US2586354A

US2586354A - Overvoltage protection for transformers

Info

Publication number: US2586354A
Application number: US158396A
Authority: US
Inventors: Merrill G Leonard; Guy Y Hager
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-04-27
Filing date: 1950-04-27
Publication date: 1952-02-19
Anticipated expiration: 1969-02-19

Description

Feb. 19, 1952 M. G. LEQNARD ET AL 2,586,354

OVERVOLTAGE PROTECTION FOR TRAN'SFORMERS Filed April 2v, 195o INVENTORS Merrill G. Leonard En Guy Y. Hoger.

ATTOR EY Patented Feb. 19, 1952 OVERVOLTAGE PROTECTION FOR TRANSFORMERS Merrill G. Leonard, Sharon, and Guy Y. Hager, Sharpsville, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 27, 1950, Serial No. 158,396

1 Claim.

The present invention relates to overvoltage protection for transformers, and more particularly to an improved mounting and arrangement l of a lightning arrester and high-voltage terminal means for protected or surge-proof transformers. or other enclosed electrical devices.

Transformers of the protected or surge-proof type are protected against lightning surges, or

other overvoltages such as may be caused by bushings in the tank wall. The terminal bushing must be provided with a terminal device for ccnnecting a line lead to the transformer, and it must be arranged to permit vconnection of the lightning arrester to the transformer lead.

Lightning arresters of the expulsion type are usually used on protected transformers. In arresters of this type, when a surge is discharged, an arc is formed in an arcing chamber lined with, or containing, material capable of evolving substantially un-ionized gas in the presence of an arc. When a discharge occurs, a large quantity of un-ionized gas is thus evolved and is expelled through a vented electrode, deionizing the arc path and blowing out the arc to interrupt the power current which tends to flow to ground following the surge. An external series spark gap is always used with lightning arresters of this type to isolate the arrester from the line under normal voltage conditions. so that the line-to-ground voltage will not be continuously applied across the arrester, and when the arrester is connected to the transformer lead on the outside of the transformer tank, provision must be made for a series gap. Open gaps are objectionable, however, because exposed live parts, either of the gap or of a high-voltage terminal, are highly undesirable. Open gaps are also undesirable because of the risk of being bridged by snow or sleet, or by birds or small animals.

The principal object of the present invention is to provide a protected transformer in which a lightning arrester is mounted on the outside of the transformer tank in association with a highvoltage terminal bushing, and connected to the high-voltage lead of the transformer through a series gap which is combined with a terminal device.

Another object of the invention is to provide means for mounting a lightning-arrester on a transformer tank in association with a high-voltage terminal device and for connecting the arrester to the terminal through a series gap, the arrangement being such that the gap and terminal device are protected and, in effect, enclosed so that no live parts are exposed and the danger of the gap being bridged is substantially eliminated.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a perspective view of a protected transformer embodying the invention, and

Fig. 2 is a view on an enlarged scale, partly in elevation and partly in vertical section, showing the details of the lightning arrester mounting and terminal bushing. f

The invention is shown in the drawing embodied in a transformer contained in a tank i closed by a cover 2. The transformer itself may be of any suitable type or construction, since the invention is applicable to transformers of any desired type or size or, in general, to any enclosed electrical device. The tank may be provided with hangers 3 for mounting the transformer on a pole or other support. The particular transformer shown has an internal circuit breaker, for overcurrent protection, with an operating handle 4 on the outside of the tank. High-voltage terminal bushings 5 for the leads from the highvoltage winding of the transformer are mounted in the tank wall diametrically opposite to each other. Suitable low-voltage terminal devices may also be mounted in the tank wall, between the high-voltage bushings, these terminals not being visible in the drawing.

The two terminal bushings 5 are identical in construction and arrangement. As shown in Fig. 2, each terminal bushing 5 is mounted horizontally in the side wall of the tank I and a lead 6 from the high-voltage winding of the transformer extends through the bushing and is connected to a terminal device 'l in the outer end of the bushing. Any suitable type of terminal device may be utilized, the particular device shown being a setscrew type terminal having an opening 8 for rcceiving a line lead and a .set-screw 9 for clamping a pressure pad l0 against the line lead to effect positive electrical connection. The set screw 9 is provided with a large insulating knob or handwheel l I for actuating the screw, the knob Il being large enough to substantially cover and close the open end of the bushing 5. Slots I2 are formed on each side of the bushingopposite the terminal device 1 for entrance of the' line lead. The bushing l also has an opening or hole I3 formed in its lower side near the outer end of the bushing and opposite the terminal device 1 The terminal device 1 is provided with a. down-i wardly extending conducting member I4, which may be a threaded stud threaded into the lower side of the terminal device 1, and which extends down through the opening Il to form one electrode of a spark gap. as hereinafter described. Ihe member I4 also serves to prevent the terminal device 1 from being rotated when the knob II is turned to tighten or release a line lead.

The transformer is protected against lightning surges, or other overvoltages, by means of a' lightning arrester I5 connected between each of the high-voltage leads and ground. While only one arrester I5 is visible in Figure l, it will be understood that a similar arrester, similarly arranged, is associated with the bushing 5 on the opposite side of the tank. Any' suitable type of lightning arrester may be utilized, the particular arrester shown being an expulsion lightning arrester of the type disclosed and claimed in our copending application Serial No. 788,370, filed November 28, 1941, now Patent No. 2,546,006, issued March 20, 1951, and assigned toWestinghouse Electric Corporation. The arrester I5 is enclosed in a porcelair` housing I6 and comprises a tube I1 of hard fiber, or other suitable insulating material capable of evolving substantially un-ionized gas when subjected to the heat of an electric arc. An upper electrode I8 is secured in the upper end of the tube I1, and a metal cap I8 closes the top of the tube. A metal stud 20 is secured in the cap I8 and extends up through the top of the porcelain housing I6 to form an upper terminal member for the arrester. A cap member 2I may be placed around the stud 28 on the outside of the arrester with a gasket to seal the housing and prevent the entrance of moisture. A hollow lower metal electrode member 22 extends from the lower part of the tube I1 through the bottom of the housing I6 and is threaded to facilitate mounting the arrester. A loose stack of alternating fiber disks 23 and fiber washers 24 is placed in the tube I1 between the electrodes to restrict the arc path and to provide additional gas-evolving material.

