US2162513A - Overspeed protective means - Google Patents

Description

June 13, 1939. P. McSHANE 2,162,513

OVERSPEBD PROTECTIVE MEANS Filed June 26, 1936 Rwerhurce a t INVENTOR WITN ESSES:

" Patented June 13, 1939 OVERSPEED PROTECTIVE MEANS Phelan McShane, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 26, 1936, Serial No. 87,368

5 Claims. (Cl. 172239) UNITED STATES PATENT OFFICE My invention relates to over-speed protection for rotating machines, and it has particular relation to the application of such protection to electric motors which are controlled by multistep adjusters and with which speed-indicating pilot generators are associated.

One object of my invention is to supplement the above equipment by over-speed protective means of a simple, inexpensive and effective character.

Another object of my invention is to provide an over-speed protective system the calibration of which may readily be adjusted through a wide range either manually or automatically.

A further object of my invention is to protect the motor upon failure of the speed indicating apparatus by restricting its operation under such conditions to speeds below a given low value.

My invention itself, together with additional objects and advantages, will best be understood through the following description of a specific embodiment when taken in conjunction with the accompanying drawing the single figure of which is a diagrammatic representation of a motorcontrol system incorporating my improved overspeed protective means.

In the drawing, the motor to be protected is generally represented at as being adapted to derive energizing current from any suitable source of power designated by the conductors l2 and I4. The motor shown is of a well-known series type commonly employed in material handling applications, such as cranes, cableways, derricks, mine hoist devices and the like.

The associated control system includes a pair of selectively-actuable reversing-control contactors l6 and I8, a group of starting resistors 20, having acceleration control contactors 22, 24 and 26 associated therewith, and a multi-step drum type of speed adjuster 28 for supervising the actuation of the devices previously named.

When the controller 28 occupies the illustrated ofi position, the several actuating circuits are open and the contactors occupy the unactuated positions illustrated. To start the motor III in a forward direction, the represented controller drum assemblage is moved to the right to position No. 1, completing at 30, the actuating circuit of main contactor Hi. This causes contact members 32 and 34 to connect the armature of motor Ill with power circuit l2l4 in series relation with the field winding 36 and starting resistors 28. Motor l0 starts to rotate in the forward direction, driving through shaft 38, the hoist or other load (not shown) at a slow speed.

Movement of the drum of controller 28 further to the right to position No. 2 completes at 40, the actuating circuit of accelerating contactor 22, causing contact members 42 to bridge the associated resistor section 20. The resulting increase in current raises the motor speed. As the controller drum is further advanced to position No. 3, there is completed at 44, the actuating circuit of accelerating relay 24, thereby causing contact members 46 to remove the second 10 section of resistor 20 from active circuit and further increase the motor speed. Advancement of the controller to position No. 4 similarly causes contactor 26 to short out the remaining section of starting resistor and cause the motor to operate at full speed.

The direction of rotation may be reversed by notching the controller back to the off position and advancing the drum in the opposite (left in the drawing) direction through the successive positions of speed adjustment. In position No. l, the actuating circuit of main contactor I8 is completed at 50, causing contact members 5?. and 54 of the contactor to reverse the direction of current flow through the motor armature. In position No. 2, the actuating circuit for accelerating relay 22 is completed at 56, causing the first step of starting resistor 20 to be cut out. In positions Nos. 3 and 4, the accelerating contactors 24 and 26 are similarly actuated. 30

In the interests of diagram simplicity, no attempt has been made to show the braking or motor decelerating system employed in a majority of applications of the type under consideration.

In such applications, it is, of course, necessary that the motor be separated by some considerable distance from the operator who adjusts the drum controller 28. In order that the operator may be apprised of the speed and direction of rotation of the motor at any given instant, it is customary to provide a pilot generator 60 which is directly connected or otherwise driven by the motor in such manner that the output voltage Es is a direct function of the motor speed. The magneto has been found to constitute a very satisfactory form of piloting machine. The desired indications of speed are then obtained from a voltmeter 62 connected, as shown, to be energized by voltage ES and conveniently positioned with respect to the operator.

The over-speed protective means of my invention now about to be described are especially adapted for application to electric motors controlled by multi-step speed adjusters of the type just considered and with which speed indicating pilot generators are associated in the manner indicated.

In one preferred form, these means comprise a voltage sensitive relay 64, the actuating Winding of which is energized by a measure of the speed-proportional voltage E5. The movable contact member 66 of this relay is adapted to bridge the stationary studs 68 when the motor I0 is at rest, and when it is operating at a creeping speed below the value normally obtained when controller 28 occupies position No. 1.

As the speed rises above this value, member 66 is moved upwardly out of engagement with the named studs, which disengage-d range of positions it occupies for all normal or desired operating speeds of the motor It. When, however, the motor speed exceeds a given or undesirably high value, member 66 moves upwardly into engagement with studs 10, thereby completing an actuating circuit for a relay (2.

In moving upwardly, the contact member 14 of this relay interrupts the control circuit for main energizing contactors l6 and i8 and for accelerating devices 22, 24 and 26. All of these devices thus move to their unactuated positions and effect a complete deenergization of the motor. If desired, of course, relay 12 may be arranged to reduce the motor energization as by deenergizing the actuating circuits of the accelerating relays 22, 24 and 26 only.

