High Voltage Protection and Isolation of telecommunications circuits and SCADA circuits to and from Hydro Sub Stations


High Voltage Protection and Isolation of telecommunications circuits and SCADA circuits to and from Hydro Sub Stations

High Voltage Protection and Isolation of telecommunications circuits and SCADA circuits to and from Hydro Sub Stations

In order to protect the continuous service of important telecommunications and control circuits to and from Hydro Sub Stations, protective devices must be applied to prevent equipment failure and protect personnel from serious shock hazards (can be life threatening). The first electronic protection devices were designed and developed by Positron Industries Inc in the early 1970s. This equipment provided high voltage isolation from the possibilities of high voltage faults and lightning damage. All communications(wire line services) between a hydro sub station and the telephone company's central office are vulnerable to the effects of Ground Potential Rise (GPR) and lightning surges which can destroy sensitive and important telecommunications circuits. In addition, any personnel working with this equipment during these situations is at risk of serious or possibly life threatening situations.

The fundamental theory of isolation devices is to isolate any high voltages and currents from propagating from the hydro sub station towards the telephone company's central office. Since the early 1970s, most hydro utilities and telephone operating companies trained their staff to evaluate and determine the safety risks associated with Ground Potential Rise and High Voltage isolation mitigation. Currently most hydro utilities deploy isolation devices, however this is not 100% widespread. To date, only 60% to 70% of all telecommunications wire line facilities are isolation protected. The balance still rely on carbon block or gas tube shunts to ground protection. This type of protection will not fully protect against the hazards of high voltage faults and lightning strikes. Even more importantly, today's control and data circuits carry more information and control functions than in the past. As a result, these circuits are becoming even more critical and cannot be interrupted at all. With this situation it is little wonder why more emphasis is placed on fail safe wire line facilities.

Historically, many cases of personnel experiencing life threatening situations have been reported and documented. These situations are less severe than in the past, with the implementation of high voltage isolation techniques. In order to keep abreast of the latest telecommunication circuit designs and advancements, vendors who manufacture protection and isolation equipment must keep up with these advances and develop products which will meet the standards established by IEEE, National Electrical Codes (UL/CSA),FCC, and Telcordia in respect to maintaining standardized levels of equipment quality, protection and isolation design standards.

One of the most important protection theory principle is the 300 Volt point. This reference level was established to ensure 100% protection for any craftsperson working on a telecommunications facility. The fundamental basis for the 300 volt point was established in conjunction with Hydro and Telephone companies to ensure the safety of both telephone company and hydro utilitiy employees. This original standard has been accepted by all regulatory bodies in North America and has been well defined in the applicable standards of these bodies. As a very fundamental description, the 300 Volt point is a zone of influence around a hydro sub station which is dependent on the ground resistivity in ohms, the amount of fault current in amperes and will define a boundary a certain distance from the location of the ground grid of the hydro sub station. Each sub station has its own unique zone of influence since the variables explained above are different for each location.

In the past 35 years, the importance of utilizing high voltage isolation equipment has demonstrated the safety and operational performance of implementing this type of protection. It is becoming even more apparent that in the future, this type of protection will even play a grater role owing to the increased amount of information that is being transmitted down the copper wire facilities.


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