. In the operation of the arrester I5, when a lightning surge occurs, an arc is formed between the electrodes I8 and 22 in the restricted annular space between the tube I1 and the stack of disks 23 and washers 24. The heat. of the arc causes a large volume of un-ionized gas to be evolved. which is expelled in a blast through the hollow lower electrode 22, and which deionizes the arc path and blows out the arc to interrupt the power current which tends to follow the surge. The gas also flows through grooves 25 in the disks 23 into the central spaces of the washers 24, the discs and washers being free to move apart axially to relieve the gas pressure without affecting the restriction of the arc path, thus preventing the development of excessively high gas pressures within the arrester.

'Ihe lightning arrester I5 is mounted on a metal angle bracket 26 which may be of any suitable construction.- The threaded lower electrode 22 is threaded into the horizontal portion of the bracket 28 and secured in position by a nut 21 and cooperating lock washer. The bracket 26 also has a vertical portion which is bolted to the wall ci' the tank I by means of bolts 28 threaded into the tank, thus connecting the lower electrode 22 of the arrester to the tank I, which is usually grounded. The bolts 28 pass through elongated slots 23 in the bracket 28 so that the arrester is adjustable in vertical position.

It will be noted from the drawing that the bracket 28 is bolted to the tank directly below the terminal bushing 5 and is arranged so that the arrester Il is directly below the outer end of the bushing with its upper terminal member 20 disposed opposite the opening I3 in the bushing and adjacent the lower end of the conducting member I4, so that the conducting member I4 and the upper terminal 28 of the lightning arrester form the electrodes of a spark gap between the arrester I 5 and the terminal device 1. The length of this spark gap may be adjusted by moving the arrester Il vertically before the bolts 28 are tightened, this movement being permitted by the elongated slots 29. When the gap has been adjusted to the desired length, the bolts 28 are tightened to hold the arrester in that position, and the bracket 26 is preferably locked in place by a locking plate 30 through which the bolts 28 pass and which extends vertically to the lower end of the bracket where it is bent over to prevent relative movement between the bolts and the bracket. Thus, a relatively simple means is provided for adjusting the position of the arrester to determine the length of the spark gap, and since the arrester and bushing are mounted on the same rigid surface, the adjustment will be maintained unchanged. It will be apparent that other suitable adjusting means might be used, such as turning the arrester in the threaded mounting bracket, or any other suitable means.

It will be seen that the lightning arrester I5 is connected to the high-voltage terminal 1 of the transformer through a series spark gap, one electrode oi which is part of the terminal device itself, so that the gap is combined with the terminal. It is to be noted that the position of the conducting member I4, which extends down through the opening I3 towards the upper terminal 2l) of the arrester, is such that the gap between the members I4 and 20 is protected and, in effect, enclosed, and that the terminal device 1 itself is enclosed in the end of the bushing 5, so that no live parts are exposed in a position where accidental contact could easily be made. The position and arrangement of the gap are also such that any risk of the gap being bridged is substantially eliminated.

It should now be apparent that an improved mounting and arrangement of a lightning arrester and high-voltage terminal device for protected transformers have been provided, by means of which the arrester is connected to the high-voltage terminal through a series spark gap which is combined with the terminal and which is protected and enclosed. A speciiic embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that various other embodiments and modifications are possible. Thus, the terminal bushing and arrester may be mounted in any desired position on the tank, including the cover. Any suitable type of terminal device may be used, and the conducting member extending from it to form one electrode of the gap may take any suitable physical form, such as a projection formed integral with the terminal device, or any other equivalent construction. Similarly, any suitable type of lightning arrester may be used, and the details of mounting the arrester on the tank and providing for vertical adjustment may be modiiled in any desired manner. It is to be understood, therefore, that although a particular construction has been shown and described, the invention is not limited to this specific arrangement, but in its broadest aspects it includes all equivalent ernbodiments and modicatons which come within the scope of the appended claim.

We claim as our invention:

In combination, a tank for an enclosed electrical device, a one-piece, integral, insulating terminal bushing mounted horizontally in a wall of said tank, said bushing having a hollow therein and being open at the outer end, a terminal device mounted within the bushing in said hollow, said terminal device having an operating knob of insulating material outside the bushing and extending over the open outer end thereof to substantially completely enclose the terminal device, the terminal device being of a type which is liable to rotational movement in the bushing when said knob is operated, the bushing having an opening in the lower side thereof near the outer end of the bushing, a conducting member on the terminai device extending downward therefrom into said opening in position to engage a side o! the opening to prevent rotation of the terminal device, a lightning arrester, means for mounting said lightning arrester below the bushing in a vertical position, the lightning rester having a terminal member at its upper end substantially in vertical alignment with said conducting member, and said mounting means including means for adjusting the position of the lightning arrester vertically to space the terminal member of the arrester a desired distance from said conducting member to form a spark gap therewith.

imam. G. LEONARD. GUY Y. miem REFERENCES crrnn The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,018,672 Hill Oct. 29, 1935 2,029,140 Treanor Jan. 28, 1936