US2877626A

US2877626A - Electric control system for fluid operated actuators

Info

Publication number: US2877626A
Application number: US652444A
Authority: US
Inventors: Gratzmuller Jean Louis
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-04-18
Filing date: 1957-04-12
Publication date: 1959-03-17
Anticipated expiration: 1976-03-17
Also published as: BE556800A; DE1244276B; NL216441A; GB831888A; FR1149930A; NL272080A; CH342625A

Description

March 17, 1959 J. L. GRATZMULLER I 2,877,625

ELECTRIC CONTROL SYSTEM FOR FLUID OPERATED ACTUATORS Filed April l2, 1957 United States Patent O ELECTRIC CONTROL SYSTEM FOR FLUID OPERATED ACTUATORS Jean Louis Gratzmuller, Paris, France Application April 12, 1957, Serial No. 652,444 Claims priority, application France April 18, 1956 l 6 claims. (c1. s0-s2) exerted on the movable contact mechanism as soon as it has completed its movement in either sense, in order to avoid mechanical overloading of the contacts and their mechanism.

Such discontinuance of effort can be achieved by means of limit switches in an electrical circuit or circuits controlling the actuating means of the section switch. However, limit switches present the serious disadvantage of requiring very precise adjustment to ensure completion of the movement of the mechanical parts without prolonging the effort exerted on and by them after completion of the movement. Should a limit switch be incorrectly adjusted or fail to operate, serious damage to the installation may be caused. y

Now, in contrast to what is required of a circuitbreaker, the rapidity of action in closing and especially in opening a section switch is not a critical factor, since a section switch is only required to connect and disconnect a line when the latter is dead. Hydraulic actuators fed by a pump, while unsuitable for circuit breakers since the pump delivery cannot produce a quick enough action, are suitable for operating a section switch.

This invention is therefore more particularly concerned with a control system for controlling the hydraulic actuator or actuators of a section switch, said actuator or actuators being fed by a pump.

Now when a pump-fed actuator has completed its stroke, the check to the pump-delivery causes the delivery pressure to rise, and this fact is made use of by the present invention to stop the operation of the pump.

The control system according to this invention therefore comprises an electric motor which drives the pump and means responsive to the pump delivery pressure for isolating the motor from its source of excitation when such pressure attains a predetermined critical value.

By suitably calibrating the pressure responsive device it is possible to ensure that the stroke of the actuator will be completed with certainty and that the pressure in the actuator and hence the effort exerted on and by the movable contact mechanism of the section switch is limited to a safe value; and at the same time that the actuator will be unloaded by the stopping of the pump as soon as its stroke is completed.

Although the actuator or actuators is/are not itself or themselves part of the combination constituting the control system of the present invention, it is contemplated that the section switch will normally be actuated by two single-acting hydraulic jacks, respectively effecting the closing and opening movements of the contact mechanism, or by one double-acting jack, which for presice . 2 ent purposes may be regarded -as a pair of oppositely acting single-acting jacks. l f

In a preferred form of construction of the invention, the pressure-responsive means comprise an electro-magnet' controlling the switch-gear of the pump motor, a switch controlling the excitation of the electro-magnet and a movable element controlling the switch, said element being subjected to the opposed efforts of the pump delivery pressure and of a calibrated spring. This arrangement has the advantage of requiring no yfurther adjustment after assembly with a spring of correct calibrafk tion and oiers the further advantage that if the actuator` or the contact mechanism actuated by it should be accidentally checked in mid-stroke the pump delivery pressure will automatically rise and operate the pressure responsive means to stop the pump motor, a result im possible of attainment with conventional limit switches.

If a positive indication of the completion of the stroke in either sense is required, the conventional limit switches, though no longer required for controlling the pump mov tor, may be retained for connection to signalling circuits;

but the present invention is not concerned with the means, if any, provided for signalling completion of the stroke, for which any suitable devices may be employed.

A section switch control system employing electrical circuits and electro-magnetic devices ought to vsatisfy the following conditions:

(a) Not only must movement in either sense of the movable contact mechanism of the section switch once initiated, be completed, but it must be impossible for the operator, either to stop such a movement once it has been started or to initiate a movement in the opposite sense before the first movement has been completed; the primary action effected by the operator should therefore be of a tripping nature, which brings about a secondary, self-maintaining automatic action; and such automatic action should at the same time inhibit any primary action by the operator for initiating movement in the opposite sense; -v

(b) The electro-magnetic devices included in` the system (other than the electro-magnet controlling the motor switch-gear) must be incapable of functioning when earthed. This impulies that each such device, when not intentionally excited, must be doubly isolated, i. e. switches must be opened on both sides of it;

(c) A current failure of the electrical supply of any of the electro-magnetic devices during a movement of the contact mechanism of the section switch should restore the whole electrical system to its original state before such movement was initiated, so that no unintentional resumption of movement can occur when the current is re-established.

