GB2382467A

GB2382467A - Three blade contactor

Info

Publication number: GB2382467A
Application number: GB0128106A
Authority: GB
Inventors: Richard Anthony Connell
Original assignee: BLP Components Ltd
Current assignee: BLP Components Ltd
Priority date: 2001-11-22
Filing date: 2001-11-22
Publication date: 2003-05-28
Anticipated expiration: 2021-11-22
Also published as: GB0128106D0; AU2002343068A1; WO2003046936A1; GB2382467B

Abstract

An electrical contactor has a contactor blade 104 which is movable to make or break contact with a fixed contact 110 or a set of fixed contacts. The contactor blade 104 comprises a plurality of contact elements 106 and the contactor incorporates an actuator 112 for driving a first set of the contact elements between the open and closed positions. A bridge element links the first element set to a second set of the contact elements for transferring the actuator drive from the first element set to the second element set.

Description

Electrical Contactor Apparatus and Method The invention relates to an electrical contactor and method, and in particular to an apparatus and a method for switching a mains power supply.

The distribution system in North America is such that domestic premises are fed with a 2-phase (180 phase relationship) utility supply, the local transformer centre tap giving an artificial Neutral for normal low-current loads at 115 V, while the voltage across phases is 230 V for power loads such as air-conditioning, motor drives and heaters. The local transformer primary is usually fed from an overhead fused 25 KV supply, so that the contactor switch contacts must safely withstand any reasonable short-circuit fault on the load side of the meter.

Granted Patent GB 2 322 971 describes the basic arrangement of the BLP Components 200 Amp, 2-pole,"twinbladed","blow-on"modular contactor, which was designed for the North American electricity metering markets. The contactor is illustrated in figure 1 and switchably isolates, on both poles, the mains electricity supply (Utility) from the domestic (metered) load. In the USA, the mains electricity supply to a domestic residence is typically supplied via utility feed cables which terminate at contacts mounted within a circular plastics housing of about 25cm diameter, termed a meter base or socket adaptor. An electricity meter housed in a substantially cylindrical housing of corresponding diameter can be connected to the meter base. The BLP components modular contactor is housed in a substantially cylindrical plastics housing of the same diameter and forms a selfcontained module, with heavy duty inlet and outlet copper

terminations, for coupling between the meter base and the meter, using sprung-jaw connections.

This contactor is electrically switchable, by means of a solenoid, and may be remotely operated. It can therefore be incorporated with Aut omatic Meter Reading (AMRi, prepayment, billing and communication systems, wrth the option of remote disconnection and reconnection of the domestic customer's supply. For safety reasons, reconnection of power requires manual intervention/Reset by the customer.

As described in GB 2322971 this contactor has several advantages over prior art designs which utilise mechanical-latching actuation and snorting-bar contacting switches requiring large coil drives of the order of 2 kWatt for satisfactory operation. On tne other hand, the BLP design uses an efficient magnet-latching solenoid actuator requiring only about 30-40 Wa pulsed coiJ drives, and a patented"blow-on"folded-back twin-blade layout, which utilises the large magnetic fields generated to good advantage, especially during high-current-fault conditions.

In existing contactors used for this type of application, disconnection isolation is only nominal complying with for example UL 508 which requires 3/8"Creepage/Clearance distance between live switch parts and the actuation means, which is considered as the User Interface. This is generally sufficient for load switching, but not for full "Service Disconnect", which demands 3mm minimum open contact gap, and 3/4"Creepage/Clearance as well. It is an object of the invention to overcome this problem.

Additionally, in recent years, electricity meters have been dramatically reduced in size due to improved energy measuring techniques and integrated electronics, to such an extent that the contactor size now represents a major part of the meter space envelope. Simply reducing the size of existing contactor designs disadvantageously results in greater temperature rise within the meterbase/socket-adaptor, predominantly due to the self-heating of the various copper bus-bars, blades and contacts employed in the switch constructions, particularly at maximum load current of 200A. In some instances, meter and contactor combinations have had to be derated to, say, 160A as a result. It is a further object of the invention to address this problem.

The invention in its various aspects provides a contactor apparatus and method and a contactor blade assembly and method as defined in the appended independent claims.

Preferred or advantageous features of the invention are set out in dependent subclaims.

