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  • 7/30/2019 Resonant Grounding





    1.1 Background of StudyIntroduction

    A large majority of three phase power system faults involves ground; therefore, a

    thorough knowledge of grounding methods and associated zero sequence current

    sources is essential to the effective protection of the power system. The particular

    method of system grounding selected will vary according to the resulting

    characteristics desired by the application. A grounding method can be used either

    to limit or entirely eliminate the level of ground fault current available so as to

    protect expensive equipment from damage under the most likely fault scenarios.

    Or, conversely, it can be used to ensure an adequate current level to aid in the

    prompt detection and isolation of fault conditions. The grounding method

    employed also may be used to reduce transient over voltages, as well as to

    facilitate compliance with regulations affecting personnel safety. With

    retirements, new hires, reorganization, cross training, and so on, this subject, like

    many others, requires regular review to maintain the experience level of our

    protection engineers.

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    1.2 Statement of Problem

    Inefficiency of grounding system in Nigerias power system.

    1.3 Purpose of Study

    The purpose of this project is to give indept insight on resonant grounding

    methods, sources of ground current, ground current flow in the power system,

    and how each impacts protective relaying with a ground fault Neutralizer used in

    Resonant grounding.

    1.4 Significance of Study

    Resonant Grounding will help the government and Power station save because

    resonant grounding combined with residual current compensation is to be one of

    the most cost efficient supply quality investments. Outage-rates will also drop

    substantially. The non-tripping fault handling also allow for full life cycle usage of

    grid assets, without jeopardizing power supply quality.

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    1.5 Scope of Study

    The aim of this project is to give insight on the efficiency, safety and the

    workability of applying resonant grounding in our power system, Using the 330KV

    transmission network in the EGBIN thermal station as a case study.

    1.5 Definition OF Terms

    Distribution Network means any connection of cables, service lines and

    overhead lines, electrical apparatus/equipment and having design voltage of

    33KV and below used to transport electric power on a distribution system

    Distribution Substation A HV Station which receives power at high voltage and

    transforms it to low voltage for supply to consumers[1].

    Earth Electrode A conducting element or electrically bonded group of conducting

    elements in electrical contact with the earth designed and generally used for

    dispersing electric currents into the earth[1].

    Earthing System A conducting electrode usually made of steel rod, steel strip,

    copper wire, or copper strip, buried in the body of the earth for the purpose of

    conducting electric current from the connected plants earthing conductors to


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    HV Station (including Distribution Sub-Station) Earthing System

    An electrically bonded arrangement of conductors including earth electrodes

    buried in the earth to which metallic fixtures and fittings of the HV Station are

    connected to conduct fault current from the station high voltage conductors to

    the earth[2].

    HV Structure Earthing System A conductor in contact with the earth which forms

    part of a structure supporting HVplant (e.g. a steel pole or transmission tower) or

    an earthing conductor or a small number of conductors in contact with the earth

    associated with an HVsupporting structure[1].

    Earthing System Potential Rise (EPR) The potential with respect to remote earth

    potential to which the earthing system rises due to the flow of fault current

    between the earthing system andearth[3].

    Earth PotentialThe actual potential of the earth, with respect to remote earth

    potential, at any point outside the perimeter of the HV Station earthing system or

    near a HV Structure earthing system[3].

    Hazard Zone For the purposes of this Guide, a hazard zone is defined as that part

    of the area around an earthing system which is bounded by a contour joining all

    points of earth potential equal to the maximum acceptable voltage limit below

    which no special precautions to protect personnel and plant need be taken[3].

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    High Voltage ( HV ) A voltage exceeding 1000 V a.c.

    HV Station An electric power station, substation or switching station in which

    plant operates at high voltage and which is connected to other HV Stations by

    overhead lines and/or underground cables[1].

    Low Voltage ( LV ) A voltage not exceeding 1000V AC[1].

    Remote Earth. The potential of an earthing system in a body of earth which is

    sufficiently far away from any current flowing in the body of earth so as to be

    unaffected by such current flows[3].

    Voltages: Voltages given in this guide are root mean square (RMS) values for

    alternating current, and average values for direct current unless otherwise


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    2.1 History of Grounding

    Grounding started way back when Thomas Edison developed the first convenient

    long-lasting electric light bulb as well as the mechanisms for generating and

    distributing electricity to American homes and businesses in the late 1870.s and

    early 1880.s. The first practical DC generating and distribution systems began with

    his Pearl Street Station in New York City September 4, 1882[1]. Significantly, for

    this state the second DC generating station to be energized in the nation was in

    Appleton, WI just twenty-six days later on September 30, 1882. Much controversy

    developed between Mr. Edison and George Westinghouse over the practicality of

    commercial DC electricity versus AC electricity. The impractical use and

    insurmountable technical difficulties associated with medium voltage, high

    current DC distribution systems gave way to the adoption and universal use of AC

    distribution systems before the turn of the century.7 Since that time, AC electrical

    distribution systems including classes of components, construction techniques,

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    and design philosophies have been standardized to a relatively uniform degree by

    electrical utilities and utility regulating bodies throughout the entire planet.

    The NEC code language, which began in August of 1897 as the .Rules

    and Requirements of the Underwriters. Association of the Middle Department for

    the Installation of Wiring and Apparatus for Light, Heat and Power applies to the

    wiring from the utility meter inwards throughout the users premises. It now

    devotes an extensive portion of its contents to the subject of grounding. The

    scope of that area includes grounding and bonding rules, as well as grounding

    conductors, locations, types, sizes, electrodes, methods, and conditions. The idea

    that commercial and residential power supply systems need to be grounded has

    been a nearly universal industry standard for a very long time. For all electrical

    systems, the basis of this standard has one fundamental theme:- that of safety -

    i.e. the protection of both humans and animals as well as the prevention of fire by

    electrical causes[1].

    Electrical engineers and electricians usually understand this concept well, but the

    general public may be confused as to why this is necessary and how it came

    about. The prime reason for grounding is safety and that has recently been

    exemplified for the citizens.

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    In the year 1985 Egbin Thermal Power Plant (located about 40km North East of

    the city of Lagos in Ijede Local Council Development Area, Ikorodu Local

    Government Area of Lagos State) was commissioned and consisted of six (6) units

    of 220MW steam turbines with a total installed capacity of 1320MW, The Step Up

    transformers were fitted with Neutral Grounding Resistors, which neutralizes

    faults from the earth and environs[2].

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    2.2 Types Of Faults

    There have been many instances of transmission and telecommunication system

    damage due to excessive impressed current and voltage from the nearby power

    system (usually during earth faults on the power system). These present a hazard

    to telecommunication system users and staff, as well as telecommunication

    system plant[3].

    The mechanisms through which this hazard or damage arises are:

    2.2.1 Induction (Magnetic Coupling)

    When an earth fault occurs in a power supply system, the net unbalanced fault

    current that flows in the power line (and returns via earth) creates a magnetic

    field. If a telecommunication cable runs parallel to the power line for a sufficient

    length, a high voltage may be induced by this magnetic field onto any metallic

    conductors in the telecommunication cable.

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