U.S. patent application number 13/736713 was filed with the patent office on 2013-07-11 for switching contactor.
This patent application is currently assigned to Johnson Electric International (UK) Limited. The applicant listed for this patent is Johnson Electric International (UK) Limited. Invention is credited to Richard Anthony Connell.
Application Number | 20130176089 13/736713 |
Document ID | / |
Family ID | 45788692 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130176089 |
Kind Code |
A1 |
Connell; Richard Anthony |
July 11, 2013 |
SWITCHING CONTACTOR
Abstract
A switching electrical power contactor having a bi-blade type
switch, has ferrous plates attached to the blades to increase the
current carrying capacity and reduce the resistance of the switch.
The contacts of the switches are arranged in pairs with at least
one pair of contacts being arranged to close before another pair of
contacts.
Inventors: |
Connell; Richard Anthony;
(Shatin, HK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Johnson Electric International (UK) Limited; |
Boldon |
|
GB |
|
|
Assignee: |
Johnson Electric International (UK)
Limited
Boldon
GB
|
Family ID: |
45788692 |
Appl. No.: |
13/736713 |
Filed: |
January 8, 2013 |
Current U.S.
Class: |
335/189 |
Current CPC
Class: |
G01R 11/04 20130101;
G01R 11/02 20130101; H01R 13/18 20130101; H01R 13/64 20130101; H01R
33/00 20130101; H01H 1/54 20130101; H01H 2205/002 20130101; H01H
1/021 20130101; H01H 50/648 20130101; H02B 1/42 20130101; H01H
50/641 20130101; H01H 50/54 20130101 |
Class at
Publication: |
335/189 |
International
Class: |
H01H 50/54 20060101
H01H050/54 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 9, 2012 |
GB |
1200331.5 |
Claims
1. An electrical contactor comprising: a first terminal connected
to a pair of fixed contacts on opposite faces of a fixed conductive
member; a second terminal; a pair of movable arms of electrically
conductive material connected to the second terminal, and carrying
movable contacts at an end remote from the connection to the second
terminal, the movable contacts and the fixed contacts forming
parallel switches and being arranged in first and second switch
pairs; and an actuating arrangement arranged to move the movable
arms so as to open and close the switches, wherein the actuating
arrangement is arranged to close the first switch pair of contacts
before closing the second switch pair of contacts.
2. The electrical contactor of claim 1, wherein the pair of movable
arms are arranged in aligned opposition to each other such that
their remote ends are on either side of the fixed conductive
member, with the movable contacts aligned with the fixed contacts,
and are separated by a predetermined gap over a major portion of
their length.
3. The electrical contactor of claim 2, wherein the movable arms
are preformed and preloaded so as to bias them towards each other
to engage the fixed contacts with a preset contact pressure keeping
the contacts normally closed in the absence of a force separating
the movable arms.
4. The electrical contactor of claim 2, wherein the actuating
arrangement includes a wedge shaped member disposed between inner
inclined surfaces of the movable arms, arranged to separate the
movable arms so as to open the contacts, the wedge shaped member
being movable from a first position in which it separates the
movable arms, to a second position where it allows the arms to move
freely towards each other.
5. The electrical contactor of claim 4, wherein the actuating
arrangement comprises an electromagnetic actuator coupled to the
wedge shaped member and the movable member, the electromagnetic
actuator effecting movement of the wedge shaped member and the
movable member, between the first and second positions.
6. The electrical contactor of claim 1, further comprising ferrous
plates attached on the outer faces of the movable arms, wherein the
arrangement of the fixed member and movable arms being such that
when the contacts are closed, current flowing through the movable
arms and the ferrous plates produces induced magnetic-field
attraction forces between the movable arms that urges the movable
arms towards each other, thereby increasing the force pressing the
movable contacts against the fixed contacts.
7. The electrical contactor of claim 6, wherein the ferrous plates
are attached to the movable arms along their formed length, whereby
when the contacts are closed, higher current flowing through the
movable arms induces magnetic fields in the ferrous plates,
generating a magnetic force of attraction urging the contacts
closed.
8. The electrical contactor of claim 1, wherein the contactor is a
two pole contactor having a pair of first and second terminals, a
pair of fixed conductive members and two pairs of movable arms.
9. The electrical contactor of claim 1, wherein each movable arm
comprises a plurality of longitudinal sections, each provided with
a movable contact at the remote end and arranged to engage with a
corresponding fixed contact, the current flow in the arms being
substantially equally divided between the sections thereof.
10. The electrical contactor of claim 1, wherein the contacts of
the first pair of switching contacts are larger than the contacts
of the second pair of switching contacts.
11. The electrical contactor of claim 1, wherein the contacts of
the first pair of switching contacts have a thicker top-layer of
silver alloy than the contacts of the second pair of switching
contacts.
12. The electrical contactor of claim 1, wherein the contacts of at
least the first pair of switching contacts have a top-layer of
silver alloy with tungsten-oxide additive inclusions in the silver
matrix.
13. The electrical contactor of claim 1, wherein the contacts of at
least the first pair of switching contacts have a tungsten rich
top-layer.
