USRE22873E - Electrical distribution system - Google Patents

Description

April 29, 1947- G. A. MATfHEws R. 22,873

ELECTRICAL DISTRIBUTION SYSTEM Original Filed Aug. 3, 1940 ,in the case of purely transient faults.

' 6 cycles, on a '60 cycle per second basis.

Rea-use Apr. :9, 947

mm .sr-ATEs PATENT OFFICE i ELECTRICAL DISTRIBUTION SYSTEM George A. Matthews, Detroit, Mich., assignor to The Detroit Edison Company, Detroit, Mich" a corporation of New York Original No. 2,288,953, dated'July "I, 1942 Serial No. 351,015, August 3, 1940. Application for reissue August 20, 1945, Serial No. 611,618

10 Claims.

This invention relates to electrical distribution systems and particularly to methods of and devices for maintaining optimum operating conditions on overhead feeder circuits.

The present practice of automatically opening a feeder circuit upon the occurrence -of a fault results in an appreciable interruption of service, usually for an interval of about 15 seconds, even The recent proposals for an ultra high speed operation on the first reclosure of circuit breakers will, if generally adopted, reduce the length of these momentary interruptions but ..any prac:- tical mechanical structures for opening and reclosing a feeder circuit will necessarily remove the voltage from the line for an interval substantially longer than that required for the deionization of the original fault path.

According to the present invention, the ma- Jority of all faults that may occur on an overhead feedercircuit are removed, without opening the feeder circuit, by connecting a shorting circuit across the line to collapse the voltage at the fault point to zero, the shorting circuit including a switch or fuse that opens the shorting circuit to restore the voltage on the line in about The shorting circuit is completed substantially simultaneously with the occurrence of the fault, for example in from ,2, cycle to 2 cycles, and the feeder circuit is therefore protected against damage from power arcs that follow-a transient fault.

The shorting circuits may supplement the usual protective equipment, such as reclosing circuit breakers or fuses, that introduce a number of time-delayed-reclosures before definitely opening the feeder circuit or the faulty section of the feeder circuit in the case of a permanent fault.

Methods of and apparatus for protecting feeder circuits fromburn ofl by power arcs resulting from transient 'faults are described and claimed in Patent No. 2,352,556,. granted June 27, 1944', Apparatus for protecting power lines. The protective equipment of that application included a normally open line shorting contactor connected across the line, an operating coil in series with the line for closing the contactor in about $5 cycle, a spring for opening the shorting contactor upon removal of the line voltage by-a-cir cult breaker, and mechanism for locking the shorting contactor in open position for a period somewhat longer than the operatingtlme, to a lock out, of a reclosing circuit breaker. The line shorting contactors protected the conductors against damage from power arcs and, for

transient faults, normal service was restored to the entire system upon the first reclosure of the circuit breaker.

An object of the present invention is to provide protective methods and protective equipment for limitingthe service interruption from transient faults to intervals substantially shorter than has been possible in the past, for example to intervals of the o'rderof 6 cycles in the case of a 60 cycle power line.. Objects are to provide methods ,of and devices for protecting electrical distribution systems from faults by short-circuitingthe line to reduce the voltage at the fault point to zero for a preselected interval that is sufllcient for the removal of the great majority of. all faults, and then removing the applied short-circuit to permit the operation of thecircuit breakers or other protective equipment in the caseof a permanent fault, An ob-.

ject is to provide an electrical distribution system having relatively slow-acting devices for repeated- 1y opening and closing the circuit in the case of a permanent fault, and a line shorting circuit including in series a normally open switch and, a

normally closed switch that operate rapidly and in sequence, upon the occurrence of a fault, to complete the. shorting circuit to collapse the line voltage to zero and then to open the shorting circuit for av period sufficient, for actuationbf the slow-acting devices in the case of a permas nent fault, An object is to provide a distribution system including circuit breakers and fuses, or repeating fuses, for the, protection of the system in the case of permanent faults, and additional protective equipment comprising normally open circuits between feeder wires; the normally open circuits including a line shorting switch that is closed automatically by abnormal current flow in the system, and a fuse or interrupting switch that opens and locks out for a preselected intervalupon a closure of the shorting switch. A further object is to provide an electrical distribution system of the type stated in which the fuse or interrupting switch is designed'or adjusted to open the shorting cir cuit in about second, whereby the service interruption in the case of transient faults is restricted to a negligible flicker of the lights on the feeder circuits.

