GB2127224A - A contactor for the control of electric motors - Google Patents

Abstract

First and second contactors are arranged within a common housing 20 and their contacts are closable by respective electromagnetic means each comprising a fixed core 1, coil 3 and armature 2 acting on bridges 10 carrying movable contacts 18a. Fixed contacts are carried on a common U-shaped support 11 provided with common terminal 12, and other fixed contacts 18 are carried on supports 13 with terminals 12A, 12B. A mechanical interlock, provided by the interengaging ends of the movable contact carrying sleeves 4 attached to electromagnet armatures 2, prevents simultaneous closure of both sets of contacts. Each electromagnetic means may act on a group of such contacts. <IMAGE>

Description

SPECIFICATION A contactor for the control of electric motors Electromagnetically operable contactors are known for controlling electric motors. In the simplest case, two contactors are arranged adjacent one another on a base plate. The terminals of the two contactors are interconnected in accordance with a specific pattern so that the switches of one contactor are closed when the motor is to run in one direction, and the switches of the other contactor are closed when the motor is to run in the reverse direction. In one conventional arrangement of two contactors, seven individual connecting conductors are required and in a conventional arrangement of three contactors, twelve conductors are required.The assembly of such a control arrangement is a very expensive operation since the wires used to connect the terminals of the contactors must be cut to length, stripped of insulation, bent to shape and fitted into place. A further disadvantage of the known contactors is the comparatively large space which they occupy, in particular a large area on the base plate, and the need for an electrical interlock to prevent simultaneous closing of the switches of both contactors and short circuits caused by vibrations.

The proposal made herein overcomes these various problems. Briefly, to save space, two contactor units are integrated into a common assembly with the switches of both units arranged generally opposite each other. The movement of the movable switch contacts of both units may be related to a common axis, so that one switch is closed by displacing the movable contact in a first direction, whereas the switch arranged opposite to it is closed by displacing its movable contact in the opposite direction. This arrangement permits the use of a simple mechanical lock-out, since a part associated with one of the movable contacts may serve to block movement of a part associated with the other.The number of electrical interconnections to be made may be reduced by providing the live contacts (or the live contacts of a respective phase) on a common U-shaped contact support which may be mounted on a beam extending transversely across a common housing in which all of the parts are contained. A terminal for connection of the live conductor may be fitted to the Ushaped contact support on or in the region of its web. By making use of a contactor incorporating two contactor units, the base area previously required by two contactors may be halved, and the volume occupied reduced by approximately one quarter, while the number of connecting wires may be reduced from seven to four.A corresponding saving in connections and space may be achieved by moving a contactor in accordance with the present proposal in combination with a conventional contactor in place of a group of three such contactors.

A contactor in accordance with a preferred construction shortly to be described in detail comprises first and second movable contacts and first and second fixed contacts disposed between the movable contacts. The first movable contact is displaceable into contact with the first fixed contacts so as to make a first circuit, and the second movable contact is displaceable into contact with the second fixed contacts so as to make a second circuit.

This arrangement is repeated for each pair of circuits required as will be the case in three phase operation. The live first contacts are carried on respective limbs of the U-shaped contact support which is fitted with the terminal for the live conductor. With this arrangement, the neutral fixed contacts may be carried on respective further contact supports, each of which is fitted with a terminal. One of the further contact supports may have a cranked portion extending away from the other further support, whereby the neutral terminals are spaced from each other by a greater distance than the neutral contacts themselves. The movable contact or contacts of each unit may be associated with a respective electromagnetic operating system, and both systems may be contained within the common housing which may be subdivided into sections.Each electromagnetic operating system may include a coil mounted between transverse plates of the housing and thus be fixed in the axial direction, and an armature guided in a tubular guide portion of the housing. Thus, two contactor units which are often all that is required for controlling one electric motor, constitute one simple constructional assembly. A compression spring may be employed to bias the armature of each magnetic system in the direction appropriate to opening the switches controlled by that system.

As mentioned above, a particular advantage gained by giving the movable contacts a common axis of movement is the possibility of employing a very simple lock-out mechanism, in which a part associated with one magnetic system blocks movement of a part associated with the other so that they cannot simultaneously adopt the operating positions. In the preferred arrangement shortly to be described, the armature of each magnetic system is guided in its pertaining tubular guide by means of an armature sleeve connected to an extension having a slot for seating the pertaining movable contact. The extension may have a slot for a plate which serves as an abutment for a contact spring and which may be equipped by way of a stirrup with a cooling plate for the movable contact.

The contact spring permits the movable contact to yield relative to the armature. Con sequently, although the movable contact is suddenly brought to a halt when it meets the fixed contacts, the armature with its associated sleeve and extension may continue to move through a short distance. The distance between the mutually facing sleeve extensions, when the contactor is contact-less, may be greater than the distance between the switch contacts, and those of the contact connector and contact terminals respectively.

