US 4,241,373 A · Switchgear voltage sensor

Abstract

A switchgear assembly which includes a vacuum interrupter, a current transformer, and a capacitive voltage sensor, all embedded within a cast epoxy housing mounted to a solidly grounded support structure. The voltage sensor includes a first capacitor, which is formed by an interrupter conductor stud, a plate, and the cast epoxy disposed therebetween, and a second capacitor, which is connected between the plate and a metal tube extending outside the housing. The tube is connected to ground through a conductive coating, applied to the housing, having an impedance which is very low in comparison to the impedance of the first capacitor. The voltage signal on the plate, which is proportional to the stud voltage, is supplied through the center conductor of a coaxial lead to one input of a voltage level sensing circuit, where it is amplified, rectified, and compared with a reference voltage to produce a positive output signal whenever the stud voltage exceeds a first value, and thereafter produce a negative output signal whenever the stud voltage decreases to less than a second value lower than the first value. The conductive shield of the coaxial lead has a first end connected to the metal tube and a second end connected to the ground terminal of the voltage level sensing circuit and to ground through a ground path having a low impedance in comparison to the impedance of conductive coating ground path between the metal tube and the grounded support structure.

Claims26

Dependent claims

A voltage level sensing apparatus for sensing at least one phase-to-ground voltage of a high-voltage alternating electric system, including at least one single phase voltage sensing circuit which comprises:

a body of cast, electrically insulating material;
a conductive rod, partially embedded within the cast body, having one end connected to one phase of the alternating power system;
a voltage sensing plate which is embedded in the cast body and spaced from the rod to define, with the rod, a first capacitor wherein the portion of the cast body between the rod and the voltage sensing plate is the dielectric of the first capacitor;
a second capacitor, also embedded within the cast body, having a first side connected to the voltage sensing plate and an opposite second side, the second capacitor having a low impedance relative to the impedance of the first capacitor;
first conductive means for defining a current path between the second side of the second capacitor and ground, which has a low impedance relative to the impedance of the first capacitor;
a coaxial lead, which includes a center conductor and an outer conductive shield, each having corresponding first ends and opposite second ends, the first end of the center conductor being connected to the first side of the second capacitor, and the first end of the outer shield being connected to the second side of the second capacitor;
second conductive means for defining a current path between the second end of the outer shield of the coaxial lead and ground, which has a low impedance relative to the impedance of the first conductive means;
and
amplifier means having an output, a first input connected to the second end of the center conductor of the coaxial lead, and a second input connected to the second end of the outer shield of the coaxial lead, for producing at the amplifier output an alternating signal proportional to one phase-to-ground voltage of the alternating electric system.

6 more elements

Switchgear apparatus for a high voltage alternating electric system which includes a grounded support structure and at least one encapsulated, single phase, circuit interrupter assembly which is affixed to the grounded support structure, and which comprises:

a vacuum interrupter having a fixed contact rod extending through one end of a vacuum enclosure and a movable contact rod extending through an opposite end of the vacuum enclosure, the movable contact rod being movable along its axis between an open position and a closed position, adjacent ends of the fixed contact rod and the movable contact rod carrying respective contacts which abut against each other when the movable contact rod is disposed in its closed position, and which are separated by a suitable distance when the movable contact rod is disposed in its open position;
a first connector stud, having one end attached to the fixed contact rod and an opposite end;
a second connector stud, having one end which carries a current exchange assembly in sliding contact with the movable contact rod, and an opposite end;
an interrupter housing of cast, electrically insulating material which includes
a central portion cast about the vacuum interrupter and defining an opening through which the movable contact rod extends,
a first end portion extending from the central portion and cast about the first connector stud, having a free end through which the opposite end of the first connector stud extends, the free end of the first end portion defining a first receiving bushing member, and
a second end portion extending from the central portion and cast about the second connector stud, having a free end through which the opposite end of the second connector stud extends, the free end of the second end portion defining a second receiving bushing member;
a first conductive coating, which is applied to the outer surface of the interrupter housing intermediate the first and second receiving bushing members, and which defines an uncoated window area, or opening in the first conductive coating, on the outer surface of one of the two end portions of the interrupter housing;
a mounting means for affixing the interrupter housing to the grounded support structure and electrically connecting the first conductive coating to the grounded support structure;
a second housing of cast electrically insulating material, having an inner surface spaced from the one end portion of the interrupter housing over the uncoated window area thereof, and external side and outer surfaces, the second housing being affixed to the interrupter housing by electrically insulating material which is cast between the inner surface of the second housing and the outer surface of the interrupter housing to completely fill the space therebetween and form a single switchgear housing;
a voltage sensing plate, positioned adjacent the uncoated window area of the one end portion of interrupter housing, which defines, with the connector stud embedded within the one end portion of the interrupter housing, a first capacitor wherein the cast electrically insulating material between the voltage sensing plate and the connector stud embedded in the one end porton of the interrupter housing is a dielectric of the first capacitor;
a conductive member, having a first end which is embedded in the second housing and a second end which extends through an external surface of the second housing;
a second capacitor, embedded within the second housing, having a first side connected to the voltage sensing plate and an opposite second side connected to the conductive member, the second capacitor having a low impedance relative to the impedance of the first capacitor;
a coaxial lead, which includes a center conductor and an outer conductive shield, each having corresponding first ends and opposite second ends, the first end of the center conductor being connected to the first side of the second capacitor, and the first end of the outer shield being connected to second side of the second capacitor, the coaxial lead extending outside of the second housing through an external surface of the second housing;
a second conductive coating, applied to the external surfaces of the second housing and to the adjacent coated surfaces of the one end portion of the interrupter housing, and to the externally extending second end of the conductive member, wherein the first and second conductive coating define a resistive current path between the conductive member and ground which has a low impedance relative to the impedance of the first capacitor, and the first capacitor, the second capacitor, and the resistive current path are connected in series between one phase of the alternating electric system and ground;
whereby, because of the low impedance of the second capacitor and the resistive current path, both sides of the second capacitor are maintained at a low voltage, and the voltage across the second capacitor is proportional to one phase-to-ground voltage of the alternating electric system.

