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During the impulse voltage comparison test, it is important to keep the waveforms smooth for obtaining consistent experiment results, especially for the front time parameter. However, steps or oscillations are often found on the front of the waveforms. The authors propose a theory that these oscillations can be caused by the resistors in the damped capacitive voltage divider, which often serves as the load capacitor in the impulse voltage generation circuit. The theoretical analysis, numerical simulation, and experimental results are performed, and a good agreement has been found in support of the proposed theory. Furthermore, the waveform parameters measured by two resistive reference standard systems were found to be influenced by the shape of the waveform and the oscillation on the front. It is recommended to avoid using a damped capacitive divider as the load capacitor but use an impulse capacitor with low equivalent series resistance instead. This would help to eliminate this common cause of oscillation on the front of the lightning impulse voltage waveform. Waveform uniformity and uncertainty of the result could then be improved during the comparison of reference measuring systems.

The series summation method is an important method in the calibration of the voltage coefficient (VC) of the standard voltage transformers (VTs), in which the key step is connecting a fully-insulated VT and a semi-insulated VT in series, and comparing them with the third VT under test. Caused by the imperfect electrical shielding of the serially-wound VTs, additional errors are introduced in the calibration. By analyzing the cause of the additional errors in the serial connection of the VTs, two methods were designed in this paper to measure the additional errors. The proposed methods were harnessed to measure the additional errors for a serial connection of a 35 kV fully-insulated two-stage voltage transformer (TSVT) and a 35 kV semi-insulated TSVT. The results show that the two methods give a consistency of better than $1.0\times 10^{-6}$ in ratio error and $2.0~\mu $ rad in phase displacement, respectively. The accurate measurement of the series additional errors and the correction of them significantly improve the accuracy of the VC measurement of a $110/\sqrt {3} $ kV TSVT based on the series summation method. Furthermore, the VC measurement result is verified by the consistency of the series summation method with the series additional errors corrected and the high-voltage standard capacitor method.

During impulse voltage comparison test, it is important to keep the waveforms smooth to get consistence experiment results, especially for the front time parameter. However, wrinkles or oscillations are often found on the front of the waveforms. The authors promoted a hypothesis that these oscillations are possibly caused by the resistor in the damped capacitive voltage divider which often serves as the load for impulse voltage generation. By computer simulations and experiments, the authors proved this hypothesis.

This paper studies and designs a wide-band current transformer, analyzes the structure of the wide-band current transformer, and establishes an equivalent circuit model. Furthermore, It gives the error analysis and error formula derivation, proposes a design scheme to reduce the error for wide-band current, and develops a wide-band current transformer prototype. Finally the performance test is given.

The paper introduces the development and tests on two types of wideband current transducers: fiber-optic current sensor for DC & power frequency up to 1 MA and electromagnetic wideband current transducer for power harmonics or high frequency up to 1 MHz, which is a joint research program aimed to resolve the onsite calibration in the special industries.

Recent improvements of voltage-doubling method for measuring voltage dependence of compressed gas capacitor up to 400 kV are described. The capacitor is compared with a standard capacitor under the same voltage and doubling voltage separately using a commercially available current comparator bridge. A 5 nF centre-tapped capacitive divider with two identical high voltage arms is employed for voltage doubling and harmonics attenuation. The applied voltages when operating in voltage doubling state are monitored by a ground floating current comparator bridge and another two standard capacitors. None of the voltage dependence of the capacitors needs to know in advance. Expanded uncertainty evaluation for the voltage coefficient and the dissipation are estimated within 5 ppm.

In order to measure the voltage coefficients of the high-voltage capacitor with compressed-gas coaxial cylindrical electrodes structure based on the tilting method, an experimental platform was developed. The high-voltage capacitor installed on the platform could be titled and rotated at high voltage. Base on the developed experimental platform, the VC of a 350 kV highvoltage capacitor was measured by the tilting method.

For clinical applications, according to IEC 60601-2-2, power calibration up to 1 MHz is required for electrosurgical units (also referred to as electrosurgical generators), electrosurgical analyzers and their accessories. This paper discusses a reference system which is built for the power calibration of electrosurgical analyzers in the frequency range of 100 kHz to 1 MHz, in combination with powers up to 400 W, voltages up to 400 V, and load impedances between 200 and 500 $\Omega$ . The principle behind the system is based on a calibration of the analyzer input impedance and voltage. Measurements of the individual components required for calibrating analyzers in this range are described. A high-frequency (HF) power source was developed to generate high power for the electrosurgical analyzer. A low-dissipation capacitive voltage divider was developed for HF voltage calibration. With the frequency response calibration of the low range and nonlinearity calibration of the high range of the voltmeter, calibration of the HF voltmeter up to 400 V was realized. The impedance of the analyzer load is measured with impedance meter and the power stability of the load impedance was tested. A summary of the uncertainty components at 1 MHz is presented. The expanded uncertainty ( $k = 2$ ) of the power calibration at 1 MHz is approximately 1.3%, which satisfies the requirements for commercial electrosurgical analyzers.

