All-optical differential current detection technique for unit protection applications

Abstract

In this paper we demonstrate a novel, all-optical differential current protection scheme. By monitoring the optical power reflected from two matched hybrid fiber Bragg grating current sensors and using a simple optoelectronic threshold detector, an immediate response to an increase in differential current is achieved. A preliminary laboratory embodiment is constructed in order to characterize the performance of the scheme. The proposed technique does not require a complex sensor interrogation scheme, usually characterized by a limited sampling frequency, and thus will be capable of facilitating inexpensive and fast-acting differential protection over long distances

Reliability of an all-optical differential current detection technique during environmental temperature perturbations

“…2) [11]. Under nominal (no fault) conditions, both current sensors detect identical ac currents and therefore the reflected sensor wavelengths shift identically -provided that the sensors are kept at the same temperature.…”

“…We previously investigated a number of different fault scenarios, of which three representative cases have been summarized here and are discussed briefly below [11]. As shown in TABLE I. during the pre-fault condition both sensors were subjected to voltages of the same amplitude and phase.…”

“…This translates to a modulation of the photodetector output voltage which, after thresholding, may be used for fault indication. Thus, by using two identical current sensors placed at the boundaries of the protected zone, a differential current sensor is produced, which may be utilized as a fast-acting and lightweight all-optical differential fault detection scheme [11]. …”

“…Preliminary laboratory tests of the proposed all-optical protection scheme carried out at room temperature demonstrated its high potential for fast-acting differential unit protection [11]. However, in a practical deployment, the sensors are likely to be at different temperatures due, for example, to their spatial separation within a protected zone.…”

“…Importantly, the speed of operation of an associated protection scheme could be extremely fast due to the all-optical nature of the differential calculation, and the simplicity of the optoelectronic or software threshold [11].…”