,These and other objects and, advantages of the invention will be apparent from the follow- I ing specification when taken with the accompanying drawing in which:

Figs. 1 and 2 are schematic diagrams of diflerent embodiments of the invention.

The invention is particularly suited to stations where the character of the load does not warrant the expense of elaborate switch gear, but may be used to advantage with any known types ofv -reclosing protective equipment as the novel apparatus operates at high speed to clear transient faultsbefore the conventional protective equipment can open the line, andthe novel ap is then locked out for a predetermined paratus N interval which permits the normal functioning of conventional equipment in the case of a permanent fault. 1

The network shown in Fig. 1 is typical of stations where a large number of circuits l radiate froin the bus 2 to supply the branch feeder circuits 3. .Where the load does not justify the fuses I on the branch feeder circuits. Voltage regulating equipment 6 may be provided between the station bus 2 and the low voltage sides of the transformers I that are fed from the high voltage line 8. Fuses 8 are usually-,placed between the transformeraand the line 8 to isolate the station in the'event of a fault in the station equipment. A typical station, including the elements so far described, will usually be of such relatively low capacity that the transformers may be directly 1 I 4 in about 1 6 second, as experience has shcwn that this short interval is sufficient for the de-ionizano of the fault path in substantially all cases of transient faults. I J The operation of the protective, system in the event of a fault! on one of the feeder circuits is as follows. Heavy'current flow due to/the fault results in afclosure of the contacts of two of the line shorting contactors SC in about l2 cycle, and the voltage at the fault is thus collapsed to zero substantially instantaneously,

1 thereby preventing the blowing of the fuses I of expense of reclosing circuit breakers, the pro-' tective equipment is usually llmitedto repeating fuses 4 on the main circuits I. and single shot" circuit 3. If-the fault was of a transient nature,

short circulted, by the highspeed apparatus of this invention without imposing objectionable shocks upon the station equipment. The shortcircuiting system includes a nornially open line shorting contactor'-SC for each conductor of the station bus 2 and normally closed bus short interrupter switches SI. When the neutral point of the three phase distribution system is not the branch circuit and the fuses 4 of the main feeder circuit. The-metallic short circuit is removed in about 6 cycles by the opening of in-- terrupter switch SI, and the voltage is thus restored to the bus system and the branch feeder the opening of the shorting circuit by switch 81 restores normal operating voltages on the entire station network, and the shorting contactors SC open at once as the current flow through the operating coils in is again at a normal load value.

The interrupter switch or switches of the shorting line are locked against reclosure, by the escapement devices "l8, and the line shorting circuit therefore remains open for a predetermined period whether the fault was transient or perman'ent. In the case of a permanent fault, the shorting contactors SC will be held in closed position by heavy current flow to the fault point. and the faulty feeder 3 will be isolated by the blowing of the fuses 5. The clearing of the fault in'this manner reduces the current flow through operating coils Hi to normal values, the shorting contactors open at once, and the interrupter switch S1 reclcses after the time delay period,

grounded, only two bus short interrupter switches are required.

The operating windings ll of the shorting contactors SC are in series in the supply lines II from the transformers 1 to. the bus system 2, and the winding may take the form of a few turns of heavy copper wire. The movable member of the normally open contacts I! of each shorting contactor SC is connected to its associated lead II by a flexible jumper l3; The stationary contact members of two of the shorting contactors SC are connected to the operating coils I4 of theinterrupter switches SI, and the stationary .contactmember of the third shorting contactor SC is bonnected directly by lead l5.to the jumper l8 that Joins the stationary contacts of the interrupter switch SI. The operating coil 14 of each of'the switches SI is connected to the movable contact of'that switch by a flexible jumper l1. and the moving system of each interrupter switch SI is connected to a timing escapement mechanism ll! of any desired type that locks the interrupter switch against reclosure for a predetermined 'period, for example three minutes,

when the moving system is displaced to open the switch by eurrent flow incoil I 4.

The line shorting contactors SC are preferably of the general form shown in Fig. 4 of Patent No.

2,352,556, but with the time delay mechanism omitted. and operate at high speed to close in about /2 cycle upon abnormal current flow through the coil ID. The interrupter switches SI are preferably similar in structure to the coil reclosing circuit breaker shown in Fig.8 of my copending application but with the reclosing timing mechanism and the auxiliary control thus restoring the protective equipment to normal condition for another cycle of operations.

