Fabrication of a current transformer test set calibrator and its applications

Abstract

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.

Difficulties in producing CT caused by the current ratio regulation in IEC standard and suggestions of modification

“…Nevertheless, it is impossible to eliminate the current error across the entire range owing to the nonlinear properties of the core materials. The permeability of ferromagnetic materials varies with different measured currents, and the exciting currents are different, thus, the errors are different [10]. It is difficult to achieve consistent error values within this range using a fixed turns ratio [11,12].…”

“…The measured current is the exciting current converted to the secondary side, and the exciting current on the primary side can be determined based on the turns ratio. The turns correction coefficient m can be derived from (10), and then the turns ratio k N and the number of secondary winding turns N 2 can be calculated using (12) with the rated current ratio k C . Certainly, this process of exciting current measurement and turns adjustment involves iterative correction, in which the CT calibration method plays a substantial role [18,19].…”

Methodological Aspects of Using Comparators for Metrological Traceability of Instrument Transformers

“…To create a procedure for verifying the correctness of the readout of the comparison device, the metrologist must analyze the sources of uncertainty of such means [15][16][17]. Several methods for calibrating comparison devices have been developed [18][19][20][21][22][23], and all they have certain features. This chapter proposes methods for characterizing comparators of almost identical alternating currents or voltages to establish the metrological traceability when using such instruments for the calibration of CTs or VTs.…”

Method for online measurement of optical current transformer onsite errors

“…Current transformers (CT) are an extremely important apparatus in electrical power systems, which are used to transfer power system currents to lower magnitudes, and to provide galvanic isolation between the power systems [1][2][3]. With the development of smart grids and intelligent substations, optical current transformers (OCTs), usually based on the Faraday effect [4], have attracted increasing attention because of their advanced advantages such as excellent electric insulation and immunity to electromagnetic interference by the dielectric nature of optical fibers, freedom from magnetic saturation, a high linear response over a wide frequency bandwidth, and their suitability for digital devices in intelligent substations [5][6][7][8].…”