Power line transients on a bus due to the operation of the electrical systems

Newly installed electronic systems on board vehicles, in general, and buses, in particular, require special consideration with respect to EMC. Collocated systems, often consuming high currents, form a significant source of switching transients on the vehicle. Sensitive electronic systems, when powered from the same power source, may suffer interference, and even damage to sensitive circuits, from those transients. Awareness to this concern led to the development of several international standards, e.g.: ISO-7637-3 and ISO-7537-3, which include specifications of transients on power lines, for the purpose of incorporating immunity measures into systems to be installed on those platforms. A newly developed vehicular system was intended for installation on buses in Israel. This system, the proper performance of which was considered of utmost importance, was required to withstand, while in operation, the electromagnetic environment in the vehicle, in particular-the transients conducted on power lines. Since, at the time, no EMI standard specifying transients on such platforms was identified, the ISO standards were adopted, However, it was deduced that actual measurements should be carried out too, in order to investigate experimentally the actual level of interference on the power lines of the bus. This paper presents the results of that investigation, and provides some comparison to the test levels as depicted in the ISO standards. The comparison shows that in most cases, the actual transient levels were significantly lower than those specified in the standards.