US2276888A - Flared-ratio differential relay and auxiliary transformer therefor - Google Patents

Flared-ratio differential relay and auxiliary transformer therefor Download PDF

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Publication number
US2276888A
US2276888A US311377A US31137739A US2276888A US 2276888 A US2276888 A US 2276888A US 311377 A US311377 A US 311377A US 31137739 A US31137739 A US 31137739A US 2276888 A US2276888 A US 2276888A
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current
currents
relay
operating
transformer
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US311377A
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William K Sonnemann
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Westinghouse Electric Corp
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Westinghouse Electric Corp
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Priority to JP2996140U priority patent/JPS25002153Y1/ja
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus

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  • My invention relates to high-speed ratio-differential relays, that is, to high-speed relays which operate when the apparent difference between the currents entering and leaving a piece of apparatus exceeds a predetermined ratio or proportion of the apparent sum of said currents, thus operating on a ratio or proportion, independently of the size or magnitude of the difference-currents. More particularly, my present invention relates to means for obtaining a flared operating characteristic in such a relay, that is, a characteristic such that a larger ratio or percentage is required under certain circumstances, such as when the currents involved are abnormally large, or when the difference-currents are greatly out of phase with the additive currents, or when there is an asymmetrical currentwave clue to the presence of a direct-current component.
  • asymmetrical faultcurrents have frequently been the cause of faulty operation of previous ratio-differential relays, either of the straight-ratio type, or of the socalled flared-ratio type.
  • an asymmetrical fault-current contains a direct-current component, which is like a halfwave of non-sinusoidal pulsating current of a half-wave length extending over a large number of cycles of the line-frequency current, usually 60 cycles.
  • the line-frequency, or 60-cycle, wave-form of the current is superimposed over this direct-current component, making the resultant pulsations of the wave-form asymmetrical with respect to the zero-current axis, hence the term asymmetrical.
  • the direct-current component When such directcu1rent components appear in the primary currents which are passed through the two current-transformers at the entrance and exit terminals of the protected apparatus, the direct-current component almost invariably saturates the current-transformers, and usuall saturates them initially at different times and each for a different length of time.
  • the principal object of my invention is to provide a novel type and arrangement of auxiliary transformer which is utilized in combination with a ratio-differential relay, to give the relay a ratiocharacteristic which is flared or increased, either when the operating current is large, or when it is greatly out of phase with the restraining current, or when it has a direct-current component.
  • auxiliary transformer built on a three-legged core having a central leg on which the primary and secondary restraint-current windings are disposed, and having two outer legs on which the operating-current primary and secondary windings are disposed, the design being such that the operating-winding currents produce a flux circulating in the two outer legs and saturating said legs during certain portions of the cycle, thereby in effect removing the returnflux portions of the magnetic circuit from the center leg which carries the restraint-windings, and thus producing the desirable characteristics which I have mentioned.
  • Figure l is a diagrammatic view of circuits and apparatus illustrating my invention in a preferred form of embodiment, and illustrating its mode of application to a protected apparatus;
  • Fig. 2 is an enlarged fragment of some of the current-wave forms which are obtained in my apparatus;
  • Figs. 3 and 4 are curve-diagrams illustrating the relation between the value of the operating current which is necessary to cause a relay-operation for various phase-angles of the operating current with respect to the restraining current, and for various values of the restraining current;
  • Fig. 5 is a curve-diagram illustrating the flaredratio characteristic of my relay, as compared to a constant-ratio relay, both with in-phase currents and with out-of-phase currents;
  • Fig. 6 is a copy of some of the traces obtained with a multiple-element oscillograph, showing the performance of my relay in the presence of asymmetrical fault-currents;
  • Figs. 7 and 8 are copies of some of the traces obtained with a multiple-element oscillograph, illustrating the performance of my improved relay during in-phase conditions and out-of-phase conditions, respectively.
  • I illustrate my invention as being utilized to protect (or to detect internal faults in) a single-phase generator G having a currentinput terminal 9 and a current-output terminal Hi, the input and output currents being derived for relaying purposes, by current-transformers II and I2, respectively, having secondary currents which are indicated as Is and I1, respectively.
  • I shall visualize the secondary current I1 as being the larger current, so that there will be a difference-current 12:11-13.
  • I1 or I3 may be the larger, and that the foregoing convention or designation is adopted merely for convenience.
  • either one of the terminals 9 or It! may be the input terminal, the particular designation being again merely for convenience.
  • a balanced-beam type of instantaneous ratio-differential relay which comprises, typically or in general, a balanced beam E3, of magnetizable material, which is weighted at N at its back end, and which has electrical contacts 15 at its front end, for controlling a relay-circuit It which may be utilized for any desired purpose, either for indication or for automatic operation or control or correction of an internal fault-condition in the protected generator G.
