US1750268A - Relay protective system - Google Patents

Description

March 11, 1930. Q, 5, JENNlNGS 3,750,268

RELAY PROTECTIVE SYSTEM Filed April 28, 1923 WITNESSES: HNVENTQR W fl/l'ver 5. Jennings BY W 4 v ATTORNEY Patented Mar. 11, 1930 UNITED s'ra'res PATENT orricr.

OLIVER S. JENNINGS, OF WI LKINSBURG, IENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA RELAY PROTECTIVE SYSTEEE Application filed April 26,

My invention relates to relay protective systems and particularly to systems to be applied to switches that are normally held closed by electromagnets.

One object of my invention is to provide a novel method of controlling the holding magnet of a switch to render the electromagnet ineffective when predetermined abnormal conditions developin a circuit to which electrical apparatus is connected.

Another object of my invention is to provide a relay system, of the above-indicated character, wherein the electromagnet may be controlled by a thermal relay of the contactclosing type.

A further object of my invention is to provide a system, of the above-indicated character, wherein the energization of the electromagnet may be controlled by different windings, the respective circuits of which are controlled by devices responsive to the effects of currents traversing different conductors of the circuit.

In practicing my invention, I provide, in addition to the single coil that usually is provided with a low-voltage closing mechanism for the switch, a second coil which is normally open-circuited. The second coil is inductively'related t0 the energizing coil and is adapted to be close-circuited by a current or thermal-responsive device associated with the circuit to be protected when predetermined abnormal conditions are developed therein. When the second coil is close-circuited, the magnetizing efiect of the energizing winding is so diminished that the electromagnet becomes insufficiently energized to maintain the switch in closed position, and the switch is thereupon permitted to open the circuit to disconnect the apparatus from the supply circuit.

The figure of the accompanying drawing is a diagrammatic view of an electrical circuit, illustrating the disposition of the various elements to function in the manner contemplated by my invention in an alternating-cue rent circuit in which the value of the current that is to be supplied to the apparatus is relatively large.

In considering the system that is illus- 1923. Serial No. 634,878.

trated in the figure, a source of energy, such as a generator 1, supplies energy to a supply circuit :2 from which it is supplied to a load circuit 3 containing electrical apparatus, such as a motor 4, through a switch 5.

The switch 5 may be of the type illustrated in my prior Patent, No. 1,557,056, dated October 13, 1925, starting safety switches, but which is herein illustrated schematically. The switch comprises, in addition to the main switching members 6,- an operating shaft 7, a spring 8, tending normally to maintain the switch members in open position, and an electromagnet 9 that is adapted, when energized, to co-operate with a cam member 10, that is disposed on the shaft 7, to maintain the switch in closed position after it has been actuated thereto.

The electromagnet 9 comprises a magnetizable core member 11 and a pivoted armature member 12 that is provided with a latch or holding portion 18 for engaging the cam 10 of the operating shaft 7. The electromagnet 9 is further provided with two windings 14 and 15 that are adapted to be controlled by relay devices 16 and 17 associated with the several conductors of the load circuit between the switch 5 and the motor 4.

The system is illustrated as a two-phase system merely by way of example and the apparatus may be equally well applied to the protection of an electrical system having a different number of phases.

The relay 17 is illustrated herein as a relay of the thermal type in which the thermalresponsive member is heated in accordance with the circuit current to follow substantially the operating temperature characteristic of the apparatus with which it is associated and is arranged to open its contact members 18 when a predetermined abnormal temperature condition is indicated in the apparatus.

Normally, the winding 15 is energized from one phase of the circuit through the contact members 18. When an abnormal temperature condition is attained in the circuit or the apparatus, the opening of the contact members 18 tie-energizes the winding 15 and, consequently, the electromagnet 9 to permit the switch in closed position.

the spring 8 to open the switch 5. It will be noted that the same result will be effected if the voltage of the circuit should decrease to, or below, a predetermined value at which the energization of the electromagnet is insufficient to maintain the switch in closed position against the restraining force of the spring 8.

In electrical circuits provided with a plurality of phases or a plurality of circuit conductors whereby currents of different values may traverse the different conductors, it is desirable to procure closer protection by providing an additional protective device.

In the present instance, the additional thermal relay 16 is provided and it is disposed in the other phase of the circuit to control the winding 14 in accordance with the 'current traversing that phase. The relay 16 is of the circuit-closing type and is arranged, when energized to a degree corresponding to an abnormal condition in the circuit of the apparatus, to close its cont-act members 19. The circuit of the winding 14 is normally open until closed by the operation of the relay 16.

Since the system is an alternating-current system, the close-circuiting of the winding 14, in view of its relatively close inductive relation to the energizing winding 15, will tend to diminish the energizing effect of the winding 15 and thereby preclude the proper energization of the electromagnet 9 to maintain The spring 8 thereupon becomes effective to open the switch to disconnect the motor from the supply circuit 2.

