ABSTRACT
Instrument transformers (ITs) play a key role in electrical power systems, facilitating the accurate monitoring and measurement of electrical quantities. They are essential for measurement, protection, and metering in transmission and distribution grids and accurately reducing the grid voltage and current for low-voltage input instrumentation. With the increase in renewable energy sources, electronic converters, and electric vehicles connected to power grids, ITs now face challenging distorted conditions that differ from the nominal ones. The study presented in this paper is a collaborative work between national metrology institutes and universities that analyzes IT performance in measuring distorted voltages and currents in medium-voltage grids under realistic conditions. Both current and voltage measuring transformers are examined, considering influence quantities like the temperature, mechanical vibration, burden, adjacent phases, and proximity effects. The study provides detailed insights into measurement setups and procedures, and it quantifies potential errors arising from IT behavior in measuring distorted signals in the presence of the various considered influence quantities and their combinations. The main findings reveal that the temperature has the most evident impact on the inductive voltage transformer performance, as well as the burden, causing significant changes in ratio error and phase displacement at the lower temperatures. As for low-power ITs, establishing a priori the effects of adjacent phases and proximity on the frequency responses of low-power ITs is a complex matter, because of their different characteristics and construction solutions.
ABSTRACT
OBJECTIVE: Evaluating preepiglottic space involvement in laryngeal cancer by CT may lead misinterpretation. We sought to understand the causes of misinterpretation in evaluating the preepiglottic space by CT and assessed the effects of misinterpretation in treatment plans of patients with laryngeal squamous cell carcinomas. METHODS: Specimen histopathology reports of 102 (99 male, 3 female) patients who underwent total or partial laryngectomy due to supraglottic and/or transglottic laryngeal carcinoma were reviewed. Neck CTs were also re-assessed for preepiglottic space involvement by three radiologists. The initial surgical treatment choices were re-examined according to the current radiological evaluation in combination with pathological results of the specimens and physical examination findings in the patients. Interobserver agreement regarding image interpretation was based on a kappa analysis. RESULTS: The interclass correlation coefficient in predicting preepiglottic space invasion was 0.74; this was considered 'good.' Among the three radiologists, sensitivity, specificity, accuracy of CT in detecting preepiglottic space involvement were 86-93%, 75-93%, and 77-93%, respectively, while the negative and positive predictive values were 97-98% and 38-50%, respectively. Given the previous treatments applied, false-positive diagnoses for PES involvement resulted in overtreatment in 2.9% of cases. False-negative diagnoses of PES involvement (1.9% of cases) did not result in any undertreatment. CONCLUSIONS: Although CT is a practical and inexpensive imaging tool for evaluating laryngeal carcinomas, the PPV of CT in assessing preepiglottic space invasion, especially in advanced tumors, is low and may lead to overtreatment.
