Abstract
This paper explores the mechanism for the harmonic voltage measurement error (HVME) of a capacitor voltage transformer (CVT) in a comprehensive way and develops a practical error correction method to improve the harmonic measurement performance of a CVT. The harmonic equivalent circuit (HEC) of CVTs with different types of dampers are established and the parameter value calculation methods of the circuit elements are presented. Characteristics of the individual inherent resonance mode of the HEC, including the resonant frequency, the resonant type and the circuit elements involved, are analyzed systematically. Centered on resonance mode formulation, an universal error correction method for CVTs in measuring harmonic voltage is proposed based on the piecewise fitting of the transformation ratio. A physical experimental platform available for low-voltage CVTs is developed in laboratory, which utilizes a 10-kV harmonic generator and a step-up transformer to provide harmonic signals with high voltage level. Moreover, a novel experimental scheme for testing the HVME of high-voltage CVTs is proposed based on alternating current/direct current (AC/DC) filters. Experiments are conducted on these experimental platforms to test the HVME of a 35-kV CVT in laboratory and a 525-kV CVT in a back-to-back DC converter station. The experimental results verify the validity of the built HECs of CVTs, the resonant mode analysis results and the resonant frequency calculation method. Finally, the effectiveness of the proposed harmonic error correction method is proved by several examples.
Highlights
capacitor voltage transformer (CVT) havs been widely adopted in high-voltage neutral grounding power networks to provide voltage signal with an apprciated accuracy to the energy metering system, relay protection system etc., due to its overwhelming advantages such as small volume, light weight, less maintenance and high margin of electric field intensity [1,2,3]
This paper studies the harmonic voltage measurement error of a CVT in a comprehensive and in-depth way and, on this basis, presents a practical error correction method that can improve the harmonic measurement accuracy to an extent acceptable in engineering
We propose a simple and effective scheme to address the problem of harmonic voltage amplification and attenuation, improving the safety of the experimental platform and the accuracy of the experimental results; 3) We present a novel harmonic voltage measurement method based on the alternating current/ direct current (AC/DC) filters for the high-voltage DC (HVDC) power transmission systems [21, 22]
Summary
CVT havs been widely adopted in high-voltage neutral grounding power networks to provide voltage signal with an apprciated accuracy to the energy metering system, relay protection system etc., due to its overwhelming advantages such as small volume, light weight, less maintenance and high margin of electric field intensity [1,2,3]. References [10] and [11] focus on the effect of the stray and coupling capacitance on the harmonic voltage transfer function of the CVT, and [12] confirms that the measurement error mainly comes from the excitation impedance and the capacitance divider These studies are case specific and take only some of the influence factors into consideration, being unable to serve as the general basis for the quantitative analysis of the HVME. We propose a simple and effective scheme to address the problem of harmonic voltage amplification and attenuation, improving the safety of the experimental platform and the accuracy of the experimental results; 3) We present a novel harmonic voltage measurement method based on the alternating current/ direct current (AC/DC) filters for the high-voltage DC (HVDC) power transmission systems [21, 22] This simple and practical method can provide accurate harmonic voltage reference signal for the determination of the HVME of CVT in high-voltage systems.
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