Current Transformer Test Research Articles

Shake Table Testing of Voltage and Current Transformers and Numerical Derivation of Corresponding Fragility Curves

Damage to devices installed in electric substations, which have shown vulnerable behaviour under strong earthquakes in the last decades, may endanger power delivery in the emergency phases during and after an earthquake. Within seismic risk assessment of power networks, the definition of the fragility functions of electric equipment is paramount. However, in the current literature the availability of such fragility models for some specific electric substation components, including instrument transformers, is relatively limited, this being the reason behind the deployment of the current experimental and numerical research endeavour. Two voltage transformers and two current transformers having different system voltage levels (respectively in the high voltage HV and extra-high voltage EHV ranges) were subjected to shake table tests, and the experimental results were used to calibrate the corresponding 3D numerical models developed in OpenSees. A number of nonlinear dynamic analyses carried out within a multiple-stripe analysis (MSA) framework allowed the derivation of 16 fragility curves for the four transformers in both stand-alone and elevated/supported configurations, considering also two different soil types. Based on the derived curves, one of the voltage transformers is expected to experience light or negligible damage due to earthquake shaking, owing to its high resonance frequencies (and hence stiffness), whilst the remaining three devices may suffer moderate damage under medium to strong shaking intensities; however, their seismic risk is in effect mitigated by the presence of the typically employed supporting column. Comparison against models available in the literature lent valuable reassurance on the adequacy of the employed methodology and the reliability of the derived fragility curves.

Research on hydrogen diffusion characteristics under typical defects of inverted oil-immersed current transformer

Inverted Oil-immersed Current Transformer (CT) is an important electrical equipment in the power system, which plays the role of current conversion and voltage isolation, also plays an indispensable role in the stable operation of the power system. Studies have shown that hydrogen is the earliest and easiest produced gas in the discharge and overheating faults of CTs, and hydrogen is also considered an early signal of equipment failure. In order to study the distribution and diffusion of hydrogen under typical defects of CTs, this paper established a 110 kV CT electric-thermal-flow multi-physics coupling three-dimensional simulation model. Using the method of finite element analysis, the internal temperature field of the CT and the distribution and diffusion of hydrogen are obtained. At the same time, an CT test platform is established to verify the accuracy and validity of the simulation results.

Frequency Response Testing of Zero-Sequence Current Transformers for Mining Ground Fault Protection Relays

W polskim gornictwie wegla sieci dystrybucyjne średniego napiecia dzialają z izolowanym punktem neutralnym. Przekladniki prądowe o zerowej sekwencji są podstawowymi czujnikami, ktore generują sygnaly wejściowe dla przekaźnikow zabezpieczających przed zwarciem doziemnym. W literaturze problem analizy odpowiedzi czestotliwościowej roznych typow przekladnikow prądowych byl wielokrotnie badany, np. [1] [2], ale jak dotąd nie dotyczy przekladnikow prądowych o zerowej sekwencji. W ramach pracy przetestowano dwa typy przekladnikow prądowych o zerowej sekwencji w zakresie od 0,1 Hz do 100 kHz. Przeanalizowano zarowno zmiane stosunku prądu, jak i przesuniecie kątowe miedzy prądem wtornym transformatora a calkowitym prądem pierwotnym.

The Device for Simultaneously Accuracy Testing of Current Transformers

This paper presents a three-channel device for simultaneous accuracy testing of three current transformers. The concept of multichannel device is one of the possible good solutions for accuracy testing in the process of automated or robotized manufacturing of low voltage current transformers. The paper presenrs a short description of the overview of calibration results.

Design of equivalent coils for anti- interference testing of heavy current transformers

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.

Design and Implementation of the CT Analyzer on the Basis of the Low Pressure Test Principle

CT analyzer is a necessary instrument of on-site verification accuracy of current transformer. Traditional current transformer testing methods is mainly the differential method. Because of the limited by the principle, the current transformer of the on-site verification is very inconvenient. The CT analyzer designed and developed in this paper use the new method of indirect test - low pressure method, which gets current transformer contrast and angle difference by measuring the internal parameters of the CT. According to the design method of intelligent instrument, by combining with the digital sampling technology, taking DSP microprocessor as the core, and using the advanced digital signal processing method, use only one instrument current transformer can be realize the field test, which effectively resolve the problems of current transformer field test.