To establish a series of ppm-level high-voltage ratio standards up to 110 kV, we propose and have designed low-voltage-excitation two-stage voltage transformers (LVE-TSVTs) for high voltage. Ratio traceability for a 10 kV/100 V LVE-TSVT is vital in this scheme. This paper focuses on the voltage ratio traceability of the 10 kV LVE-TSVT by measuring the errors of the reference voltage and the voltage coefficient separately. A 1 kV double-TSVT with a 1 kV/100 V TSVT and a 100 V/10 V TSVT in cascade was developed and calibrated, and then was used to calibrate the error of the 10-kV LVE-TSVT at 10% rated voltage. The voltage coefficient was measured by comparing with a high-voltage capacitive divider through a current comparator bridge. The measurement was implemented in the range of 10%–120% rated voltage. The calibration results showed that the ratio errors of the 10-kV LVE-TSVT were less than $0.95 \times 10^{-6}$ in magnitude and $-1.26\,\,\mu $ rad in phase displacement at the 10% rated voltage. The expanded uncertainties are about $1.8 \times 10^{-6}$ in ratio and $2.2~\mu $ rad in phase, respectively, with coverage factor $k = 2$ .

This paper focuses on the calibration of the voltage coefficient (VC) for the high accuracy 10 kV TSVT with the summation method by connecting other two VTs in series. Preliminary tests show that the VC of the 10 kV TSVT is around ${-4.3\times 10^{-6}}$ and ${+1.2\ \mu\text{rad}}$ in magnitude and phase displacement from ${10\%\ U_{\text{n}}}$ to ${120\%\ U_{\text{n}}}$ .

In order to reduce measurement uncertainty of the resistance $\pmb{(10^{-1} \Omega\sim 10^{5}\Omega)}$ due to the uncertainty component from the automatic direct current comparator resistance bridge (ADCCRB) ratio error, a novel method based on a direct current comparator (DCC) and two same nominal resistances is presented. The measurement uncertainty of the ADCCRB ratio error is largely dependent on DCC and Type A uncertainty of the ADCCRB. It is shown by the experimental results that the measurement uncertainty from the ADCCRB (ratio: 10:1) is less than $\pmb{3\times 10^{-8}, k=2}$ .

Electrified railway in China has been actively developed. At the same time, as a kind of impact load, the load of electrified railway traction substations has brought in a significant impact to the accurate measurement on the electric energy. This paper measured and analyzed the field electric parameters of several electrified railway traction substations, and analyzed the causes of the metrology result differences between the impact load electric energy meter and the ordinary electric energy meter. This work laid the foundation of further research on the accurate measurement of harmonic electric energy.

A non-ideal step response of the digitizer may introduce significant errors in the impulse voltage measurement. Deconvolution is a good method to correct the step response. However, it is sensitive to noise. We studied on the influence of the frequency bandwidth limit on the deconvolution processing, with the results reported in this paper. This correction method was applied to the step responses recorded with three different commercial digitizers, and the error introduced by the corrected step responses were all reduced to less than 0.1%, which would be negligible in the impulse measurement.

In the measurement of high voltage loss, a voltage signal and a current signal which were nearly orthogonal to each other need to be measured accurately. If the phase of the voltage signal was shifted by 90° accurately, thus the phase angle between the voltage and the current would be nearly 0°. The two signals would be then easily to measure accurately together. A digital phase shifter was developed. The phase and the magnitude error of the digital phase shifter is less than $\pmb{6\ \mu}\mathbf{rad}$ and $\pmb{110\times 10}^{-6}$ up to 150 Hz and 120 V, respectively.

To ensure the traceability and reliability of the electrical defibrillation pulse energy, this paper presents the development of an integral source-meter setup for the calibration of defibrillator analyzers, that has been designed to generate and measure both typical monophasic and biphasic waveforms. By synchronously sampling the pulse voltage and current to calculate the energy, the 0.2%E+0.1 J uncertainties of pulse energy from 0.1 J to 360 J are achieved and independent of the load.