14. A 2-pole electrical contactor comprising: a first terminal
connected to a fixed contact on a face of a first fixed conductive
member; a second terminal; a first movable arm of electrically
conductive material connected to the second terminal, and carrying
a movable contact at an end remote from the connection to the
second terminal, the movable contact and the fixed contact forming
a first switch and being arranged in first switch pair of contacts;
a third terminal connected to a fixed contact on a face of a second
fixed conductive member; a fourth terminal; a second movable arm of
electrically conductive material connected to the fourth terminal,
and carrying a movable contact at an end remote from the connection
to the fourth terminal, the movable contact and the fixed contact
forming a second switch and being arranged in a second switch pair
of contacts; and an actuating arrangement arranged to move the
movable arms so as to open and close the switches, wherein the
actuating arrangement is arranged to close the first switch pair of
contacts after closing the second switch pair of contacts.
15. The electrical contactor of claim 14, further comprising a
plurality of first movable arms and a plurality of second movable
arms.
16. The electrical contactor of claim 14, wherein each movable arm
comprises a plurality of longitudinal sections, each provided with
a movable contact at the remote end and arranged to engage with a
corresponding fixed contact, the current flow in the arms being
substantially equally divided between the sections thereof.
17. The electrical contactor of claim 14, wherein the contacts of
the first pair of switching contacts are larger than the contacts
of the second pair of switching contacts.
18. The electrical contactor of claim 14, wherein the contacts of
the first pair of switching contacts have a thicker top-layer of
silver alloy than the contacts of the second pair of switching
contacts.
19. The electrical contactor of claim 14, wherein the contacts of
at least the first pair of switching contacts have a top-layer of
silver alloy with tungsten-oxide additive inclusions in the silver
matrix.
20. The electrical contactor of claim 14, wherein the contacts of
at least the first pair of switching contacts have a tungsten rich
top-layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This non-provisional patent application claims priority
under 35 U.S.C. .sctn.119(a) from Patent Application No.
GB1200331.5 filed in United Kingdom on Jan. 9, 2012.
FIELD OF THE INVENTION
[0002] This invention relates to an electrical power switching
contactor and in particular, to a single-pole or two-pole contactor
capable of switching currents of more than 80 amps at mains
voltage.
[0003] This invention also relates to the types of high-current
switching contactors employed in modern electricity meters,
so-called "smart meters", for performing a pre-payment or
safety-disconnect function at normal domestic supply (mains)
voltages, e.g. 100 V AC to 240 V AC. It has a particular
application to electrical contactors having a bi-blade contact
arrangement as described in U.S. Pat. No. 7,833,034.
BACKGROUND OF THE INVENTION
[0004] Many contactors of this type are capable of switching
nominal current at say 100 Amps or 200 Amps, for a large number of
switching load cycles, satisfactorily, the switching being done by
suitable silver-alloy contacts containing certain additives, which
prevent welding. The switching blades are configured to be easily
actuated for the switching function, with minimal self heating at
the nominal currents concerned.
[0005] Most meter specifications not only stipulate satisfactory
Nominal-current Endurance switching--without the contacts
welding--but also demand that at moderate short-circuit fault
conditions they must also not weld, and must open on the next
actuator-driven pulse. At much higher related "dead-short"
conditions the switch contacts may weld, but must remain intact,
not explode or emit any dangerous molten material during the
"dead-short" duration, until protective fuses rupture, or circuit
breakers drop-out and disconnect the mains supply to the load,
safely. This shorting duration may be for a maximum of 6 cycles of
the mains supply.
[0006] U.S. Pat. No. 7,833,034 introduced the basic configuration
of the "bi-blade" switch comprising a pair of parallel movable
spring-copper arms or blades, of a particular thickness, width and
active length, with a small defined gap there between. The blades'
fixed ends are terminated together by rivets, screws, or
semi-shears, to a moving-blade-carrier terminal, with movable
contacts attached on the inner faces of the free ends, which close
naturally on fixed contacts attached to the other
fixed-blade-carrier terminal of the switch.
[0007] In the basic embodiment, the contactor uses a bi-blade
switch construction, in which the switch has a pair of movable arms
(also known as blades), which are strip-punched and pre-formed so
that they close on the fixed contacts with a defined
"contact-pressure" force--for achieving a relatively low switch
resistance--and the open ends are formed outwardly with a sloping
portion. The arms extend parallel to each other and separated by a
small gap so that under high current situations the currents
through the arms create forces of magnetic attraction urging the
arms towards each other and increasing the force applied to the
fixed contacts disposed between the distal ends of the arms. This
force of attraction offsets the repulsive force urging the contacts
apart, and is also due to the high current passing through the
contacts. This arrangement is shown in FIGS. 1 to 3. FIGS. 1 &
2 show a single-pole contactor 10 with the cover removed to show
the workings. FIG. 3 is a schematic view of the arms 30 of one
switch. Each arm has a strip of spring copper having a first end 34
attached to a first terminal 24, known as the movable terminal as
it is connected to the movable arms. A second terminal 22, known as
the fixed terminal has fixed contacts 23. The distal end 36 of each
arm is fitted with a movable contact 25. Each arm 30 has a sloping
section or portion 38 to create an offset between the ends of the
arms such that the fixed contacts can be accommodated between the
movable contacts. The two arms extend parallel to each other except
at the sloping portion. The movable contacts are arranged to align
with the fixed contacts and in the relaxed state of the arms, the
movable contacts bear against the fixed contacts with a
predetermined contact force. The arms are able to move or flex
within the plane of the drawing about the connection to the first
terminal. A rib 39 is formed in the arms to stiffen the arms
against excessive flexing.
