own single module MCB housings 10-1, 10-2, 10-3, which
are attached directly or indirectly to the extended housing, and then pass
through the opening 32 of the extended housing 10 and hence through the
core T. Each of the housings 10, 10-1, 10-2, 10-3 has a pole (pair of contacts),
such as the pole 18 in Figure 4, in the load conductor P1, P2 , P3 or N passing
through that housing. All such poles are mechanically coupled to the pole in the
extended housing 10 so that all poles are opened in the event of any one pole
being opened due to an overcurrent or a residual current condition (it will be
understood that in this and other embodiments the extended housing 10 still
retains overcurrent detection and tripping means of the standard, unmodified
MCB). In accordance with the requirement of RCD product standards for “trip
free operation”, such mechanical coupling will ensure tripping of all poles even if
one or more toggle switches are held in the closed position.
The arrangement of Figure 5 is shown for a VI RCD. To facilitate the use of an
electronic RCD, a power connection like the lead 34 of Figure 4 can be made
from the extended housing 10 to the supply N and/or each supply phase for
each MCB fitted so as to ensure operation of the VD RCD when any two supply
connections are available to the RCD.
Figure 6 shows an embodiment wherein an extended 2-pole MCB housing 10-4
and two standard single pole MCB housings 10-1 and 10-2 are used as the
basis of a 4-pole RCD for a supply comprising three phases P1, P2 and P3 and
neutral N. In this arrangement, the two internal conductors 50, 52 of the 2-pole
housing 10-4, respectively connected to the P1 and N supply conductors, are
passed through the core T internally of the housing 10-4 (only the P1 load
conductor is shown in the housing 10-4 in the side view but the N load
conductor which is not shown will be located behind and in line with the P1
conductor within the two-module housing). The other phase conductors P2, P3
extend through their own single module MCB housings 10-1, 10-2 and then
pass through the opening 32 of the extended housing 10-4 and hence through
the core T. Each of the housings 10-1 and 10-2 has a pole 18 (not shown) in
the load conductor P2 or P3 passing through that housing. All such poles are
mechanically coupled to the pole in the extended housing 10-4 so that all poles
are opened in the event of any one pole being opened due to an overcurrent or
a residual current condition.
The embodiment of Figure 6 may be extended to 3-pole RCDs by omitting the
module housing 10-2, in which case any two load conductors pass inside the
RCD module 10.4 and the third load conductor passes via the module 10.1
through the opening 32 as before.
Various changes can be made to the foregoing embodiments. For example, the
embodiments may be converted to RCCBS by omitting the overcurrent sensing
elements from the MCB modules as appropriate. The extended housing can be
arranged to be fitted to the left or right of the MCBs. The opening 32 can be
located at the top or bottom end of the extended housing as convenient.
In the foregoing embodiments the invention has been described in relation to an
AC supply using a current transformer with a toroidal core as a differential
current sensor. However, other types of sensor may be used, based upon the
use of a toroidal or other apertured core (e.g. Hall effect current sensor), or
otherwise. The invention may also be applied to DC applications provided that
the residual current sensor is of a type which can detect DC residual currents.
The use of DC-responsive RCDs is common in DC installations supplying
underground trains, and in photovoltaic generators, etc.
The invention is not limited to the embodiments described herein which may be
modified or varied without departing from the scope of the invention.
Claims (5)
1. A residual current device for an electricity supply, the device comprising: a housing having an opening extending between opposite sidewalls of the housing, at least one load conductor inside the housing connected in series between the supply and a load and including a set of contacts by which an electrical connection between the supply and the load may be made or broken, at least one further load conductor outside the housing and passing through the housing via the opening, a sensor inside the housing and responsive to the currents in the load conductors to produce an output in response to a non-zero vector sum of said currents, and circuit means inside the housing and responsive to the output of the sensor to open the contacts if the non-zero vector sum of currents meets predetermined criteria as to amplitude and/or duration.
2. A residual current device as claimed in claim 1, wherein the residual current sensor comprises an apertured core and wherein the at least one load conductor passes through the core inside the housing and the at least one further load conductor passes through the core via the opening.
3. A residual current device as claimed in claim 2, wherein the opposite sidewalls of the housing are substantially parallel, wherein the core is disposed between and generally parallel to the sidewalls, wherein the housing opening extends between the sidewalls and passes through the core, and wherein the at least one further load conductor passes thorough the core via the opening.
4. A residual current device as claimed in claim 1, 2 or 3, wherein the supply comprises live and neutral, and wherein the first load conductor is connected to live and the at least one further load conductor is connected to neutral. 12 connected to live and the at least one further load conductor is connected to neutral.
5. A residual current device as claimed in claim 1, 2 or 3, wherein the supply comprises a plurality of phases and neutral, wherein the first load conductor is connected to one of the phases, and wherein there are a plurality of further load conductors, one of the further load conductors being connected to neutral and the other load conductor(s) to respective other phase(s).
Publications (2)
Publication Number | Publication Date |
---|---|
IE20070390U1 IE20070390U1 (en) | 2008-03-19 |
IES84850Y1 true IES84850Y1 (en) | 2008-03-19 |
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