US3436598A - Control system safety relay - Google Patents

Description

April l, 1969 J. L.. GUERRISI CONTROL SYSTEM SAFETY RELAY Sheet Filed July 17, 1967 I @QM v April l, 1969 .1.1.. GUERRISI CONTROL SYSTEM SAFETY RELAY Sheet Filed July 17, 1967 vE/vrof? JOHN L. GUERR/S/ BYMMN* rrof/vfys United States Patent O M 3,436,598 CGNTRDL SYSTEM SAFETY RELAY John L. Guerrisi, 300 Eddington Ave., Harrisburg, Pa. 17111 Filed July 17, 1967, Ser. No. 653,300 Int. Cl. H02h 7/06 U.S. Cl. 317-13 11 Claims ABSTRACT OF THE DISCLOSURE A protective relay for reversible motordriven devices such as hoists, overhead cranes and the like which prevents operation of the motor in the event of failure in the direction control contacts. A relay coil is connected to the direction control contacts so as to be energized before the master controller is operated if any of the contacts have frozen shut. When energized, this relay coil opens a normally-closed contact to prevent operation of the motor and thus avoids possible motion of the hoist or crane in the wrong direction.

Field of the invention The present invention relates, in general, to protective systems for reversible machinery, and, ymore particularly, to an emergency relay which responds to malfunctioning directional contacts to prevent energization of the drive motor for such machinery.

Background of the invention In virtually every industrial operation some use is made of crane hoist equipment, overhead traveling cranes, and similar equipment. Usually, this machinery is driven and operated by electric motors and suitable control circuits which must be capable of handling heavy loads while maintaining a high degree of control at all times. These motors and their control circuits often operate under highly adverse conditions which can disable the controls and cause improper operation of the machine.

Most crane hoist equipment includes many standard safety features which are designed to protect the users of these machines in the event of anticipated failures in the control circuits. The usual series wound D.C. motor employed in crane hoists and the like is controlled as to its speed by a series variable resistor and as to its direction by two pairs of relay contractors which serve to reverse the direction of current ilow through the motor armature. Series magnetic brakes are often provided to prevent movement of the cable drum or motor armature in the absence of power to release the brake shoe, On many controllers the olf position short circuits the eld and armature to give dynamic braking in the event that the magnetic brake should fail. Limit switches to prevent motion beyond predetermined limits are well known, as are overload relays which serve to open the motor circuit in the event of excessively high currents.

With all of these safety features, however, many accidents still occur in the use of this type of machinery, and much effort is being devoted to improving their safety. One problem area is the use of directional contacts which can malfunction and cause a crane or hoist to move in a direction opposite to that expected by the operator. By the time the operator can react to such a malfunction to shut down the machinery, a great deal of damage to property or person can occur. Although this problem is known to exist, the prior art has indicated no solution, and there is no automatically responsive safety equipment available for preventing such an occurrence.

Summary of the invention It is, therefore, an object of the present invention to Patented Apr. 1, 1969 provide an emergency relay system which will detect malfunction of directional contacts to prevent energization of the machinery controlled by such contacts.

A further object of the invention is the provision of an emergency relay system for crane hoists and the like which is responsive to an accidentally closed directional contact to prevent energization of the crane drive motor, thus preventing possible operation of the drive motor in the wrong direction.

The usual master motor controller for D.C. motors used in crane hoists and the like has a neutral, or off position, a plurality of forward positions and a plurality of reverse positions, the forward and reverse positions providing motor direction and speed control by energizing selected relay coils and thus incrementally varying a series resistor, in known manner. The motor armature is reversibly connected across the D.C. supply lines to provide the directional control, with relay contacts being connected to direct the current flow. The relay coils are selectively energized by the controller. The directional switch contacts are interlocked so that when the forward contacts are selected, the reverse contacts cannot be closed.

Occasionally it happens that one of the directional switches, or switch contacts, accidentally becomes closed while the controller is in the neutral, or off, position. This can occur when the contacts become burned closed by an arc or an excessive current, or when some other short circuit occurs in the system to bypass the master controller. In prior art devices, the operator of the motor control syste-m had no way of knowing that this short circuit condition existed until he tried to start up the system. If, for example, the reverse contacts had malfunctioned and were closed when the controller was off, and the operator wished to energize the motor in the forward direction, the instant he closed the motor circuits the motor would start to move in reverse. Such an unforseen motion can, and has in many instances, produced a great deal of damage.

By connecting an emergency relay (ER) to the motor directional contacts in the manner set forth herein, the foregoing results of contact malfunction can be avoided. With this relay, as soon as a direction switch contact remains closed when the controller is in the neutral position, the emergency relay coil is energized, opening a corresponding contact in series with the motor operating relay coil to prevent energization of the motor. At the same time an alarm is sounded to warn of the malfunction. With the motor relay coil deenergized, operation of the controller has no effect, and the system remains inoperative until the directional contacts are repaired.

