US3638157A

US3638157A - Combination motor starter

Info

Publication number: US3638157A
Application number: US828466A
Authority: US
Inventors: Zelco J Kruzic
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-05-28
Filing date: 1969-05-28
Publication date: 1972-01-25
Anticipated expiration: 1989-01-25
Also published as: GB1268731A; CA941444A; FR2043743A1; FR2043743B1

Abstract

An improved combination motor starter with low overload protection; adjustable low-level fault protection; heavy short circuit interrupting capacity; and a coordinated protection system that protects the motor, the cable and the components of the combination motor starter. More specifically, the low-level fault protection is given by a resettable circuit breaker, and a current-limiting fuse is used both to provide heavy short circuit protection and to also operate fast enough and at low enough currents to protect against burnout or damage of the heater or other current-responsive element of the device protecting the motor against overloads.

Description

United States Patent Kruzic [54] COMBINATION MOTOR STARTER [72] Inventor: Zelco J. Kruzic, New Brighton, Pa.

[73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: May 28, 1969 [21] Appl. No; 828,466

[52] US. Cl ..337/6 [51] Int. Cl. .,H0lh 85/00 [58] Field ofSearch .337/6, 49, 48,78,38, 107, 337/161, 7, 54; 317/13, 37, 116; 335/9, 126, 142

[56] References Cited UNITED STATES PATENTS 2,411,351 11/1946 Armstrong ..337/54 X 2,843,702 7/1958 Edmunds ..337/7 3,009,036 11/1961 Dorfman et a1 ..337/7 3,354,356 11/1967 Pettit et a1. ..317/116 2,506,272 S/195O Koci ...337/l07 2,965,809 12/1960 Edsall ..317/13 [4 1 Jan. 25, 1972 3,211,955 10/1965 Soos, Jr. "317/13 3,265,831 3/1966 Ramsey.... .....337/48 3,291,940 12/1966 Kozacka 337/161 3,353,127 11/1967 Francis .335/9 3,409,851 11/1968 Scheib .335/126 Primary ExaminerHarold Broome An0rneyA. T. Stratton, Clement L. McHale and W. A. Elchik [5 7] ABSTRACT An improved combination motor starter with low overload protection; adjustable low-1evel fault protection; heavy short circuit interrupting capacity; and a coordinated protection system that protects the motor, the cable and the components of the combination motor starter. More specifically, the lowlevel fault protection is given by a resettable circuit breaker, and a current-limiting fuse is used both to provide heavy short circuit protection and to also operate fast enough and at low enough currents to protect against burnout or damage of the heater or other current-responsive element of the device protecting the motor against overloads.

13 Claims, 8 Drawing Figures COMBINATION MOTOR STARTER CROSS-REFERENCES TO RELATED APPLICATIONS AND PATENTS Components of the subject combination motor starter are of the general type, more specifically described in the U.S. Pat. Nos. 3,265,831, 3,296,567 and 3,296,393, and in the applications Ser. No. 703,409, filed Feb. 6, 1968 now US. Pat. No. 3,575,679, and Ser. No. 752,848, filed Aug. 15, I968. The patents and applications will be further identified in the specification hereinafter with reference to the components of the combination motor starter.

BACKGROUND OF THE INVENTION 1. Field of the Invention Combination motor starter for controlling and protecting motors and motor circuits.

2. Description of the Prior Art It is old in the art to provide a fuse-switch combination motor starter comprising a contactor with overload relays for automatically opening the contactor to open the motor circuit upon the occurrence of lesser overload currents occasioned by overloads on the motor; current-limiting fuses for interrupting low-level to high-level and short-circuit fault currents; and a manually operable switch for permitting manual opening and closing of the motor circuit.

It is also old in the art to provide a fuse-breaker combination motor starter comprising a contactor with overload relays for opening the contactor to open the motor circuit upon the occurrence of lesser overload currents; a manually operable circuit breaker automatically operable to interrupt the motor circuit upon the occurrence of low-level to high-level faults and current-limiting fuses that operate upon the occurrence of a heavy short-circuit current having a value in a range from just below the interrupting rating of the breaker to a value above the interrupting rating of the breaker to interrupt the circuit with a current-limiting action and to trip the circuit breaker, the circuit breaker and fuse time-current curves being coordinated as described in Dyer US. Pat. No. 3,077,525, issued Feb. 12, 1963.

SUMMARY OF THE INVENTION The invention provides an improved combination motor starter providing an improved coordinated protection system. The device includes a circuit-interrupting device for opening the circuit to the motor and a motor overload responsive device for initiating opening of the motor circuit with a time delay upon the flow of an overload current in the range between a current above the full-load current to the motor and the locked rotor current of the motor. There is a currentresponsive device operable upon the flow of an excess current greater than the locked rotor current of the motor and this current-responsive device initiates the opening of the motor circuit faster than the motor overload responsive device. There is also a current-limiting device operative upon the flow of heavier excess currents to limit the current flow to a value which does not damage the motor overload responsive device. More specifically, the starter comprises a contactor, overload means for operating the contactor and an adjustable currentlimiting circuit interrupter for interrupting fault currents to protect the motor, cable and the components of the starter. The overload relay means operates, with a time delay, upon the occurrence of motor overloads of, for example, 1.25 times full-load current of the motor and higher up to locked rotor current, to effect opening of the contactor. The adjustable current-limiting circuit interrupter operates, faster than the relay means, to interrupt the motor circuit upon the occurrence of fault currents starting at a predetermined current within the range of from two to 13 times full-load current. Preferably the circuit interrupter comprises a manually operable adjustable automatic tripping resettable circuit breaker that automatically trips, faster than the relay means, from a first predetermined overload current within the range of from breaker. This opens all conductors leading to the motor and prevents single-phase operation of three-phase motors, whereas if only fuses were provided, one might blow and allow the motor to operate on single phase. The current-limiting fuse unit provides an effective interrupting capacity of 100,000 amperes at 600 volts even though the interrupting capacity of the circuit breaker may be only [0,000 amperes. The circuit breaker is a motor circuit protector. Each motor has a different locked rotor current value. Thus, each motor should be protected by a circuit breaker with precisely the right tripping point.

