US1787277A

US1787277A - Protective arrangement

Info

Publication number: US1787277A
Application number: US387523A
Authority: US
Inventors: Luke F Kennedy
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1929-08-21
Filing date: 1929-08-21
Publication date: 1930-12-30
Anticipated expiration: 1947-12-30
Also published as: FR699766A; GB355940A

Description

Dec. 30, 1930. L. F. KENNEDY PROTECTIVE ARRANGEMENT Filed Aug. 21, 1929 Mfr Inventor: LuKeF. K ennedg, y

(4,440; We, Attorn e3.

Patented Dec. 30, 1930 ,UNITED;

. LUKE r. x iimrmi, or

P TE T io F1c ELECTRIC COMPANY, A CORPORATION OF NEW YORK v 'rnor'norrvn ARRANGEMENT App l icatio nfil ed August 21, 1929.; Serial 1%. 387,523;

' My invention relates to improvements'in protective arrangements for electric circuits, and more particularly forcircu-its including the windings of electric apparatus sub- -ject to transient magnetizing currents and an object of my invention is to provide an improved protective arrangement whereby to avoid unnecessary interruptions due to tr'an sient. magetizing currents and yet maintain the desired degree of sensitivity of protection under ordinary'steady state conditions.

Whenever electric apparatus having windings subject to transient magnetizing cur- 'rents, for example, a power-transformer,1s

connected toa source of E. M. F. due to the momentarily great intensity of this current A which may be several-times normal loadcurrent, depending on the point of the M. wave at which the circuit closure occursand the magnetic condition of the iron, theprotective gear frequently operates and causes the opening of the circuit unnecessarily; Va-

rious expedients have been'adopted to avoid this difliculty, :Among these are permanently decreasing the sensitivity ofthe protective gear or setting it to operate at a point above any expected intensity of transientmagnetizing current and givin'gthe protectivegear a time setting sufiiciently. great to avoid'oporation during the probable maximum period 1 of the transient. Both these may be and oftenare objectionable since they involve a sacrifice ofprotection under normal steady state conditions. Otherarrangements have involved either manually or automatically According to my inventiomlpropose in efiect to decrease thesensitivityof the relay in accordance with a. characteristic'of the-transient magnetizing current which is characterized by one or more harmonicsof which-the second is in general predominating. In this way. the time and intensity of the efiect are controlled by thevery factor causingithe trouble.

My invention will better understood" from'the following description when considered in connection with the accompanying drawing,andits scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 illustrates diagrammaticaly a protective arrangment embodying my invention, and Fig.

of'the embodiment of invention shown in the embodiment of invention shown in Fig. 1, electricapparatus, 'subjectto transient magnetizing currents, such as apower transformer 5,- isarranged to have the'circult of its'primaryand secondary windings.

6 and 7 controlled so as to be connected to a source of E. M. F., not shown, by suitable circuit interrupting means illustrated as a latch closed circuit breaker 8;having,a trip'coil 9.

For controlling the circuit breaker 8'1 through its trip coil,"I have shownmeans, including a relay 10, which is arranged to con trol contacts 11 in circuit with the trip coil and which according to my invention is pro vided with means for'restraining the opera, ltion of the relay connected to 'be energized only'qin accordance withi a predetermined harmonic of the transient magnetizing current ofthe transformer 5. 7

disk type and includes a movable member such' asthe disk'12 with which are inductively associated electromagnetic means, such as restraining and operating motor elements 13, 14, whose windings 15, 16 are respectively connected to' be energized in accordance with the sum of and the difference between the currents in'the windings 6 and 7 of the transformer 5. For this purpose the: re-

straining winding 15 may be connected in series in a protective circuit includng the secondaries of current;

transformers

17 and 18 connected in series for normally circulating current while the operating winding 16 is connected across

points

19 and 20 in' As shown,-the relay '10 is of the induction PHILADELPHIA, PENNSYLVANIA, Assrdnon T0. GENERAL 2 illustrates diagrammatically a modification In order to avoid this this circuit normally at the same potential, the

current transformers

17 and 18 being connected in the circuits of the power transformer windings 6 and 7 respectively. The

motoring elements

18, 14 are arranged to ex ert on the disk 12 opposing torques whose respective directions are indicated by the arrows 3, 4. The ratio of these torques may of course be any desired value which can be governed, for example, by the relative number of turns in the windings 15 and 16.

