BC Hydro conquers stray voltage on dairy farms

BC Hydro is one of the first utilities in Canada to test and install equipment on its electrical distribution system for the reduction of stray voltage. The equipment is called a Variable Threshold Neutral Isolator (VT/NI). There are several types of stray voltage which can be felt by some farm animals, such as cows. They are (1) Neutral-to-earth Voltage, (2) Transient Voltage, (3) Induced Voltage, or (4) Ground Loops. Expert believe that cows are sensitive to stray voltage down to one mA at two milliseconds of duration that could possibly impact milk production. Several methods have been developed for reducing stray voltage on farms and most of them involve devices placed on the secondary electrical service. They range from simply balancing loads on each 120-volt leg to installing saturable reactors. The latest technique involves sophisticated, intelligent electronic equipment that constantly injects voltages equal and opposite to any voltages that occur on any conductive surfaces on farms. The variable threshold neutral isolator (VT/NI) , generally installed on the utility pole beneath the farm's distribution transformer, and recently improved by BC Hydro, is described. Unlike some of the other newer systems, to date VT/NI has proven to be a consistently reliable and cost-effective technique for mitigating stray voltage over time. 3 figs