LIGHTNING CONSULTING REQUIRES A THOROUGH KNOWLEDGE OF GROUND POTENTIAL RISE (GPR) AND THE EFFECTS OF HIGH FREQUENCY CURRENTS ON GROUNDING SYSTEMS AND EQUIPMENT

FOR IMMEDIATE RELEASE
Castle Rock, Colorado, United States of America (Free-Press-Release.com) May 4, 2011 -- Ground potential rise (GPR) from lightning is costing the United States billions of dollars every year, yet few engineers are even aware of the phenomenon. The damage is passed off as the result of last night’s thunderstorm. Electrical damage from a GPR occurs when there is a potential difference between two grounded locations that have common wire (metallic) lines conntecting them. The connections may be anything from power to communications. As an example, campus type locations are the most prone to damage from lightning induced ground potential rise (GPR).

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LIGHTNING CONSULTING REQUIRES A THOROUGH KNOWLEDGE OF GROUND POTENTIAL RISE (GPR) AND THE EFFECTS OF HIGH FREQUENCY CURRENTS ON GROUNDING SYSTEMS AND EQUIPMENT

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Ohm's law dictates that a voltage potential will result when current of any magnitude or frequency flows through a grounding impedance. Power substation GPR is the result of a 60Hz earth return fault current flowing through a substation ground grid impedance. With lightning, a high-frequency l00Hz to 2.0MHz current flows through a grounding system structure and generates a high-frequency GPR. Either high-current source can damage communication equipment connected to a remote location via wire-line cable facilities.

Damage occurs when a GPR voltage appears on one side of a communications device (or service technician) within an elevated ground reference location during the instant it naturally is seeking a lower ground reference at a remote location. This is the special case of transferred potential defined in IEEE Std. 80. People and equipment most susceptible to GPR are located at power substations, power generating facilities, tall grounded radio towers such as emergency 9-1-1 locations, cellular radio sites and microwave communication buildings.

There are recorded cases where 60Hz GPR lasted more than 15 minutes, causing millions of dollars in damage. But a lightning strike GPR may last a very short time, i.e., 50 nanoseconds or less. These strikes cause most of the electronic circuit damage on wire-line facilities at radio tower sites. They may not destroy every circuit immediately, but may weaken individual components that will fail later on and is known as latent damage.

The most important consideration in protecting equipment from a possible GPR is the design of the grounding system. A lightning consulting expert will design a grounding system that will dissipate the lightning strike as fast as possible and keep the GPR as low as possible. The best grounding system design uses radials instead of ground rods and has a resistance to remote earth of less that 2 ohms if possible.

The second most important consideration for the lightning consultant when protecting equipment from a GPR is the ineffectiveness of standard electrical protection methods using gas tubes, and metal oxide varistors (MOVs). These devices normally are placed at each end of a cable communication facility and are designed to direct foreign voltage impulses into a grounding system. During a GPR, these devices merely offer an additional path to remote ground reference and actually provide a path for current to flow in the reverse direction from which they were intended to operate. The protection of equipment from even a direct incoming surge (not a GPR) requires the speed of an SAD which will fire in less than 5 nanoseconds.

Properly protected GPR locations designed by lightning consultants and maintained by trained employees will significantly reduce maintenance costs, improve productivity and increase equipment reliability. Your company's bottom line at the end of the year will directly depend upon how well your equipment was protected and the size of your maintenance budget. Acquire the services of an expert lightning consultant and improve your bottom line.

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