The embodiment of the invention that is shown diagrammatically in Fig. 2 is generally similar to,

the Fig. 1 system in that shorting contactors SC are provided for each conductor ll of the distribution system, the line shorting circuits are 1 automatically opened after a preselected short interval, and the sh'orting circuits are then held open'for a period suflicient to isolate a branch on which there is'a permanent fault. Each interrupting device is. a repeating fuse assembly a RF comprising a series of fuses 20 that each have a terminal connected through the jumper l3 to the movable member of the contacts I! of the associated shorting contactor, and a terminal connected to a contact point of a selector switch, the contact arm ii of theswitch being connected to conductor "II, at the load side of the shorting contactor, by a lead 22. The moving contact of one shorting contactor is connected directly to its operating winding by a jumper l3 and the stationary contacts of all shorting contactors SC-are connected by a lead It With these connections, the energization of any two shorting contactors by a fault current will comswitch omitted. The operating coil l4 of the I interrupter switch. is designed toopen the switch ductors affected by the fault.

The contact arm 2| of a fuse selector switch is advanced automatically by the return movement'of the core III of the associated shorting contactor SC, and the advance of the selector switch to connect a new fuse into the shorting circuit therefore does not take place so long as there is an abnormal current flow in the operating .coll' ll! of the shorting contactor. The mechanism for coupling the contactarm of a selector switch to the associated core l0 may be ea ers of'anydesired form such as, for example, the

time for the de-ionization of the original fault path in the case of transient faults.) and is so short that the interruption of service is reduced current flow in the operating coils iii of two shorting contactors, and the contacts l2 of those contactors' close in about cycle to complete a shorting circuit through the associated repeating fuse assemblies RF. The fuses 20 blow at the 'end of an interval of the order of 6 cycles, thus opening the shorting circuit. In the case ofa transient fault that cleared in the 6 cycle interval, normal service is restored on the entire system by the removal of the short circult, and the normal load current through the operating coils II) is not sufficient to hold the shorting contactor-s in closed position. The cores ill of the shorting contactors are lifted by springs, not shown, and operate the pawl and ratchet mechanism 23 to advance the contact arms 2| one step to connect another set of fuses 20 into the shorting circuit. If the fault is still on the line when the shorting circuit is opened .by the blowing of one'set of fuses 20, the fault current flows through the operating'windings Ill of the shorting contactors and holds the contactors in closed position, thus preventing movement of cores Ill. The contact arms 2| of the fuse selector switches do not advance to insert new fuses 20 in the shorting circuit, and a heavy current flows through the fault until the branch feeder is isolated by the blowing of its fuses 5. The repeating fuses 4 of the main feeder I may also blow, but service is quickly restored upon having therein a switch normally retained in open to a negligible flicker of the transient faults.

I claim:

l. The method of protecting an electrical dis tribution system including a plurality of parallel feeder circuits against faults which comprises connecting acrossthe system a shorting circuit position by a spring, developing from the fault current a force to close said switch substantially instantaneously to reduce the voltage at the fault point toazero within not more than two cycles after fault inception, opening the shorting circuit after an interval equal to that required for deionization of the original fault path, thereafter removing voltage from and restoring voltage to only'the faulty feeder circuit ofsaid system a plurality of times to an eventual isolation of. the

faulty circuit in the case of a permanent fault,

' and preventing a reclosure of the shorting circuit ductors a shorting circuit having in series a shortduring the ing switch normally retained in open condition by a spring and a repeating type of circuit interv rupter, developing from a fault current a force all of the network except the isolated branch feeder circuit} by the repeating fuse 4. The load current drops to normal values upon the 7 isolation of the defective feeder circuit, and the shorting contactors SC then open and advance l the contact arms 2| of the associated repeating fuses RF, thus resetting the high speed protective equipment for another cycle of operations.

Itis to be noted that the coupling of the selector switch to the moving system of the asso-; ciated shorting contactor eliminates the timing mechanism that is present in the Fig. lsystem to prevent repeated reclosures of the shorting circuits in the case of a permanent fault. The repeating fuse type ofinterrupter for the shorting circuits is simpler and less expensive than the magnetic switch type of interrupter.

