US2011136A - Protective apparatus - Google Patents

Description

Aug. 13, 1935. A. o. AUSTIN 2,011,1 36

PROTECTIVE APPARATUS Filed July 30, 1931 3 Sheets-Sheet l INVENTOR flrf/zur 0. H116 fin n; w W I ATTORNEY Aug. 13, 1935.

A. 0. AUSTIN- 2,011,136

PROTECTIVE APPARATUS Filed July so, 1951 3 Sheets-Sheet 2 INVENTOR flrf/zur 0. flush/7 ATTORNEY PROTECTIVE APPARATUS Filed July 30, 1931 3 Sheets-Sheet 3 INVENTOR Arf/rur 0 Ausf/h Y ATTORNEY Patented Aug. 13, 1935 UNITED STATES PATENT OFFICE PROTECTIVE APPARATUS Jersey Application July 30, 1931, Serial No. 554,034

19 Claims.

This invention relates to protective devices for high potential electrical apparatus and insulation, and has for one of its objects the provision of an arcing gap which will be more reliable and effective than gaps heretofore used.

A further object of the invention is to provide an arcing gap equipped with means for regulating the relative voltages at which discharge will take place for negative and positive potentials.

A further object of the invention is to provide an arcing gap in which the time lag for discharge will be less than the time lag of the apparatus protected.

A further object is to provide an arcing'gap having the advantages of a large sphere gap without the disadvantages thereof.

Other objects and advantages will appear from the following description.

The invention is exemplified by the combination and arrangement of parts shown in the accompanying drawings and described in the following specification, and it is more particularly pointed out in the appended claims.

- In the drawings:

Fig. 1 is a graph or curve sheet illustrating the operation of the invention.

Fig. 2 is a somewhat diagrammatic elevation of an arcing gap having one form of the invention applied thereto.

' Fig. 3 is an elevation of a modified form of arcing terminal.

Fig. 4 is a section on line 4-4 of Fig. 3.

Figs. 5 and 6 both show other forms of arcing terminals.

Fig. 7 is an elevation of one terminal of a gap like that of Fig. 2 but having a different circuit arrangement.

Fig. 8 is a view similar to Fig. 2 showinganother modification.

4'. Fig. 9 is a top plan of the terminals of Fig. 8.

Fig. 10 is a view similar to Fig. 2 showing another modification.

Figs. 11 and 12 are vertical sections showing.

forms of arcing terminals.-

In the protection of high voltage electrical equipment subject to lightning, it has been common practice for many years to limit the voltage to which the equipment is subjected by the use of discharge gaps to carry oflf abnormal-charges 5.) when the voltage exceeds a predetermined value. In many cases, owing to cost or time lag in the operation of the lightning arrester, the limiting gap is used either with the lightning arrester or in place of the lightning arrester. In order that a limiting gap be effective, its discharge cham t'filj-i istics should be under control to a very considerable extent. If the gap is to protect apparatus or insulation for very high voltages, particularly those due .to a stroke of lightning in the immediate vicinity, it is essential that the time lag between the time of the impressed voltage and the time at which the gap discharges sufficient energy to lower the voltage; be such that the gap will operate in advance of the fiashover of the insulation which the gap protects. words, to ailord protection, the gap should have such characteristics that it will flash over in advance of the insulation it protects for all conditions to which it is subjected. Many forms of iii In other 10 gaps have a high effective flashover for very short 15 periods and a rather low effective flashover, when the gap is subjected to a stress for a considerably longer time. In these cases, the gap is apt to fiashover, causing unnecessary interruptions under mild conditions, and does not afford surficient protection to apparatus or insulation for the most severe conditions.

Fig. 1 shows the voltage time lag characteristics for some types of insulation. It will be seen that for very short periods of time the insulation will 2 withstand a very high flashover voltage but as the time "is increased, voltage which will cause flashover may be materially reduced. Curve A shows the potential time lag characteristics for an insulator under negative impulse, and curve B under positive impulse. C shows the impulse time characteristics for an ordinary protection gap under negative impulse, and D under positive. impulse.

