US2043399A - Electrical protective system - Google Patents

Description

June 9,1936. L, K, SW'ART 2,043,399

ELECTRICAL PROTEGTI VE SYSTEM Filed Feb. 20, 1935 INVENTOR ATTORNEY Patented June 9, 1936 UNITED STATES PATENT OFFICE ELECTRICAL PROTECTIVE SYSTEM Application February 20, 1935, Serial No. 7,451

2 Claims.

This invention relates to electrical protective systems. More particularly this invention relates to arrangements for simultaneously grounding a plurality of circuits when induced voltages become impressed. thereon.

Protector blocks having air gaps which break down at predetermined potentials have recently been used in the telephone art for the protection of telephone circuits from high voltages set up therein by one or more sources extraneous to the circuits themselves. Various arrangements have been used to accomplish this result. Some of the arrangements employed a resistor or a saturating reactor interposed in the ground connection of said protector blocks. The resistor or reactor as the case may he, carries all of the operating current of the blocks associated therewith. The impedance drop across the resistor or reactor is rectified by a rectifier which generally is of the copper-oxide type. The rectified current is applied tothe winding of a relay which, when operated, shunts the protector blocks so that any induced current or currents are carried through the heavy duty contacts of the relay.

In other arrangements a saturating reactor or transformer has been employed to operate a common master relay which applies a local battery potential to the windings of a multiplicity of short-circuiting relays to cause simultaneous grounding of all conductors associated therewith. There is an advantage in eliminating the maintenance expense in connection with the dry cell batteries frequently used on the latter type of relay protector system, especially where these protectors are located in outlying districts.

It is not quite satisfactory to use rectifying apparatus of the copper-oxide type as now generally employed in short-circuiting relay protectors, since the characteristics of the rectifiers change rapidly with age and are subject to wide variations due to humidity. Moreover these rectifiers seldom return to their original state after a severe application of voltage or after the passage of a large current. Furthermore, the characteristics continuously change with variations in temperature. The most serious drawback to their use lies in the narrow range of operating current. Even with elaborate shunting arrangements, the range of operation from minimum to maximum operating current is decidedly limited and it is relatively easy to apply voltage to the copper-oxide rectifier discs which can exceed the safe value of the disc. When this limit is exceeded a rupture in the surface insulation of the disc takes place, rendering them thereafter ineffective. All of the described defects substantially affect the sensitivity of the device and reduce its range of operation, and any arrangement, therefore, depending upon the use of cop- 5 per-oxide rectifiers is especially undesirable.

As is well known in the art, the saturating transformer can be relied upon to hold the root mean square values of voltage to low values, even though the currents applied to the primary may rise to several hundred times the minimum operating current of a device applied to said transformer. However, it is known that peak voltages may be obtained on the secondary winding of the saturating transformers for very short periods of time. These voltages are of steep wave front and if directly applied to rectifiers of the copper-oxide type, these rectifiers would be almost immediately rendered ineffective due to the puncture of the surface insulation of the rectifier discs. These steep wave front surges, however, could be suppressed by the use of thyrite. This becomes undesirable due to the space dimensions of the thyrite required.

By employing gas tube rectifiers of the cold cathode type the possibility of damage (to the copper-oxide rectifiers) is greatly removed along with all the inherent disadvantages.

Furthermore, the gas tube devices can be made to operate only above a certain desired value of voltage. The current, therefore, passing to ground through the saturating transformer or reactor can be required to exceed a certain known value before operation of the short-circuiting relay takes place. Steep wave front voltages ob- 35 tained on the secondary winding of the saturating transformer will not damage the gas tube rectifiers. Moreover, the gas tube rectifying devices can be designed to have a wide margin between the breakdown value of voltage and the 40 voltage required to sustain the glow in the gas within the tube. This wide margin of Voltage renders immediately available considerable energy for the operation of the short-circuiting rer lays. By employing the combination of asaturating reactor or transformer which permits of wide operating values of the device, with gas tubes of the rectifier type and sensitive direct current relays, short-circuiting of the protector blocks can be accomplished at high speed for currents to ground in eXcess of a certain desired value and without possibility of damage to the rectifier tubes and without the inherent limitations of the copper-oxide rectifying devices. The socalled sharply defined marginal or trigger operation that is obtained by the use of gas tubes which operate at values only in excess of certain predetermined values provides a decided advantage in that it does not short-circuit nor ground the conductors for such steep wave front short-lived impulses as are obtained from small cloud discharges or static as commonly found on openwire telephone conductors. Only currents of magnitudes which will damage the protector blocks would cause operation of the relay protectors.

By employing a multiplicity of short-circuiting direct current relays the windings of which are connected either in series or in multiple or by employing a common inulti-contact shortcircuiting direct current relay, the short-circuiting of practically any number of conductors may be accomplished with but small'amounts of power derived from the protector blocks to ground. Short-circuiting relays even though designed to carry considerable current will operate within a few thousandthsof a second after current is passed. across theopen spaced protector blocks and these; relays will restore to normal and removethe short circuit. from said protector blocks in a few 'thousandthsof a second after withdrawal of the potential between the exposed conductors and-earth.

Furthermore biasing direct current potentials maybe-used to raiseor lower the operating value of thegas-tubes and where the use of biasing potential becomes feasibleand where this. potential isproperly poled, there-is an added advantage in its-use in that. the direct current through the relay will be increased.