Heavy current transformers (HCTs) for large generators are intensively interfered by the stray magnetic field produced by heavy adjacent currents, and therefore, anti-interference testing is a crucial process to assure the robustness of HCT products. However, the generation of the interference involves multiphase heavy currents, which are difficult to produce in testing environments, and equivalent testing coils have become an emerging solution to the testing. In this paper, an improved parameter determination algorithm is proposed for the traditional two-segment testing coil configuration, and furthermore, a novel multi-segment testing coil configuration is proposed for better equivalence of the multiphase interference. The effectiveness of the two configurations are thoroughly analyzed by FEM-based simulations as well as physical experiments.

This paper describes the development of a 300-kV standard full lightening impulse measurement system. The high-voltage (HV) arm of the impulse resistive divider was constructed with an air-insulation frame wound with nichrome alloy resistance wire using the Ayrton-Perry winding method. The winding inductances of different frame cross-sectional shapes were studied. The result showed that the rectangular shape gives the least winding inductance compared with the circular and square cross sections under the condition of the same circumference. The HV arm was divided into 10 sections, and the stray parameters were subtracted with Finite Element Method method; the step response of the system is simulated with Simulink of MATLAB to optimize shield ring design. The low-voltage arm is composed of 24 low-inductance metal film resistors, which is similar in design to that developed by a Russian national metrology institute. The step response measurement result showed that the partial response time was less than 5 ns. The convolution method is used to evaluate uncertainty due to different waveform shapes based on the normalized step response. The expanded uncertainty evaluation of peak value gives 0.5% ( $k =2$ ), and the time parameter $T_{1}$ is 2.6% ( $k=2$ ) and $T_{2}$ is 1.3% ( $k =2$ ).

This paper presents a new structure of a two-stage voltage transformer (TSVT) with toroidally wound ring cores excited by low voltage for high-voltage measurement. In the new TSVT, two high-voltage windings are wound on two separate groups of toroidally wound ring cores, respectively. This avoids the insulation problem in the traditional TSVT structure for high voltage and high accuracy, in which, the high-voltage excitation and ratio windings need to be wound together around overlapped cores. Three TSVTs, 10, 35, and $110/\sqrt {3} ~\textrm {kV}$ , were developed based on this scheme. The uncertainties of magnitude and phase of these TSVTs are all less than $3.2\times 10^{-6}$ and 1.1 $\mu $ rad, respectively, at reference voltage. Comparative measurements with a high-voltage capacitive divider and a current comparator illustrate that in the range of 20%–120% rated voltage, variations of no-load errors of new TSVTs are as follows: 2– $4\times 10^{-6}$ and $2~\mu $ rad in magnitude and phase, respectively, which reach class 0.0005 to class 0.001.

In this work, a linear birefringence measurement method is proposed for an optical fiber current sensor (OFCS). First, the optical configuration of the measurement system is presented. Then, the elimination method of the effect of the azimuth angles between the sensing fiber and the two polarizers is demonstrated. Moreover, the relationship of the linear birefringence, the Faraday rotation angle and the final output is determined. On these bases, the multi-valued problem on the linear birefringence is simulated and its solution is illustrated when the linear birefringence is unknown. Finally, the experiments are conducted to prove the feasibility of the proposed method. When the numbers of turns of the sensing fiber in the OFCS are about 15, 19, 23, 27, 31, 35, and 39, the measured linear birefringence obtained by the proposed method are about 1.3577, 1.8425, 2.0983, 2.5914, 2.7891, 3.2003 and 3.5198 rad. Two typical methods provide the references for the proposed method. The proposed method is proven to be suitable for the linear birefringence measurement in the full range without the limitation that the linear birefringence must be smaller than π/2.

Applying shielding coils is a practical way to protect current transformers (CTs) for large-capacity generators from the intensive magnetic interference produced by adjacent bus-bars. The aim of this study is to build a simple analytical model for the shielding coils, from which the optimization of the shielding coils can be calculated effectively. Based on an existing stray flux model, a new analytical model for the leakage flux of partial coils is presented, and finite element method-based simulations are carried out to develop empirical equations for the core-pickup factors of the models. Using the flux models, a model of the common four-segment shielding coils is derived. Furthermore, a theoretical analysis is carried out on the optimal performance of the four-segment shielding coils in a typical six-bus-bars scenario. It turns out that the “all parallel” shielding coils with a 45° starting position have the best shielding performance, whereas the “separated loop” shielding coils with a 0° starting position feature the lowest heating value. Physical experiments were performed, which verified all the models and the conclusions proposed in the paper. In addition, for shielding coils with other than the four-segment configuration, the analysis process will generally be the same.