Brief description of the drawings The foregoing and additional objects and features of the invention will become more fully appreciated when considered in the light of the following specification and accompanying drawings, in which:

FIG. 1 is a schematic diagram of a crane trolley motor control system incorporating the protective relay of the invention; and

FIG. 2 is a partial schematic diagram of la crane hoist motor control system utilizing the protective relay of the invention.

Description of preferred embodiments Referring now to FIG. l of the drawings, there is illustrated a conventional crane trolley motor control system with the protective relay of the invention added to prevent operation of the system in the event of malfunction in the directional contacts. As shown, the motor being controlled includes an armature 10 having an armature winding 12 and a series eld 14. The D.C. motor is connected between the positive and negative terminals 16 and 18, respectively, of a suitable source of direct current (not shown) by means of power supply knife switches 20 and 22, respectively.

Connected in series with the D.C. motor are a number of control elements which are utilized in known manner to operate the motor. An overload relay coil OL-1 is connected between the positive terminal knife switch 20` and a positive motor supply junction point 24. The negative terminal knife switch 22 is connected through a second overload relay coil OL-Z, a normally-open main line relay contact 26a, yan ammeter 28 (if used), an accelerating resistor 30, a series brake 32 (if used) and the series field 14 to a negative motor supply junction point 34. Connected in bridge configuration between the positive and negative junction points 24 and 34 are the normally-open reversing contact pairs 1F, 2F and 1R, 2R which serve to reverse the direction of current flow through the motor 4armature circuit, and thus control the direction of motor rotation. The contact pairs are contained in opposite legs of the bridge arrangement whereby upon closure of the forward contacts 1F, 2F, current will flow from junction 24 to contact 1F, down through the armature circuit (as illustrated in FIG. 1), through contact 2F to junction 34. Closure of the reverse contacts 1R and 2R will result in current flow from junction 24 to contact 2R, up through the armature circuit to contact 1R, and thence to junction 34.

A controller, or master switch 40, and its associated relay and contactor circuits 42 are also connected between the positive and negative source terminals 16 and 18 in parallel with the D.C. motor circuit. Controller 40 and control relays 42 are connected to the D.C. source by way of knife switches 44 and 46 and fuses 48 and 50. The controller is a conventional tive-point crane motor control, having a neutral, or off, position and five forward and five reverse positions for starting and accelerating the motor in the desired direction by way of its `associated relay circuits 42. Since the operation of such devices is well known, it will not be described here, except to note that controller 40 energizes a main line relay coil 26 in all of the forward and reverse positions, while energizing the forward relay coils 52 and 54 in all five forward positions and energizing the reverse relay coils 56 and 58 in all five reverse positions. The portion of accelerating resistor 30 in circuit with the motor is varied in accordance with the position of the controller in known manner.

The protective circuit of the present invention comprises a normally-closed main line relay contact 26b in series with an emergency relay coil 60, the series protective circuit being connected between the reversing contact bridge arrangement and the negative terminal 18, thus paralleling the main line contact 26a, 4as well as the series eld 14 and the accelerating resistor 30. Associated with the emergency relay coil 60 is a set of normally-closed contacts 60a connected in series with the main line relay coil 26. Upon opening of these emergency contacts, energization of the main line relay coil 26 is prevented, and, consequently, misoperation of the motor due to malfunction of the directional contacts is averted. The series emergency circuit is shown as being connected to the positive junction point 34, and bypasses the main line contact 26a so as to permit energization of emergency relay coil 60 before closure of main line contact 26a.

An alarm circuit is provided in conjunction with the present emergency relay, and comprises a siren 64, or other suitable alarm device, connected in series with a normally-open emergency relay contact 60b and a knife switch 66 between the positive and negative power supply terminals 16 and 18. A pushbutton switch 68 is provided across the contacts 60h to permit manual operation of the siren. A further indication of malfunction may be provided by a neon lamp 70 connected across the main line contacts 26a. This lamp will be illuminated if there is any current flow in the motor circuit while the main line contacts are open. Such `a current indicates a malfunction in the system.

Under normal operating conditions, with knife switches 20, 22, 44, 46 and 66 closed and the controller 40 in the off position, directional contacts 1F, 2F and 1R, 3R are open, and no current can flow to motor armature 10. Movement of the controller 40 to one of its oper-ating positions immediately energizes the appropriate pair of directional relay coils 52, 54 or 56, 58, while at the same time energizing the main line relay coil 26. If the forward direction is selected, relay contacts 1F and 2F will be closed by relay coils 52 and 54, respectively, and main cont-act 26a will be closed by relay coil 26. Energization of relay coil 26 also will open the normallyclosed contacts 26b, to insure against operation of the emergency relay. Since the directional contacts are interlocked in the usual fashion so that selection of the forward contacts precludes operation of the reverse contacts, the motor will operate in the forward direction at the speed determined by the value of the accelerating resistor.

If a malfunction of some sort had occurred in the directional contacts, so that the reverse contacts 1R and 2R had frozen shut, and remained closed while the controller 40 was olf, a serious accident could occur upon operation of the system in the absence of the emer- Vgency relay of the invention. Without the emergency relay, movement of the controller switch 40 in a direction to energize the forward contacts would energize relay coils 52, 54 `and 26 as before, but would not close contact 1F and 2F. Contact 26a would close, however, and, contacts 1R and 2R being accidentally preselected, the motor would operate in reverse without warning.