In a preferred embodiment the invention thus provides a contactor blade assembly which comprises three moving blade elements. The blade elements are arranged in a row and cantilevered from a base, each extending parallel to the others from the base to a tip near which it carries a contact electrode. At their tips the blade elements are linked by a bridging element. In the embodiment an actuator drives a first set of the blade elements, namely the outer elements at the ends of the row of elements, between a contact-open position, in which the contact electrodes are spaced from a corresponding set of fixed electrodes, and a contact-closed position, in which the contact electrodes are urged against the fixed electrodes.

The bridging element transfers the actuator drive from the

first set : of blade elements to a second set, namely the inner element positioned in the row between the outer elements.

Advantageously, the bridging element may either be ~j eleME, n-L ma-, either be fabricated separately from the blade elements or form an integral part of one or more blade elements. In the latter case, for example, a portion of one element may extend to overlap another element so as to link their motion.

Pre-lerably the brid Preferably the bridging element is situated at a portion of the blade elements which do not carry significant current, such as beyond the contacts carried by the blade

elements. A7 elements. Alternatively the bridging element may be nonricicincj e conducting, allowing more freedom to site it without affecting the electrical performance of the contactor.

Advantageously the bridging element is shaped so that as the blade elements are driven, the inner element moves ahead of the outer elements so that it reaches the contact-closed position before the outer elements. The inner element (the second set of elements) thus acts as a sacrificial electrode.

Similarly, it is preferable to shape the bridging element so that when the outer elements are driven to break the contact, the inner element moves away from the contactclosed position just after the outer elements.

Preferably the bridging element is resilient and is fabricated so that when the first set ol elements is in the contact-made position and is urged against the fixed contact (s) with a predetermined force, the bridging element urges the second set of elements against the fixed

contact (s) with a predetermined force. If all the blade elements are of similar construction, the predetermined contact forces for each can advantageously be set to be substantially equal.

In a particularly preferred embodiment, the blade elements are resilient and their neutral position is the contactopen position. The bridging element is then either fastened to one or more elements in the second element set and has a resilient portion extending in front of one or more elements in the first (driven) element set, or is fastened to one or more elements in the first element set and has a resilient portion extending behind one or more elements in the second element set. In both cases the driven elements in the first set urge the bridging element, and thus the second set of elements, from the contact-open position to the contact-closed position, and when the first element set is driven to the contact-open position, the second element set returns to the contactopen position through its own elasticity.

In a particularly preferred embodiment, a three-element moving blade is used in each of two contact sets in a twopole contactor of similar layout to that of figure 1.

This advantageously enables a compact contactor which gives less self-heating than prior art contactors. For example, a contactor of similar layout and size to that of figure 1 may be fully rated at 200A when switching a US mains supply. Additionally, the layout, construction and actuation-means can be changed to give 3mm minimum open contact gap, and 3/4"Creepage/Clearance isolation as well.

In the prior art contactor of figure 1, two-element moving blades are used. The load current is shared equally

through each half-blade and contact. Since these two are in parallel, they give a total switch resistance of about 0. 25mOhm, and a self heating of 10 Watts per side, or 20 Watts in total, at 200A maximum current. This typically represents a temperature rise of approx 0"C within a meter-base/socket-adaptor housing, whic ; can exceed the allowable meter specification limit of 85 C under certain conditions. For the proposed new electronic meters, much lower temperatures are desirable.

With the new tri-blade design, widei inet bus-bars and "triple" blades can be employed on each side, which now being three in parallel reduces the total switch resistance to about 0. 15 m.Ohm, giving a self-heating of only 6 Watts per side, or 12 Watts n total, at 200A maximum current. This Level of self-healing represents a reduced temperature rise of about 3 :. -40 C (instead of 50 C), some 10-15"C cooler than the contactor of figure 1 This reduced temperature rise may advantageously allow closer integration of the contactor and the metering or

--rc,-iics-D switching electronics, particularly as ower temperature rises may allow less costly, lower performance, electronic components to be used.

It is particularly desirable to be able to integrate a contactor and an electricity meter into a common housing in order to reduce the overall size of the appliance. In this context the use of multi-element blades enabled by the apparatus and method of the invention is particularly advantageous as it reduces electrical heating during normal use and during failures. A contactor and a meter, even an electronic meter, may then be integrated in a single housing of compact size.