The circuit breaker utilized in this combination is preferably externally adjustable and comprises selective locking means for providing that the trip adjustment cannot be set higher than the maximum locked rotor current, which may be about 13 times the full-load current of the motors that are to be protected by the breaker.

The fuse unit is removably mounted and connected to the circuit breaker, providing the advantage that the circuit interrupter or fused circuit breaker combination can be made up utilizing a circuit breaker that has utility without the fuse unit.

The novel combination of this invention has an advantage over the above-mentioned fused switch combination motor starter in that the circuit breaker is adjustable and resettable following tripping operations of the breaker. Another advantage of the novel combination of this invention is that in the low-level fault area the magnetic trip device of the circuit breaker will clear a fault faster than a fuse which is inherently a thermal sensing device with a built-in time delay to override the initial inrush peaks. In the subject invention the breaker comprises a magnetic trip that is a constant-time device requiring one-half to three-fourths of a cycle to clear in the area of low-level faults. In the area of low-level faults, which comprise the majority of faults encountered, the breaker will clear the circuit perhaps 10 to 15 cycles faster than a fuse.

The novel combination of this invention has an advantage over the above-mentioned fused-breaker combination motor starter in that the time-current tripping curve characteristics of the combination of this invention are such that the currentlimiting fuses serve to interrupt the circuit and limit the current at a current level that otherwise could cause heater burnout and damage of the overload relays and also possible damage to the contactor itself.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view, with parts broken away, of a combination motor starter constructed in accordance with principles of this invention;

FIG. 2 is a schematic wiring diagram illustrating an application of the motor starter of FIG. I;

FIG. 3 is a side sectional view through the center pole unit of the circuit interrupter of FIG. 1;

FIG. 4 is a partial view illustrating the trip-adjusting means and locking means for selectively changing the range of adjustment of the circuit breaker of FIG. 3;

FIG. 5 is a side sectional view through one of the pole units of the multipole contactor of FIG.

FIG. 6 is a plan sectional view of the multipole overload relay of FIG. 1;

FIG. 7 is a side sectional view taken generally along the line VIIVII of FIG. 6; and

FIG. 8 is a diagram of the combination time-current characteristics of an application of the combination motor starter of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is disclosed in FIG. 1, a combination motor starter 5 comprising an enclosure 7, a circuit interrupter 9 that comprises a multipole circuit breaker 9 and a multipole fuse unit 11, a multipole contactor 13, and a multipole overload relay 15.

The enclosure 7 is of the type more specifically described in the patent to R. V. Rimmer et al. U.S. Pat. No. 3,296,393, issued Jan. 3, 1967. Thus, only a brief description of the enclosure will be provided herein. The enclosure 7 comprises a receptacle 17 having a front flange portion 19 thereon and a hinged cover (broken away) 21 movable to open and close the receptacle. A handle operating mechanism 23 extends from the flange portion 19 to permit external manual operation of the circuit breaker 9. A claw-type member 25, which is operated by the handle operating mechanism 23, is operatively connected to the handle 27 of the circuit breaker 9 to manually operate the circuit breaker 9 upon operation of the handle operating mechanism 23.

The circuit breaker 9 is of the type more specifically described in the application of James P. Ellsworth et al., Ser. No. 703,409, filed Feb. 6, I968. Thus, only a brief description of the circuit breaker will be provided herein. The circuit breaker 9 (FIG. 3) comprises an insulating housing 29 having an opening in the front thereof through which the handle 27 extends. The circuit breaker is a three-pole circuit breaker with the center pole unit being shown in FIG. 3. Each pole unit comprises a conducting strap 31 having a terminal connector 33 at the outer end thereof and a stationary contact 35 at the inner end thereof; a movable contact arm 37 having a movable contact 39 thereon; a switch arm 41 pivotally carrying the contact arm 37 at one end thereof and being fixedly connected to a common insula,ing tie bar 43 at the other end thereof; a flexible conductor 45 connected at one end thereof to the associated contact arm 37 and at the other end thereof to a terminal 47; and a coil 49 connected at one end thereof to the terminal 47 and at the other end thereof to a terminal 51. The circuit for each pole unit extends from the terminal connector 33 through the conductor 31, stationary contact 35, movable contact 39, contact arm 37, flexible conductor 45, terminal conductor 47, coil 49, to the terminal 51.

