GB2154371A - Contact breaker - Google Patents

Abstract

A contact breaker enabling domestic A.C. loads to be broken in response to a remote signal has load carrying contacts (17, 18) which can be separated by for example .5mm by means of an actuator consisting of an electro-magnet energised with pulses of energy from a remote source and co-operating with a permanent magnet armature (25) carrying the moving contact 18 in a very compact arrangement. The applied pulse is of low power e.g. 3 or 4 watts and of short duration compared with the duration of one A.C. cycle. <IMAGE>

Description

SPECIFICATION Contact breaker This invention relates to contact breakers which term can be construed widely to cover generally electric switches in which at least one contact is movable into contact with and out of contact from another contact to make or break an electrical circuit. Operation may be in response to an external signal for example a signal from a control system whether received directly over electrical conductors or by radio.

It may be desired that a short duration pulse signal should be sufficient to operate the contact breaker which then remains operated until a further signal is received for closing the contacts again.

An object of the invention is to provide a design of such a contact breaker which may be capable of breaking a substantial current of perhaps between 30 and 1 OOA while yet the contact breaker is not bulky or expensive The invention may be considered to reside in any of the following features taken either alone or in any combination.

To reduce the disadvantages associated with excessive arcing whilst breaking a current of at least 30 amps, the contacts might be separated by only 0.5, 1.0, or 1.5 millimetres. Alternatively, if a larger separation is used, the speed of opening is kept low, perhaps .03, .1 or .15 millimetres/ millisecond by making the inertia of the moving parts sufficiently high relative to the operating forces.

Operation may be by means of a magnetic actuator consisting of a permanent magnet armature co-operating with an electro magnet.

Thus, command signals might be received as low power pulses, perhaps of 3 or 4 watts of 1, 3 or 10 millisecond duration for energising windings on the electro-magnet in one sense or the other which can be sufficient to switch the armature from one position to another while the permanent magnet is sufficient to hold the armature in that position after the pulse has passed. One of the load contacts can be driven by the armature.

The moving contact may be mounted on a magnetic armature through a spring arm or the like arranged to be deflected after the contacts have been brought together to provide a load biasing the contacts together.

In a compact arrangement of components, a magnetic actuator may be positioned between two power connectors, one of which carries one load contact while the other load contact is positioned adjacent the first load contact and is electrically connected to the other power conductor by a flexible connection in association with a movable component of the actuator.

An electro magnet for use as a component of an actuator of a contact breaker can have a core carrying two electrical windings either of which can be energised in dependence on whether the contact breaker is to be opened or closed.

In a preferred form of magnetic actuator an electro magnet has two spaced poles while an armature is positioned between the poles and has its own pole pieces cooperating with the poles of the electro magnet, the armature being pivotally mounted to be capable of rocking movement in dependence on energisation of the electro magnet. The armature may include a permanent magnet and may carry the moving contact of the contact breaker.

Desirably an extension of the axis of pivotal movement of the armature extends directly between and parallel to the length of the spaced poles of the electro magnet, so producing a particularly compact arrangement.

By virtue of its capability of switching high power in response to low energy control signals, the invention may be particularly applicable in providing a contactor suitable for use in remotely controlled power switching systems, perhaps incorporating microprocessors or similar microelectronic devices, and using radio signals, signals superimposed on the electricity supply, optically transmitted signals, or direct electrical signals. Such systems may be used in controlling either the supply or the consumption of electricity.

The invention is particularly suitable for switching domestic loads which may be no more than about 30 amps. Domestic loads tend to have a high power factor, and so there is likely to be little arcing; this appreciation enables substantial loads to be broken with small contact movement.

The invention may be carried into practice in various ways, and two embodiments will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a rather diagrammatic perspective view of a switch embodying the invention; and Figure 2 is a front elevation of the switch of Figure 1.

The switch of Figures 1 and 2 is required to break a current of 80 amps on a 240 volts 50 cycles per second A.C. supply, preferably at the first zero cross after opening of the contacts using no more than about 3 or 4 watts of power to open the switch.

Operation of the switch may be in response to receipt of an electronic signal which may be conveniently supplied from the mains, or a self-contained source, and capable of giving short operating pulses of one or other polarity depending on whether the switch is to be opened or closed.

Signals from the operating power supply (not shown) are received at a terminal block 11 and supplied to one or other of two windings 1 2 on respective legs of a "U" electro magnet core 14 having poles 15 and 1 6. The windings 1 2 are double windings to reduce flux leakage.

The fixed and moving power switch contacts 1 7 and 1 8 are carried one on a brass block 21 at one side of the electro magnet, and the other on a flexible braid connector 22 screwed at 23 to a brass block 24 at the other side of the electro magnet.

There are conventional arrangements 1 9 for connecting the blocks 21 and 24 in the power circuit. The contacts 1 7 and 1 8 are about one quarter of an inch in diameter and 3/16thus of an inch thick.

For operating the moving contact 10, a magnetic actuator 25 is mounted in association with the magnet poles 1 5 and 16, as can be seen best from FIGURE 2.