It is also desirable to install other electronic components within the same casing as a contactor. For example remote switching of a mains supply contactor enables an electricity supplier to cut off the supply to a user who has not paid their bills. It is desirable however to let such a user retain a limited supply up to, for example, 5A or lOA for safety reasons. An electronic current limiter may be integrated with the contactor of the invention due to the low heating of the contactor and may be used to switch off the supply whenever more than preset maximum current is drawn. The current limiter may sense current by using coils surrounding the bus bars leading into or out of the contactor and may be remotely controllable by the electricity supplier or locally controlled for example if payment is made using a coinbox.

Specific embodiments and the best mode of the invention will now be described with reference to the drawings, in which; Figure 1 is a plan view of a prior art contactor; Figure 2 is a cut-away view of a contactor according to a first embodiment of the invention implemented as a modular contactor; Figure 3 illustrates the installation of a modular contactor between a meter base and an electricity meter; Figure 4 is a plan view of the contactor of the first embodiment; Figure 5 is a three-quarter view of a three-element contactor blade of the contactor of figure 4;

Figure 6 is a cut-away, three-quarter view of the contactor of figure 4 ; Figure 7 is a further cut-away, three-quarter view of

the contactor of figure L ; Figure 8 is a three-quarter view of the actuator of the contactor of figure 4 ; Figure 9 shows the upper short half-lifter of the contactor of figure 4 ; Figure 10 shows the lower short half-lifter of the contactor of figure 4; Figure 11 shows the upper 10D ? half-lifter of the contactor of figure 4; Figure 12 shows the lower long half-lifter of the contactor of figure 4; Figure 13 is a perspective view of the moving blade of the contactcr of figure 4 ; Figure 14 is a side view of the moving blade of the contactor of figure 4; Figure 15 is a plan view of the moving blade of the contactor of figure 4; Figure 16 is a perspective view of the bridging element of the contactor of figure 4 : Figure 17 is a side view of the bridging element of the contactor of figure 4 ;

Figure 18 shows top, bottom and end views of the bridging element of the contactor of figure 4.

Figure 2 shows a contactor according to a first embodiment of the invention implemented as a modular contactor 50 for installation between a meter base 52 and an electricity meter 54, as illustrated in figure 3. The contactor 56 is shown in plan view in figure 4.

The contactor comprises a moulded plastics casing 60 forming a base in to which are mounted two separate balanced and symmetrical switching systems.

In order to avoid unnecessary repetition of references in the drawings, only the left-hand parts of the switch will generally be referred to, it being understood that the right-hand parts are essentially similar except where specifically stated.

Power is fed to the contactor from an inlet bus-bar 100 which is connected by a thin spring portion 102 to a three-element moving blade 104 having three inlet contacts 106 formed at the ends (see also Figure 5). Power is delivered out of the contactor from an outlet bus-bar 108 which has three fixed contacts 110 for mating with the inlet contacts 106.

Mounted centrally between the ends of the outlet bus-bars 108 is a solenoid actuator 112 comprising a ferrous plunger 114 slidable within a solenoid drive coil 116.

A spigot 118 connected to a yoke 120 engages loosely within an aperture 122 in the plunger 114, to which it is connected by a pivot pin. At each end of the yoke 120, its lower face engages with a compression spring 124,

while a pair of projections 126 on its upper face engage with a pair of shaped leaf-springs i28, held at their centre by a pin 130 of a holder cast-rrom aluminium.

The end of each spring 128 engages In a slot of a moulded sliding lifter 132 of which the opposite end engages with one of the blades 104.

It should be pointed out here that the Layout of the blades 104 is not only mirrored, but is symmetrical and balanced about the axis of the colenid actuator 114, thus presenting a consistent deflecting anc actuating force via the two pairs of lifters 132 to each set of contacts in turn.

The moving blade 104 is thinned at one end for flexibility and suitably attached to the bus-bar 10 by soldering, brazing or ultrasonic welding. During manufacture of this assembly it is important not to generate excess heat, which could seriously distort the shape of, or affect the spring quality of the moving blade. Each assembly is tightly located and contained in slots and barriers within the moulded casing 8. Suitable barriers within the casing provide the required safety isolation between the two individual switches which are at mains supply voltage, and the drive coil 116 which is at low voltage.

