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Project: T194700 #5180

In this project, a review is conducted on different types of instrument transformers in terms of operation principles, installation, technical characteristics, and application. Comparisons among these instrument transformers are made to highlight their relative advantages and disadvantages.

Detailed descriptions are provided on traditional inductive, electronic, and modern optical structures with respect to design; permanent vs. portable types with respect to installation; and metering vs. protection classes with respect to application scenarios.

The main focus of this project is the technical characteristics of instrument transformers – in particular, the frequency response that has direct impact on power quality measurement. For various types of instrument transformers, their frequency bandwidth, accuracy level, and vulnerability to electromagnetic interference are analyzed and the typical ranges presented.

When addressing frequency response characteristics, evaluation is made on the attenuation or amplification in harmonics measurement, as well as the phase shift at both fundamental and harmonic frequencies. Due to the lack of a commonly agreed definition on reactive power in the presence of harmonics, the impact of harmonics on practical reactive power measurement is discussed for reference purposes.

Typical types of voltage and current transformers are adopted as examples in this study. Criteria of selecting instrument transformers are discussed, taking into account the technical specifications, application requirements, and operating environment.


Instrument Transformers, Frequency Response, Accuracy Class, Harmonics, Electromagnetic Interference, Power Quality, RMS.