Анализ частотных характеристик токовых датчиков цифрового трансформатора тока и напряжения

Traditional differential protection systems are applied on large power transformers using current transformers (CTs). However, because of high secondary currents (often exceeding 100 kA RMS) differential protection systems for electric arc furnace (EAF) transformers have not been applied in the past due to the lack of commercially available CTs. This paper will present differential protection systems that have been in use for many years using Rogowski Coil (RC) current sensors. These protection systems use high precision printed circuit board (PCB) Rogowski coil (RC) current sensors. The paper reviews the characteristics, designs, and application of these RC sensors for advanced protection, control, and metering systems with new multifunction relays. The paper compares performance characteristics of new solutions based on RC sensors with the conventional differential protection systems based on CTs, demonstrating that the new systems do not have the limitations of conventional technology. Operating experience from several site applications will be included.

Rogowski coil is used for measuring the alternating current (AC) and high-speed current pulses. However, the technology makes the Rogowski coil (RC) come out with more improvement, modification and until today it’s still being studied for the new application. The Rogowski coil has a few advantages compared to the high frequency current transformer (HFCT). A brief review on the basic theory and the application of Rogowski coil as a current sensor measurement that been done by previous researchers are presented and discussed in this paper. Additionally, the review also focused on the capability of Rogowski coil for high current sensor measurement and their application for fault detection, over voltage current sensor, lightning current sensor and high impulse current detection. The experimental set up, techniques and measurement parameters in models also been discussed. Finally, a brief review on the performance analysis of current sensor measurement of Rogowski coil likes sensitivity, the maximum and current detection which could be used as a guideline to another researcher in order to develop an advanced RC as high current sensor in future is presented. This review reveal that the RC has a very good performance in high current sensor detection in term of sensitivity which is up to a few nanosecond, higher bandwidth, excellent in detection of high fault and also could measuring lightning current up to 400kA and has many advantages compare to conventional current transformer(CT).

The calibration of measurement transformers represents a classical task in the practice of electrical measurements. Most commercial instruments that are expressly designed for this purpose found their working principle on a scheme that is based on the idea of Kusters and Moore. Although they can assure very high accuracy, the need to employ a high-performance electromagnetic circuit makes them very expensive and usually not suitable for measurements at frequencies that are higher than 50 or 60 Hz. For this reason, these kinds of instruments cannot be employed for the calibration of the new generation of current and voltage transducers, such as electronic measurement transformers, whose employment is growing in all the applications where wide bandwidth is required. In this paper, a new method for the calibration of electromagnetic voltage and current measurement transformers (VTs and CTs) and electronic voltage and current measurement transformers (EVTs and ECTs) is discussed, and a deep metrological characterization is carried out. The novelty of the proposed method is represented by a completely different approach to the measurement of the ratio and phase errors of the measurement transformers. The method is based on the proper digital signal processing of the signals that are collected at the secondaries of the transformer under test and of a reference transformer when the same signal is applied to their primary. Since no auxiliary electromagnetic circuits are required, this solution can be easily implemented in a simple and cost-effective way. In spite of its simplicity, the tests that are developed on a prototype clearly point out that the proposed system is suitable for the calibration of measurement transformers with precision class up to 0.1 in the frequency range from 50 Hz to 1 kHz.

This paper describes the results of performance evaluation of ratio errors of a high voltage current transformer (CT) and a high voltage combined current and voltage transformer (CT/VT) with the aim of discovering the behavior of the CT ratio errors at different operating high voltages, different power factor loads on the transmission line in which the CT (or CT part of the CT/VT) was connected and the effects of the VT burden (in case of the CT/VT).

A sampling current ratio measurement system has been developed, tested, and validated for the accurate complex ratio measurement of ac current transducers. Calibrations can be performed for primary currents up to 10 kA with typical expanded uncertainties of 5 · 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> in magnitude and 5 μrad in phase (k = 2). A unique property of the system is the use of digitizers for sampling of the secondary current signals and step-down transformers with a large number of current ratios. Therefore, the system does not require the current transducer under test to be a current transformer having a nominal ratio equal to the reference current transformer. Furthermore, it allows for the accurate calibration of a large variety of different current transformers and other types of current transducers. A bilateral comparison between VSL and NRC confirms the stated uncertainty.