The feed bus-bar 100 anc. moving blade 104 are formed in such a way that they lie parallel to each other for a certain distance, with a small defined gap between, along their length. A larger gap exists at the flexible attachment of the spring portion 102 where the blade is relatively weak, to prevent damage when loaded under fault

conditions. This blade arrangement-s the basis of the so-called"blow-on"layout (as descr'bed and claimed in UK

Patent Application Serial No. 2295726) which is designed to give increased contact force and hence superior switching performance, especially under excessive or short-circuit current fault conditions.

Under such excessive/short-circuit fault conditions the current in the feed bus-bar 100 is in the opposite direction to that flowing in the respective adjacent moving blade 104, so that electrodynamic forces are generated between them, trying to force them apart. The force is approximately proportional to the square of the current. Since the feed bus-bar 100 is comparatively rigid, these forces act directly upon the moving blade, thus increasing the forces between the contacts 106,110 over and above the optimal overtravel force which is set when the solenoid adjustment takes place.

As shown in figures 4 to 8, adjacent its contact end the moving blade 104 is formed with a slightly U-shaped portion 134 which engages with the sliding lifter 132.

As shown in figure 8, and in more detail in figures 9 and 12, the sliding lifter comprises upper and lower halflifters, each of which engages at its rear end with one of the two leaf springs 128 of the contactor's actuator assembly and carries a hook 136,138 at its front end.

The half-lifters engage each other and are slidably mounted in the contactor housing. The hooks face away from each other and each engages the U-shaped portion of one of the two outer elements 104A, 104C of the three contact elements of the moving blade 104. Movement of the slider thus drives the outer elements towards and away from the corresponding fixed contacts 108A, 108C. In addition, a portion of each hook passes between the respective outer element and the inner, or central,

coneact element 104B, maintaining the spacing therebetween during operation of the contactor.

The leaf-spring holder is freely pinned to the solenoid actuator plunger and lies symmetrically between the two lifter/moving blade systems, to ensure tnat actuation forces translated from trie solenoid plunger to the blades via the two leaf springs are evenly distributed on both sides, thus giving similar, distributed contact forces and reliable switching.

In the three-element moving blade, the outer elements 104A, 104C are driven by the actuator. The inner element 104B is linked to the outer elements by a bridging element 140 so that it moves with them. Tne bridging element is positioned at the end of the moving blade, beyond the contact electrodes, as shown in figures b to 7. Figures 13 to 15 show the moving blade without the bridging element fitted and figures 16 to 18 show the bridging element itself.

The moving blade 104 comprises three parallel blade elements each carrying an electrode 186 near its tip. The root 102 of each element is integral with a common blade base 142, and is thinned to allow the element tips to move to make and break contact with the fixed electrodes 110.

The bridging element 140 is fabricated from spring steel.

It comprises a central portion 144 whLch Ls bent to fit over and grip the tip of the inner element 104B of the moving blade. The central portion includes a flat section 146 from which a tab 138 protrudes, so as to clip into a corresponding hole or recess 148 in the surface of the inner blade-element tip adjacent the electrode and secure the bridging element in place. From the flat section,

leaf springs 150A, 150C extend towards both outer blade elements. Each leaf spring is formed with a dimple 152A, 152C which bears on the flat surface of the respective outer element, adjacent the respective electrode, during use.

Each blade element is formed so that, when no force is applied to it, it rests in the contact open position. When the solenoid actuator 112 is operated to make the contact, the half-lifters draw the outer elements 104A, 104C into contact with the fixed contact electrodes 110 and urge them against the fixed contact electrodes with a predetermined contact force; the force is preset by the strength of the actuator leaf springs and the solenoid position. As the outer elements move, they bear on the dimples in the bridging element leaf springs and move the inner element into contact with the fixed contact electrodes 110, and urge it against the fixed contact electrodes with a predetermined force; this force is predetermined through selecting the strength and shape of the bridging element leaf springs and the position and throw of the solenoid.

In addition, in a preferred embodiment, the bridging element leaf springs are shaped so that the inner element provides a sacrificial electrode, moving ahead of the outer electrodes and making an early closure with its fixed contact electrode, just before the outer elements make contact. Preferably, the inner element moves about 0. 25mm ahead of the outer elements.

The pre-tensioning of each leaf spring, both in the bridging element and the actuator, is designed in such a way that at the end of overtravel stroke all three contacts of both sets receive approximately the same,

consistent nominal contact : closure force. Also. since the ; layout utilises the"blow-on"electrodvnamic force, now distributed in a"tn-blade"contact sec (instead or a "twin-blade set as in the prior art. ; a considerably lower nominal contact force may be applied for operation at normal current levels (in this case 200 Amps rms).

