US2298126A - Signaling system for transformers - Google Patents

Description

Oct. 6, 1942- J. K. HODNETTE SIGNALING SYSTEM FOR TRANSFORMERS Filed Aug. 5, 1940 INVENTOR 200.551.) Cal/A650 WITNESSES:

Patented Oct. 6, 1942 SIGNALING SYSTEM FOR TRANSFORMERS John K. Ho'dnette, Sharon, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 3, 1940, Serial No. 350,381

Claims.

The invention relates to a light signaling system for transformers.

In the usual power and light distribution systerns employed for supplying cities and rural sections, innumerable distribution transformers are located'at different points throughout the areas supplied. The loads imposed on these distribution transformers located at a distance from the power stations fluctuate continuously with changes in demands in the different localities.

In order to ascertain whether or not a particular transformer is being subjected to an overload, it has been necessary in the past to send out service men with graphic instruments to measure the load. The application of the instruments is usually rather difllcult, and the reading of the instruments consumes time, thereby making the method expensive. Further, in order to have good records, it is necessary to test all transformers at short intervals, which greatly increases the service charges.

The usual practice when designing distribution systems is to provide transformers with excess capacity in order to provide for future increases in load. In many instances, this results in unnecessary expenditures in equipment and greatly increases the overhead expense. Even with this excess capacity, transformers are often excessively loaded with the result that they may be burned out and the service interrupted. This is expensive and brings complaints from customers.

It is the object of the invention to provide a source of energy for illuminating a signal lamp associated with a transformer without subjecting the signal lamp to any appreciable surge current which might cause a burnout as the result of lightning disturbances on the distribution system.

Other objects of the invention will, in part, be obvious, and, in part, appear hereinafter.

The invention, accordingly, is disclosed in the accompanying drawing and comprises the features of construction, combination of elements and arrangement of parts which will be exemplifiedin the structure hereinafter set forth and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following detailed description taken in connection with the accompanying drawing in which:

Figure 1 is a view in section showing how the signal coil is disposed on the transformer core and. insulated from the transformer windings, a d

Fig. 2 is a diagram of the circuit connections of the transformer showing how the coil for supplying the signal lamp is disposed with relation to the core and windings of the transformer.

With the advent of the completely self-protecting transformers such as disclosed in the applicants Patent No. 2,066,935, issued January 5, 1937, an effort was made to provide a visual signal which would function in conjunction with the protecting apparatus to indicate when a transformer had been subjected to overload conditions. The intention was to provide a signal lamp which would be connected across a source of power to illuminate it when the transformer was subjected to overload conditions which were greater than the rated capacity of the transformer but less than the overloading required to operate the apparatus provided for disconnecting the transformer from the system. The provision of a power source for illuminating the signal lamp became a problem.

To provide a source of power other than the transformer would be very expensive and probably more burdensome than to provide the excess transformer capacity aswas the practice in the older distribution systems. It became apparent that the only economical and sound method of providing a source of supply for th lamp was to utilize the transformer itself, in some way, to provide the necessary current.

The obvious thing to do would be to utilize the low-voltage winding of the transformer for the source of energy for the signal light. Where this was tried, it was found that the signal lamp was vulnerable to surges imposed on the line as a result of electrical disturbances of one kind or another.

These surges imposed a voltage across th low voltage winding comparable in magnitude to the surge voltage on the system. When the signal lamp is connected across the low voltage winding it is actually a low resistance circuit connected in parallel with an inductive member and the result is an initial high current flow through the signal lamp.

Attempts to utilize a low-voltage lamp which would have a correspondingly large filament supplied by taps taken from the winding as near the grounded end as possible were also unsuccessful. Even under this condition the'surge current conducted through the lamp was found to be sufficient to burn out the lamp filament in spite of its greater cross-section.

In Patent No. 2,223,530, issued December 3, 1940, and assigned to the Westinghouse Electric visible signal when the transformer was subjected to an overload.

Facing these difliculties, the present applicant conceived the idea of providing a separate coil of few turns disposed on the transformer core in such position as to be only loosely coupled, to the other, transformer windings. This arrange ment proved effective since the loose coupling does not transmit the full inductive effect of the lightning surge, and it wasfound that even in the case of severe lightning strokes, no damage resulted to the signal-lamp filament.

The next step was the matter of designing the signal-lamp coil with the proper number of turns for the rating of the transformer or the system with which it was to be utilized and so disposing the coil as to prevent the flow of surge current through it. This requires that there be no metallic connection between the low-voltage windings of the transformer and the signal-light coil.

Referring now to Fig. l in particular, a standard type of transformer I is illustrated. The transformer comprises a core H provided with a low-voltage winding [2 disposed between the usual low-voltage and high-voltage barriers I 3 and M, respectively. The low-voltage winding I2 is wound on the core II in the usual manner.

In accordance with my invention an auxiliary winding or coil l 5, provided for supplying the si nal lamp I6, is inductively disposed on the leg of the core I I, and located near one end of the leg. As illustrated, the coil I5 is separated from the low voltage winding l2 by spacers l1 and a Fuller board channel l8. The Fuller board channel is provided with an offset which extends partially around the coil l5. This Fuller board channel extends alongside of the yoke l9 of the core.

In this particular embodiment of the invention the coil I 5 is separated from the core-iron by means of a layer of paper 20. As illustrated, the paper 20 is bent at right angles to' separate the coil l5 from the leg and the yoke of the core I l. The high voltage winding 2! is also spaced from the coil 15.