Fabrication of a current transformer test set calibrator and its applications

A current transformer test set (CTTS) calibrator consisting of capacitors and resistors was fabricated. The calibrator was utilized for the calibration of several commercial CTTSs and covered a ratio error and phase error range up to ±10% and ±10 crad, respectively. From the calculated and measured values of the corresponding readings, the errors in the ratio and phase readings are derived. The calibration results for several commercial CTTSs are presented with the measurement uncertainty and are compared with the specifications provided by the manufacturer. The absolute uncertainty of a CTTS for both the ratio and the phase for the entire investigated range was obtained. The absolute uncertainty for the ratio error range of –0.1% to +0.05% was found to be less than 10 × 10−6 and the absolute uncertainty of the phase error range of –0.1 to +0.1 crad was not more than 6 µrad.

Analysis on Line Differential Protection Based on Transient Saturation Characteristics of TPY-Type Current Transformer

Transient saturation characteristics of TPY-type current transformer have great impact on the right action of line differential protection. This paper proposes an analytical method of line differential protection under current transformer saturation by utilizing current transformer model and test methods. The true current value of primary side can be obtained by our proposed method and therefore it yields correct assessment of line operating status. This method has high reliability applying to practical engineering examples of differential protection.

A Wideband Current Transformer Bridge

The development and testing results of a new current transformer (CT) test set at Physikalisch-Technische Bundesanstalt are described. The operation range for the ratio based bridge is intended for frequencies from 16.7 Hz up to 20 kHz. Equal setups of magnetically shielded current comparators with primary windings for rated currents from 100 mA up to 5 A convert the secondary currents of the standard CT and of the transformer under test (TUT) into proportional voltages. The errors of the TUT are calculated from the subsequent measurement of the complex voltage ratio. This current bridge and the voltage-ratio-based method allow comparing CTs with nonequal ratios. At 50 Hz, the measuring system offers an extended measurement uncertainty of less than 2 ppm or μrad, respectively. The bridge is verified for use with uncertainties of below 200 ppm or 400 μrad at a frequency of 20 kHz.

A Complex Current Ratio Device for the Calibration of Current Transformer Test Sets

A Complex Current Ratio Device for the Calibration of Current Transformer Test SetsA practical method with high accuracy in generation and application of error values for calibration of current transformer test sets is described. A PC-controlled three-phase power source with a standard wattmeter is used for generating the nominal and error test currents while an electronically compensated current comparator is used to provide summation and subtraction of them, precisely. With this method, any ratio error and phase displacement values could be generated automatically and nominal and test currents could be grounded on the test set safely. Because of its high accurate ratio and phase error generating capability, any type of test set regardless of its operating principles could be calibrated.

Development of an on-site calibration method for a current transformer testing system and its application

The ratio error and phase displacement of a current transformer (CT) are measured by using a CT testing system, which consists of a current source, a standard CT, a CT under test, a CT comparator and a CT burden. Methods for on-site calibration of the components in CT testing systems in industry have been developed recently, which do not require any component to be detached from the systems. The method utilizes several travelling transfer standards: standard CTs, non-reactive standard resistors, a calculable wide-ratio error CT and non-reactive shunt resistors. The travelling standard CT is used for absolute evaluation of a current source and a standard CT of industry. The non-reactive standard resistors and the calculable wide-ratio error CT are used to evaluate the linearity of the errors in the CT comparator. The shunt resistors are used to evaluate the CT burden of industry. The on-site calibration method using these travelling transfer standards has been successfully applied to calibration of CT testing systems in industries.

A new method for calibrating standard current transformers up to 20 kA

We have developed a method to obtain the ratio error and phase displacement of a single-stage current transformer (CT) by measuring four parameters in a CT equivalent circuit. The method was applied to CTs under test with a primary current in the range 10–20 000 A and a secondary current of 5 A. By determining the errors of the CTs under test using this method, the ratio error and phase displacement of the standard CTs used as a reference in a CT test system could be obtained. This implies the establishment of a traceability chain of a national standard for CTs. The ratio error and phase displacement of the standard CTs obtained in this study are consistent with those measured at the Physikalisch-Technische Bundesanstalt in Germany using the same standard CTs within an expanded uncertainty (k = 2) in the overall primary current range investigated.