A current transformer (CT) system centered on Rogowski coil is introduced to measure the low frequency heavy current of the linear induction motor (LIM) powered by the H-bridge sine pulse width modulation (SPWM) inverter. The frequency of the output current of the inverter ranges from 1 hertz to 200 hertz. The current test apparatus is made of the sensor head of Rogowski coil and the post-processing circuit. The post-processing circuit has characteristics of high reliability, high accuracy, low saturation, and low distortion. The voltage from the processing circuit is acquired by the Nicolet acquisition system, which has a fast speed of analyzing the current in real time. The fundamental current can be gained by means of the Fourier transformation. Both theory analysis and experimental results can verify the feasibility of the proposed CT instrumentation.

The use of microprocessor devices for relay protection and automation, devices for measuring and determining electric power quality permits the introduction and development of digital circuits leading from primary current and voltage transformers. The use of optical channels for digital circuits addresses the problem of offsetting electromagnetic interference and voltage shift. Creating optical and digital current and voltage transformers with digitization of signals already at high measuring transformer voltage is the best solution for the above problem of mechanical engineering in the field of electromagnetic compatibility of high voltage measuring transformers. However, a difficulty arises in ensuring electromagnetic compatibility of sensors and microelectronic equipment adjoining live parts. The present study is devoted to examining the impact of electromagnetic fields on sensors and solving the problems of electromagnetic compatibility of optical and digital current and voltage transformers.

The aim of this master thesis is to develop a high-bandwidth current sensor for a nominal design current of 100 A and a nominal design bandwidth of 100 MHz. After an analysis which properties are important to develop a current sensor, a requirement list was stated. Several current sensing methods were described and their qualification for the stated requirements were evaluated. With the resulting sensing concept, consisting out of Rogowski coils and magneto resistors, a system design was elaborated. One requirement was to develop a current sensor which needs less effort in series production than a regular Rogowski coil. Therefore, a planar Rogowski coil was proposed for this sensor development. Furthermore, a magnetic field simulation was designed. Based on the results, a optimal placement simulation for both sensors was carried out. In the final design phase, the galvanic insulation requirements of 4.8 kV based on the corresponding standards were investigated and implemented. The test equipment used in this thesis was designed and build in-house at IPE (KIT-ADL). Commercial solutions did not offer the suggested requirements for generating a double pulse with the necessary rise time to characterize the current sensor’s bandwidth. The test equipment was able to apply pulses with a maximum current of 200 A and a rise time of 1 ns to the device under test. The prototype is able to sense a current up to ±100 A with a bandwidth of 20 MHz.

In real-world scenarios, deviations in the frequency response of instrumentation transformers can lead to distorted harmonic measurements, highlighting the critical role harmonic measurement plays in assessing power quality. The blind channel equalization technique offers a potential solution to improve the frequency response of a large number of instrumentation transformers already installed in substations. These transformers were designed to accurately measure only the fundamental phasor component. Therefore, in order to use them for harmonic phasor measurement, methodologies for reducing frequency distortion must be applied. In this work, we propose a novel approach to improve the frequency response of the instrument transformer using adaptive blind equalization. The blind technique can compensate for distortions caused by voltage and current transducers without requiring prior knowledge of input signals or circuit characteristics. The proposed methodology uses a Linear Prediction Filter to convert the colored noise present at the channel output into white noise. Furthermore, a genetic algorithm is used to find a pole to cancel possible zeroes present in the frequency response of some transducers. The main advantage of blind equalization with the genetic algorithm is its independence, operating without clear information about the channel or the input signal. Through extensive experimentation, we demonstrate the effectiveness of the proposed methodology in significantly reducing the absolute error in ratio and phase caused by current and voltage transformers. Simulated and laboratory experiments are presented in this paper.