It will be seen that for very severe over-potentials, the insulator will flash before the protecting gap. As, however, the conditions become more favorable, the gap will flash-over and protect the insulation. Where it is desired to protect the in- Sula-tion, an ideal gap would have the characteristics approximating those shown by curves E and F in which the flashover voltage of the protecting gap bears a constant relation to the flashover of the equipment which it is desired to protect. Under this condition, protection would be provided but, at the same time, unnecessary flashovers would be reduced to a minimum. It is evident that the insulation may have a large difference in flashover, depending upon the polarity of the impressed transient or voltage, and also the time lag may be materially different. In a protectng gap it is therefore highly desirable that a gap be provided so that the difference in flashover under different polarities can be controlled. It is also advisable to so design the gap that the time lag may be under control. 5

In my improved type of gap, these features can cuit breakers, lightning arresters or other devices used for clearing the line after the passage of the charge causing the over-voltage.

In the embodiment of the invention shown in Fig. 2, the gap terminal conssts essentially of two parts. an arcing head or tip it] and a control or screening system H. The arcing tip it! is connected by a suitable mounting member 62 to the incoming lead I 3. The gap head consisting of the tip l0 and control system H is mounted on a suitable insulator It. The head maybe moved in or out by adjusting the clamp I5, and the tip 88 may be adjusted relative to the screening members l l by loosening the clamp l6 and sliding the rod l2 in or out.

The gap head located on the ground side consists of a tip I? and a control system l8, although in some cases the latter may not be necessary. The lead I9 is connected to the tip 87 and extends to ground through a resistance 20 and fuse 2|. Either the resistance 20 or fuse 2| or, in some cases, one or both may be omitted. The functon of the resistance is to limit the amount of current discharged, and the function of the fuse is to clear the line automatically. As previously explained, this latter function may be carried out by an air or oil circu't breaker or by a lightning arrester. The screening systems of II and [8 each consists of radially extending metallic arms having their extremities inclosed in porcelain insulators.

Although an ordinary sphere gap may be used to limit the voltage impressed on station or other apparatus, the sphere gap is very unreliable under wet conditions unless the spheres are small. On the other hand, if the spheres are small, the length of the gap becomes quite large for a given fiashover voltage, particularly for transients which are most common to the system. For very severe over-voltages, the time lag of the long gap is such that protection will not be aiforded, as the characteristics of the gap will be similar to those of curves C and D, Fig. 1.

With the improved type of gap, it is possible to use small electrodes or tips l0 and I! so that the fiashover will not be materially affected by wet conditions but, at the same time, it will also be possible to bring the two tips nearer together due to the screening efiect' of the field set up by the control systems II and I1.

Although, for a given field density, the air will break down at a much lower voltage under positive potential than under negative potential, it is possible by the present invention to raise the positive fiashover to approximately the same voltage as that of the negative by regulating the efi'ective area or curvature of the two electrodes or tips as will be more fully explained.

If in Fig. 2 the control systems II and it! are omitted and we assume that the tip I0 is negatively charged when the tip I! is at ground potential, it will require a considerably higher negative voltage than positive voltage to start discharge, as the discharge streamer may be regarded as starting from the positive electrode l1 and advancing to the negative electrode l0. Owing to the field set up by the ground and surrounding objects, the electrical gradient in the air will be much greater in the vicinity of'the electrode it than in the vicinity of the electrode i1.

Before discharge can take place, the voltage must reach the point where ionization will start and a streamer will develop. Since a considerably higher negative than positive stress is required to start a streamer, it will naturally follow that when the electrode I0 is negative the stress must reach a point such that ionization will start on the electrode H which normally has a much weaker field. If, on the other hand, the electrode in is positive, a much less voltage may start a discharge owing to the high stress around the electrode at. The relative negative and positive potentials which will cause discharge of the gap may be controlled by controlling the field about the tips l0 and I7.

If we assume that the tips In and H are in position and the controls H and I8 are omitted, the negative fiashover voltage may be 'much higher than the positive fiashover voltage. By making the electrode I! smaller than II], it may be possible to balance approximately the negative and positive fiashover voltages; As previously stated, however, under this condition the gaps may be materially changed under wet and dry conditions and it is not possible to change the characteristics of the gap materially without entirely changing the electrodes. In addition, the time lag cannot be controlled without a change in the size of the electrodes. negative, we will assume that the discharge streamer starts from H. Since the gradient about the electrode H, owing to the field set up by ground potential, will be much less than at It even though the electrodes have the same curvature, it is seen that it is desirable to increase the lines of force or field density about the electrode I! as compared to Hi. This may be brought about by increasing the size of the tip I0 or preferably by increasing the charged surface by the use of the insulated control system H. The addition of the control system ll sets up a larger field of negative potential, thereby increasing the lines of force or stress at the surface of electrode l1.