Advantageously, each contact force in tie set may be lower, in the region of 150-250 gF, inn'-ead of 300-400 gF as used with the "twin-blade" version previously, making even less demands on the solenoid drive requirements. In reality, a safe margin is set tc allow for reliable operation and possible contact erosion through the life of the contactor.

This is the basis of a "tri-furcated sacrlf1cial" contact pair/set, the central contact taking tne brunt of the early closure and late c'pening, which together with the outer contacts carry the load current. In practice, all three contacts should share the load current equally.

This arrangement has the inherent advantage of lower contact resistance and reduced self-heating.

In order to achieve 3/4"Creepage/Clearance distance, bv comparison with the contactor of GB 232) 971, the lifter sets on each side are lengthened by approx 4mm, and the solenoid moved outward on axis to suit. The solenoid assembly and adjusting means of screw fixing and glueing are predominantly the same as before.

The advantages of three-element contacts with a sacrificial contact pair include the as following : a) Since the total load current is equally shared

between three contact sets, the total heating effect is approximately reduced by a factor of three. b) This reduction of the load current through each pair of"sharing"contacts more than halves the total resultant contact repulsion force which is attempting to open the contacts. c) The combined effect of a) and b) above allows a lower actuator leaf spring force to be utilised. This also makes the blow-on layout less critical, while still giving an improved reliable switching life to the contactor.

Alternatively it may allow a more compact, lower power solenoid and actuator to be used.

The solenoid actuation is latched by rare earth magnets 152 and only requires a short DC pulse for its operating and release functions, the latched hold force being considerably greater than the total contact force exerted via the double leaf-springs 124 of the actuator. This surplus hold ensures that the contactor function is not susceptible to shock and vibration, or excess current forces.

The actuator thus being magnet latching, and only requiring a short momentary DC pulse to perform the operating and release functions, no quiescent power is necessary. This virtually eradicates any self-heating, as is the case in a non-magnet latching solenoid. In the embodiment, typical coil actuation power is only of the order of 20 to 30 W (compared with 2000 W for the known contactors cited earlier), with actuation times of typically 20 ms.

To assist the release function, the two push-off springs are located between the leaf spring header a d the contactor casing. The solenoid axial position is adjustable so that a minimum contact force is achieved, which is then fixed witr, a pair of scrsws in holes in the casing, and glued for aoded retention during the contactor life. A moulded top cover provided witn suitable catches tightly contains and integrates the entire assembly within the casing.

Claims

Claims 1. A contactor comprising a contactor blade having a plurality of contact elements, an actuator coupled to a first element set for driving the one or more elements in the first element set to make or break an electrical contact with an opposing contact, and a bridge element linking the first element set to a second element set for driving the one or more elements in the second element set to make or break contact with the opposing contact.
2. A contactor according to claim 1, in which the contact elements are coplanar and parallel to each other, and each is cantilevered at one end and carries an electrode at the other.
3. A contactor according to claim 1 or 2, in which the contactor blade comprises three elements, of which the first element set comprises two outer elements and the second element set comprises the remaining element, positioned between the two outer elements.
4. A contactor according to any preceding claim, in which the bridge element links the second element set to the first element set so that, when the actuator drives the first element set to make a contact, an element in the second element set makes contact before any element in the first contact set.
5. A contactor according to any preceding claim, in which the bridge element links the second element set to the first so that, when the actuator drives the first element set to break a contact, an element in the second element set breaks contact after any element in the first set.

<Desc/Clms Page number 18>
6. A contact-cor according to any preceding claim, in which the bridge element is resionent and is arranged se that when a contact is made, all elements in the first and second element sets are urged against the opposing contact with substantially equal force.
7. A contactor according to any preceding cJaim, in which the bridge element comprises a leaf spring which 18 securable to an element in the second element set and bears on an element in the first eJement set.
8. A contactor blade for a contactor as defined in any preceding claim.
9. A method for operating a contactor comprising a

contactor blade having a plurality of contact elements, comprising the steps of ; using an actuator to drlve a first contact element or set of contact elements to make or creak contact ; and transferring the drive motion from the first element or set of elements to a second contact element or set of contact elements by means of a bridging element linking the first and second contact elements or sets of contact elements.