US2168769A - Protector - Google Patents

Description

Patented Aug. 8, 1939 PROTECTOR-. A

Earl L. Fisher, Newark, N. J.,

Telephone Laboratories,

asnsignor to Bell Incorporated, New

York, N. Y., a corporation of New York Applicationugust 31, 1937, Serial No. 161,753

a claims. This invention relates tb protectors and more specifically to protectors for telephone substation equipment.

Protectors of this type usually comprise a high resistance path from each line conductor to ground. These paths are of such high resistance as to prevent for practical purposes the flow of the low voltage telephone and ringing currents to ground. However, if a high voltage from a power line, lightning or other source is accidentally applied to the line it passes over the'high resistance path to ground rather than through the equipment. A common form of protector is an air-gap between line and ground, -which air-gap is broken down by the application of a high voltage, allowing current to ow to ground. A more recent development employs in place of the airgap, a resistance material having a non-linear voltage-current characteristic and commonly referred to as a non-ohmic material. Since with such a material the resistance decreases with increase of applied potential, this material may be defined as one having an inverse resistance-voltage characteristic. Materials which have been found to' possess the desired characteristics are 'Ihyrite, carborundum and certain other refractory materials. The preferred material for this protector is Thyrite, which has been known in the electrical art for some time. Its physical properties and some of its applications are described by T. Brownlee, General Electric Review, vol. 37, No. 4, April 1934, pages 175 et seq. The advantage of this type of protector is that it is capable of withstanding repeated discharges due to abnormal potentials.

The inherently higher resistance of this type of protector, however, may produce a re hazard under conditions of long contact with the source of high voltage, such as an adjacent power circuit, unless units of impracticable size are used or unless some special preventive auxiliary device is employed.

An object of this invention is to combine a protector of this type with a thermally responsive means to short-circuit the protector to ground before a dangerously high temperature exists.

A further object is to employ a mounting for the protector in which the generation of excessive heat by the protector will cause a thermostatic metal member to short-circuit the protector.

A feature of the invention is the production of a substationprotector unit which includes a conductor element having an inverse resistance-voltage characteristic as the high resistance path and a. mounting in which is incorporated a thermally responsive means for short-circulting the high resistance only during the persistence of an abnormally high temperature in the unit.

An exemplary embodiment of the invention is illustrated in the accompanying drawing in 5 which:

Fig. l is a perspective view of the protector device mounted on a suitable base;

Fig. 2 is a central section taken at right angles to the plane of the protector disc; and 10.

Fig. 3 is a partial section taken on a plane parallel to the protector disc.

The protector is mounted on a perforated base member I of ceramic or other suitable material. The ground contact element 2 is in the form of l5 a disc with a reduced portion 3, which has a right angle projection 4 which comprises a combined support and connecting means. The parti is mounted on the base I by means of the terminal bolt 5 and nut 6. Projected from either side of 20 the portion 3 and rmly attached thereto are ange members 1. These members provide additional support for the ground contact element 2 and also carry the auxiliary ground contact member 8, the function of which will be described 25 in due course.

On either side of the ground contact 2 are the line contacts I0. These are in the form of discs of the same size as the ground contact discs.

These contacts are supported on the base by 30 resilient bracket members Il which also serve as electrical connectors between the contacts III and the terminals I2. The terminals I2 are in the form of bolts by means of which the brackets are attached to the base. The contact discs I0 35 are slotted part Way through the vertical diameter as at I 3. Within the vertical slots are located thermally warpable strips I4. 'I'he contacts I0, brackets II and strips I4 of each group are secured together by the fastening means I5 which 40 may be screws or rivets. Between the ground contact 2 and each line contact l0 is mounted a disc I6 of Thyrite or other material having the desired resistance-Voltage characteristic. 'Ihese discs I6 are frictionally held in place due to the 45 pressure applied by the resilient bracket members Il.

In practice, connection is made from terminal 5 to ground and from each of terminals I2 to a line conductor. 50

The operation of the device is as follows:

Under conditions of normal Voltage the very high resistance of the conductors I6 prevents for all practical purposes, the iiow of current from the line wire to ground. However, upon the 55 application oi abnormally high potentials the resistance of members I6 goes down and current ows to ground. If this Aflow is sustained for a predetermined period suiiicient heat may be generated to cause the thermally responsive members I4 to deflect. These members are arranged to warp outwardly from the slot I3 into contact with the auxiliary ground contacts 8. This provides a low resistance shunt around the disc i6. The generation of heat to a dangerous degree is thus prevented. Upon reduction of temperature the thermal elements Il recede, opening the shunt path. If the high voltage persists the cycle is repeated. However, if the high voltage has been removed the protector assumes normal effective condition. By means oi this invention continuous protection is achieved Without the disadvantages attendant upon use of other protectors of this general type.

Although the invention has been described with relation to the particular embodiment illustrated in the drawing, it is understood that it is not limited thereby but only by the scope of t the appended claims.

auxiliary contact connected to the other electrode and located adjacent said slot in a position to be contacted by the bimetalllc element when a dangerously high temperature exists in the device.

2. A protective device comprising a pair of electrodes separated by a member of 'high resistance material having an inverse resistancevoltage characteristic, a bimetallic elementmounted in a slot in one of said electrodes and having one end in contact with said high resistance material, and an auxiliary contact connected to the other electrode and located adjacent said slot in a position to be contacted by the bimetallic element upon a predetermined increase in temperature of said device.

3. A protective device comprising a pair of electrodes separated by a member of high resistance material having an inverse resistancevoltage characteristic, a bimetaliic element mounted in and substantially closing a slot in one of said electrodes and vhaving one end in contact with said high resistance material, and an auxiliary contact connected to the other electrode and located adjacent said slot in a position to be contacted by the bimetallic element upon a predetermined increase in temperature of said device.

EARL L. FISI-IER.

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