In the center pole unit a toggle 53, comprising a pair of pivotally connected toggle links, is pivotally connected at one end to the center pole switch arm 41 and at the other end to a releasable trip member 55 that is mounted for pivotal movement on a pin 57. A pair of overcenter tension springs 59 are connected at one end thereof to the knee pivot of the toggle 53 and at the other end thereof to the bight portion of an inverted U-shape operating lever 61. The operating lever 61 is pivotally supported at the inner ends of the legs thereof on a pair of stationary supporting plates in a well-known manner. The handle 27 is connected to the lever 61 to provide for manual operation.

The releasable trip member 55 is latched at the free end thereof, against clockwise (FIG. 3) tripping movement, by means of a roller latch member 63 that is pivotally mounted on a pin 65. The trip member 55 is latched by a roller 64 that is supported for movement in a slot on the member 63 and biased to the latching position by means of a torsion spring 66. The roller latch member 63 is latched against clockwise unlatching movement by means of an insulating trip bar 67 that is common to all three pole units and that is supported for pivotal movement about the elongated axis thereof, which axis is normal to the plane of the paper as seen in FIG. 3.

In each pole unit, an electromagnetic trip device comprises the coil 49, a stationary magnetic member 69, that is supported within the coil 49, and a movable magnetic armature 71 that is supported for pivotal movement about a pin 73. Each armature 71 comprises an extension 75 having an actuating screw 77 threadedly secured thereto at the upper end thereof. Each of the actuating screws 77 extends through an opening in a common adjusting bar 79 that is pivotally supported at the opposite ends thereof on the ends of the tie bar 67.

A single adjusting cam member 81 (FIG. 4), comprising a cam surface 93 that cooperates with the adjusting bar 79, is supported within the breaker for movement about an axis normal to the plane of the paper as seen in FIG. 4. A lockpin 35 is selectively mountable in a selected one of a plurality of openings (FIG. 1) in the front of the housing to change the range of adjustment of the tripping characteristics of the circuit breaker in the manner more specifically described in the above-mentioned application of James P. Ellsworth et al., Ser. No. 703,409, now U.S. Pat. No. 3,575,679.

Referring to FIG. 3, the circuit breaker 9 is shown in the closed position. The circuit breaker is manually operable to the open or off" position by counterclockwise movement of the handle 27, which movement changes the line of action of the springs 59 to cause collapse of the toggle 53 and simultaneous opening movement of the contact arms 37. The circuit breaker is manually closed by clockwise movement of the handle 27 to the on or closed position which movement changes the line of action of the springs 59 to cause erection of the toggle 53 and simultaneous closing movement of the three contact arms in a manner well known in the art.

With the circuit breaker in the closed position, when an overload within the tripping range of the circuit breaker 9 occurs in any of the pole units the armature 71 of that pole unit will be attracted to the magnet 69 whereupon the associated screw 77 will engage the trip bar 67 to pivot the trip bar 67 in a counterclockwise direction to release the roller latch member 63 which then releases the trip member 55. Upon release of the trip member 55 the springs 59 rotate the trip member 55 in a clockwise direction to the tripped position changing the line of action of the springs 59 which operate to collapse the toggle 53 to effect opening movement of the three contact arms 37.

Following the automatic tripping operation, the circuit breaker 9 must be reset and relatched before the breaker can again be closed. Resetting and relatching is effected by moving the handle 27 to a position slightly past the full off" position. During this movement, a projection 89 on the operating lever 61 engages a shoulder 91 on the trip member 55 to pivot the trip member 55 in a counterclockwise direction. During this movement the trip member 55 wipes by the roller 64 and engages a part of the roller latch member 63 to move the roller latch member 63 to the latching position, whereupon spring means 95 biases the trip bar 67 into the latching position wherein the trip bar 67 again latches the roller latch member 63 so that upon release of the handle 27 the roller latch member 63 will again latch the releasable trip member 55 against clockwise tripping movement. Thereafter, the circuit breaker 9 can be manually and automatically operated in the same manner as was hereinbefore described.

The fuse unit 11 is a multipole fuse unit constructed generally in the manner described in the above-mentioned patent application of James C. Wilson Ser. No. 752,848, filed Aug. 15, 1968, except that the fuses of the fuse unit 11 are constructed to interrupt the circuit at a significantly lower level of fault current than the fuses of the application Ser. No. 752,848, which were specifically designed to operate within and close to the interrupting capacity of the circuit breaker of the fused-breaker combination. That is, the current-limiting fuses of this invention will blow faster than the circuit breaker will trip on currents just below those currents which could cause heater burnout or overload relay damage, whereas the fuses formerly used did not blow until close to the interrupting capacity of the circuit breaker which is often 10,000 amperes or more and way beyond the currents which cause heater burnout or relay damage.

The fuse unit 11 comprises an insulating fuse unit housing 99 having insulating barrier means forming three adjacent compartments therein for the three poles of the fuse unit. Each pole unit comprises a pair of

terminal conductors

101, 103 supported therein and having the bent-over lower leg portions extending out from opposite ends of the housing 99. The terminal 101 of each pole unit is connected to the associated pole unit of the circuit breaker 9 by means of a bolt member 195. A separate solderless terminal connector 197 is mounted on the end portion of each of the terminals 103. A plurality of fusible elements 109 (6 as seen in FIG. 3) are connected between the spaced faces of the

conductors

101, 103. A fusible strain wire 112 is connected to an indicator 113 that is biased by a spring 114.

