Measurement Techniques for Instrument Transformers
Summary
Instrument transformers, encompassing current transformers (CTs) and voltage transformers (VTs), are indispensable for scaling high-voltage or high-current signals to levels suitable for protection, metering and power-quality monitoring. Measurement techniques have evolved from classical excitation and comparative methods to wideband frequency-response analyses that characterise behaviour from power-frequency up to kilohertz ranges. Modern approaches address nonlinearities of the ferromagnetic core, compensating harmonic distortion via adaptive polynomial models or simplified nonlinear representations. Self-calibration methods enable in-situ assessment without external references, enhancing utility in remote or automated systems. High-frequency techniques employ sine-sweep and multi-tone excitations, revealing resonance phenomena and phase displacement at harmonics. Concurrently, digital signal processing and black-box compensation schemes deliver real-time correction of transformation errors, facilitating accurate harmonic and interharmonic measurements. These advances underpin reliable power-quality assessment amid increasing renewable integration and non-linear loads, supporting global grid stability and enabling smart-grid applications such as phasor measurement units and distributed monitoring devices.
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Measurement Techniques for Instrument Transformers publication trend
The graph below shows the total number of articles in measurement techniques for instrument transformers across all publications each year (not limited to Nature Index journals).
Technical terms
Instrument transformer: A device that steps down high currents or voltages to measurable levels for protection and metering equipment.
Current transformer (CT): A transformer designed to produce a scaled secondary current proportional to a primary current.
Voltage transformer (VT): A transformer that provides a reduced secondary voltage proportional to a high primary voltage.
Harmonic distortion: Deviation from a pure sinusoid caused by nonlinearities, producing integer multiples of the fundamental frequency.
Frequency response: The variation of a transformer’s amplitude and phase characteristics over a range of frequencies.
Volterra series: A mathematical model for representing weakly nonlinear, time-invariant systems using a series of integral kernels.
References
- Adaptive Polynomial Harmonic Distortion Compensation in Current and Voltage Transformers Through Iteratively Updated QR Factorization. IEEE Transactions on Instrumentation and Measurement (2023).
- Measurement Based Linear and Nonlinear Time Invariant Representations for High Voltage Inductive Transformer Frequency Response up to 10 kHz. IEEE Access (2024).
- Wideband Self-Calibration Method of Inductive CTs and Verification of Determined Values of Current and Phase Errors at Harmonics for Transformation of Distorted Current. Sensors (2020).
- How Instrument Transformers Influence Power Quality Measurements: A Proposal of Accuracy Verification Tests. Sensors (2022).
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