A further object of the invention is to provide an elec-v trical and electro-magnetic system for actuating the valve. I

means controlling the hydraulic actuator or actuators lof a section switch and the switch-gear of the pump motor that will satisfy the three conditions above set forth.

A preferred form of my improved contnol system there fore comprises, in addition to the features previously described, the following further features:

(i) 'Ihe valve means controlling the Iactuator or actumeans are excitable through a holding circuit which includes an isolating switch mechanically coupled to the pump motor switch-gear so as to open when the motor' is isolated, and the exciting circuit of the electro-magnet controlling the motor switch-gear includes a switch or; switches sol actuated by the valve-,operating` electrol.,

magnetic means as to close only when the latter is/ are excited.

(ii) The valve-operating electro-magnetic means is/ are initially excitable through a starting circuit or circuits in parallel with the holding circuit and including a controllable starting switch or switches which is/are normally open.

(iii) The closing and opening movements respectively of the section switch lare effected by two separate singleacting hydraulic actuators (or a single double-acting actuator equivalent thereto as hereinbefore stated) each Such actuator being controlled by a separate valve and each such valve operated by a separate electro-magnet; and each such electro-magnet has a starting circuit which includes in addition to a normally open starting switch an isolating switch so actuated by the other such electromagnet as to open when the latter electro-magnet is excited;

(iv) Each starting switch is a double-pole switch adapted to isolate its associated electro-magnet on both sides when opened.

(v) Each valve-operating electro-magnet when excited closes la holding switch in its holding circuit, such holding switch and the isolating switch mechanically coupled to the motor switch-gear being disposed on opposite sides of the electro-magnet so as to isolate the iatter on both sides when both such switches are open.

It will be evident that of the three conditions above stipulated, condition (a) is satisedby features (ii), (iii) 'and (v) in combination, condition (b) is satisiied by features (iv) and (v) in combination, and condition (c) is satised by feature (i).

The pump motor is preferably of the three-phase A. C. variety, the exciting circuit of the electro-magnet controlling the motor switch-gear being connected across two of the three-phases of the motor supply.

An embodiment of the invention is illustrated by way of example only in the single gure of the accompanying drawing, which is an electrical circuit diagram including schematic representation of certain hydraulic components.

Referring to the drawing, the movable contact mechanism of a section switch (not illustrated) is actuated by two hydraulic actuators, such as single-acting jacks (not illustrated), one of which effects the closing movement and the other the opening movement of the contact mechanism. These actuators are respectively controlled by valves denoted 1 and 2 each of which can selectively connect a combined feed and exhaust pipe a or b counected to the actuator it controls, either to the delivery pipe c of a pump 3 -or to an exhaust pipe d. Each valve is provided with a ball member which cooperates with a seat in the valve body to constitute an inlet valve means and a fluid pressure responsive valve component which cooperates with outlet ports to define an outlet valve. The arrangement is such that the outlet valve, when moved by its plunger in one direction, opens the inlet valve while maintaining the outlet ports closed, whereas fluid pressure from the conduit a moves the outlet valve in. the other direction to establish a communication between the conduit a and the exhaust pipe d through the outlet ports while the inlet valve remains closed.

Pump 3 is driven by a threephase A. C. electric motor 4 supplied from a three-phase current source 5, 6, 7 and is controlled by a switch-gear here represented for the sake of simplicity by a three-blade switch 28, 29, 30 `actuated by the armature 31 of an electro-magnet 32 so as to close when the, electro-magnet is excited, the switch 28, 29, 30. being biased to the Open position by a spring 34. In practice the motor switch-gear will preferably be of the kind which is standard equipment for three-phase motors.

The'el'ectro-magnet 32 is excitable through la circuit 411, 421,43-, 44 containing a switch 39 actuated through a rod 3@ by4 a piston 37l sliding in a cylinder 36 and subjected to the Opposed eiorts of a calibrated spring 40 and the delivery pressure of pump 3 applied through a pipe 35. When the pump delivery pressure exceeds a predetermined critical value to which spring 40 is calibrated, lthe latter yields and allows piston 37 to open switch 39 and isolate the electro-magnet 32, thus causing the motor switch 28, 29, 30 to open and isolate the motor 4, thus stopping the pump 3 and preventing further build-up ot pressure in the pump delivery pipe c.