The possibilities of use of the contactor described above may be increased with the addition of no more than a few components.

In particular, auxiliary contacts may be arranged in chambers within the housing adjacent to the main contacts, the auxiliary contacts being reversible from the normally open position to the normally closed position. In this way, the use of the contactor may be doubled by changing or commutating the aux iliary contacts. The auxiliary contacts may have cranked portions, adjacent which are screw-threaded holes for the screws of the terminals. The auxiliary contacts may be clamped in apertures of the housing which extend from the auxiliary contact chambers to the chamber in which the main contacts are disposed. The apertures have, on mutually facing sides, grooves for contact plates situated on the auxiliary contacts, against which the contact plates of the movable contacts bear.This commutating of the auxiliary contacts is also possible subsequently, without the contactor needing to be dismantled for this purpose.

For change-over contactors, at least two normally closed contacts and two normally open contacts must be present. Where contacts are present which have four switch chambers with small switching capacities (up to 9 amps) the auxiliary contact can be replaced by a main current contact. This is not possible for larger switching capacities, because there are only three main switch chambers and no main current contacts with fit into the auxiliary contact chambers. It has hitherto therefore been necessary in the known arrangements to use two contactors for commutating.

The contactor described above may be modified by omitting the electromagnetic operating system pertaining to the upper of the two units. A restoring spring may then be supported in a section of the housing opposite to the remaining electromagnet an can act by way of a hood or the like upon a sleeve in which a switch contact is axially guided against the pressure of a contact spring. This part of the housing may then be used for making other connections. When the lower movable contact is in its closed position, the upper contact is positively opened by the mechanical interlocking. It is closed by the restoring compression spring which is stronger than the contact spring, which is then compressed. The contact spring bears against a further switch contact which is guided together with that already mentioned in a slot in the sleeve.Opposite to the sleeve acted upon by the restoring compressing spring is a sleeve carrying further switch contacts, which is connected with the movable component of the magnetic system of the directly controllable contactor. Only a few contactors are therefore needed for a plurality of switching possibilities. The lower part is always the same, whereas the upper part may either incorporate an electromagnetic operating system or the restoring spring arrangement together with further connections. In additon, the commutatable auxiliary contacts are present. With these components, contactors may be used as reversing contactors and as change-over contactors even at fairly large switching capacities and up to three-pole commutation, one chamber still remaining free for auxiliary contacts.

In the drawings: Figure 1 is a longitudinal section through a contactor for the making and breaking of two groups of circuits, Figure 2 is a section taken on the line ll-ll in Fig. 1, Figure 3 illustrates the wiring arrangement and Fig. 3a the disposition on a base plate of the contactor shown in Fig. 1, to demonstrate the savings in connections and space compared with, Figure 4 which shows the conventional connections and Fig. 4a the conventional disposition on a base plate of a pair of contactors, Figure 5 shows the connectors and Fig. 5a the disposition on a base plate of a contactor as shown in Fig. 1 in combination with a contactor for making and breaking one group of circuits to illustrate the saving in connections and space compared with, Figure 6 which shows the conventional connections and Fig. 6a which shows the conventional disposition on a base plate of three individual contactors, Figure 7 is a section taken on the line Ill-Ill in Fig. 2, Figure 8 is a section taken on the line IV-IV in Fig. 7, Figure 9 is a view looking the direction "A" of Fig. 8, and Figure 10 is a longitudinal section through a changeover contactor.

Referring first to Fig. 4 and 4a, a control system of known type for an electric motor includes two separate contactors A and B mounted side by side on a base plate. Each contactor incorporates four switches operated by an electromagnetic system. The switches are interconnected in accordance with the wiring diagram shown in Fig. 4 to enable the lines of the three-phase system to be made in two alternative configurations for driving the motor in either direction, or breaking the circuits altogether. The electromagnets are wired appropriately to ensure that the switches on both contactors cannot be closed simultaneously. To assemble the control system both contactors must be mounted on the base plate and the wires 1 9 interconnecting the terminals of the contactors cut to length, stripped of insulation at the ends, and fastened to the terminals.These operations must be carried out on seven individual wires.

In accordance with the present proposal as shown in Figs. 3 and 3a, a common housing contains upper and lower contactor units A and B which perform the functions of the two separate contactors shown in Figs. 4 and 4a.

Furthermore, the interconnections designated 11 are constituted by built-in conductors, so that only four wires 1 9 need to be applied during assembly. As all of the switches are disposed within the common housing, the space requirement on the base plate is reduced by one half. There is also a substantial reduction in the total volume occupied by the control system.

