- High Voltage Isolation and Ground Potential Rise
This article outlines the principles of High Voltage Isolation (HVI) and Ground Potential Rise (GPR). Most often questions of concern arise to anyone associated with the use of any communication signal (analog or digital) via a metallic or
fiber optic cable. Providers of telecommunications, electric service, wirelessservice or CATV, or operating in an isolated manufacturing or mining location, may be working in a hostile electric environment. An unprotected or improperly protected system is unsafe for the public and personnel, and exposes equipment to service interruptions or permanent damage.
People who are new to this profession or those who have many years of experience, whether an engineer, architect, tower erector, equipment installer, manager, tradesperson or safety supervisor, need to know or learn the following:
* what the level of exposure may be
* the protection equipment necessary for the work location
* the necessary safety precautions
* the accepted codes, standards and practices for addressing
The Basic High-Voltage Problem
When hydro power faults occur in electric power systems or when
lightningstrikes, a Ground Potential Rise (GPR) occurs, which can damage equipment and injure personnel working on the equipment unless proper isolation or protection is provided. The GPR produces a dangerous potential difference between the power stationor PCS tower and a remote ground connection located at a telephone company central office, remote terminal, distant manufacturing building or other sites. Telecommunications cable damage can occur if grounding takes place across the potential difference caused by a power fault or lightning strike.
Note: Any type of cable such as a
twisted pairtelephone cable or coaxial cableand any type of cable plant construction such as aerial, buried or underground,can experience damage. Also, any type of service can be interrupted if proper protection is not provided.
In general, special protection equipment, corporate policies and procedures are necessary to ensure the safety of personnel and protection of equipment including cables, termination equipment, etc. The reliability of communications circuits is questionable when they are in an unprotected
high voltageenvironment. Disturbances on electric power systems and lightning can cause GPR, voltage induction on telecommunications cables, power surges and high-voltage transients.
ervice Performance Objectives (SPO) or Quality of Service
Telecommunications service is expected to operate with a standard performance objective as outlined below:
* Class A - Service must be available before, during and after the fault event
* Class B – Service must function before and after, but not necessarily during, the fault event
* Class C – Interruptible, non-critical service
Levels of Protection
Standard protection devices are designed to work under the following GPR conditions:
Basic Protection Level I
* Cable stress below 300 Volts peak asymmetrical
* All SPO classes of service (A, B and C)
Basic Protection Level II
* Cable stress below 1000 Volts peak asymmetrical
* SPO Class B or Class C services
Basic Protection Level III
* Above 1000 Volts peak asymmetrical
* Should require a High Voltage Isolator (HVI)
* All SPO classes of service
Common Protection Devices
Protection devices listed below are designed to work under the following categories and levels:
Basic Protection Level I and II
* Carbon blocks
* Solid state protectors
* Solid state hybrid protectors
* Spark gaps
* Mutual Drainage Reactors (MDR)
Protection devices listed below are designed to work under the following:
Basic Protection Level III
* Neutralizing transformers (Old technology)
* Copper HV electronic isolators
* Fiber HV electronic isolators
Electric Power System Telecommunications Equipment and Applications
There are many types of protective relaying and system control equipment used in the electric power industry which require communications circuits to clear faults, operate the system, protect personnel and equipment, and maintain system reliability.
Advanced protective relaying schemes that require “Class A” communications circuits are commonly used by the electric power industry to open High Voltage (HV) circuit breakers at remote locations. Examples of this type of equipment are listed below:
Protective relaying communications
* Audio tones
* DC pilot wire relaying Applications
* Transfer trip
* Breaker failure
* Permissive overreaching
* Directional comparison
Electric power systems use “Class B” communications circuits for the following services:
* Supervisory Control and Data Acquisition (SCADA)
* Telephones for safety, metering and automation circuits
Ground Potential Rise (GPR)
Earth potential rise"The definition of GPR, according to IEEE Standards 487 and 367, is: “the product of a ground electrode impedance, referenced to remote earth, and the current that flows through that electrode impedance.” The total station GPR is equal to the product of the station ground grid impedance and that portion of the total fault current that flows through it. In other words, GPR follows basic Ohm's lawcalculations for example, voltageis equal to current times resistance. When a ground fault occurs, fault current will divide among all circuit paths back to the source including metallic, earth return, etc. Metallic return paths include overhead ground wires, multi-grounded neutrals, bonding conductors, station ground grids, messenger wires, metallic cable shields and other conducting materials.
