US783533A - Transformer protection. - Google Patents

Description

No. 788,583. PATENTED FEB. 28, 1905. W. S. MOODY.

TRANSFORMER PROTECTION.

APPLICATION FILED JULY 25, 1904.

\AHTNEI55E5 INVENTOR UNITED STATES Patented February 28, 1905.

PATENT OEEIcE.

WALTER S. MOODY, OE SCHENECTADY, NEIV YORK, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TRANSFORMER PROTECTION.

SPECIFICATION forming part of Letters Patent No. 783,533, dated February 28, 1905.

Application filed July 25, 1904. Serial No. 218.032.

To all whom, it may concern.-

Be it known that I, WALTER S. MOODY, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New I York, have invented certain new and useful Improvements in Transformer Protection, of which the following is a specification.

This invention relates to systems of electrical distribution in which current at high potential is distributed to points near the place of consumption and there tlitIlSfOl'Il'lBd or converted into current of suitable working pressure. In transformers used in such systems the primary or high-pressure circuit and the secondary or low-pressure circuit are normally insulated from each other; but if by any accident the insulation should fail the secondary circuit, together with all the instruments or power apparatus connected to it, would be raised to the potential of one side of the primary circuit. Under these conditions a discharge might occur through ground to the other side of the primary, thus endangering life and property along the secondary circuit.

It is old in the art to protect the secondary circuit from the high voltage of the primary by providingapermanent connection between the secondary and ground. This arrangement is sometimes insufficient to protect the secondary circuit, for the reason that the current discharged through the secondary and the ground connection is sometimes sufficient to fuse the part of the secondary traversed by the discharge and to burn off the connection with the ground-wire. This leaves the remainder of the secondary winding and the entire secondary network at the dangerously high potential of the primary circuit. In the present invention this difficulty is overcome by connecting the secondary to the core of the transformer or converter and grounding the core through a heavy connection in a manner hereinafter described.

While the invention is readily applicable to various forms of electrical apparatus, it is particularly useful in connection with transformers of the type commonly designated as current-transformers and used inconnection with central-station instruments.

The accompanying figure shows diagrammatically the application of the invention to such a device.

1 indicates the source of power, and 2 3 the high-potential distributing-mains. The annular iron cor-e4 represents the core of the current-transformer, having a primary 5, consisting of a straight cylindrical conductor, carrying the high-potential current of the-line, and a winding 6, connected to the switchboard instrument 7. The winding 6 is insulated from the iron core 4 throughout its length, except at 8, whereit is permanently grounded to the core. In the finished transformer this grounded point is preferably about midway between the two ends of the secondary coil. The insulation 10 between the core and the secondary winding is comparatively thin and is weak enough to be punctured if sub jected to the voltage of the primary circuit. The iron core 4: is permanently connected to earth by a conductor 9, capable of carrying the full primary current. The transformer may be provided with a metal case 11, surrounding the windings. Bushings 12, 13, and 14: serve to insulate the case from the winding-terminals, and a conductor 15, capable of carrying the full primary current, connects the case with the ground-conductor 9.

IVith the arrangement described if the secondary winding is subjected to the dangerous voltage of the primary circuit because of the failure of the insulation or similar cause the high-pressure current will escape through the connection 8 to the ground-conductor 9 and then to earth. If this leakage-current is of sufficient magnitude to fuse the grounded end of the secondary winding, the escape of the high-voltage current to ground will not be prevented thereby, but will take place through the thin core insulation, .and thus from the core to ground, as before.

The excessive heating of the secondary materially assists in breaking down this thin core insulation, and so long as any of thesecondary winding remains intact there will be a low-resistance path to earth for the highvoltage current.

I f the primary becomes grounded to the case in any manner, as by failure of the bushing 13, the high-potential current will be carried to earth by the heavy conductors 15 and 9, thus preventing a possible breakdown of the secondary bushings and the destruction of the secondary terminals by the high-potential current.

WV hat I claim as new, and desire to secure by Letters Patent of the United States, is

1. In a transformer, a core, a winding therefor, an electrical connection between the core and winding, and means for connecting the core to earth.

2. In a transformer, a core, a winding therefor, and an electrical connection between said winding and core.

3. A transformer comprising a case, acore, a high-potential winding, a low-potential winding, an electrical connection between said low-potential winding and core, and means for connecting said case and core to earth.

L A transformer comprising a core, a lowpotential winding, thin insulation between said winding and core, an electrical connection between the core and winding near the center of the winding, and means for connecting the core to earth. i

5. A transformer comprising a core, a winding therefor, thin insulation between said winding and core, an electrical connection be tween said core and winding, and means for connecting the core to earth.

6. A transformer comprising a core, a winding therefor, an electrical connection between said core and winding near the center of said. winding, and means for connecting the core to earth.

7. A transformer comprising a case, a core, a winding for said core, an electrical connection between said core and winding near the center of said winding and means for connecting the caseand core to earth.

8. A transformer comprising a case, a core, a low-potential winding for said core, thin insulation between said winding and core, an electrical connection between the core and Winding near the center of the winding, and means for connecting the case and core to earth.

In witness whereof I have hereunto set my hand this 21st day of July, 1904.

WALTER S. MOODY.

\Vitnesses:

BENJAMIN B. HULL, HELEN URFORD.

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