By giving this field suflicient effective area, the discharge voltag for a given distance between the electrodes may be lowered so that the fiashover voltage under negative potential may bereduced to or made lower than that when the electrode I 0 is positive. The addition of the control system H will have not only the eifect of starting a discharge from electrode 11 at a lower voltage when the tip I 0 is negative but will reduce the lines of force for a given area in the vicinity of the tip II). This will tend to raise the voltage at which a streamer will start from the tip l0 when the latter is positive. It will therefore be seen that the addition of the control system II will tend to lower the negative fiashover voltage and raise the positive fiashover voltageso that the two may be made equal if desired or the positive may be made to exceed the negative.

The control systems I and 18 may be made in any desiredform such as an insulated ring in two or more parts or in the form of insulated horns or separate insulated controls, as shown in Fig. 2. Several forms of insulated controls' are shown in my prior Patent No. 1,521,743. It will be seen that the use of the. control system II will tend to increase the positive fiashover voltage but will tend to decrease the negative fiashover voltage. If we consider the positive When the tip I0 is value only, the distance between the electrodes i0 and i! can be decreased for a given fiashover voltage. Decreasing this distance will cut down the time lag for fiashover of the gap, as the electrodes will more nearly approach the characteristics of spheres of larger size.

If, on the other hand, a control system 18 is used to screen electrode H, the negative impulse can be increased or a smaller electrode or tip I1 used for a given fiashover voltage. By using control systems II and iii the small electrodes may approach the characteristics of much larger electrodes so that the striking distance and time lag may be reduced. The insulators of the controls l l and I8 placed over the conducting shields prevent a discharge from the metal inner charged surfaces. The nature of this operation is explained in my prior patent referred to above.

The construction of the gap is such that polarity effects may be compensated or corrected and time lag may be materially reduced so that the characteristics of the protecting gap may be changed so as to approximately conform to the insulation which it is desired to protect.

In operation transients of negative polarity are usually more severe at the station, owing to the fact that corona losses are lower under negative than under positive polarity and do not cause so much attenuation. Many types of insulation have a much higher impulse resistance under negative impulses than under positive impulses, and where this characteristic prevails, the protecting gap may be so arranged as to have a higher voltage setting for negative than for positive impulses. If, on.the other hand, the insulation to be protected has a higher flashover for positive impulses than for negative, the gap may be so changed as to change the characteristics accordingly. If the control system on the live side is advanced so as to screen more completely the tip on that side, the positive flashover voltage will be increased and the negative flashover voltage decreased. If, on the other hand, the control system screening the electrode on the ground side is moved so as to screen the grounded electrode more completely, the positive flashover voltage will be decreased and the negative flashover voltage increased.

The control systems may be advanced or retracted with respect to the tips or the tips moved with respect to the screening or control system. In general, the electrodes may be small enough so that their wetting under rain will have little, if any, appreciable effect on the flashover voltage. It is possible, however, to change the electrode if desired so that water will not form in drops or streams so as to affect the flashover voltage.

One way to prevent accumulation of rain is to give the lower face of the metal sufficient slope that the water will be thrown off at a point where the discharge will be screened by the insulated control system. The tips i0 and I! may be formed with a series of vertically disposed plates 22 arranged close together, as shown in Figs. 3 and 4, or have a roughened surface 23, as shown in Fig. 5, so that the surface will be approximately the same both wet and dry. Where the electrode is made of a number of parallel plates, the capillary spaces between the plates can be used as capillary ducts to carry off any drip water. The plates can also be formed so as to form what might be termed an arcing horn 24 and a drip member 25, as shown in Fig. 6.

Owing to the fact that the field is largely com trolled by the insulated control system which is not materially affected by a wet and dry condition, no great amount of provision is necessary for the wet condition except where a very fine control is desired or conditions are unusually severe. In operation the gap may discharge and limit the voltage on the apparatus or at least reduce the time during which the apparatus or insulation is subjected to the over-voltage. If the fuse 2| is placed in the lead l9, this may blow and clear the line as soon as the normal frequency energy starts to pass the gap.