With proper design, accurate current ratios of direct current comparators (DCCs) can be achieved between series and parallel connections of n sections of primary windings with the same nominal number of turns. Based on this principle, a DCC could be calibrated with the windings connected in series, then operated in parallel, at rated current and therefore have its current ratio accurately extended by n times. By keeping the geometric position of the primary windings symmetrically and rigidly fixed to the cores, the leakage fluxes and their effects on the DCC current ratios would be minimized and relatively unchanged between the series and parallel connections. Four DCCs with current ratios of 10 A:1 A to 5 kA:5 A have been developed with relative ratio errors less than 2×10-8 to 5×10-7, and calibrated by the series parallel method through only four step measurements. These measurement techniques for the self-calibration of DCCs with current ratios of 10 A:1 A to 5 kA:5 A and corresponding uncertainties from 1.2×10-8 to 1.6×10-7(k=2) are described.

A double current method is presented for absolute measurements of the current dependence (power variation) of dc resistors. Based on the resistance measurement principle of a direct current comparator (DCC), and adding another DCC-based extender with a turn ratio 1:1, the testing current in resistors to be tested is accurately doubled. Through three comparative measurements with two reference standard resistors connected in series as Kelvin resistive bridge inner arms, the change of resistance caused by doubling the currents is measured. Cyclically done, absolute measurement of current or power factor is realized. Examples of the current dependence of some commercial low-temperature coefficient 1 Ω standard resistors are given using the presented method and their results are analyzed.

This paper describes a new method for determining phase angle errors of shunts with rated currents at 50 and 100 A at frequencies from 25 to 100 kHz. The method is based on the use of a three-branch binary inductive current divider to measure the phase angle errors of high current shunts against a phase angle reference standard with only one step. An inductive high current shunt has been designed using a 100:1 current transformer connected in parallel with a 1- $\Omega$ shunt. The phase angle errors of resistive high current shunts and the inductive high current shunt have been measured. The level dependence in phase angle errors of three different types of high current shunts has been evaluated at currents from 1 to 100 A. The measurement results and standard uncertainties of the phase angle errors of high current shunts are reported.

In order to overcome the drawback that the measurement uncertainty of the ultra-high resistance over 1014 Ω may be deteriorated severely due to insufficient resolution of the electrometer in conventional scheme, a novel method based on the dual sources high resistance bridge and non-contact voltage measurement is presented. The measurement uncertainty is largely dependent on the standard resistance and determined by the resolution of the electrostatic voltmeter. It is shown by the experimental results that the measurement uncertainty for the resistance of 100 TΩ to 1000 TΩ is better than 0.2%, k = 2.

According to the demands of the calibration of high-frequency power of electrosurgical analyzer, we developed a power source. It could output sinusoidal wave with the frequency of 100 kHz to 1 MHz, the maximum power of 200 to 400 W and the stability of 0.2 %/3 minutes. It satisfied the high frequency power tracing requirement of electrosurgical analyzer, and also could be used for calibrating the power of other high-frequency instruments.

Two-stage voltage transformer with low voltage excitation(LVE-TSVT) was designed for high accuracy. However, currently the voltage ratio standard and standard voltage transformer can not meet the need of its calibration accuracy. This paper is focus on quantity traceability for 10 kV LVE-TSVT with the method of measuring the error of reference voltage and voltage coefficient. Preliminary tests show that voltage error and phase displacement of 10 kV LVE-TSVT are both less than 1×10−6 at the 10% rated voltage, and its voltage coefficient is better than 5×10−6.

The paper presents the development of a 35 kV fully-insulated two-stage voltage transformer(TSVT), and its applications by connecting in series with another 35 kV semi-insulated TSVT to determine the voltage dependence(VD) of a 110 kV TSVT. The result showed the VD of the 110 kV TSVT is around −1.6×10−6 and +1.6 μrad in magnitude and phase, respectively.

According to the HF power measurement principle of electrosurgical analyzer, we proposed a voltage-impedance method to solve the HF power calibration problem of the analyzer, by calibrating the frequency characteristics of the load resistors and measuring the voltage on the resistors. At 100 kHz to 1 MHz and 50 W to 400 W, the relative uncertainty of measurement is 0.6%-1.0% (K=2).