13 more elements

a vacuum interrupter having a fixed contact rod extending through one end of a vacuum enclosure and a movable contact rod extending through an opposite end of the vacuum enclosure, the movable contact rod being movable along its axis between an open position and a closed position, adjacent ends of the fixed contact rod and the movable contact rod carrying respective contacts which abut against each other when the movable contact rod is disposed in its closed position, and which are separated by a suitable distance when the movable contact rod is disposed in its open position;
a first connector stud, having one end attached to the fixed contact rod and an opposite end;
a second connector stud, having one end which carries a current exchange assembly in sliding contact with the movable contact rod, and an opposite end;
an interrupter housing of cast, electrically insulating material which includes
a central portion cast about the vacuum interrupter and defining an opening through which the movable contact rod extends,
a first end portion extending from the central portion and cast about the first connector stud, having a free end through which the opposite end of the first connector stud extends, the free end of the first end portion defining a first receiving bushing member, and
a second end portion extending from the central portion and cast about the second connector stud, having a free end through which the opposite end of the second connector stud extends, the free end of the second end portion defining a second receiving bushing member;
a first conductive coating, which is applied to the outer surface of the interrupter housing intermediate the first and second receiving bushing members, and which defines an uncoated window area, or opening in the first conductive coating, on the outer surface of one of the two end portions of the interrupter housing;
a mounting means for affixing the interrupter housing to the grounded support structure and electrically connecting the first conductive coating to the grounded support structure;
an annular-shaped second housing of cast electrically insulating material, having an inner peripheral surface extending about the one end portion of the interrupter housing over the uncoated window area thereof, and external side and outer peripheral surfaces, the second housing being affixed to the interrupter housing by electrically insulating material which is cast between the inner peripheral surface of the second housing and the outer surface of the interrupter housing to completely fill the space therebetween and form a single switchgear housing;
a current transformer embedded within the second housing, having an annular-shaped core of magnetic material which encircles the connector stud embedded within the one end portion of the interrupter housing, a secondary winding which is wound about the magnetic core, and two insulated conductor leads having first ends connected to respective ends of the secondary winding and second ends which extend outside of the second housing;
a voltage sensing plate, positioned adjacent the uncoated window area of the one end portion of interrupter housing, which defines, with the connector stud embedded within the one end portion of the interrupter housing, a first capacitor wherein the cast electrically insulating material between the voltage sensing plate and the connector stud embedded in the one end portion of the interrupter housing is a dielectric of the first capacitor;
a conductive member, having a first end which is embedded in the second housing and a second end which extends through an external surface of the second housing;
a second capacitor, embedded within the second housing, having a first side connected to the voltage sensing plate and an opposite second side connected to the conductive member, the second capacitor having a low impedance relative to the impedance of the first capacitor;
a coaxial lead, which includes a center conductor and an outer conductive shield, each having corresponding first ends and opposite second ends, the first end of the center conductor being connected to the first side of the second capacitor, and the first end of the outer shield being connected to second side of the second capacitor, the coaxial lead extending outside of the second housing through an external surface of the second housing;
a second conductive coating, applied to the external surfaces of the second housing and to the adjacent coated surfaces of the one end portion of the interrupter housing, and to the externally extending second end of the conductive member, wherein the first and second conductive coating define a resistive current path between the conductive member and ground which has a low impedance relative to the impedance of the first capacitor, and the first capacitor, the second capacitor, and the resistive current path are connected in series between one phase of the alternating electric system and ground;
whereby, because of the low impedance of the second capacitor and the resistive current path, both sides of the second capacitor are maintained at a low voltage, and the voltage across the second capacitor is proportional to the one phase-to-ground voltage of the alternating electric system.

14 more elements

Dependencies are inferred from the claim text.

Switchgear voltage sensor

Life of this patent

Switchgear voltage sensor

Life of this patent

Abstract

Claims26