Zone of Influence (ZOI) and the 300-Volt Point
GPR decays outward in an exponential manner. The ZOI is the area around the ground grid dissipating the energy. Depending on soil
resistivityand the size of the ground grid, the distance to the 300-Volt point on the ZOI can be calculated.
Total Electrical Cable Stress
The total electrical stress on a communications cable is the vectorial sum of the GPR and the induced voltage on the cable under fault conditions. When a faulting electric power line parallels an overhead or underground telecommunications cable, a potentially dangerous voltage is electromagnetically induced on the communications conductors. Excessive induction, by itself, can damage equipment and indirectly injure personnel.
Power and Lightning Fault Current Distribution
GPR will occur at several locations simultaneously. Fault current will divide among all circuit paths back to the source (metallic and earth return, for example) and create GPRs in the process. Metallic return paths include overhead ground wires, multi-grounded neutrals, bonds, station ground grids, and other conducting materials.
General safety considerations
Hazardous voltages can appear suddenly as a result of power faults or lightning strikes. Conductive objects (metal, damp saline soils, etc.) can become energized or carry a harmful potential that, if not properly protected, can cause serious injury. Safety of personnel can be achieved through education, proper facility design, and approved and tested insulated safety equipment. Personnel should use approved and tested rubber gloves and/or insulating blankets when working on the highvoltage interface (HVI) equipment.
Touch potential is the difference between the voltage gradient that one is standing on and the voltage gradient one is touching. A significant difference in touch potential can be hazardous. Step potential is the difference in voltage gradients between a person’s two feet. Shoes, gloves, etc. can provide insulation to touch and step potentials.
Basic personal safety equipment
:"See warning on "Proper personal protection equipment, procedures and tools can help job safety and efficiency.
Rubber Gloves, Leather Protectors and Cotton Liners
All rubber gloves and other personal protection equipment have to meet safety standards established by national organizations like the
American National Standards Institute(ANSI) and the American Society for Testing and Materials (ASTM).
Cell sites on electrical towers
Installing HVI equipment on cell sites is similar to power substation installations. Both copper and fiber optic high-voltage protection equipment are available for cell sites on regular and electric towers. Each situation needs to be carefully analyzed for possible GPR problems. Proper isolation is a primary consideration. Electric power service (i.e., 120/240 Vac) can introduce a remote ground hazard.
It is of utmost importance to always determine the proper protection scheme when dealing with telecommunication wire line circuits between Hydro sub stations, PCS towers, 911 communications centers and any location where high voltage and high current equipment is co-located with these circuits. The most effective protection will always utilize High Voltage Isolation (HVI) designs and is the most effective against high ground potential rise (GPR) and lightning strike scenarios. It is always best to design for the worst case situation, since more likely than not, this can happen. Protection against both High voltage and ground potential rise is the best precaution against equipment failures and human injury.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Ground Potential Rise — Articles on Ground Potential Rise include: * Earth potential rise * High Voltage Isolation and Ground Potential Rise … Wikipedia
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 StationsIn order to protect the continuous service of important telecommunications and control circuits to and from Hydro Sub Stations,… … Wikipedia
Earth potential rise — In electrical engineering, Earth Potential Rise (EPR) also called Ground Potential Rise (GPR) occurs when a large current flows to earth through an earth grid impedance. The potential relative to a distant point on the Earth is highest at the… … Wikipedia
Business and Industry Review — ▪ 1999 Introduction Overview Annual Average Rates of Growth of Manufacturing Output, 1980 97, Table Pattern of Output, 1994 97, Table Index Numbers of Production, Employment, and Productivity in Manufacturing Industries, Table (For Annual… … Universalium
Zoi — may refer to: * Zone of influence, see High Voltage Isolation and Ground Potential Riseee also* Zoe … Wikipedia
Electrical substation — An electrical substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several… … Wikipedia
Transformer — This article is about the electrical device. For the toy line franchise, see Transformers. For other uses, see Transformer (disambiguation). Pole mounted distribution transformer with center tapped secondary winding. This type of transformer is… … Wikipedia
Transformer types — Circuit symbols Transformer with two windings and iron core. Step down or step up transformer. The symbol shows which winding has more turns, but not usually the … Wikipedia
Shunt (electrical) — In electronics, a shunt is a device which allows electric current to pass around another point in the circuit. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a… … Wikipedia
Russia — /rush euh/, n. 1. Also called Russian Empire. Russian, Rossiya. a former empire in E Europe and N and W Asia: overthrown by the Russian Revolution 1917. Cap.: St. Petersburg (1703 1917). 2. See Union of Soviet Socialist Republics. 3. See Russian… … Universalium