The actuator 25 consists of a permanent magnet 26 polarised in the vertical direction as seen in FIGURE 2, together with two ferro magnetic pole pieces 27 each of which is in the form of an elongate strip permanently secured to one face of the magnet 26, and extending to left and to right in FIGURE 2 to be closely spaced above the electro magnet poles 1 5 and 16, or below them as the case may be.The magnet 26 is mounted in bearings 29 to be capable of pivoting about an axis parallel with the lengths of the legs of the core 14, that is perpendicular to the plane of FIGURE 2, so that either the left hand end of the upper pole piece 27 and the right hand end of the lower pole piece 27 are in contact with the poles 1 5 and 1 6 respectively or, the right hand end of the upper pole piece and the left hand end of the lower pole piece are in contact with the poles 1 6 and 1 5 respectively.The magnet 26 ensures that in the absence of magnetisation of the electro magnet, the actuator will be retained in one or other of those positions, in a first of which the contact 1 8 is spaced above the contact 1 7 as shown in Figure 2, whereas in the second position the contact 1 8 is pressed firmaly into contact with the contact 1 7 by means of a spring strip 31 secured to the upper face of the upper pole piece 27, and underneath the braid connection 22. A contact bias is provided by a bent wire spring 41 having a loop 42 urging strip 31 downwards, depending side loops 43 passing around locating pins 44 on either side of the actuator, and ends 45 located against either side of an upstanding pin 46 at the left-hand end of the strip 31.

Movement of the pole piece 27 in the clockwise direction in Figure 2 causes the spring strip 31 and spring 41 to deflect after the contact 1 8 is seated on the contact 1 7 to provide a spring bias urging the contacts together. The strip is formed to provide some wipe of the contact 10 over the contact 1 7 as they close.

It will be appreciated that a positive direct voltage pulse applied to one of the windings 1 2 can magnetise the electro magnet sufficiently to move the magnetic actuator 25 from one position to the other while a similar pulse applied to the other winding can move the actuator back again. After the pulse has passed, the actuator remains in the operated position due to the magnet 26, and there is this pulse-operated, positive action both for opening and closing the contacts 1 7 and 1 8.

The arrangement is very compact. The disposition of the bearings 29 substantially between the legs of the electro-magnet, the disposition of the actuator 25 substantially between the poles of the electro-magnet, the disposition of the connecting blocks 21 and 24 at either side of the electro-magnet, and the disposition of the terminal block 11 near the yoke of the electro-magnet enable the complete switch to be generally within the confines of a hypothetical rectangular block perhaps little larger than a matchbox.

The gap between the contacts 17 and 1 8 when the switch is open may be no more than about 0.5mm but the magnetic actuator is not particularly fast actuating, and provided it can open the contacts in not more than about 5 milliseconds, it has been found that the power current can be broken at the first zero cross of the mains supply after opening. The distance the contact 10 has to move can be as small as necessary to prevent restriking at the mains voltage involved.

The actuator may be quite light and it has to move a very short distance, and can be relatively slow acting as described above, and it has been found that operation can be successively achieved using pulses of energy with a power of 3 or 4 watts lasting for about 60 milliseconds. They can be provided by a capacitor in the operating supply circuit, which can be re-charged within one second without requiring a re-charging circuit with a high rating. For most applications the switch is not required to operate more than once per second.

Preferably, the armature closing movement before contact is made is at least 50% of the total armature movement.

Claims (11)

1. A contact breaker capable of breaking a domestic AC load current (e.g. a current of at least 30 amps) comprising a pair of co-operating contacts one of which is arranged to be moved towards or away from the other by an electromagnetic actuator in response to a low power electrical pule of short duration compared with the duration of one A.C. cycle.

2. A breaker as claimed in Claim 1 in which the actuator includeJan armature in spaced relation to a pole or poles of an electromagnet.

3. A breaker as claimed in Claim 2 in which the armature comprises a pair of parallel spaced ferro-magnetic arms mounted in magnetic circuit on either side of a permanent magnet with one end of each arm on either side of one pole of an electro-magnet and with the other end of each arm on either side of the other pole of the electro-magnet.

4. A breaker as claimed in Claim 3 including a pivot bearing for the armature,the axis of which bearing passes through the permanent magnet.

5. A breaker as claimed in any of the preceding claims in which when moving from the open to the closed position the one contact has to move through at least 50% of the movement corresponding to the total movement of the actuator before it comes into contact with the other contact.

6. A breaker as claimed in Claim 5 in which further movement of the actuator after the contacts come together is accompanied by wipe of one contact over the other.

7. A breaker as claimed in Claim 5 or Claim 6 in which further movement of the actuator after the contacts come together is accompanied by stressing of a spring for providing a bias holding the contacts together.

8. A breaker as claimed in any of the preceding claims in which the one contact is mounted on a flexible conductor capable of carrying 30 or 50 or 80 amps.

9. A breaker as claimed in any of the preceding claims in which the maximum separation of the contacts in the open position is less than 1 mm.

1 0. A breaker as claimed in any of the preceding claims in which the contact can be moved to the open or to the closed position in response to a pulse of energy of less than 10 watts.

11. A breaker as claimed in any of the preceding claims including two load current carrying conductors spaced apart, one of which carries one contact while the other carries the other contact through a flexible lead, the actuator being positioned between the two load current carrying conductors.

1 2. A contact breaker constructed and arranged substantially as herein specifically described with reference to the accompanying drawings.

1 3. A method of breaking an electrical circuit capable of carrying a current of at least 30 amps by use of an electromagnetic actuator in response to a low power electrical pulse of short duration compared with the duration of one A.C. cycle to move one of a pair of load current carrying conductors away from the other.