A device for measuring the electrical potential of the inner conductor in an encased high-voltage switching mechanism filled with a gaseous insulator includes an active, capacitive voltage divider. One capacitor of the voltage divider is located within the grounded metal casing of the switching mechanism and is connected with an input terminal of an amplifier. The amplifier is supplied with power from the inner conductor and has a feedback path including the second capacitor of the voltage divider. In order to accurately perform voltage measurements independent of the pressure and temperature of the insulator within the casing, the feedback capacitor is also installed inside the metal casing. This arrangement enables the ratio of the capacitances of the two capacitors, which determines the quality of the voltage measurement, to remain constant over a large pressure and temperature range.

A self contained hot stick mounted radio transmitting module may be temporarily pushed against the power conductor of an electrical transmission line. The module is capable of measuring the temperature of the conductor, and the temperature of the ambient air. It may also measure the electrical potential of the conductor. An alternative module is also capable of measuring current, potential, frequency and power factor (or the Fourier components thereof). The modules transmit these parameters to a local receiver where the data may be displayed. The receiver also may be connected by an appropriate data transmission link, to a power control center. The modules are donut shaped and open like a pair of jaws. One or more spring loaded temperature probes are located such that they may be pushed against a power line when a "donut" is mounted to a hot stick with the jaws open. Power to an open module is supplied by a battery. Power to a closed module, mounted on a conductor, may be supplied by the battery or by power derived from the conductor. A donut may be left on the power line for an indefinite time and the hot stick removed, or instantaneous measurements may be made with the hot stick attached, and the module then immediately removed. The temperature probe of the present invention comprises a pair of concentric spring loaded tubes. A beryllia insert is mounted between a temperature sensor and the power conductor.

The invention provides a high voltage capacitor suitable for measuring the voltage of an overhead power line. The capacitor dielectric is mounted directly on to the power line conductor, which serves as one electrode of the capacitor. The other electrode of the capacitor is mounted on to the outer surface of the dielectric, and is protected at each side by a guard ring. Stress control is provided between the outer capacitor electrode and the guard rings and also at the outer edges of the guard rings. The capacitor may be enclosed in an earthed housing, which can contain one or more current transformers. The apparatus can be used for fault detection and location, and may be used in combination with a power cable or a switch.

A toroidal shaped metallic housing, mounted on and electrically connected with a high voltage transmission line, is adapted with a metal plate and an intervening dielectric sheet adhered to its exterior surface. The housing, tied to the transmission line voltage, and the metal plate constitute the electrodes of a first capacitor of a capacitive voltage divider, while the capacitive coupling of the metallic plate with the surrounding environment provides a second voltage divider capacitor. The voltage appearing on the plate is processed by circuitry within the housing to derive a signal indicative of the transmission line voltage.

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.