Calibrating Sensors to Measure Braking Chopper Currents in DC Traction Units

A large part of the energy involved in the braking stage of conventional DC railway traction units is dissipated in rheostat resistors, which is controlled by means of a braking chopper. A setup was developed to calibrate transducers used to measure the resulting high-current chopped DC current signals under conditions mimicking the real application. Preliminary results indicate that the reference transducer used in this setup can accurately measure chopped signals with magnitudes up to at least 250 A and pulse repetition rates up to 500 Hz with uncertainties better than 0.01 %.

Calibrating Sensors to Measure Braking Chopper Currents in DC Traction Units

A large part of the energy involved in the braking stage of conventional DC railway traction units is dissipated in rheostat resistors, which is controlled by means of a braking chopper. A setup was developed to calibrate transducers used to measure the resulting high-current chopped DC current signals under conditions mimicking the real application. Preliminary results indicate that the reference transducer used in this setup can accurately measure chopped signals with magnitudes up to at least 250 A and pulse repetition rates up to 500 Hz with uncertainties better than 0.01 %.

Wideband Self-Calibration Method of Inductive CTs and Verification of Determined Values of Current and Phase Errors at Harmonics for Transformation of Distorted Current

Self-calibration of a designed wideband inductive current transformer (CT) was carried out in the ampere-turns condition. This method does not require a reference transducer. The values of current and phase errors at the harmonics of frequencies from 100 Hz to 5 kHz were determined for the distorted primary current of the rated main frequency equal to 50 Hz. These results were verified based on the comparison of values measured between two CTs and calculated as the difference between values obtained from their calibration. Moreover, from vectorial diagrams drawn for transformation of the higher harmonics, the source of the change in the values of current and phase errors with frequency is explained. Furthermore, the method for calculation of the values of the corresponding harmonics of the current associated with the active power losses in the core and the magnetization current is presented.

Application of an Improved Model for the Determination of Acoustic Resonances in Indicator Passages for Combustion Pressure Measurements

The acoustic resonances in indicator passages are often modeled using either a Helmholtz or a so called organ pipe acoustical model. However, in practice these models often indicate natural frequencies which are too high. This paper proposes the Bergh and Tijdeman model [1] which is more accurate and which was originally developed for pressure measurements in turbomachinery. This paper presents the theoretical basis for the Berg / Tijdeman model and then uses it to explore signal distortion from a variety of indicator passage geometries. In order to validate the approach, a flush-mounted water-cooled Kistler reference transducer was used to measure accurate in-cylinder combustion data in an automotive Diesel engine. An additional sensor was recess mounted with passages of different geometries. The Bergh Tijdeman model was then applied to investigate the acoustic distortion of the indicator passages. The results show excellent agreement with the experimental data, which are much closer than using the Helmholtz or the organ pipe model. Further the Bergh and Tijdeman model is applied to complex indicator passage geometries with multiple cavities. Again, for comparison, a flush-mounted Kistler reference transducer was used to measure accurate in-cylinder combustion data in a large-bore natural gas engine. Three additional sensors were mounted using different indicator passage geometries. The engine was operated under base line and knocking combustion conditions. The Bergh Tijdeman model was then applied to model the acoustic distortion of the three indicator passages and again showed good agreement with the experimental data. Finally, the paper proposes simple rules for implementing indicator passages in large gas engines.