Another method of clearing the are as shown in Fig. 7 is to provide a resistance or resistances 3D shunted with fuses 3|. When the gap discharges, the fuses will take the electrostatic discharge. When power current at normal frequency follows, however, the fuses will blow and the inserted resistances will carry the current, thus reducing the current in the discharge, which will tend to reduce the transient disturbance on the line. In addition, the power current may be used to-operate a relay 32 which will open the switch 33 and a relay 34 which will throw a strong air blast upon the gap from nozzles 35. The air blast from 35 may be used to clear the are as this may be easily carried out after the resistance 30 is inserted. The resistance may be of any convenient form but must be able to withstand the impressed voltage under the various conditions without an are flashing over and shunting same.

Another form of the gap is shown in Figs. 8 and Q in which the general arrangement is similar to that shown in Fig. 2 with the exception that the electrodes 36 and 31 are rotatable so that the length of the arc and resistance of the discharge path may be materially increased following the discharge of the gap. The electrodes .36 and 31 are actuated respectively by a motor 38 and a strong spring 39; the motor 38 operating through a shaft 40 and bevel gears H. An arc striking between the nearest points of the electrodes 36 and 31 will be lengthened as the electrodes rotate in a direction to move the arcing surfaces upwardly. This movement of the arc may be facilitated by an air blast from nozzles 42, 43 and 44. When the electrostatic potential reaching the point that discharge will take place across the space between the electrodes 35 and 31, the power current flowing will operate the relay 45 which, in turn, will release the spring 38. This will rotate the electrode 31 very rapidly providing a cool metal surface for the arc and greatly increasing the length of the arc.

In the form illustrated in Fig. 8, the necessary energy to drive the electrode 36 on the live side is supplied by an electrostatic coupling or a current transformer 45' connected to the main line, thus avoiding the necessity of any connections to ground. The revolving electrode will not accumulate water, consequently, can be used on comparatively short distance.

In Fig. the rotating electrode 46 may be provided' with radially extending blades separated by slots 41 which will discharge air owing to the rotation of the electrode; the air entering between the blades andbeing discharged in the direction of the axis of rotation in the well known manner of ordinary electric fans. The electrode 46 may be rotated by a fluid motor 45'. Under this arrangement the electrode is practically a. fan

whose axis may be placed in a vertical position if desired, so that the arcs between the electrodes 48 and 49 will be free to move upward. The gaps can be controlled with the insulated control system 56 so as to give the necessary regulation. If desired, several rotating gaps with necessary control system can be used.

In the form of arcing electrode shown in Fig. 11, a metal arcing tip 51 is surrounded by a circumferentially continuous screening member 52 of dielectric material having a recess 53 on its rear side which may be metalized as shown at 54. The spider 55 which supports the control screen 52 is adjustabl; mounted onthe support 55 for the arcing tip 5| and is electrically connected to the metalized surface 54.

In Fig. 12 the arcing tip 51 is screened by a control 58 of porcelain or other suitable dielectric material and has an internal recess provided with a metalized surface 59. The screen in Fig. 12 has an inwardly opening recess and is of flatter form than that of Fig. 11.

I" claim:

1. The combination with an arcing gap, of a resistance and fuse in parallel with each other and in series with said. gap, and a relay in parallel with said resistance and fuse.

2. The combination with an arcing gap, of a resistance and fuse in series with said gap, a relay in parallel with said resistance and fuse, and means controlled by said relay for directing a blast of air across said gap for extinguishing an arc across said gap.

3. The combination with an arcing gap, of a switch for opening the gap circuit and disconnecting the gap from ground, means for blowing out the are formed by said switch, a relay in series with said switch for controlling said blowing means, and a fuse in shunt with said relay adapted to blow when power current follows an arc across said gap.

4. A discharge terminal for an arcing gap comprising metallic plates having capillary spaces therebetween for conducting moisture from the surface of said terminal.

5. An arcing gap having a discharge terminal, a flux control for said terminal, and means for discharging water from the surface of said terminal at a position screened by said flux control.

6. An arcing gap comprising a rotary discharge terminal the discharge surface of which is a continuous surface of revolution concentric with the axis of rotation of said terminal, a spring for ro-- tating said terminal, means for holding said terminal from rotation and means controlled by discharge across said gap for releasing said holding means and permitting said spring to rotate said terminal.

