Jan Sroka

Electric and magnetic field measurements performed in the high-current la-boratory (HCL) revealed recurring disturbances in the form of damped oscillations. An analysis of the test procedures and a detailed investigation of the system configuration in-dicated that the likely cause of these disturbances was the asynchronous operation of con-tacts in a medium-voltage (MV) vacuum circuit breaker. This hypothesis was verified us-ing both field and circuit simulations. The non-uniform test circuit of the HCL was repre-sented as a cascaded equivalent model based on segmentation and distributed electrical parameters. The obtained simulation results confirmed the proposed hypothesis and high-lighted the significant impact of the switching process on the generation of electromagnet-ic disturbances in the MV supply path.

This article deals with the issue of identification and quantification of uncertainty components in shielding effectiveness measurements carried out in accordance with the standard EN 50147-1. It describes problems accompanying such tasks and presents baseline uncertainty budget. Issues related to uncertainty of the antenna factor, uncertainty of measurement receiver and mismatch of the measurement path were taken into consideration. Further topics requiring consideration have also been identified, such as the type A evaluation of uncertainty, variations of the reflection coefficient at the input of antenna and uncertainties of measurements of S-parameters used to calculate mismatch of the measurement path.

The electric arc is a very complex phenomenon, therefore numerical modeling is not an easy issue. The aim of this article is to present the phenomenon known as showering arc and to compare the results obtained during laboratory measurements with simulations using ready-made element offered in the program Matlab Simulink. This phenomenon is based on a rapid ignition and extinguishing of the electric arc between the relay contacts when opening them. The effect of this phenomenon are electromagnetic disturbances, the maximum voltage of which might be many times greater than the nominal voltage. For this reason, these disturbances may cause malfunctioning electronic devices or lead to its damage.

The article deals with the issue of electromagnetic disturbances caused by electromechanical relays. Electromagnetic compatibility (EMC) is important for the reliable work of electrical and electronic devices. Our research focused on the low-voltage relay, which is the source of electrical fast transients (EFT)/burst disturbances. The voltage and current waveforms were tested on the constructed stand while opening the relays’ contacts. We investigated one-circuit topology with varied element parameters in order to observe their influence on the burst phenomenon. The new technologies in the measurement equipment allow us to observe many detailed aspects of the burst phenomenon, which were not reported up to now. In order to analyze the disturbances, they have been fragmented into restoration, ignition and arc times. The number of disturbance cycles differs depending on the value of the circuit capacitance on the load side. The effect of capacity on times of restoration, ignition and burning arc was also observed. The division into cycles allowed us to observe changes in the studied phenomenon along with the increased distance between the relay contacts during its opening. There were also discrepancies between the presentation of the phenomenon in the standard defining the method of measuring the resistance to interference EFT/burst and the measurement results.

The paper is a continuation of the research works of the authors. The aim of it is identifying the electromagnetic environment in which the control equipment of the short-circuit test stand operates. Exceptional attention was devoted to the issues related to the operation of the time-phase controller system. Measurements and identification of the electromagnetic environment were carried out on a specific short-circuit test stand, where short-circuit currents are generated by the medium-voltage (MV) short-circuit transformers. Short circuit tests are always preceded by powering the MV side of the test transformer by unloading the low-voltage (LV) side. Thereafter, the controller must wait for the release of the operator to start the test. Sometimes an electromagnetically disturbed controller starts the test without release. Such situation is undesired and can be destructive for the tested objects. Identification of the transient fields during the powering of the test transformer is indispensable for assessing the hazard of EM interference of the controller. Earlier research by the authors showed that the repetitive damped oscillating waves (DOW) are a component of the electromagnetic environment. Adequate instrumentation to cope with the problem are D-dot and B-dot field probes is needed. The paper reports such measurements along with recording the voltage signals. It was suspected that repetitive ignition and extinction of the short arc by closing the circuit breaker in the MV circuit is the origin of the DOW. Additional investigation of the circuit breaker in stand-alone operation is excluded in this hypothesis. The only possibility of the DOW is pulse traveling back and forth in the MV circuit, which is a line with distributed parameters.

The paper presents problems related to the processing of signals recorded with differential field probes E and H. The fundamental problem to which special attention has been paid is the result of the integration operation. Due to the presence of constant/slowly-varying components in the raw signal, there is a drift present in the outcome of integration. This line wander can be enormous. This is particularly evident if the integration is performed in a standard manner, uniformly over the entire recorded waveform. The paper contains the Authors’ proposition to segment the signal and perform the integration independently in each of the sub-regions. This approach is based on the assumption of a local mean value instead of its global character for the recorded waveform. Although this leads to more complex signal processing, it gives significantly better results as it is suppressing the deterioration drift in the integrated signal more than 400 times. The results are presented on laboratory recordings and outdoor tests. In the first case, voltage pulses with durations of about 50 ns and rise times in the range of single ns were recorded. In the second case, high-energy electromagnetic pulse signals were used. It was formed by sinusoidal waveforms packets of 3 GHz frequency with a single packet duration of 5 μs and packet repetition frequency f ≤ 300 Hz.

Common Mode Absorption Devices CMADs are absorbing clamps required in the set ups for measurement of radiated disturbances. They should be verified with Vector Network Analyzers (VNAs), which unfortunately have coaxial ports. A CMAD can be connected to the VNA only if it is embedded in adapters. In the verification process, the clamp must be deembedded, i.e. the contribution of adapters must be extracted from the measured S-parameters. The Thru-Reflect-Line TRL calibration of the VNA is a suitable tool for that task, provided the necessary hardware and software facilities of the VNAs are available. If not, alternatives are required. In this paper, the alternative calibration is presented. The symmetry of adapters allows omitting the Reflect-step, providing this approach is preceded with the Short-Open-Thru-Match SOTM calibration. The method presented here consists of two steps only: the Thrustep in which adapters are cascaded face to face and the Linestep in which the rod line is inserted between the adapters. These two standards can have unknown S-parameters. Validation of the method consists in verification of the CMAD available on the market. There is entirely satisfactory convergence of the derived parameters with the data published by the manufacturer in the technical specification.