A sensor apparatus for measuring power parameters on a power conductor, such as a high voltage transmission line may include a corona structure, an electronics assembly and a conductor mountable device. The corona structure may define an outer boundary surrounding the electronics assembly and the conductor mountable device. The corona structure may shield the electronic assembly and conductor mountable device from a corona produceable with the power conductor. The conductor mountable device may be a power parameter measurement device, such as a current sensor assembly. The current sensor assembly may be a split-core design that includes multiple transformer cores. The electronics assembly and the conductor mountable device may powered from a line voltage suppliable on the power conductor. Data may be wirelessly transmitted and received with the sensor apparatus.

Current sensor assembly

The review makes a brief overview of traditional methods of measurement of electric current and shows in more detail relatively new types of current sensors. These include Hall sensors with field concentrators, AMR current sensors, magneto-optical and superconducting current sensors. The influence of the magnetic core properties on the error of the current transformer shows why nanocrystalline materials are so advantageous for this application. Built-in CMOS current sensors are important tools for monitoring the health of integrated circuits. Of special industrial value are current clamps which can be installed without breaking the measured conductor. Parameters of current sensors are also discussed, including geometrical selectivity. This parameter specific for current sensors means the ability to suppress the influence of currents external to the sensor (including the position of the return conductor) and also suppress the influence on the position of the measured conductor with respect to the current.

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Electric current sensors: a review

With the fast-paced changing technologies in the power industry, new references addressing new technologies are coming to the market. Based on this fact, there is an urgent need to keep track of international experiences and activities taking place in the field of modern transformer design. The complexity of transformer design demands reliable and rigorous solution methods. A survey of current research reveals the continued interest in application of advanced techniques for transformer design optimization. This paper conducts a literature survey and reveals general backgrounds of research and developments in the field of transformer design and optimization for the past 35 years, based on more than 420 published articles, 50 transformer books, and 65 standards.

Transformer Design and Optimization: A Literature Survey

An HV dielectric spectroscopy system has been developed for diagnostics of water tree deteriorated extruded medium voltage cables. The technique is based on the measurement of nonlinear dielectric response in the frequency domain. Today's commercially available systems are capable of resolving low loss and small variations of permittivity as a function of frequency and voltage. Experience from more than 200 field measurements was combined with laboratory investigations. Small samples were used in an accelerated aging test to elucidate the correlation between water tree growth and dielectric response. Furthermore, field aged cables were investigated in the laboratory. It has been shown that the dielectric response of water tree deteriorated crosslinked polyethylene (XLPE) cables can be recognized and classified into different types of responses related to the aging status and breakdown strength. The influence of termination and artifacts such as surface currents was investigated. The measurement method enables us to separate the response of the cable from the influence of accessories. Finally, two different field studies of the implementation of the diagnostic method are presented. The field studies show that the fault rate decreased significantly when replacement strategy was based on the diagnostic criteria formulated.

Dielectric spectroscopy for diagnosis of water tree deterioration in XLPE cables

An apparatus for sensing the current in a power line of a power system and systems incorporating the apparatus are disclosed. The apparatus may comprise an enclosure providing a window operable to permit the passage of the power line therethrough.

Power line sensors and systems incorporating same

The development of a computer-controlled current-comparator-based test system for calibrating high-voltage revenue metering equipment under actual operating conditions of high voltage/high current with sinusoidal or nonsinusoidal voltage and current waveforms is described. Measurements can be made at any power factor from zero lead or lag through unity, at line-to-ground voltages up to 100 kV and currents up to 2000 A. The magnitude and phase uncertainties (k = 2) of the new calibration system are estimated to be not more than 100 μW/VA and 100 μrad, and 200 μW/VA and 200 μrad for sinusoidal and nonsinusoidal conditions, respectively. The calibration system can be used in the laboratory or on-site in high-voltage substations.

Computer-Controlled System for Calibrating High-Voltage Revenue Metering Equipment Under Actual Operating Conditions

A current comparator bridge for measuring the value of an unknown capacitor includes a current comparator having a first comparator winding with an adjustable tap which is connected to one side of a standard capacitor and a second comparator winding connected to one side of an unknown capacitor, a high voltage source being connected to the other side of the capacitors. The current comparator is provided with a detection winding for detecting when the ampere-turns in the first and second comparator windings are equal and opposed to each other. In addition to the current through the standard capacitor being applied to the first comparator winding, the bridge includes a circuit to add a current through a standard conductance to the first comparator winding as well as circuits to compensate for errors. The detection winding is connected to a current-to-voltage converter with an adjustable gain which provides a signal to a phase sensitive detector. A reduced replica of the high voltage source is also applied to the phase sensitive detector which provides output signals Eo and E90 to indicate when the bridge is balanced for both in phase and quadrature components respectively. The values of the capacitance and dissipation factor for the unknown capacitor can then be determined from the balanced condition of the bridge which is designed so that it can be automatically controlled by a microprocessor and switch controller.

Microprocessor-controlled high-voltage capacitance bridge

A current comparator technique is applied to four-terminal resistance measurements for obtaining a highly accurate AC resistance bridge at power frequencies of 50 Hz to 60 Hz. Active circuits are used to establish equal voltage drops between the potential terminals of the two resistances being compared. The bridge is suitable for measuring resistances from 10 μΩ to 100 kμΩ. A cascading technique using two two-stage current transformers provides extension of the ratio range to 100,00,000 with a maximum applied current of 10,000A. The bridge features measurement with a resolution of 0.1×10 −6 . The total combined uncertainty (2σ) of the bridge including the range extenders, at power frequencies, is estimated to be less than 5 μΩ/Ω.

Current-comparator-based four-terminal resistance bridge for power frequencies

An overview of the development and performance of a special high precision multi-ratio three-stage CT and its application for loss measurements of EHV three-phase shunt reactors with test voltages up to a phase voltage of 1100 kV at Royal SMIT Transformers are presented and discussed. It features current ratios of 500 A/1 A, 400 A/1 A, 300 A/1 A, 200 A/1 A, and 100 A/1 A with ratio errors within $3 \times 10 ^{-6}$ in both magnitude and phase with burdens up to $1.0~\Omega $ and at power frequencies of 50–60 Hz.

A High-Precision Current Transformer for Loss Measurements of EHV Shunt Reactors

A current-comparator technique is applied to power measurements for obtaining a highly accurate high-voltage low-power-factor wattmeter. The instrument has two time-division-multiplier-type wattmeters. One wattmeter, in conjunction with a digital signal processing block, is used to provide automatic balancing of the quadrature component of the load current in a current comparator against a quadrature current from a high-voltage quadrature current reference source. The other wattmeter is used to measure the residual loss component of the load current. This new current-comparator-based high-voltage low-power-factor wattmeter has an order of magnitude improvement in accuracy, and a lower power factor measuring range, than a previously developed instrument. It has an estimated uncertainty with respect to its readings of less than 0.02% at 0.1 power factor and higher, 0.2% at 0.01 power factor, 0.5% at 0.001 power factor, and 5% at 0.0001 power factor. In addition to power, the high-voltage low-power-factor wattmeter measures source voltage, current, power factor, and reactance of the load.

Eddy So

Papers

Computer-Controlled System for Calibrating High-Voltage Revenue Metering Equipment Under Actual Operating Conditions

Microprocessor-controlled high-voltage capacitance bridge

Current-comparator-based four-terminal resistance bridge for power frequencies

A High-Precision Current Transformer for Loss Measurements of EHV Shunt Reactors

A new current-comparator-based high-voltage low-power-factor wattmeter