A new wide bandwidth current probe for power applications based on a Hall sensor as well as on a Rogowski coil is presented in this paper. Employing these two sensors allows to eliminate the integrator circuit needed for the Rogowski signal. This paper shows that using a special way to merge the output of the Hall sensor with the Rogowski coil, a current probe can be realized which combines the advantages of both sensors. With this new probe DC currents as well as current transients with di/dt's of several kA/us can be measured. Keywords-Wide Bandwidth current probe, Sensors, Power semiconductor devices, New devices, Rogowski coil, Hall sensor

Robust energy measurements for household consumption billing are important for consumer confidence. Recent studies have shown electromagnetic interference problems with static energy meters, this results in incorrect billing. The interfering current waveforms are pulsed currents with a short pulse duration, fast rising slope, and large crest factor. These kinds of waveforms are largely present in modern low-voltage networks. The root cause of the interference on static energy meters that use a Rogowski coil is known, however for meters that use a current transformer as their current sensing element this is unknown, while those meters contribute to errors up to 200%. Therefore, this article researches the root cause of interference on static energy meters that use the current transformer principle for current sensing. It was found that the current transformer exhibits droop and the current pulses to be measured are not properly reconstructed. As a result, when the power/energy is calculated errors occur. This explains why current transformer-based static energy meters are prone to electromagnetic interference.

A typical approach for the compensation of voltage transformers (VTs) is based on the generation of an auxiliary voltage that has to be added to the secondary electromotive force. The auxiliary voltage has to compensate the voltage drops due to the current flowing in the primary circuit. At this aim, the compensating circuit has to sense the primary current in the different working conditions. It is clear that the accuracy of the employed current transducer affects the compensation effectiveness, since it modifies the auxiliary voltage. In the paper an analysis of the sensitivity of the performances of VT compensation with respect to the variation of the current transducer accuracy is performed. The obtained results allow the selection of the proper current transducer that represents the suitable trade off between the transducer costs and the achievable accuracy class for the compensated VT.

With the worldwide realization and application of High Voltage Direct Current (HVDC), the additional effects of HVDC transmission technology on power system have caused extensive concern. The DC magnetic bias caused by HVDC may exacerbate the saturation degree of the current transformer (CT) during the external fault, which probably leads to the mal-operation of the transformer differential protection. In this paper, the state of CT transient saturation is divided into two kinds. Saturated characteristic and error analysis are presented in detail. Afterwards, two cases of CT saturation with and without the DC bias current have been compared in order to verify the effect of the biased flux on the time-to-saturation of the CT. Furthermore, based on the fact that time-difference method fails to block the external fault under the acceleration of CT saturation, this paper proposes an improved protective scheme to re-partition the ratiorestrained characteristic and sets a time-delay action region to avoid the mal-operation of the differential protection. What is more, CT saturation will affect the performance of the protective relay and threaten the security of power system, to which should be paid adequate attention.

The measuring accuracy of the electric energy meter, voltage transformer and current transformer shows a dynamic state under the influence of its factors and external factors. The error of the voltage transformer and current transformer cannot be measured by traditional method. This paper establishes a multidimensional error analysis and fault diagnosis system for power metering based on Hadoop architecture and Spark memory calculation. The platform extracted the error signal from the measurement data and calculated the characteristic value of the error signal. Then, dependent cloud and dynamic time rules are used to estimate the transformer's and voltage transformer's continuity. Then, a half-step membership degree cloud generation algorithm is constructed to overcome the error bias randomness and fuzzy characteristics under the influence factors. Finally, the system uses the dynamic correction method to estimate the similarity of error timing and quantitative factors to realize the error calculation of the current transformer and voltage transformer. The power metering error processing system was built with the support of Hadoop and Spark. The timing increment is introduced in the process of data collection. Dependent cloud and dynamic time-repair methods can improve the accuracy of diagnosing errors in electric energy metering. The parallel optimization of big data platforms by belonging to the cloud and dynamic time-warping algorithm is verified.

Instrument current and voltage transformers remain the basic apparatus used in measurements of energy in electrical grid. Increasing importance of distributed energy sources necessitates more precise measurements of consumed as well as generated electrical energy. Both types occur in low voltage network where the main focus is on current transformers for electronic-type electrical energy meters. These current transformers should fulfil many requirements for precise electrical energy measurements. This paper presents a modern system for measurement of various metrological features of current transformers.