  • the beam I3 is intermediately pivoted on a pivot l1.
  • the ratio-differential relay is directly energized in accordance with these socalled additive and differential currents, respectively, the relay has a substantially straight-line characteristic, such as is represented by the line 24 in Fig. 5, when the restraint-current is in phase with the operating-current.
  • I provide means for causing the ratio-differential relay to depart from the constant-ratio characteristic just described.
  • I utilize, for this purpose, an auxiliary transformer having a three-legged iron core 21 having a central leg 28 and two outer legs 29 and 39.
  • I pass the summation-current (Ii-l-Ia) through a primary winding 32 which is disposed on the central leg 28, accomplishing this purpose by connecting the outer terminal of the first current-transformer I2 to the terminal I of the auxiliary transformer, which terminal is connected to one end of the primary winding 32, and connecting the outer terminal of the second current-transformer l l to the terminal 3 of the auxiliary transformer, the latter terminal being connected to the end of the primary winding 32, while the inner terminals of other end two current-transformers l I and [2 are connected together as indicated at 33.
  • This primary winding 32 is utilized for the purpose of energizing the restraint windings R1 and R2 of the ratio-differential relay, a highvoltage secondary winding 34 being disposed on the aforesaid central leg 29, for this purpose, as illustrated in Fig. 1.
  • I utilize two identical primary windings 35 and 36 for developing the flux which produces the secondary current Io energizing the operating winding 0 of the ratio-differential relay,
  • These two operating-current primary windings 35 and 38 being respectively disposed on the two outer legs 29 and 39 of the auxiliary transformer.
  • the two operating-current primary windings 35 and 36 are connected in series with each other, between the central point 31 of the restraintcurrent primary winding 32 and the aforesaid common return-point 33 of the two currenttransformers II and I2, so that the two operating-current primary windings 35 and 36 are traversed by the difference between the currenttransformer currents I1 and I3, said differencecurrent being designated I2.
  • Each of the outer legs 29 and 39, where the operating-coil primary windings 35 and 35 are disposed is provided with an operating-current secondary winding, these two secondary windings being designated by the numerals 39 and 40, respectively.
  • These two operating-current secondary windings 39 and All are connected in series with each other, and are utilized to energize the operating coil 0 of the ratio-differential relay.
  • the two operating-current primary windings 35 and 36 produce fluxes which both circulate around the two outer legs 29 and 39 in the same direction, so that, because of the balanced construction, there is substantially no magnetomotive force tending to divert any of said fluxes through the center leg 23, assuming that the relative conditions of saturation of the two outer legs 29 and 39 remain substantially identical. Consequently, the operating-current fiux 0 is opposed by the restraint-current flux m, in one of the outer legs, such as the leg 39, as indicated by the arrow (01/2R), while, in the other leg, such as the leg 29, the operating-current flux is augmented by the restraint-current flux, as indicated by the arrow (o+ /2R), representing conditions prevailing at some assumed instant within the auxiliary transformer.
  • Fig. 7 shows the results of oscillographic tests which were made upon such a transformer, in order to study its performance.
  • Asubstantially sinusoidal (SO-ampere, GO-cycle, current I3 was caused to flow through the terminal 3, with other connections such as to apply a substantially sinusoidal Gil-cycle voltage tending to produce a differential current-flow I2.
  • the first two traces, in Fig. 7, show these currents I3 and I2 respectively.
  • the third and fourth traces respectively show the relay-restraining voltage Ea which was developed in the secondary winding 34, and the relay-operating current Io delivered by the two serially connected secondary windings 39 and 49.
  • the last two traces, in Fig. '7 show the wave-form of the currents flowing in the respective restraint-windings R1 and R2, the former having the resistor 2
  • Fig, 2 in which I have reproduced the waveforms of I2, 12 Io, as derived from the first, second and fourth traces of Fig. 7.
  • the auxiliary transformer is unsaturated, thus tending to limit the differential-current I2 to a small value which would have reached a peak value as indicated by dotted lines at e in Fig. 2.
  • the auxiliary transformer was performing with its true ratio, so that its secondary current In was increasing normally from a to b, and would have reached a peak value as indicated by dotted lines at f, if the transformer-ratio had not broken down tremendously.
  • the films which are reproduced in Figs. 7 and 8 differ in that the Fig. 7 film was taken for conditions in which the differential-current I2 was approximately in phase with the through-current I3, whereas the Fig. 8 film was taken for the case in which the difierencewurrent I2 was leading the through-current I3 by approximately 90.
  • a comparison of the two films will show that there is very little difference in the operatingcoil currents In which were obtained, in the two cases, the first one having a peak-to-peak Value of 11.8 amperes, and th second one having a peak-to-peak value of 10.4 amperes.
  • I have corrected this low-burden difliculty by adding an artificial burden in the form of a resistor 50, as shown in Fig. 1.
  • I could have redesigned the auxiliary transformer to utilize either a smaller number of primary turns 32 on the central leg 28, or I could have short-circuited a small percentage of the turns in the winding 34, so that the central leg 28 would not saturate before, say, to amperes, (or two or three times normal load-current) were passed through the primary winding 32, even with the low-burden restraint-windings R1 and R2 of the particular form of differential relay which I utilized.