[0008] The basic parallel "bi-blade" configuration, as used in a
100 Amp nominal current contactor, creates dynamic magnetic blade
forces in excess of the contact repulsion forces during
short-circuit faults. The blade geometries and contacts were
optimised to avoid welding at the specified operating conditions.
This basic 100 Amp switch uses 4 contacts; two movable and two
fixed, with 50 Amps in each parallel blade. This basic arrangement
was not capable of withstanding much higher nominal and
short-circuit currents, as the blade geometries and current-sharing
parameters limited the balancing of the blade forces and
particularly the greater contact repulsion forces, resulting in
much lessened endurance life, and serious contact welding issues
during higher short-circuit faults.
[0009] U.S. Pat. No. 7,833,034 also introduced the divided blade
concept, allowing a 200 Amp nominal current contactor able to
balance the dynamic magnetic blade forces and contact repulsion
forces during short-circuit faults, the geometries and contacts
being optimised to avoid welding at the specified conditions.
[0010] To evenly share the current sharing--and to balance the
repulsive contact forces and blade magnetic attraction forces--each
adjacent parallel "bi-blade" was sub-divided into longitudinal
half-blades, with a movable contact at each of their free ends,
mating with respective fixed contacts, thus constituting 4
half-blades in parallel with 8 contacts per switch, or 16 in total
for the 2-pole, two-phase disconnect contactor. This lower current
sharing in each half-blade significantly reduces the contact
repulsion forces.
[0011] Thus at 200 Amps, each half-blade will be carrying only 50
Amps, reducing the burden per half-blade when switched, minimising
self heating, and avoiding welding at the higher nominal and
short-circuit currents. Importantly, all half-blade currents flow
in the same direction, thus maximising the magnetic attraction
forces between half-blades in the working gap, especially at high
current, to keep the contacts tightly closed.
[0012] The existing 100 Amp switch designs using simple parallel
spring-copper "bi-blades" are very limited by the geometries and
gap between, each blade in the "bi-blade" set being capable of
generating certain magnetic attraction forces at high shared
current, one with-respect-to the other, balanced and acting against
the contact repulsion forces--both being proportional to the square
of the current--in order to ensure that the contacts remain closed
during short-circuit faults. It is very difficult to get this
balanced ratio of forces exactly right for a particular
configuration. Hence the divided blade version was optimised for
use at 200 Amps, but used longer blades and 16 contacts in
total.
[0013] The divided bi-blade configuration provided a good solution
for the 200 Amp contactor but at a price as the silver contacts are
expensive and the divided blades take up space. There is also a
market want for the 100 Amp and 200 Amp contactors to be made
smaller to save space. Thus there is a desire to reconfigure the
simpler, basic parallel "bi-blade" 100 Amp switch geometry and
configuration, so it was capable to operate at the higher 200 Amps
nominal current with a greater short-circuit capability, in full
compliance with various National requirements such as the ANSI
C12.1 meter-disconnect specification.
[0014] Certain embodiments of the present invention provide a
smaller, simpler, cost-reduced switch, using a new "bi-blade"
switch arrangement, which not only uses less copper blade material,
but requires only 8 switching contacts per 2-pole contactor instead
of the current 16 required in the present design for a contactor
rated at 200 Amps nominal current. Silver-alloy contacts represent
a significant proportion of all high-current contactor cost
breakdowns, so a reduction in the number of contacts required for a
particular switching function is a major cost-saving benefit.
Teachings from the improvements to the 200 Amp contactor can be
applied to contactors rated at 100 Amps or less, to reduce its
size.
SUMMARY OF THE INVENTION
[0015] Accordingly, in one aspect thereof, the present invention
provides an electrical contactor comprising: a first terminal
connected to a pair of fixed contacts on opposite faces of a fixed
conductive member; a second terminal; a pair of movable arms of
electrically conductive material connected to the second terminal,
and carrying movable contacts at an end remote from the connection
to the second terminal, the movable contacts and the fixed contacts
forming parallel switches and being arranged in first and second
switch pairs; and an actuating arrangement arranged to move the
movable arms so as to open and close the switches, wherein the
actuating arrangement is arranged to close the first switch pair of
contacts before closing the second switch pair of contacts.
[0016] Preferably, the pair of movable arms are arranged in aligned
opposition to each other such that their remote ends are on either
side of the fixed conductive member, with the movable contacts
aligned with the fixed contacts, and are separated by a
predetermined gap over a major portion of their length.
[0017] Preferably, the movable arms are preformed and preloaded so
as to bias them towards each other to engage the fixed contacts
with a preset contact pressure keeping the contacts normally closed
in the absence of a force separating the movable arms.
[0018] Preferably, the actuating arrangement includes a wedge
shaped member disposed between inner inclined surfaces of the
movable arms, arranged to separate the movable arms so as to open
the contacts, the wedge shaped member being movable from a first
position in which it separates the movable arms, to a second
position where it allows the arms to move freely towards each
other.