Referring now to Figs. 1 and 2, the housing of the contactor is designated 20 and it is shown to be bolted onto the base plate depicted at 24. Each of the interconnections 11 shown in Fig. 3 is constituted by an electrically conductive contact support in the form of a strip formed into a U-shape and fixed to a tranvserse beam 21 of the housing. In Fig. 1, only one contact support 11 is visible and will be described hereinafter together with the associated parts, but it will be appreciated that three such supports are arranged in a row at the edge of the beam. Also mounted on the upper and lower surfaces of the beam are conductive contact supports 1 3 to which respective neutral terminals are fitted. Each of the contact supports has a respective contact plate 1 8 adjacent the end remote from the terminal.The beam is apertured in the region between adjacent contact plates to permit the passage of the operating system. The lower of the two contact supports 1 3 has a cranked portion 1 4 so that the neutral terminal 1 2a is spaced from the neutral terminal 1 2b by a greater distance than the two contacts 1 8.

The terminals 12, 1 2a and 1 2b are readily accessible from the exterior of the housing as can readily be seen, thereby facilitating the connector of the live and neutral conductors.

A circuit may be completed between the contact plates on the upper side of the beam or between the contact plates on the lower side of the beam by means of a movable switch contact including a conductive yoke 10 fitted with contact plates 1 8. The movable contacts of each contactor unit are displaceable by an electro-magnetic system pertaining to all those contacts and disposed at the appropriate end of the housing. Each of the two systems includes a coil 3 arranged at a respective end of the housing and held by a transverse plate 22 of the housing. The coil surrounds a fixed core 1. A movable armature 2 is fitted in a sleeve 4 which is guided in a tubular guide 23 of the housing. The base 5 of the sleeve is integral with or fixed to a row of extensions 6, each of which is formed with vertically extending slots 7 and 8.Each yoke 10 is received within the slot 7 of a respective extension. The slot 8 of each extension receives a plate 1 5 which serves as an abutment for one end of a compression contact spring 9 which bears against a stirrup 1 7 of a cooling plate 18. The cooling plate bears against the yoke 10 as best seen in Fig. 2.

The slot 8 extends through substantially one half the length of the contact spring 9.

As shown in Figs. 1 and 2, the magnetic system of unit A is in its energized condition, and that of unit B is deenergized. Upon energization of the magnetic system, the armature is attracted into contact with the fixed core 1 thereby to advance the sleeve and sleeve extension as far as possible in the axial direction. Assuming that the sleeve of the other contactor unit has been fully retracted, there is a small clearance between the ends of the sleeve extensions 6 of the two units. If the sleeve extensions of the deenergized contactor units had not fully retracted they would be driven home by the advancing sleeve extensions of the energized contactor unit.

Each of the yokes 10 is carried with its sleeve extension so as to bring the movable switch contact plates 1 8a into contact with the fixed contact plates 1 8 on the contact supports 11 and 13, where they are held under the bias of the contact spring 9. Lost motion then takes place between the yoke 10 and the sleeve extension as the latter continues to advance and the yoke is pressed back in its slot against the spring bias.

Retraction of the sleeve and sleeve extensions of the deenergized contactor unit is carried out by restoring springs 25 arranged between the sleeve and a transverse plate 22a of the housing. As made clear above, any failure of the restoring springs to operate fully cannot lead to simultaneous closing of all switches because of the effective mechanical lock-out provided between the ends of the sleeve extensions.

Reference has already been made to Figs. 3 and 3a and 4 and 4a from which it will be seen that in a contactor according to the present proposal, only the four lines 1 8 have to be fitted in accordance with the desired circuit arrangement, the connections 11 already being effected by the built-in U-shaped contact supports. This represents a consideration simplification compared with the known arrangement in which seven separate lines 1 9 must be fitted in order to connect the two separate contactors.

As shown in Figs. 6 and 6a, some conventional control arrangements require the provision of three separate contactors each of which has a single group of switches. In this case, twelve separate lines 1 9 need to be fitted to interconnect the terminals of the contactors. Use of a contactor in accordance with the present proposal to replace two of the separate contactors permits a simplification, whereby only seven of the lines need to be fitted.

Arranged adjacent the lateral edge of the housing are chambers containing auxiliary switches and the associated contacts and terminals. The sleeve of each electromagnetic system has an extension with a slot 7 receiving a pair of yokes 10 with oppositely facing contact plates 1 8. A compression spring is disposed between the yokes of each system.

Mounted within chambers 28 are auxiliary contact supports 26 with screw-threaded openings 26b for the screws 27 of terminals 1 2. Each of the auxiliary contact supports is of cranked configuration and the portion bearing the terminal is fitted in a slot 29 having an undercut 29a for the contact support. The contact supports may be demounted and reversed so as to occupy the position shown in chain lines instead of the position shown in full lines. In the illustrated arrangement, the lower switch is normally closed, whereas the upper switch is normally open when the magnetic system is deenergized. By positioning the contact supports in the chain line positions, the lower switch becomes that which is normally open, and the upper switch becomes that which is normally closed. In this case, the contact plates of the upper switch occupy a position slightly lower than that illustrated.