  • the transformer-operation may be interpreted as follows.
  • the directcurrent component 55 of the difference-current I2 saturates the two outer legs 29 and 30 (Fig. 1) of the auxiliary transformer with a unidirectional bias, and when this occurs, the operating current Io which is produced in the secondary windings 39 and 40 on the same legs is not very high, notwithstanding the fact that the primary currents I2 on the same leg have extremely high peaks.
  • the primary current I2 diminishes to a very small value, and yet there is a very material value indicated for the secondary current Io on the same legs of the transformer.
  • my auxiliary transformer which is built on the three-legged core 21, provides a very simple means for giving a ratio-differential relay a flared ratio-characteristic which will enable it, not only to automatically increase the ratio between difference-current and through-current at which the relay will operate during excessive-current conditions when current-transformer saturation is inevitably obtained, but which will also enable it to have a still more steeply flared ratio-characteristic when the difference-current is greatly out-of-phase with respect to the through-current, which is normally the case when there is an external fault resulting in heavy through-currents, and which will also enable the relay to have a flared characteristic during asymmetrical current-conditions, so as to enable the relay to ride through severe asymmetrical current-conditions without a faulty relay-operation.
  • a flared-ratio differential relay assembly for use in connection with current-responsive input and output transforming-means for deriving additive and differential relaying-currents, respectively, from a differentially protected device, said differential-relay assembly comprising the combination, with said relaying-current transforming-means, of a differential relay element having an operating winding or windings and a restraining winding or windings, and an auxiliary transformer, said auxiliary transformer having a three-legged magnetizable core having a center-leg magnetic circuit and an outer-leg magnetic circuit, an additive-current primary winding-means and a restraining-current secondary winding-means both disposed upon one of the magnetic circuits of the auxiliary transformer, a differential-current primary windingmeans and an operating-current secondary winding-means both disposed upon the other magnetic circuit of the auxiliary transformer; the additive-current primary winding-means being electrically connected so as to circulate an additive-current flux around its magnetic circuit of the auxiliary transformer, the differentialcurrent primary winding
  • a flared-ratio diflferential-relay assembly for use in connection with current-responsive input and output transforming-means for deriving additive and differential relaying-currents, re-
  • said differential-relay assembly comprising the combination, with said relaying-current transforming-means, of a differential relay element having an operating winding or windings and a restraining winding or windings, and an auxiliary transformer, said auxiliary transformer having a three-legged magnetizable core, an additive-current primary winding-means and a restraining-current secondary winding-means both disposed upon the central leg of the auxiliary transformer, a differential-current primary winding-means and an operating-current secondary winding-means both disposed upon one of the outer legs of the auxiliary transformer, and a similar pair of dififerentiahcurrent primary winding-means and operating-current secondary winding-means both disposed on the other outer leg of the auxiliary transformer; the two differential-current primary winding-means being electrically connected so a to cumulatively circulate a differential-current flux around the two outer legs of the auxiliary transformer, the two operating-current secondary wind
  • Electrical translating-apparatus comprising, in combination, two diverse input-circuits, two diverse output-circuits, and a transformer for couplin said output-circuits to the respective input circuits, said transformer hav'mg a threeleggcd magnetizable core, primary and secondary winding-means disposed on the central leg of the core, primary and secondary winding-means disposed on, and divided between, the two outer legs of the core so as to cumulatively circulate their magnetic flux around said outer legs, circuitconnections for energizing the respective centralleg and 0uter-leg primary winding-means from the respective input-circuits, and circuit-connections for energizing the respective output-circuits from the respective central-leg and outerleg secondary winding-means.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Emergency Protection Circuit Devices (AREA)
  • Breakers (AREA)
  • Protection Of Transformers (AREA)
US311377A 1939-12-28 1939-12-28 Flared-ratio differential relay and auxiliary transformer therefor Expired - Lifetime US2276888A (en)

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US311377A US2276888A (en) 1939-12-28 1939-12-28 Flared-ratio differential relay and auxiliary transformer therefor
JP2996140U JPS25002153Y1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1939-12-28 1940-12-17

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2425759A (en) * 1945-03-15 1947-08-19 Westinghouse Electric Corp Impedance type distance relay
US2644118A (en) * 1951-01-29 1953-06-30 Hydraulic Res And Mfg Company Relay
US2892974A (en) * 1956-08-10 1959-06-30 Gen Electric Magnetic amplifier sensing and motor control combinations

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2425759A (en) * 1945-03-15 1947-08-19 Westinghouse Electric Corp Impedance type distance relay
US2644118A (en) * 1951-01-29 1953-06-30 Hydraulic Res And Mfg Company Relay
US2892974A (en) * 1956-08-10 1959-06-30 Gen Electric Magnetic amplifier sensing and motor control combinations

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JPS25002153Y1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1950-03-30

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