[0019] Preferably, the actuating arrangement comprises an
electromagnetic actuator coupled to the wedge shaped member and the
movable member, the electromagnetic actuator effecting movement of
the wedge shaped member and the movable member, between the first
and second positions.
[0020] Preferably, ferrous plates are attached to the outer faces
of the movable arms, the arrangement of the fixed member and
movable arms being such that when the contacts are closed, current
flowing through the movable arms and the ferrous plates produces
induced magnetic-field attraction forces between the movable arms
that urges the movable arms towards each other, thereby increasing
the force pressing the movable contacts against the fixed
contacts.
[0021] Preferably, the ferrous plates are attached to the movable
arms along their formed length, whereby when the contacts are
closed, higher current flowing through the movable arms induces
magnetic fields in the ferrous plates, generating a magnetic force
of attraction urging the contacts closed.
[0022] Preferably, the contactor is a two pole contactor having a
pair of first terminals, a pair of second terminals, a pair of
fixed conductive members and two pairs of movable arms.
[0023] According to a second aspect, the present invention provides
a 2-pole electrical contactor comprising: a first terminal
connected to a fixed contact on a face of a first fixed conductive
member; a second terminal; a first movable arm of electrically
conductive material connected to the second terminal, and carrying
a movable contact at an end remote from the connection to the
second terminal, the movable contact and the fixed contact forming
a first switch and being arranged in first switch pair of contacts;
a third terminal connected to a fixed contact on a face of a second
fixed conductive member; a fourth terminal; a second movable arm of
electrically conductive material connected to the fourth terminal,
and carrying a movable contact at an end remote from the connection
to the fourth terminal, the movable contact and the fixed contact
forming a second switch and being arranged in a second switch pair
of contacts; and an actuating arrangement arranged to move the
movable arms so as to open and close the switches, wherein the
actuating arrangement is arranged to close the first switch pair of
contacts after closing the second switch pair of contacts.
[0024] Preferably, the contactor has a plurality of first movable
arms and a plurality of second movable arms.
[0025] Preferably, each movable arm comprises a plurality of
longitudinal sections, each provided with a movable contact at the
remote end and arranged to engage with a corresponding fixed
contact, the current flow in the arms being substantially equally
divided between the sections thereof.
[0026] Preferably, the contacts of the first pair of switching
contacts are larger than the contacts of the second pair of
switching contacts.
[0027] Preferably, the contacts of the first pair of switching
contacts have a thicker top-layer of silver alloy than the contacts
of the second pair of switching contacts.
[0028] Preferably, the contacts of at least the first pair of
switching contacts have a top-layer of silver alloy with
tungsten-oxide additive inclusions in the silver matrix.
[0029] Preferably, the contacts of at least the first pair of
switching contacts have a tungsten rich top-layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Preferred embodiments of the invention will now be
described, by way of example only, with reference to figures of the
accompanying drawings. In the figures, identical structures,
elements or parts that appear in more than one figure are generally
labeled with a same reference numeral in all the figures in which
they appear. Dimensions of components and features shown in the
figures are generally chosen for convenience and clarity of
presentation and are not necessarily shown to scale. The figures
are listed below.
[0031] FIG. 1 is a plan view of a single pole contactor having
bi-blade movable arms, according to the prior art, the contactor is
shown with a cover removed;
[0032] FIG. 2 is a perspective view of the contactor of FIG. 1;
[0033] FIG. 3 is a schematic view of a pair of bi-blade movable
arms according to the prior art;
[0034] FIG. 4 is a schematic view similar to FIG. 3, of a pair of
bi-blade movable arms according to the preferred embodiment of the
present invention, engaging contacts of a fixed member;
[0035] FIG. 4a is a plan view of a variation of the movable arms of
FIG. 4;
[0036] FIG. 5 is a plan view of a two-pole contactor incorporating
the movable arms of FIG. 4, with a cover removed;
[0037] FIG. 6 is a schematic view, similar to FIG. 4, of a pair of
bi-blade movable arms according to a second embodiment of the
present invention, shown in the open position;
[0038] FIG. 7 is a schematic view, of the pair of bi-blade movable
arms of FIG. 6, shown in the closed position;
[0039] FIG. 8 is a schematic isometric view of the movable arms of
FIG. 5 and the associated fixed member and terminals;
[0040] FIG. 9 is a schematic plan view of a two-pole contactor
according to a third embodiment of the present invention;
[0041] FIG. 10 is an enlarged partial view of the contactor of FIG.
9, showing the contacts of one pole in the fully open position;
[0042] FIG. 11 is a view similar to FIG. 10, showing the contacts
in the partially open position;
[0043] FIG. 12 is a view similar to FIG. 10, showing the contacts
in the fully closed position;
[0044] FIG. 13 is a side view of a prior art meter enclosure;
[0045] FIG. 14 is a plan view of the meter enclosure of FIG.
14;
[0046] FIG. 15 is a side view of a meter enclosure according to the
present invention;
[0047] FIG. 16 is a plan view of the meter enclosure of FIG.
15;
[0048] FIG. 17 is a schematic view of a wall box fitted with a
disconnect meter according to the present invention; and
[0049] FIG. 18 is a schematic view of a 2-pole contactor having
lead/lag switches.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Four important improvement concepts (the improvements) will
now be described to illustrate the present invention. Each
improvement will be discussed with reference to one or more
preferred embodiments offered by way of example to describe the
invention. While each concept can be combined with the teachings of
the other concepts, certain concepts can be applied individually to
prior art contactors of different construction.
