Power Over Fiber Shines at Voltage Isolation

Jul 25, 2007 11:46 AM
By Mark Valentine, Technical Editor, Power Electronics Technology

A low-level power transmission system based on laser light conducted through fiber optics promises to reduce the risk of interfacing to physical communications channels on the electrical grid. The system, available now and referred to as power over fiber (PoF) by developer RLH Industries (RLH), provides practically infinite voltage isolation capability between a central office in a telecom network, and a high-voltage transformer substation (see Figure 1). According to Jim Furey, Senior Design Engineer for RLH, this increases the protection from hazards associated with ground-potential rise (GPR), which is common to high-voltage zones such as those surrounding power transmission equipment.

Figure 1. PoF technology provides an option for terminating telcom copper lines to a modem outside the GPR zone surrounding a substation

Utilities may lease communications lanes on their infrastructures to communications providers, as well as for their own system-management functions, such as supervisory control and data acquisition (SCADA). It is often necessary to interface such grid-based networks with conventional telecom networks. In cases where conventional ac power is unavailable, and options such as solar or wind power are not practical, this could mean running copper data lines directly to substation equipment. However, such installations are particularly prone to GPR hazards.

To preclude these hazards, the PoF system enables the copper-based data link from the telecom office to terminate into a remote fiber-optic modem. This modem then receives power (and sends and receives data) at a safe distance from the substation via optical fibers (see Figure 2). The all-dielectric nature of these optical fibers provides an electrical isolation across their entire length (unlike galvanic isolation, which is restricted to the insulation barriers within a transformer).

Figure 2. A complete system based on PoF technology uses separate optical fibers for optical power delivery, optical power integrity monitoring, and optical data transfer. click image for larger version

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