7. An arcing gap comprising spaced discharge terminals and a rotary electrode between said terminals, said electrode having vanes to produce an air current for extinguishing an arc between said terminals.

8. An arcing gap comprising spaced dischargeing from said bar in the rear of the discharge tering one of said electrodes, arms of conducting material connected with said bar and projecting radially therefrom at a point in the rear of said electrode, the outer ends of said arms being inclined toward the other electrode, coverings of dielectric material enclosing the outer ends of said arms, said arms being adjustable along said bar toward and from said electrode, and means for supporting said electrodes in adjustable relation to each other.

11. An arcing gap comprising spaced discharge electrodes, one of said electrodes being grounded and the other of said electrodes being insulated from ground said electrodes comprising equipment for controlling the electrostatic field about said gap, one of said electrodes being provided with a fiux control differing from the equipment of the other electrode to modify the relative values of the discharge voltages for positive and negative charges on said electrode.

12. An arcing gap comprising spaced electrodes, one of said electrodes being grounded and the other of said electrodes being insulated from ground said electrodes comprising equipment for controlling the electrostatic field about said'gap, said insulated electrode having a flux control connected therewith and difiering from the equipment of the grounded electrode to equalize the discharge voltages of said gap for negative and positive charges respectively on said electrode.

13. An arcinggap comprising spaced electrodes having an unobstructed path for discharge between the most closely adjacent points thereof, said electrodes each comprising a spherical discharge surface and a conical portion substantially tangent tosaid spherical surface, the axes of said conical portions coinciding with the axis of the path of discharge between said electrodes, and means for controlling the field about one of said electrodes and for screening drip water falling from the base of the conical portion of said electrode, said means comprising arms of conducting material projecting radially from the axis of said electrode and electrically connected with said electrode and dielectric coverings over the outer ends of said arms, the axis of the conical portion of said electrodes being disposed in a substantially horizontal position.

14. An arcing gap comprising spaced electrodes, one of said electrodes being grounded and the other of said electrodes being insulated from ground, and means for controlling the electrostatic field about sald electrodes to equalize the discharge voltage of said gap for positive and negative charges, the control means for the field about the insulated electrode being greater in extent than that for the field about the grounded electrode.

15. An arcing gap comprising spaced discharge terminals, one of said terminals being grounded and the other of said terminals being insulated from ground, andmeans for controlling the electrostatic field about said gap, said means being more effective for distributing the flux about one of said terminals than about the other to control the relative discharge potentials of said gap for charges of difierent polarities.

16. An arcing gap comprising spaced discharge terminals, one of said terminals being grounded and the other of said terminals being insulated from ground, and means for controlling the electros tatic field about said gap, said means being more efiective for distributing the flux about said insulated terminal than about said grounded terminal to equalize the discharge potentials of said gap for charges of different polarities.

17. An arcing gap comprising a pair of discharge electrodes having an unobstructed discharge path along the shortest line between said electrodes, one of said electrodes having a substantially spherical discharge portion at one end of said path, arms of conducting material electrically connected with said electrode and projecting from said electrode in symmetrical arrangement relative to said line and in radial directions relative to said line and spaced angularly from one another, and coverings of dielectric material enclosing the outer ends of said arms.

18. A discharge gap comprising a pair of spaced electrodes having an unobstructed discharge path along the shortest line between said electrodes and means for controlling the electrostatic field about one of said electrodes, said means comprising arms of conducting material disposed symmetrically relative to said line and projecting from said electrodes in radial directions relative to said line, said arms being angularly spaced from one another and having the ends thereof inclined toward the opposite electrode, and coverings of dielectric material disposed on the outer ends of said arms.

19. An arcing gap comprising a pair of spaced discharge electrodes having an unobstructed discharge path along the shortest line between said electrodes, one of said electrodes having a substantially spherical discharge portion at one end of said path, arms of conducting material electrically connected with said electrode and projecting from said electrode in symmetrical arrangement relative to said line and in radial directions from said line and spaced angularly from one another, and coverings of dielectric material enclosing the outer ends of said arms, said arms being adjustable relative to said electrode in the direction of said line, and said electrodes being adjustatble in the direction of said line toward and away from each other.

ARTHUR ,0. AUSTIN.

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