[0051] FIG. 4 is a schematic view of a pair of bi-blade movable
arms 30 of an electrical contactor, according to a preferred
embodiment of the present invention. Each arm is similar to the
prior art arms of FIG. 3 except that the stiffing ribs 39 are
replaced by ferrous plates, in the form of steel laminations 40,
intimately attached to the outer surface of the arm. The steel
lamination 40 extends over a majority of the length of the arm 30
and preferably extends over the sloped portion 38 and the distal
end 36 of the arm. In FIG. 4, the fixed terminal 22 and the fixed
contacts 23 are shown disposed between the movable contacts 25 with
the arms 30 in the relaxed state such that the contacts are
engaged, known as the closed position. As before, the two arms 30
face each other across a small gap 33 for a majority of their
length. The steel laminations allow the contact arms to be shorter
for the same current rating and also reduces the resistance of the
switch. The steel laminations 40 are fixed to the arms 30 by
riveting, preferably using upset rivets 41 formed in the steel
lamination and passing through holes in the arms.
[0052] This design allows the construction of a smaller,
cost-reduced switch, with shorter, narrower spring-copper
"bi-blades", which would have a lower nominal resistance and self
heating, but which is also capable of generating much larger
magnetic attraction forces, to overcome the inevitably larger
contact Repulsion forces at the greater shared currents, with using
fewer contacts.
[0053] With the standard, longer parallel copper "bi-blade"
geometry, there is a defined magnetic attraction force between them
at high shared short-circuit fault current, the strong individual
magnetic fields being in close proximity to each other, across the
gap, augmenting each other, creating some deflection (inwardly) in
both, and closing the related gap at the same time. If the
short-circuit fault current is very high--as for example during AC
peaks--there is a danger that the blades may deflect too far, touch
and possibly re-bound the contacts off, which will momentarily Open
the switch and destroy the "bi-blade" effect, with potentially
catastrophic explosive consequences.
[0054] FIG. 4a illustrates a variation of the blades shown in FIG.
4. While the steel enhanced bi-blade construction is designed to
avoid using divided blades, for contactors with a very high current
rating, over 200 Amps or for very compact contactors, a steel
enhanced bi-blade switch arrangement may be useful, especially if
the number of longitudinal sections can be reduced by using the
steel laminations. Hence, in FIG. 4a is an example of a steel
enhanced, divided, bi-blade switch of a contactor. The switch has a
pair of bi-blade arms 30 extending from a movable terminal 24 to
which they are riveted (only one visible), to a fixed terminal 22
having fixed contacts 23 opposing movable contacts 25 fixed to the
distal ends of the arms. Each arm is divided into a plurality of
longitudinal sections (two shown) by a slot 43 extending from the
distal end towards the fixed end. Each longitudinal section has a
steel lamination 40 fixed to an outer surface, preferably by use of
an upset rivet 41.
[0055] FIG. 5 illustrates a two-pole contactor 10 with a cover
removed. The contactor has two switch sets 12, one on either side
of a solenoid 16. A lifter 18 is fixed to a plunger of the solenoid
and carries a wedge 50 and two pegs 52 for each switch. The wedge
is disposed between the arms and arranged to separate the arms when
driven into the gap 33. The two pegs 52 are disposed on opposite
sides of the pair of arms in the region of the sloping portion 38.
In the closed position as shown in FIG. 5, the pegs press against
the outer surface of the sloping portion 38 of the arms, either
directly or indirectly via the steel laminations, to urge the
contacts to the closed position. When the solenoid moves the lifter
to the open position, to the left as shown, the pegs disengage the
arms allowing the contacts to open as the wedge enters into the gap
33 moving the distal ends of the arms apart opening the contacts.
In FIG. 5, the contacts are obscured by the lifter 18, however
opening and closing of the contacts can be seen in FIGS. 6 &
7.
[0056] The solenoid 16 may be a self latching solenoid, preferably
a magnetic self latching solenoid which is pulse operated and
spring biased to the closed position. Thus in operation, the
solenoid is pulsed to change state, to latch in the open position
or de-latch to the closed position. This saves energy as the
solenoid is only momentarily energised to change positions.
[0057] The shorter, narrower steel-enhanced "bi-blades" give the
advantage that the switch nominal resistance is typically halved,
while the magnetic attraction forces between the movable arms are
increased by at least a factor of five, as compared with the
standard longer blades of the prior art.
[0058] The plug-in switch terminals or "stabs" for the standard
2-pole meter contactor, are normally tooled from 2.38 mm thick
copper sheet or strip, for plugging-into the meter base sprung
jaws. These copper tooled shapes generate considerable scrap loss.
Since the steel-enhanced switch resistance is typically halved, it
is possible to replace these copper terminals with brass terminals
of the same thickness, achieving a further cost saving of
approximately 40%, due to the price difference between copper and
brass. FIG. 5 illustrates a 2-pole plug-in meter contactor
incorporating the shorter, narrower steel-enhanced "bi-blades".