A modified contact is shown in Fig. 10 in which the upper magnetic system previously described is omitted, and the upper contact sleeve 6 is continuously biased towards the lower sleeve 6a by a restoring compression spring 25 which bears against a hood 31 of the housing. Energization of the magnetic system closed the upper switches and opens the lower switches, whereas deenergization of the system results in the restoring spring opening the upper switches and closing the lower switches.

Claims (22)

1. An electromagnetically operable contactor for the control of an electric motor, wherein two fixed contacts are carried by a Ushaped contact support and first and second movable contacts are arranged for movement alternately into contact with the fixed contacts; the first and second movable contacts being disposed opposite each other and associated with a lock-out to prevent simultaneous contact of both movable contacts with the fixed contacts.

2. A contactor according to claim 1, wherein a terminal is provided on or in the region of the web of the U-shaped support.

3. An electromagnetically operable contactor for control of an electric motor, comprising first and second movable contacts and first and second sets of fixed contacts disposed between the movable contacts, the first movable contact being displaceable into contact with the first set of fixed contacts so as to make a first circuit and the second movable contact being displaceable into contact with the second set of fixed contacts so as to make a second circuit, and a lock-out for preventing the simultaneous making of both circuits; live contacts of both sets being carried on respective limbs of a U-shaped contact support fitted with a terminal on or adjacent its web portion.

4. A contactor according to claim 3, wherein neutral contacts of the sets of fixed contacts are carried on respective further contact supports each fitted with a terminal, one of the further contact supports having a cranked portion extending away from the other further support, whereby the terminals are spaced from each other by a greater distance than the contacts.

5. A contactor according to any preceding claim, wherein all of the heretofore-mentioned components are contained in a common housing.

6. A contactor according to claim 5, wherein the housing is subdivided into sections.

7. A contactor according to claim 5 or claim 6, wherein each movable contact is associated with a respective electromagnetic operating system contained in the common housing.

8. A contactor according to claim 7, wherein each electromagnetic operating system includes a coil mounted in the housing and an armature movable in a tubular guide mounted in the housing.

9. A contactor according to claim 8, wherein a compression spring biases the armature of each magnetic system in the direction appropriate to opening the contacts controlled by that system.

10. A contactor according to claim 8 or claim 9, wherein each armature is guided in the pertaining tubular guide by means of an armature sleeve connected to an extension having a slot for seating the movable contacts and a slot for an abutment for a spring serving to bias a stirrup towards the stirrup of the other system.

11. A contactor according to claim 5, including first and second auxiliary switches, each including a fixed contact and a movable contact, the first switch being normally open and the second normally closed; the fixed contacts being repositionable thereby to render the second switch normally open and the first normally closed.

12. A contactor according to claim 11, wherein supports for the auxiliary fixed contacts have cranked portions in the region of which are screw-threaded bores for the recep tion of screws of terminals.

1 3. A contactor according to claim 12, wherein the supports for the auxiliary contacts are held within apertures opening into chambers in which the contacts are disposed.

1 4. A contactor according to claim 13, wherein the apertures have widened portions to receive contact plates.

1 5. A contactor according to claim 5 or any of claims 11 to 14, wherein both movable contacts are operable by a common electromagnetic system, force applied by which is opposed by a restoring compression spring disposed at the end of the housing remote from the magnet, the spring engaging a cover of the housing, the switch contacts being movable against the force of a contact spring.

1 6. A contactor according to claim 1 5, wherein the restoring compression spring is stronger than the contact spring.

1 7. A contactor according to claim 1 or claim 16, wherein one of the sleeves is connected with the armature of the electromagnet.

1 8. A control arrangement for an electric motor comprising a contactor in accordance with an preceding claim mounted adjacent a contactor having a single group of switches.

1 9. A control arrangement according to claim 18, wherein the housings of the contactors are fixed to a base plate.

20. A contactor substantially as hereinbefore described with reference to and as illustrated in any Figure of the drawings.

21. A contactor comprising first and second groups of switches arranged within a common housing, the movable contacts of both groups of switches being displaceable parallel to a common axis, the movable contacts of each group being associated with a stop member, the stop members being engageable to prevent the simultaneous closing of both groups of switches.

22. A contactor comprising first and second switches, the movable contacts of which are displaceable parallel to a common axis, the first switch being normally open and the second normally closed, the fixed contacts of both switches being relocatable to render the second switch normally open and the first normally closed.