Konrad Janisz

Solid-state switch for capacitors bank used in reactive power compensation

This paper describes a new concept of a three phase switch dedicated for low voltage capacitor bank for reactive power compensation (RPC). The switch combines electromagnetic relay with a solid-state valve. In contrast to state-of-the-art solution where thyristors are used, the proposed device utilizes fully controllable IGBT transistors. IGBT gives possibility to turn-on the switch without inrush current at the voltage zero-crossing, and moreover, turn-off in a moment which ensures that capacitors in all phases are discharged and there is zero voltage across its terminals. This solves well known phenomena of thyristor based solutions, where an increased voltage stress for a switch and capacitor exists. The advantage of the proposed circuit is that the capacitor bank can be turned on immediately after its disconnection. As a result, response time of reactive power compensation system can be significantly shortened. Reactive power compensators (RPC) capacitors are often dealing with distorted grid voltages. Therefore the detuning inductors are required to cut-off higher harmonics currents. It creates a problem for the proposed hybrid switch with interrupting inductive currents. Paper describes structure of hybrid switch and its operation with capacitor bank and detuning inductor. Descriptions are verified by laboratory model measurements.

Low-cost planar coupled-line sensor for permittivity measurement of low-loss dielectric materials in a wide frequency range

This paper presents novel non-destructive method for dielectric sample characterization in a wide frequency range. Recently proposed sensors based on differentially excited shortended coupled-line section has been used to determine the permittivity of an unknown dielectric sample. A simplified calibration and calculation procedure is proposed in the presented approach while maintaining a good measurement accuracy. Since the sample permittivity is obtained based on the measurement of the odd-mode effective permittivity, which is mainly related to the mutual capacitance between coupled strips, high sensitivity on the covering sample is achieved. The proposed measurement technique has been theoretically investigated and experimentally verified. A good agreement between predicted and obtained from measurement results has been obtained in a wide frequency range up to 7 GHz with percent error not greater than ± 5%.