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Presented

By

H.JAYAKUMAR

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WHY GROUNDING IS REQUIRED?

GROUNDING PLAYS A VITAL ROLE INPOWER SYSTEM OPERATION. EFFECTIVE

GROUNDING IS NECESSARY FOR THEPROPER OPERATION AND CO-ORDINATION OF PROTECTION

SCHEMES IN THE POWER SYSTEM ASWELL AS FOR PERSONNEL SAFETY.

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PURPOSE OF EARTHING

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GENERAL REQUIREMENTS

LOW VALUE OF EARTH RESISTANCE.

ACCEPTABLE SURFACE POTENTIALGRADIENTS

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INDIAN ELECTRICITY RULES 1956.

IS: 3043/1966, 1987 : CODE OF PRACTICE

FOR EARTHING.

BS : CP 1013:1965

CBI & P RECOMMENDATIONSIGRE APPLICATION GUIDE

ANSI / IEEE STD.80/ 1961,1967,1986.

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TYPES OF EARTHING SYSTEM EARTHING.

PROTECTIVE EARTHIN

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SYSTEM EARTHING

EFFECTIVELY EARTHED SYSTEM(Xo / X1) < 3

(Ro / X1) < 1

Xo= ZERO SEQUENCE REACTANCE.

X1= POSITIVE SEQUENCE REACTANCE.

Ro= ZERO SEQUENCE RESISTANCE.

UNDER THE FAULT CONDITIONS THE VOLTAGES

OF THE OTHER TWO HEALTHY PHASES WILLNEVER BE MORE THAN 80% OF THE LINE TO LINEVOLTAGE OF THE SYSTEM. THIS IS ALSO CALLEDCO-EFFICIENT OF EARTHING.

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BENEFITS Improved reliability

Improved fault protection

Fewer Faults.

Simplification of locating faults.

Greater Safety

Limitation of transient over voltages.

Lower cost and less maintenance.

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Function of Earthing

Transformers Holding the neutral shift within limits.

Permitting the circulation of unbalanced load current

in the neutral. To limit the current during ling to earth fault.

To earth the system.

To provide single phase line to neutral load.

Can be used with resistance / reactance / arc

suppression coil.

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SPECIFICATION (IS:3151)Voltage : Line to Line voltage of the system.

Current: The maximum neutral current.

Time : 10 sec for protection 60sec for feeders.

Reactance: This quantity is a function of thepositive sequence short circuit reactance of the

power system or x1