The inside cavity of each pole unit is filled with an arcquenching filler material 117, such as sand. Upon the occurrence of an overload in any of the pole units, in the operating range of the fuse unit, the fusible elements 109, which are in parallel in the circuit of the associated overloaded pole unit, will fuse or blow instantaneously to interrupt the overload with a current-limiting action. The heat that is generated by the circuit interruption is conducted through the filler material to the fusible strain wire 112 which fuses, whereupon the spring 114 biases the indicator 113 frontward to provide a visual indication that the fuse has blown.

When a maintenance man sees that a particular fuse has blown, he can remove the fuse device and replace the blown fuse in the housing 99 with a similar fuse. During the course of replacing the blown fuse, the filler material 117 can be replaced with filler material that has not been subjected to a circuit interruption. Thereafter, the fuse device 11 can be installed and connected to the circuit breaker 9.

The contactor 13 (FIGS. 1 and 5) is of the type disclosed in the patent to John P. Conner et al. U.S. Pat. No. 3,296,567, issued .Ian. 3, 1967. Thus, only a brief description of the contactor 13 will be provided herein. The contactor 13 comprises a metallic baseplate 123 with an insulating housing structure 125 supported thereon. A U-shaped magnetic core member 127 is stationarily mounted on the baseplate 123 within the housing 125. A coil 129, comprising conducting coil means supported in an insulating capsule, is supported in the housing 125. A U-shaped magnetic armature 131 is supported for var tical (FIG. 5) rectilinear movement toward and away from the pole faces of the stationary magnetic member 127. An insulating contact carrier 133, spring biased to the unactuated position by spring means 135, is connected to the armature 131 to move with the armature 131.

The contactor 13 is a four-pole contactor with each pole unit comprising a pair of

stationary contacts

137, 139 and a movable bridging contact member 141. Each of the bridging contact members 141 is supported on the insulating contact carrier 133 for movement with the contact carrier 133 between open and closed positions. A separate contact-pressure spring means 143 is provided at each pole unit to provide contact pressure between the bridging contact member 141 and the associated

stationary contacts

137, 139. In each pole unit, the stationary contact 139 is supported on a conducting strap 147 and the stationary contact 137 is supported on a conducting strap 149. Suitable terminal means 150, 152 (FIG. I) are connected to the outer ends of the

straps

147, 149 to permit connection of each pole unit in an electric circuit. Externally accessible terminals 153, 154 (FIG. 1) are provided for enabling connection of the coil 129 in an electric circuit.

The contactor is shown in FIG. 5 in the deenergized or unactuated position with the bridging contact member 141 in the normally open position and the armature 131 in the upper unactuated position. Upon energization of the coil 129, the armature 131 is attracted downward toward the stationary magnetic member 127 to simultaneously move the four bridging contact members 141 of the four-pole units from the open position seen in FIG. 5 to the closed position. Upon deenergization of the coil 129, the springs 135 return the armature 131 and contact carrier 133 to the unactuated normally open position seen in FIG. 5.

The multipole overload relay is of the type more specifically described in the patent to J. B. Ramsey et al. U.S. Pat. No. 3,265,831, issued Aug. 9, 1966. Thus, only a brief description of the relay 15 will be provided herein. The relay 15 comprises an insulating housing 153. A separate actuating bimetal 155, for each of the pole units, is suitably supported in the housing 153. For each pole unit, a separate replaceable heater member 157 is removably secured in place by means of

screws

159, 161, and a separate pair of terminals 163, are provided to enable connection of each of the heater members 157 in an electric circuit.

An insulating actuating bar 169, common to all three-pole units, is pivotally supported at 171 (FIG. 7). The actuating bar 169 comprises a projection 173 (FIG. 6) that engages a compensating bimetal 175 that is connected to an operating structure 177. Upon movement of the compensating bimetal 175, the operating structure 177 is operated to move a movable contact arm 179 that carries a movable contact 181 thereon for cooperating with a stationary contact 183 that is mounted on a stationary contact arm 185.

The relay is seen in FIG. 6 in the normaily closed position. When the relay is in the normally closed position, a circuit extends from a terminal 187 through a conducting bracket 189, the movable contact arm 179, the movable contact 181, the stationary contact 183, the stationary contact arm 185, to a terminal 191. As is more specifically described in U.S. Pat. No. 3,265,831, the relay could be wired for normally open operation by connecting the conducting lines to the terminal 187 and a terminal 193 that is electrically integral with another stationary contact 195.

The operating structure 177 comprises an overcenter spring 197 that is connected to the contact arm 179 to move the contact arm between open and closed positions upon operation of the compensating bimetal 175 and operating structure 177 in the manner more specifically described in the patent to Ramsey et al. U.S. Pat. No. 3,265,831. A calibrating screw 201 (FIG. 7) is provided in each pole unit to adjust the position of the associated bimetal 171 to calibrate the pole unit.

