Patented wiring system reduces ground currents to 0, extends motor life

Today’s proliferation of variable-frequency drives (VFDs), uninterruptible power supplies (UPSs), servo systems, and computer-controlled equipment generate high-frequency ground currents, which traditionally have been grounded to “earth” for safety reasons.

06/23/2005


Today’s proliferation of variable-frequency drives (VFDs), uninterruptible power supplies (UPSs), servo systems, and computer-controlled equipment generates high-frequency ground currents, which traditionally have been grounded to “earth” for safety reasons. However, direct physical grounding of equipment can adversely affect other sensitive electrical/electronic equipment, claims Zero Ground LLC , the developer of a special wire/shielded conduit system—patented for its technology and installation method—that reportedly eliminates ground currents and related issues.

motors, drives, motion control

Cables and conduits of Zero Ground System Solution are UL listed and approved for use in hazardous areas (Class 1, Div. II).

Zero Ground (ZG) “System Solution” takes a different approach—accomplishing grounding through the cable system rather than at the component, while meeting grounding requirements of NEC 250. Other differentiators from conventional wiring include use and rating of ground wiring on the input and output of a drive (not only on output); also ability to retain what’s inside the cables as well as keep interference outside. The solution typically includes cabling that runs from drive to motor, drive to power supply, as well as a return path.

ZG System Solution is designed for motors, VFDs, and equipment using IGBTs (and other power-switching devices) in applications rated 1-500 hp at 480 V ac (3-phase) and 1-250 hp at 240 V (3 phase) input. All cables are rated for 2,000 V ac rms. The system works without active components, such as filters, and consists of phase conductor cables, flexible conduit shielded for EMI/RFI, and standard industry fittings/installation components. It outperforms input line reactors, drive output filter, and EMI/RFI filters, according to the manufacturer.

Because of its “more effective ground,” ZG System Solution reportedly:

  • Reduces unplanned downtime and maintenance costs associated with VFD/IGBT wiring systems;

  • Reduces high-frequency ground currents to zero;

  • Extends motor life;

  • Directs hard fault currents away from hazardous locations; and

  • Reduces motor bearing currents.

Other system benefits include:

  • Containing/mitigating stray capacitance, inductively or capacitively coupled energy, and common mode voltage;

  • Minimizing corona inception voltage (CIV) in motor cable leads; and

  • Eliminating motor frame voltage to ground, crosstalk between adjacent cables, and stray voltage.

Testing done at motor and drive manufacturers’ labs supports Zero Ground’s claims.

—Frank J. Bartos, executive editor, Control Engineering, fbartos@reedbusiness.com





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