Home

Experience

Case Histories

Facts and
Fallacy

Protection
Checklist

Protection
Guide

Reference
Material

Lightning
and
Cell Site
Articles

Training
Courses

Consulting
Services

Links

 

 

Failure to Isolate Communications from a Ground Potential Rise (GPR)
Guarantees Blackouts

by Jack Duckworth, P.E. & Ernest M. Duckworth, Jr., P.E.


In a deregulated power market, the successful power companies not only have effective power system operation and maintenance organizations, but also reliable wire-line communication networks when fiber is not cost effective. Very reliable wire-line communications networks, require a properly isolated network to avoid the effects of Ground Potential Rise (GPR).

There are many different kinds of problems that may jeopardize the integrity of wire-line communications. However, the most overlooked or ignored problem is that of the GPR which may only last for a fraction of a second, but damages or destroys wire-line communications equipment at substations, powerplants, and switchyards throughout most of the United States.

A GPR results when the earth and grounding system develops a potential from a lightning strike or a power line fault. Since all communications circuits are grounded and have a very limited resistance to a high-voltage ground spike, a GPR event causes a high-voltage current to jump normal communications isolation and energize the communications circuits as it seeks a path to a lower voltage potential ground through the communications system.

Standard protection for communication circuits, i.e., a shunting gas tube or solid state surge arrestor will fire backwards when subjected to a GPR and will provide a path for a high-voltage current to enter the communications equipment rather than blocking the current flow. The only method to protect wire-line communications equipment is to provide total isolation from ground by employing isolation equipment.

Isolation of communications facilities costs money, and the cost must be compared to the costs, as well as the legal consequences, of doing nothing. However, with rare exception, the cost of isolation is a small fraction of the costs that may be incurred from doing nothing. There are three major costs which need to be considered when evaluating the need to isolate communications equipment from GPR. The first is the direct cost of having to replace destroyed or damaged equipment. The second is the direct cost of increased power operations and lost revenue from the failure of real-time communications with critical metering and switching equipment. The third is the direct cost of a total blackout, or the death of a worker because the communications circuit electrocuted him.

PROTECTION PHILOSOPHIES

There are detailed and well established guidelines that discuss the technicalities of calculating GPR as well as how to adequately isolate against its effects. This information may be found in IEEE Std. 487-2000.

There are two protection philosophies that existed in the regulated power market, which must be carefully reexamined in the context of the new deregulated power market. The first philosophy is the ALet it fail, because the probability of failure is small@ or the ALet it fail@ philosophy. The second philosophy is the AProtect it", because although the probability is small, the cost of failure is too high@, or the AProtect it@ philosophy.

The successful market player in this new age will be the company that adopts the AProtect it@ philosophy, where the benefits of protection exceed the cost of protection. This player will insulate themselves from being the responsible company to a blackout. The unsuccessful power companies will be those who maintain the ALet it fail@ philosophy without evaluating the risks and costs of not adequately protecting their vital lines of communication and will most likely be responsible for a major blackout.

Operations and maintenance costs in the new free market will be much more highly scrutinized than they ever were in the past. The cost of failing to provide needed communications protection will not be acceptable by a nation used to total reliability in the old regulated power market.

CONCLUSIONS

In the deregulated power market, costs are being scrutinized like never before. It is one thing to gamble that the cost of replacing communications equipment damaged by GPR will be lower than the cost of protecting that equipment. However, it is a whole different matter to gamble that the increased costs for system operations, due to the loss of real time information, will be less than the cost of communications protection. It is quite evident that the electric companies using isolation equipment on their wire-line communication facilities will be better prepared to compete head-on in the new age of the deregulated power market and be less likely to be blamed for the coming blackouts.

Articles