In accordance with my invention, I provide an additional restraint which is effective during the transient magnetizing current perod. As shown in Fig. 1 this may be ac complished by providing a circuit tuned to a harmonic of the magnetizing current such for example as the second harmonic. For this purpose a condenser 21 may be connected across a part, such as a half. of the restraining winding 15 and tuned therewith to form a parallel resonant circuit for such harmonic. If the power transformer 5 is subject to energization from eitherside then a further resonant circuit including the condenser 22 and the other half of the restraining winding 15 may be provided. 7

If two parallel resonant circuits are thus provided there is the probability of transformer action between the two halves of the restrainingwinding when energized by the selected harmonic of the transient magnetizing currentwith the possibility of the additional restraint being more or less nullified. I may provide the relay 10, as shown in Fig. 2, with two independent electromagnetic restraining elements 23, 24, having

windings

25, 26 arranged in series resonantcircuits tuned to the second harmonic of the transient magnetizing current. As shown, these circuits include the condensers 27, 28, and are connected across the secondaries of the

current transformers

17, 18, respectively. These restraining elements may operate for example on a second disk12 secured to the same shaft as the disk 12 on which the main restraining and operating elements 13 and 14: operate. IVith this arrangement one or the other of the harmonic restraining elements 23, 24, depending on which winding of the transformer is initially excited, will exert a restraining torque assisting the torque of the restraining element 13, and proportional to the second harmonic of the transient magnetizing current in the associated power transformer winding. Inasmuch as the additional restraint is substantially dependent on the existence of the second harmonic which occurs only during the transient magnetizing pe riod, this restraint does not affect the sensitivity of the relay 10 so that it can function with the usual sensitivity under the ordinary steady state conditions.

\Yhile Iliave shown and described my invention in considerable detail, I do not desire to be limited to the exact arrangements shown, but seek to cover in the appended claims all those modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is 1. In combination with an electric apparatus having windings subject to transient magnetizing currents and a circuit interrupter for controlling't-he circuit of said windings, means for controlling said interrupter ineluding a differential relay having a movable member, restraining and operating means for controlling the movement thereof respectively connected to be energized in accordance with the sum of and the diiference between the currents of said windings, and means for additionally restraining the movement of said member only in accordance with the second harmonic of the transient magnetizing current of said apparatus.

2. In combination with an electric apparatus having a winding subject to transient magnetizing currents, and a circuit interrupt er controlling the circuit of said winding, means for controlling said interrupter including a relay having a restraining winding circuit tuned to a predetermined harmonic of the transient magnetizing current of said.

apparatus.

8. In combination with an electric apparatus having a winding subject to transient magnetizing currents and a circuit interrupter for controlling the circuit of said winding, means including a relay for controlling said interrupter, means for restraining the operation of said relay connected to be energized only in accordance with a predetermined harmonic of the transient magnetizing current of said apparatus.

4. In combination with an electric apparatus having a winding subject to transient magnetizing currents and a circuit interrupter for controlling the circuit of said winding, means for controlling said interrupter including a relay having a movable member, operating and restraining means for controlling the movement thereof and means for additionally restraining the movement of said member only in accordance with a predetermined harmonic of the transient magnetizing current of said apparatus.

5. In combination, a power transformer, a circuit interrupter controlling the circuit thereof, means for controlling said interrupter including a differential relay having a movable member, restraining and op erating means for controlling the movement thereof respectively connected to be energized in accordance with the sum of and the difference between the currents in the primary and secondary windings of said transformer and means for additionally restraining the movement of said member including a restraining winding circuit tuned to the second harmonic of the {transient magnetizing current of the transformer;

6. In combination with a power transformer, a circuit interrupter for controllin the circuit thereof, meansfor controlling sai interrupter including'a relay having a movable induction disk means, electromagnetic means inductivelyassociated with said disk means" and arranged 'toexert opposing torques thereon, and means for increasing the effect of one of said torques only in response to the second harmonic of the transient mag netizing current of the transformer.

7. In combination with electric apparatus having a winding subject to transient magnetizing' currents," and a circuit interrupter controllingthe circuit of said winding, means for controlllng said interrupter. including a relay having a movable member and electromagnetic'means arranged to exert opposing torques on said member, and means fOIlIlcreasingthe effect of one of said torques'only in response to a predetermined harmonic of the transient magnetizing current of said ap- I 1 paratus.

8. In combination with a power transformer and a circuit interrupter for controlling the. circuit thereof, means for controlling said interrupter including a relay having restraining and operating elements re spectlvely connected tobe energized in accordance with the sum of and the difference 7 between the currents in the primary and secondary windings of the transformer [and means for exerting an additional restraining effect connected to be energized in accordance with a predetermined harmonic of the transient magnetizing current of the transformer. V

9. In combination with a power transformer and a circuitinterrupter for control- I ling the circuit thereof, means for controlling said interrupter including a relay having restraining and operatingwindings respectively connected to be energized in accordance with the sum of and the difierence between the currents in the primary and secondary windings of the transformer and means for exerting an additional restraining effect connected to be energized in accordance with the second harmonic of the transient magnetizing current of the transformer.

10. In combination with electric apparatus having a Winding subject to transient magnetizing currents and a circuit interrupter for controlling the circuit of said winding, means for controlling said interrupter including a relay and means responsive to a' characteristic of the transient magnetizing current otherthan the fundamental thereof for preventing operation of the relay.

In Witness whereof, I have hereunto set my hand this 17th day of August, 1929.

LUKE F. KENNEDY.