Abstract: A bypass conduit is connected to a primary conduit and has tandem reservoirs formed therein. Continuous measurements are taken from the respective reservoirs of the electrical current generated by the relaxing fluid therein and flowing to ground. These respective measurements are inputted to a microcomputer through respective electrometer elements and converted into a single measure of charge density along with readings of the moisture, conductivity and temperature of the fluid. In a preferred embodiment, the fluid constitutes the oil (or other coolant) circulated in respective conduits between a power transformer and an external heat exchanger. The microcomputer may trigger an alarm (or a control mechanism) whenever the charge density generated in the circulating coolant reaches a predetermined threshold level, thereby avoiding a potential hazardous condition due to the build-up of static electrical charges in the protected transformer or other device.