When the current through any of the pole units of the relay 15 reaches a predetermined value such, for example, as 1.25 times the full-load current of the motor that is to be protected by the combination motor starter, the heat generated in the associated heater structure 157 will cause the associated actuating bimetal 155 to flex to the left (FIG. 7) to thereby rotate the common actuating bar 169 clockwise (FIG. 7) about the pivot 171. During this movement, the projection 173 (FIG. 6) on the common actuating bar 169 moves to move the compensating bimetal member 175 to thereby move the operating structure 177 to operate the overcenter spring 197 and contact arm 179 to move the movable contact 181 to an open position disengaged from the stationary contact 183. Following an operation of the relay 15, when the actuating bimetal cools to the straightened position, the relay is reset in the normally closed position seen in FIG. 6 either automatically or by a hand-resetting operation as described in the above-mentioned U.S. Pat. No. 3,265,831. As is described in U.S. Pat. No. 3,265,831, the heaters are replaceable by heaters having different ratings and an external adjustment is provided to enable a plus or minus adjustment of the relay.

The operation of the combination motor starter will be best understood with reference to FIGS. 1 and 2. As can be seen in FIG. 2, the combination motor starter 5 is shown diagrammatically to illustrate an application of the motor starter for controlling and protecting the motor circuit of a motor M. A pushbutton switch PB may be mounted outside of the receptaole of the combination motor starter 5 and wired to the motor starter 5 as shown. The pushbutton switch may also be mounted on the motor starter enclosure if desired. The overload relay is calibrated and provided with a rated heater that will effect deenergization of the contactor to thereby open the motor circuit, with a time delay, upon the occurrence of overloads just over the motor full-load current, such as an overload, for example, of 1.25 times the full-load current of the motor. The circuit breaker is calibrated and adjusted to trip faster than the relay at a first predetermined current which is within a first predetermined range of from two to 13 times full-load current of the motor, and preferably within the range of from five to 13 times the full-load current of the motor. The currentlimiting fuse unit is constructed to operate faster than the circuit breaker to interrupt the circuit at a second predetermined current which is within a second range of from 50 to 200 times the full-load current of the motor and preferably within the range of from 100 to 150 times the fullload current of the motor. The current-limiting fuse unit will operate from the second predetermined current to the maximum fault current that the combination starter can interrupt with the current-limiting fuses operating to limit the current thereby providing a high interrupting capacity combination motor starter.

With the components connected and wired as shown in FIG. 2, an operator can manually close the circuit breaker 9 and then operate the pushbutton 209 to energize the motor M. Upon a closing operation of the normally open pushbutton 209, a circuit is closed from the line L1 through a line L4, the pushbutton 209, a line L5, a line L6, the coil 129 of the contactor 113, the normally closed

contacts

181, 183 of the overload relay 15, a line L7, to the line L2. This circuit energizes the coil 129 of the contactor 13 to pick up the armature 131 (FIG. of the contactor 13 to thereby close the four pole units of the contactor 13. As can be seen in FIG. 2, three pole units of the contactor 13 are in the three phases L1, L2, L3 of the motor circuit and the fourth pole unit is provided to. hold in the contactor upon release of the pushbutton 209. With the

contacts

139, 137, 141 of the fourth pole unit of the contactor 13 closed, the contactor coil 129 will remain energized, to maintain the contactor 13 closed, upon the release of the pushbutton 209 through a circuit that extends from the line L1, through the line L4, normally closed pushbutton 213, a line L8, the

contacts

139, 137, 141, the line L6, the coil 129 of the contactor 13, through the normally closed

contacts

181, 183 of the relay 15, the line L7, to the line L2. The motor circuit will remain closed until the pushbutton 213 is manually operated to deenergize the circuit of the coil 129 or until one of the

protective devices

9, 11, 15 is automatically operated in response to an overload.

A specific example of a time-current application curve of the combination starter is provided in FIG. 8. The combination starter characteristics are illustrated in FIG. 8 as applied to control a l-horsepower motor operating at 480 volts with a full-load current of 1.8 amperes. As can be understood with regard to FIG. 8, the motor will operate continuously at 1.8 amperes and at a very slight overload of up to about 2.25 am peres. Upon the occurrence of an overload of from about 2.25 amperes up to about amperes, the overload relay will operate, with a time delay according to the heavy dotted overload relay curve from its top to point Z, to deenergize the contactor to thereby interrupt the motor circuit. Upon the occurrence of a fault current of from about 20 amperes to about 240 amperes the circuit breaker will automatically trip within a small fraction of a second to interrupt the motor circuit according to the heavy solid circuit breaker trip curve from Z to Y. Upon the occurrence of a fault current from about 240 amperes to the interrupting capacity of the current-limiting fuse unit, it will operate, with current-limiting action, to interrupt the motor circuit in a time shown by the heavy dot-dash line from Y to its lower end. The heavy dotted line curve plus the heavy solid line curve and the heavy dot-dash line curve represents the overall coordinated time-current curve characteristic of the complete combination motor starter.

The current-limiting fuse unit has been successfully tested to interrupt a 600-volt circuit in which 100,000 amperes symmetrical is available and could flow when subjected to a short circuit if the current-limiting function of the fuse were not present. The fuses do not actually interrupt a current of l00,000 amperes but have the property of limiting the rise of current and of interrupting the circuit quickly, in a fraction of a half cycle, before the instantaneous value of the current has risen to a peak value more than a small fraction of the available short-circuit current of the circuit. Thus, when the current-limiting fuse is rated as having an interrupting capacity of l00,000 amperes it means that the fuse will safely interrupt a circuit in which 100,000 amperes could flow when subjected to a short circuit, if the current-limiting function of the fuse were not present. Upon interruption by a fuse of the currentlimiting fuse unit, enough current is let through to automatically trip the circuit breaker, thereby preventing the condition of having a three-phase motor operate under single-phase power if a fault on a single conductor of the three-phase circuit should blow only one fuse.

