Reactance type relay

April 20, 1948.

2,439,944

A. C. MEHR1NG

REACTANCE TYPE RELAY

Filed Feb. 9, 1945

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INVENTOR /IrfhurC. Mehr/ngr.

ATTORNEY

Patented Apr. 20, 1948

2,439,944

UNITED STATES PATENT OFFICE

2,439,944

REACTANCE TYPE RELAY

Arthur C. Mehring, East Orange, N. 3., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania

Application February 9,1945, Serial No. 576,973

Claims.

My invention relates to an improved reactancerelay for protecting an alternating-current line.

More specifically, my invention Is an improvement over the reactance-relay shown in Fig. 3 of the Lewis Patent 1,967,093, granted July 17, 1934, and assigned to the Westinghouse Electric and Manufacturing Company. This relay, as used for more than ten years, has suffered from the disadvantage that it would not closely follow the characteristic of an ideal reactance-relay, which should be a straight horizontal line when plotted on R and X coordinates, of line-resistance R, and line-reactance X. In cases where the resistance-component of the fault-impedance was several times as large as the reactance-component which was supposed to be responded to, tne Lewis reactance-relay characteristic has dropped away from said ideal, so much so that, under severe conditions, as on very short lines or on short lines grounded through a high-resistance neutral, where the arcing ground-current resistance was many times the line-reactance, the relay would not always operate, or would not always operate correctly.

The prior-art Lewis relay was a balancedbeani differential relay having a voltage-response on its restraint end, and both voltage and current-responses on its operationg end, the two voltage-responses being equal when the current was zero, and a phase-shifter being applied so as to obtain a 90° phase-shift between the voltageresponsive and current-responsive flux-components at the operating end of the beam, at unity power-factor. This phase-shifter means, as previously used, has required a capacitor, and it has required holding the capacitor, reactor and coilimpedances to close tolerances to obtain the required 90° phase-shift.

The Lewis reactance relay has also required a current-type coil, as well as a voltage-type coil, at the front end of the beam.

An object of my invention is to provide a reactance-relay having a characteristic which more nearly approaches the ideal characteristic than the Lewis relay.

A further object of my invention is to provide a reactance-relay in which the current-responsive flux-component is obtained with an excitingcircuit utilizing a mutual reactance, or air-gap transformer, which has the inherent action of maintaining an induced secondary voltage which lags the primary current by 90 electrical degrees.

A still further object of my invention is to provide a simplified reactance-relay comprising only one air-gap transformer and one balanced-beam (Cl. 175—294) relay, or other differential relay, requiring only a single, untapped, voltage-type coil for producing the operating flux.

With the foregoing and other objects in view, 5 my invention consists in the combinations, systems, methods, apparatus and parts, hereinafter described and claimed, and Illustrated in the accompanying drawing, wherein

Fig. 1 is a diagrammatic view of circuits and 10 apparatus showing my invention, and

Fig. 2 is a characteristic-curve diagram.

As shown in Fig. 1, an alternating-current line 2 is protected by my invention, comprising a differential relay, which is shown as a balanced15 beam relay 3, having a balanced beam 4, which is operated upon, at the front end, by a voltagetype operating-coil 5, and which is operated upon, at the rear end, by two out-of-phase voltage-coils 6 and 7, the fluxes of which are kept approxi20 mately 90° out of phase with each other, as by means of a phase-shifting capacitor C, connected in series with the coil 7, so that the restraintforce will be non-pulsatory, as is well known.

A potential transformer 8 is utilized to supply 25 the line-voltage E, or a line-derived, voltage-responsive relaying-voltage, to the relay. A linecurrent transformer 9 is utilized to derive the line-current t, or a line-derived, current-responsive relaying-current.

³⁰ In accordance with my invention, I provide a mutual reactance ?M, in the form of a variableratio air-gap transformer, the primary winding of which is provided with taps K. The line-derived current i is circulated through the primary 35 winding, having the taps K, and the secondary winding of the mutual reactor ?M is connected in series with the operating-coil 5. The operatingcoil 5, with its serially connected mutual-reactance winding jM, is energized across the second⁴⁰ ary winding of the potential transformer 8. The restraint-winding 6, and the dephased restraintwinding 7 with its serially connected capacitor Ci, are also energized across the secondary wind45 ⁱⁿS of the potential transformer 8.

^relay ³ I^s provided with a make-contact 10, at the front, or operating-coil, end of the beam 4.

As in all differential-type reactance-relays, the design-constants must be such that the voltage50 responsive operating and restraining forces must be equal, when there is no current on the operating end of the relay.

The restraint-flux is responsive to the linevoltage E, and the restraining force on the relay ⁰⁰ may be written as E³.

The operating-flux is responsive to its applied voltage, which is

E-jKMt = E—ΚΜΪLQ0°=E-KMIZ (90°-0) =

Eⁱ+K^tMⁱlⁱ—2EIKM cos (90°-0) where 9 is the angle by which the line-current i lags the line-voltage E. The operating force on the relay may be written, therefore, as

Ε^+Κ²Μ²Ι²—2EIKM sin 9

Equating the operating and restraining forces, and remembering that the line-reactance

X=®sin0 the balance-point of the relay js found to be when

2,439,944 means in response to the line-voltage alone, and current-compensated voltage-responsive exciting-circuit means, Including, as a compensator, a variable-turn air-gap transformer, for exciting the operating-coil flux-producing means in response to both the line-voltage and the linecurrent, the two voltage-responses being substantially equal when the line-current is zero.

2. A differential-type reactance-relay, having 10 an operating-coil flux-producing means, a restraint-coil flux-producing means, a reactancemeans, means for exciting said reactance-means in response to the line-current, means for producing a relaying-voltage in response to the line18 voltage, exciting means for exciting said operating-coil flux-producing means with both said relaying-voltage and the voltage-drop across said reactance-means, and exciting means for exciting said restraint-coil flux-producing means 20 with said relaying-voltage alone, the voltage-responses of the operating-coil and restraint-coil flux-producing means being substantially equal, when there is no current applied to said reactance-means. ARTHUR C. MEHRING.

REFERENCES CITED

The following references are of record in the file of this patent:

UNITED STATES PATENTS

Name ’ Date

Stoecklin___________Feb. 4,1930

Leben et al.________Aug. 9,1932

Crichton et al.----July 17, 1934

Traver____________July 2,1946

FOREIGN PATENTS

Country Date

Switzerland_________Apr. 1, 1937

Germany__________Jan. 26, 1932 _y KM 2

Fig. 2 shows the comparative performancecurves of my relay, as compared with the Lewis reactance-relay. The full-line curves Ii and 12 show the actual performance of a typical Lewis relay at different voltage-conditions, as marked. The dotted-line curves (3, 14 and 15 show the much better performance-curves of my new relay, under similar operating conditions.

While I have illustrated my invention in but a single preferred or illustrative form of em- 30 bodiment, my invention is not limited to this precise form, in all its details, and I desire that the appended claims shall be accorded the broadest construction consistent with their language.