Before the motor can be reenergized following a reclosure of relay T2, the system shown makes it necessary that the controller 28 be returned to the off position. This requirement is desirable to prevent excess restarting current and is achieved by the use of a lock-out relay l6 which, when deenergized, as by an actuation of relay (2, opens the main control circuit at 18.

Once moved to the unactuated position, the holding contact of relay 16 becomes ineffective until after the relay has been reactuated by reclosure of the actuating circuit at 8|. This is effected by a return of the controller drum to the off position.

The over-speed protective system just explained allows different over-speed settings readily to be obtained. This change of calibration is preferably efiected by the use of impedance-adjusting apparatus, shown in the form of resistors 82 and 84, in the circuit through which the speed responsive relay 64 is energized by a measure of the pilot generator Voltage. Associated with these resistors are a pair of shunting relays 86 and 88, which when actuated through the medium of a multi-point control switch 90, insert these resistors into active connection with the relay circuit.

If desired, of course, the resistors illustrated may be replaced by a conventional form of manually adjustable rheostat, or any other device, such as an adjustable inductance which acts to vary the impedance of the relay energizing circuit, and thereby alter the value of voltage E5 to which it is responsive.

When the switch occupies the uppermost position, both resistor sections 82 and 84 are shunted from the circuit and the relay 64 will complete an actuating circuit for motor deenergizing relay 2 at a comparatively low value of motor over-speed. Movement of switch 90 to the mid-position causes relay 86 to insert resistor 82 into the active circuit. The resulting rise in impedance requires that the speed proportional voltage Es be increased before speed sensitive relay 64 responds. Further movement of switch 90 to the lower position causes relay 88 to insert a larger block of resistance 84 into the circuit, which in turn, further raises the calibration of the overspeed protective system.

Calibration adjusting switch 96 may, of course, be manually operated in accordance with conditions directly observed by the motor operator. In other instances, the use of automatic operation in accordance with a predetermined condition of the motor or driven load may be found desirable.

In mine hoisting applications, for example, it may be desirable to insure a different speed of operation as the cage reaches its upper or lower limit of travel. To effect this assurance, switch 90 may automatically be operated through a reduction gear mechanism, generally indicated at 92, which causes the switch blade to shift its position as the hoist changes its elevation. An alternate arrangement for accomplishing the same thing is to employ cams or similar devices directly driven by the hoist.

In other applications, such as cable-ways, and derricks, where it is desired to insure that heavy loads will be handled at slower speeds "than light loads, the desired automatic operation may be provided by actuating the calibration changing switch 90 in direct accordance with the change of position of a member 94, which moves in accordance with the drum of controller 28.

From the foregoing, it will be seen that the over-speed protective system of my invention when applied to a motor controlled by a speed adjuster and provided with a speed-indicating pilot generator requires the use of very simple and inexpensive relay devices and interconnections. It lends itself readily to either manual or automatic calibration adjustment control, and in addition, it is effective in preventing operation of the motor at speeds above a given low value in the event of failure of the speed-piloting equipment.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the scope of the appended claims.

I claim as my invention:

1. In an over-speed protective system for an electric motor comprising means for producing a voltage proportional to the speed of the motor. a speed-reducing relay and a circuit for impressing upon the relay a measure of said voltage, the combination of calibration-altering means comprising impedance-adjusting apparatus included in the relay-energizing circuit and means for operating said apparatus in accordance with a condition of said motor.

2. In a system comprising an electric motor adapted to change the mechanical position of an object and having means for producing a speedproportional voltage associated therewith, the combination of over-speed protective means comprising a speed-reducing relay, a circuit for impressing thereon a measure of said speed-proportional voltage, and means for altering the calibration of the protective system in accordance with the position of said object comprising apparatus responsive to said position for changing the impedance of the relay energizing circuit.

3. In a system comprising an electric motor, a speed-adjusting controller therefor, and means for producing a speed-proportional voltage associated therewith, the combination of over-speed protective means comprising a speed-reducing relay, a pilot generator, a circuit for impressing on the relay a measure of the pilot-generator voltage, and means for altering the calibration of the protective system in accordance with the position of said controller comprising apparatus responsive to said position for changing the impedance of the relay energizing circuit.

4. In a system comprising an electric motor having over-speed protective equipment, including a circuit in which there acts a speed-proportional voltage, associated therewith, the combination of means responsive to a failure or said equipment for preventing the motor from being operated at speeds in excess of a given low value comprising a relay energized by said speed-proportional voltage and adapted to deenergize the motor when the motor speed is attempted to be increased if said voltage is less than a given value.

5. In a system comprising an electric motor, a multi-step speed-adjusting controller therefor, and means for producing a speed-proportional voltage associated therewith, the combination of over-speed protective means comprising a voltage-sensitive relay, a circuit for impressing thereon "a measure of said speed-proportional voltage, a device for disconnecting the motor from its source of power, and actuating means for said device sensitive to an advance of the motor controller beyond a given low-speed point when the voltage impressed upon said relay is less than a given value.

PHELAN McSHANE.

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