This invention and the principles underlying it, some-of which-have been described hereinabove, will. be better understood from the description hereinafter following when read in connection with theaccompanying drawing in which Fig. 1 represents one embodiment of. the invention and Fig. 2 represents a modification of some of the apparatus shownin. Fig. 1..

In Fig. 1 reference. charactersWi, W2, W3 and W4: represent four: of. a plurality of conductors to which. are connected individual open spaced protectorblocksPi, P2,.P3 and P4, respectively. The remaining terminals ofsaid protector blocks are multipled together andconnectedto the primary winding of; a. saturating transformer or reactor T. Tothesecondary. winding of said'satm'ating transformer are connected a pair of gas rectifying, tubes. N21 and N22. To said gas tubes are also. connected the windings of short-circuiting relays. R10. and R20, only two of which are shown. Theremaining terminals. of the windings of said relays R1u.and.R2o are connected to the midpoint of the. secondary of the saturating transformer T or. to said. transformer terminal in series with a source of biasing potential B, as shown. The biasing potential. should at all times be less than the. voltage required to sustain the glow within the. gas. tubes, otherwise the tubes when once operatedwould lock said short-circuiting relays R10 and. Rain. the operated position.

The short-circuiting relays each have two windingsin order thatthere be some ballast resistance in thecircuitv connected between the cathodes of the rectifying tubes. Gas tubes do not totally blockcurrents when poled in the reverse direction with respect to the alternating current cycle and the introduction of impedance to the flow of current in-the reverse direction is required to prevent. damage to the gas tubes.

Operation. in. Fig. l isv as follows: Voltage applied to any one or all conductors W1 to W4 inclusive of suflicient amplitude to cause the breakdown of any one of the protector blocks P1 to P4 inclusive results in the passage of current through the primary winding of the transformer T. This current introduces a potential in the secondary winding of said transformer and if of sufficient amplitude will cause current to pass from the anodes (designed by the arrows) to the cathodes or the gas tubes N21 and N22 and thence through the windings of the short-circuiting relays R10 and R associated therewith and thence to the midpoint: of' thesecondary winding of the transformer '1 through the source of biasing potential, if such asource is present and employed in the system. If the potential at l of the transformer T is positive and at 2 negative, the gas tubeNzi will function and allow current to flow through the left-hand winding of relays R10 and R20. If, however, the polarity is reversed, the gas tube N22 will'function and allow current to flow through the right-hand windings of relays Rio andRm. The passageof current through either of the windings of relays R10 and R20 causes the armatures to be attracted to their contacts, resulting-in'thesimultaneous short-circuiting of the protector blocks P1 to P4, respectively. Current from the conductors to earth will continue to pass through the transformer T and the short-circuit ingrelays associated with said transformer will be held operated until the disappearance of the applied potential or until it has dropped to a value less than that required to sustain the glow within the gas tubes.

In Fig. 2 full wave. rectification is also obtained. by utilizing four gas rectifying tubes of the cold'cathode type. If the potential is positive at I, current will pass through the gas tube N23 and through the left-hand windings of the short-circuiting relays R30. and R40 associated therewith to the gas tube N24 and returning to the transformer at 2. For a potential of opposite polarity, current will pass through the gas tube N25 to the right-hand windings of the shortcircuiting relays R and R associated therewith and-thence through gas tube N20 and returning to the transformer at I.

It will be understood that the individual shortcircuiting relays can bereplaced by a single shortcircuiting relay having a multiplicity of armatures and contacts, said individual relay containing two windings, provided the gas tubes can pass current in the inverse position of the alternating current wave. Where cold cathode gas tubes can be designed to pass current in but one direction,.a single wound relay need only be employed. It will be furthermore understood that the gas tubes of the cold cathode type may be replaced by gas tubes of the hot cathode type, in which case but a single winding will be required on the short-circuiting relays, as will be apparent to those skilled in this art. It will be furthermore understood that a condenser C or condensers C may, if desired, be used to shunt the windings of the relays to prevent chatter of said relays by supplying current during the period in the alternating current cycle when there is no current being passed by the gas tube rectifiers.

While this invention has been described and shown in said particular arrangements merely for the purpose of illustration it will be understood that the general principles may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. Apparatus for the protection of a plurality of circuits exposed to inductive interference comprising a plurality of protector blocks one terminal of each of which is connected to a correspond ing circuit, a transformer the primary winding of which is connected between the other terminal of each of said protector blocks and ground, two two-electrode cold cathode gas-filled rectifier tubes, a relay having two windings each of which is connected in series with one of said tubes and one-half of the secondary winding of said transformer, and means responsive to the operation of said relay for simultaneously shunting all of said protector blocks.

2. Apparatus for the protection of a plurality of circuits exposed to inductive interference comprising a plurality of protector blocks one terminal of each of which is connected to a corresponding circuit, a transformer the primary winding of which is connected between the other terminal of each of said protector blocks and ground, two two-electrode cold cathode gasfilled rectifier tubes, a biasing battery having a terminal voltage which is less than the voltage for sustaining ionization with said tubes, a relay having two windings each of which is connected 10 in series with one of said tubes and the biasing battery and one-half of the secondary winding of said transformer, and means responsive to the operation of said relay for simultaneously shunting all of said protector blocks.

LELAND KASSON SWART.

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