The locked rotor current of most motors is approximately six to 10 times the full-load current of the motor that is being protected. Some motors may have locked rotor currents as low as three times or as high as l3 times the full-load current. The commercially available overload relays and contactors can safely operate to interrupt the motor circuit upon the occurrence of the overloads of from, for example, 1.25 times full-load current to six to ID or l3 times full-load current. Any current that exceeds the locked rotor current can be considered a fault current. Fault current, as the name implies, is a direct result of some faulty condition in the motor or its electrical circuit which reduces the resistance and allows current to flow which is in excess of the intended design values.

The circuit breaker 9 can be adjusted to trip upon the occurrence of, for example, six to 10 times full-load current to thereby interrupt the normal or low-level fault currents of the motor circuit. For most applications, it is desirable to provide that the trip adjustment of the circuit breaker cannot be set higher than about 13 times the full-load current of the motor that is to be protected by the combination motor starter. Thus, the circuit breaker 9 comprises selective stop means (that can be selectively positioned when the full-load current is determined) for providing that the trip adjustment cannot be set higher than 13 times the full-load current of the motor. When the stop means is selectively positioned on the breaker, an operator will not be able to adjust the breaker to start tripping at a current higher than l3 times the full-load current of the motor.

The overload relay 15 has predictable heater burnout characteristics. As can be seen in FIG. 8, the particular overload relay in this application has a heater burnout or overload relay damage curve, shown as a light dotted line, starting at approximately 27 amperes. Prior to the crossover point (about 240 amperes) between the current-limiting fuse curve and the circuit breaker curve, the circuit breaker will interrupt the current to protect the heaters and overload relay. If the current-limiting fuse unit were not utilized in the combination, the heaters would be destroyed upon the occurrence of an overload above about 350 amperes since the breaker would not operate fast enough to protect the heaters at this level of fault current. The damage in this case could be substantially more severe than merely the heater burnout since the relay and contactor could also be severely damaged at this level of fault current if the circuit breaker were to be relied on for interruption. lt is noted, however, that with the total coordinated curve the current-limiting fuse unit curve crosses the circuit breaker curve at the point Y and in front of the crossover point X of the overload relay and circuit breaker to thereby provide protection of the overload relay heaters, overload relay and contactor, along with more adequate protection of the motor and cable of the motor circuit. Depending on the components and characteristics of the combination motor starter and motor circuit, the current-limiting fuse unit is designed to operate within a range of from 50 to 200 times the motor full-load current and preferably within the range of from to l50 times the motor full-load current to protect the components of the combination motor starter, the cable, and the motor of the motor circuit.

As was hereinbefore set forth, the current-limiting fuse unit operates, with current-limiting action, from the predetermined current within the hereinbefore set forth range to the maximum fault current that the combination motor starter can interrupt. Upon interruption of the motor circuit by the current-limiting fuse unit the circuit breaker 11 sees enough letthrough current to effect an automatic tripping operation.

It is seen from the foregoing description of the preferred embodiment of the invention that there has been provided a combination motor starter having the following advantages:

l. A closely coordinated protection system has been devised for motor circuits with (a) a motor overload relay having a time delay to prevent needless interruptions when there are harmless overloads on the motor for only a short time, (b) a circuit breaker having an instantaneous magnetic trip which is operable by low-fault currents above the locked rotor current of the motor, and (c) a current-limiting fuse which blows on a lower current than the current at the intersection of the circuit breaker time-current curve with the heater burnout or relay damage time-current curve, so as to protect the motor overload relay from damage by larger fault currents which could cause relay damage and other damage before the circuit breaker opens the circuit.

2. The use of the magnetically tripped circuit breaker in the combination gives maximum low-level fault protection and has the advantages over the use of a fused disconnecting switch that (a) the magnetically tripped circuit breaker can clear the fault faster than a correctly applied fuse, because the fuse is inherently a thermal device requiring time at low-fault levels to acquire heat, and must have a time delay built in to override the initial inrush current peaks of motor starting, (b) there is a minimum of downtime since the circuit breaker can be reclosed without the time required to obtain replacement fuses, (c) single-phase operation of a three-phase motor is prevented since the circuit breaker opens all phases, ((1) the cost of fuse replacements is greatly reduced since the fuses used with the circuit breaker blow only on the infrequent occasions when there is a high-level fault current, and (e) the faster action of the circuit breaker in clearing low-level faults minimizes the damage to the motor, its circuit and the components of the combination motor starter. This is because most faults are caused by insulation breakdown with a low level of fault current at inception because of the high impedance of the fault, but if not quickly arrested more insulation is burned away with a broadening of the physical area of the fault and a lowering of the impedance of the fault and a rapid rise in the fault current which will do more extensive damage to all of the equipment in the circuit.