A fiber-optic current sensor based on the Faraday effect is proposed as a value transfer standard to calibrate the direct high current for the electrowinning industry. The spun high birefringence optical fiber with strong resistance to accumulative bend-birefringence in the case of multi-turns sensing coil is packaged into a sensing element. The closed-loop signal-detecting scheme is utilized to improve the linearity of the sensor over the large dynamic range. The good linearity between the sensor output and current-induced Faraday phase shift is proved experimentally. The sensor achieves accuracy within ±0.1% for the equivalent current between 10 kA and 200 kA.

EEG feature identification and body's sensing are used together to confirm that the current flowing through the human body reaches the perception threshold, since the existing test method is sensitive to the subject's subjective awareness and experimental data's reliability and consistency are not good. Based on the test method, the relationship is studied among the human body's perception current effect threshold and many influencing factors such as touch voltage, touch area, touch pressure, skin type, environmental temperature and humidity, the time period in which the current passes through the human body, current frequency, current waveform, current path, etc. to explore the combined effect of those factors on human body's perception current threshold. The model of the human body's perception current threshold is established based on BP neural network to evaluate comprehensively the leakage current effect on the human body's perception current threshold and the model accuracy is about 99%.

Ordinarily electronic voltage transformers (EVTs) are calibrated off-line and the calibration procedure requires complex switching operations, which will influence the reliability of the power grid and induce large economic losses. To overcome this problem, this paper investigates a 110 kV on-site calibration system for EVTs, including a standard channel, a calibrated channel and a PC equipped with the LabView environment. The standard channel employs a standard capacitor and an analogue integrating circuit to reconstruct the primary voltage signal. Moreover, an adaptive full-phase discrete Fourier transform (DFT) algorithm is proposed to extract electrical parameters. The algorithm involves the process of extracting the frequency of the grid, adjusting the operation points, and calculating the results using DFT. In addition, an insulated automatic lifting device is designed to realize the live connection of the standard capacitor, which is driven by a wireless remote controller. A performance test of the capacitor verifies the accurateness of the standard capacitor. A system calibration test shows that the system ratio error is less than 0.04% and the phase error is below 2', which meets the requirement of the 0.2 accuracy class. Finally, the developed calibration system was used in a substation, and the field test data validates the availability of the system.

This paper presents a new method of calibrating de voltage ratios from 20 V: 10 V to 1000 V: 10 V. A new battery-powered differential voltage detector has been developed to reduce the uncertainty of the measurement system. An absolute self-calibration process was used and traceability to a voltage ratio standard is not necessary. The uncertainties of dc voltage ratios (20 V to 1000 V): 10 V were less than 2 /spl times/ 10/sup -7/.

Electric and electronic products are required to pass through the certification on electrical safety performance before entering into the market in order to reduce electrical shock and electrical fire so as to protect the safety of people and property. The leakage current is the most important factor in testing the electrical safety performance and the test theory is based on the perception current effect and threshold. The traditional method testing the current threshold for perception only depends on the sensing of the human body and is affected by psychological factors. Some authors filter the effect of subjective sensation by using physiological and psychological statistical algorithm in recent years and the reliability and consistency of the experiment data are improved. We established an experiment system of testing the human hody's current threshold for perception based on EEG feature analysis, and obtained 967 groups of data. We used wavelet packet analysis to detect a wave from EEG, and used FFT to do spectral analysis on alpha wave before and after the current flew through the human body. The study has shown that about 97.72% alpha wave energy changes significantly when electrical stimulation occurs. It is well proved that when the EEG feature identification is applied to test the human body current threshold for perception, and meanwhile alpha wave energy change and human body sensing are used together to confirm if the current flowing through the human body reaches the perception threshold, the measurement of the human body current threshold for perception could be carried out objectively and accurately.

This paper describes how to calculate the magnetic shielding effectiveness of current comparator, considering air gap which is inevitable for the magnetic shielding. The method was verified to be accurate and effective by finite element method (FEM).

The requirement to the response time and dynamic behaviors of a standard impulse resistive divider is very strict. Main influence factor contributes to the measurement error of the divider is caused by stray capacitance to the earth. This paper calculated the stray capacitance and distribution capacitance parameters of the divider's high voltage arm with finite element method (FEM) and boundary element method (BEM). The simulation results of electric-field and compensation effect on the stray capacitance to the earth with different shield ring structure are analyzed.

Stray flux (leakage or interference flux) in the iron core of DCC due to the primary eccentric bus-bar and the external adjacent current-carrying conductor were calculated by electromagnetic analytical methods. The equivalent relations between the leakage fields and the interference fields were derived. Based on the relations, the effect of leakage fields caused by the eccentric bus-bar on the DCC error can be easily evaluated by the interference fields generated by the neighboring current-carrying conductor, and a new shape of DCC primary coils has been designed.