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

This paper investigates the practice of correcting the results of no-load loss measurements of power transformers for the effect of distorted supply voltage waveform. A three-phase 700-MVA power transformer is tested twice: first with its low-voltage windings connected line-to-neutral, with nearly sinusoidal test voltage conditions, and then for the second test with its windings connected line-to-line with more distorted voltage waveforms. The test data obtained during the measurement was reproduced at the National Research Council (NRC) Laboratory to demonstrate the limits of the application of the loss correction formula currently used.

Measurements and correction of no-load losses of power transformers

The results of an intercomparison of power meter calibrations conducted during 1987 between the National Research Council of Canada, Ottawa, the US National Bureau of Standards, Gaithersburg, the Physikalisch-Technische Bundesanstalt, Braunschweig, and the Institut Mihailo Pupin, Belgrade, are described. The comparison was implemented by a transfer standard consisting of a time-division multiplier watt-converter developed at the Institut Mihailo Pupin. The measurements were made at 120 V, 5 A, and 50 and 60 Hz, at power factors of 1.0, 0.5 lead and lag, and 0.0 lead and lag. An agreement between the laboratories of better than 20 ppm is obtained. >

An international comparison of power meter calibrations conducted in 1987

The application of a computer-controlled current-comparator-based load loss standard to the in-situ calibration of two different types of high voltage three-phase transformer loss measuring systems at SMIT Transformers is described. The load loss standard simulates a high voltage inductive load at power frequencies which can provide load currents up to 2000 A at any power factor with a resolution of 1/spl times/10/sup -6/, and at test voltages up to 200 kV. It basically provides a known and stable power loss or reference power, determined by the test voltage and the power factor setting, to the transformer loss measuring system, such that its accuracy can be characterized over different voltage, current, and power factor ranges.

In-situ calibration of high voltage three-phase transformer loss measuring systems

The 60 Hz insulation loss current measurements in high voltage cable insulation containing water trees are described. To isolate the small insulation loss current from the significantly larger, quadrature (capacitive) current, a current-comparator-based high voltage capacitance bridge was used. It is shown that water trees introduce higher harmonics into the insulation loss current waveform and that the harmonic distortion of the loss current can be correlated with the length of water trees. Current waveforms for insulation free of water trees or insulation in which the water trees were completely dried out showed negligible harmonic distortion. Insulation with partially dried water trees maintained significant harmonic distortion of the loss current even though the loss tangent was very much reduced. The diagnostic aspect of the described measurements is discussed.

Measurement of the harmonic distortion of the insulation loss current as a diagnostic tool for high voltage cable insulation

A measurement setup is developed for the accurate ratio measurement of ac current transformers (CTs) for primary currents up to 5 kA. A unique property of the system is the use of high-quality digitizers for sampling of the secondary current signals and step-down transformers with different current ratios. This allows for accurate comparison of CTs even when their nominal ratios are not equal. The calibration results of the key components in the setup show that the sampling current ratio bridge has a ratio uncertainty of better than 2 $\mu{\rm A/A}$ in magnitude and 0.8 $\mu{\rm rad}$ in phase for CT-under-test current ratios that do not differ by more than a factor of 5 from one of the ratios in the reference CT. The linearity of the bridge for input currents changing between 1% and 120% of nominal input current is better than 4 $\mu{\rm A/A}$ in magnitude and 0.5 $\mu{\rm rad}$ in phase.

Eddy So

Papers

Measurements and correction of no-load losses of power transformers

An international comparison of power meter calibrations conducted in 1987

In-situ calibration of high voltage three-phase transformer loss measuring systems

Measurement of the harmonic distortion of the insulation loss current as a diagnostic tool for high voltage cable insulation

High-Current CT Calibration Using a Sampling Current Ratio Bridge