[0059] The 2-pole contactor has a symmetric layout of the two
steel-enhanced switches with the centrally-placed solenoid 16,
driving a lifter 18 attached to the solenoid plunger, having two
wedges 50 for opening the blade sets. The terminal "stabs" 22, 24,
enable the 2-pole contactor to be plugged into the meter socket. By
making the terminal stabs out of brass instead of copper, the cost
of the contactor is further reduced. The solenoid is preferably of
a long narrow construction, disposed between the two sets of
blades, to allow the contactor to have a relatively small width,
allowing the contactor to fit between the sprung jaws of the meter
socket so that the standard wall box and meter configuration can be
used.
[0060] In the 2-pole contactor shown in FIG. 5, with shorter
spring-copper "bi-blades", the presence of the stiffer steel
laminations 40 attached intimately to the copper arms 30 has
removed the flexibility seen in the standard blade design, which
readily deflected inwardly under high short-circuit fault
conditions, giving some contact wiping which reduced melt-pool
tack-welding.
[0061] There is a concern that under high short-circuit fault
conditions, stiffer arms such as the steel-enhanced bi-blades
described above, may vibrate and bounce off briefly under the
massive blade attraction and contact repulsion forces being
balanced in the strong magnetic fields. Similarly, during nominal
current switching, there is a concern that the rigid blades could
generate some unwanted contact bounce, potentially causing tack
welds, worsening endurance life and contact delamination.
[0062] In order to eradicate these concerns, the contact or distal
ends 36 of the arms 30 of the bi-blades are formed with a flexible
tang 44 formed at one side as shown in FIGS. 6 to 8. As illustrated
in FIGS. 5 and 6, the plunger of the solenoid 16 is attached to a
lifter 18 with wedge shaped extensions (wedges 50) which are placed
between the offset distal ends 36 of the blade pairs, so when the
solenoid is driven, the blades and contacts are opened via the
wedge being moved into the gap 33 between the arms and pressing
against the inner blade faces of the sloping portion 38.
[0063] The lifter 18 also has pairs of "pegs" 52 which sit astride
the outer sides of the sloping blade faces. The pegs 52 are spaced
from the arms 30 when the lifter 18 is in the open position with
the wedge 50 holding the arms apart. When the lifter is in the
closed position, in which the wedge is disengaged from the arms,
allowing the arms to close on the contacts, thus closing the
switch, the pegs 52 engage with and deflect the tangs 44 inwardly,
clamping the contacts gently so to prevent bounce. Also, during
high "carrying" short-circuit and "dead-short" fault conditions,
any vibration due to the massive blade attraction and contact
repulsion forces being balanced, the peg 52 and tang 44 clamping
reaction prevents bounce and spurious contact opening.
[0064] The tangs 44 are formed by making a longitudinal slit 46 in
the distal end 36 of each arm, extending through the sloping
portion 38 of the blade face. The tang does not contact the fixed
contact and thus carries no current. While the tang is shown
extending to the end of the arm, as the pegs only contact the
sloping surface, the tang may be suitably modified and adjusted to
provide a desired level of additional contact pressure. The tang is
not covered by the steel plate 40.
[0065] The flexible tang concept, while shown as part of the steel
enhanced bi-blade construction, could be applied to simple bi-blade
switches to enhance the contact pressure and thus reduce normal
contact resistance and improve resistance to contact bounce during
contact closing.
[0066] In contactors described above, which use multi contacts (up
to 16 in total) for even current sharing at Nominal current or high
short-circuit fault levels, it is important that the contacts used
have adequate "top-lay" silver-alloy thickness, in order to
withstand the arduous current "switching" and "carrying" duties
involved. Typical top-lay thickness of an 8 mm diameter bi-metal
contact is in the range 0.6 to 1.0 mm, which equates to
considerable cost, especially when 16 contacts are used in a 200
Amp, 2-pole contactor as used in prior art designs utilising a
divided bi-blade construction.
[0067] One method of reducing the total silver-alloy cost is to
control the top-lay thickness in some contacts of each switch, by
introducing a special switching concept referred to as "lead/lag",
which lends itself very well to the way the bi-blade arms are
actually adjusted, set up and actuated during the pulse-driven
switching function. This is even more important in the
shorter-blade, steel-enhanced switch proposed above, which only
uses 8 contacts instead of 16. The contacts will be sized to suit
the Endurance life requirements.
[0068] With the "lead/lag" principle, as illustrated in FIGS. 9 to
13, chosen blades 30 and contacts 23, 24 in each set are adjusted
and set up in such a way that during closing of the contacts a
defined but critical time delay is introduced between the contacts
that first closes (the "lead" contacts 60) taking the brunt of the
switching load current, and the delayed contacts (the "lag"
contacts 62) which closes a fraction later in time. This always
ensures that the lag contacts only carry load current, keeping it
relatively clean and hardly eroded. Thus the lag contacts 62 can
have a much thinner top-lay silver-alloy thickness as compared with
the lead contacts.
[0069] On the other hand, the lead contacts 60 taking the brunt of
the switching load current (especially if the load is inductive)
requires a thicker top-lay than the lag contacts, to enhance
endurance life and reduce contact-delamination. Thus when the blade
adjustment, set up and pulse-drive is optimised for lead/lag, it is
possible to make considerable savings with the rationalised
contacts as described.
