Susceptibility Issues of Control Instrumentation in Electromagnetic Environment of High Current Laboratory

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.