The size of the barrier II, the thickness of the Fuller board channel I8, and the thickness of the paper layer 20 will all depend upon the transformer for which the coils are designed. It will be noted that the low-voltage Winding l2 has been shortened to accommodate the mounting of the signal-lamp coil l5 on the leg of the core H. While this shortening of the low-voltage winding did not at first seem to be altogether desirable; from the standpoint of the ordinary design and operation of the transformer, it has been found that a transformer can be designed so as to render this slight change in the design of the low-voltage winding l2 immaterial. It was found in practice, in the year 1939, that this change after all involve no appreciable disadvantage in the construction and operation of the transformer. When the coil I5 is mounted in the manner described, that is, spaced from the primary and secondary windings it is substantially unaffected by surge voltages impressed on the transformer windings but it will impress on the lamp IS a voltage which has a predetermined reiation to the rated voltage of the transformer.

The completely self-protecting transformer disclosed in applicants patent identified hereinbefore was received by the trade as being quite revolutionary in the transformer art. An extensive installation was made, but to the great disappointment of those concerned, the signal lamps which were mounted in the transformer were grammatic showing, switching-means shown generally at 22 are shown for connecting the lamp l6 across the coil I5. While various types of switching apparatus may be employed for this purpose, it is preferred to utilize the apparatus provided in conjunction with the completely selfprotecting transformer and which is shown and described in the Patent 2,223,530, issued Decemher 3, 1940, hereinbefore referred to.

This apparatus, provided for disconnecting the transformer from the line, connects the signal lamp across the coil when a predetermined overload is imposed on the transformer. The signal lamp is so disposed that it can be readily observed from the ground, and a service man who makes regular rounds can easily see from a distance Whether or not the transformer has been subjected to an overload. If he suspects that the overload is of a temporary nature, he may reset the apparatus as described in the application referred to, and if the signal lamp is soon re-lighted, then it is evident that the transformer is being continuously overloaded.

When the breaker illustrated schematically in Fig. 2 stands closed, the contact members 23 and 24 stand in spaced relation as illustrated. If the transformer is overloaded, the bimetal 9 raises the latch 25 and the dog 26 is. actuated by the spring 27 to close the switch 22. A lighting circuit is established which may be traced from one side of coil l5 through the lamp l6, conductor 28, contact members 23 and 24, switch arm 32, conductors 29 and 30, back to the coil IS. The lamp 15 will be illuminated for signaling purposes.

In this manner the operating staff of any distribution system is made aware of the fact that the transformer is not of suificientcapacity for the locality in which it is located and that a transformer of greater capacity should be sup plied.

By employing the completely self-protecting transformer and a signal light supplied by the applicants coil, a great saving in the initial installation costs of a distribution system may be made. It is not unusual to make installations in which apparatus of 20% smaller capacity may be safely employed without any serious interruptions in service. This signaling system has made it possible to eliminate almost completely the previous practice of checking loads with graphic instruments.

In some instances, the oil will be disposed on only a portion of the magnetic core. A good example is in the case of large transformers where even one turn in the signal coil would give a voltage in excess of the rated voltage of the signal lamp. The core may also be slotted to receive the coil l5.

In conclusion, it is pointed out that, while the illustrated example constitutes a practical embodiment of my invention, I do not limit myself to the exact details described, since the materials may be considerably varied without departing from the spirit of the invention as defined in the appended claims.

I claim as my invention:

1. In a light-signaling system for a transformer provided with a core and high-and low-voltage windings, in combination, an electric lamp for giving a visible signal when predetermined load conditions develop, a coil for supplying electric current to the lamp, means responsive to load conditions for connecting thelamp to the coil, the coil being so spaced from the transformer windings that substantially no change in voltage across the lamp results from the surges impressed on the transformer windings and so looped around the core that it will impress a predetermined voltage on the lamp when the transformer is subjected to load conditions which efiect the operation of the connecting means.

2. In a light-signaling system for a transformer provided with a core and high and low voltage windings, in combination, an electric lamp for giving a visible signal when predetermined load conditions develop, a coil for supplying electric current to the lamp, a switch responsive to load conditions for connecting the lamp to the coil, the coil being so disposed on the core that there is no metallic connection with the windings, and loose electrostatic and electromagnetic connections with the windings permitting leakage whereby the coil and therefore the lamp is substantially unaffected by surges impressed on the transformer windings.

3. In a light-signaling system for a transformer provided with a core and main transformerwindings, in combination, an electric lamp for giving a visible signal, and a lamp-energizing means including a coil disposed on the core in such position as to have loose electrostatic and electromagnetic couplings to the main transformer-windings whereby the coil and lamp are substantially unaffected by surge voltages impressed on the transformer windings.

4. In a light-signaling system for transformers provided with cores and high and low voltage windings, in combination, an electric lamp for giving a visible signal when predetermined load conditions develop, a coil for supplying electric current to the lamp, a circuit breaker disposed to connect the lamp across the coil, the coil being so spaced from the transformer windings that it is substantially unaffected by surges impressed on the transformer windings and so coupled with the core that it will impress a voltage on the lamp which has a predetermined relation to load conditions.

5. In a light signaling system for a transformer provided with a core and primary and secondary windings, in combination, an electrically operated lamp for giving a visible signal, a coil for energizing the electrically operated lamp, the coil being looped around the core, the coil being spaced from the primary and secondary windings, and insulation barriers disposed between the coil and the primary and secondary windings, the insulation and the spacing of the coil from the primary and secondary windings being of predetermined dimensions whereby when surge voltages are impressed on the primary and sec ondary windings the inductive effect on the coil is so small that there is substantially no increase in voltage across the lamp.

JOHN K. HODNE'ITE.

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