[0070] It is possible, for example, to optimise a lead/lag contact
set for relatively thick top-lay on the switching lead contacts,
and much thinner top-lay on the carrying lag contact, making a
considerable reduction in the silver-alloy content. Also the
carrying lag contacts may be smaller in diameter.
[0071] In a simple arrangement, the wedge 50 which opens the arms
30 of the bi-blade switch, may be set slightly offset such that the
wedge does not close the contacts or move the arms evenly. In
particular, the wedge 50 will move one arm 30 slightly ahead of the
other arm causing one arm, the lead arm, to close the switch
(movable contact engages the fixed contact) slightly before the
other arm, the lag arm, closes. FIG. 9 illustrates the switching
mechanism of the contactor 10. FIGS. 10 to 12 are partial views
which illustrate one set of switch contacts 23, 25, moving from the
open position to the partially closed position and to the closed
position, on an enlarged scale. In FIG. 10, the contacts are open
with the wedge 50 holding the arms 30 apart, representing an open
switch. In FIG. 11, the wedge 50 has moved to a position
intermediate the open and close positions. At this position, one
set of contacts, the lead set 60 have already made contact and thus
the switch is closed. However, the other set of contacts, the lag
set 62 are still held apart, thus no current can flow through the
lag contacts 62. In FIG. 12, the wedge 50 has moved to the close
position, releasing both arms 30 allowing both sets of contacts,
the lead contacts 60, and the lag contacts 62, to close thus
sharing the current flow through the switch.
[0072] In a 2-pole contactor, each switch may have a lead/lag
contact arrangement as described above. Alternatively, as the two
switches are effectively in series with the load between the supply
terminals, one switch may be designated as the switching switch and
the other switch as the carrying switch. In this case the carrying
switch closes slightly before the switching switch so that it
closes under a no current condition and the switching switch closes
under full load conditions. Thus in terms of timing, the lead and
lag roles are reversed but as before one set of contacts can be of
lower current rating or using less expensive material, saving costs
in the manufacture of the contactor. In this arrangement of 2-pole
contactor, again the timing of the switching operation can be
arranged by suitable positioning of the wedges which separate the
arms, such that on release, one arm or one switch will close before
the other.
[0073] FIG. 18 is a schematic diagram of a 2-pole contactor with
lead contacts set at different switches. The contactor 10 has a
first switch 12 and a second switch 12'. The first switch has a
first terminal 22 carrying a fixed contact 23, a second terminal 24
connected to a first movable arm 30 carrying a movable contact 25
at an end remote from the connection to the second terminal. The
fixed contact 23 and the movable contact 25 form a first switch
pair of contacts 60. The second switch 12' is similarly
constructed. The second switch has a third terminal 22' carrying a
fixed contact 23', a fourth terminal 24' connected to a second
movable arm 30' carrying a movable contact 25' at an end remote
from the connection to the fourth terminal. The fixed contact 23'
and the movable contact 25' form a second switch pair of contacts
62. A solenoid 16 moves a lifter 18 between first and second
positions. A first wedge 50 integral with the lifter moves the
first arm 30 to open and close the first switch. A second wedge 50'
integral with the lifter moves the second arm 30' to open and close
the second switch. The wedges are arranged, preferably by being
offset, such that when the contactor closes, that is going from an
open state to a closed state, the first switch pair of contacts 60
close after the second switch pair of contacts close. That is,
there is a delay in the closing of the first switch compared with
the second switch. In this configuration the contacts of the second
switch take on the role of the lead contacts and handle the
switching load while the contacts 23, 25 of the first switch 12
handle only carrying or load current and thus can be smaller. The
contactor is shown with each switch having two arms but the concept
works with switches having one or more arms.
[0074] There is a distinct cost advantage of incorporating a well
adjusted and set up "bi-blade" set with "lead/lag" contacts as
described above. If not properly pulse-driven, even at nominal
current, some lead contacts can tack weld during operational life,
since with the erosion that occurs, some points on the switched
silver-alloy surface can become silver-rich, which promotes more
tack-welding randomly. This is especially a problem if the
pulse-drive is not strong enough to break the tack-welds that occur
with switching bounce. Also depending on when this might happen
through operational life, a tack-weld could occur during a moderate
short-circuit fault for the same reasons.
[0075] One arrangement to improve this tack weld problem is to use
a silver alloy top-lay which is tungsten rich. In particular, a
special silver alloy top-lay with tungsten-oxide additive
inclusions in the silver matrix, particularly for the lead
switching contact. Addition of tungsten-oxide additive in the
matrix has several important effects and advantages:
[0076] 1) it creates a more homogeneous "top-lay" structure,
puddling the eroding surface more evenly, but not creating as much
silver-rich areas, prone to tack welding,
[0077] 2) it raises the general melt-pool temperature at the
switching point, which discourages tack-welding, and
[0078] 3) because the tungsten-oxide additive is a fair proportion
of the total "top-lay" silver mass, for a given thickness, there is
also a small cost advantage.