3. The use of the circuit breaker and current-limiting fuse in the combination motor starter makes it possible to safely use the combination device in circuits having an available shortcircuit current up to 100,000 amperes without losing the main advantages of a circuit breaker device, and at the same time to protect the motor relay against heater burnout or other damage.

I claim:

1. A combination motor starter for controlling a motor circuit having a predetermined full load motor current, said motor starter comprising current-responsive low overload protecting means operable with a time delay upon the occurrence of overloads of a first predetermined current and higher to effect interruption of said motor circuit, said currentresponsive low overload protecting means comprising a contactor and overload relay means operable with a time delay upon the occurrence of said overloads of said first predetermined current and higher to automatically effect operation of said contactor to interrupt said motor circuit, said motor starter comprising current-responsive fault-protecting means operable within a fraction of a second upon the occurrence of overloads of and above a second predetermined current and higher to interrupt said motor circuit, said current-responsive fault-current protecting means comprising an automatic tripping resettable circuit breaker and current-limiting means, and said current-limiting means effectively operating to limit the current that said current-responsive fault-current protecting means interrupts at fault currents starting at a predetermined fault current within the range of from 50 to 200 times said full-load motor current,

2. A combination motor starter according to claim 1, and said current-limiting means effectively operating to limit the current that said current-responsive fault-current protecting means interrupts at fault currents starting at a predetermined fault current within the range of from 100 to 150 times said full-load motor current.

3. A combination motor starter according to claim said first predetermined current being a current within the range of between one and two times said full-load motor current, and said second predetermined current being a current within the range of between three and I3 times said full-load motor current.

4. A combination motor starter for controlling a motor circuit having a predetermined full-load current, said motor starter comprising current-responsive low overload protecting means operable with a time delay upon the occurrence of overloads of a first predetermined current and higher to effect interruption of said motor circuit, said low overload protecting means comprising a contactor and an overload relay operable with a time delay upon the occurrence of said overloads of said first predetermined current and higher to effect operation of said contactor to thereby effect interruption of said motor circuit, an automatic tripping resettable circuit breaker automatically operable faster than said low overload protecting means upon the occurrence of overloads on and above a second predetermined current higher than said first predetermined current to interrupt said motor circuit, current-limiting fuse means automatically operable faster than said circuit breaker upon the occurrence of overloads on and above a third predetermined current higher than said second predetermined current to interrupt said motor circuit, said first predetermined current being a current within the range of from one to two times said full-load current, said second predetermined current being within the range of from two to 13 times said full-load current, and said third predetermined current being within the range of from 50 to 200 times said full-load current.

5. A combination motor starter according to claim 4, said circuit breaker comprising a unitary molded case-type circuit breaker, and said current-limiting fuse means comprising a unitary molded case-type fuse unit removably connected to said unitary molded case-type circuit breaker.

6. A combination motor starter according to claim 5, said combination motor starter comprising an enclosure, said contactor said overload relay said circuit breaker and said ourrent-limiting fuse means being supported within said enclosure, said circuit breaker comprising an operating handle, and an external handle mechanism on said enclosure operatively connected to said operating handle to permit external manual operation of said circuit breaker.

7. A combination motor starter according to claim 4, said first predetermined current being a current within the range of from one to L5 times said full-load current, said second predetermined current being a current within the range of from four to 13 times said full-load current, and said third predetermined current being within the range of from to times said full-load current.

8. A combination motor starter according to claim 7, said second predetermined current being a current within the range of from five to 13 times said full-load current, and said circuit breaker comprising magnetic-only trip means operable within one-half of a second and no ionger to operate within the full range from said second predetermined current to said third predetermined current to trip said circuit breaker to interrupt said motor circuit.

9. A combination motor starter according to claim 8, said circuit breaker comprising a unitary insulating housing-type circuit breaker, said current-limiting fuse means comprising a unitary insulating housing-type fuse unit, said combination motor starter comprising an enclosure, said fuse unit said circuit breaker said contactor and said overload relay means being mounted in said enclosure, and said combination motor starter comprising externally operable operating means operatively connected to said circuit breaker.

10. A combination motor starter for controlling a motor, said combination motor starter including a motor overload responsive device, an excess current responsive resettable circuit breaker separate from said motor overload responsive device, and a current-limiting fuse means, said motor overload responsive device having a time-current characteristic which is faster than both said excess current-responsive circuit breaker and said current-limiting fuse means to interrupt the current to said motor upon the flow of overload current occasioned by an overload on the motor, said excess currentresponsive circuit breaker operating faster than said currentlimiting fuse means to interrupt the current to said motor on low-level fault currents above motor overload currents, and said current-limiting fuse means being faster than the excess current-responsive circuit breaker to interrupt the current to said motor on heavier fault currents which could cause damage to the motor overload responsive device before the circuit breaker operates on such heavier fault currents.

11. A combination motor starter according to claim 10, said motor overload responsive device comprising thermal actuating means automatically operable with a time delay to effect interruption of overload currents within a first full range from a first current to a second current, said circuit breaker comprising magnetic tripping means operating always within onehalf of a second to trip said circuit breaker to interrupt lowlevel fault currents within a second full range from said second current to a third current, and said current-limiting fuse means operating to interrupt heavier fault currents within a third full range from said third current to the maximum current that said combination motor starter can interrupt.