In- situ measurement of the current transformer burden in a current transformer testing system using a shunt resistor

Both the ratio error and phase angle error of a current transformer (CT) are significantly affected by the CT burden connected in series to the secondary terminal of the CT. Thus, the precise measurement of this CT burden is required for the evaluation of the CT errors. A method for measuring the CT burden in- situ in a CT testing system (CTTS) has been developed by employing the non-reactive type shunt resistor. For the measurement of the CT burden, the shunt resistor was connected in parallel to the secondary terminal of the CT under test in the CTTS. The burden values represented by the apparent power and the power factor can be calculated from the resistance (and reactance), which was obtained by measuring the ratio error (and phase angle error) as a function of the resistance of the shunt resistor. The uncertainties in the measurements of the apparent power and the power factor for the rated burdens studied were found to be less than 2.1%. The CT burden values obtained using our method were consistent with those measured using a digital multimeter within the corresponding uncertainties.

Evaluation of errors in a current comparator system used for current transformer testing

An error evaluation method for a current transformer (CT) test system using a current comparator is described, and evaluated results of the CT test system are given. The CT test system is designed for use at power frequencies, and at winding ratios of 1:1 to 20:200 with in-phase and quadrature errors of less than 1 ppm and 2 mu rad, respectively, over this range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Transistorized Cathode-Ray Phase-Sensitive Null Detector

A tuned cathode-ray null detector developed for use with a current transformer test set is described. Apart from the cathode ray tube, the detector is completely transistorized and has been designed to detect signals as low as 20 µV at frequencies of 50, 60, and 400 c/s. The third harmonic is down at least 40 dB from the fundamental.

Techniques for the calibration of standard current transformers up to 20 kc/s

When standard current transformers are tested at high audio frequencies the errors and uncertainties in the measurements are liable to be great owing to the effects of stray magnetic fields on the large unshielded resistors which of necessity have to be used. The sources of stray fields are examined and means are suggested for substantially reducing them. It is shown that the 4-terminal resistance standards used in current-transformer testing bridges are very frequency-dependent and present techniques limit the accuracy of measurement at 20 kc/s to 2 parts in 104 in ratio and 0.8′ in phase.New techniques are described by which the errors and uncertainties can be reduced to give an accuracy of 5 parts in 105 and 0.1′ at 20 kc/s.

Discussion on the two papers “Leakage phenomena in ring-type current transformers” and “Current-transformer testing”, by Dr. Arnold, before the Meter and Instrument Section, 1st December, 1983

Discussion on the two papers “Leakage phenomena in ring-type current transformers” and “Current-transformer testing”, by Dr. Arnold, before the Meter and Instrument Section, 1st December, 1983

Precision testing of current transformers

The paper describes in detail how the testing of current transformers may be carried out with speed and accuracy by means of a potential-divider bridge. The corrections to be made to the readings are deduced from the theory of the bridge; and it is shown that, by taking a few simple precautions, an accuracy of 0.01 per cent for ration measurements, and of 0.1 minute for phase-angle measurements, is attainable if the transformer characteristics are stable to this limit. A very sensitive and accurate bridge, which is not so convenient for general purposes as the potential-divider bridge, is than described. Results obtained with this bridge are compared with those obtained with the potential-divider bridge, and found to be in close agreement.

Discussion on the papers “A new null method of testing instrument transformers, and its application”, by Mr. Shotter, “Some accessory apparatus for precise measurements of alternating current”, by Messrs. Spilsbury and Arnold, and “Precision testing of current transformers”, by Dr. Arnold, before the Meter and Instrument Section, 7th February, 1930

Discussion on the papers “A new null method of testing instrument transformers, and its application”, by Mr. Shotter, “Some accessory apparatus for precise measurements of alternating current”, by Messrs. Spilsbury and Arnold, and “Precision testing of current transformers”, by Dr. Arnold, before the Meter and Instrument Section, 7th February, 1930

The testing of current transformers

A method of testing the phase angle and ratio of current transformers using a polyphase wattmeter and phase shifter is described. Results of tests are given showing the effect, on the accuracy of a transformer, of allowing it to be run with the secondary open-circuited.