US1790024A - Device for determining the condition of transformers - Google Patents

Description

Jan. 27, 1931. 5 RUM]: 1,790,024,

DEVICE FOR DETERMINING THE CONDITION OF TRANSFORMERS Filed March 2, 1926 Patented Jan. 27, 1931 UNITED STATES PATENT-O FICE SIGURD BUMP, F BOSTON, MASSACHUSETTS, ASSIGNOR TO ALMIERICAN BROWN BOVERI ELECTRIC CORPORATION, OF NEW YORK,.N. Y., A CORPO RATION DEVICE FOR DETERMINING THE CONDITION OF TRANSFORMERS Application filed March 2, 1926. Serial No. 91,768.

In operating transformers of large output it is important that internal damages, which may occur, and which are generally invisible, and therefore are not noticed for long periods of time, may be determined as early as possible in order that they may be removed. Such damages, especially short circuits between core laminations and other defects in insulation, increase in time and lead to sudden serious overheating and burning, sometimes to fire and to complete uselessness of the whole apparatus.

Successful use has been made of the gas development which is due to local heating and forming of arcs on the damaged part in order to determine defects. Such gas development, however, occurs only when the heating is sufficient to evaporate or decompose a certain amount of oil.

The present arrangement for protection, however, acts earlier and indicates the defect in a station where a gas development has not started. The method is based on the invariable appearance of watt losses in a damaged part. Such losses must certainly be balanced by the network and they are always balanced only by one side, that is, either by the high tension side or by the low tension side of the trans former. The current of both trans-tori or sides compared and referred to a ratio of transforn'iation 1, results normally in a differential current which is equal to a certain watt loss, namely, the iron loss plus copper loss, which is caused by the magnetizable current.

This watt loss is constant as long as the pnmary voltage of the transformer is constant, therefore, the differential current equals the watt loss. The differential current or differential output has already been used for indicating defects in transformers as well as for operating safety devices as soon as such current or output exceed their normal values. Each watt consumption resulting from any losses can, theoretically, be replaced by a resistance which would cause the same losses. Such theoretically compensation resistance although practically not present can be measured with an ohmmeter. According to the invention, an ohmmeter really will therefect.

fore be used for indicating a transformer de- The drawing diagrammatically shows one application form of the invention.

a indicates the low tension winding and b the high tension winding of the transformer: to be pro- .tected. On both sides are connected current transformers c and d, the secondary windings of which are connectedwin opposition and are arranged in the circuit of an ohmmeter e, which is constructed in accordance with the cross coil principle. The stationary coil f and coil 9 of the movable system, which are connected in series, are traversed by the differential current. Coil h of the movable relay system'lies at a constant .angle to coil 9 and is fedby thev voltage transformer z, the, primary coil of which is connected to the low tension.side of the transformer. By the action of the ohmmeter arm m connected to the movable system, a

contact is of an auxiliary circuit, diagrammatlcally shown inthe drawing, 1S operated,

ing, alarm or protection apparatus.

which auxiliary circuit contains the indicat- It Will be understood from the foregoing that the movable system of ohmmeter e coniprises coils g. and h and the arm m. these parts being fixedly connected hfigetlu-r to move as a unit with relation to coil The ohmmeter is so (-(mstructed that the arm on operates contact k in the c'vcntthc con'ipensation resistance increases a certain amount over the normal no-load losses of Therefore the connections can be adjusted so that the arrangement will be sensltive to a very small excess over the allowable losses.

the resistance. f

The new arrangement may also be made other apparatus and electric machines.

with certain modifications for protection of all events, it can be used wherever internal damage causes a change of the resistance value of the winding to be protected.

I claim:

1. The combination of a transformer having primary and secondary lead connections, of a protective system therefor comprising a pair of differentially-connected transformer windings associated with the primary and secondary lead connections, and a relaydevice in series with said differential transformers energized by the differential effect of the currents of said windings to operate only in response to the variations of-the watt component of said differential current.

2. In electrical protective systems for transformers comprising a pair of serially connected transformer windings, differentially energized by the primary and secondary currents of the transformer to be protected, a relay device having a pair of movable coils fixedly connected and a stationary coil cooperating there-With, one of said movablecoils and said stationary coil being connected in series with said serially-connected transformer windings, the other of said movable coils being energized by a current proportional to the voltage across the trans former to be protected to actuate said relay in response to the Watt component of the differential current in said serially-connected transformer windings.

'3. In a protectlve system, a transformer having primary lead connections and second- 'ary lead connections, a current transformer in the primary lead connections, a current transformer in the secondary lead connections, an ohm-meter relay comprising a stationary coil and a pair of movable coils, and said movable coils being fixedly connected and differentially actuated by said stationary coil, the secondary windings of said current transformers being differentially connected in series with the serially.v connected stationary coil and one movable coil of said relay, the other of said n'lovablc coils being supplied fro-m across said transformer.

all

4. In a protective system, a main transformer, a pair of secondary transformers respectively connected to the windings of said main transformer, the secondary windings of said secondary transformers being differentially connected in series, an ohmmeter in series with said differentially connected transformers,and a transformer connected across the primary of said main transform-er,the secondary of said last mentioned transformer being connected in series with the voltage coil of said ohmmeter.v

In testimony whereof I hereunto sign my name.

SIGURD BUMP.

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