Design and Implementation of a Passive Autoranging Circuit for Hybrid FBG-PZT Photonic Current Transducer

Abstract

In this paper, we present a novel technique for passively autoranging a photonic current transducer (PCT) that incorporates a current transformer (CT), piezoelectric transducer (PZT) and fiber Bragg grating (FBG). Due to the usage of single-mode fiber and FBG, multiple PCTs can be interconnected and distributed over a long distance, for example along a power network, greatly reducing the cost of sensor deployment and offering other unique advantages. The autoranging technique relies on the usage of multiple, serially connected CT burden resistors and associated static MOSFET switches to realize instantaneous shortening of the resistors in response to increasing measured current. This functionality is realized passively, utilizing a modular, μW-power comparator circuit that powers itself from the electrical energy supplied by the CT within a small fraction of the 50/60 Hz cycle. The resultant instantaneous changes in sensor gain will be ultimately detected by the central FBG interrogator through real-time analysis of the optical signals and will be used to apply appropriate gain scaling for each sensor. The technique will facilitate the usage of a single PCT to cover an extended dynamic range of the measurement that is required to realize a combined metering- and protection-class current sensor. This paper is limited to the description of the design process, construction, and testing of a prototype passive autoranging circuitry for integration with the PCT. The two-stage circuitry that is based on two burden resistors, 1 Ω and 10 Ω, is used to prove the concept and demonstrate the practically achievable circuit characteristics. It is shown that the circuit correctly reacts to input current threshold breaches of approximately 2 A and 20 A within a 3 ms reaction time. The circuit produces distinct voltage dips across burden resistors that will be used for signal scaling by the FBG interrogator.

The Performance of a Passive Autoranging Method for a Photonic Current Transducer

“…However, FBG/PZT-based optical current sensors (OCSs) and photonic current transducers (PCTs) face constraints in dynamic range and accuracy when compared to fiber-optic current sensor (FOCS)-based NCITs [5,11,12]. Notably, meeting the combined 0,2S and 5P20 class standards [13], which demand both a wide dynamic range and high accuracy across an extended current range, remains a challenge for current technology [14,15]. The PCT technology solution previously proposed by the authors adheres to the IEC/IEEE standards, demonstrating the potential to comply with either the 5P protection class or the 0,2 metering class.…”

“…Furthermore, employing two or more FBGs reduces the overall optical bandwidth, limiting the number of sensors that can be addressed by a single interrogation unit. The novel autoranging technique proposed by the authors of [15] has the potential to concurrently achieve both 0,2S and 5P20 classes with a single photonic current transducer (PCT) by dynamically extending the measurement range.…”

“…The foundational work by Mir, Niewczas, and Fusiek [15] introduced a novel technique for autoranging an FBG/PZT-based optical current sensor in which a passive autoranging (AR) circuit can be integrated with a CT, burden resistors, and a low-voltage transducer (LVT), resulting in an extended-range PCT. The LVT is a low-voltage variant of a PZT/FBG transducer [9,10,15]. The integration of autoranging capabilities into these sensors presents a breakthrough, enabling passive adjustments to measurement sensitivity and range.…”

“…The autoranging enhancement brings the potential to position the FBG/PZT-based optical sensor as a competitive alternative to FOCS-based NCITs, additionally offering multiplexing and remote interrogation capabilities. To validate this approach and demonstrate circuit characteristics, a prototype AR circuit was previously implemented in a laboratory using two MOSFET switches and serially connected burden resistors [15].…”

“…As before, the PCT utilizes a CT, PZT, and FBG. The autoranging technique incorporates static MOSFET switches to instantaneously short individual serially connected CT burdens (1 Ω and 16 Ω in the modified circuit) [15]. The circuit is now complemented by an algorithm capable of detecting distinct switching events produced by the AR circuit to apply appropriate scaling factors to reconstruct the measured current from optical signals.…”