The excitation of the electro-magnet 32 is derived from two of the phases 6, "I, of the three-phase supply for the motor 4, so that a temporary failure of this supply will not only stop the motor but by stopping the excitation of electro-magnet 32 will cause the motor to be isolated. When the motor supply current is restored the electromagnet 32 will not be re-ex-cited to start the motor again because, as hereinafter explained, the opening of the motor switch 28, 29, 30 causes the exciting circuit of the electro-magnet 32 to be interrupted at another point, and it can only be re-established by a purposive action of the operator.

The control valves 1, 2 are operated by electro-magnetic means excitable from an independent D. C. supply 49, S4. Each valve 1, 2 has an operating plunger 8 or 14 carried by an extension of the armature 9 or 15 of an electro-magnet 10 or 16. Excitation of either of theseelectro-magnets causes its armature 9 or 15 and plunger 8 or 14 to be depressed and set the valve 1 or 2 to connect the pump delivery pipe c to the feed pipe a or b of the corresponding hydraulic actuator and energize the same to move the Contact mechanism of the section switch, in the closing or opening sense according to which of the electro-magnets 10, 16 is excited.

Electro-magnet 10 is initially excitable through a starting circuit 49, S0, 51, 52, 53, 54 closable by a doublepol'e starting switch 24, 25 which is normally kept open by a spring 22 and can be closed by a push-button 20.

vWhen open, switch 2li, 25 isolates electro-magnet 10 on both sides since the contact 24 is in the

positive branch

49, 50, 51 of the starting circuit, the contact 25 being in its negative branch 52, 53, 54. Similarly, electro-magnet 16 is initially excitable through a starting circuit 49,. 55, 56, 50, 57, 58, 59, 69, 54 containing a double-pole starting switch 26, 27 normally held open by a spring 23 to interrupt both the positive and negative branches of the starting circuit and closable by a push-button 21.

The armature of each electro-magnet 10, 16 further carries the movable Contact members of three switches, viz 11, 12, 13 and 17, 18, 19 respectively.

Switch 12 is an isolating switch in the negative branch 58, 59 of the starting circuit of electro-magnet 16 and is closed except when electro-magnet 1t) is excited. Similarly, switch 18 is an isolating switch in the negative branch 52, 53 o the starting circuit of electro-magnet 1t) and is closed except when electromagnet 16 is excited. Thus excitation of either electro-magnet 10 or 16 opens the starting circuit of the other and renders its starting switch inoperative to excite it.

Switches 11, 17 are holding switches for their respective electro-magnets. Thus, when electro-magnet 10 is rst excited it closes Switch 11, previously open, and establishes its holding circuit through conductors 62, 63, Sil, S1, 52, 64, 65, 61. Similarly, initial excitation of electro-magnet 16 closes its holding circuit 62, 63, 57, 58, 66, 61 when switch 17 is closed.

Thus excitation of either electro-magnet 10, 16, once tiipped by momentarily closing its starting switch 24, 25 or Z6, 27 is continued, so that the corresponding valve 1 or 2. remains set to energize the actuator controlled thereby until the latter has completed its stroke, whereupon the holding circuit of the electro-magnet is opened by other means hereinafter described.

These means comprise an isola-ting switch 33 in the positive branch 62 63' of the holding circuit of both electroLmagnets 10', 116. Switch 33 is mechanically coupled' to the motor switch 28, 29, 3l) and is `opened when the latter opens. Therefore, when the pump delivery pressure rises above the critical f-Lilue on completion of the stroke of either actuator and opens the switch 39, not only is the motor switch opened as previously explained but switch 33 is likewise opened, thereby opening the holding circuit and terminating the excitation or" the electro-magnet lil or 16 concerned,

The type of switch-gear which is standard equipment for a three-phase motor usually includes, in addition to various protective relays, a holding switch, which closes when the main motor switch closes to maintain the main switch in closed lposition. In the system herein described this holding switch may he utilized as the switch 33 labove mentioned, by disconnecting it from its normal circuit and connecting it to the conductors 62, 63 as illustrated. Alternatively, if as is often the case, the switch-gear includes a spare switch which opens and closes with the main motor switch and has terminals for connecting an external circuit, e. g. a signalling circuit, such spare switch may be used as the switch 33, its terminals being connected to conductors 62, 63.

Switches 13 and 19 are connected in parallel branches 47, 48 and 45, 46 respectively of the exciting circuit 41-44 of electro-magnet 32. They are open when electro-magnets lil and 16 are not excited, but when one of these electro-magnets is excited, say 10, the associated switch 13 closes and completes the exciting circuit 41-44 of electro-magnet 32.

