Temperature control and monitoring system for power transformer windings using fiber optic sensors
On-line monitoring of function and condition parameters and the efficiency of the cooling system are key elements in determining the working condition of transformers. This paper presents the implemented hardware and software solutions for carrying out the winding temperature on-line monitoring system using fiber optic sensors. The actual winding temperature is a measurand which defines the condition, load capacity and operating life of transformers. By carrying out the temperature control and monitoring system for power transformer windings using fiber optic sensors, ICMET Craiova aligned itself to the requirements of the international standards.
Design and Performance Test for Fiber Bragg Grating Sensors of Transformer Winding Temperature Measurement
In order to directly measure the winding temperature of oil-immersed transformers,the winding electromagnetic wire with built-in fiber Bragg grating(FBG) sensors was designed and its production process was discussed.The structure of winding electromagnetic wire and the winding production process were improved.The strain of FBG sensors was monitored in the electromagnetic wire production process,and the temperature sensing performances of FBG sensors were obtained.The results show that the strain in the electromagnetic wire production process has minor impact on the mechanical strength and the temperature sensing performances of FBG sensors.The linearity of the FBG sensors is above 0.99,and the sensitivity is about 10 pm/°C,and the accuracy is about ±0.5 °C,indicating that the winding electromagnetic wire built-in FBG sensors can be used to measure the winding temperature of oil-immersed transformers accurately.
Two-dimensional gravitational anomalies, Schwinger terms and dispersion relations
Abstract We are dealing with two-dimensional gravitational anomalies, specifically with the Einstein anomaly and the Weyl anomaly, and we show that they are fully determined by dispersion relations independent of any renormalization procedure (or ultraviolet regularization). The origin of the anomalies is the existence of a superconvergence sum rule for the imaginary part of the relevant formfactor. In the zero mass limit the imaginary part of the formfactor approaches a δ-function singularity at zero momentum squared, exhibiting in this way the infrared feature of the gravitational anomalies. We find an equivalence between the dispersive approach and the dimensional regularization procedure. The Schwinger terms appearing in the equal time commutators of the energy momentum tensors can be calculated by the same dispersive method. Although all computations are performed in two dimensions the method is expected to work in higher dimensions too.