12. A combination motor starter according to claim 11, said thermal actuating means having a time-current damage curve, said circuit breaker protecting said thermal actuating means from damage within said second full range, and said currentlimiting fuse means protecting said thermal actuating means from damage within said third full range.

13. A combination motor starter according to claim 12, said circuit breaker comprising a unitary insulating housing-type circuit breaker, and said fuse means comprising a unitary insulating housing-type fuse device removably connected to said circuit breaker.

Claims

1. A combination motor starter for controlling a motor circuit having a predetermined full-load motor current, said motor starter comprising current-responsive low overload protecting means operable with a time delay upon the occurrence of overloads of a first predetermined current and higher to effect interruption of said motor circuit, said current-responsive low overload protecting means comprising a contactor and overload relay means operable with a time delay upon the occurrence of said overloads of said first predetermined current and higher to automatically effect operation of said contactor to interrupt said motor circuit, said motor starter comprising currentresponsive fault-protecting means operable within a fraction of a second upon the occurrence of overloads of and above a second predetermined current and higher to interrupt said motor circuit, said current-responsive fault-current protecting means comprising an automatic tripping resettable circuit breaker and currentlimiting means, and said current-limiting means effectively operating to limit the current that said current-responsive fault-current protecting means interrupts at fault currents starting at a predetermined fault current within the range of from 50 to 200 times said full-load motor current.

3. A combination motor starter according to claim 1, said first predetermined current being a current within the range of between one and two times said full-load motor current, and said second predetermined current being a current within the range of between three and 13 times said full-load motor current.

4. A combination motor starter for controlling a motor circuit having a predetermined full load current, said motor starter comprising current-responsive low-overload protecting means operable with a time delay upon the occurrence of overloads of a first predetermined current and higher to effect interruption of said motor circuit, said low-overload protecting means comprising a contactor and an overload relay operable with a time delay upon the occurrence of said overloads of said first predetermined current and higher to effect operation of said contactor to thereby effect interruption of said motor circuit, an automatic-tripping resettable circuit breaker automatically operable faster than said low-overload protecting means upon the occurrence of overloads on and above a second predetermined current higher than said first predetermined current to interrupt said motor circuit, current-limiting fuse means automatically operable faster than said circuit breaker upon the occurrence of overloads on and above a third predetermined current higher than said second predetermined current to interrupt said motor circuit, said first predetermined current being a current within the range of from one to two times said full-load current, said second predetermined current being within the range of from two to 13 times said full load current, and said third predetermined current being within the range of from 50 to 200 times said full load current.

5. A combination motor starter according to claim 4, said circuit breaker comprising a unitary molded-case type circuit breaker, and said current-limiting fuse means comprising a unitary molded-case type fuse unit removably connected to said unitary molded case-type circuit breaker.

6. A combination motor starter according to claim 5, said combination motor starter comprising an enclosure, said contactor said overload relay said circuit breaker and said current-limiting fuse means being supported within said enclosure, said circuit breaker comprising an operating handle, and an external handle mechanism on said enclosure operatively connected to said operating handle to permit external manual operation of said circuit breaker.

7. A combination motor starter according to claim 4, said first predetermined current being a current within the range of from one to 1.5 times said full-load current, said second predetermined current being a current within the range of from four to 13 times said full-load current, and said third predetermined current being within the range of from 100 to 150 times said full-load current.

8. A combination motor starter according to claim 7, said second predetermined current being a current within the range of from five to 13 times said full-load current, and said circuit breaker comprising magnetic-only trip means operable within one-half of a second and no longer to operate within the full range from said second predetermined current to said third predetermined current to trip said circuit breaker to interrupt said motor circuit.

10. A combination motor starter for controlling a motor, said combination motor starter including a motor overload responsive device, an excess current responsive resettable circuit breaker separate from said motor overload responsive device, and a current-limiting fuse means, said motor overload responsive device having a time-current characteristic which is faster than both said excess current-responsive circuit breaker and said current-limiting fuse means to interrupt the current to said motor upon the flow of overload current occasioned by an overload on the motor, said excess current-responsive circuit breaker operating faster than said current-limiting fuse means to interrupt the current to said motor on low-level fault currents above motor overload currents, and said current-limiting fuse means being faster than the excess current-responsive circuit breaker to interrupt the current to said motor on heavier fault currents which could cause damage to the motor overload responsive device before the circuit breaker operates on such heavier fault currents.

11. A combination motor starter according to claim 10, said motor overload responsive device comprising thermal actuating means automatically operable with a time delay to effect interruption of overload currents within a first full range from a first current to a second current, said circuit breaker comprising magnetic tripping means operating always within one-half of a second to trip said circuit breaker to interrupt low-level fault currents within a second full range from said second current to a third current, and said current-limiting fuse means operating to interrupt heavier fault currents within a third full range from said third current to the maximum current that said combination motor starter can interrupt.

12. A combination motor starter according to claim 11, said thermal actuating means having a time-current damage curve, said circuit breaker protecting said thermal actuating means from damage within said second full range, and said current-limiting fuse means protecting said thermal actuating means from damage within said third full range.

13. A combination motor starter according to claim 12, said circuit breaker comprising a unitary insulating housing-type circuit breaker, and said fuse means comprising a unitary insulating housin type fuse device removably connected to said circuit breaker.