It will now be evident why after an interruption of the excitation of electro-magnet 32 iby a temporary supply failure, restoration of the supply will not re-excite electro-magnet 32, the reason being that failure of the excitation of electro-magnet 32 causes switch 33 to open and this provokes opening of whichever of switches 13 and 19 was closed; and until one of the latter switches is re-closed by depressing one of the buttons 20, 21 to complete the starting circuit of one of the electro-magnets 10, 16, electro-magnet 32 cannot be re-excited and the motor 4 re-started.

The sequence of actions is as follows:

Initially the various components of the system are in the positions shown in the drawing and all circuits are open and the electro-magnets 16, 16, 32 and motor 4 are not excited. The section switch whose actuators are controlled by valves 1, 2 is in one of its possible positions, e. g. open. To close it, the appropriate button, e. g. 20 is momentarily depressed. This closes the starting circuit of electro-magnet `by means of switch 24, 25 and excites the electro-magnet, whose armature 9 is thereby moved to close switches 11 and 13 and open switch 12, thus closing one branch of its own holding circuit, opening the starting circuit of electro-magnet 16, so that the latter cannot be excited if button 21 is prematurely depressed, and closing the exciting circuit of electro-magnet 32, thereby causing the main motor switch 28, 29, 30 to close and start the motor 4 to drive pump 3, and also causing switch 33 to close and complete the holding circuit of electro-magnet 10. At the same time the armature 9 has depressed the plunger 8 of valve 1 rand set the latter to connect pipe a to the delivery pipe c of pump 3, thereby energizing the appropriate section switch actuator.

On -completion of the stroke of the energized actuator, the consequent rise of pressure in pipe 35 opens switch 39 and isolates electro-magnet 32 Icausing switches 28, 29, 30 and 33 to open, thus stopping the motor 4 and pump 3 and opening the holding circuit of electro-magnet 10, which therefore ceases to be excited and allows plunger 8, and switches 11, 12, 13 to return to their original positions. It is therefore now possible to close the starting circuit of electro-magnet 16 by means of button 21, since switch 12 is again closed.

The sequence of actions consequent on depression of button 21 need not be described as it is exactly similar to that described above.

It the wrong button is depressed, the associated actuator being at the end of its stroke cannot move and the immediate result of starting the pump motor will be a rise of pressure in pipe 35 suicient to open switch 39 and thereby restore the system to its original state as shown in the drawing with none `of the electro-magnets, nor the motor, excited.

lt will be noticed that when the system is in the inert state as shown in the drawing both electro-magnets 10, 16 are doubly isolated, i. e. `on cach side, by the doublepole switches 24, 25 and 26, 27 in the starting circuits and by switches 11, 17 and 33 in the holding circuits.

What is claimed is:

l. An electric control system for a pressure lluid operated actuator, comprising, in co-mbination, a pump, an electric motor for operating the pump, a switch-gear for controlling the circuit to said motor, an electro-magnet connected to said circuit for operating said switch-gear, pressure operated means to break the circuit of said electro-magnet when the delivery pressure of said pump reaches a predetermined value to thereby allow said switch-gear to break the circuit to said motor, a valve device for controlling the ilow of liquid from said pump to said actuator or from the latter to the exhaust, electromagnetic means for operating said valve device and including a holding circuit, an isolating switch in said holding circuit movable with said switch-gear so as to interrupt said holding circuit when said switch-gear is moved into open position, and switch means in the circuit of said electro-magnet so actuated by said electro-magnetic means as to close only when said electro-magnetic means are energized.

2. A control system as claimed in claim l, in which the Valve-operating electro-magnetic means is initially `excitable through a starting circuit in parallel with the holding circuit, said starting circuit including a controllable starting switch which is normally open.

3. A control system as claimed in claim 2 for controlling two lluid operated actuators comprising a valve device controlling each actuator and an electro-magnetic means operating each valve device, a separate starting circuit for each electro-magnetic means, each starting circuit including a starting switch and also an isolating switch so actuated by the electro-magnetic means controlled by the other starting circuit as to `be opened when said last mentioned electro-magnetic means is excited.

4. A control system as claimed in claim 3, wherein each starting switch is a double pole switch adapted when opened to isolate the electro-magnet controlled thereby on both sides.

5. A control system as claimed in claim 3, in which each electromagnetic means when excited closes a holding switch in its holding circuit, the isolating switch movable with said switch-gear and said holding switch being disposed on opposite sides of the electro-magnetic means, so as to isolate the latter on both sides when both such switches are open.

6. A control system as claimed in claim l, in whichsaid electric motor is of the three-phase alternating current type, the circuit of said electro-magnet being connected across two of the three conductors of the threephase source from which the motor is excited.

Hateld et al. May 7, 1929 Hartman Dec. 28, 1948