[0079] All the improvements described above can be used to create a
smaller, cost-reduced, meter-disconnect contactor, which would
normally be mounted inside a meter casing. This improved design is
smaller than all the existing meter-disconnect contactors, enabling
it to be mounted not only inside the meter casing conventionally,
but also to be moved outside of the meter envelope interface,
either still attached to the under-side of the meter base
enclosure, or integrated and nestled between and within the sprung
jaws of the meter terminal block of the wall-box. The sprung jaws
are the terminals of the meter socket that allow the mains meter to
be simply plugged into the terminal block for easy installation and
replacement. As such the sprung jaws are arranged according to a
fixed conventional layout to allow compatibility between brands and
models.
[0080] The schematic diagrams of FIGS. 13 & 14 show a typical
plug-in meter arrangement with the existing, larger
disconnect-contactor 10 mounted inside the meter casing 70,
notionally plugged into sprung jaws of a meter socket in a
"wall-box" for safely connecting the meter via it's copper terminal
stabs to the supply and load cables mounted in the rear of the
wall-box.
[0081] The existing larger meter-disconnect contactor mounted
inside the plug-in meter casing as shown in FIG. 13 is too large to
be mounted and attached below the meter-base molding, as the meter
"stabs" 74 centers would not be compatible with the sprung jaw
centers in the wall-box.
[0082] To fit between the stabs, the meter-disconnect contactor
would have to be narrower, similar to the improved steel-enhanced
contactor described above, for normal stab plugability of the meter
into the wall-box sprung jaws, as shown in the schematic diagrams
of FIGS. 15 & 16.
[0083] The smaller meter-disconnect contactor 10 able to be
produced using the improvements described above, is able to be
mounted completely outside the meter enclosure 74, either on the
back of the meter enclosure between the meter stabs as shown in
FIGS. 15 & 16 or between the sprung jaws of the meter socket of
the typical wall-box, as shown in FIG. 17, actually switching the
sprung jaw connection.
[0084] In FIGS. 15 & 16, the contactor 10 is directed mounted
to the back of the meter enclosure 74 between the terminal stabs 74
of the meter. Actually, two terminals of the contactor will be
connected to two of the stabs. The meter enclosure 74 has four legs
76 which are disposed close to respective stabs but outside of the
space defined by the stabs. The legs 76 provide some protection for
the stabs during transport and when installed the legs sit against
the wall box or the meter socket to ensure correct positioning of
the meter.
[0085] The 2-pole contactor of FIG. 17 is similar to the contactor
shown in FIG. 5 and described hereinbefore. The contactor 10 has a
symmetric layout with two switches 12 having steel-enhanced blade
sets, and a centrally-placed solenoid 16 driving a lifter 18 for
opening the blade sets. The solenoid 16 is preferably of a long
narrow construction, disposed between the two sets of blades, to
allow the contactor to have a relatively small width, as required
to fit between the meter sprung jaws so that the standard wall box
and meter configuration can be used. The terminals 22, 24, of the
contactor are connected between a sprung jaw on the meter outlet
side and the load connection. This allows the meter stabs to be
plugged into the sprung jaws in the conventional manner.
[0086] A wall box 80 fitted with a disconnect contactor 10 is shown
in FIG. 17. The wall box has a meter socket arrange to receive
stabs from a standard meter enclosure. The meter socket includes a
plug-in terminals known as sprung jaws 82, 83. A supply cable 84
and a load cable 86 and shown entering the wall box and connecting
to cable clamps 90 associated with the meter socket. The supply is
a 2 phase supply with phase wires A1, A2 and an earth or neutral
wire E. The earth wires are shown passing under the contactor where
they are joined together. The supply phase wires A1, A2 connect to
sprung jaws 82 in which meter stabs are to be plugged in to connect
the supply directly to the meter. The meter stabs representing the
outlet from the meter plug into sprung jaws 83 which are isolated
from the cable connectors to which the load cable is connected.
Instead, these isolated sprung jaws connect to terminals (here the
movable terminals 24) of the contactor 10 and the other terminals
(here the fixed terminals 22) of the contactor are connected to the
cable connectors 92 to which the load phase wires A1', A2' are
connected. Thus the supply is fed directly to the meter so that the
meter electronics always has power available and the load is
supplied from the meter via the disconnect contactor 10, allowing
the load to be isolated without turning off the power to the
meter.
[0087] An advantage of mounting the meter-disconnect contactor
outside the meter and inside the wall-box, between the sprung jaws,
is that it would be possible to control the switched "disconnect"
sprung jaw connection, remotely and independently, of the meter
control circuit itself, using telemetry or so-called
"power-line-carrier" data transmission techniques, which are very
well developed. It also allows for a simple arrangement to provide
an independent remote connect/disconnect facility using a simple
plug-in type mains meter without a built-in contactor, which is
typically smaller and cheaper.
[0088] This "integrated" arrangement allows the separation of the
meter and disconnect contactor so that repair or replacement of
defective parts can be carried out quickly and easily without
replacing additional parts which are still in good working order.
It also allows for a remotely controlled "integrated" disconnect
contactor in every wall-box installation for remote control of the
domestic load connection.
[0089] In the description and claims of the present application,
each of the verbs "comprise", "include", "contain" and "have", and
variations thereof, are used in an inclusive sense, to specify the
presence of the stated item but not to exclude the presence of
additional items.
[0090] Although the invention is described with reference to one or
more preferred embodiments, it should be appreciated by those
skilled in the art that various modifications are possible.
Therefore, the scope of the invention is to be determined by
reference to the claims that follow.
* * * * *