The high operating speed of the equipment in the line shorting circuits is a characteristic and important feature of the invention as it reduces the interruption of service to the negligible interval of about second in the case of transient faults are not of a transient nature. Conven-- tional protective'equipment, 'such as the illustrated sectionalizing fuses or circuit breakers must be included in the network, and the shorting circuits must "look out for a. predetermined interval or until thefaulty section is isolated. I

The operating time of the equlpment in the shorting circuits may be increased beyond about 6 cycles or reduced below that value; audit is therefore to be understood that the invention is not restricted to any particular operating time. An operating time of from 6 to 10 cycles is preferred, at least on typical distribution circuits with, which I am familiar, as it affords ample to close said shorting switch against the opposition of the spring in a time interval of not inore than two cycles after fault inception, thereby to reduce the voltage at the fault point to zero, opening the circuit interrupter in a time interval of I the order of 6 second after the closure of said shortin switch, thereafter operating said slow acting'means-to isolate only the faulty portion of said system from and to re-connect it to' the current source a plurality of times to an eventual lockout in the case of a permanent fault, and preventing a reclosure on said shorting circuit during the period required for a lookout.

3. In an electrical distribution system, the combination with a current source, and apparatus for initially opening the system after a short predetermined time interval in the case of a fault; of a, normally open shorting circuit connected across said system between said apparatus and said currentsource; said shorting circuit including a shorting switch spring-biased to open position and having an operating coil in series in said system for quickly closing said shorting switch in response to abnormal current due to a fault, thereby to collapse the voltage at the fault point to zero, and voltage-restoring means to open said shorting circuit prior to the expiration of said predetermined time interval required for operation of said apparatus initially to open said system, whereby said apparatus is inoperative to open said system in the event of a transient fault [that terminates prior. to the opening of said short- I ing circuit by said voltage restoring means.

4. In an electrical distribution system, the combination with protective apparatus for opening the system after a predetermined time interval in the case of a fault and for then repeating a opening up lights in the case of period required for isolation of the "of a current source and conductors extending from said current sourceto said system, means to complete a shorting circuit across said conductors leading to the system in not more than 36 second after fault inception, meansfor opening said shorting circuit in an interval of the order of s second after it is established by said short circuiting means, and means to prevent a re-' establishment of said shorting circuit prior to the elapse of a period equal to the operating time to lockout of said protective apparatus.

1 wherein said circuit interrupters switches having operating windings in series with p wherein said circuit interrupters comprise re- 5. In an electrical distribution system, a current source, a plurality of feeder circuits, conductors A extending from said source to said circuits,;and

means responsive to a fault on a feeder circuit for completing a shorting circuit. between said conductors, said means comprising in series between said conductors a normally open switch and a normally clos'edcircuit interrupter switch,

means responsive to an abnormal current in said conductors to close said normally open. switch, said circuit interrupter switch having an operating coil energized by current flow through said shorting circuit to open the same, and time delay means for locking said circuit interrupter switch against reclosure for a predetermined interval after movement thereof into open circuit position upon an energization thereof of said operating coil.

6. In an electrical distribution jsystem,the combination with conductors feeding a plurality of branch circuits, and relatively slow acting means for opening a branch circuit in event of a permanent fault on that circuit, of normally open shorting contactor switches having operating windings in series in said conductors, normally closed circuit interrupters in series with the con- I tacts of said shorting contactor switches for completing shorting circuits betweensaid conductors upon closure of said normally open switches, and means responsive to short circuit current flow through said shorting circuits'for opening said circuit interrupters prior to the opening of a branch circuit by said slow acting means.

7. An electrical system as claimed in claim 6,

.8 8. An electrical system comprise the normally open shorting contactorswitches.

9. Anelectrical system as claimed in claim 6,

peating fuses and means responsiveto an' opening of the associated shorting contactor switch for F connecting a new fuse in circuit through the repeating fuse. I

10. In a distribution system, the combination with a three phase source of current, a load circuit, three line conductors connecting said curvent operation of the protective devices on said load circuit in response to transient faults; said means comprising three normally open switches having operating windings inseries in the respective line conductors, a pair of normally closed circuit interrupters, circuit elements connecting said circuit interrupters in a shorting circuit extending between two of said conductors, said shorting circuit including in series the circuit interrupters and the contacts of the normally openswitches whose operating windings are in series with the said two conductors, and circuit elements connecting one contact of the third normally open switch to the third conductor and the other contact to said shorting-circuit at a point between said circuit interrupters.

GEO. A: mmmwa, anrsanucns crrnn The following references are of vrecord in th I file of this patent:

UNI ED STATES PATENTS Number Name .Date

Nicholson Oct. 17, 1916 1,201,610 OTHER REFERENCES Standard Handbook for Electrical Engineers, sixth edition, published by McGraw Hill, 1933, p 1543, section 15, paragraph 161.

as claimed in claim a.

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