'After the abnormal conditions, such as overload or faulty conditions in the circuit or the apparatus, are cleared, the switch 5 may be again reset and the electromagnet will be immediatel re-energized, since the relays are of the sel -resetting type.

The relays may be so adjusted that the circuit-closing relay 16 will ordinarily operate to close its contacts before the relay 17 will operate to open its contacts 18. This condition is desirable since it is preferable to have protection effected bythe closing of contacts in relays of this type rather than by the opening of contacts, whereby the bad effects of sparking in the contact members are considerably diminished and, to a great extent. eliminated. The relay 17 may thus be adjusted to operate only upon the failure of the relay 16 to close the circuit of the coil 14.

The method which I have illustrated and described herein is particularly applicable to, and desirable for, circuits with which are employed enclosed switches of the type illustrated in my copending application, pre viously referred to. Since the thermal re lays associated with this switch are relatively small, it is advantageous and desirwill permit the use of circuit-closin in order to limit the effects of spar 'ing on the contact members.

My invention thus contemplates the application of thermal relays of the circuit-closing type to control the electromagnets usually employed to maintain switches in closed 0- sition, according to the method herein isclosed.

My invention is not limited to the preferred form of apparatus illustrated and described, but may be variously modified without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

1. In combination, a switch mechanism, means tending to maintain the switch mechanism in open position, an electromagnet for holding the mechanism in closed position including a holding winding, and a normally open auxiliary winding, means serving normally to maintain said holding winding energized and means for automatically closecircuiting the auxiliary winding under predetermined electrical conditions to render the electromagnet ineffective to hold the switch mechanism in closed position.

2. In an electrical circuit, the combination with an apparatus and a switch for connecting the apparatus to the circuit, of means tending to hold the switch in open position, means for holding the switch in closed position including an electromagnet provided with a holding winding and a normally open auxiliary winding, means including an auxiliary switch for connecting said holding winding to the circuit to energize it therefrom, means for opening the auxiliary switch under predetermined current conditions in one conductor of the circuit and means for close-circuiting the auxiliary winding responsive to the electrical condition of another conductor of the circuit.

3. In an electrical circuit, the combination with an apparatus and a switch for connecting the apparatus to the circuit, of means tending to hold the switch in open position, means for holding the switch in closed position including an clectromagnet provided with a holding Winding and a normally open auxiliary winding, means for energizing said holding winding in accordance with a voltage derived from the circuit and means for controlling the circuit of the auxiliary winding in accordance with the value of the current traversing the circuit.

4. In an electrical circuit, the combination with a switch mechanism including an electromagnet for maintaining said mechanism in closed position, of two windings for controlling the energization of the electromagnet, and means for controlling the windings including means responsive to the thermal effect of the circpit cur-rem for; permitting the enerimiafi relaysthe thermal efiect of the CUI1K1t is less than a predetermined value and tor precluding such energization when the thermal effect errceeds such Value, and a second means responsive to the thermal effect of the circuit current for close-circuit-ing the second winding.

5. In an electrical circuit, the combination with a switch and an electromagnet provided with a winding energized from the circuit to maintain said switch in closed position, of a normally open-circuited winding inductively related to the first winding and means dependent upon a predetemined electrical condition of the circuit for close-circuiting said last mentioned, winding.

6; In an electrical circuit, the combination with a switch and an electromagnet provided with a coil energized from the circuit to maintain said switch in closed position, of means for rendering said electromagnet inefifective to hold the switch in closed position including a relay embodying movable and stationery contact members and responsive to a predetermined condition of the circuit to efiect engagement of said contact members, and a coil connected to said contact members and positioned on said electromagnet to limit the flux traversing the electromagnet.

7. In an electrical circuit, the combination with a switch and an electromagnet provided with a coil energized from the circuit to maintain said switch in closed position, of a thermal device operated in accordance with the load in said circuit, and means including said thermal device and electrically independent of said coil for rendering said electromagnet ineflective to hold said switch in closed position.

8. In an electrical circuit, the combination with a switch and an electromagnet provided with a coil energized from the circuit to maintain said switch in closed position and an auxiliary coil, of a thermal relay in said circuit for short-circuiting said auxiliary coil upon the occurrence of an overload in said circuit to render said electromagnet inefifce tive to hold said switch in closed position.

9. In combination, a switch mechanism, means tending to open said switch mechanism, an electromagnet for holding said mechanism in closed position including a holding winding and an inductively-related auxiliary winding, means for energizing said holding winding and a thermal relay for ciose-circuiting said auxiliary winding on overload to render the electromagnet ineffective to hold the switch mechanism ciosed.

In testimony whereof, I have hereunto subscribed my name this 23rd day of Aprii, 19239 OLIVER S. JENNIN

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