By the addition of the emergency relay of the present invention, the problems presented by the foregoing type of accidental operation are completely avoided. If contacts 1R and 2R are frozen closed or otherwise short circuited while the controller 40 is in the off position and the several knife switches are closed, current will flow from positive terminal 16 to junction 24, through contact 2R, armature 10, contact 1R, normally closed contact 26B, and emergency relay coil 60 to negative terminal 18, energizing coil 60 and opening normally-closed contact 60a. Opening of this Contact disconnects main line relay 26, .and prevents its energization upon operation of controller 40, thereby preventing closure of relay contact 26a or operation of the controlled motor. Further, energization of relay coil 60 closes contact 60b to activate warning siren 64. The flow of current through armature 10 during a fault condition also illuminates neon lamp 70 to provide visual warning of the condition. Thus, as soon as the directional contacts accidental close, and before the controller 40 is moved from its off position, the emergency relay circuit acts to prevent a malfunction of the motor by opening the energizing circuit of the main operating relay 26. Movement of the controller after energization of the emergency relay will not energize the motor.

FIG. 2 of the drawings illustrates the manner in which the protective system of the present invention can be applied to another motor control system. In this case, the system is a crane hoist control wherein the D.\C. motor 10 is reversibly operable to hoist (H) or lower (L) a load. In this figure, elements corresponding to tho-se of FIG. l are similarly numbered. In place of the bridge reversing contactors of the device of FIG. l, however, the present system is operated by means of hoist and lower contacts a and 82a, respectively, which perform the same function of reversing the current flow through the motor armature circuit. This circuit has the added feature of a dynamic braking resistor 84 of known type.

The operation of the system of FIG. 2 is similar tothat of the system of FIG. 1, insofar as the emergency relay 60 is concerned. This relay is again connected in parallel with the series field 14, the accelerating resistor 30 and the main line contact 26a, thus providing a warning of unwanted current fiow through either the hoist or lower contacts 80a or 82a. A neon lamp is provided across contact 26a to give visual indication of `a malfunction, or fault condition, in the directional relay contacts.

Thus there has been described a protective relay system for reversible electric motors which will disable the motor controller circuitry in the event of a short-circuit condition in the motor directional relay contacts.

I claim:

1. A protective relay system for reversible electric motors comprising an electric motor having an armature circuit; normally open first and second switch means in circuit with said armature circuit; controller means yfor selectively closing one of said switch means to energize said motor; an emergency relay having coil means connected to said first and second which means and operable to sense a short circuit condition in said first or second switch means; and emergency relay contact means responsive to operation of said emergency relay coil means to prevent energization of said electric motor.

2. The protective relay system of claim 1, wherein said controller means includes a main line relay coil for energizing said electric motor, said main line relay including a first contact in series with said armature circuit and a second contact in series with emergency relay coil, whereby operation of said main line relay energizes said electric motor and simultaneously disables said emergency relay coil.

3. The protective relay system of claim 2, wherein said emergency relay contact means comprises a contact in series with said main line relay coil, said last-named contact serving to disable said main line relay.

4. The protective relay system of claim 1, further including alarm means responsive to operation to operator of said emergency relay coil means.

5. The protective relay system of claim 2, further including fault indicator means connected in parallel with said first contact of said main line relay, said fault indicator responding to current fiow in said armature circuit when said first contact of said main line relay is open.

6. A protective relay system for a reversible electric motor comprising a source of electric power; said motor having an armature circuit reversibly connectable across said source for energization thereby; said armature circuit being connectable across said source for energization thereby; said armature circuit being connectable in a series 8. The protective relay of claim 6, further including controller means having directional relay coils selectively energizable for operating said directional relay contact means to control the direction of operation of said motor; said controller means further including a main line relay coil energizable to close said normally-open main line relay contact to energize said motor.

9. The protective relay of claim 8, wherein said directional relay contact means comprises a pair of forward contacts and a pair of reverse contacts in a bridge arrangement, two opposing corners of said bridge being connected in said series circuit, said armature circuit being connected to the remaining two corners of said bridge, said emergency relay means being connected to said bridge arrangement for energization upon occurrence of a short-circuit in any of said directional contacts.

10. The protective relay -of claim 9, said emergency relay means including first, normally-closed emergency contact means in series with said main line relay coil for disabling said last-named coil upon energization of said emergency relay means, whereby energization of said motor is prevented.

11. The protective relay of claim 10, further including alarm means responsive to energization of said emergency relay means.

References Cited UNITED STATES PATENTS 3,187,246 6/1965 Garten 317-13 X 3,293,521 12/ 1966 Vroonhoven 318-281 3,373,316 3/1968 Palmer 317-13 LEE T. HIX, Primary Examiner. I. D. TRAMMELL, Assistant Examiner.

U.S. C1. X.R. 318-281

Images