It is possible to avoid the effects of floating capacitance, and to measure a voltage with a simple operation and in a non-contact manner, without measuring the floating capacitance. A measurement method for measuring an AC voltage applied to a conductor, without contacting the conductor, using a detection probe, provided with a detection electrode capable of covering part of a surface of insulation for insulating the conductor and a shield electrode for covering the detection electrode, and an oscillator for outputting a signal having a certain frequency, wherein one end of each of a core wire and a sheath wire of a shield cable are connected to the detection electrode and the shield electrode, and a floating capacitance effect is substantially made zero by establishing an imaginary short-circuit state between each of the other ends, the measurement method comprising the steps of measuring impedance between the detection electrode and the conductor by applying the signal from an oscillator to the detection electrode via the shield cable, measuring a current discharged from the detection electrode attributable to the voltage applied to the conductor, and obtaining the applied voltage based on the measured impedance and current.

Non-contact voltage measurement method and device, and detection probe

Self contained radio transmitting state estimator modules are mounted on power conductors on both sides of power transformers in electrical substations and on power conductors at various places along electrical transmission lines. They are electrically isolated from ground and all other conductors. These modules are capable of measuring current, voltage, frequency and power factor (or the fourier components thereof) the temperature of the conductor, and the temperature of the ambient air. The modules transmit these parameters to local receivers. The receivers are connected by an appropriate data transmission link, to a power control center which allows determination of the state of the power system. Appropriate control signals are transmitted back to the electrical switchgear of the system to bring it to the appropriate optimum state. Direct local control may also be effected, for example, the prevention of overloading a transformer. A "donut" state estimator module comprises a novel hot stick operated hinge clamp and a novel voltage sensor which measures the current between an isolated capacitor plate and ground. The donut measures the fourier components of voltage and current over a number of cycles and transmits the components to the local receiver. The local receiver derives the desired electrical measurements such as voltage, current, power factor, power, and reactive power and transmits them to local or remote control stations. Up to 15 donut modules may transmit on a single channel to a single local receiver. Each transmits at intervals which are an integral number. The intervals between transmissions of all donuts do not have a common factor and the average interval is the desired transmission rate. Each donut uses the zero crossover of current of its conductor to establish its transmission interval. The system is self-calibrating using known reference signals within the donut module.

Apparatus for measuring the potential of a transmission conductor

A current interrupter assembly includes an insulating structure, a current interrupter embedded in the structure, a conductor element embedded in the structure, a current interchange embedded in the structure and connected to create a current path between the current interrupter and the conductor element, and a semiconductive layer covering at least a portion of the conductor element so as to reduce voltage discharge between the conductor element and the structure.

Solid dielectric encapsulated interrupter

The present invention relates to an apparatus for sensing and measuring the HV surge arrester current It comprises two toroidal current transformers arranged coaxially with respect to the earth wire of the surge arrester, means for sensing the current signals emitted by the said transformers and for converting the said current signals in digital signals, and means for transmitting the said digital signals to an information network and analog state signals by relay activation The two toroidal current instrument transformers are associated, respectively, one to means for sensing the normal leakage current, and the other to means for sensing the impulsive current, the latter comprising a circuit (TRIGGER) discriminating between “switching” and “lightning” signals, in which the basis for discrimination is a signal duration threshold, of about 35 μs

Current detector for surge arrester diagnostic and overvoltage assessment in high voltage substations

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.

Apparatus for monitoring voltage on a high voltage overhead transmission line

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.

Eugene G. Mara

Papers

Switchgear voltage sensor