Neutral Grounding Resistors
By pdamon28 March 2016
Testek, a supplier of custom test equipment for industrial, agricultural, military, marine and automotive applications, has developed a line of neutral grounding resistors to complement its range of industrial load banks. The neutral grounding resistors are used in industrial power systems for resistance grounding of wye-connected generators or transformers.
Testek said the use of resistance grounding versus conventional solid grounding limits the ground fault current to a low, safe level — typically 25 to 400 amps — which is sufficient enough to operate protective relays while still preventing large and damaging fault currents, which can reach 10,000 amps or more. The resistors are rated in line-to-neutral voltage, initial fault current and maximum time on.
The resistors are designed to dissipate the required energy without exceeding the temperature limitations as defined by IEEE Standard 32-1972. That includes, the company said, a short time (10 seconds to 60 seconds maximum) temperature rise of 760°C, an extended time (greater than 10 minutes but no more than an average of 90 days per year) of 610° C and a continuous (an indefinite time period) maximum temperature of 385°C.
Testek’s resistor coils incorporate stainless steel edgewound elements wrapped around high temperature refractory ceramic cores, supported on stainless steel rods. Glazed porcelain insulators are attached to the end of each coil and are fastened to a heavy gage, corrosion resistant frame. The resistor elements are joined in series or parallel by stainless steel busbars which are welded in place to form a continuous electrical path.
Enclosures are manufactured from corrosion resistant galvanized steel (standard) with screened or louvered side covers. Enclosure finishes include powder coated steel, aluminum, or stainless steel. A wide variety of other options are available including entrance bushings, current transformers, elevating stands, and/or disconnect switches, the company said.